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ID Date Author Type Category Subject
1460   Thu Jul 21 10:08:19 2011 Alastair & ZoeElectronicsGYROAmplifiers for temperature sensor readout

Yesterday we changed the circuits for the temperature sensor readout. We got rid of the black box entirely and added a second board to the NIM crate with the amplifiers. The current setup is as follows:

Voltage regulators in NIM crate give +-15V. +15V goes to temperature sensor through red wire. Temperature sensor creates CURRENT, proportional to temperature, which is sent directly to NIM crate through black wire. Red and black wires are twisted together and connected into the NIM crate using a 2 pin connector (not a BNC cable/connector). Current from temperature sensor goes to an inverting transimpedance amplifier with a 10k feedback resistor and then to an inverting summing amplifier. At the input of the summing amplifier, the voltage from the transimpedance amplifier goes through a 10k resistor is added to the voltage from a +5V voltage reference which has gone through a 15k resistor and a 2k resistor in series, effectively making it +2.93V. The summing amplifier has a feedback resistor of 10M to make its gain. This means that after both amplifiers the output that comes out of the NIM crate in a BNC cable is the DIFFERENCE between the measured temperature and 293K, with 1V = 1K. So 1V represents 294K, 2V represents 295K, etc. We chose the gain we did to make the range of output +-10K (not to minimize noise).

Picture below shows both circuits in the NIM crate. The board on the left has the voltage regulators and transimpedance amplifiers; the one on the right has the voltage reference and summing amplifiers.

2248   Wed Aug 29 17:43:05 2018 John MartynDailyProgressHomodyneAn Elusive Short Circuit and a Functional BHD

Last week, I worked on adding bypass capacitors and new op amps (with higher slew rates and lower noise) to my BHD circuits in order to reduce noise and improve their performance at high frequencies. Unfortunately, in the process of this, I accidently created a short circuit, and the circuits ceased to work. After I couple days of unsuccessful troubleshooting, I decided to create new circuits for the BHD. These are identical to the ones used before. A schematic of the circuits and a labelled picture of them are attached to this elog entry. The labelled picture shows where the different parts of the circuit are located, in case anyone would like to make adjustments to them. One comment I have about these circuits is that OP27's were used. Rana recommend that we use op amps that will perform better than the OP27 at high frequencies, and we opted for the OP37 instead. However, the OP37's did not arrive in time for me to install them (I believe they arrived this week). Nevertheless, I installed op amp mounts on the BHD circuits, so the OP27's can be easily taken out and replaced by OP37's without having to do any soldering.

I have also attached labelled images of the panels of the box in which the circuit lies. These display where the input power goes, and how the outputs from the circuits are configured.

Once the circuit was set up, Andrew and I tested it out in QIL. Andrew fixed some configuration issues with the ADC that had plagued us earlier (the cables were not matched correcly), and I hooked up the BHD circuit box to our optical setup. The circuits were powered by the +12V, -12V, and ground pins from the back of an SR560. Some pictures of this setup are attached to this elog.

We first injected a sinusoidal signal of 123Hz and peak to peak voltage of 2V into the ADC in order to calibrate it. After collecting and analyzing the data produced by the ADC, we found the factor for converting from ADC counts to volts to be roughly$6.098 \cdot 10^{-4} \frac{V}{\mathrm{Counts}}$. A plot of the sinusoidal voltage signal obtained with the ADC is attached to this entry for justification.

To test the BHD, we amplitude modulated the laser at 1.234 kHz and analzed the noise produced at the BNC2 outputs of the circuit. Some resulting plots are attached to this elog. The first was obtained by performing signal subtraction with the SR785, and adjusting gain on the SR560's to balance the signals. The next plot was obtained via digital subtraction from ADC data. When the signals are unbalaned, there is a large spike in the noise spectrum at 1.234 kHz, corresponding to the noise in the modulated light. When the signals are balanced, this noise peak decreases significantly.

In order to decrease the noise in our spectrum, we used SR560's to amplify the BNC2 output of the BHD circuit before sending the signals to the ADC. This allowed us to decrease the noise floor to roughly $20.2 \frac{\mathrm{pA}}{\sqrt{\mathrm{Hz}}}$ when the gain was set to 1000. This value is close to the noise floor of the BHD of $12.6 \frac{\mathrm{pA}}{\sqrt{\mathrm{Hz}}}$, which is shown in the same plot.

Overall, the BHD is functioning properly, but improvements could be made. In particular, we would ideally like to further decrease its noise (and noise floor) below the shot noise of the incident light. A few changes should improve its performance:

• Amplify the signal at a higher gain (the SR560 overloaded past a gain of 1000, which limited our noise reduction abilities. A low noise pre-amplifier would come in handy here)
• Bias the photodiode
• Add bypass capacitors to the +V and -V pins on the op amps
• Replace OP27's with new op amps (OP37's have arrived!)
Attachment 1: BHDCircuitDiagrams.pdf
Attachment 2: Panels.pdf
Attachment 3: Setup.pdf
Attachment 5: BHDSR785IRNoise.pdf
Attachment 6: BHDIRNoise.pdf
1919   Thu Apr 30 21:41:38 2015 KateMiscSeismometerAnalytic estimate of primary mass moments of inertia and frequencies

I made a crude model of the primary mass to compute an order of magnitude check of its moment of inertia compared to the Solid Works model results.

I treated the system as a set of 4 infinitely thin rods and 2 cuboids. The rods each have mass 0.5 kg and the cuboids 5 kg and the system is 0.82 m tall. My script is attached, which calculates the moments of each object about its own center of mass and then uses the parallel axis theorem to find the moments about the system's pitch axis. I get a pitch moment of 2.02 kg m^2 and roll of 1.98 kg m^2 (the difference is due to the cuboid being deeper than it is wide). This is reasonable in comparison to Stephanie's results of 1.43 kg m^2 and 1.40 kg m^2. The SolidWorks yaw result is 1.19 kg m^2; I still need to compute my estimate.

From Malik's single loop suspension document (T000134), the pitch and yaw resonant frequencies are, respectively:

$\omega_\theta ^2 = \frac{m_{tot} g}{I_\theta L} b (L+b) \newline \omega_\phi ^2 = \frac{m_{tot} g}{I_\phi L} R_1 R_2$

and quantities are defined as in the script below. L is the wire length; b the separation from the wire suspension point and the system's center of mass; R1 and R2 are the separations between the wires at the top and bottom suspension points, respectively.

Using the SolidWorks moments of inertia with my estimates of the other parameters (defined in script and with R1 and R2 of 5 cm and 20 cm), the resonant frequencies are:

• pitch = 46 mHz
• yaw = 210 mHz
Attachment 1: MOI.m
%% tilt-free seismometer primary mass
% estimate of pitch moment of inertia
% KLD Apr. 30, 2015

%  ===========       <-- cuboid mass
%  |         |
%  |         |
%  |         |
%  |         |
%  |         |       <--> pitch axis about which system rotates

... 61 more lines ...
1763   Fri Sep 7 03:33:03 2012 ZachLaserGYROAnatomy of the current noise floor

I think I am getting pretty close to understanding the current noise floor.

What I know (or think I know):

• At high frequencies---well outside the gyro band---the primary gain is too low, and so noise spills over into the secondary loop as apparent gyro signal. This is a repeatable, well-understood effect.
• At low frequencies, some RAM-like effect dominates, and that is why we often see strong coherence between the gyro noise and the OOL RAM monitors here.
• We are also now very close to the predicted "FSR modulation noise" at low frequencies, and, depending on the RAM level at any particular time, this may be the dominant effect below a few tens of mHz.
• This has not ever been definitively measured, but it is a pretty straightforward thing to estimate geometrically: it is just the residual differential component of the cavity length fluctuations seen between the counter-propagating beams due to their being on adjacent axial modes.
• Until last week, we were naively thinking we would have to physically stabilize the cavity length to get rid of this. This is completely unnecessary as the noise can be subtracted very well using a simple constant-gain feedforward.
• Between these two regimes, there is some flat noise at a level of ~80 (nrad/s)/rtHz.
• Repeated, systematic gain redistribution tests and detailed noise estimates suggest that this is not caused by any kind of electronic noise.
• It is not oscillator phase noise; using a lower deviation setting of 100-1000 Hz ensures that the phase noise level is well below here.
• Also, the low-frequency noise can be made MUCH worse by misaligning the beams going into the cavity. This is always something to check if the LF noise seems particularly bad. I have locked the actuators since the last realignment, and the LF noise has not deteriorated over days.
• Also, it seems that placing foil over the unenclosed CCW input path (the part that doesn't fit in the IOO box) helps to avoid excess LF noise.

