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ID Date Authorup Type Category Subject
  1157   Wed Nov 10 01:21:49 2010 KojiComputingComputingWiki is down...

Seems fine, now...

Quote:

 The ATF wiki is down.  So is the 40m one.  The elogs are still running and I can ssh into Nodus which is where the ATF wiki now lives.  I'm having a bit more of a look at this now.

 

  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.

3. RFAM adjustment

  • 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
cabling.jpg
Attachment 2: reduction.jpg
reduction.jpg
Attachment 3: IMG_3714.jpg
IMG_3714.jpg
Attachment 4: IMG_3715.jpg
IMG_3715.jpg
  1178   Fri Nov 26 19:43:34 2010 KojiLaserGYROGyro OLTFs and current noise spectrum

It seems that the gyro noise level looks much better than that in entry 1150. Can you overlay the improvement of the gyro signal?

Note that your latest gyro signal is not valid above 1kHz considering you only have OLG of less than 10 above 1kHz.
(i.e. error in the noise level estimation is more than 10% above 1kHz unless you conpensate the effect of the control.)

- I wonder how I can obtain 0.67 (rad/s)/V from this formula... (In other word, I like to know the freq stability measured by the VCO.)

- How do we characterize / reduce the low frequency noise? Does going to vacuum really improve this noise? What is expected?

- Where is the VCO phase noise level now?

- We definitely need to have better PHD circuit. Probably we can use the box but should replace the board.

- We should start to look at the beat signal.

Quote:

500 kHz/V (VCO gain) x (c * 3.15 m) / (4 * 0.62 m2) ~ 0.67 (rad/s)/V

 

  1198   Wed Dec 8 22:22:51 2010 KojiLaserGYROGyro relocked

Gyro relocked GPS time at around 975910000. I leave the lab while it is kept locked.
Another elog entry is coming later.

  1199   Thu Dec 9 02:53:22 2010 KojiLaserGYRODouble Hacky? Trio? Even Hacky quartet!

[Koji, Zach, Alastair, Frank]

After our very hacky trials, we found the noise source in the low frequency band:
It is the air current on the input/output optics even though the mechanism is still unknown.

We need:

- to know why the air flow in the I/O optics causes the noise.
- to make firm wind shield for the input/output optics too.


First Zach, Alastair and Koji started the afternoon experiment.

1. The first attempt was to put the Al foil on the table in the box to prevent the air flow from the table holes.
We practically saw no improvement.
Frank later pointed that the holes of the table are individually sealed. Therefore it was reasonable not to see any improvement.

2. The second attempt was to introduce He gas into the box just in order to see any possible change in the noise spectrum.
We went to the biology stock room to get the tubing for the gas introduction. As soon as we introduced the gas into the box,
the optical path length started to show drastic change (doe to reflactive index of He?). At the same time we started to see vertical
misalignment. We no longer could lock the cavity on TEM00. It may be caused by the temperature change in the box as the
introduced He was indeed quite cold due to adiabatic expansion? We also observed our voices got strange as we expected.

The He cyrinder is still in the lab. We may prepare some reservoir to accumulate the gas and let it heat???

At this point Zach and Alastair left the lab.

3. The third attempt was to put the air baffles made by Al foils along the cavity path. It made no change in the noise.

4. I was checking the PDH box. I found that the phase setting of the VCO loop was at the edge (10.00). I added a short BNC in the PD path.
Now the phase for the maximum optical gain is 9.60. The phase was adjusted such that the servo starts oscillation with as lower gain as possible.

I was observing the VCO feedback (the current gyro signal). It has ~100mVpp 40MHz signal coupled. It turned out that this signal comes from the
DAQ. I put a 5MHz LPF between the PDH box out mon and the DAQ cable.

The signal is also sent to SR560 to filter out the high freq fluctuations which makes the observation quite tricky.

5. I found that if the PZT output goes to negative on the oscilloscope, the gyro signal have larger noise than usual.
I put an offset to the slow servo such that it does not go into the negative side.

6. As the noise below 100Hz has non-stationary behavior I tried to find any sign of scatteriing / clipping. No luck.

Then I started the attept of putting Al foils to cover the input/output optics.
It indeed helped to reduce the noise between 0.1-20Hz! The improvement is factor of ~5 between 1~10Hz.
See the plot and the first photo. This was one of the hackiest work I ever had...

