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ID Date Author Typeup Category Subject
  145   Thu Jun 3 23:55:38 2010 taracLaserLaserAligning AOM 2: the Return of the Beam

I'm aligning double pass AOM. After maximizing the power of the 1st order of the transmitted beam, I place the R=0.3m mirror to reflect the beam  back to the AOM.

The mirror is mounted on a translational stage for a fine adjustment.

At the right distance L away from the AOM(L = ROC), the size of the reflected beam at the AOM should be the same as the incoming beam.

Thus, there are 3 things to adjust.

First is the angle of the quarter wave plate that rotates the polarization of the beam after 2 passes by 90 degrees.

Second, the angle of the mirror, and

third, the distance of the mirror. At right position the power of the 1st order beam should be maximized.

 

I might have to change the position of the PBS that reflected the AOM double passed beam. Currently, the PBS is placed before 2 mirrors that move the

beam to the side of the table to avoid the insulation box. The problem is the double passed beam might clip on the mirror. So now I put the PBS after the steering mirrors, just in front of the AOM, but this limits the space for mode matching. I'll have to check which one will be better. From the attached picture,  two PBS's are placed on two possible locations. On the bottom right the, and down at the middle next to the AOM.

Attachment 1: Photo_38.jpg
Photo_38.jpg
  147   Fri Jun 4 22:10:24 2010 taracLaserLaserprogress on PSL setup

The maximum power after AOM double pass is 37%, worse than the expected 50% efficiency, but it should be enough.

The good news is, a new mode matching (RefCav and ACav) is calculated, and all positions for the lenses are clear.

I got all the lenses, and borrow one plcx-24.5-51.5-c-1064 from 58C

The problem about the position of the PBS is solved. It will be at the original place, since the clipped beam is the 0th order of the reflected beam which we do not use.

I'll put the lenses in their places and try to lock RefCav again.

  148   Fri Jun 4 22:48:24 2010 ranaLaserLaserprogress on PSL setup

Quote:

I'll put the lenses in their places and try to lock RefCav again.

 Groovy.                   

  150   Sun Jun 6 23:01:58 2010 taracLaserLaserRefCav is almost locked

When I try to lock the cavity, it's not very stable yet. The transmitted power fluctuates alot.

I try changing the gains, but still could not stabilize the lock . The transmitted beam power is about 60% during the stable lock (I got it nicely locked for 5- 10 mins.)

After RefCav is locked, I'll try to optimize the transmitted power, by adjusting the lenses' positions before moving on to work on ACav

 

  151   Mon Jun 7 19:24:04 2010 taracLaserLaserRefCav is locked

RefCav is locked , the beam is more stable than yesterday setup. I'll write down the values of the setting for a quick reference.

I'm not sure what universal names for all these channels are. I just explain them in more details for my future reference and next generation archeologists.

fss controller:

Common Gain(  for both fast and PC paths): 23.6 dB (fast path controls the PZT which changes the length of the NPRO, PC path controls the phase

shift of the beam)

Fast Gain ( for PC path only): 12.5 dB

Phase shift: 0 + 180 degree. ("+180 degree" means phase flip)

RF Amplifier Adj (power for 35.5 MHz sidebands): 6.28 V.

Thermal control ADj (a voltage calibrator connected to slow channel of the laser controller): -0.010V

PMC controller

Servo gain Adj (over all gain of the demodulated signal): 27.75 dB

Output DC offset (offset voltage that governs the length of the PMC): -3.12 V

Phase shift: 2.87 V + 180 degree

RF Amp Adj (power for 21.5 MHz sidebands): 5.36V.

 

Now I'm working on ACav path. I made a cable for a photo diode.

I'm not sure if the last PD is a working 35.5 MHz PD, I'll see if it works or not.

Now I'm using two 2-channel monitors to simultaneously see the  beams after PMC and RefCav. It will be more convenient if I use a 4 channel monitor, I'll  clear some space for it.

 

  152   Tue Jun 8 03:16:21 2010 FrankLaserLaserRefCav is locked

nice good job!

you can get the names for the channels if you click on the corresponding object (slider, button, textbox, ...) using the center mouse button. You will get a green on black box containing the full channel name...

both 35.5MHz photodetectors should be ok as we used them in the previous setup already...

  153   Tue Jun 8 20:16:21 2010 taracLaserLaserscanning ACav

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

Attachment 1: aom_eff.png
aom_eff.png
  154   Wed Jun 9 03:55:40 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  156   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  155   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  157   Thu Jun 10 00:21:15 2010 taracLaserLaserscanning ACav

I'm scanning the laser to align ACav. It's a long day of adjusting 4 knobs and 1 lens (and one periscope for a while.) 

