This operation is normally conducted every 2 years in average during the winter shut-down of August.

Blanco Aluminization test 2009 summary [31]

The entire process takes about 6 days (from the moment the mechanics team start until they leave the telescope ready for optical alignment). This is a picture [32] of the 1998 aluminizing team.

Before the aluminizing chamber (start with the mirror set up on its pedestal in the washing area)

Inside the aluminizing chamber

 

Before the aluminizing chamber  (4 hours typ.)

This is done ideally with 6 people: 3 outside the mirror, 2 inside the central hole, 1 preparing materials.

Here is a list of materials [33]. THINK SAFETY! Wear plastic suit all the time. Wear heavy gloves, goggle and respiratory mask when manipulating acids.

Have a plan for what to do in case of acid accident.

 

 

A. MIRROR PREPARATION AND WASHING

A.0. Pour natural sponges in a bath of HCl+H₂O (to disolve any residuals of shells), rinse with water and cycle 5 times in washing machine.

A.1. For rough degrease: 200 gr of soap into 10 liters of filtered water (poured into 3 buckets)

A.2. For removing aluminium : 10 liters HCl + 10 liters filtered water + 200 grams CuSO₄. !!CHANGE: a 15% HCl solution is enough (see how to apply it below)!!

A.3. For final degrease: 1 kg KOH into 20 liters of filtered water

A.4. Clean the mirror with CO₂ snow, measure reflectivity and photograph mirror

A.5. If necessary, lay lab wipes on oil spots to absorb oil

A.6. Wear surgical gloves

A.7. From now onto the drying phase, ALWAYS keep the mirror wet.

Rinse entire mirror with filtered water (3 hoses) for 5 min. NO contact.

A.8. Pour soap onto entire mirror around the circumference. NO contact. Rinse with filtered water. REPEAT this step twice.

A.9. Blot mirror with soapy sponges using only the weight of the sponge. NO wiping. 3 people on outside of mirror make 2 complete circles. 2 people in the central hole make 3 complete circles.

A.10. Wash sides of mirror with soap and dedicated sponge NOT to be used on mirror optical surface.

A.11. Rinse the entire mirror with filtered water.

A.12. REPEAT step A.9 to A11.

[34]

Figure 1: Mirror preparation & washing

 

B ALUMINIUM REMOVAL AND DEGREASING

B.1. Wear new surgical gloves + heavy gloves + goggle + respirator

B.2. One person pours HCl/CuSO₄ around circumference of mirror while the 5 others drag-wipe with balls of cotton. Each cotton ball is used only for a maximum of 3 drag-wipe actions then replaced. Continue until aluminium is removed. !!CHANGE: cover the mirror with Kimwipes and pour HCl solution on them, they will keep the acid longer in contact with the coating and dissolve it without the need for a large quantity of acid!! Residual Al spot can we drag-wiped individually with a Kimwipe ball.

B3. Rinse with filtered water until pH is neutral. Rinse 2 minutes more with filtered water.

B4. Change to clean surgical gloves

B.5. One person pours KOH around circumference of mirror while the 5 others drag-wipe with cotton balls. Each cotton ball is used only for a maximum of 3 drag-wipe actions then replaced.

B.6. Rinse with filtered water until pH is neutral.

B.7. REPEAT steps B.5 to B.6

B.8. Rinse with filtered water 2 minutes more. Rinse carefully the mirror edge and the radial support mounts and holes.

C. DRYING (this is the tricky part !)

C.1. Change to clean surgical gloves AND dust mask

C.2. Rinse with 50 liters DOUBLE distilled water pouring around the circumference. Check out that water flows uniformly on the surface, not leaving 'holes'that would be signs of broken surface tension of the liquid passing on a still-contaminated area.

C.3. 6 people using nozzle guns blow dry nitrogen from the outer diameter to the inner, making sure the water drops flows uniformly radially inward (look at them against the lights on the other side of the mirror. Dry as fast as possible to avoid water drying on its own. No contact with mirror during that phase. Bidistilled water is clean enough that the process doesn't leave water marks. Perform the breath test to detect any drying or contamination spots in any suspicious areas (breath gently on the mirror -dry your mouth first!- and watch out any pattern on the surface covered with moisture).

C.3. BIS. Old procedure: Have at least large 50 balls of Kimwipes ready and someone preparing more if necessary. They must be thick and wide, bigger than your hand. Rub (for the first time in the entire process) the mirror applying about 1-2 kg force on the Kimwipes balls. Do not overdo it! M  he ball slowly to suck the water. Use each ball ONLY FOR ONE drag-wipe action then replace it (this is very important!!!). Work moving regularly around the mirror. As the mirror dries, you will have to work faster. Constantly check the entire mirror surface for areas that need attention. MAKE SURE your (dirty) sleeves are not touching the glass when you dry reaching far with your arm!! DO NOT let the mirror dry on its own! DO NOT wipe dry areas! Use Balzers virgin optical cotton cloth for touch ups. Check any visible stains and streaks with bright light and different viewing angles. It is hard to make the mirror better but easy to make it worse.

C4. Dry sides of the mirror and holes of the radial support mounts with Kimwipes. Use dry nitrogen to CAREFULLY blow out holes. Take care not to spray water on the optical surface.

C5. Hang up mirror in its hook. Clean with acetone the bottom of the mirror especially the 3 pads. Dry bottom of mirror with Kimwipes. DO A THOROUGH cleaning of all the non optical surfaces of the mirror for complete degreasing and drying.

C.6. Setup mirror on aluminizing tank floor. Blow off dust with CO₂: MAKE ABSOLUTELY sure the substrate is free of dust (other wise the coating will be full of pinholes). Put 4 clean microscope test plates (coating witness samples) on edge of mirror. Seal tank.

 

Inside the aluminizing chamber  (4 hours typ.)

Note: units used are : 1.3x10^-6 atm = 1 micron (Hg) = 1 millitorr (=0.13 Pa)

Vacuum gauge positions: (to be checked)

1 is chamber

2 is holding pump

3 and 4 are the diffusion pumps

5 is roughing pump

Be careful: do not disconnect a vacuum sensor turned ON. Let any pump run for 1 min (listen the noise) before turning ON any vacuum gauge.

We indicate a typical elapsed time.

 

A. PREPARATION OF CHAMBER (a few days before)

See pictures of the inside of the chamber: (Figure 2) general view of the chamber ceiling where you can recognize : the filaments in the round holes cut in the baffle sheet, the upper window used for checking the evaporation rate of aluminium and the cable feed-though port; (Figure 3) close view showing: the 4 concentric filament annuli (number of filaments per ring, from outermost to innermost: 36, 32, 20, 16 = 104 in total), the glow discharge ring (between annulus 2 and 3), part of the entrance conduit of one diffusion pump, the nitrogen pipe (near the bottom).

 

[35] Figure 2: Inside the chamber

[36] Figure 3: Inside the chamber (close view)

 

 A.1. Work inside the chamber with clean white suit, gloves and shoes protectors. Wash the internal walls, windows and chamber floor with acetone (DON'T remove the side windows, it is hard to re-seal them). Chase any greasy spots!

A.2. Wash with HCl (strip off the aluminium) the feed-through cables contacts, the holding ring insulator.

[37]

Figure 4

 

A.3. For better thickness uniformity, it is recommended to put filaments only in the outer rings. ±9% uniformity is reached that way (versus ±27% with all the arrays!). Check carefully all the filaments and replace the damaged ones: knock them with the finger to see if they don't break, they must be straight when loose (i.e. unstressed), not covered with blobs of aluminium. The filaments shall not touch the baffle mesh (to avoid short circuits) and be all at the same distance above the baffle (0.25 to 0.5"). IMPORTANT: tighten the filaments with a torque wrench to about 15 in-lbs so that the current that flows in them is uniform.

A.4. Hang 3 aluminium clips at both extremities of each filaments

[38]

Figure 5: Filaments

 A.5. Clean and lubricate the chamber Orings with high-vacuum grease. Don't lubricate the entire flange (but just the Oring). Don't put grease in excess! Close the chamber and put the C-clamps around the perimetral flange.

A.6. Run a typical vacuum sequence as described in B.1 to B.44 with 30 minutes minimum of glow discharge and eventually filament heating -but NOT LOADED with Aluminium clips!- to outgass them all (especially the new ones).

 

B. ALUMINIZING (see picture of control panel for location of all knobs and valves, (figure 4))

[39]

Figure 6: Control Panel

 

Most useful schematic diagram of the valves

[40]

Figure 7: Diagram of the valves

Install the mirror and the coating monitor [41] in the chamber (check that it works!). Put test plates on the edges of the mirror along the perimeter. Close the chamber and put C-clamps.

B.1. Connect flexible pipe of roughing pump to chamber (clean and lubricate Oring) and loosen the 2 adjusting rods.

[42]

Figure 8

B.2. Connect 3 cylinders of liquid nitrogen (N₂): one on each diffusion pump, one for the internal circuit (Meisner trap)

B.3. Open air valve in lateral wall (red flexible pipe)

B.4. Connect water lines to the coating monitor. Open water circuit (diffusor cooler): 2 valves -input/output- on pipes in backside wall ; (roughing pump is cooled with oil)

B.5. Check air pressure on diffusion pump: must read 70-75 psi (compressor is 100psi and feeds all valves)

[43]

Figure 9

B.6.1. Connect roughing pump to energy on the wall (and unplug the M floor 'helicopter' fan). Turn ON air extractor on P floor (otherwise smoke will come out the roughing pump grey pipes).

B.6.2. Check switches: "manual" (key) and "all valves closed" (black knob). TURN ON power of control panel.

B.7. Test-cycle all valves (open/closed). The holding pump must be ON for the holding valves to work. Throttle valves leds don't shine (just watch the meter). Leave them all CLOSED including the mechanical needle valve for air inlet during glow discharge.

B.8. 0min: TURN ON roughing (mechanical) pump and immediately open foreline valves 1 and 2 (this starts pumping the diffusion pumps).