7. As I could not believe this improvement by myself, I told the story to Frank who was in the room at this time.
He got excited and proposed several ideas.

7a. First we removed the Al foils in order to confirm the effect is real. Yes it is real.

7b. The imptovement could have been given by settling the air flow or shadowing the ambient light.
Frank pointed out that our PD is sensitive to the visible wavelength. He brought the VIS light blocking
filters from PSL lab. The filters didn't help the noise level.
The noise from the ambient light was rejected at least for now.

7c. We partially put the Al foils on the table. The effect was not quite localized but relatively strong at the downstream side of the input optics.
There is the air conditioning working above those optics. We put the Al foils to block the A.C. air. It improved the noise level by factor of 2-3.
Anyway, we confirmed that the main cause is the air flow.

7d. Frank found the plexiglas plates at the edge of the room. We constructed the temporary wind shield by them. See the second photo.
It improved the noise level as shown in the plot, although the effect was not as good as the Al foil case.

8. We decided to finish the work of the day. We cleaned up our mess (expect for the foil on the table in the box).
The stray Al foils were disposed. The Al reel was returned to the suspension lab.

 

Attachment 1: Gyro_Spectra_101208.pdf
Gyro_Spectra_101208.pdf
Attachment 2: 100_1158.jpg
100_1158.jpg
Attachment 3: 100_1162.jpg
100_1162.jpg
  1208   Fri Dec 10 13:43:07 2010 KojiLaserGYROupdate

We need some bias to the PZT out.

> 5. I found that if the PZT output goes to negative on the oscilloscope,
> the gyro signal have larger noise than usual. I put an offset to the slow servo
> such that it does not go into the negative side.

Quote:

I noticed that there was a (slow) error signal offset of about 4000 cts. Koji had recently put in a manual offset of the same amount to counteract what was an offset in the other direction before. I turned this off and was able to get the error signal back to around 0 by clearing the servo memory (i.e. just turning the filter block off and on and then reengaging the output).

 

  1223   Thu Dec 16 13:13:02 2010 KojiElectronicsGYROEOM circuit

I talked with Kiwamu the EOM master.

- The coil craft's indication like "1:16" means the turn ratio n=4.

- You saw 400Ohm with a single 1:16. This means the resonant impedance of 400*16=6.4KOhm.

- When you connected the second 1:16 transformer, the resonant impedance is 23*16^2= 5.9KOhm. This is reasonable if you consider the loss in the transformers.

- When you connected the second 1:16 with the half-tap point of it,  the turn ratio n=2 was added. This means that the transformer worked as 1:4 rather than 1:8
  although we were not sure why the resonant impedance was higher (150*16*4 =9.6KOhm) the other cases.

- Solution1: Ideally what you need is an additional 1:8. That is realized by 1:2 and 1:4 cascaded. This case the total turn ratio is n=Sqrt(2*4*16)~11. That is your gain. We are not yet sure about the loss by the triple cascade of the transformers.

- Solution2: Put the terminator at the primary side while leaving the first 1:16. As your EOM had 400Ohm with the 1:16, the input impedance will be converted to 44Ohm which is not so bad. The gain will be 4 (=n).
  (By the way this is equivalent to put a 800Ohm resister in parallel to the EOM)

- Solution3: Put the 75Ohm resister at the primary side while using the half tap point of the additiional 1:16. As your EOM had 150Ohm with this condition, the input impedance will be 50Ohm. The gain will be 8.
  (This is equivalent to put a 4.8kOhm resister in parallel to the EOM)

Quote:

 I finally asked Frank if I could just borrow the impedance test kit to measure the EOM resonant circuit impedance, as I have been having problems with the voltage transfer function method. I took the measurement and found that the peak impedance was 400 Ω (see first figure below). Pleased by the round number, I figured I could just add another transformer at the input to divide this down to 50 Ω.

The results weren't as nice as I'd like. First, I forgot that while the voltage ratio is in proportion to the turn ratio, the impedance ratio is in proportion to the turn ratio squared. So, for lack of a 1:8 RF transformer in the kit, I took another 1:16 transformer and only bridged across half of the secondary coil, so as to presumably get a turn ratio of 1:8 (though admittedly I wasn't sure about this). This resulted in a surprising peak impedance of around 150 Ω, though I do not have data for this

Knowing that I needed a larger ratio, I decided to just connect across the full secondary coil (so that I now had two cascaded 1:16 transformers). The resulting peak impedance is now 23 Ω (see second figure---note also that I have adjusted the tunable inductors to make the resonant frequency 33 MHz, instead of the 37 MHz it was in the first plot).