Since there has been some limited success with RAM subtraction, what worries me the most is the middle region where we can't really explain what is happening.

I was doing some noise estimation/subtraction testing when I noticed that the sum of the estimated FSR noise and the manually scaled OOL_CW come pretty close to explaining the noise level (really the OOL_CW by itself, since the FSR noise is much lower by 100 mHz). It is only below the measured noise by a factor of a few:

Until tonight, I had assumed that I was just seeing the dark noise of the PD above ~300 mHz, especially since I was just using a PDA255 with relatively low optical power before. Now that the noise is so close, and now that I'm using a high-quality aLIGO BBPD, it seems worth double-checking.

Here is a comparison of the OOL_CW signal while the gyro is running with the dark signal. Full disclosure: the dark noise was measured the other day using a slightly different setup, but I'm fairly confident I have the calibration right. The 60 Hz line seems to be a pretty good indicator that it is.

So, it looks like the flat noise in the OOL_CW signal is actually on the light, which means that it could explain the gyro noise, as well. If you zoom in on the other plot above, there are plenty of places where the OOL and gyro signals match up pretty well. Unfortunately, I don't have the corresponding OOL_CCW data because I was using the demod setup for the PLL readout, BUT, I would be willing to bet that the sum of the two OOL PD signals here gets pretty close to the gyro floor. I will investigate this tomorrow.

It seems like messy business to subtract two similar flat noise levels and expect ~1% residual noise, so I'd rather get to the bottom of what is causing this noise floor.

Anyone have any idea what could be doing it? Let me know!

232   Thu Aug 6 09:55:39 2009 AidanComputingDAQAnd it all comes crashing down again ...

It appears that the frame builder has stopped writing to file again. Actually what I see if the following:

1. I can't retrieve any data from the last couple of days in dataviewer or DTT
2. I can see data from three days ago.

I'm not sure why this is. Perhaps the disk is full again. Restarting the frame builder didn't help so we need to start digging a little deeper I think.

114   Fri Apr 17 20:05:59 2009 AidanLab InfrastructureGeneralAnother workbench and a filing cabinet

We're starting to accumulate a lot of loose data sheets and other paraphernalia. We should arrange to get a small filing cabinet down here. I'm sure Office Depot can serve us well on that one.

Also DMass and I think we should get a third IAC Industries workbench (the white ones with the Linux machines on them).

A.

2138   Mon Jul 17 19:27:27 2017 awadeMiscGeneralAnts in the lab

There are an unusually high number of ants in the ATF and PSL lab. Maybe 1 ant /m^2 on the optical tables. I've bought ant bait called 'Combat Kill Ant Bait' and placed it close the the ant trails around the edge of the room. After almost a week it appears to be failing to attracting ants or be diminishing their numbers.

Its a bit hard to keep them still enough to look closely but they are brown or red and slightly musty smelling but not strongly formic acid when crushed. Many ants around Pasadena crave fats and oils, so standard sugar based baits may not work as effectively.  Its not clear from the manufactures information what the active attracting agent is as they only list the toxic component, hydramethylnon.  It is likely a sugar bait. We may need to shop around or make our own usining boric acid.

---

I've also placed roach bait up and down the hall, in the EE workshop, cryo lab, ATF lab and PSL lab as there are roaches in the hallways.

2139   Mon Jul 17 19:36:59 2017 KojiMiscGeneralAnts in the lab

I thought the ants we usually have around us are Argentine Ants. I agree that they are not primarily attracted to sugar but like protains(raw meet etc).

Steve found "Terro" and it worked pretty efficiently at the 40m. I bought the same at home and it worked brilliant. This attracts ants and prevent them to spread randomly. So it should be placed at their entrance points. Otherwise, you just increase the number of ants in your lab. But in a few days, a colony will become completely silent.

Someone (Aidan?) bought Terro for the subbasement labs a while ago, if I'm correct.

2619   Mon Jul 26 22:49:00 2021 KojiSummaryCryo vacuum chamberAquadag painting

[Stephen Koji]

We decided to paint the silicon test mass with Aquadag to increase the emissivity of the test mass.

Stephen brought the Aquadag kit from Downs (ref. C2100169) (Attachment 1)

It's a black emulsion with viscosity like peanut butter. It is messy and smells like squid (Ammonium I think) (Attachment 2)

We first tried a scoop of Aquadag + 10 scoops of water. But this was too thin and was repelled easily by a Si wafer.
So we tried a thicker solution: a scoop of Aquadag + 4 scoops of water. (Attachment 3)

The thicker solution nicely stayed on the Si wafer (Attachment 4)

We want to leave the central area of the barrel unpainted so that we can put the suspension wire there without producing carbon powder. (Attachment 5)
1.5" from the edge were going to be painted. The central1" were masked.

The picture shows how the Si test mass was painted. The test mass was on a V-shaped part brought from the OMC lab. The faces were also painted leaving the mirror, while the place for RTD, and the magnet were not painted. (Attachment 6)

It looked messy while the painting was going, but once it started to dry, the coating looks smooth. It's not completely black, but graphite gray. (Attachment 7)

After the test mass got dry, another layer was added. (Attachment 8)

Then made it completely dry. Now the mask was removed. Nice! (Attachments 9/10)

Attachment 1: 20210726164254_IMG_0768.jpeg
Attachment 2: 20210726164530_IMG_0769.jpeg
Attachment 3: 20210726164225_IMG_0766.jpeg
Attachment 4: 20210726164957_IMG_0772.jpeg
Attachment 5: 20210726173608_IMG_0774.jpeg
Attachment 6: 20210726174523_IMG_0775.jpeg
Attachment 7: 20210726182715_IMG_0783.jpeg
Attachment 8: 20210726192042_IMG_0784.jpeg
Attachment 9: 20210726192837_IMG_0790.jpeg
Attachment 10: 20210726192853_IMG_0791.jpeg
2645   Sun Aug 15 00:33:15 2021 KojiSummaryCryo vacuum chamberAquadag painting on the inner shield

[Stephen Koji]

We applied Aquadag painting on the inner side of the inner shield.

• Upon the painting work, we discussed which surfaces to be painted. Basically, the surface treatment needs to be determined not by the objects but by the thermal link between the objects.
• We want to maximize the heat extraction from the test mass. This means that we want to maximize the emissivity factor between the test mass and the inner shield.
• Therefore the inner barrel surface of the inner shield was decided to be painted. The test mass was painted in the previous test.
• For the same reason, the lid of the inner shield was painted.
• It is better to paint the cold plate (table) too. But we were afraid of making it too messy. We decided to place the painted Al foil pieces on the table.

• The outer surface of the inner shield and the inner surface of the outer shield: Our outer shield is sort of isolated from the cold head and the steady-state temp is ~240K. Therefore we believe that what we want is isolation between the inner and outer shields. Therefore we didn't paint these surfaces. (note that in Mariner and beyond, the outer shield will be cooled, not isolated, and the radiative link to the outer shield would be strong by design)
• I believe that this is not the ideal condition for the inner shield. We need to model the cryo stat heat load and take a balance between the isolation and the conduction between the outer shield and the cold head so that we gain the benefit of the outer shield as a "not so hot" enclosure.