B.9. When diffusion pumps are below 20 microns (35 at least), TURN ON holding pump.

B.10. When holding pump is below 20 microns, close foreline valves 1 and 2, and open holding valves 1 and 2. Check vacuum in diffusion pumps (should remain the same at 20 microns). TURN OFF roughing pump (the holding pump is now holding the vacuum in the diffusion pumps).

B.11. TURN ON diffusion pumps 1 and 2 (it won't work if the water flow is below 3 GPM or if the diffusion pump pressure is above 25 torrs). TURN ON liquid level controllers (LN2 to diffusion pumps) and open slowly the 2 nitrogen cylinders valves (20 psi) to avoid freezing the controllers. Leave them open.

B.12. When the roughing line is at atmosphere, TURN ON the roughing pump and immediately open upper and lower roughing valves if not already opened (the roughing pump is now pumping the chamber). Check no excessive heat of diffusors.

B.13. Fan of roughing pump will power off (NOISE) automatically after 25 minutes, sign that vacuum is getting better.

B.14. 45min: When chamber pressure is around 20 microns, close upper and lower roughing valves. If vacuum in chamber doesn't seem to progress below 25 microns after some time, turn on the more reliable high vacuum gauge (cold cathode).

B.15. When the roughing line reads 10 microns, open foreline valves 1 and 2 (the roughing pump is now pumping the diffusion pump as is the holding pump).

B.16. Open throttle valves 1 and 2. Open high vacuum valves 1 and 2, waiting about 1 min between the aperture of both valves in order to prevent oil backstreaming (the diffusion pumps are now pumping the chamber).

B.17. Close holding valves 1 and 2. TURN OFF holding pump.

B.18. TURN ON high vacuum gauges (if the cold cathode is dirty, it might takes a while before it starts reading). When chamber reaches 5x10^-5 torrs, TURN ON nitrogen cylinder valve for Meisner trap and corresponding liquid level controller.

B.19. 1h45min: When chamber reaches 1x10^-5 torrs, reverse the process to be able to do the GLOW DISCHARGE:

B.20. Turn off high vacuum gauges, close high vacuum valves 1 and 2 and throttle valves 1 and 2.

B.21. TURN ON holding pump, close foreline valves 1 and 2. Open holding valves 1 and 2 (the holding pump pumps the diffusion pump). Check pressure in diffusion pumps.

B.22. Open upper and lower roughing valves (the roughing pump pumps the chamber).

B.23. Open air inlet needle valve by 1.25 turn and use the inlet switch to set and maintain the chamber pressure at 35 microns, which is the appropriate pressure to run the glow discharge safely. Glow discharge provides outgassing of the substrate through heating, conversion of organic substances into their volatile components and desorption of films through electrons impact.

B.24. Turn on glow discharge controller. Slowly raise the current to 3 Amps in 2 minutes. Voltage will read about 3000 Volts (if the meter works!). A uniform purple color will be visible inside the chamber. If pink arcs or flashes show up (usually at 30mic), the pressure is too low, so open air inlet valve to raise the pressure back to about 35-40 microns. The ionized air will bombard the residual sticky hydrocarbons and, by transfer of kinetic energy, help to remove them from the surfaces (especially the mirror's). Monitor the discharge for 10 to 30 minutes. Reduce the current to 0 in 30 seconds. CLOSE the needle valve by hand.

[44]

Figure 10

B.25. 2h20min: close upper and lower roughing valves. When the roughing line reads 10 microns, open foreline valves 1 and 2.

B.26. Open throttle valves 1 and 2. Open high vacuum valves 1 and 2 with the same 1-min waiting precaution (the diffusion pumps are now pumping the chamber again).

B.27. Close holding valves 1 and 2. Turn off holding pump.

B.28. TURN ON high vacuum gauges. They should read 1x10^-5 torrs in a few minutes.

B.29. 2h45min: cold cathodes should read around 8x10^-6 torrs.

B.30. 3h30min: cold cathodes should read at least around 6x10^-6 torrs, which is just enough to aluminize (the higher the vacuum beyond that limit, the better):

B.31. Turn off all kinds of fans (Pump floor for example) to avoid vibrations in the floor.

B.32. 4h40min: Install the coating monitor [41] on top of the chamber near the window and check its parameters. With the 4 filament arrays, the chamber deposits an uneven film: 65% at r=20", 100% at r=45" and 50% at r=80". The tickness monitor is measuring at r=20", so in order to obtain 1000 Angstroms maximum thickness on the mirror, the firing should be stopped when the thickness monitor indicates 650 Ang. After you power off the filaments, the evaporation still goes on for about 70 Ang., so you should power off at about 580 Ang.

• Using remote hand paddle from the top of the chamber, depress the "Decrease" button for at least 15sec.
• Depress the "ON" button on the control panel to energize the outer array and zero the time counter of the Thickness monitor.
• During the first minute, JOG the "Low Heat" button (1-2sec) of the hand paddle for small increases in power to filament up to 300A on #1. Watch filament color (yellow) through the top window and check for uniformity of all filaments.
• JOG a few times the "High Heat" button for small increase (1sec) to reach 400A (#1) at 2'00.
• Keep jogging "High Heat" to reach 500A at 3'00. Kepp watching the color uniformity.
• Around 530A (3'15), the aluminium clips will start to melt and wet the filaments which will darken suddenly. The coating monitor starts showing activity: deposition has started.
• Keep jogging "High Heat" to increase the current to 750A (#1). At 3'35, there is already about 500 Angstroms deposited and the deposition rate is around 45A/s. The window is already completely aluminized to the edges, preventing you to see inside.
• When thickness reaches 580 Angstroms, depress the "decrease" button until evaporation rate is 0 and current is 0. A thickness of 650 Ang. on the coating monitor will correspond to a maximum thickness of 1000 Ang. in the middle area of the mirror.
• At 4'00, the game is over, the thickness monitor should be near 800A. Press "Off". TOTAL TIME of power in filaments: 4 min, TOTAL TIME aluminizing: 45sec.

B.35. Let the filaments cool for 15 min.

B.36. TURN OFF all gauges control.

B.37. CLOSE high vacuum valves 1 and 2. CLOSE throttle valves 1 and 2. TURN OFF liquid level controllers.

B.38. CLOSE foreline valves 1 and 2. TURN OFF roughing pump. TURN ON holding pump.

B.39. When pressure in holding lines is below 20 microns, OPEN Holding valves 1 and 2. TURN OFF Diffusion pumps.

B.40. Release slowly for 1min air to the chamber (big manual valve in the back) then open it completely. Let air get in 20min.

B.41. UNPLUG the LN2 cylinders and clean the lines with compressed air.

B.42. When the chamber is at atmospheric pressure, disconnect the head of the roughing pump and open the chamber. Remove test plates and mirror. Close the chamber.

B.43. When the diffusion pumps are cool to touch, CLOSE holding valves 1 and 2. TURN OFF Holding pump. TURN OFF control power. TURN OFF key switch.

B.44. TURN OFF air and water to diffusion pumps. CLOSE big manual air release valve.

 

** The goal is to deposit a layer of Aluminium of 950 Angstroms (±5%) of thickness on the glass (the chamber is capable of ±10% thickness uniformity when using the outer array only). Above 1000 Ang. thick, the coating will start showing more and more surface roughgness which will increase scatter. A thickness of at least 500 Ang. is required to maintain the transmission through the coating below 0.1%. The faster the evaporation rate is better because the vapour of Aluminium doesn't get much time to be contaminated with oxygen or other residual gases in the chamber. A rapidly deposited coating is more compact and show less surface roughness. Once the Al coating enters in contact with air, a 30 to 40 Angstroms-thick layer of Aluminium oxide (Al2O3) will quickly form on the surface and protect the Aluminium from tarnishing. This layer also hardens tremendously the Al (Knoop hardness of 2100 kg.mm^-2 compared to 140 kg.mm^-2 for bulk Al). Final experiments to check quality of aluminizing: look for water marks; put some sticky tape on edge of mirror and watch for aluminium peeling off; look at bright incandescent bulb from the edge of the mirror through the glass: the bulb should barely be visible. Inside the chamber, check the status of all the filaments : broken ones, clips not melted, eventual short circuits,... which will give you a better idea of the thickness uniformity.

 

Note: chemical processes in the obtention of the vacuum

• Low vacuum: the gas is like the atmosphere and the number of molecules of gas is large compared to what is covering the surfaces. The process rarefy the existing gas from atmospheric pressure to 10^-2 torrs.
• High Vacuum: what is left is 70 to 90% of water vapour. Most of gas molecules are located principally on surfaces and their mean free path equals or is greater than the dimension of the enclosure. Vacuum goes from 10^-3 to 10^-7 torrs.
• Glow discharge won't work at high vacuum because there is no conductive medium (gas). Inlet of ambient air (rather than dry air) is good because oxygen is reactive and helps removing the hydrocarbons.

Schematic diagram of the diffusion pump

[45]

Figure 11

Maxime Boccas, last revision on 2th of August 2000.