Clearly, I need something in between, but I am not sure how to do this without a THIRD transformer, which seems gratuitous. Perhaps I can measure the reflected power and decide if we can deal with it?

400_ohms.png

 

25_ohms.png 

 

  1232   Wed Jan 5 14:45:53 2011 KojiLaserMOPAChiller is crying

The water chiller at ATF is crying with error "Di (or D1)". What should we do? ==> Frank

The water level seems to be higher than the minimum.

It also shows temp of 19.5Cdeg.

  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.

PD_box.pdf

 

 

 

  1262   Tue Jan 25 00:05:57 2011 KojiElectronicsGYROPDH servo

1. I don't like the logarithmic variable gain. I like the dial on the box which indicates the number proportional to the gain. This means that the variable gain stage is to be an inverting amplifier with the potentiometer in the feedback path. I recommend it as far as AD829 does not get screwed up by the stray reactances of the potentiometer.

2. Let's put buffered test points before and after the excitation input. These test points should be connected to the panel connector. There should be a manual (or remote?) switch that disconnect the exc input such that we can avoid the noise injection through it.

  1264   Tue Jan 25 01:39:00 2011 KojiElectronicsGYROPDH servo

I don't see any particular reason to disconnect the loop for the sweeping.

I rather like to have a summing amplifier stage for the excitation so that we can use it to measure the open loop TF.
The input impedance of the summing stage should be high enough (~10K) such that we don't have the calibration
error between 0ohm and 50ohm signal sources.

AD829 may get unstable when the gain is small. Read the data sheet carefully, and put additional pads
so that we can put additional compensation components as described in the data sheet.

  1266   Tue Jan 25 02:18:17 2011 KojiElectronicsGYROPDH servo

Gotcha!

Quote:

The EXC input for the digital injection is indeed an equal-ratio summing amplifier; it adds the excitation in along with the loop signal (admittedly, I'm not quite sure how it works when the invert is flipped, but this is how it is set up with Rana's modification to the current box, also). The input resistance for each of the inputs is 10K.

 

  1270   Wed Jan 26 06:20:03 2011 KojiElectronicsGYROPDH servo

- LF356 is too slow. GBW is lower than that of OP27 (8MHz). We don't want to have the phase retardation by the opamps.
- LF357 is not unity-gain stable. You have to use it with the gain larger than 5. i.e. this is not for us.
- OPA604 is a good alternative. This is a JFET opamp with vin=10nV/rtHz, GBW=20MHz and made by BurrBrown!

We had an unreasonable behaviour of AD8336. i.e. increasing the gain increased the input reffered noise, though I did not understand what was happened.
I definitely like the linear gain inverter. Maybe with OPA604 in stead of AD829 to avoid possible oscillation?

Quote:

  I have updated the PDH servo schematic to include:

  • LF356's instead of AD829's for the switchable stages. Rich said it was a good idea to have FET input op amps in this case (like on the universal board). The LF356's have a relatively low GBW of 5 MHz. This shouldn't be a problem since we don't use them at high gain, but in any case we can switch to the LF357 which has a GBW of 20 MHz.
  • External compensation capacitors for the AD829's, which we will still use for the input, output, and buffered monitor stages.
  • Buffered monitors before and after the EXC injection (for TF purposes)
  • RF phase shifter with independent +12 supply (not exactly sure why that is there, but that's the way it is on the universal board)
  • LED indicators for
    • +12
    • -12
    • +12a (RF)
    • Boosts 1-4
  • Test points for
    • +12
    • -12
    • +12a
    • +5 (comparator supply)
    • various places around the circuit we might want them

I hope to be able to position all the BNC/SMA/LEDs on one edge of the board so that we can have them sticking out the face of the NIM module. We can use Front Panel Express to make a fancy face.

We still need to talk about the variable gain stage. Koji doesn't like the linear-in-dB unit, so the other alternative is to have an amplifier with a pot in the feedback path. Does anyone else have any feelings for/against this?