• OK, so we painted the inner barrel of the inner shield, the lid of the inner shield, and some Al foils (shiny side).
• Stephen made the Aquadag solution. The solution was 2 scoops of Aquadag concentrate + 6 scoops of water, and the adhesion/runniness test was done on a piece of aluminum foil.
• The barrel and the lid were painted twice. Attachment 1 shows the painting of the inner shield cylinder. Attachment 2 shows a typical blemish which necessitates the second coat.
• To accelerate the drying process, we brought the heat gun from the EE shop --> (update - returned to EE shop, see Attachment 3)

• We took some photos of the process. They are all dumped in the QIL Cryo Vacuum Chamber Photo Dump album in the ligo.wbridge account.
Attachment 1: IMG_9636.JPG
Attachment 2: IMG_9632.JPG
Attachment 3: IMG_9646.JPG
2505   Wed Sep 2 08:13:18 2020 StephenDailyProgressCryo vacuum chamberAssembly of QIL Setup and other updates from 2020 Sep 01

2020 Sep 01, StephenA with remote assistance from RaymondR

Highlights

• Silicon Mass - Rana had dropped off the Silicon mass in the first room, so I found it when I arrived - thanks!
• Organization - It was my first time accessing the QIL lab, but everything was pretty well organized and easy to find. All tools for modifications to parts were used in the EE lab which was also well organized. Raymond helped me to figure out where to access things on a few occaisions.
• Packages - received from Downs Logistics room the Electropolished shield set, a Grainger order with deburring tool and step drill bit, and a McMaster order with a range of bolts - these have all been transported to the lab. Also transported the QIL machined parts that I had received from Machining Solutions to the lab.
• Koji's Photodiode holders are in the QIL lab ready for pickup.
• Summary of progress
• Assembled frame (using torque values from T1100066- #8-32 used 20 in*lb)
• Assembled brackets to frame
• Hung silicon mass from music wire
• Wire is captured under #4-40 SHCS with washers ((using torque values from T1100066- #4-40 used 5 in*lb)
• Did the hang hold?
• Do we want to have the layered Electropolished and Plain shields during the first installation? Or some sanded state?
• Assembly requires oversized #8-32 washers which I wasn't able to track down from inventory - these are now on order, along with some more supplies for roughening the surface.

Full Details

• Assembly work
• Refer to the DCC - T2000538 - for the videos capturing this assembly effort. I've snagged some screenshots which I've dropped into the attachments.
• There is a tree catching procedures and other experiment documentation for the QIL Setup at T2000539
• Issues - there were four issues with the fabricated parts, three of which required small modifications;
• D2000299-01 small angle rails had threaded holes where there should have been clearance holes for the interface (no issue on big angle rails)
• modified by drill press to drill out clearance holes at same location
• D2000308 interface cubes all were threaded only partially through.
• No action taken, just paid attention and made sure the threads I needed were adequate. Seemed like an offset of only a turn or two, suggesting the CAM program was just a little off (this can happen with tapping, the tap is tapered and the machinist needs to thread deep enough to have the thread major diameter realized through the hole.)
• D2000307-04 frame upper spacer had threaded holes that were not tapped all the way through.
• I ran a tap through all of these threads.
• D2000299-02 large angle rails had threaded holes that didn't pass all of the way through, and we happened to be inserting screws into the wrong side.
• I ran a screw through these threads, which required a little bit more force than I would have liked, and forcing the screw provided an adequate thread.
• Note that I anticipate that there will be an issue similar to this, with similar resolution, on the D2000299-01 small angle rails. The shield panels installed on the sides are to be installed from the inside. This can be resolved with a screw coming in from the outside.
• There was also some inability to access certain screws with the long torque driver, especially if loosening/tightening after putting the frame together.
• This was managed by use of an L allen key, which of course meant those joints were not torqued to spec. I'm not worried about this compromise.
Attachment 1: photos_cit_qil_lab_cryo_shield_test_assembly_20200901.zip
Attachment 2: T2000538-v1_Part_3_Assembly_of_QIL_Test_Setup_20200901_end_result.jpg
Attachment 3: IMG_7582.JPG
811   Fri Jun 11 20:33:17 2010 DmassComputingDAQAttempt at oven transfer functions

The plot I attached and didn't explain is:

• Green = Voltage across the Ohm Ranger as driven and read out by the (unknown) bridge of the Newport 3040
• Red = Voltage across a high power 5 Ohm resistor I am using on the current output of the Newport 3040
• Units are standard DAQ conversion ~ 1600 counts / Volt

Notes:

• I use an SR560 to buffer the signal from the ohm ranger before inputting it into the AA chassis
• The resistance between the inner BNC leads of the AA box was ~2 kOhms - FOR SEVERAL DIFFERENT CHANNELS
• I have the PI (no D) servo set at its lowest settings, so lowest integral gain, and lowest proportional gain.
• I make step responses in the green curve via the ohm ranger.
• I should see step responses of the red from the proportional term, and changes in the slope of the integration following these step responses.
• I see SLOPE IN THE GREEN. This is weird.
• The slope in the green goes away when I unplug the voltage (from the TEC drive current) across the 5 ohm resistor from the front end.
• The slope in the green stops when the current rails.
• I don't understand the coupling, but since I don't have circuit diagrams for the 3040 - I stopped thinking about it, and just used a USB stick in a scope to take this data.

Moral:

• The 3040/ front end acts funny when you try to read out the current and the voltage of the thermometer.
• I don't really care that this is the case.
• The front end seems to be working close to all the way
Attachment 1: dmassFE.png
815   Wed Jun 16 15:54:20 2010 DmassComputingDAQAttempt at oven transfer functions

3040 P/I settings -

I = Slow <=> 0.0162 A/s/K

P = 2 <=> 0.0172 A/K

816   Wed Jun 16 23:10:28 2010 DmassComputingDAQAttempt at oven transfer functions

 Quote: 3040 P/I settings - I = Slow <=> 0.0162 A/s/K P = 2 <=> 0.0172 A/K

A Couple more measurements yielded:

• I = Slow <=> 0.0172 A/s/K
• P = 1 <=> 0.0098 A/K

And

• I = Fast <=>0.0848 A/s/K

Next I am hooking up the RS232 connector to one of the computers to see if I can get temperature logged, so that I can actually do something with it.

818   Thu Jun 17 15:14:58 2010 DmassComputingDAQAttempt at oven transfer functions

And a measurement of the oven's step response

• I used a lab power supply as a current source for the TEC on the oven
• I tweaked the current nob to make a current step
• I looked at the step response
• I used a phone video of the readout on the front of the Newport 3040 to get time stamps b/c it was so easy
• (I will still be hooking up the RS232)

Results

• I get a time constant of 60 seconds
• This is an oven pole frequency of 16.7 mHz

Attachment 1: CuOvenIStepResponse.pdf
820   Fri Jun 18 18:04:23 2010 DmassComputingDAQAttempt at oven transfer functions

 Quote: And a measurement of the oven's step response I used a lab power supply as a current source for the TEC on the oven I tweaked the current nob to make a current step I looked at the step response I used a phone video of the readout on the front of the Newport 3040 to get time stamps b/c it was so easy (I will still be hooking up the RS232) Results I get a time constant of 60 seconds This is an oven pole frequency of 16.7 mHz The gain is 0.368

821   Fri Jun 18 18:07:53 2010 DmassComputingDAQAttempt at oven transfer functions

This was wrong.

1741   Tue Aug 21 04:54:26 2012 ZachElectronicsGYROAttempted "very fast" path

We have been trying to improve the primary loop gain, and we have often mentioned the possibility of using a TTFSS setup on the gyro, so I figured I would try a homebrew version. TL;WR: it didn't work yet, but that's because it was very hasty.

I added a broadband ThorLabs EOM into the optical path before the resonant one used for the PDH sidebands. It did not seem to distort the beam much.

I think the PZT/PC crossover should be somewhere around 1-3 kHz, since I want the range of the PZT for where the real noise is, but need the PC to take over well below the PZT resonance at 25 kHz. I put a 4.7-uF capacitor to ground in a pomona box at the output of the uPDH box to the NPRO; this---coupled with the 10-ohm output resistance---puts a pole at 3.3 kHz, which effectively cancels out the highest zero of the uPDH box and makes the fast path go to 1/f2 above the cavity pole (also at a few kHz).

I then took the buffered output monitor of the uPDH box and fed it to an SR560 (AC coupling and a pole at 300 kHz to roll the gain off more above the target UGF). The output of the SR560 was fed to a simple G = 10 HV driver I built with an OPA452 HV op amp. The driver was powered by the Sorensen HV supply, single sided at +80 V, so that the output was riding on 40 VDC. The driver also has a high-pass at 100 Hz.

Hooking it all up and adjusting the PC path gain, I couldn't get any stabler lock than before. It got late and I got tired.