This operation is conducted every 6 months. This is a 5 people job: 2 persons are needed for the washing and at least 3 assistants (one near the mirror to pass on the goods and change the hose connections, one near the buckets to change the water pump from one to the other, and one on the M floor to open water and check water exhaust). Here follows a list of materials used, a description of the process and some images:

Materials:

•  2-4 natural sponges rinsed thoroughly in washing machine (they need to be absolutely free of particles, have a close look)
• 1 large yellow plastic bucket with 50l of bidistilled water. Put a lid on the bucket until the moment you use it in order to avoid contamination of the water.
• 1 large yellow plastic bucket with 50l of tap filtered water for pump rinsing
• 1 large yellow plastic bucket with 50l of WARM tap filtered water with Orvus soap (make a rather concentrated solution)
• 2 NEW nitrogen gas cylinders with full pressure with 2 spraying guns each. The cylinders must be FULLY charged (high pressure) otherwise the drying is too slow and will leave some thin water streaks.
• LIGHTS: it is fundamental to have an intense illumination all over the mirror to see very well what one is doing and detect all the residal spots while washing and especially drying. Install the 3 sets of double lamps used for the 4m Aluminizing (borrow them from Gale) and hopefully an additionnal one, in the 4 corners of the telescope guirder.
• the balcony bracket and its 2 wooden boards (remove the interior M1 ring baffle before putting the balcony)
• 2 white plastic suits
• 1 submersible pump
• 1 green water hose connected to the water exhaust down to a large bucket on the M floor
• 1 yellow water hose connected to the filtered water tap on M floor and with a quick connect fitting at the other extremity
• 1 yellow water hose connected to the pump and with a quick connect fitting on the other extremity
• 1 yellow water hose with a T fitting and 2 secondary hoses equipped with water spraying guns
• 4 nitrogen gas guns with corresponding hoses
• 2 nitrogen gas cylinders
• 2 pairs of surgical gloves
• 'water' vacuum cleaner in case of problem in the exhaust pipe
• a few boxes of Kimwipes drying papers

 

Process:

• Count 1 hour for the preparation of all the materials and 2 hours for the washing process to be completely done.
• DO NOT FORGET to seal very carefully with wide strong adhesive tape (Duct tape) the gap between the interior seal and the flange on the chimney above it (there are holes there and unless they are sealed definitively with silicone, they need special sealing to avoid water getting into the chimney and the mirror cell)
• Beware that the grounding plate at the top of the mirror prevents locally the pneumatic seal to do good contact with the mirror. Do not spray water into that tiny area or put some tape to seal it.
• Inflate the exterior and interior pneumatic seals. Inspect visually that they are making good contact with the mirror. Tape the interior seal connector and the temperature sensor to the chimney.
• Remove the ring baffle around the chimney and install the balcony.
• Clean separately any greasy spots or any other weird marks like bird drops that could contaminate later the sponges and the rest of the mirror.
• Hose water down into the exhaust hole until water flows at the output of the pipe. Then start spraying tap filtered water on the mirror for a few minutes to remove the dust.
• At any time, the person on the M floor should check that there are no water filtration through the chimney, rotator and mirror cell (you would eventually see water leaking to the ground).
• Spray the Orvus solution and start sponging the mirror. One has to climb on the chimney to reach easily the top of the mirror
• Rinse a few minutes with tap water and repeat the Orvus sponging. Rinse again with tap water.
• Put the pump into the filtered water bucket and keep rinsing the mirror until no more Orvus solution comes off the hose. This is to clean off Orvus from the pump and the hoses.
• Reconnect to the tap filtered water for a few minutes (there is much more pressure than the filtered water in the bucket so you can eliminate all traces of Orvus).
• Put the pump in the bidistilled water and spray generously all over the mirror until you have about 10l left.
• Start drying the mirror: one person on the chimney dries out the surroundings of the mirror with Kimwipes, then blows nitrogen gas from the top to the bottom until it reaches a sufficient height to keep drying from the balcony. Remove the sealing tape around the chimney and dry with paper the water in the holes. MAKE SURE you don't blow that water back onto the mirror as it will leave water marks (this 'trapped' water is not perfectly clean).
• Dry as fast as possible always from top to bottom (high pressure is needed in the cylinders). One person on each side with one gun in each hand.
• A third person needs to maintain wet the lower part of the mirror by keeping spraying bidistilled water, especially below the chimney, until the drying persons are ready to get to that area.
•  TAKE A LOT OF CARE at the end of the process of removing with paper all water on the surrounding of the mirror to avoid late contamination. Use Kimwipes to suck the pool of water left at the botttom.

 

[50]	For our first in-situ washing test (august 00), we had not yet received the exterior inflatable seal so we used duct tape and plastic sheet.
[51]	Detail of how the balcony is attached to the chimney with a special bracket.
[52]	Detail of the interior inflatable seal (between mirror center hole and chimney) and its valve.
[53]	Water is being sprayed on the mirror.
[54]	A small pool is forming at the bottom and being sucked up immediately by a water pump.
[55]	Detail of spraying water.
[56]	Detail of drying the mirror with dry nitrogen.

 

Last revised on February 2, 2001, Maxime Boccas

Al & W from (1975-2001)

 

W stands for washing; Al stands for aluminizing

 

Date	4.0-m	1.5-m	1.0-m	0.9-m	Schmidt	instruments
3-Oct-01		W M1
4-Aug-01	W M1
30-Apr-01		W M1
9-Apr-01				W M1
8-Mar-01	W M3 (TT box)
1-Feb-01	W M1
30-Jan-01	Al M2(F8)
3-Nov-00		W M1
2-Nov-00				W M1
9-Oct-00	W M2(F8)
6-Sep-00		W M1
Aug-00	Al M1
12-Apr-00				W M1
21-Mar-00		W M1
9-Nov-99						Al mirror(?) Hydra 4m
24-Aug-99		Al M2s
31-May-99				Al M1+M2
1-Dec-98			Al M1+M2
25-Sep-98						Al col Hydra 4m
31-Aug-98		Al M1
5-Aug-98	Al M1
9-Dec-97				Al M2
16-Jun-97				Al M1
9-Apr-97		Al M1
17-Aug-96	Al M2(F14)
28-Jun-96	Al M1
12-Jul-95		Al M2s
25-Apr-95			Al M1
18-Oct-94				Al M1
10-Aug-94	Al M1
23-Jun-94		Al M1
29-Dec-93	Al M2(F8)
14-Oct-92				Al M1
5-Oct-92			Al M1
8-Sep-92		Al M2s
17-Jul-92	Al M1
23-Oct-91		Al M1
9-Sep-91						Al Cam Echelle 4m
30-Aug-91	A M2(F7.5)
27-May-91	Al M1
5-Aug-90				Al M1+M2
13-Aug-90			Al M1+M2
19-Jul-90					Al M1
15-Nov-89		Al M1
19-Dec-88		Al M2(F7.5)
26-Aug-88						Al col spectro 4m
30-Aug-88	Al M1
30-Jun-88				Al M1
31-May-88			Al M1
Jan-88					Al Newton
18-Aug-86		Al M1
21-Mar-86	Al M1
28-May-85				Al M1
7-May-85			Al M1
12-Jun-84		Al M1+M2(F7.5)
23-Aug-83			Al M1
21-Jul-83	Al M1
24-May-83		Al M1+M2(F13.5)
24-Nov-82				Al M1
3-Aug-82	Al M2(F8)
13-Jul-82				Al M2
8-Jun-82			Al M2
13-Apr-82		Al M1
8-Sep-81			Al M1
15-Jul-81	Al M1
14-Apr-81				Al M1
25-Nov-80		Al M1
20-Nov-80						Al 4m rotator mirror
28-May-80		W M2(F13.5)
31-Aug-79	Al M1
21-Aug-79			Al M2
9-Jul-79		Al M1
14-Jun-79					Al M1
9-Apr-79		Al M2s
13-Mar-79			Al M1
21-Aug-78			Al M2
14-Aug-78				Al M1+M2
18-Jul-78		Al M1
12-Jun-78	Al M1
29-Nov-77					W corrector
22-Nov-77				Al M1
26-Oct-77			Al M1
7-Jul-77						Al 4m rotator mirrors
29-Jun-77		Al M1
30-Mar-77						Al Col. Spectro 4m
28-Sep-76				Al M1
Jul-76		Al M2s
Jun-76				Al M2
18-Apr-76			Al M1
13-Nov-75					Al M1
Aug-75				Al M1
Date	4.0-m	1.5-m	1.0-m	0.9-m	Schmidt	instruments

 

Small Telescopes Aluminizing Procedures

 

(chamber in the 1.5m dome)

This aluminizing chamber accepts mirror up to 1.5m in diameter and is used for all CTIO mirrors but the 4m M1.

Mirror washing: see 4.0-m procedure [57].

Picture of the 0.9m tel M1 mirror [58] after sitting 2 years in the tube without any cleaning and a picture of the washing [59] (aluminium removal with acid).

Note: units used are : 1.3x10^-6 atm = 1 micron (Hg) = 1 millitorr (=0.13 Pa)

Vacuum sensors and controllers: on the main panel, there is an analog controller NRC725 (Norton) for the Varian 524-2 cold cathode (1 input, reading from 10^-3 to 10^-7 torrs), and for Varian 531 thermocouples (2 inputs: not used not working anymore!). On top of the panel, there is an extra analog controller NRC721 fot 531 thermocouples (2 inputs: one for the diffusion pump and one for the tank, both reading from atm to 5 microns). There is also a thermocouple in the roughing line, which can be used to check good funcionning of the pump (turn off the meter, unplug the diffuser sensor and plug into the roughing line). Calibration of that dual thermocouple meter must be checked: when rough vacuum is reached in the roughing line (close diffuser and tank valves and plug the sensor in the roughing line), press the 'fil MA' button and turn the 'fil adj' knob until the needle reads 200 on the top red scale.

We indicate the elapsed time for the aluminizing (rather slow in this example, the entire process could last as little as 3h00).

 

A. PREPARATION OF CHAMBER (90 min)

A.1. Put a roll of paper on the bottom of the chamber to step inside without leaving dirt.

A.2. Replace all the damaged filaments (there are 24 of them on a single diameter): they must be straight when loose (i.e. unstressed), not covered with aluminium (drops). See picture [60] of this operation inside the chamber. Press gently the filaments with the fingers : if they are stressed, they break immediately. Filaments can usually be used for 2-3 aluminizings. Handling of the filaments must be done with gloves to avoid their contamination with grease.

A.3. Prepare 96 aluminium clips and wash them in acetone. Hang 4 clips per filament : one on each loop. Again use gloves to hung the clips.

A.4. Check thoroughly cleanliness of chamber, wash walls with acetone and all the surfaces touched by hands or tools, check the chamber Orings (clean and lubricate)

A.5. Use mouth mask from the moment the mirror is dried out until the chamber is closed. Wash with acetone the inside of the mirror holding ring and attach to the mirror. Bring the mirror into the aluminizing tank (picture [61]). Wash with acetone the outside of the mirror holding ring and any spots touched by tools.

