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ID Date Author Type Category Subject
1345   Wed Mar 9 09:31:50 2011 ranaLaserPurchasesRF amplifiers : Cougars

The Cougar superiority comes from the low gain and high output level. Since it can put out ~20 dBm without distortion and has a gain of +10 dB, it can handle inputs with +10 dBm.

The other two amps can only handle inputs of around -10 to -5 dBm before they saturate highly. So the true noise performance is actually worse for those once you consider our setup:

namely, that we have a gain of 10 opamp ahead of it which is putting out ~20 nV/rHz of noise at all times. So the difference between 1 dB NF and 3 dB and 5 dB is totally inconsequential. The 3 dB NF is just an input noise of 1 nV/rHz.

In reality, the transmission readout doesn't need any of these since the signal is so large. The PDH diodes will have in-loop signals of somewhere between -10 and 0 dBm going into the Cougar. I believe we can only use those high gain, low output power RF amps in the case where we have very low light.

1169   Mon Nov 15 23:03:39 2010 ZachLaserGYRORFAM

On Friday evening, I acquired the primary error signal into the ADC with the cavity obstructed so that it would not resonate. I tuned the HWP before the EOM so that the error signal was centered about zero. I wanted to see if the RFAM was truly oscillating in amplitude or just monotonically increasing to some level after I had minimized it. Here is a short (5-hour) time series beginning right around then. The following 48 hours looked essentially the same, with a slight variation in the oscillation period and peak-to-peak level.

Today, I tried to get a quantitative handle on the RFAM level, but I was sidetracked by the weird behavior. I once again tried to minimize the circular light getting through the input optics by iteratively adjusting the initial QWP and the HWP immediately after it and minimizing the P light getting through the PBS. I was able to obtain a maximum contrast of 55.5 uW to 159 mW over the full range of the HWP for the optimal QWP setting, so that only ~0.03% of the light remained circularly polarized.

Then, I adjusted the HWP just down the line (immediately before the EOM) to center the far-from-resonance error signal about zero. I observed the same drift as before. I then put my hand on the metal case of the EOM and the drift increased rapidly, indicating that the time dependence of the RFAM is likely due to thermal coupling.

I verified that the beam was not clipping on either end of the EOM (there was some scatter from the edges of the beam, but the spot was centered on the aperture). I tried changing the alignment slightly to see if the drift lessened, but this failed.

I then tried swapping out the HWP for another---no dice. Then, I swapped the EOM for another broadband ThorLabs modulator of the same model. This seemed to work for a few minutes, as the drift appeared less pronounced, but it worsened quickly. It also responded the same way to the "grab the damn thing" test.

An interesting observation: the HWP orientation that minimizes the RFAM when looking at the signal from the PD on the RF analyzer IS NOT the same one that centers the error signal DC level at zero (in fact, the cavity will not lock at this setting). Conversely, when the error signal is centered at zero by setting the HWP, the PD signal shows strong RFAM (~40 dBm above noise level). This is baffling.

As my frustration was maturing, I caught the following sight (several of them, actually, but this was the only one I froze in time) on the scope:

Green is TRANS_DC, yellow REFL DC, blue ERR_INMON (note the offset), and purple the actuation signal to the PZT. The cavity has been locked for quite some time, but the slow loop is not engaged. As the length of the cavity slowly drifts, the feedback signal hops discretely from one level to another. This particular one is about a 3.5-volt step, corresponding to about 14 MHz. I am no expert, but this looks to me like some sort of mode hopping. There is not (and has never been) a dedicated faraday isolator at the experiment input, so I think it is quite possible that back-reflections are getting back into the laser head. From what I understand, mode hopping is uncommon in a short NPRO, and I'm not sure how this would affect the output polarization of the laser, but it seems suspicious. By the time I gave up, the circular light contrast had decreased by a factor of more than 4 (i.e. the minimum achievable power with the same QWP orientation was > 200 uW).

1170   Thu Nov 18 09:27:18 2010 KojiLaserGYRORFAM & Sprious RF coupling
• Checked the alignment of the beam at the input optics
• Checked the RF leakage to the PD.
• It turned out the isolation transformer and the cable at the function generator caused the main leakage source.
• By removing them the leakage was improved 20~30dB.
• At the end of the experiment the RFAM level (RF leakage + RFAM) was -85dBm for the beam of ~100mVDC
• The alignment of the interferometer is now totally screwed up.

1. Alignment check of the IO

The original angle reads of the wave plates were 316deg and 38.0deg for the QWP and HWP, respectively.
The beam power before the EOM was 284mW.

• FIrst, the wave plates after the laser were adjusted so as to minimize the PBS transmission.
• The PBS was also aligned to minimize the transmission.
• With the angle setting of 318.2deg and 78.3deg, the power of 48uW reached the EOM.

• Rotated the HWP to maximize the PBS transmission.

At the last state, with the angle of 318.2deg and 33.7deg, the power of 284mW reached the EOM.

• Beam alignment to the EOM was checked. It was OK, but the slight touch of the alignment was made.

After the adjustment the power after the EOM was 274mW. The transmission efficiency of 96.5% sounds pretty fine.

2. RF leakage investigation

• The primary cavity RF PD was aligned to the beam. I temporarily removed the attenuation mirror. The DC output (with 50ohm) was 90.9mV
• I tried to minimize the 18MHz RFAM by tuning the HWP for the EOM.
• I minimized the RFAM but I noticed that the amount of the RF is comparable with and without the beam

• The leakage RF power at 18MHz was ~70dBm. This corresponds to the RIN of 10-3. It was there even without the beam on the PD.

• I tracked down the cause of the leakage and found that the leakage power was reduced when the cable between the isolation transformer and the coupler is replaced to the SMA cable.
• Another discovery was that the leakage decreased when the isolation transformer is removed.
• See the attached photo 1.

• The overall improvement was 20-30dB (seen in the attachment 2) although the peak height is continuouwly changing.

• It is always difficult to understand how the RF leakage is improved: The isolation transformer isolate the grounding of the RF source and the others. The line is somehow grounded at various places. Maybe at the EOM or/and the LO ports? They may have not low impedance to the reference ground of our system and cause fluctuation of the voltage level on the table, the aluminum frame of the table, or the power line. Then they couples to the PD???
• I imagine that we previously cancelled the RF leakage by putting an artificial RFAM by the EOM. But both the amount of the leakage and the RFAM was always changing. They may have caused the locking problem.

• Now I went back to the HWP before the EOM. The HWP was adjusted to minimize the RFAM peak (forgot to record the angle!).
Also Yaw alignment of the EOM was slightly adjusted to minimize this peak further.
• The resulting RF leakage of -85dBm was recorded. Shown in the attachment 3. This corresponds to the RIN of 2x10-4.

4. Power supply AC path

• I noticed that one of the AC tap is obtained the power from the ceiling while another one is taking the power from the wall.
(Attachment 4)
Is this what you really want? I am afraid of having big ground loop.