1. I need to CALCULATE the required gains for the crossover I want---I was too lazy to do this.
2. I'm not sure I actually want a HV bias on the PC. Part of this was autopilot from setting up the PMC servo, whose PZT needs a bias, and the other part was the convenience of a single supply.
3. Lastly, the speed of the uPDH is an issue. I think it has too much lag to expect much higher a UGF, even with the fast actuator. The right thing to do is to fix the PDH2 TF, put some AD829s back in with Rana's trademark "use 68 pF for all compensation caps" technique, and use it for the primary.

83   Tue Sep 2 15:06:42 2008 AidanLaserFiberAttempted calibration of fiber noise ... issues!

I tried to calibrate the fiber phase noise measurements in DTT by determining the fringe visibility (peak-to-peak size) in counts (to determine radians per count). I shifted the carrier on the VCO by 100Hz to 200.0001MHz and left the other signal generator (LO for both mixers) at exactly 200MHz. The demodulated signals from the PDs then looked like nice 100Hz sine waves. It was only then that I noticed that the amplitude of these sine waves was varying by 50% over a timescale of 20 seconds to a number of minutes.

NPRO level: 1.500A

I plotted 20 minutes worth of Max-Min data from the 2 PDs in DataViewer (see attached pdf) - there was 100Hz frequency difference between the signal generators for all but the first four minutes or so of this plot. In principle this plot shows the fringe visibility in counts and can be used for calibration purposes. As you can see, though, the pk-pk value is fluctuating with time. Presumably, as nothing has been altered on the table over the last week, the fringe visibility has been fluctuating for all previous noise measurements. Therefore only a rough calibration is possible. So here it is ...

Eric G happened to come in shortly after I had discovered this. He suggested that the mode-matching between the two beams may not be good enough. I will look into this.
Attachment 1: peak_peak_calibration.pdf
85   Tue Sep 2 23:09:38 2008 AidanLaserFiberAttempted calibration of fiber noise. NPRO current = 1.903A

 Quote: I tried to calibrate the fiber phase noise measurements in DTT by determining the fringe visibility (peak-to-peak size) in counts (to determine radians per count). I shifted the carrier on the VCO by 100Hz to 200.0001MHz and left the other signal generator (LO for both mixers) at exactly 200MHz. The demodulated signals from the PDs then looked like nice 100Hz sine waves. It was only then that I noticed that the amplitude of these sine waves was varying by 50% over a timescale of 20 seconds to a number of minutes. NPRO level: 1.500A I plotted 20 minutes worth of Max-Min data from the 2 PDs in DataViewer (see attached pdf) - there was 100Hz frequency difference between the signal generators for all but the first four minutes or so of this plot. In principle this plot shows the fringe visibility in counts and can be used for calibration purposes. As you can see, though, the pk-pk value is fluctuating with time. Presumably, as nothing has been altered on the table over the last week, the fringe visibility has been fluctuating for all previous noise measurements. Therefore only a rough calibration is possible. So here it is ... C2: OMS-SUS_TOP1_INI_65536: pi radians: [-2750, -700] counts -> ~1500 urad/count C2: OMS-SUS_TOP2_INI_65536: pi radians: [-3600, 4000] counts -> ~410 urad/count Eric G happened to come in shortly after I had discovered this. He suggested that the mode-matching between the two beams may not be good enough. I will look into this.

I repeated this measurement with the NPRO drive current set to 1.903A as per noise measurements made by Masha before she left. The same behaviour in the fringe visibility was seen. Additionally I noticed that the SR560 for channel 2 was periodically overloading. I didn't alter the gain on this amplifier because this was the state that the system was in for Masha's measurements. Attached is the max-min counts in the presence of a 100Hz frequency difference between the VCO and LO carrier frequencies. The following estimates for the radians/count calibrations are quite rough.

Attachment 1: peak_peak_calibration_1903mA.eps
111   Thu Apr 9 10:02:24 2009 alastairLab InfrastructureGeneralAudio/mp3

We now have the right cable to connect audio equipment with a standard 2.5mm headphone jack (ipods etc) to the hi-fi.  Just set the stereo to 'game' and you're away.

2669   Thu Sep 16 10:33:59 2021 AidanComputing2um PhotodiodesAutomation and analysis scripts for 2um data taking

The attached files are the scripts used to take data during the PD temperature cycling/testing and to retrieve and analyze data after the fact.

• ~/JPL_PD/scripts/autorun2021.sh
• ~/JPL_PD/scripts/piezo_mirror/maximize_output_power.py
• ~/JPL_PD/data/A1_analysis/A1_analysis.py
Attachment 1: autorun2021.sh
#diode name
i=1001
diode=A1
caput C4:TST-FM15_OFFSET 0
sleep 1
while :; do
#-----------------------------------------------------
# dark current
echo =======================
echo ----- TOP OF LOOP -----

... 141 more lines ...
Attachment 2: maximize_output_power.py
# script to maximize the output power of the piezo
import serial
import time
import os, sys, subprocess
import numpy as np

def slowDownJog(ser):
ser.write('1SU50\r\n')
time.sleep(0.1)

... 195 more lines ...
Attachment 3: A1_analysis.py
# analysis od the A1 JPL PD diode
# Aidan Brooks - 10-Sept-2021

import cdsutils
import numpy as np
import matplotlib.pyplot as plt
import os, glob
import scipy.signal


... 172 more lines ...
2670   Mon Sep 20 14:26:38 2021 ranaComputing2um PhotodiodesAutomation and analysis scripts for 2um data taking

you can put these in the GIT repo for the QIL Cryo tests that Radhika set up. Otherwise, they'll get lost. And we should probably change autorun to a .py script and document these in the README on the repo.

 Quote: The attached files are the scripts used to take data during the PD temperature cycling/testing and to retrieve and analyze data after the fact. ~/JPL_PD/scripts/autorun2021.sh ~/JPL_PD/scripts/piezo_mirror/maximize_output_power.py ~/JPL_PD/data/A1_analysis/A1_analysis.py

2035   Fri Feb 26 10:00:18 2016 KojiNMiscPD QEBEDF measurement for wide angle

The BRDFs at 0 deg and 15 deg in incident angle were measured for the wide angle with the same way as elog2034 and Fig. 1 but finer scaning.

The results for P-pol and S-pol are shown in FIgs. 2 and 3.

It looks that there is no difference for polarization.

The tendency that the BRDF increases from -75 deg is consistent to the previous result of the BRDF measurement of the viewport used in LIGO.

Between -40 deg and -70 deg, we face the sensitivity limit of the PD (PDA100A). (In this range, the estimated power is 1 nW and the power range of the PDA100A is 500 pW in the specsheet.)

For comparing the two BRDF, the BRDF plot in which the BRDF at 15 deg incident angle is shifted by 30 deg is shown as Fig. 4.

In this plot, the BRDF for P-pol is picked.

It looks that there is no difference between 0 deg and 15 deg in incident angle from -40 deg to 40 deg.

Attachment 1: BRDF_setup.pdf
Attachment 2: BRDFat0deg_log.pdf
Attachment 3: BRDFat30deg_log.pdf
Attachment 4: BRDF_log_P.pdf
1756   Tue Sep 4 01:41:00 2012 ZachLaserGYROBEST gyro sensitivity ever with RAM subtraction

After several improvements (increasing optical power, lowering Marconi deviation, etc.), I ran the gyro the other night, including the OOL RAM monitors and a DC TRANS monitor, and with some post-processing was able to record the lowest gyro noise level ever.

The sensitivity of ~3 x 10-7 (rad/s)/rtHz at 200 mHz puts us within a factor of ~40 of the tip of the requirement, which is much better than ever.

The already-lower raw noise spectrum showed considerable coherence with the secondary-loop RAM monitor:

So, using some simple flat-gain subtraction, I was able to reduce it by up to an order of magnitude below 1 Hz. Here is a partial noise budget with the raw noise level, the subtracted level, and some mechanical and phase noise estimates (the Marconi noise is in black; I don't know why it is magenta in the legend):

While I was able to do some subtraction with the off-resonance REFL noise before, this is the first time that I have succeeded in subtracting RAM noise from the live gyro signal.

I did some further testing and found some sparing coherence between the subtracted noise and both the DC TRANS noise and the primary actuation signal (FSR noise).