A.6. Install the thickness monitor: it must face the center of the filament array and be at the same distance from the filaments as the mirror (otherwise you need to enter a 'Tooling' coefficient in the thickness monitor meter. Check that it is working (see instructions [41])

A.7. Blow off laterally dust with dry nitrogen. This is a critical step to ensure that the mirror is absolutely free of dust. Close tank and seal it by tightening the 4 bolts. Add at least 2 C-clamps near the top (original bolts are missing).

B. ALUMINIZING (see picture [62] of control panel for location of all knobs)

B.1. 0 min: Connect black and orange power cables (filaments and glow discharge) on the side of the main control panel. Connect 2nd black cable from glow discharge controler to valve at the rear of the tank (on the air inlet tube). Connect main thick black power cable to wall plug.

B.2. Take the extremity of the black flexible exhaust water pipe outside the building.

B.3. Open the water circuit valve (green pipe), the valve to the roughing pump and to the thickness monitor.

B.4. Close the copper tube valve (water to diffuser) on the right side of the control panel

B.5. See all following elements described on picture 1 [63]. Connect the tank vacuum gauge. Close both valves (diffuser and tank): the handle of the tank (top valve) should be on the left side and the handle of the diffuser (bottom valve) should be on the right side.

B.6. Picture 2 [64]. Turn on the air compressor: it must show 100 lbs to be able to open/close the diffuser valve. Make sure the voltage wheels for glow discharge and filaments are at 0 and their respective controllers off.

B.7 Turn on the roughing pump, plug a thermocouple into the line and check the meter calibration (as described above) once good vacuum is reached (5 um). Reconnect the sensor to the diffuser and open the diffuser valve.

B.8. When diffuser gets to 5 microns, close diffuser valve and open tank valve. Some smoke is generated by the compressor for a few minutes: close the doors and turn on the room air extractor.

B.9. 25 min: When tank vacuum reads 200 microns, turn on the power knob on the control panel to start the glow discharge. Turn control knob to raise current progressively up to 500mA (about 700V) (picture [65]) and check the ionization color in the tank (watch out for arcs). The vacuum should drop around 30 microns. Maintain glow discharge for 20min. Decrease slowly to zero the voltage, switch off the controller and turn off the glow discharge power knob on the main control panel.

B.10. 1h35min: When tank is at 5 microns, close the 2 valves (diffuser and tank) and open the poppet valve (diffuser-to-tank valve) by switching on the appropriate knob (this makes a loud noise, don't panic!). Turn on the diffuser, the refrigeration and open the copper tube water inlet. Turn off the vacuum gauge and turn on the cold cathode on the first scale (10^-3 to 10^-5 torr).

B.11. Open the diffuser valve (so that the roughing pump starts pumping the tank through the diffuser).

B.12. 3h50min: the tank reaches 4x10^-5. Check the thickness monitor [41] is ready to use. Turn on the filaments power on the main panel (left 'low voltage' knob) and on the filament controller.

B.13. Always reading the values of the current on the wheel -not on the small meter- (picture [66]), raise slowly to 35A and check for 2-3 min until the filaments color is uniform.

B.14. Raise to 45A for 1 min, then to 55A for 2 min: you should see the aluminium melt on the filaments (the filaments darken, then redden again). The aluminizing process is initiated and you should see some activity on the thickness monitor display.

B.15. Raise to 65A for 30sec: all clips should be melted and the filaments of a uniform color with a deposition rate around 15A/sec. Raise to 80A for 30 sec then 90A until thickness reaches 890A (maximum rate should be around 17A/sec). Decrease the power down to 0 in 10 sec. Switch off the power on the controller and on the main panel. Real aluminizing time should be around 1min30sec and final thickness should be around 950A.

B.16. Close the poppet valve, and turn off the compressor. Switch off the diffusion pump. Turn off the cold cathode and disconnect it.

B.17. Open a little the air inlet valve to the tank (with a piece of cloth on the pipe entrance). When diffuser cooling water exhaust is cool again, close the diffuser valve, turn off the roughing pump, the refrigeration and close the main water valve on the wall (leave the copper tube opened).

B.18. It will take about 20 minutes for the tank to be at atmospheric pressure so that you can open it (listen when air leaking in stops).

B.19. Inspect carefully the coating and look for water marks with intense light shining on the coating. Check visually that there is no transmnission through the coating (ie. thickness is adequate) nor tiny 'dust' holes in it by shining a bright light from behind the mirror. Do the adhesive tape test on the edge of the mirror to check the quality(adhesion) of the coating. Measure the reflected and scattered light in 3 different places to compare with data before aluminizing.

Total: 4h30min.

 

Max Boccas, last revision on February 1st, 2001

Always check that you have plenty of pressure and reserve in the nitrogern gas cylinders before you start the washing process in order to make the drying fast and optimum.
 

1.5-m Telescope

Washing done in-situ. Remove chimney. Put telescope at ZD60deg to the south. Raise the platform as much as possible. Remove northern petal covering M1, install the pneumatic seal around M1 so that it protrudes about 20mm above the mirror edge, and inflate it. Seal VERY carefully the space between the chimney base and the inner hole of the mirror with duct tape. If you don't remove the instrument from the telescope, make very sure all the seal are effective! Prepare a warm and highly concentrated solution of orvus soap and water (lot of foam). Rinse with tap water and hose. Use the vacuum cleaner to suck water. Contact-wash with the natural sponge and the soapy solution, and try to maintain the glass wet and covered with foam for 5 minutes (the idea is to unstick the dust and also degrease). Rinse with tap water. As usual, observe how the water is flowing on the surface, any abnormal surface tension showing up will indicate a residual grease that has to be removed. Never let the mirror dry. Finally rinse with bidistilled water (about 6-8 liters needed in small 1 liter bottle) and dry with at least one high pressure nitrogen gas gun (check you have plenty of pressure in the nitrogen cylinder before you start). Dry carefully with KImwipes all the water drops remaining around the mirror. With lot of care to avoid trapped water jumping, remove the inflatable seal and unstick the adhesive tape.

 

0.9-m Telescope

Remove the cell from the tube, incline it by 5-10deg. Mirror stays in cell. Seal the inner hole by forming around it a 2"-high cylindrical wall with duct tape and seal the outer diameter with the special plastic round skirt and duct tape. Contact-wash with sponge and soapy solution. Suck the water from the lower side of the mirror with vacuum cleaner. Dry with 2 nitrogen gas guns. The entire process takes about 3-4 hours (the washing itself takes 30min at most) and can be done without engineering time as the telescope collimation is not affected once the cell is reinstalled.
 

 

4m CFADC top surface (sol-gel AR coated):

Bring the telescope at D=30deg North (same position as M1 cleaning) and work inside the chimney with proper working light. First blow off dust with dry nitrogen. Only about 100ml of dichlorodimethylsilane (DDMS) is used in a goose-neck plastic bottle. A large plastic bag is taped on the lower half of the cell perimeter to force water to flow directly into it. Two Orings seal the top element with the cell and the cell itself so that no liquid can get inside the corrector assembly (see CH2903-E003) but you still need to take some care. Use some Kim-wipes towels placed at the bottom of the lens to suck liquid as it flows down the glass, and change the towels once they are too wet. Dry off with nitrogen gas. The entire process takes at most 1h.

IMPORTANT: solgel coatings are hygroscopic (they absorb water) and deteriorate over time. Waterproofing is achieved by rinsing the coating with a solution of DDMS with ethanol to a concentration of 5 parts per million. Alcohol is not good because it will wash off the DDMS and leave the solgel unprotected against humidity! Be careful, DDMS is very nasty stuff. Prepare the dilution in 2 steps: first 0.1ml of DDMS into 100ml of ethanol and then 0.5ml of this solution into 100ml of ethanol.
 

 

M3 in F/14 TT BOX (gold coated):

Remove cell from box, remove mirror from cell (it is pushed against a reference corner with 2 plungers), and wash in a soapy and warm bath, rinse and dry with nitrogen gas. Some minor tilt adjustment is needed when its cell returns into the box (do it with Osiris pupil imagery).

 

 

Reports

0.9-m Washing 5Feb09 [67]

1.0m Washing 5Feb09 [68]

 

April 11, 2001, Maxime Boccas

 

• R.D. Mathis Co. [69] (filaments for the 4m chamber)
• R.H. Cheney Inc [70]. (sells 99.99% Al clip evaporant, at only a few dollars for a bag of 10,000!, tel 508 226-7300)
• Sigma instruments [71] (thickness monitors)
• Midwest Tugsten Service [72] (about metal evaporation)
• Osram Sylvania emissive products [73] (filaments for the 1.5m chamber, tipe 116586, code X238D)
• Newport Thin Films Laboratory [74] (optical coatings)
• Varian vacuum technologies [75] (vacuum gauges and others)
• Thin Film Technologies Inc. [76]
• Denton Vacuum [77]
• United vacuum materials [78] (evaporation and sputtering)
• Sotware Spectra Inc [79] (thin film software)
• AVS, the Science and Technology Society [80] (buyers guide)
• Target materials Inc. [81]
• Chemical elements on the web: tungstene [82]

 

• Vatran C02 cleaning [83]
• www.co2clean.com [84]
• DMO reflecto-scatterometers [85]
• Schmitt Industries [86] (Micro-Scan reflecto-scatterometer)
• Minolta's spectro-photometers [87]

 

• Photonics directory [88]: metallic coatings buyers guide
• Sputtering targets suppliers [89]
• Atkinson Thin Film systems [90]
• Barr Associates Inc. (filters) [91]
• NASA materials databases [92]
   

How to use zz.cl for reducing Hartmann screen data

Revision of J. Baldwin's notes from 6 July98

All the updated programs are stored in /ua76/boccas/4m/to_run_shap/

SETUP:

•  LOAD IRAF TASKS:
  • images
  • proto
  • lists
  • digiphot
  • apphot
• GET THE FOLLOWING EXECUTABLES AND FILES into the directory you are using:
  • shap
  • shapav9
  • newshap
  • map4
  • setup.cl
  • zz.cl
  • modcheck.cl
  • ann_zer.ann
  • ela_ann.dat

plus a .coo file appropriate for the telescope/f-ratio you are using:
• • 36 INCH: 36inch.coo
  • 4m pf and f/8: model.coo
  • 4m f/14: f14.coo
  • 4m f/30: f30.coo

 

• THEN:
  • task setup=setup.cl
  • task modcheck=modcheck.cl
  • task zz=zz.cl
  • task $shap=$shap9

 

• PLUS A COUPLE OF HANDY ALIASES
  • alias te 'textedit \!* &'
  • alias lpflip 'enscript -r -l -fCourier9 -Pnpt0x2 \!*'

 

• SET TELESCOPE AND CCD PARAMETERS in setup:
    epar setup TASK = setup image = obj134 Image: coofile = f14.coo coordinate file: (pixsize= 0.048) CCD pixel size (mm) (apfill = 1.0733) Hart screen fill factor, 4m=1.0733, 36in=1.0881 (mirdia = 3947.7) Mir dia (mm), 4m=3947.7, 36in=914 (fratio = 14.45) 4m=14.45,7.8,2.904; 36in=13.5 (cursor = ) (coof2 = f14.coo) (mode = al)

• TAKE A FIRST TEST FRAME as early as possible in the night.