• Suggestion:
• Get some isolation transformers for the AC / define the grounding point of the experiment.
• Also ground the optical table and the Al frame.

Attachment 1: cabling.jpg
Attachment 2: reduction.jpg
Attachment 3: IMG_3714.jpg
Attachment 4: IMG_3715.jpg
1362   Thu Mar 24 09:07:17 2011 Alastair & ZachLaserGYRORFAM re-measured

Here is the RFAM measurement redone.  First plot is the full spectrum from DC to 100MHz.  Second plot is put together from multiple scans to give higher resolution in the area of interest.  We used the same setup as before, but with an 1811  instead of the PDA255 to improve bandwidth.  The steps in the plot at 15MHz and 25MHz are the points where the scans have been joined.

Attachment 1: full_spectrum_RFAM.png
Attachment 2: 5_MHz_to_35_MHz.png
1363   Thu Mar 24 11:35:38 2011 ranaLaserGYRORFAM re-measured

I guess that this is a transfer function between the source out of an RF analyzer and the RF output of the New Focus 1811 PD (which goes up to 125 MHz). If so, It looks like the EOM is nicely free of mechanical resonances in the band we care about, Nice job, Thorlabs.

1323   Thu Feb 24 01:29:09 2011 ZachElectronicsGYRORFPD #01 TF

I chose the "final" component values for the first RFPD as follows. Consult the schematic here.

• AC coupling
• L6 = 6.8 uH
• 66 MHz notch
• L2 = 1 uH
• C10 = 5.8 pF (1.5 - 15 pF tunable)
• C2 = 24 pF
• C4 = 7 pF (1.5 - 15 pF tunable)
• L3 = 750 nH

I have taken a transfer function with the Jenne Laser setup and the result is reasonable but not exactly what we expect. Below is a comparison of the measured transfer function with the prediction from LISO. To get these in a comparable form, I took the raw output of the spectrum analyzer (the ratio of the responses of the DUT and the New Focus 1611 reference PD), multiplied by the flat AC transimpedance of the reference PD (700 V/A), and subtracted the 10 dB of gain from the Cougar (AP1053).

Some notes:

• As far as the readout and 2f rejection are concerned, the two transfer functions match up fairly well with the exception of a discrepancy in Q.
• Though the two phases show the same basic behavior, there is a large overall shift across the measurement band. I have no idea why this is.
• The most staggering difference is that the peak from the AC coupling resonance is much higher in frequency for the measured data. I have been using C = 200 pF for the diode in simulations, while Perkin-Elmer claims that this should be < 150 pF when biased as we have it, but even decreasing it to this level doesn't account for the higher measured frequency.

I have a suspicion that just subtracting 10 dB does not accurately negate the effect of having the Cougar on the end. Though it says nothing about it on the datasheet, I have heard that they have some sort of internal AC coupling, and so this odd behavior could be explained by that somehow. I think I will take the transfer function again, this time using a probe to sense before the Cougar instead of after it, and hopefully then it will conform with the model. In the end, all we care is that it behaves as expected near where we expect to have appreciable input signals (e.g. 33 MHz and 66 MHz), but it;s nice to be able to say that we know what's going on everywhere.

Another thing I noticed on the Cougar datasheet is that the noise figure goes up pretty quickly as you go below ~50 MHz. Using naked-eye extrapolation, I estimate that it is about 3.7 dB @ 33 MHz. I have taken a noise spectrum of the PD, but I am not comfortable enough with the TF calibration to trust the analysis yet. Stay tuned.

1324   Thu Feb 24 03:54:29 2011 FrankElectronicsGYRORFPD #01 TF

Nice work!

According to your schematic the bias is 5V. If that is the case the capacitance is usually much less than 150pF!
If you check the typical graph in the datasheet the capacitance is ~120pF@5V.
According to the data i measured i expect it to be below 120pF @5V.
Old LIGO diodes had about 105pF@ 7V. The diode you are using is one of those old batches.
If you like we can measure it tomorrow with my pulsing setup. Doesn't take longer than 5 minutes including setting everything up and getting the data

 Quote: I chose the "final" component values for the first RFPD as follows. Consult the schematic here. AC coupling L6 = 6.8 uH 66 MHz notch L2 = 1 uH C10 = 5.8 pF (1.5 - 15 pF tunable) 33 MHz readout C2 = 24 pF C4 = 7 pF (1.5 - 15 pF tunable) L3 = 750 nH I have taken a transfer function with the Jenne Laser setup and the result is reasonable but not exactly what we expect. Below is a comparison of the measured transfer function with the prediction from LISO. To get these in a comparable form, I took the raw output of the spectrum analyzer (the ratio of the responses of the DUT and the New Focus 1611 reference PD), multiplied by the flat AC transimpedance of the reference PD (700 V/A), and subtracted the 10 dB of gain from the Cougar (AP1053). Some notes: As far as the readout and 2f rejection are concerned, the two transfer functions match up fairly well with the exception of a discrepancy in Q. Though the two phases show the same basic behavior, there is a large overall shift across the measurement band. I have no idea why this is. The most staggering difference is that the peak from the AC coupling resonance is much higher in frequency for the measured data. I have been using C = 200 pF for the diode in simulations, while Perkin-Elmer claims that this should be < 150 pF when biased as we have it, but even decreasing it to this level doesn't account for the higher measured frequency. I have a suspicion that just subtracting 10 dB does not accurately negate the effect of having the Cougar on the end. Though it says nothing about it on the datasheet, I have heard that they have some sort of internal AC coupling, and so this odd behavior could be explained by that somehow. I think I will take the transfer function again, this time using a probe to sense before the Cougar instead of after it, and hopefully then it will conform with the model. In the end, all we care is that it behaves as expected near where we expect to have appreciable input signals (e.g. 33 MHz and 66 MHz), but it;s nice to be able to say that we know what's going on everywhere. Another thing I noticed on the Cougar datasheet is that the noise figure goes up pretty quickly as you go below ~50 MHz. Using naked-eye extrapolation, I estimate that it is about 3.7 dB @ 33 MHz. I have taken a noise spectrum of the PD, but I am not comfortable enough with the TF calibration to trust the analysis yet. Stay tuned.

1339   Sun Mar 6 00:43:02 2011 Zach ElectronicsGYRORFPD #02 TF

I took a transfer function of RFPD S/N 02 tonight with the Jenne Laser. It was much easier to calibrate this one because I didn't have to worry about what the Cougar was doing (since I didn't put one on this board). I also noticed that for some reason the power leaving each port of the beamsplitter was not equal---there was about 2x the power going to the reference PD as to the DUT---this explains why I was getting less gain than expected by about this factor with the last PD.