I have some more optimizing to do (including increasing the secondary loop UGF, which was very low at only a few 10s of Hz here for no particular reason at all), but this is very promising.

2239   Tue Aug 14 10:14:11 2018 John MartynDailyProgressHomodyneBHD Circuits and Set Up

I constructed two circuits (one for each photodiode) that prcoess the signals from the photodiodes. A schematic of one cicuit is attached to this elog entry.

Aside from transimpedance amplifiers, the circuit consists of buffers and passive RC filters; the resulting output signals are sent to BNC or LEMO connectors. Here are some pictures of the circuit (in its box) with the setup:

I connected the output of the photodiodes to the input of the circuit, and sent the output of BNC2 (in the circuit) to two SR560's. The output of the SR560's was sent to the SR785, which I used to measure the difference of these signals with the A-B mode of the SR785. I then amplitude modulated the laser with a 1.222kHz sine wave of amplitude 100 mV produced by a function generator, and varied the gain of the SR560's until the noise peak at 1.222kHz vanished and reached the noise floor. I collected data on the input referred noise and transfer function of the difference of the two photodiode signals, and made plots:

One feature worth noting is that the noise floor is just slightly higher than expected. Since the transimpedance amplifier contributes the majority of the noise in this circuit, we expect the input referred current noise to be $n(f) \approx \sqrt{2eI+\frac{fk_BT}{R}} = \sqrt{\frac{2\eta e^2 P}{h \nu}+\frac{fk_BT}{R}} \approx 16.6 \frac{\mathrm{pA}}{\sqrt{\mathrm{Hz}}}$

Aside from a 1/f roll up at low frequencies, the noise shown in the plot above attains a floor of roughly $20 \frac{\mathrm{pA}}{\sqrt{\mathrm{Hz}}}$, which is just slightly higher than expected. The rest of this noise can be attributed to the noise in the other parts of the circuit (other than the transimpedance amplifier), the noise in SR560's, and the noise floor of the SR785.

As Andrew mentioned in his last post, we have connected the BHD to the ADC in the CrImE lab via BNC cables. Today, I will work with the ADC to balance the signals from the BHD and analyze the noise in the detector.

Attachment 1: BHDPictures.png
Attachment 2: BHD_TF3.pdf
Attachment 3: BHD_Noise.pdf
Attachment 4: BHDCircuit1.pdf
2234   Fri Aug 10 21:55:52 2018 John MartynDailyProgressHomodyneBHD Electronics

Earlier this week, I constructed two transimpedance amplifier circuits with buffers and filters on two breadboards. These are to be used as amplifier circuits for the photodiodes in the BHD. With these sample circuits wired up to the photodiodes, I sent the output of the amplifiers to two SR560's, and adjusted the gain of the SR560's until the difference of the two signals from the photodiodes obtained its lowest level of noise (ideal for balanced homodyne detection). I measured the transfer function of this setup as well, and attached a plot of it to this elog entry. In general, it is relatively stable over the bandwidth analyzed, and displays no unusual behavior.

Recently, I have been tweaking the circuit that will be used in the final BHD electronics so that it acquires a minimum level of noise. I will post schematics of the circuit once its design is completed. With the low noise circuit constructed, I will aim to route its output to an ADC, which will be used to perform digital subtraction of the signals from the photodiodes, a necessary component of balanced homodyne detection.

Attachment 1: BHD_TF2.pdf
2238   Mon Aug 13 19:15:47 2018 awade, John MartynDailyProgressHomodyneBHD Electronics, digitizing

John and I routed a pair of BNC cables between the QIL lab and the CrImE lab so that John and digitize his pair of detector signals and ballence them in post processing.  For now he's using single ended signals out of each detector, well see how noisy that is.  I believe he's made a single to differential circuit on board, so it should be easy to switch.

Here is a minimum working example of how to access the data using nds2:

First ssh in ws1 from within the network (or from outside if you know how):

> ssh -Y controls@10.0.1.34

Then open ipython terminal

> ipython

and type the following (note, we are using channels previously used for a seismometer):

>import nds2
>c = nds2.connection('cymac3.ligo.caltech.edu', 8088)
>channelA = 'X3:TST-ACC_Y_OUT_DQ'
>channelB = 'X3:TST-ACC_Z_OUT_DQ'
>gpstime = [enter start time here]
>gpslength = 1000
>OutputDataStruct = c.fetch(gpstime, gpstime + gpslength, [channelA, channelB])

From there you can extract your data using OuputDataStruct[0].data and OuputDataStruct[1].data for the two channels. This data will be in counts, you need to inject a test waveform to calibrate back into volts.

Note that the GPS time is in seconds and that the data length must not go into the future.

## Set up of channels

The channel names and sample rate are noted here: CRIME_Lab:456.  Should be 65 kHz, more than enough for now.

 Quote: Earlier this week, I constructed two transimpedance amplifier circuits with buffers and filters on two breadboards. These are to be used as amplifier circuits for the photodiodes in the BHD. With these sample circuits wired up to the photodiodes, I sent the output of the amplifiers to two SR560's, and adjusted the gain of the SR560's until the difference of the two signals from the photodiodes obtained its lowest level of noise (ideal for balanced homodyne detection). I measured the transfer function of this setup as well, and attached a plot of it to this elog entry. In general, it is relatively stable over the bandwidth analyzed, and displays no unusual behavior.  Recently, I have been tweaking the circuit that will be used in the final BHD electronics so that it acquires a minimum level of noise. I will post schematics of the circuit once its design is completed. With the low noise circuit constructed, I will aim to route its output to an ADC, which will be used to perform digital subtraction of the signals from the photodiodes, a necessary component of balanced homodyne detection.

2209   Mon Jul 2 11:23:06 2018 John MartynDailyProgressHomodyneBHD Optical Setup

Over the past week, I have begun setting up the optical elements of the BHD, including waveplates, a Faraday rotator, and beam dumps. These elements will allow us to control the power entering the detector when the final BHD is constructed. The next step in constructing the BHD is to conduct beam profiling and ensure that our setup is operating with a Gaussian beam in the TEM00 mode. Beam profiling will allow us to measure the parameters that characterize the light being emitted from the laser, and determine how closely our light matches the ideal TEM00 mode.

Moreover, I have set up two RC low pass filters to be used in the LIGO outreach detector. I aim to conduct some tests on these circuits to ensure that they operate properly, and then solder them to a circuit board for their implementation.

Lastly, I will be typing up my first progress report this week, as it is due on Monday, July 9th.

1127   Tue Nov 2 22:40:31 2010 ZachElectronicsGYROBLP-1.9+

Attached is the attenuation plot for the BLP-1.9+ we are using after the mixer from the spec sheet.

381   Wed Oct 14 20:18:52 2009 FrankLab InfrastructureGeneralBNC cables and patch panels

a whole bunch of BNC cables (1ft to 10ft) and the BNC patch panels arrived today. the custom made 35ft for the patch panels are still in production. i installed the panels at the tables and in the rack (above the DAQ breakout boxes)

2036   Fri Feb 26 23:13:02 2016 KojiNMiscPD QEBRDF measurement around the peak

The BRDF of the PD (C30665GH) for 15 deg incident angle was measured arond the peak with the same was as elog2035 and elog2034 but with the additaional Iris as shown in Fig. 1.

For calculating the BRDF. the fomular in elog2034 is used.

(Please note that r_l becoms the radius of the Iris in front of the PDA100A and d becomes the distance between PD (C30665GH) and the Iris)

The Iris diameter is 3.5 mm.

There is no difference for polarization as the wider scan.

The result for p-pol is shown in Fig. 2 with the wider scan (the relsult of the elog 2034). This result was wrong.

There is a asymmetry around the -30 deg and the data around -35 deg are not consistent to the previous data.

We think these are come from the slight tilt of the Iris.

We will confirn that after tomorrow.

Attachment 1: BRDF_log.pdf
Attachment 2: BRDF_setup_fine.pdf
2037   Sun Feb 28 15:47:06 2016 KojiNMiscPD QEBRDF measurement around the peak

The result shown in the elog2036 looks not to consistent to the previous result.

Thus we checked the alignment of the Iris.

First, the effect of the tilt of the Iris was checked and it was found that the tilt effect is very small.

Second, we found that the center of the Iris was off from the center of the lens.

This off effect is dominant in the BRDF measurement.