• RUN setup. Mark a pair of spots in the top and bottom rows of the Hartmann pattern... their separation is used by Shap so you cannot just pick any spots anywhere in the pattern. Note screwy feature where you must mark 1st spot with cursor + any key, then get cursor back to IRAF window and hit RETURN in order to get prompt for 1st spot number. Setup will produce files shap.par, modshap.coo, and zz.input setup obj134 f14.coo

• Use textedit or any other editor to remove bad spots from modshap.coo

• Run modcheck to be sure you have everything set up correctly.
    modcheck obj134

• NOW EPAR A FEW VITAL PARAMETERS FOR phot:
    centerp: cbox should be set to pacing between points maxshift same fitskypars: annulus tune to dot size dannulus tune to spacing between dots photpars: aperture set to same value as annulus

• CHECK SHAP CALIBRATIONS, ANGLE ZERO POINTS, ETC:
  • determine directions on sky using offset command.
  • take shap data while forcing in in 4 mu astig at PA 0, PA 90.

• MAKE SKY MAPS WITH CORRECTIONS OFF.

• NOW RUN zz ON EACH IMAGE. 3 exposures 30 sec each.
  • For each new object or telescope configuration: 'newshap' (enter title. If mapping sky, enter ha, dec in hh.h dd.d format; eg. degrees and fraction of degree, rather than deg.min)
  • For each image: zz objxxx
  • as needed: shapav9, tail shap.work, tail shap.sumry

•  where shapav9 averages together all data between successive applications of newshap and writes detailed log file in shap.sumry, averages in shap.av

• TO PLOT RESULTS OF SKY MAP: use texteditor to copy relevant sections of shap.av into temporary file. map4

 

 Maxime Boccas, 4Feb01

INSTRUCTIONS TO BUILD LOOKUP TABLES FOR THE 4M ACTIVE OPTICS

Revision of J.Baldwin's notes from 17Dec98 

All the updated programs are stored in /ua76/boccas/4m/make_lookup/

STEP 0:

• Do a sky map with Iman or Shap at the standard positions all over the sky (see "Calibration Positions for 4MAP Lookup Tables [101]"). There are 2 plotting programs, one for Iman data and one for Shap data, that will produce graphs of the sky in (HA,Dec) coordinates showing the aberration vectors (the center of the graph is the zenith):
• In order to plot the sky map data taken with Iman (which measures aberration amplitude in microns), use the program 'listmap' with the input file 'list.in' (which is a copy, that you can edit, of 'iman.log.av'). See the format of 'iman.log.av' in paragraph 4.5 of the Iman manual [102]). You will simply be asked for the aberration desired. Output can be displayed by selecting '/Xwin' or copied into a poscript file by selecting 'name.ps/ps'. 'Listav' is another useful program that will calculate the average aberrations in your sky map (especially useful when there is a constant aberration over the sky).
• In order to plot the sky map data taken with Shap (which measures aberration amplitude in nanometers), use the program 'map4' with the input file 'shap.in' (which is a copy, that you can edit, of 'shap.av'). You will be asked to specify the columns containing HA, Dec, aberration value, aberration pa. In 'shap.av', HA is column 1, Dec is 2, Defocus is 3, Spherical is 4, Coma is 5, Coma pa is 6, Astig is 7, Astig pa is 8, Tref is 9, Tref pa is 10, Quad is 11, Quad pa is 12. Output can be displayed by selecting '/Xwin' or copied into a poscript file by selecting 'name.ps/ps'.

STEP 1:

•  Use the fortran program 'xyiman' or 'xyshap' (depending on whether the data are in iman or shap format) to convert (r,theta) results for aberrations into (x,y) vector components. Either program writes its output into the files 'xgrid.out' and 'ygrid.out'.
• For xyiman, the input is read from file 'xyiman.in', which is in the format written by the program 'imanav' (see paragraph 4.1 of the Iman manual [103]) into the file 'iman.log.av'.
• The normal way to run 'xyiman' is:
  • cp iman.log.av xyiman.in
  • textedit xyiman.in (cut out any unwanted runs)
  • xyiman [aberration]
  • aberration = number from list below
    • + 1 = defocus
    • + 2 = decenter
    • + 3 = coma
    • + 4 = spherical
    • + 5 = astigmatism
    • + 6 = trefoil
    • + 7 = quadrafoil
• For xyshap, the input is read from file 'xyshap.in' (a copy of 'shap.av'), and you will be asked to specify the columns containing HA, Dec, aberration value, aberration pa. In 'shap.av', HA is column 1, Dec is 2, Defocus is 3, Spherical is 4, Coma is 5, Coma pa is 6, Astig is 7, Astig pa is 8, Tref is 9, Tref pa is 10, Quad is 11, Quad pa is 12. HA and Dec must be in decimal format (this is done when you use 'newshap', see shapzz.help [94]).

STEP 2:

• Then use the IRAF routine ctio.stsdas.toolbox.imgtools.xyztable to fit to x components, and provide output x components interpolated to the standard "Calibration Positions for 4MAP Lookup Tables [101]". The desired output HA and Dec are in the file outpos.in.
• lpar xyztable

 

intable1=	"xgrid.out")	input files to fit to
intable2=	"outpos.in")	positions at which to evaluate fit
outtable=	"xinterp.out")	list of output tables
(xname=	"c1")	name of column for X values
(yname=	"c2")	name of column for Y values
(zname=	"c3")	name of column for Z values
(xorder=	3)	number of coefficients in X
(yorder=	3)	number of coefficients in Y
(x1=	INDEF)	minimum X value for fit
(x2=	INDEF)	maximum X value for fit
(y1=	INDEF)	minimum Y value for fit
(y2=	INDEF)	maximum Y value for fit
(cross_terms=	yes)	include cross-terms?
(function=	"chebyshev")	function to be fit
(verbose=	yes)	print file names?
(coefficients=	no)	print coefficients?
(Version=	"8February1994")	date of installation
(mode=	"al")

STEP 3:

•   Use xyztable again for ygrid.out --> yinterp.out

STEP 4:

• At this point, there are a pair of files xinterp.out,yinterp.out which list the standard position HA & Dec, and then either the x or y component of the coma vector at that position.
• Now run the fortran program 'tabmake'. It reads in the files xinterp.out and yinterp.out, assuming that THE FIRST DATA VALUE IS FOR THE ZENITH, and writes an output file in the correct format for the lookup table.
• If you are making a coma lookup table, it needs to be referenced to zero coma at the zenith. The program tabmake does this if you answer 'Y' or 'y' to the question "Is this a coma lookup table?". tabmake then converts the output (r,theta) values into the units wanted by the TCP keyboard entry command for tilting the f14 secondary.
• If you answer that it is not a coma lookup table, then tabmake produces an astigmatism (or trefoil, or quadrafoil) lookup table, for which the value at zenith is NOT subtracted off.
• Tabmake writes 12 lines of output in the correct format for the lookup table (amplitude must be in nm for astigmatism, trefoil and quadrafoil lookup tables, and in degrees for a coma lookup table). BUT, you must now use a texteditor to copy the first line of output to also be a final (13th) line. At the same time you can add comment lines at the start, with a * as their first character.
• Here is a sample coma lookup table called f14jul98.cof:
  • f14tbl.cof
  • skymap for f14 tilt. Made 9 Jul '98 using data taken 12 Mar '98 and 8 Jul '98
  • J.Baldwin, M.Boccas
  • zenith collimation value obtained 9 July was:
  • secondary tilt .0650, PA 147 for primary tilt NW,S,NE=-19.2,-5.0,-13.5
  • the first 5 columns are amplitudes and the last 5 are angles
  • each line corresponds to a zenith distance, in steps of 15deg

    0.0000	0.0170	0.0360	0.0568	0.0793	0	191	190	190	190
    0.0000	0.0122	0.0253	0.0373	0.0455	0	181	182	183	185
    0.0000	0.0056	0.0121	0.0167	0.0158	0	155	163	169	177
    0.0000	0.0053	0.0074	0.0085	0.0084	0	90	90	102	119
    0.0000	0.0117	0.0177	0.0172	0.0129	0	90	90	90	90
    0.0000	0.0162	0.0291	0.0356	0.0263	0	90	90	90	90
    0.0000	0.0156	0.0293	0.0412	0.0511	0	90	90	90	90
    0.0000	0.0098	0.0141	0.0165	0.0457	0	356	343	288	240
    0.0000	0.0042	0.0117	0.0271	0.0495	0	287	247	229	221
    0.0000	0.0095	0.0237	0.0412	0.0604	0	220	217	216	217
    0.0000	0.0154	0.0339	0.0538	0.0743	0	206	206	208	213
    0.0000	0.0183	0.0389	0.0616	0.0857	0	198	198	199	202
    0.0000	0.0170	0.0360	0.0568	0.0793	0	191	190	190	190

STEP 5:

• Tabmake also writes a file called 'tabmake.out' (with 4 columns: HA, Dec, aberration amplitude, aberration pa), which can be used as the input file to the program 'map4'. You should run map4, and check that this map looks like a smoothed version of the input data.