PDH2.pdf

 

  1284   Fri Feb 4 08:08:39 2011 KojiElectronicsGYROPDH2 PCB layout

Board

  • The lines looks too thin
  • The chips should always be the same direction
  • The connectors / the potentiometer should be on the panel. Not on the board.
  • There is no extra pads for future modification of the TF
  • Have a universal pattern for future expansion

Schematic diagram

  • Increase the gain of the 1st stage for the low input noise
  • What's the purpose of TP7-10? They only shows 0V when their are correctly working...
  • Strange wiring at around U3
  • Are +/-12V power intentional choice? Why not +/-15V?
  • Why U7 is an attenuator in stead of an amplifier?
  • Use 7805 in stead of using the voltage divider for the power supply.
    The current consumed by the comparator changes the divided voltage. This changes the reference level of the comparator.
    In the worst case this causes the oscillation.
  • Is it a good idea to pull up the boost input with the +5V source through a reasonably high resistance?
    This will allow us to use a terminator plug (or a potentiometer) to control the boosts.
  • Write the threshold voltages of the comparators on the schematic diagram for the easy understanding of the boost control.
  • The comparators have no hysteresis (positive feedback). What do you do about chattering of the comparators?
  • Is it OK to get the phase shift ctrl form the voltage division of the +12V supply? Don't we need a reference voltage?
  1288   Fri Feb 4 20:23:13 2011 KojiElectronicsGYROPDH2 PCB layout
  • [About the thin lines] Thin lines are not so immune to heat. They may peel off from the board if someone put too much heat on the soldering. Probably 10mil is ok as you are going to ask a company to make resist-coated PC boards. Also, we always modify the circuit in some unknown reasons. If the lines are thicker, we can patch the stages in a flexible ways. Of course, the
     
  • [Chip directions] You will know if you build 20 of different circuits with the chips arranged randomly. The board made by industries are fine as their components are put on the board by a machine and use paste solder and an oven. Our board is made by ourselves. Also we test the board by ourselves. It is always good to have the chips in a single direction. This helps the debugging a lot.
  • [Connectors on the panel] I could not get whether the connectors are mechanically fixed on the front panel or not. We don't want to put strain by the cables to the board because it may crack the soldering of the connectors SOME YEARS LATER. If you have threads on the connectors and fix them on the panels that is nice, but we will have some trouble to fix the board in the box in this case.
     
  • [Extra pads / Extra pattern] There was some confusion because of my short explanation. What I wanted to say was that if you have one or two opamps extra stages which is not connected anywhere, we can use them as a universal board for some unknown purpose in future. i.e. Someone wants to put some signal goes into the loop ==> insert a summing amplifier somewhere in between the stages. Someone needs whitening stage for DAQ. Etc.
     
  • [Components values] This is the philosophie of the low noise circuit: The input stage should decide the input referred noise level of the circuit. It is VERY sad too see the performance of AD829 is spolied by the misuse of the high resistance with low gain at the first stage. The shot-noise level may be higher than 10nV/rtHz, it is good to know the basic rule that the first stage should decide the input referred noise.
     
  • [TP7-TP10] They must be misplaced. You will not be able to measure any sensible transfer functions. Review the schematic and replace the TPs.
     
  • [+/-15V power supply] Review the data sheet. If you can exploit full +/-10V range of the ADC by +/-12V supply, that is still good.
     
  • [Pull up / Pull down] If you pull down the port, we can't turn on/off by plugging a short plug there. Pull up is the way.
     
  • [Chattering] Between the steps the control voltage acrosses the thresholds. If the comparator is enough fast (I suspect so), the comparator switches multiple times. That may cause the multiple switchings of the relays. The relay may be enough slow to remove the chattering. I have no experience of relays.
     
  • [Vref] It is always nice to have Vref on the board.
     
  • [Final remark] Don't forget to make the extra oards for the purpose of the others as the board will be very useful to everyone!
  1303   Tue Feb 15 09:12:11 2011 KojiElectronicsGYROUniversal PDH box noise problem identified

Yes, I am happy about that. For the new box, we confirm the noise levels of the boxes with various gains before they are in use.

Quote:

Second, Koji will be pleased to hear that I think I have traced the excess low-frequency noise seen in this measurement to the AD8336 variable gain stage.

 

  1347   Sat Mar 12 16:11:35 2011 KojiLaserGYROcurrent gyro noise

What is the reason that the AOM actuation (blue) and the PLL actuation (green) are different by factor of ~50?

Of course, the VCO noise of the AOM couples into the blue curve, Do you claim the blue is completely dominated by this, including the mechanical structure between .5Hz - 100Hz?