Here is a transfer function:

Some notes:

• With the resonant notch (aka "aLIGO style") readout, the easiest way to tune the readout notch using an optical transfer function like this is to actually tune the parasitic parallel resonance that occurs nearby to the frequency predicted by a model such as LISO. Before I tuned RFPD01, I found that for a 33 MHz notch and a 200-pF diode capacitance, this resonance occurred at ~35 MHz. As I learned after doing that, the diode capacitance with a 5V bias is more like 100 pF (which explains why the AC coupling resonance of the first PD did not match with the model). I had "35 MHz" stuck in my head today when I tuned the second PD, which means that the readout notch is actually at a lower frequency than 33 MHz. I adjusted the readout notch capacitor in the model so that the TF matched the one I took and it gives a value of about 31 MHz. I will retune it to the proper value (and do the same for the first PD).
• Another, perhaps easier, way of making sure the readout notch is at the right frequency is to just look at the voltage above the readout capacitor (instead of at the output, which is an amplified version of the voltage between the capacitor and inductor). Here, the readout notch looks just like the rejection notches and can be tuned directly. I think I'll just do this rather than rely on unknown or sketchily known parameters.
• Besides slight differences in frequency and Q, the measured and predicted transfer functions match up very well, as opposed to the case with the Cougar involved (see link in last bullet). For this reason and more importantly for reasons that will be highlighted in my next post, I propose that we do away with the Cougar altogether for the time being. You can read ahead or just remember that the noise figure of the AP1053 is >3.5 dB at 33 MHz; It's not worth it for this application.
• I took a noise measurement of this PD, but I forgot to turn off the light source before doing so. The noise is a factor of ~1.5-2 worse than predicted, which could either be a non-ideality in the circuit or else it comes from noise on the light amplified by the PD. New measurement after the retuning.
1076   Wed Sep 22 00:58:47 2010 ZachElectronicsGYRORFPD LISO model

Attached are a transfer function and noise estimate for a proposed gyro (TRANS) RFPD circuit, generated by LISO. It is topographically identical to the one that Rana made a while back, with the two following modifications:

• the components have been adjusted to change the resonant frequency from 80 MHz to 95 MHz to reflect the current setup, and
• the "resonant readout" and "AC coupling" inductors have been interchanged, in line with how it is done on the aLIGO board.

Here I have included reasonable series resistances for the large and small inductors.

If you compare with the above-linked post, you can see that the noise is at about the same level, with a slight increase because we are right at the MAX4106's bandwidth limit for the prescribed gain of 450/50 = 9.

I am not sure what the other options for photodetector circuitry are, but it seems that this sort of LC design will work (at least for the TRANS PDs, where the signal will be limited by the shot noise of the REFL PDs that gets imprinted on the cavity light, as mentioned in Rana's post), and it can be done on the aLIGO boards.

1290   Fri Feb 4 23:45:40 2011 ZachElectronicsGYRORFPD board problem solved

I was going to continue stuffing board #2 this evening, but I got the urge to take another stab at the problem with the first board. I removed some other components and was able to make the short go away.

It went something like this:

• I realized that even though I had removed all capacitors and diodes touching the -15V supply, I hadn't removed the AD620 itself, which was powered by it. Once I did this (and replaced it with a new one), the resistance between -15 V and GND was Mohms.
• I plugged everything back in and turned on the power, but the lab supply still current limited the negative voltage.
• Knowing that the AD620 was at least part of the problem opened the playing field to a much wider part of the board. I found that the 4.7uF capacitor in the bias path had failed, so I removed it. This was a polar tantalum cap that I had made very sure to put in facing the right way (which I did). I'm not sure what caused it to fail.
• Again I plugged everything back in and turned on the power. This time, the current was below the limit, but still way too high (~250 mA). I found that the LMH6624 was getting pretty toasty, so I replaced this one too.
• Finally, the board was acting normally. I replaced the +/-15 V regulators, as well as the -5 V one (during the tests I was just supplying +/-15 V to the test points) with new ones. I also replaced the bypass capacitors. I did not yet replace the tantalum cap, which I don't think is crucial at the moment.

So, we have a working board that is ready for (real) testing.

1253   Sat Jan 22 19:54:20 2011 ZachElectronicsGYRORFPD box

I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together.

The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish.

The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box.

I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order.

As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.

Click on the picture to open the multi-page PDF.

1254   Sat Jan 22 21:59:46 2011 AlastairElectronicsGYRORFPD box

Nice!

Maybe we can have a different name than "Generic PD" on the box though.  I only called the files that because the board is designed to be generic until it is stuffed.

 Quote: I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together. The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish. The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box. I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order. As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.   Click on the picture to open the multi-page PDF.

1255   Sun Jan 23 12:17:45 2011 ZachElectronicsGYRORFPD box

Yeah, I was imagining that this would be a box for any such PD. I thought we would order some and have them sitting on the shelf next to the boards. In any case, we could have 4-5 of them made special for the gyro; that sounds like fun.

Quote:

Nice!

Maybe we can have a different name than "Generic PD" on the box though.  I only called the files that because the board is designed to be generic until it is stuffed.

 Quote: I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together. The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish. The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box. I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order. As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.   Click on the picture to open the multi-page PDF.

1256   Mon Jan 24 00:47:54 2011 KojiElectronicsGYRORFPD box

I could not get how the PD is mounted to a pedestal.

The PD should not move back and forth by the rotation so that the beam can not be defocussed.
Horizontal translation of the PD by the rotation is barely tolerable if the tilting of the PD by ~20deg makes the translation of the center by several mm.
Otherwise, the PD may escape from the range of the steering mirror everytime when we tilt the diode against the beam.
This naturally limit the distance of the diode surface from the rotation axis to ~10mm.

But the rotation axis should not be too much distant from the center of mass so that the PD can stably stand without a fork.

Considering the density of the optics on the table, a slim, thin, and tall (but not too much tall) PD which is left-right symmetric is the natural choice.

Then, we may need some amount of compromise in the above conditions.

Ed: I opened the PDF and got that the PD is actually skinny and tall. I was a bit confused by the page 5 as the side panels at P.5 is actually the top and bottom plates
as far as I understand. The only improvement I can thing about is that the PD is not at the symmetric location with regard to the mounting hole at the bottom.

Quote:

Yeah, I was imagining that this would be a box for any such PD. I thought we would order some and have them sitting on the shelf next to the boards. In any case, we could have 4-5 of them made special for the gyro; that sounds like fun.

Quote:

Nice!

Maybe we can have a different name than "Generic PD" on the box though.  I only called the files that because the board is designed to be generic until it is stuffed.

 Quote: I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together. The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish. The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box. I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order. As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.   Click on the picture to open the multi-page PDF.

1257   Mon Jan 24 12:06:14 2011 ZachElectronicsGYRORFPD box

You are right about the side panels in the figure from the manual will actually be the top and bottom panels; I did it this way so that the un-tappable side profiles will not be on the top or bottom (where we will mount the PD to the base). The dimensions will be in a different ratio to what is seen there. If you are facing the PD so that the diode is looking at you, it will be 120 mm wide x 70 mm tall x 42 mm deep, something like an old digital camera.