STEP 6:

• Finally, once you have your lookup table all made and edited, run the fortran program 'maplookup' on it. This will produce a sky map in the same format as is produced by map4.
• If it is an astigmatism (or trefoil, or quadrafoil) lookup table, the map of the lookup table should look like the sky map of aberrations which you are trying to correct, with the vectors pointing in the SAME directions in the two maps.
• For a coma lookup table, you should see that the vector value at the zenith has been subtracted at all points on the sky.

 

 

 

Maxime Boccas, 4Feb01

 

Collimation Procedure for the 1.5-m Telescope

The collimation of this telescope is difficult mostly because the secondary mirror cells don't have position gauges (allowing control of what you are doing) and the f/13.5 cell is not kinematic at all but rather a complex puzzle where center and tilt are sometimes coupled on a single screw... So follow this guideline to avoid a nightmare. For your reference, the best images (FWHM) obtained for typical R-band 30sec exposures are: 0.60" at F/13.5 on-axis (classical Cassegrain) and 0.85" at F/7.5 over the FOV. (RC Cassegrain)

• By design and fabrication, and as our starting hypothesis, the primary mirror cell is such that it is centered with the instrument rotator. The primary mirror (M1) is centered in its cell through 4 radial adjustable pads inside the chimney (check exact procedure).

• Set the instrument rotator in the nominal position (30deg), install the 3 dial gauges in the back of the M1 cell (make sure you see the indicators move as they touch the mirror and you tighten them). The dial gauges fit in open holes of the cell at the same angle as the 3 collimation screws: East, Northwest and Southwest. The dial gauges, which have 3 readings each (tenths, hundredths and thousandths of an inch) are about 680mm off-axis thus a 1/1000" (smallest division) corresponds to a 7.7 arcsec tilt of M1. The collimation screws have 20 threads/inch so 1 turn moves the mirror up and down by 1.27mm. Located at an off-axis distance of 500mm, one turn of the screw thus corresponds to a 0.14deg tilt of M1.

• Install the K&E base plate on the rotator with the 3 short conic-head screws at 120deg (they provide an autocentering of the baseplate). Install the K&E in its support. Secure it with the 3 tightening screws on the left side of the support (the left one is used to open up the tube if the K&E is hard to remove). Through the window in the GAM, install the K&E target on the extremity of the optical tube. Make sure the target itself is not loose and slide at maximum on the tube. Orientate the target marks with the cardinal directions. Make sure the dials positionning the reticle of the K&E are set at 0. Never touch them later and check regularly that they are at 0.

• Install a light at the GAM window so that it shines on the target AND upward to the corrector (in the chimney), and another lamp at the top of the chimney shining upward to the secondary mirror.

 

F/7.5 : start with this focus, it is easier!

• The F/7.5 cell has 2 basic adjusments: radial (3 points at West, Northeast and Southeast) for centering, and longitudinal (3 points at East, Northwest and Southwest) for tilt. Two of the centering screws push directly on pads in contact with the secondary mirror (M2) and the third one (West) pushes on the mirror via a strong spring and has a locking nut. In thee back of the mirror, there are 3 hard points (screws with square head) that one needs to rise by a few mm when starting to tilt in order to open us space for M2 to go up, and tighten up when the collimation is done (use a 5 to 7/1000" shim to leave a tiny gap between these hard points and the glass for thermal expansion). The central hole in the mirror is fitted with a sleeve and a bolt which pulls up on the mirror to a system of counterweight supposed to hold the mirror figure against gravity. The 3 counterweights bars should go through the center of their support (if they don't, screw/unscrew the bottom nut holding the sleeve until they are centered). This has to be done at the end once the mirror tilt is set.

• Looking through the K&E, focus on the sleeve and the bolt/nut on the surface of M2. There is a tiny dot in the center of the bolt: this is the reference that needs to be centered with the reticle. The bolt diameter is 1/4" to give you the scale (you can also measure any decenter with the reticle dials but DON'T forget to reset them to 0 after measuring).

• The next step is very important: MAKE SURE that the K&E is perfectly perpendicular to its base plate (the centering has good locking screws but check it with a caliper, measuring the gap between the centration bolt blocks and the disk holding the K&E). Sight the bolt and make a zoomed drawing (direction and distance) of where the reticle is compared to the dot. Now, taking extreme care at not bumping the K&E in its baseplate (which has some play unfortunately -to be checked-), unscrew the 3 conic head bolts and rotate by 180 the baseplate onto the rotator (beware: you can not use the rotator to rotate because the bearing is not perfect and the rotation doesn't happen in a plane and thus your alignment will never converge!). Tighten up again and sight. Draw the new relative position. If the position of the reticle with respect to the dot has not changed before and after the 180deg rotation, it means the K&E is perpendicular to its support, so you can proceed. If it wasn't the case, determine the center of rotation (half way between the 2 reticle positions) and use the 3 tilt screws (with nut) of the K&E mount to set the reticle on that virtual rotation center. This is difficult because you need to maintain the wished position while you tighten the tilt screws. Once you have passed that tricky exercise, sight the bolt again, draw the respective positions of the dot and the reticle and rotate the baseplate of the K&E as described before. The new sights should show no difference. If this is not true yet, iterate the previous process.

• The K&E is now perpendicular to the rotator and thus defines the mechanical axis of the telescope onto which the optical axis of M1 and M2 must be brought. Use the radial screws in the M2 cell to center the mirror. Next, defocus slightly the bolt and you shall see the white K&E target imaged by M2: by tilting the mirror, center the image of the target with the reticle. The optical axis of the F/7.5 M2 coincides now with the mechanical axis.

• Drive the telescope to 45deg zenith distance in the 4 cardinal directions and sight each time at M2 with the K&E to detect any loss of alignment (sign that the mirror might not be held properly in its cell, i.e. not tight enough). Next flip to F/13.5.

 

 

F/13.5: the tough one!!

• The F/13.5 cell also has 2 'basic' adjusments:
  • Centering : 4 radial push-pull screws at the cardinal directions, each of them has a locking nut (but the East one), which need to be loosened first with a 25/32 tube key, and tightened at the end. These screws (use a 1/4" allen key) are accessible through holes in the wall of the Secondary Cage but you need to run the focus to the correct value to have these holes open up and be able to put the tools through them. These 4 screws are push-pulling on a belt attached to the mirror. Normally, you will be able to push one screw when the other 3 are loose (principle of the push-pull system). The problem of these centering screws is that they also introduce 'random' tilt and astigmatism if too tight!!
  • tilt : 3 outside screws driving pinions and teethed sectors at West, Northeast and Southeast. They require a special key that is a tube with 2 pins at one extremity and a central long allen key. First, locate the allen key in the lock screw of the pinion, loosen it, and rotate the tube until the pins enters the pinion. You can then rotate the tube and see the pinion rotates. The full range of each pinion corresponds to a tilt of about 5 arcmin (the star goes Northeast if you rotate the Northeast pinion to see the teethed sector go to the left). Tighten the lock screw at the end. Finally, there is also, inside the Secondary Cage (enters the tube standing up on the chimney), one push-pull screw rising up and down the entire cell mechanism from the south side thus allowing tilt in a quasi North-South direction (in theory this is in addition to the West pinion, also tilting the mirror in North-South). Use a special 1/8 long allen key for that adjustment.

• Once again, sight M2 through the K&E. You will see the large central hole in the glass (about 60mm in diameter). Center the hole with the K&E field of view (the 2 circles are quite close so this is easy and accurate typically within 0.5mm) or use the special aluminium target in the center of M2 (and center the tiny dot with the reticle). Next, defocus very slightly the glass and you will see the image of the corrector (down in the chimney just above the K&E) and especially its perimeter as a thin bright line just outside (very close) the hole of M2. Make that circle concentric with the hole in M2. The optical axis of the F/13.5 M2 coincides now with the mechanical axis. In principle, you ought to center first and then attempt tilting with the 4 dedicated tilt screws (but if you don't have enough range, use the tilt introduced by some centering screws and iterate...)

• Now comes the funny part (hey,hey the game is not over!): tighten the mirror without loosing the adjustments... Don't forget all the locking nuts (6) and make sure that the 4 radial screws for centering are all pushing hard against the belt (otherwise the mirror will move when you flip). With a bit of patience and practice, all that goes actually quite well. Always check any screw adjustment you are doing with someone looking in real time through the K&E (or do it alone but be ready for about 100 trips back and forth between the K&E and the mirror). Finally, check that there is no loss of alignment versus telescope position. Eventually, do a flip to check F/7.5, and then back to F/13.5.

• LAST STEP: bring the optical axis of M1 onto the mechanical axis (therefore also the optical axis of the M2s). In theory, you can use anyone of both foci to do that final adjusment (but whatever focus you use, it is highly rercommended to check the other focus later). It has to be done at night-time with direct imaging (look at through-focus sequences and 'zero the coma' on axis) or with the Hartmann screen. Use the tilt dial gauges of the M1 cell to monitor the collimation iterations.

 

IN PRACTICE, start with F/13.5. Tweak the tilt of M1 to get proper collimation at F/13.5. Then flip to F/7.5 and if the collimation is not adequate, use ONLY the adjustment screws (center and tilt) of M2 to get it right. DO NOT modify the tilt of M1 anymore obviously. The reason of that strategy is that you can't re-tweak the F/13.5 M2 at night-time while you can with the F/7.5 M2. I repeat: DO NOT in any case use the adjustment screws of F/13.5 M2 at night time because you will mess up everything.