Quote:

gyro_noise_with_contribs_3_11_11.png

 

  1349   Sat Mar 12 19:20:19 2011 KojiLaserGYROcurrent gyro noise

I understand your explanations. Now I feel these points.

- This AOM feedback should agree with the calibrated error signal of the secondary cavity.  This is not confirmed.

- This noise is suppressed by the loop gain of the secondary cavity. (The spillover noise of the secondary.) This is not shown. Also the OLTF of the secondary is not shown.

- The AOM feedback at around 100Hz shows the same level as the primary spillover. Does this suggest that the loop gain of the secondary is higher than 1k???

- Of course we like to see the OLTF of the PLL.

Are you working with the measurements, Zach?

Quote:

This is the answer I would give:

  • The magnitude is lower because the differential noise of the input optics is suppressed by the secondary (CW) loop gain in the PLL readout (but not in the AOM readout). This was the main advantage to this readout scheme in the first place (see this post)
  • The shape above ~100 Hz is different either because the residual primary loop noise ("spillover noise") is also suppressed in the PLL readout OR because the PLL bandwidth is lower than this. We don't have an OLTF of the PLL yet, but we can see which one it is by carefully reviewing the diagram in the above post to see if the spillover noise should indeed be suppressed (we didn't think it would).

 

  1351   Sun Mar 13 00:27:29 2011 KojiLaserGYROcurrent gyro noise

Ah, "- This AOM feedback should agree with the calibrated error signal of the secondary cavity. This is not confirmed." was

The AOM feedback (calibrated) with the loop closed = The secondary error (calibrated) without the loop closed

"- This noise is suppressed by the loop gain of the secondary cavity. (The spillover noise of the secondary.) This is not shown. Also the OLTF of the secondary is not shown."

The spillover noise exist for the primary and the secondary.

The measurement with the beat signal relys on the fact that each laser frequency is following the resonance of the cavity.

In your case the real gyro signal is way smaller than the PDH error felt by the cavity because of the differential input optics or whatever.
If this noise is not suppressed by the servo, the noise transmits the cavity and felt by the beat. Therefore,

We need to know
1) The free run secondary error level
2) The suppressed secondary error
3) The OLTF of the secondary

"Here are both of the OLTFs:"

The difference between the AOM feedback and the beat measurement is ~50. This is 34dB, while the OLTF below 100Hz is larger than 50dB.
So presumably, the spillover noise is smaller than the measurement. This is a minimum confirmation of the secondary spillover noise.

Quote:

I'm not sure I understand your points..

"- This AOM feedback should agree with the calibrated error signal of the secondary cavity.  This is not confirmed."

I think you mean that the secondary error signal calibrated into Hz via the optical response ([V/Hz]) should be the same as the suppressed noise calculated by multiplying the AOM feedback signal through the AOM response ([Hz/V]) and dividing by the OLTF, as I did for the primary loop here. If so, then no, I haven't done this yet. I was about to do it now but I must have left the CCW error signal disconnected from the DAQ 

 

"- This noise is suppressed by the loop gain of the secondary cavity. (The spillover noise of the secondary.) This is not shown. Also the OLTF of the secondary is not shown."

I don't think I know what you mean here. The spillover noise from the primary cavity (which can be calculated from the primary error signal) is present in the AOM actuation signal, as it tries to cancel the noise that the primary loop has failed to.

Here are both of the OLTFs:

OLTFs_3_11_11.png

 

"- The AOM feedback at around 100Hz shows the same level as the primary spillover. Does this suggest that the loop gain of the secondary is higher than 1k???"

In frequency bands where the residual common-mode noise is higher than the differential noise, the AOM feedback spectrum should be the same as the calculated spillover noise (blue and red, respectively). This appears to be true above ~100 Hz. It was true above 30 Hz in the old budget. It makes sense that the residual common-mode noise has gone down a little below 100 Hz, because the primary OL gain has gone up a bit from the extra integrator I added, but it is strange that there is still about the same level of noise below 100 Hz in the AOM signal as there was before, despite the fact that we replaced PDs. It could be that the optical gain is still low enough that electronics noise dominates here, but we won't know that until I plot the PD/demod noise alongside it. I will do that tonight or tomorrow.

"- Of course we like to see the OLTF of the PLL."