I see higher order TEM modes at the back of the cavity, but still cannot see TEM 00 yet.

Thu Jun 10 00:20:39 2010

 

I saw TEM 00 and trying to minimize the reflected power on the PD.

I just realize that the beam path is very close to the edge of the hole (see attached.) Part of the beam might be clipped.

I'll check that with IR viewer tomorrow.

The value for Voltage Calibrator is 6.17 V.

Thu Jun 10 00:58:56 2010

 

Attachment 1: Photo_42.jpg
Photo_42.jpg
  158   Fri Jun 11 01:04:42 2010 taracLaserLaserscanning Acav2

From yesterday, after getting TEM 00 out of the cavity, I checked the beam if it's clipped on the edge of the hole or not. There is small light on as seen by an IR viewer. Since it seems to be very small, I'll leave it as it is for now.

There was one problem. The beam was almost on the edge of the periscope's top mirror, I decided to change the height and move the periscope , and other optics in the row, side way, since the beam was really close to the edge of the opening ( I set the beam path to the center of the hole before, so it's bit off ( 5mm, 0.2") from the cavity's natural axis), and made sure that the beam is on the center of every mirror. Then, it's 4 knob adjustment which takes me a whole day again

As of now, I got TEM00, out of the cavity. I still have to adjust the lens' position to minimize the reflected beam. Before doing so, I'll prepare a mixer, a power splitter for locking the cavity.

 

One thing about the AOM, the beam after double pass is quite elliptic. I'm not sure how to correct it, and whether it's going to be a problem or not. I'll find something to read about this.

Fri Jun 11 01:00:17 2010

  168   Wed Jun 16 19:43:00 2010 taracLaserPMCPMC and EOM alignment

We try optimizing the PMC transmission in P wave. The maximum we can get for now is ~82%.

The 21.5 EOM is prealigned. We will do fine adjustment again when insulating cables are made.

EOM alignment means to align the polarization of the beam to match the applied electric field in the EOM. This will minimize the amplitude modulating effect.

There are 3 degrees of freedom, 2 for EOM positions, another one is the polarization of the beam.

The 35.5 EOM is also pre aligned, the signal is very small, probably because of its broadband type. I use 4395A spectrum analyzer to see the peak at 35.5 MHz, but it's really hard to tell if I minimize it or not.

I see the thermal effect on EOM crystal clearly when I adjust the EOM. After I minimize the Amplitude Modulation (AM) and left the EOM for awhile, the misalignment gradually increase.

Frank suggests that the calibration of the error signal should be done, so that we can approximate how well the temperature must be controlled to reach our noise budget. I'll think about that measurement.

As I finished my elog, the peak at 35.5 just went up. Case in point.

  170   Mon Jun 21 19:19:12 2010 taracLaserPMCProgress on PSL setup: Tuning phase shift/RF power for PMC

All SMA cables for locking RefCav are made and wired up in their places.

We decide to turn the power up to 50mW before it enters PMC. With ~80% efficiency, we get 40 mW out.

I adjusted RF power and phase shift for PMC and saved it in the init file so that next time we reboot the crate, the values will be set.

Next: I'll lock the RefCav and optimize the alignment.

  174   Wed Jun 23 23:52:48 2010 taracLaserRefCavRefCav is locked and optimized

I adjust the mode matching lenses and align the beam so that the transmitted power is ~97% of the input power. Actually I scan the beam and look at the reflected power. The reflected beam has power ~3%. The knobs on one of the periscope mirror acting weird. There's still thread (~ 4 or 5 turns, I guess) left but it seems to be very sensitive to my hand pressure when I rotate the knob, making fine adjustment rather hard .

Phase shift is adjusted by looking at the error signal. The laser is scan while the error signal from the fss servo mixer out is monitored. Feedback signals from the servo to EOM and laser must be removed.

RF power for RefCav is tuned. I assume that all sidebands' power will be reflected, and only power in the carrier will be transmitted, and to maximize the error signal's slope, we need Pcarrier/ Psideband ~ 2 [Black] .

So I measure the power of the incoming beam and adjust the RF power so that the transmitted beam's power is 1/2 of the input power. Another 1/2 of the input power will be the power of 2 sidebands that reflect back. 

 I use a photo diode to see the transmitted power and adjust the gain. The goal is to maximize the gain and have a stable transmitted power. However, the power still oscillates even when I decrease the gain, more than that and it loses lock. So I can only minimum the osicllation (You can see the beam spot pulsating on the monitor.)

All values are saved in the "startup.cmd" file.

a

  175   Thu Jun 24 09:37:16 2010 ranaLaserRefCavRefCav is locked and optimized

For the sideband power, you don't really want to make it so large. All that you really want is to make sure that the shot-noise signal is bigger than the electronics noise.