About the PD not being centered, I did it this was to minimize the size of the box (since the PD is not centered on the PCB). I could move one of the mounting holes to be directly below it, but I guess I imagined that we will---at least eventually---use a solid base instead of a post, so we will be rotating the entire block and then clamping it down with dogclamps or something.

I am of course open to suggestions about this, but I think Rana didn't like the idea of using posts.

Quote:

I could not get how the PD is mounted to a pedestal.

The PD should not move back and forth by the rotation so that the beam can not be defocussed.
Horizontal translation of the PD by the rotation is barely tolerable if the tilting of the PD by ~20deg makes the translation of the center by several mm.
Otherwise, the PD may escape from the range of the steering mirror everytime when we tilt the diode against the beam.
This naturally limit the distance of the diode surface from the rotation axis to ~10mm.

But the rotation axis should not be too much distant from the center of mass so that the PD can stably stand without a fork.

Considering the density of the optics on the table, a slim, thin, and tall (but not too much tall) PD which is left-right symmetric is the natural choice.

Then, we may need some amount of compromise in the above conditions.

Ed: I opened the PDF and got that the PD is actually skinny and tall. I was a bit confused by the page 5 as the side panels at P.5 is actually the top and bottom plates
as far as I understand. The only improvement I can thing about is that the PD is not at the symmetric location with regard to the mounting hole at the bottom.

Quote:

Yeah, I was imagining that this would be a box for any such PD. I thought we would order some and have them sitting on the shelf next to the boards. In any case, we could have 4-5 of them made special for the gyro; that sounds like fun.

Quote:

Nice!

Maybe we can have a different name than "Generic PD" on the box though.  I only called the files that because the board is designed to be generic until it is stuffed.

 Quote: I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together. The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish. The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box. I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order. As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.   Click on the picture to open the multi-page PDF.

1258   Mon Jan 24 12:57:15 2011 ranaElectronicsGYRORFPD box

Quote:

You are right about the side panels in the figure from the manual will actually be the top and bottom panels; I did it this way so that the un-tappable side profiles will not be on the top or bottom (where we will mount the PD to the base). The dimensions will be in a different ratio to what is seen there. If you are facing the PD so that the diode is looking at you, it will be 120 mm wide x 70 mm tall x 42 mm deep, something like an old digital camera.

About the PD not being centered, I did it this was to minimize the size of the box (since the PD is not centered on the PCB). I could move one of the mounting holes to be directly below it, but I guess I imagined that we will---at least eventually---use a solid base instead of a post, so we will be rotating the entire block and then clamping it down with dogclamps or something.

I am of course open to suggestions about this, but I think Rana didn't like the idea of using posts.

You can right click to delete these annoying yellow boxes.

You can right click to delete these annoying yellow boxes.

You can right click to delete these annoying yellow boxes.

You can right click to delete these annoying yellow boxes.

Quote:

I could not get how the PD is mounted to a pedestal.

The PD should not move back and forth by the rotation so that the beam can not be defocussed.
Horizontal translation of the PD by the rotation is barely tolerable if the tilting of the PD by ~20deg makes the translation of the center by several mm.
Otherwise, the PD may escape from the range of the steering mirror everytime when we tilt the diode against the beam.
This naturally limit the distance of the diode surface from the rotation axis to ~10mm.

But the rotation axis should not be too much distant from the center of mass so that the PD can stably stand without a fork.

Considering the density of the optics on the table, a slim, thin, and tall (but not too much tall) PD which is left-right symmetric is the natural choice.

Then, we may need some amount of compromise in the above conditions.

Ed: I opened the PDF and got that the PD is actually skinny and tall. I was a bit confused by the page 5 as the side panels at P.5 is actually the top and bottom plates
as far as I understand. The only improvement I can thing about is that the PD is not at the symmetric location with regard to the mounting hole at the bottom.

Quote:

Yeah, I was imagining that this would be a box for any such PD. I thought we would order some and have them sitting on the shelf next to the boards. In any case, we could have 4-5 of them made special for the gyro; that sounds like fun.

Quote:

Nice!

Maybe we can have a different name than "Generic PD" on the box though.  I only called the files that because the board is designed to be generic until it is stuffed.

 Quote: I've used Front Panel Express's design program to build a box for the RFPD. The attached PDF has 4 panels (front, back, top, bottom). The other two sides are fixed-width (42mm) side panels that are made by FPE. I have attached one page of their enclosure design manual so that you can get a rough idea of how it is put together. The overall dimensions are 120 mm x 70 mm x 42 mm. All panels except for the bottom are 4 mm thick anodized blue, while the bottom is 1 cm thick (for rigidity) with natural finish. The PCB that Alastair designed and has ordered will mount onto the front face of the box (where the PD will emerge from the bottom of the board), with the voltage regulator contacts mounting to the top of the box. I am fairly sure that I've done it correctly, but the one thing I am not sure about is the SMA flange mount, which was not built in as a macro so I had to do it myself. In building it I realized that it is not really clear how we will connect the SMP ports on the board (for DC & RF Out) with the BNC and SMA outs on the back of the box. I assume that there are adapters for just this purpose, but we should double-check this before we put out the order. As it stands now, the total quote (including the panels and hardware but not including the connector flanges which they don't sell) is \$172. That seems a bit pricey, but we might be able to trim a little off by changing the design slightly. For example, they charge \$10 for each of the panels on which they have to mill the bottom side. They have to do this for the front and back panels so that the edges fit into the side profiles. Presumably, the entire panel is anodized, so we can just have the edges milled out on the front side when we don't have to have anything written on it (like the front panel where the PD sticks through). All I would have to do is reposition the hole for the PD accordingly. Of course, the price goes down slightly if we order 5+.   Click on the picture to open the multi-page PDF.

1259   Mon Jan 24 13:16:01 2011 ZachElectronicsGYRORFPD box

cool.

1269   Wed Jan 26 01:42:44 2011 ZachElectronicsGYRORFPD box

I've updated the box model to have D-holes instead of flange mounts for the BNC and SMA outputs. We will make short patch cables that go from SMP->SMA and SMP->BNC inside the box. The D-sub-9 in on the board will likely have a ribbon cable connecting it to the back panel of the box where there will be a through connector. Since our initial PCB order didn't go through, we may have one last chance to revise this, but it certainly won't be the end of the world if we can't.

I have changed the spacing of the 1/4-20 taps in the bottom panel so that one of the outer ones is directly below the PD. This doesn't sacrifice the integrity of the design and it makes it so that we don't have to worry about rotating the PD out of the beam path during the initial phase when we just use posts to mount the boxes to the table.