The off was about 1 mm. However, the diameter of the Iris was 3.5 mm and 1 mm is about 30% and large to 3.5 mm.

Thus we re-align the Iris and measure the BRDF of the PD (C30665GH) at the 15 deg incident angle again as shown in Fig. 1.

Figure 1 shows that the new result is consistent to the previous wide range measurement in the error.

The reason why the error at -29 deg and -31 deg is very large is the effect of the main reflected beam.

The result that the new data arond peak and the previous wide range data are combined for p-pol and s-pol is also attached.

Note that the incident beam is at 0 deg and the angle is that we must take care in terms of the back scattering.

Attachment 1: BRDF_log_compare.pdf
Attachment 2: BRDF_log_all_wide.pdf
Attachment 3: BRDF_log_all_narrow.pdf
Attachment 4: BRDFat30deg.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm)
-70 5.43 0.029 280.8 280.2 276.2 23
-60 5.44 0.030 280.3 282.1 271.8 23
-50 5.44 0.030 283.0 284.2 266.7 23
-45 5.45 0.029 311.5 317.2 267.2 23
-40 5.43 0.029 348.1 350.1 267.1 23
-35 5.44 0.029 468.6 470.1 263.9 23
-25 5.43 0.027 440.3 439.7 270.6 23
-20 5.43 0.028 349.5 349.1 278.6 23
-15 5.45 0.029 329.5 324.3 278.5 23

... 3 more lines ...
Attachment 5: BRDFat30deg_again.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm) d(cm)
-35 5.44 0.029 276.5 276.5 261.4 23 0.35
-36 5.44 0.027 288.2 289.1 276.4 23 0.35
-37 5.43 0.028 293.6 291.3 280.5 23 0.35
-23 5.43 0.027 295.2 295.1 277.6 23 0.7
-25 5.43 0.030 290.2 287.2 283.2 23 0.35
2166   Tue Aug 15 20:34:40 2017 Amani GarvinDailyProgressScatterometerBack of the Envelope Calculation

Assuming Rayleigh Scattering (which is a rough approximation), I calculated how much scatter would come from SiO2.

n = 1.431, d = 100nm

The rayleigh cross section is 2.36*10^-18 m^2

For a number density of about 10 si02 scatter sites/ volume of silicon, N = 1.736 * 10^5 cm^-3

N*cross section = amount of light scatted per distance traveled

That's 4.09*10^-15 ammount of light scattered per centimeter. The distance between the silicon and the lens is 9cm

Over 9cm the intensity of light recorded is 1.87*10^-13 Watts.

Our calibration constant is 2.99 *10^-12 counts/m^2/str.

This means that for a scatter source of this size, index of refraction, and at 1550, the camera will record less than 1/10th of a count.

Moving Forward:

I will get a signal before I leave Saturday morning! It will happen!

I'm going to play around with the distance between the lens and the silicon, try to really zoom in on the scatter.  If that doesn't work, maybe put a larger lens in front of it. I don't know, I'll do anything. I'm desperate. :D

Attachment 1: Screen_Shot_2017-08-15_at_20.20.51.png
2048   Mon Mar 7 15:34:46 2016 KojiNMiscPD QEBack reflection measurement with the chopper

Background:

We are still suffering from excess amount of back reflection compared with the predicted number from the BRDF measurement. Assuming this light is not coming from the target PD, we want to reduce the scattering from other optics. As an attempt, we decided to use a BS instead of the combination of a cube PBS and a QWP. This way we can reduce the number of the optics involved, particularly the PBS which may cause more scattering than others.

What we did:

The PBS and the QWP were removed, and then a 50:50 BS was inserted as shown in Fig. 1.

The distance between the target PD and Iris2 was measured to be 38.1 cm. The diameter of Iris2 was set to be 7 mm.

As a part of the calibration, the incident power on the target PD was measured using PDA100A (Gain 0dB). The measured value was 3.973 V with no chopper blocking the beam.

An HR mirror was then placed before the target PD to measure the reflected light power with the chopper still halted and the iris 1 is oped using PDA100A (Gain 0dB) which is placed at the position as shown in Fig. 1. It was measured to be 1.253 V. This means that the reflectivity of the BS is about 0.315. This reduction is considered to be the clipping at Iris1 as the returning beam has the bigger beam size (i.e. the iris worked as a sort of mode cleaner).

(==> There might be a misunderstanding because of my not clear explanation. So, I edited this paragraph again. KN)

Then, the chopper was started at 253 Hz. The reflected light from the HR mirror was measured using a FFT analyzer to be 642 mVrms (PDA100A gain 0 dB).
(==> mVrms? KA ==> mVrms. I fixed. KN)

Throughout the measurement, the opening of Iris1 was adjusted such that the clip level was less than 0.1% of the incident power (see also elog2047).This yielded the Iris1 diameter of 1.8 mm.

Finally, the back reflection was measured in the same way as elog 2040 , and also with Iris1 opend as much as possible.

Result:

The measured voltage with Iris1 with the diameter of 1.8 mm: 720 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.4 x 10-3 [1/sr].

The measured voltage with Iris1 completely open: 640 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.2 x 10-3 [1/sr].

These values are much (x40) larger than the BRDF value expected from the BRDF measurement (5x10-5 [1/sr], see also elog2045).
In fact, these are much (x2) larger than the ones with the PBS & the QWP (8x10-4 [1/sr], see also elog 2047).

(It is not so clear how these numbers were calculated. How these calibrations were used? How did you incorporate the BS transmissivity and reflectivity??? KA)

==> For calculating the BRDF, the fomular as shown elog2034 is used. Seeing the fomular, we need the ratio of the incident light power and the scattered (reflected, in this measurement) light power, the incident angle, and the solid angle. The ratio of the incident light power and the scattered light power can be obtained by taking the ratio of the measured voltage with the chopper as a part of the calibration, Vin (642 mVrms), and the measured voltage with Iris1 with the diameter of 1.8 mm (720 uVrms) or with Iris1 completely open (640 uVrms), Vsca, considering the difference of the PDA100A gain. In this calculation the BS reflectivity and transmissivity do not appear, see also Fig. 2. In addition, using the incident angle, 15 deg, and the solid angle from the PD(C30665GH) to the Iris2, 2.6x10-4 sr, the BRDF can be calculated.

And when the Iris was closed, the value was larger. This means that the Iris may make a scattering.
(==> This didn't make sense compared with the numbers above. KA ==> The numbers were written conversely. I fixed. KN)

[Ed.: KA]

Attachment 1: setup.pdf
Attachment 2: BRDF_cal.pdf
2049   Mon Mar 7 15:47:03 2016 KojiNMiscPD QEBack reflection measurement with the chopper

To reduce the scattering, we did some try and error.

The setup was same as the elog2048.

First, to reduce the scattering from the Iris 1, in front of the Iris 1 the aluminum foil which has the hole for the laser was placed.

We made several foils, different hole sizes and different shapes.

We cannot found the reasonable tendency, but with the best foil the measured scatterd value became 350 uVrms (BRDF = 7.1 * 10^(-4) [1/sr]).

This is the comparable value to the BRDF measured with PBS and QWP (elog2047).

After that, we changed the steering mirror #2 from Newfocus 5104 to Newport 10Q20HE.1.

Then, without aluminum foil, i.e. in completely same setup as elog2048, the measured scatterd value became 11 mVrms.

And we tried to place the best aluminum foil and the measured valued as reduced to 820 uVrms.

610   Thu Feb 18 18:49:21 2010 DmassElectronicsDoublingBad PD?!

One of my switchable gain Si detectors appears to have particularly bad noise perfomance.

I compared the dark Voltage noise of my Thorlabs PDs. I am barely below the ADC noise on one of my PDs, and it onlyu gets worse at lower frequencies, so for Beta, on my current setup, the PD noise is limiting me below about 5 Hz.

 Detector Noise (V/rtHz) @ 10 Hz Gain Setting Alpha(532) 600 n 47500 V/A Beta(532) 4 u 47500 V/A Gamma(1064) 40 n 4750 V/A Delta(1064) 200  n 4750 V/A

612   Thu Feb 18 21:16:01 2010 DmassElectronicsDoublingBad PD?!

Quote:

One of my switchable gain Si detectors appears to have particularly bad noise perfomance.