Once you guys start working on the noise budget, you will see that the input referred noise of the RFPD is equivalent to roughly 2 mA of photocurrent. So, for a reasonable

signal you should set the modulation depth (Gamma) equal to ~0.3-0.5.

Remember that we are also going to be fighting against the residual RFAM from the EOM, so its important to maximize the signal amplitude relative to the RFAM. The RFAM

signal will increase with increasing modulation depth...

  176   Fri Jun 25 18:27:59 2010 taracLaserLasermode matching to ACav

  The new driver for AOM is working, the maximum power is ~1.3w. There's a switch for int/ext signal.

We use internal signal to drive the AOM for alignment purpose.

The mode matching for ACav is on hold. Because the1st order beam coming out of the AOM looks very elliptic.

I'm not sure if it's the result of the large beam size in the AOM or the alignment problem.

the beam might clip on the edge of AOM, the beamsize is quite large, the data sheet give 80% 1st order efficiency for 1100 um diameter spot [AOM] and I adjusted the beam size to maximize the power before. I'll try decrease the beam size and see if this reduce the elliptical shape of the beam. Once the beam size on the AOM is determined, the rest of the mode matching can be calculated.

 

  1   Thu Nov 5 07:07:40 2009 ranaMiscRC noiseFrank's pictures in other log

http://nodus.ligo.caltech.edu:8080/AdhikariLab/423

  12   Fri Nov 13 12:46:35 2009 ranaMiscRefCavheaters for the other two chambers

For the heater, my main concern is on the residual thermal gradients after stabilization. The Alnis, Hansch, et al papers described how they had trouble with using multiple heaters and multiple sensors.

Our experience from the 40m is also that the single out of loop sensor (AD590) shows a much larger signal than the residual in-loop noise. This is only an issue below 10 mHz, so its not worth worrying about if it makes things take longer in the near term.

 

  13   Tue Nov 17 12:01:54 2009 FrankMiscRefCavheaters for the other two chambers

IQuote:

For the heater, my main concern is on the residual thermal gradients after stabilization. The Alnis, Hansch, et al papers described how they had trouble with using multiple heaters and multiple sensors.

Our experience from the 40m is also that the single out of loop sensor (AD590) shows a much larger signal than the residual in-loop noise. This is only an issue below 10 mHz, so its not worth worrying about if it makes things take longer in the near term.

 

my hope is that if we choose the right heaters with the same heating power density that we will not have large thermal gradients. e.g. if we choose 4 heaters in total, 2 small ones and 2 large ones and we choose the right values for the resistance (you have the choice of 5 different values)  then e.g. we first could connect a small and a large one in series and then both pairs in parallel or so. I don't wanna have individual drivers for the individual heaters. That should give us a fairly even temperature distribution of the entire chamber.

So far our plan is also that we add 5 or more sensors on each layer of insulation/heating in order to measure the thermal distribution and gradient throughout the entire insulation system.

  14   Wed Nov 18 20:45:52 2009 FrankMiscRefCavleaking vaccum valve

after getting the o-ring from the drever lab for the adapter to the turbo pump to pump the second chamber i figured out that the installed CF2.75 valve is leaking.
So while pumping with an external pump everything is fine but after disconnecting the external pump the ion pump can"t handle the leak rate and the pressure increases to a level where the ion pump switches off
.
The leak is so large that you can"t disconnect the external one and quickly close the open port with a blank one until the pressure reaches the limit for the ion pump.
Because we don"t have a spare valve i decided to close this leaking port and don"t use this valve for further pumping. Instead i build an adapter to the small valve for a tiny hose (<1/4") already installed.
By using this adapter the pump rate is tiny but i still have the chance to lower the pressure below the limit of the ion pump.
By now the pressure is low enough to switch on the ion pump. The current is less than 10mA by now and decreasing, so i think the pressure should be ok tomorrow.
 

In parallel i started building the thermal insulation for that chamber.

  18   Sat Nov 21 17:27:32 2009 FrankMiscRefCavold Minco heaters

found four old Minco heaters (model HR5494-106) (from 1995) .  This type with 106 Ohms is not in their system anymore.
But corresponding to their data the maximum current for this type of heater is about 7.5A. So driving this heater with 24V would give us 5.4W of heating power beeing well below the limit. Using the standard power supply for heating refcavs we can get even more power. Due to the age (14years!) the adhesive back is not sticky anymore so i will use aluminum tape for first tests.