We should start thinking about how we want our mounts to look. They will probably be blocks of brass or something that have holes countersunk from the bottom so that we can screw them to the bottom of the PD boxes. In between the base and the box, we should have an insulating layer thick enough to avoid capacitative ground loop coupling. I'm not sure what kind of screws we'll use to avoid DIRECT coupling...

1278   Fri Jan 28 17:40:28 2011 ZachElectronicsGYRORFPD box

[Alastair, Zach]

Here is the (hopefully) final draft of the RFPD box. Alastair is currently drafting a design for the base, so any comments must come quickly.

For the front face, the idea is to mill a hole and cavity in a circular copper plate that fits snugly around the diode. The diode will then be held in place between the front of the box and this ring once it is screwed on. This will also serve as a thermal contact between the diode and the box, and we can make the contact better by applying some thermal compound between them. There are three 4-40 taps around the PD hole so that we can screw the plate on from the front.

As I mentioned before, I have spaced out the 1/4-20 taps in the bottom, 1-cm panel so that one of the holes is directly beneath the PD. This is so that we don't rotate the diode out of the beam path when we initially use a simple post to mount it to the table (while we wait for the solid bases).

734   Fri Apr 23 17:20:34 2010 ZachElectronicsGYRORFPD circuit

I finished stuffing our first RFPD board with everything we want (for now) this afternoon. This one will be used for one of the transmission PDs, so I tuned it to 95 MHz. The transfer function looked a little funny (it was oscillating at ~130 MHz), but Rich thinks this will go away once the diode is installed.

On Monday, I'll install the diode, do some more stuff with the test input, and then we can try some optical demod funny business.

1216   Wed Dec 15 15:41:45 2010 Alastair & ZachElectronicsGeneralRFPD design

Here is our layout for the RFPD in Altium. We are working on routing the board now.

Attachment 1: RFPD_1.pdf
1219   Wed Dec 15 22:29:27 2010 FrankElectronicsGeneralRFPD design

you don't wanna have 4 power supplies to power the detector, way too complicated. I would change it to power the entire thing by +/-24V and regulate that to +/-15V. Then use the already regulated +/-15V to regulate it down to something else in addition.

 Here is our layout for the RFPD in Altium.  We are working on routing the board now.

1220   Wed Dec 15 22:36:05 2010 AlastairElectronicsGeneralRFPD design

You mean we don't want two +/- connectors run from two separate supplies?  I only put them on there because we are planning on running it from the NIM crate.  You're right though that we should make it just one +/- supply because it is meant to be a general design.  I'll alter it so the 5v regulators are powered from the 15v ones.  Thanks.

I do have a question for someone about how we make up the board.  At the moment we're modifying the aLIGO design, and it has all the power planes inside the board.  My question is this - do we want to add in two extra planes to take the +/-15v to the other opamps?  The number of layers is starting to look like a lot.

Quote:

you don't wanna have 4 power supplies to power the detector, way too complicated. I would change it to power the entire thing by +/-24V and regulate that to +/-15V. Then use the already regulated +/-15V to regulate it down to something else in addition.

 Here is our layout for the RFPD in Altium.  We are working on routing the board now.

1221   Thu Dec 16 03:50:33 2010 ranaElectronicsGeneralRFPD design: comments
1. Add pads around all the voltage regulators for diodes to prevent transient spikes (e.g. preventing the 7815 output from spiking higher than its input).
2. Add pads to allow more capacitors around the voltage regulators; the large caps ought to be bypasses by little ceramic caps.
3. May want to add an L between the +15V and the power supply pin on the RF amp. This is sometimes done for RF amps to keep the RF out of the supply for the other guys who need +15V.
4. The 4107 can develop DC offsets. Should AC couple the output going in to the RF amp.
5. Add a series L-C in parallel with the R8. Sometimes we like to put a notch in the feedback of the 4107 to get extra notch action.
6. Put a note on the schematic (almost obvious) that all resistors must be metal film. If any resistors require more than a 1/8W power rating, it should be indicated on the schematic.
7. Since the 4107 is nearly obsolete, you ought to also scope out another amp and list it in the schematic notes as a good replacement choice.
8. Put a note on there about what the hell a AP1053 is.

Otherwise, looks pretty good to me. Make sure to calculate the input-referred noise of the AD620 with the gain setting that's there to make sure you're happy with the circuit's RIN sensitivity.

1224   Thu Dec 16 15:27:12 2010 AlastairElectronicsGeneralRFPD design: comments

The 4107 replacement that Rich suggests using is the LMH6624MA.  It's pin for pin compatible with the 4107, which is why I hadn't changed the part on the board - I'll do that now though just to avoid confusion.

The AP1053 is a teledyne-cougar RF amp.  Highlights are:

• Gain doesn't roll off till above 1GHz
• 50 ohm input and output
• Power output of 26dBm.
• This is the 10dB gain model, but it is pin for pin compatible with a whole load of others in the range so we can swap in whatever gain we want.
• Rich tells us the input will be internally AC coupled, so we don't need to do this on the board.  Looking at the website and the datasheet this isn't explicitly mentioned though.

 Quote: Add pads around all the voltage regulators for diodes to prevent transient spikes (e.g. preventing the 7815 output from spiking higher than its input). Add pads to allow more capacitors around the voltage regulators; the large caps ought to be bypasses by little ceramic caps. May want to add an L between the +15V and the power supply pin on the RF amp. This is sometimes done for RF amps to keep the RF out of the supply for the other guys who need +15V. The 4107 can develop DC offsets. Should AC couple the output going in to the RF amp. Add a series L-C in parallel with the R8. Sometimes we like to put a notch in the feedback of the 4107 to get extra notch action. Put a note on the schematic (almost obvious) that all resistors must be metal film. If any resistors require more than a 1/8W power rating, it should be indicated on the schematic. Since the 4107 is nearly obsolete, you ought to also scope out another amp and list it in the schematic notes as a good replacement choice. Put a note on there about what the hell a AP1053 is. Otherwise, looks pretty good to me. Make sure to calculate the input-referred noise of the AD620 with the gain setting that's there to make sure you're happy with the circuit's RIN sensitivity.

1228   Fri Dec 17 22:07:00 2010 AlastairElectronicsGeneralRFPD design: comments

Do we need to add extra caps to both the input and output sides of the regulators, or just the output side?

RA: Both. There are multiple schools of thought on what gives the best performance, so its best to have both possibilities. The large electrolytic caps give good filtering of the low frequency stuff but also have a big inrush current when the supply is first activated. Even so, it would be good to have a pad available so that we can have a large-ish cap on the input and output with a 35V or higher rating. Its not necessary that it be surface mount - could also use tantalum. There's no need to make it larger than 100 uF.

2786   Tue Jun 21 10:35:15 2022 Clare NelleDailyProgressEmissivity estimationRTD Calibration

RTD Calibration Plan Developed on 16-06-2022:

1. Prepare an ice bath and liquid nitrogen bath to calibrate the RTD.

1. Ice bath: fill cup (?) with ice. Fill with water until 2 inches below the top of the ice. Let sit for 2 minutes before calibration.