I compared the dark Voltage noise of my Thorlabs PDs. I am barely below the ADC noise on one of my PDs, and it onlyu gets worse at lower frequencies, so for Beta, on my current setup, the PD noise is limiting me below about 5 Hz.

 Detector Noise (V/rtHz) @ 10 Hz Gain Setting Alpha(532) 600 n 47500 V/A Beta(532) 4 u 47500 V/A Gamma(1064) 40 n 4750 V/A Delta(1064) 200  n 4750 V/A

Attachment 1: PDDarkNoise.pdf
613   Fri Feb 19 01:04:35 2010 DmassElectronicsDoublingBad PD?!

I will be using a Thorlabs DET110 with something like a 5 or 10k load resistor, and an SR560 for gain to replace the really crappy thorlabs PD for green.

614   Fri Feb 19 07:54:14 2010 ranaElectronicsDoublingBad PD?!

 Quote: I will be using a Thorlabs DET110 with something like a 5 or 10k load resistor, and an SR560 for gain to replace the really crappy thorlabs PD for green.

Now I really wish we had made those low noise DCPDs...I guess that you can steal the ISS PDs for now. Just move them into the appropriate place and use the ISS box to power them and read them out. We can just continue to use some Thorlabs diode + SR560 as an ISS for now.

268   Tue Aug 18 02:45:39 2009 DmassElectronicsGeneralBad Scope?

While trying to calibrate my channels, I noticed a factor of 10 difference between power according to a PDA10CS from thorlabs (as measured on a Hi-Z scope) and the power according to the newport wand I was using.

Turns out the Tektronix TDS1001B oscilloscope was giving me traces that are a factor of 10 higher than they actually are.

I double checked with one of the LASCAR DC power supplies, and got a reading on my scope of 150V when I put 15V in.

I tried pressing the "default setup" button, but I still had the extra factor of 10.

I have pulled it and left it on the bench with an "NFG?" sticker on it.

271   Tue Aug 18 09:15:21 2009 DmassElectronicsGeneralBad Scope?

 Quote: I have pulled it and left it on the bench with an "NFG?" sticker on it.

Sometimes scopes are in their 10x probe mode which gives a factor of 10.

2016   Thu Feb 11 00:03:24 2016 KojiNMiscPD QEBeam Adjustment

For adjusting the beam, the setup was prepared as shown in Fig. 1.

Our taget is 80 um beam waist in radius as shown in Fig. 2.

(Please note that the axes of Fig. 1 and Fig. 2 do not have the same zero point.)

The waist position is not much took care to if the position can be accessed easily.

In our simulation using the beam measured yesterday, when the lens #2 (f=-200 mm) and the lens #3 (f=150 mm) are placed at z = 0.260 m and z = 0.474 m, respectively, the target radius could be obtained at z = 0.74 m.

However, in this setup we cannot obtain the target beam and the waist size seemed to be larger and the waist position seemed to be farther.

Thus the lenses were moved iteratively.

Finally, the lens #2 and #3 are placed at z = 0.114 m and z = 0.483 m, respectively, and the measured beam is as shown in Fig. 3.

(The beam profiler seemed to be saturated. Thus the additional ND filter (O.D.=4.0) is put and the saturation seemed to be extinguished as shown in Fig. 4.)

As a result, the beam waist radius and the beam waist position are 86 um and z = 0.750 m (for the x-direction) and 89 um and z = 0.750 m (for the y-direction), respectively.

These parameters can still be improved by refining the positions of the lens #2 and #3.

162   Wed Jul 8 17:29:46 2009 Connor Mooney, Michelle StephensLaserFiberBeam Divergence of 495mW NPRO

We made a set of beam width measurements of the 495 mW laser using the Beamscan. All values were taken at (1/e^2) of the peak intensity, in micrometers. The distances were taken in units of inches (no metric-based rulers).

Here is our data:

Distances (in inches): [2 3 4 5 6 7 8 9 10 12 14 16 18 20 22]

Beam Diameters (in micrometers): [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999]

Again, we least-squared fit the data to the characteristic curve parametrized by the waist location and size, and found that the waist size is 178 micrometers, located 4.6 cm. in front of the aperture.

THINGS TO NOTE:

First, DMass mentioned he suspects that the beamscan is impaired, so we're not sure how well it is acting.

Second, Rana noted that the best indicators of the parameters of interest are data points taken far from the waist, where the beam width grows close to linearly with distance.  We took  lots of data points in the nonlinear regime, as seen on the attached plot. It might be a good idea to take more data points further away and refit our data.

Lastly, this laser is more stable than the 1W NPRO, with fluctuations of only 1-3 micrometers around the reported beam width values rather than the 40-50 we saw for the 1W.

The directory for our code is /users/cmooney/Beamscan_495mW.m

Here is the code:

%This is a graphical representation of beam width data taken for the 495 mW NPRO
%Laser, taken on July 8, 2009.

%W1 is the full width at 1/(e^2)*(peak intensity) taken at 1.00A driving
%current (around 150 mW) for the axis A1 as labelled on the BeamScan. Measurements are
%in micrometers.

W1 = [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999];

%S1 is the standard deviation of the measurements given in W1.

S1 = [0.3 0.3 0.4 0.4 0.4 1.2 0.8 0.8 1 1 2.7 2.9 1.6 1.6 2.2];

d = 2; %distance from laser aperture to its base, from which it is easier to measure distance
D = [0 1 2 3 4 5 6 7 8 10 12 14 16 18 20]; %distances (in inches) at which measurements were taken
Ds = 2.54*(D+2)/100; %conversion to meters

W1s = 0.5*W1/(10^6);
S1s = S1/(10^6);

errorbar(Ds,W1s,S1s,'.')
title('Beam Width vs. Distance from Laser');
xlabel('Distance (m)');
ylabel('Beam Width (m)');

%This is a brief program to assist in the measurement of width of a
%Gaussian beam. Its wavelength is 1064 nm.

xdata = Ds;
ydata = W1s;

a0 = [.0001, .2]  % Starting guess
[a] = lsqcurvefit(@myfun,a0,xdata,ydata)

w_0 = a(1);
Zo = a(2)
L = 1064*10^(-9);
Dmax = 1;
sh = 0.35;
dt = (Dmax+sh)/10000;
Z = -sh:dt:Dmax;

Wt = w_0*(1+(((Z+Zo).*L)/(pi*w_0^2)).^2).^(1/2);

hold on;
plot(Z,Wt);

Attachment 1: beamdiv495mW.pdf
171   Tue Jul 14 15:08:07 2009 Connor MooneyLaserPSLBeam Divergence of PSL

A while ago, Dmass made some beamscans of the PSL beam after it passed through two lenses. Here is a link to the Dmass Modematching elog.

We wanted to make sure that these measurements are consistent with what we think the incoming beam parameter is.  I wrote a matlab file which works backwards from his data to find the incoming beam parameter using ABCD matrices.  I used the focal lengths indicated on the lenses.

I found a disagreement of 20cm in the PSL waist location with a yesteryear elog entry  Dmass checked to see if my computation matched with his, and got the same result.

The first thing that we thought might have been wrong is that the focal lengths need to be switched, but switching them didn't significantly our change our results (in fact, it made them worse).

We also suspected that the engineering tolerance of the lenses might allow for the difference. I tried changing the focal lengths of the lenses by 10% for both lens orientations, but the computations made only small changes to our original result, so this is probably not the culprit.