Model
HR5494 
Silicone Rubber heater :
4.00" x 8.00"
(101.60 mm x 203.20 mm)
Heater Shape
Effective Area : 30.3 in2
(195.484 cm2)
 
Lead Gauge : AWG 24
 
Max. current : 7.5 Amps
 
Configure this model in Kapton
Application Information Actual Current : 0.21 Amps
Operating Temperature : °C   Heat Output at Volts
Resistance in Ohms
378 1.52 Watts 0.05 W/in2 (0.0078 W/cm2)
189 3.05 Watts 0.1 W/in2 (0.0155 W/cm2)
114 5.05 Watts 0.17 W/in2 (0.0264 W/cm2)
55.1 10.45 Watts 0.34 W/in2 (0.0527 W/cm2)
37.6 15.32 Watts 0.51 W/in2 (0.0791 W/cm2)
26.3 21.9 Watts 0.72 W/in2 (0.1116 W/cm2)
13.1 43.97 Watts 1.45 W/in2 (0.2248 W/cm2)
Leadwire Length
Units Inches    Centimeters
Up to 12" included in price. Over 12", up to 80" add $3.00
Heater Backing - Based on Operating Temperature (see above)
Type Temperature Maximum Allowable
Watt Density
A No Backing -45 to 235° C    
    Installation options for unbacked heaters
    #20 Stretch Tape -45 to 200° C   1545.3 W (51 W/in2)
    #6 RTV -45 to 235° C   887.4 W (29.3 W/in2)
    Factory Vulcanized -45 to 235° C   1656.4 W (54.7 W/in2)
B #12 PSA -45 to 177° C   1292.4 W (42.7 W/in2)
D 0.003" Aluminum Foil Backing -45 to 235° C    
E Foil with Acrylic PSA -45 to 150° C   1100.4 W (36.3 W/in2)
F Foil with #12 PSA -45 to 204° C   1100.4 W (36.3 W/in2)
UL Component Recognition
Check to have heater marked for UL component recognition
Part Number (as configured):   HR5494R114L12B
  58   Mon Feb 8 18:08:53 2010 FrankMiscAOMthermal images of AOM

took some images with the thermal imaging camera of the AOM installed in the PSL so far. The first three pictures show the AOM driven with 75MHz, 80MHz and 85MHz.

85MHz:
IR20100208_0013.jpg

80MHz:

IR20100208_0014.jpg

75MHz:
IR20100208_0012.jpg

it is interesting that the hottest zone is at the end of the crystal, not where the pzt is mounted. It looks like the crystal is not proper mounted. Here a normal image for comparison...
P1410925.JPG

so i took some pictures of a different AOM, but same model. Here are the pictures for different power levels @ 80MHz:

IR20100208_0029.jpg

IR20100208_0030.jpg

IR20100208_0024.jpg

this looks normal...

*** Rana: I've replaced Frank's AOM picture with a zoomed in one. This circuit looks a little sloppy to me - why are the coils so loose?

Attachment 4: P1410925.JPG
P1410925.JPG
Attachment 7: IR20100208_0024.jpg
IR20100208_0024.jpg
  68   Thu Feb 18 15:07:39 2010 FrankMiscLaserboth IR viewers missing

so please bring it back - we are waiting for it and can't go on without those... For the future: if you take it, bring it back and don't wait until someone is missing it...

  90   Tue Mar 23 00:26:43 2010 Frank, TaraMiscRefCavongoing work

over the weekend we baked the two AR-coated windows for the new chamber.  Bob doesn't need the oven the next couple of days so i restarted the baking again and will continue to bake the remaining parts the next couple of days. We also set up peters old vacuum pump. We got lots of stuff from 40m and cleaned all parts today. The pump is now running and pumping the whole system including the hose to the chamber. We also wrapped some heaters around the parts and started heating the stuff to make it a bit cleaner as no one knows for what the parts have been used before. They all looked pretty clean and wiping everything didn't show any obvious contamination. We can't bake it to high as some parts are viton sealed.

The new, insulated feet should be finished by wed or so. Tomorrow we start cutting the remaining foam to size and glue the parts together. I ordered the remaining heaters, one is already attached to the chamber and it fits good except that the sticky back is not sticky enough to hold it in place. The bending force is too high, so i added some aluminum tape which holds it in place now (the corners didn't want to stick). We have plenty of space for temp sensors and we will add several AD590 and a couple of platinum sensors. If we find out that the AD590 is not good enough we can easily switch to the other sensors. We should discuss how many we want and especially where. My guess is that we should add some more on this first prototype to get a feeling for the gradients or so. We can then reduce the amount on the second chamber if we want. The platinum sensors are cheap. Typically one is about $8-10 each, but  I bought a pack of 100 directly from the manufacturer and so its about $1 each only.

  91   Tue Mar 23 21:17:56 2010 Frank, TaraMiscRefCavfoam cut & partly assembled

we've cut the rest of the foam parts to fit on the smaller diameter (the main tube with the heaters). We already started to glue them together and have two halfs by now with a length of about 20". We have to make two thinner slices tomorrow to finish this inner part. We also have to glue the end caps together.