 

 

Notes about gravity effects and mirror flips:

• After doing the K&E alignment, move the telescope 45deg off the zenith in one cardinal direction. Even when the mirror is tightly held in the cell, you will probably notice about a 1mm 'fall' of the mirror, probably due to a sag of the secondary cage. I find about the same fall amplitude at both focii and in all cardinal directions. Curiously the tilt seems to remain unchanged. This 1mm decenter is obviously a collimation limitation (at ZD45deg). This sag must somehow be related to the M2 focus encoder drift by about 30um when moving from zenith to ZD45deg (the drift was more like 100um before some maintenance was done to the focus drive mechanism in July 00). Actually, when the mirror is held tight in the cell so that it doesn't move on its own, adding to the cage sag, it is frequent to see trefoil and/or astigmatism, so that you need to loosen a bit the pressure, taking the risk of allowing decenter.

• Reading the axial dial gauges of M1 when going off-zenith shows that M1 is stable in its cell, within a 1-2/1000" at ZD45deg (7-14 arcsec tilt of M1).

• Doing repeated flips from F/7.5 to F/13.5 can alter the collimation (try it by sighting with the K&E), decentering the mirrors by up to 1mm, which is another collimation limitation. In order to minimize that effect, the flip has to be done by making sure both conical pins of the top ring are tightened slowly and equally.
•  

Some useful notes for the Hartmann screen method:

• Use the model newha1.coo (116 holes) and Baldwin's shapzz.help

• Reduce the data on ctio60 (Solaris) with the following version of ximtool (type: /usr/local/combin/ximtool -gui /usr/local/combin/ximtool-alt.gui)
• Use binning 2x2 (faster), one amplifier so you access the axis properly

• Use star mag 9 (clear sky), defocus the telescope by about 8000 units (don't put spacers, the focus mechanism axis is sufficiently colinear with the mechanical axis)

• Angle convention of Shap: 0deg is South, 90deg is West....(this is with the normal Tek2K orientation, i.e. arcon box facing North). With that orientation in mind, lower M1 on the side indicated by the coma angle in order to decrease the coma (for example, coma angle is 270deg=East, lower=unscrew the East collimation of M1).

• Equivalence between wavefront error (1 micron) measured with Shap and the resulting image blur (EE80 in arcsec) for each aberrations: spherical 0.29", coma 0.37", astigmatism 0.88", trefoil 1.04", quadrafoil 1.12".

• Check out the focus thermal sensitivity on this graph [104]

 

Maxime Boccas, 9sept00, last updated 19june01

Collimation Procedure for the 4.0-m Telescope at Prime Focus

There are 3 adjustments possible:

• 1. Tilting M1: this is done by moving in or out the 3 defining hard points of the mirror cell. The screws are located in the roof of the Cassegrain cage and are equipped with dial indicators. The screws are actionned with a special tool. The scale of the dials is usually set so that it reads 0 when air is OFF. The dials are located on a radius of 54 inches while the hard points are on a radius of 68 inches. Therefore a 1/1000" turn of one screw, while the other 2 are fixed, will create a tilt of 2.34 arcsec of the mirror.

• 2. Centering the PF pedestal (ie. Prime Focus Corrector + Mosaic): there is a centering mechanism on both the northern and southern sides, that works in a push-pull mode. A ±5mm range is available for centering. Dial indicators are installed and precise centering can be done. Holding screws (22 of them) must be loosen first.

• 3. Tilting the PF pedestal: there are 10 push-pull screws all around the pedestal but no indicators are provided. Holding screws must be loosen first.

Only option 1 is readily doable any time at the telescope. Options 2 and 3 require more delicate adjustment inside the PF cage (see CH2150.540-C030 for details) as it has to be done at zenith with someone standing in the cage.

A 'pure' focal plane tilt (revealed by a defocus slope across the field) can be corrected by tilting MOSAIC at its interface with the PFC with push-pull screws. Beware at the installation of Mosaic: these captured screws must normally be loose to avoid a non-intentional focal plane tilt (it happened once)!

The PFC is designed to deliver a 48 arcmin non-vignetted field with FWHM under 0.5arcsec at the edge of the field (see Tom Ingerson's paper [105]). The PFC optics include a field corrector for coma (paraboloidal M1) and spherical aberration (Ritchey-Chretien M1) and an Atmospheric Dispersion Corrector (2 pairs of rotating cemented prisms).

In terms of alignment requirements, the PFC optics have little optical power (1.076) thus are relatively insensitive to tilt, and behave like the M2 of a Cassegrain telescope where lateral centering is important to avoid misalignment coma. If decentering coma is present, the PFC optics must be translated laterally. In practice, for small corrections, we do tilt M1 instead. Zeroing the coma on-axis is not a sufficient condition. It is also important to check the field astigmatism off-axis (see simulations below). On-axis astigmatism doesn't reflect a misalignment problem but rather a problem with the cell of the primary mirror ("mirror pinched") and must be corrected via the active optics lookup table. If spherical aberration and/or field curvature are present, the longitudinal position of the PFC is not optimum and must be corrected by adjusting the back focal distance as Mosaic does not focus independently of the PFC (this was done once in Nov99 after the installation of MosaicII).

 

How to correct coma by tilting M1?

This can be done quickly by looking at a through-focus sequence for an on-axis star (9x100um steps is ideal, usually coma shows up nicely 200um away from best focus for a reasonnably bright star). Determine the cardinal direction of the coma (from the coma head to the tail): this side of M1 must be raised. The cardinal directions of the Mosaic field in the image display are: east is up, north is right. Alternatively, you can look for the minimum coma point in the entire field and consequently lower that part of the mirror. Iterate the adjusting tilts until the on-axis through-focus sequence is round and uniform. When wavefront errors are available from the Hartmann screen data, 1/1000 inches tilt is equivalent to an OPD of 230nm at the edge of the pupil, thus would correct about 230nm of coma measured on-axis. This is about the smallest correction that one can do with confidence and repeatability. Always keep a record of the tilt values of M1 (ie. values of the 3 hard points -south, northeast, northwest- dial gauges with air ON).

 

SIMULATIONS:

The following simulations are made at 650nm at zenith (ADC neutral). Only coma and astigmatism patterns do change; the trefoil pattern is not modified by misalignments. Reference field aberration maps for an aligned telescope are to be found in the PF imaging section of the main optics web page.

• See on this coma [106] field aberration map the effect of a 1mm decenter of the PFC+Mosaic (with respect to M1). The field astigmatism [107] pattern changes very slightly.
• A 1mm decenter of the PFC+Mosaic (with respect to M1) corrected by the appropriate tilt of M1 (25 arcsec) returns to the ideal case of 0 coma on-axis but the astigmatism pattern [108] worsens a bit.
• Sensitivity of the 3 types of misalignments: 1660nm (=0.23" in d80) of on-axis coma is produced by 1mm decenter of the PFC, or 25arcsec tilt of M1 or 0.35deg tilt of the PFC.
• When on-axis coma is present, if one really wants to know whether it comes from a tilt of M1 or a decenter of the PFC, it is possible to look at the differences between the field astigmatism patterns. For a same amount of coma, the case of a M1 tilt does generate more astigmatism and with a particular pattern [109], where the vector axis always points away from the axis thus rotates around the field (beware, when you examine images, this pattern becomes apparent only for a minimum amount of tilt).
• Besides generating misalignement coma, a large tilt of the PFC, 0.2deg in this case, will produce very particular astigmatism patterns: radial inward if the tilt is in the Y direction [110] (ie. north-south, which is the prism axis in neutral position), and circular if the tilt is in the X direction [111]. A subsequent appropriate tilt of M1 to zero the coma on-axis would almost not decrease the astigmatism pattern.
• Conclusion:

 

How to quickly correct astigmatism with the active optics of M1?

If astigmatism is present on-axis in a through-focus sequence, it is possible to correct for it with a TWEAK of the primary mirror (read first the TWEAK section of the 4m active optics on-line manual!). This is a 'quick-and-dirty' method but it can improve the images when the lookup table is not working well. On-axis astigmatism is caused by a non ideal support of M1 in the cell: that problem typically varies with telescope position, thus a TWEAK is valid only for a specific telescope position ±5deg (ie. about ±20min of exposure time). So if you follow the same object, you should actualize the TWEAK about every 40min.

Run the IRAF task mscexam on each out-of-focus image of a single star and look at the ellipticity angle (called 'pa') with the ',' option for example. To make sure that you are in presence of astigmatism, pa should flip by 90deg across best focus and be fairly stable on each side of the best focus. If the pa exhibits large variation and/or does not change roughly by 90deg across focus, don't even try that method!

Following is a list of measured pa for the IN-FOCUS image (called 'pa in') and the corresponding angle to enter in the tweak table of the tcp (called 'pa tweak'):

• if pa in > 0, pa tweak = 360 -2*(pa in)
• if pa in < 0, pa tweak = -2*(pa in)
• Hint for double-checking: a 'pa in' of 90deg is equivalent to a vertical astigmatic image in the mscexam xgterm window (not in the main image display), while a 'pa in' of 0deg is equivalent to an horizontal astigmatic image.

Examples:

• pa in 90 -> pa tweak 180
• pa in 67.5 -> pa tweak 225
• pa in 45 -> pa tweak 270
• pa in 22.5 -> pa tweak 315
• pa in 0 -> pa tweak 0
• pa in -45 -> pa tweak 90
• pa in -67.5 -> pa tweak 135

What amplitude shall you enter in the tcp tweak table? This is even more empirical: in reasonnable seeing of 0.8", a 1um astigmatism will be visible at 100um off the best focus, but hardly visible at 50um... Once again, although this technique works, it is experimental and must be used with care until a better lookup table can be built. This method can actually also be used to update the astigmatism lookup table using the seeing images recorded every night (ie. not waiting for a dedicated engineering night).

 

Note: SCALE OF THE WAVEFRONT ERRORS (optical path difference at the edge of the pupil): at the 4m, 0.1" image degradation in d80 is produced by 0.70u of coma, 0.30um of astigmatism, 0.26um of trefoil, 0.24um of quadrafoil.