2210   Fri Jul 6 22:30:20 2018 John MartynDailyProgressHomodyneBeam Profiling

For our balanced homodyne detector (BHD) setup, we desire the light entering the interferometer to be a stable TEM00 mode. In order to determine the identity of the light being emitted by the laser, I conducted beam profiling on our setup. Specifically, I first chose five locations along the lab bench, each equally spaced by 10 cm and located at different distances from the laser. At each point I placed a horizontal razor blade in front of the beam. I then varied the height of the razor blade so that it blocked part of the beam, and simultaneously measured the voltage produced by a photodiode in the path of the beam. The photodiode responds to the beam by generating a voltage in response to the power it receives from the beam. With the razor blade at height u from the center of the beam, the power received by the photodiode is (ignoring diffraction effects)

$P(z) = \int I(\vec{x}) dA \propto \int_{-\infty}^{\infty} \int_{u}^{\infty} dx dy \Big(\frac{w_0}{w(z)}\Big)^2 e^{-\frac{2r^2}{w(z)^2}} \propto w_0^2 \Big(1-\mathrm{erf}\Big(\frac{\sqrt{2}u}{w(z)}\Big)\Big).$

Next, we expect the voltage produced by the photodiode to be linear in the power it receives. However, I must note that the height of the razor blade that I recorded, denoted by h, is not equal to the height above the center of the beam, which is u. Instead, there is a constant difference between these: u = h + b, where b is parameter corresponding to the height of h = 0 above the center of the beam. Taking this into account, we expect

$V(h,z) = V_0 + a\Big(1-\mathrm{erf}\Big(\frac{\sqrt{2} (h+b)}{w(z)}\Big)\Big),$

where V0, a, b, and w(z) are variable parameters at each location. I then fit the data to this curve in a Jupyter notebook by minimizing $\chi^2$ with respect to the parameters. The voltage data and the curve of best fit obtained at the first location are displayed in the first attacthed image. The fits at the other four locations were quite similar. In general, the fits appear pretty good and the residuals are low in magnitude. However, the residuals display a distinct pattern and are not randomly distributed. Therefore, it is likely that there is an effect not accounted for in this fit, such as diffraction or a non-TEM00 mode contaminating the laser beam.

Once these fits were completed, I had obtained five empirical values of w(z) at different distances from the laser. Specifically, I recorded the distances from the razor blade to a reference point near the laser, which I chose to be the base of a beam dump, and denoted this quantity by D. This distance differs from z in our coordinate system by a constant: z = D +c. With this fact noted, I then fit these empirical values to the equation of a beam waist for a Gaussian beam by treating w0 and c as fitting parameters and minimizing $\chi^2$ . Doing so yielded a minimum beam waist of w0 = 1.871·10−4 ±1.419·10−9 m and a constant offset of c = 0.3274 ± 4.557·10−6 m, both of which are reasonable values for this laser and setup. The data and fit for the beam waist are displayed in the second attatched image. (Note: in these plots, the uncertainties were much smaller than the variations in the data, and cannot be seen well.)

Attachment 1: VoltageFit1.png
Attachment 2: wFit.png
2113   Fri May 26 18:29:59 2017 DhruvaLaserWOPOBeam Profiling of Diabolo's 1064nm laser
Today, Andrew and I attempted to profile the Diabolo Laser's 1064 beam using the DataRay Scanning Slit Profiler. These are the results for the x and y spot size vs axial distance measurements. We used two single surface coated laser windows( W1-PW1-1025-UV-1064-0) to attenuate the beam down to 3mW. I have attached two images of the beam profiling setup, having indicated the z=0 reference on one of them.

z(cm) w_x(microns) w_y(microns)
0 1972 1882
2.54 1976 1928
5.08 2004 1988
7.62 2113 2050
10.16 2124 2097
12.7 2135 2137
15.24 2177 2194
17.78 2218 2246
20.32 2226 2288
22.86 2254 2322
25.4 2284 2370
27.94 2328 2413
30.48 2354 2438
33.02 2366 2478
35.56 2405 2512
38.1 2453 2571
40.64 2498 2591
The z = 0

On attempting to fit this data, I got these results for the beam waist size and waist location

x : 262micron waist at z =-1.5m

y : 192micron waist at z = -1.08m

Now there is obviously something wrong with this as the beam waist location is behind the laser and there's a 50cm difference between the x and y waists.
Attachment 1: 1064_WOPO_1.jpg
Attachment 2: 1064_WOPO_2.jpg
Attachment 3: 1064_profile.pdf
2120   Mon Jun 12 17:18:19 2017 DhruvaLaserWOPOBeam Profiling of Diabolo's 532nm laser

Using the same setup as before, I profiled the 532nm beam of the Diabolo Laser

z (cm) w_x(microns) w_y(microns)
2.54 1034 1099
5.08 1154 1226
7.62 1259 1341
10.16 1350 1428
12.7 1454 1548
15.24 1570 1685
17.78 1672 1789
20.32 1758 1887
22.86 1800 1961
25.4 1891 2052
27.94 1951 2088
30.48 2077 2187
33.02 2192 2272
35.56 2244 2358
38.1 2344 2420
40.64 2417 2500
43.18 2470 2542

The results look more reasonable than those obtained for the 1064nm profiling (60.5(x) and 56.6(y) microns approxiamately 31 centimetres behind z=0)
Attachment 1: profile.pdf
126   Wed May 13 17:13:29 2009 DmassLaserPSLBeam Scans

In the course of troubleshooting the PMC locking I took some beam scans of the PSL output.

They can be compared to the old scans

The scan in the attachement was taken right after the polarizing beam splitter.

Do we now have two beams coming out of the PSL?

I will wait for Rana or Stefan to get back before I chase th at one, as it's inside the PSL

Attachment 1: afterPBS.bmp
927   Thu Aug 12 18:32:37 2010 AlastairLaserGYROBeam overlap etc

We started out today by trying to improve the beam overlap.  After talking to Aidan, and with Koji and Rana's suggestions, we began by beating the beams on the BS at the output.  We replaced the lens before the PD with a ~3cm focal length one.  Then we used the adjuster on the BS itself to make the beams overlap at the PD.  We got the signal to increase up to -31dBV (this was about 2% contrast).

We tried to improve this by adjusting the overlap by altering the BS, and one of the steering mirrors before the BS, but we couldn't improve it much.

Based on the 20mV signal from the DC input it seemed like we were only getting 27uW out of our 50uW on the actual photodiode.  It is difficult to get the lens exactly the correct distance from the PD because we have to focus down so small (it's impossible to see how big the beam is using an IR card or viewer).  We tried mounting the lens on a translation stage and maximising the power on the PD.  We managed to get about 60% increase in power doing this.

Looking at the 95MHz signal on the spectrum analyzer the frequency shifts back and forward quite a bit (~100kHz).  This goes away if you turn off the frequency modulation input on the VCO driving the AOM.  Looking at the CW beam (the AOM direction beam) on the monitor the mode appears to be a little unstable even though the CCW beam is not.  At this point we started looking at the reflection locking path for the AOM.  The PD for this locking scheme was getting a bit saturated so we installed an 80% BS to reduce the power on the PD down to about 1.5mW.

At this point we looked at the errror signal from the CW direction while sweeping the laser.  It looked a bit strange (see TEK00000.PNG  below.  The blue trace is the PD signal and the yellow is the error signal) and after making sure the beam was on the PD correctly we decided to check the polarization of the beam going into the cavity.  We found that it had become slightly rotated.  It probably got altered when we were aligning the beam through the Faraday.  We rotated it back to S and checked that the  cavity was still locking.  We put a power meter on the transmission side and maximized the power transmitted by steering the beam into the cavity.  The max we got was CCW 2.21mW out from 7.4mW in.  We checked the CW polarization which was still correct, and also maximized it's power out (this side does not have a good mode matching solution in place) and we are getting 4.5mW our of 25.9mW.  Since the output beams were now a little uneven in power we rotated the polarizer that controls the relatvie power in the two arms such that we are now getting ~12uW of power on the PD from each direction.

The error signal from the CW side looked much improved after changing the polarization (TEK00001.PNG) but the CW mode still looked unstable.  When we lock both directions of the cavity and look at these signals again we see this (TEK00002.PNG) oscillation in the signal.  It is massive.  It basically takes up the full error signal and is no doubt the reason why the mode looks unstable.

If you turn off the FM input on the VCO driving the AOM then the oscillation is 50% smalller but still there.  We wondered if this was coming from the Tektronix, so we swapped the AOM over to the Marconi, but we see exactly the same noise with this if the FM deviation is set to ~300kHz.  It does go lower if we lower the deviation setting on the Marconi below about 100kHz.  This might be the noise we're seeing in the 95MHz signal in transmission.

**Edit** we just spoke to Frank who thinks this may be because we have the gain too high in this loop (though turning down the PDH box to almost zero didn't get rid of the oscillation).  Tomorrow we'll try reducing this further.

Attachment 1: TEK00000.PNG
Attachment 2: TEK00001.PNG
Attachment 3: TEK00002.PNG
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