The current plan is to make 3 parts:

- one main section including the endcap parts divided into two parts which you put on the chamber from the sides

- one full endcap, which you put on the window from the end next to the edge of the table for easier access if we want to open the chamber

The current plan is to add one layer of aluminum foil and tie the three parts with aluminum tape together. We only need little force to put them together without any gap as we decided to use a 0.1" thick intermediate layer of foam which is typically used for wrapping stuff (its soft, flexible and Rod has plenty of it for packing things). This intermediate layer on top of the heater helps us to fill the gap between the heater, sensors and free space and the really stiff yellow foam. If we want to change things in vacuum we simple cut the aluminum tape along the junction and remove the endcap. This gives us full access to all the screws to open the chamber.

 

The new insulated legs should be finished by tomorrow morning...

  92   Thu Mar 25 13:05:59 2010 FrankMiscRefCavall parts baked

by now all parts are baked and ready for assembly. The only part we couldn't bake is the chamber itself. But Bob said that putting everything together and using the heaters on the chamber to "bake" the whole thing at lower temperature would be ok. So the plan is to assemble everything including an old 8l ion pump and bake the whole thing. As soon as all the insulation, temp sensors and stuff is ready we move the cavity into the (hopefully) clean chamber and replace the 8l pump by the 20l pump currently used on the other chamber.

  93   Mon Mar 29 17:46:41 2010 Frank, TaraMiscRefCavassembled new vacuum chamber

we cleaned and assembled the new vaccum chamber. we installed an electical feedtrough (for sensors we might wanna have inside, e.g on the thermal shields or the stack), an electrical isolator part for the ion pump( to avoid ground loops with the high voltage source for the pump) and the first AR-coated window. We will replace the second one after we moved the cavity. Right now we only have to mount the ion pump and then we can bake the whole thing before we finaly move the cavity to its new home.

The mechanical workshop has to rework the new insulated feet we got today. The upper part where the cavity sits on was machined really badly. It didn't fit to the chamber at all... 

We are still waiting for the additional heaters. They claim that they already shipped them last week so we don't know what happened to them. A week from San Diego to Pasadena? Who knows where they shipped it to (Antarctica?)

We've cut the last two parts of the insulating foam and glued everything together. Next we have to cut the holes for the flanges and feet of the chamber. The hole for the beam will be cut after we aligned the beam into the cavity

 

  94   Wed Mar 31 20:46:22 2010 FrankMiscRefCavion pumps

i've made a cable to test the two Varian ion pumps we have.  Before we move the cavity to the new chamber i would like to bake it and pump it using one of those pumps to see if everything is ok. Unfortunately we don't have a driver and a cable for those pumps. So i made a cable to use it with a Stanford high-voltage power supply. I hooked up the first pump to a test setup and it seems to be ok, but the valve i used is leaking so i gonna replace it by a spare one from 40m i got this afternoon. I will test the second one later. So as at least one is working we should buy a driver for that pump, maybe a used one or so. Right now we don't have any spare pump at all. Unfortunately the pumps used for the current chambers are different too ( totally different drivers and pumps), so we can't replace the failed part easily. I don't think that we have to worry but it might be handy to have one, e.g. if we want to use the third chamber to design and test the in-vacuum thermal shields.

  95   Thu Apr 1 15:38:38 2010 FrankMiscDAQRT DAQ equipment arrived

this afternoon the PSL RT DAQ equipment arrived and we moved all the stuff down to the PSL lab. We now have to expansion chassis, 6 A/D and 2 D/A cards available for the PSL stuff. Some of the stuff we have to share with Peter's power stabilization experiment, but some we can use for the cavity experiment. The current plan is to install a second front-end computer in the PSL lab which we can use for high-speed sampling of important signals of the stabilization setup. 

  96   Fri Apr 2 00:35:00 2010 FrankMiscRefCavnew chamber almost ready

the new chamber is almost ready. I've attached three of four heaters, the fourth one has a fabrication error and has to be replaced. The chamber is currently pumped using the old varian ion pump. Current is already down to 100uA and one can watch it further decreasing. So my guess is that it will be clean beginning next week. I turned on two of the heaters to "bake" it a little bit. I baked the ion pump this afternoon while pumping with the turbo at 250C. The new insulated feet are ready and fit now to the chamber. Next task will be cutting the remaining holes into the foam and putting the temp sensors on the chamber.

Here a picture of the current status:

100_0692.JPG

 

  101   Sun Apr 11 21:04:08 2010 FrankMiscRefCavheating power requirement

measured the power required to heat the new chamber to ~40C in order to design the driver circuit.