2. We will use a DMM to measure the resistance across the leads. Right now, we are thinking that we will connect the leads to the resistor using alligator clips or solder them together.

3. Use linear fit to calibrate the RTD value as a function of resistance using these two reference values.

4. Repeat for all three RTDs

-----------------------------------

1. Q: What is the tolerance of the resistor?

1. 100 ohm +/- .06%. Means that our calculation if done correctly will be between 99.4 → 100.6 ohms in the ice bath. Our RTD is class A, which has tolerance +/- .15 degrees. Pt-100 SHOULD be 100 ohms at 0C – the temp changes linearly.

2791   Wed Jun 29 09:39:01 2022 Clare NelleDailyProgressEmissivity testingRTD Calibration Day 2

We debonded the RTDs from the chamber using isopropanol and acetone, then soaked the RTDs in isopropanol for about 15 minutes to remove residue. We then took resistance measurements in ice water detailed below:

Ice Water Calibration Measurements (completed 28-06-2022):

1) Prepared ice water bath by filling beaker with crushed ice and then water to one half inch below the ice surface. Let the ice bath sit for about 1 minute.

2) All six RTDs were measured (labeled A-F). For each RTD, the resistance in the ice water bath was measured by swirling the RTD held by the DMM leads in the water until the DMM readout stabilized.

3) These measurements were repeated in the reverse direction (Started with RTD F).

*Note: in the process of ice bath calibration, RTD D broke.

 RTD Trial 1 ($\Omega$) Trial 2 ($\Omega$) A 100.2 100.15 B 100.15 100.3 C 100.1 100.1 D X X E 100.1 100.1 F 100.1 100.1

Liquid Nitrogen Calibration Measurements (completed 30-06-2022):

Procedure: We clipped the DMM leads to the RTDs and taped the two clips together. This is very secure - good method for the future. We dipped the taped clips with the RTD into the LN2, and swirled under the liquid surface until the DMM readout stabilized. We only took one set of measurements because we are very confident of the boiling point of N2.

*Note: RTD A broke. This is because we spread the RTD wires out to put into the aligator clips, making them very prone to snapping when we move them. This means that we do not have an RTD on the cold head.

Results (ohms):

A: X

B: 19.8

C:18.2

E:18.5

F:19.8

Attachment 1: ice_bath_calibration.xlsx
2602   Mon Jul 12 14:42:42 2021 StephenDailyProgressCryo vacuum chamberRTD attached to coldhead with spring clamp, Si mass to be installed this week

Brief summaries of the last week's progress and the coming week's plans (plots will be posted soon!):

- progress Friday 09 July: Opened the cryostat up at the cold head, and attached an RTD to the cold head with a spring clamp (instead of relying purely on the cryo varnish).

- progress Monday 12 July: Found 65 K workpiece temp and 63 K cold head temp. RTD was apparently held successfully by spring clamp, and we will continue to collect cold head temperature in future runs. Warmup was started, with old data collection completed (cooldown_20210709) and new data collection commenced (warmup_2021_07_12). Note that warmup started at 1:14 pm, and it took me ~ 5 minutes to stop and restart the script to changeover to the warmup data collection.

- table plan Wednesday 15 July: Complete in-air optical layout. Make one flat face of Si mass reflective.

- chamber plan Thursday 16 July: Open up main volume and drop in frame with Si mass. Connect RTDs. Start cooldown. Confirm cooldown is going ok (optical alignment, especially), and revert if necessary before things get too cold.

- table plan Friday 16 July: Maybe measure stuff, maybe better to wait till coming week and use controlled heating to hit different temperature setpoints.

797   Thu Jun 3 03:24:41 2010 DmassLab InfrastructureFuglyRack terrible-ness

The rack has been moved away from the wall, and the 300V power supply to the PZT is half perched on/in the blue ADC box, whose top is partially hanging into the box itself. This was very much not the state it was last seen in.

Attachment 1: 00001.jpg
31   Sat Feb 16 15:33:25 2008 DmassLaserPSLRadial Beam Profile
The following were taken with the beam scanner (having gone through a number of optical elements).

After leaving the main laser housing, the beam hits:
polarizer -> PBS -> low reflectivity pickoff mirror -> 1m lens -> 0.5m lens -> 45-P HR mirror -> 45 P HR mirror -> beamscan.

In taking my initial waist measurements, I had the beamscan after the LR pickoff, and the beam looked similar.
Attachment 1: 2_16_0835w.bmp
2276   Fri Dec 7 16:08:45 2018 RahulDailyProgressCryo vacuum chamberRadiation shields

The cold plate and radiations shields (100K, 50K and bottom 100K shields) are at 40m for cleaning and baking. The outer shields will be cleaned and then sent for gold plating. The inner shield and cold plate be baked after cleaning.

Attachment 1: shields_1.jpg
Attachment 2: shield_2.jpg
Attachment 3: shields_bottom.jpg
2429   Thu Oct 10 17:28:33 2019 Raymond, ChrisDailyProgressCryo vacuum chamberRadiation shields unpacked

Today we unpacked the radiation shields and started to puzzle out how to assemble them. Attached are photos of the parts as we guessed they are intended to stack up. We didn't see how the outer shield would be supported and isolated from the cold plate, so we are contacting Rahul to clarify.

One detail not shown in these photos is the rather poor weld quality on the interior of the outer shield.

Attachment 1: IMG_20191010_150645.jpg
Attachment 2: IMG_20191010_150700.jpg
Attachment 3: IMG_20191010_150711.jpg
Attachment 4: IMG_20191010_150757.jpg
Attachment 5: IMG_20191010_150817.jpg
Attachment 6: IMG_20191010_150826.jpg
2695   Fri Nov 12 14:31:38 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

In this phase, we are working toward improving our setup with a rigid copper bar, and obtaining a new data point for our radiative cooling thermal models for a suspended silicon mass. Since the past cooling runs of a silicon test mass did not yet incorporate aquadag-painted shields, we wanted to obtain a new data point in the model (in other words, we painted the shields in QIL/2645, but the next test was a PD measurement, so this is the first silicon test mass measurment after shields were painted). The improvement to the thermal linkage, now using a rigid copper bar with higher conductivity (ref. QIL/2666), is a second variable being changed simultaneously in the spirit of improving the cooldown time.

Refer to the prior post (QIL/2694) for the bulk of the blow-by-blow of configuring the chamber to use the rigid copper bar linkage. This post will describe the mounting of the Si mass, and the pump down and cool down.