 

 

Maxime Boccas, 28March01

 

Facts about coating and cleaning

Maxime Boccas

Mirror cleaning and coating conference

Palomar Observatory

25-27 April 2001

 

 

1. Coating

1.1.- Coating plants for Aluminium evaporation - 4m chamber (used only for M1 of 4m tel.)

• 6-day process, 4-6 people
• 104 filaments on 4 rings (original NOAO plant): thickness uniformity +/-25%
• Glow discharge (3000V, 3A, 20min)
• 6.10^-6 Torrs with 2 diffusion pumps
• 600-1000 Å deposited, 43Å/s max
• Total time of power in filaments: 4’ ; total aluminizing time: 45”
• Sigma SQM160 thickness monitor
• Total time of coating process: about 6 hours

 

1. Coating

1.1.- Coating plants for Aluminium evaporation - 1.5m chamber (all other mirrors)

• 1 day process, 2-3 people depending on mirror size
• 24 filaments on 1 ring
• Glow discharge (700V, 0.5A, 20min)
• 4.10^-5 Torrs (at least) with 1 diffusion pump
• 950 Å deposited, 17Å/s max
• Total time of power in filaments: 5’ ; total aluminizing time: 90”
• Sigma SQM160 thickness monitor
• Total time of coating process: about 5 hours

 

 

Typical fresh Al reflectivity (%)
measured with IRIS 908RS

 

	470nm	530nm	650nm	880nm
4m plant	92.6	93.0	89.3	88.0
1.5m plant	92.4	92.7	89.1	89.0
Quoted by G. Hass	92.1	91.6	90.5	88.0
Scatter (both plants)		0.4% typical
Micro-roughnes		30 Å typical

 

 

 

TO DO:

4m chamber

• Fix leaks of the 4m chamber for higher vacuum and even better purity of coating BUT reflectivity excellent
• Modify filament configuration for better thickness uniformity (KPNO reached ±10%) BUT 400Å is acceptable (~l/10)

1.5m chamber

• Last coating done under 4.10^-5 T was about 2% below ideal: gas contamination due to poor vacuum? Do leak testing.

 

OBSERVATIONS:

• 45-90s aluminizing time doesn’t seem to show any difference in coating micro-roughness
• 6.10^-6 Torrs is low but enough for high purity and reflectivity
• Substrate free of dust when chamber is sealed to avoid pinholes in coating

 

2. CLEANING

• Cleaning before aluminizing
• Regular in-situ washing: every 6 months for M1s
• CO₂ snow cleaning : every 15 days

CLEANING BEFORE ALUMINIZING

• Rinse with tap water
• Soap + contact with natural sponges. Rinse
• HCl (50%) + CuS0₄ (1%) + H₂O + contact with Kimwipes. Rinse
• KOH (5%) + H₂O + contact with Kimwipes. Rinse
• Rinse with plenty of medical grade bi-distilled water (80 liters at 4m M1)
• Dry with nitrogen gas guns (2-4 people depending on mirror size)

 

USUALLY NO WATER MARKS LEFT, EVEN IF WATER DRIES ON ITS OWN!

 

2. CLEANING - REGULAR IN-SITU WASHING

 (since March 00)

• OPEN TUBES (4m, 1.5m tel.): M1 washed in-situ with inflatable seals on inner/outer diameters and water exhaust tube. Telescope at ZD 80°
• CLOSED TUBE (0.9m tel.): M1 cell removed from telescope (but mirror stays in cell). No collimation required.
• How long does it take? 4m: 3h ; 1.5m: 1.5h ; 0.9m: 4h !
• No need for dedicated engineering: day-time activity
• think safety: operator and mirror!

'RECIPE':

• Use garden hoses for all rinsing. Plenty of working light.
• Filtered water rinse (5’)
• Warm soapy water highly concentrated rinse. (5’)
• Soap + natural sponge contact. (10’)
• Filtered water rinse. (5’)
• Bi-distilled water rinse. (5+’)
• Dry with nitrogen gas guns (5+’)
• NO alcohol used (bad experience)

 

 

In-situ washing can be done anytime after ‘dust event’ or ‘rain leak accident’, when contamination is still fresh…
 

2. CLEANING - IN-SITU M1 WASHING
RESULTS

0.9m tel.

• No C0₂ cleaning, semi-annual wash
• 22 months, 3 washs
• From fresh Al: only 1%reflection loss and 0.2% scatter loss!

 

1.5m tel.

• Monthly C02 cleaning (for 19 months), semi-annual wash
• 25 months, 3 washs
• From fresh Al: only 1%reflection loss and 0% scatter loss!

 

4m tel.

• Bi-weekly C02 cleaning, semi-annual wash
• 6 months, 1 wash
• From fresh Al: 0%reflection loss and 0.1% scatter loss!

 

CONCLUSION: 0.5% refl. loss per year

• Regular CO2 cleaning doesn’t seem to be relevant to help recovering reflectivity by washing, and only very slightly for scattering.
• M1 in closed (with extraction fans) and open tubes seem to behave equally.
• We now intend to wait 4 years (or more) between recoatings and maintain reflectivity above 90% at 550nm\
• 3-4 extra nights for science per year (compared to our old bi-annual Al schedule)
• Purchase of 2 water distillers to produce our own bi/tri-distilled water. Investment paid in 1 year (we need about 600l/year at $3.4/l)

 

OTHER OPTICS IN-SITU WASHING

• Secondary mirrors: telescope looking at horizon, mirror vertical, sealing skirt easy to put around mirror, contact wash. Monthly loss rate is typically R-0.15% and SC+0.10%
  => do not disregard them. Semi-annual monitoring and annual washing?
• Upward looking field corrector: our Ø0.5m CFADC cell is sealed. Telescope looking at horizon, liquid collection bag attached below cell. Rinse (no contact because sol-gel AR coated) with 100ml bi-distilled water and 50ml isopropyl alcohol in squeeze bottle.
  => it is usually not much extra work, in the design phase of ANY large optical component exposed to ambient air, to think about seals to allow easy and safe in-situ washing. Seal retrofit usually possible.

 

CO2 SNOW CLEANING

 

Gain per cleaning session in pre-washing era (August 98- March00):

	R400nm	R700nm	SC400nm	SC700nm
4m tel.	+0.35%	+0.38%	-0.24%	-0.32%
1.5m tel.	+0.70%	+0.71%	-0.20%	-0.41%

 

We do bi-weekly sessions at 4m and monthly sessions at 1.5m tel: 

=> Refl. can wait one month to be recovered but scat. can not.

=> CO2 helps maintaining mirrors cleaner between washings.

 

Seasonal variations:

due mostly to ambient RH?

• Wet season, Oct-Apr, 32%<RH<55% : R loss is 0.63% per month
• Dry season, May-Sep, 12%<RH<32% : R loss is 0.05% per month

 

MONTHLY VARIATIONS in %
(average at 550nm)

 

 

	R0.9m	R1.5m	R4m	SC0.9m	SC1.5m	SC4m
Sep98 - Mar00	-0.70	-0.20	-0.21	+0.44	+0.17	+0.17
Mar00 - Nov00	-0.66	-1.30	-0.71	+0.32	+0.55	+0.31
Nov00 - Apr01	-2.2	-1.0	-1.3	+1.2	+0.7	+0.71

 

 

CONCLUSION:

stronger-than-usual variations since roughly Nov 00 !

• No correlation with wind (‘summer’ is quiet, 1.8m/s average wind)
• Dust events?
• Pollens? (intense ‘desierto florido’ last spring in area starting 50km NW of CTIO, prevailing wind is NE...)
• Need for permanent site monitoring with a particle counter?

 

4m tel. M1 coating grounded in August 00 in order to minimize dust retained by electrostatic forces : no obvious effect...

 

 

CLEANLINESS OF SITE:

basic dust collection experiment in 4m and 1.5m tel. domes with horizontal microscope slides left exposed to ambient air for 21 months (June99-Apr01)

• Both indicate av. scatter increase of 1.11% (+/-0.02) per month.
  Note: For comparison, Schmidt telescope M1 (tube closed with corrector): reflectivity and scatter worsen by 1% per year (average over 10 years)
• About 60 particles with 5 < size < 10 mm per mm2
• About 8 particles with size > 10 mm per mm2
• Purchase of a Metone particle counter. Will be used to detect ‘dust event’ and for GSMT site-testing in Atacama
• Replace the now-dusty summit soil cover with new gravel-type material (test Dimm at ground level was found covered with dust)

 

All this information

 

 

is under ‘Telescopes’ item of CTIO web site
http:// www.ctio.noao.edu/telescopes/opteng/optics.html [114]

 

 

• Note: This page does not contain images, so the slides from the graphic version [113] are not contained here.
• Table of contents [115]

back to top [116]

 

links

Author: Maxime Boccas

Presentation given in the "Mirrror cleaning and coating conference"
Palomar Observatory
25-27 April 2001

graphic version [113]

                Text version [112](one page)

 

Table of Contents

Cleaning and coating 1 - TITLE [113]

Cleaning and coating 2 - COATING [117]

Cleaning and coating 3 [118]

Cleaning and coating 4 [119]

Cleaning and coating 5 [120]

Cleaning and coating 6 [121]

Cleaning and coating 7 - CLEANING [122]

Cleaning and coating 8 - CLEANING BEFORE ALUMINIZING [123]

Cleaning and coating 9 [124]

Cleaning and coating 10 - REGULAR IN-SITU WASHING [125]

Cleaning and coating 11 [126]

Cleaning and coating 12 - IN-SITU M1 WASHING RESULTS [127]

Cleaning and coating 13 - CONCLUSION [128]

Cleaning and coating 14 - OTHER OPTICS IN-SITU WASHING [129]

Cleaning and coating 15 - CO2 SNOW CLEANING [130]

Cleaning and coating 16 [131]

Cleaning and coating 17 [132]

Cleaning and coating 18 [133]

Cleaning and coating 19 [134]

Cleaning and coating 20 - CONCLUSION [135]

Cleaning and coating 21 [136]

Cleaning and coating 22 [137]

 

 

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