The heating consists of four silicone insulated heaters wrapped around the chamber, forming two identical halfs consisting of two heaters in parallel each (all heaters have the same power density)
both halfs can be connected in series or parallel, depending on our decision to drive more current or have a higher voltage.

I measured 11V / 0.47A for half of the heaters to reach a chamber temperature of 41.5C, so my guess is that we should connect them in series a power them by a single 24V power supply.
Total heating power required for 40C is therefore about 10W, compared to about 25W for the old chamber, even the new one is not totally insulated yet.

  112   Sun May 2 19:18:36 2010 FrankMiscRefCavreference cavity moved to new chamber

i finally moved the reference cavity to the new chamber and pump it since Friday. The legs are now insulated and it comes with a removable, thick insulation using the good CertiFoam25 insulation.The sensors for stabilization are now glued to small pieces of Kapton tap which is sticks directly to the chamber surface. I'm still using the four AD590 sensors as we have all the electronics available and ready to use. I modified the temperature sensor readout box a little bit to gain a little more SNR. The gain in the first stage (TIA) is now 29.4k (~9.2V output). The individual outputs are now connected to the DAQ. In addition the sum of all four is subtracted from a reference voltage (AD586 reference) so that the output is 0 at 35C with a range of +-5K (we need at least 4.5K for tuning one FSR, so to not be stuck at either ends i made it a bit larger ). This signal is also connected to the DAQ. An additional sensor (PT1000)  is now connected to the top plate of the stack, right below the reference cavity. Readout electronics is in preparation, as well as for the other platinum sensors we can put on the outside of the chamber (not done yet). I'm also planning on replacing the noisy power supplies by low-noise current sources to drive the heaters. The required heating power could be reduced a lot to ~10W total now, measured with a not fully sealed insulation and missing parts. So i expect even less when we are done with that.

  116   Thu May 6 11:01:03 2010 FrankMiscRC noisemodel now in the svn

i created a folder "frank" in the 40m-svn. It currently contains a subfolder "comsol" and another one "refcav".

The folder contains two files, one function "cavityStrain.m" and the main file "main.m" which contains the loop and other stuff. The three parameters are cavityStrain(constr, pltcnt, meshdensity):

  • constr is the value for an offset of the groove position from the original one in meters, so '0' is the original groove position
  • pltcnt is not used at the moment, it would create a 3d-plot of the result for each iteration
  • meshdensity is the fem mesh density using the same notation as comsol, so 9 is extremely course and 1 is extremely fine

the configuration right now creates a movie of all the results, with a name specified in the main file. The two plots created at the end show the strain and the tilt of the mirror.

You have to run the files from matlab. You can't open them in comsol.

  117   Fri May 7 15:51:43 2010 FrankMiscRefCavupdated schematic for new setup

refcav-setup_v1.png

  118   Mon May 10 00:29:04 2010 FrankMiscRefCavion pump current still too high

i checked the current of the ion pump. It's still at 75uA, much too high. So i think i have a tiny leak somewhere but i can't find it using isopropanol and we don't have a leak detector. The only changes from the bakeout setup are one of the windows, the replaced ion pump and the feedthrough for the temp sensor. I will wait some more days but my guess is that it won't be much better. It's already pumping for one week. If it doesn't change i will start replacing/checking the feedthrough seals and the ion pump. If that doesn't help it can only be the large window. That's in fact the only part never been tested before, all other parts were attached to the old or the current chamber before and OK.

  160   Mon Jun 14 10:16:54 2010 taracMiscOtherweird TF from PMC servo

Since the VCO has been borrowed, I decide to work on RefCav path again. To optimize the RefCav alignment, PMC will be locked to the laser while the laser frequency is modulated by a function generator. This is where a problem comes in. The PMC servo cannot catch up with the laser. Even though I lower the modulating frequency and amplitude to 4 Hz, 1 Vpp ,which roughly corresponds to ~1MHz shift in laser frequency, the PMC servo cannot stay stable for longer than a minute. so I measure the transfer function of the PMC servo, and it does not look right, see figure1. The real magnitude which goes to the PZT has higher value, since the signal comes out of the out mon channel passes through a voltage divider.

I also measured TFs of FSS servo, both Fast and PC paths look ok. I measure TF by using swept sine measurement , the source is split by a T connector, one goes to chA of SRS785, another one goes to TF1 test (where demodulated signal goes.) The output is taken from out mon (for PMC servo), fast mon (for FSS' fast path), PC mon (for FSS's PC path), and connected to chB of SRS785.