• The silicon mass with Aquadag barrel was dropped into the existing frame, with the previous wire arrangement and with no particular requirement on position or orientation (just best effort centering and leveling). Adjustments were done chamberside as access was easier.
• The frame was lifted into the chamber, with the hanging mass supported by auxiliary fingers, and placed in an available area. Since conductive cooling was not a dominant mode of heat transfer in this setup (ref. QIL/2647), clamping to the baseplate was simply a single dog clamp on each foot of the frame.
• The cigarette paper was cryovarnished to the surface in the bare central position. Once the cryovarnish was set, the RTD was cryovarnished to the cigarette paper pad. No  strain relief or thermal anchoring considerations were implemented. RTD continuity was verified.
• Lids were bolted down and shields were finalized (avoiding shorting to copper bar, making sure foil drapes covering apertures were well positioned, etc.
• Vacuum pumps on at ~3 pm, cryocooler on at 3:30 pm. At 4 pm, things are still looking good!

Closeout photos will be posted to the QIL Cryo Vacuum Chamber photo album.

Attachment 1: IMG_2738.jpeg
Attachment 2: IMG_2741.jpeg
Attachment 3: IMG_2742.jpeg
Attachment 4: IMG_2745.jpeg
Attachment 5: IMG_2747.jpeg
2697   Fri Nov 19 14:01:40 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

[WIP]

11/16 was the first Megastat cooldown after exchanging the copper braid linkage for a copper bar. Attachment 1 compares the cooldown trends for the test mass, inner and outer shields, and cold head. The solid curves are the new cooldown trends (copper bar), and the faded dashed curves are the previous cooldown trends (copper braid).

Immediate observations:

- The coldhead has a reduced heat load, and interestingly a second time constant governs cooldown from ~2-35 hours.

- The inner shield time constant is reduced significantly, but the inner shield experiences a slightly greater heat load at steady state.

- The test mass cooling is improved as expected, given inner shield cooldown.

- The coupling between the outer shield and inner shield has increased, resulting in greater cooling of the outer shield. This could explain the added heat load to the inner shield.

Attachment 1: comp_cooldown_728_cooldown_1116.pdf
2701   Fri Dec 10 15:58:57 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity

Started a new run this afternoon, with the following goals:

1) confirm that the first run (QIL/2695) went smoothly, by performing a visual inspection in the chamber while setting up for the first run.

- kapton tape affixing inner shield RTD lead junctions to inner shield had fallen. These junctions were simply hanging - not ideal, but apparently not too harmful. Not likely to impact temperatures, in my opinion, but could have led to shorts or glitches in data.

- all RTDs appeared to be fixed and well-contacted to surfaces

- Everything seemed to be in good shape with the copper bar, no apparent issues

2) obtain a second run with similar configuration, now that the rigid copper bar linkage has been implemented.

3) vary a single important parameter relative to the first run, namely the inner surface emissivity of the inner shield, so that the impact of that parameter may be observed.

- Added Aluminum foil (matte side visible) to the inner shield inner surfaces (lid and cylinder, both). Anywhere there was previously black Aquadag, there is now matte aluminum foil.

- Kept the same apertures for viewport access and for electrical and thermal connection passthrough, basically attempted to achieve identical shield coverage.

- There is one small sliver of black aquadag visible at the location of the electrical leads, but I didn't worry about patching that small area.

Run Details:

- Pumps on at  ~3:40 pm

- Cooling started at 4:13 pm (pressure ~6 mTorr, rapidly falling with turbo pump spinning up from ~70% to ~85% over a 1 minute interval). Coldhead RTD is responsive.

- All photos will be posted to the QIL Cryo Vacuum Chamber photo album.

- Note from check in on Monday afternoon, ~ 69 hours after start: everything looks good, and the workpiece temperature (~127 K) seems to reflect the emissivity change.

2702   Thu Dec 16 15:54:44 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - CTC100 temperature control success

This post will host plots and trends from this radiative cooling run. At a glance, the tuned CTC100 PI control was able to control the workpiece steady state temperature in this radiative cooling test within .005 K.

Run description: At 4 pm Wednesday, the workpiece temperature was at steady state from the QIL/2701 cooldown, a little less than 120 K. From 4pm Wednesday thru 5pm Thursday (25 hours) the CTC100 controller was actuating on the workpiece RTD temperature (cryovarnished to the suspended Si mass) using the resistive heater (dog clamped to baseplate with indium foil gasket). The conductive heating of the cold plate, and therefore the inner shield, led to radiative heating capacity (via ΔT)  that actuated on the temperature of the suspended test mass. As found in QIL/2643, the suspended Si mass is well isolated from conduction to the cold plate.

Before the run, the CTC100 PID controller was allowed to autotune using a long lag (600 s) and a moderate acutation step (10 W). After autotuning, the D term was still 0, which seemed fine.

Data: Attachment 1 plots cooldown curves for all RTDs during this run. Attachment 2 compares this run's test mass and inner shield temperature curves to those from the previous run (Aquadag on inner surface of inner shield). The expected result of this change (coating inner surface of inner shield with Al foil) is a weakened radiative coupling between the inner shield and test mass, leading to less effective cooling of the test mass.

Initial observations from data:

1) The cold head temperature curve again suggests 2 time constants, and cooldown is identical.

2) The inner shield's cooldown is roughly unchanged.

3) The outer shield's temperature drops significantly more, indicating a stronger coupling to the inner shield. We will check for a conductive short the next time we open up.

4) The test mass's cooldown matches expectations (weaker radiative coupling).

[WIP - The data will be fitted and discussed]. More detailed analysis from fit to come, including from heater runs.

Attachment 1: cooldown_12-10_all.pdf
Attachment 2: cooldown_12-10_vs_11-16.pdf
2704   Tue Dec 21 15:33:39 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - next run repeating

I opened the QIL cryostat today for a health check and visual inspection before the next run. Because I saw a couple of interesting issues, I decided to redo the same run with more attention to detail on the closeout. I'm worried the outer shield may have been linked to the inner shield and baseplate enough to affect comparability with the prior run.

issues with this  run, requiring redo:

• RTD wire for outer shield was clamped under lid of inner shield - this might have created a conductive link between the inner shield and the outer shield
• outer shield was more wobbly than usual, and could have possibly been off of the three spacers - this might have created a conductive link between the outer shield and the baseplate

run details:

• pumping started at 3:45 pm
• turbo started with 15 minute delay at 20 torr
• cryocooler started at 4:15 pm with active ion gauge pressure at 3 e-4 torr.

And since I didn't get to implement any of the intended next runs, here are some notes on other future runs of interest:

• Si mass covered with Al foil (matte side facing out) - interested in making the emissivity of the test mass equal to that of the inner shield in the new config, for modeling.
• (of course, this emissivity equivalence would be an approximation, as there is a large area of the test mass which is bare silicon)
• outer shield clamped/resting on baseplate - this is predicted by Koji to be the most efficient cooling configuration.
• shielding attached to structure holding Si mass (electropolished aluminum, aquadag aluminum, bare aluminum surfaces are all available.
2705   Wed Dec 31 15:59:59 1969 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - retry run was successful

This post will host plots and trends from this radiative cooling run (QIL/2704).