I made sure that I switch to the right path in the medm control screen when I measure the TFs

Attachment 1: PMC_bode.png
PMC_bode.png
Attachment 2: FSS_fast_bode.png
FSS_fast_bode.png
Attachment 3: FSS_PC_bode.png
FSS_PC_bode.png
  165   Tue Jun 15 21:28:57 2010 FrankMiscPMCPMC servo problem fixed

found the problem why the PMC servo card wasn't working: the medm screens on the sun workstation didn't have a toggle button for the disable signal for the variable gain amplifier (AD602). this signal was set to "disabled" by default and because there was no button to enable it Tara couldn't get the servo to work. added a toggle button on the screen, PMC is now locked stable

the PMC seems to be very dirty. If we lock it in s-pol the transmitted power is only 7%, even if 60% are going into it (didn't try to optimize it). the rest is dumped in the pmc. switched back to p-pol but should think about cleaning the mirrors. we also have first contact. i think it's worth a try and we can't loose much. peter has also spare mirrors (and a spare spacer)

  167   Wed Jun 16 10:26:01 2010 FrankMiscComputerslatest medm screens from Hanford

got the latest screens from Hanford in order to avoid such problems again in the future. Someone has to search and replace the channel names for the ones we wanna use. They are currently located in the home directory on fb1. will copy them to the sun workstation asap...

  172   Tue Jun 22 18:02:32 2010 FrankMiscRefCavheater-to-can time constant

measured step function from heater to can temperature. All four sensors show the same.

time constant ~7.5 hours, have to download and fit data for a more accurate value

StepResponse_Heater-Can.png

  173   Wed Jun 23 03:24:30 2010 ranaMiscRefCavheater-to-can time constant

In the entry below, Frank meant to add some commentary explaining that he thinks this long time constant is anomalously long.

At the 40m, it is much shorter. The insulation there is much thinner, and the can is somewhat shorter, but I think the main effect is that the steady state temperature of this can is too low. The temperature setpoint should be set to 35-40 C.

Then the time constant can be remeasured by doing a small step (~1 deg). We can't assume linearity over 10 deg - what we care about is the small signal time constant at the quiesscent temperature. Although the heating time and the cooling time will be slightly different, they will be comparable for small steps.

If the quiesscent temperature is set to be equal to the room temperature, it is insanity. We need to count on the room acting as a conductive and convective cold load since we only have a heater for an actuator and not a cooler.

  1704   Thu Aug 11 16:25:44 2016 awadeMiscDocumentationCertificates PO 75-S290726 and 75-S291757

Edit: I have moved the compliance docs to a private location.

 

Items for PO 75-S290726 and 75-S291757 have arrived.  

The following labels were generated and stuck to the box for future mounting
PBSO-1064-050
PLCX-25.4-1030.2-UV-1064
QWPO-1064-05-2-R10 x4
 

Items have been put in the lab and their certificates of compliance are attached here, on the wiki and their hard copies are in the lab.

 

  1706   Sun Aug 14 21:24:11 2016 awadeMiscTempCtrlKapton stick on resistive heaters

 

Edit: Datasheet was removed.

We have some kapton heaters, I found them in a draw when cleaning. These should be useful for our new shield temperature control.

These are from the kit KH-KIT-EFH-15001.  I don't know how old they are or if Kapton stickiness goes off, but here is a list of remaining available sick on resistive heaters and their Ohmage:​

Kapton resistive heaters in stock
Quantity Dimensions  Resistance [Ohm] Shape
1 0.75"x2.5" 23.5 Rectangular
1 0.75"x3.25" 33.2 Rectangular
1 1"x3" 40 Rectangular
2 2"x3" 103.7 Rectangular
2 2.5"x2.5" 108.6 Rectangular
2 1.5"x8" 252.0 Rectangular
3 3"x3" 153.7 Rectangular
1 1.5"x4.5" 120.3 Rectangular
1 6"x1" ? Rectangular
2 1.5"D 32.8 Circular
1 2"D 59.4 Circular
1 3"D 169.0 Circular

 

Data sheet is attached. Note that heating ranges from 3-8 W per square inch at the 12 V supply level for various different choices of shape and wire pattern.

 

  1707   Thu Aug 25 07:36:06 2016 ranaMiscTempCtrlKapton stick on resistive heaters

I think we'll need a sketch of the physical layout in order to do the plant modeling for the heating loop. OzGraffle.

  1710   Tue Aug 30 10:28:07 2016 AidanMiscTempCtrlKapton stick on resistive heaters
I've ordered a few of these Kapton heaters to fit the new shields: https://dcc.ligo.org/DocDB/0122/D1500403/002/D1500403-v2.PDF

 - KHLV-204/2-P

 - KHLV-0502/5
  1723   Mon Sep 26 19:52:52 2016 awade & AidanMiscDocumentationHeat shields arrived, checked

Aidan has received the two heat shields (D1500403 rev2) and four caps (D1500213 rev3) back from the manufacturer. We unpacked them to inspect and check the caps fitted in. They do. Attached are the photos for the record. They all appear to be in acceptable condition. The paper wrapping appeared to be the type to release a lot of particles, parts will need cleaning by the people doing to gold plating before adding a layer of Au.

Next they are to be sent to be gold coated.

 

 

> > I've ordered a few of these Kapton heaters to fit the new shields: https://dcc.ligo.org/DocDB/0122/D1500403/002/D1500403-v2.PDF > > - KHLV-204/2-P > > - KHLV-0502/5

Attachment 1: 20160926_New1.45inchRefCavShieldsAndCaps.zip
  1724   Tue Sep 27 10:05:36 2016 awade & AidanMiscDocumentationHeat shields arrived, checked

Google photos link: https://goo.gl/photos/9SbnGPHjuHfVd3sg7

Quote:

Aidan has received the two heat shields (D1500403 rev2) and four caps (D1500213 rev3) back from the manufacturer. We unpacked them to inspect and check the caps fitted in. They do. Attached are the photos for the record. They all appear to be in acceptable condition. The paper wrapping appeared to be the type to release a lot of particles, parts will need cleaning by the people doing to gold plating before adding a layer of Au.

Next they are to be sent to be gold coated.

 

 

> > I've ordered a few of these Kapton heaters to fit the new shields: https://dcc.ligo.org/DocDB/0122/D1500403/002/D1500403-v2.PDF > > - KHLV-204/2-P > > - KHLV-0502/5

 

  1725   Tue Sep 27 18:32:13 2016 awadeMiscEnvironmentLab cleaning: testing different swiffer pads

I wasn't sure if wet or dry swifter pads would pick up more debris from the ground so I got sample packs of both. The dry ones seem to do ok and don't leave a surfactant residue or scent which can be overpowering after a few layers on the lab floor.

I ran the dry cloth type over the PSL lab and then the wet. This isn't really a good controlled experiment but you can see there wasn't so much left over for the wet (pad with green strip) to pick up. This would indicate that the dry pad got most of the dust.

 

Dry polyester swiffer cloth left, wet sweeper pad right. First pass with dry pad followed by wet pad.

The dry pads are made of felted polyester which quickly generates a electrostatic charge that draws in dust. With a simple test after rubbing over the floor, it seems statically attract and hold an optics cleaning tissue with reasonable strength.  The only issue is that it does have some small fibers, I'm not sure if any of these would escape, they seem reasonably contained within the pad.

  1727   Tue Sep 27 22:17:40 2016 awadeMiscVacuumNew windows on ends of vacuum can

We want to down size the size of the view port windows so we can have a higher quality IBS AR coated windows and also lower the surface area of fused silica. Fused silica has a relativlty high emissivity at far IR wavelengths at about ~0.75, this will lead to stronger coupling to the lab temperature variations.

Rana has suggested maybe a cone shaped end cap: https://goo.gl/photos/QfRoyrRAczHSjbpr5 . This comes to a point where a conflat mountable assembly with a small window could be fitted. We could also use a flat plate and attach a window to that. This seems like it would easier to manufacture. 

After talking to people, it turns out the cryo people are planning on making their own (Johannas is supposed be drafting something like this I think). We should probably try to have one standard size between experiments to save work.  

Before talking to cryo people, I had drafted up a simple assembly (attached below) that would make use of the following off the shelf parts:

This may be faster to build than a cone and serve the same basic purpose of minimizing the area of window. These accuglas 1.33"CF mounts take optics that are diameter 0.874" (thickness.159"), which seems propriatory and maybe not ideal if we want to get our own custum coatings or make changes in the future.  It sound like there might be a few 1" wedged AR coated windows maybe at the 40 m, if this is the standard size, then it might be better to find a different mount.
 
I have attached drafts of the above parts put together as a first draft and kick off elog posts on topic.
 
 
 
 
 
 
Attachment 1: DMountStyleWindowMounting1.JPG
DMountStyleWindowMounting1.JPG
Attachment 2: DMountStyleWindowMounting4.JPG
DMountStyleWindowMounting4.JPG
Attachment 3: 110032_10InchBlank_WtHolesForPorts.PDF
110032_10InchBlank_WtHolesForPorts.PDF
  1729   Thu Sep 29 19:41:47 2016 awadeMiscSafetyLaser containment curtain

I have asked Nichole Washington to book a maintenance job to have the laser curtain installed in the PSL lab.  I unpacked the items from delivery tube and they are consistent with the packing list.  All the necessary parts are in the entrance area of the lab.  

 

ELOG V3.1.3-