Preliminarily, it looks like the reconfiguration to remove a hardware mistake or two led to a healthier run. The comparison below clarifies the two runs:

• QIL/2702 - conductive link between inner shield and outer shield (twisted pair from an RTD lead accidentally clamped); possibly another conductive link between outer shield and baseplate (outer shield more wobbly than usual on spacers)
• this data set should only be used to study the impact of a known conductive link between inner and outer shields.
• this run demonstrates that there will be more effective, faster cooling if the outer shield is conductively cooled!
• QIL/2704 - resolved above mistakes!
• this data set may be used to gain understanding of the impact of emissivity changes to the inner surface of the inner shield.
• may be compared to QIL/2695, a run that is equivalent except with a higher emissivity inner surface of the inner shield

Run ended with cryocooler shutdown at 12:27 pm (actual duration just under 92 hours). System will warm up with pumps on for the rest of the break, unless I am inspired to come in and run one of the next intended runs discussed in QIL/2704. I did not run any heat input test for this data set, as I am not planning to come in frequently enough to monitor the heating safely.

Data:

Attachment 1 compares QIL/2704 (solid) to QIL/2702 (dashed). As expected, the outer shield temperature from the latter run stays warm since the conductive short was resolved. Due to the reduction of the inner shield's thermal load, the inner shield is able to cool faster and plateau at a colder temperature. As Stephen pointed out, however, the test mass is not cooled as efficiently compared to when the outer shield was conductively cooled.

Fitting Results:

Attachment 2 is a current model diagram of the various components being considered, and their thermal couplings. Attachment 3 plots the fitted model (dashed) over the temperature data (solid). The fit parameters were the following emissivities: aluminum foil, rough aluminum, and aquadag. Notes from the fit:

1. With the conductive shorting of the outer shield resolved, the model (which considers only radiative cooling of the OS) is well fit to the OS temperature data

2. The inner shield model is missing some key term(s) affecting its time constant and steady state temperature.

3. The above error propagates to the test mass model (I believe).

Given these caveats, the fit results are as follows: aquadag e = 0.92, Al foil e = 0.04, rough Al e = 0.19. These all initially seem reasonable, and I'm happy to see that the aquadag emissivity is higher than previously estimated.

Next steps:

1. Separate the cold plate from the inner shield, and model their conductive and radiative link. Also model the radiative link between the cold plate and the test mass.

2. Cover the test mass in foil (to best of our ability) to refine the radiative link between the test mass and inner shield. Doing so will mean both elements have the same emissivity, so there is only one unknown parameter.

Attachment 1: cooldown_12-21_vs_12-10.pdf
Attachment 3: 12_21_cooldown_fit.png
2078   Fri Dec 16 12:41:50 2016 awadeLab InfrastructureGeneralRain, lab checkup

It has rained (something on the order of 50 mm) in the last two days.  I checked the ATF lab, no water inside.

2060   Mon Aug 8 17:05:28 2016 ranaMiscGeneralRaspberry Pi beam profiles: possible student project

UCLA project. Should we try to make one of these?

2063   Tue Aug 16 16:01:21 2016 awadeMiscGeneralRaspberry Pi beam profiles: possible student project

Looks kind of cool. Could probably skip the LCD interface and have it screen forward to any laptop or maybe python imbedded in a self hosted html webpage or iPad app?

Many CCDs seem to have some pretty low saturation points which makes them a pain for profiling some beamsI remember an undergrad experiment I did with a setup where we had a razor blade on a stepper motor. If accuracy of step precision was good enough (and repeatable enough) with a reasonable PD could make a beam profiler with a much bigger dynamic range on power. The only problem was that there was some strange relaxation in razor blade position.

It would be cool if we could fit it on something like a linear stage or an old scanner bed stepper to get a full automatic profile of a beam.

 Quote: http://hackaday.com/2015/12/21/raspberry-pi-laser-beam-profiler/ UCLA project. Should we try to make one of these?

177   Thu Jul 16 04:59:38 2009 DmassLaserPSLRazor Blades!

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Attachment 1: Photo_1.jpg
Attachment 2: Photo_3.jpg
178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!

 Quote: Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below. I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

179   Thu Jul 16 17:43:59 2009 DmassLaserPSLRazor Blades!

Quote:

 Quote: Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below. I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

I got about a .002" error using a micrometer with my other setup, I expect this will suffice. If the errors in position end up too large I will use the new setup.

182   Fri Jul 17 15:39:31 2009 DmassLaserPSLRazor Blades!

 Quote: Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below. I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Using the setups in the quoted post, I took manual beamscans 23" in front of the PSL enclosure, before the first steering mirror, and fit P = A erf(B*x + C)

I measured the relative position of my razorblade with a micrometer and calculated the error from an estimated uncertainty of it's angle. This seemed to agree with repeatability of measurements for a given experimental state. Uncertainty < .002"

I watched the Power meter for ~ 60 seconds for each measurement, it fluctuated around some point and seemed to not be drifting @ DC, so the upper and lower error bars of each point included are the bounds of the fluctuation of the power meter. These were less than +/- 5mW about my points, so a fractional uncertainty of about 2% at my maximum power.

I got waists of:

Vertical: 799 +/- 4.5 microns

Horizontol 827 +/- 1.2 microns

Attached plot includes data w/ error and functional form of fit

As expected, my Chi^2 is "bad" since I am fitting the input beam to the PMC with a 00 mode description of the waist, which ignores all higher order modal content.

Attachment 1: RazorScans.pdf
184   Mon Jul 20 23:19:49 2009 ranaLaserPSLRazor Blades!
Yeah, real micrometer with a reading is > plain screw.
188   Tue Jul 21 20:41:56 2009 DmassLaserPSLRazor Blades!

 Quote: Yeah, real micrometer with a reading is > plain screw.

Converting from flemish ells was hard. I'll just use a mic next time.
1286   Fri Feb 4 16:58:39 2011 AlastairLaserGYRORb Clock data

Here is the data from our Rb clock frequency noise measurement that was on the 40m elog here.

Attachment 1: RbMeasurements.txt.zip
1780   Sat Nov 3 13:20:27 2012 AidanComputingComputingRe-compiled Real Time Model with TCS channels

I saved the existing ATF model as atf.mdl.ctrl and built a modified version for some temporary TCS real-time work for aLIGO. The new ATF model is saved as atf.mdl.tcs (and currently as atf.mdl).

The new model compiled and was installed. It still runs all the GYRO stuff (which was all unaltered) but I replaced the defunct CTRL block from the doubling experiment with a new TCS block.

- should the old model need to be replaced, this can be done by copying aft.mdl.ctrl to atf.mdl and compiling with fb0:/cvs/cds/advLigo\$ make atf install-atf

Attachment 1: Screen_Shot_2012-11-02_at_11.51.42_AM.png
ELOG V3.1.3-