I plan to measure this, but it is a little difficult since I don't have an electrical summation point for this as I do for the locking loops. I think I can do it by sweeping the AOM frequency (with the secondary loop open, that is), but I haven't worked it out yet.

 

  1554   Tue Oct 18 23:42:47 2011 KojiLaserGYROPMC Finesse measurement

[Koji Zach]

We have made a quick measurement of the finesse of the gyro PMC by sweeping the SLOW input of the NPRO
with 0.03Hz triangular wave.

The time elapsed between the two FSRs: 3.53 +/- 0.01 sec
FWHM: 21.6 +/- 0.8 ms

==> Finesse: 163 +/- 6

Cavity length: 0.324m

==> FSR 925MHz, fc = 2.8MHz


Cavity incident: 168 +/- 1mW
Forward Transmission: 92.5 +/- 0.2 mW
End Transmission: 1.80 +/- 0.02 mW
Reflection: 21.7 +/- 0.2 mW
AR reflection: 12.6 +/- 0.1 mW
==> Transmission: 60%, Loss: 25%

  1557   Thu Oct 20 17:02:34 2011 KojiLaserGYROPower Budget of the PMC

Power budget of the PMC has been considerd.

AR Reflectivity (rAR2): 7.50% (<- HUGE)
Round trip mirror (3 loss) : 0.499%  (<- HUGE)
Transmission of the flat mirrors (t12): 1.65% (<-OK)
Transmission of the curved mirrors (t22): 302ppm (<-OK)
Modematching (1-Rjunk):: 86.5% (<-hmm, OK for now)
Raw cavity transmission (t1 gcav): 86.2%

I wonder how the loss of 5000ppm comes from.
Frank suggested that there may be the spot not at the center of the curved mirror.
I checked the spot position at the end and it is actually very close to the edge of the hole. (See photo)
Of course the beam has the angle because of the short triangular cavity. So it is difficult to say this is still ok or not.

The AR seems to have huge reflection, but this is real.


Assumptions:

- Two flat mirrors are identical

- Losses are distributed on the three mirrors equally.

- AR surface has no loss.

- AR of the end transmission is ignored as the beam will not be separated on the PD

Those conditions give us the five undetermined variables: rAR, t1, t2, loss, Rjunk
where they are amplitude reflectivity of AR, that of the flat mirrors, that of the curved mirrors, loss in power, power ratio of the unmatched light in the incident beam, respectively.

We have 5 independent measurement after the normalization of the power measurements by the incident power. So there is a unique solution.
After a bit painful solutions serach, the numbers below have been obtained.

rAR -> 0.2739, t1 -> 0.1283, t2 -> 0.01737, Rjunk -> 0.1347, loss -> 0.00166271

Converting this result into useful numbers, we obtain the following quantities:

AR Reflectivity (rAR2): 7.50%
Round trip mirror (3 loss) : 0.499%
Transmission of the flat mirrors (t12): 1.65%
Transmission of the curved mirrors (t22): 302ppm
Modematching (1-Rjunk): 86.5%
Raw cavity transmission (t1 gcav): 86.2%

 

Quote:

==> Finesse: 163 +/- 6

Cavity incident: 168 +/- 1mW
Forward Transmission: 92.5 +/- 0.2 mW
End Transmission: 1.80 +/- 0.02 mW
Reflection: 21.7 +/- 0.2 mW
AR reflection: 12.6 +/- 0.1 mW
==> Transmission: 60%, Loss: 25%

 

Attachment 1: PMC.pdf
PMC.pdf
Attachment 2: PA201622.jpg
PA201622.jpg
  1559   Tue Nov 1 22:45:26 2011 KojiLaserGYROWierd (LF noise still there)

This power fluctuation of the cavity transmission is really strange.

- The transmitted powers of the PMC and ring cavity change every time they are locked.
This may be justified as the temperature of the crystal is everytime different.

- The ambient air flow seems to be affecting the power fluctuation, but it is not everything
  as power fluctuation of the ring cavity changes in every lock.

- Even if the cavity is precisely aligned by the last steering mirror before the ring cavity,
I can easily improve the transmission by pushing or pulling the chamber of the ring cavity.

(TO BE CONTINUED)

Left the lab with the following condition:

The laser is on.
The shutter is closed.
LF Boost of the PDH box is off.
LF Boost of the PMC servo is off.
The thermal control on the CDS is off.

Quote:

The low frequency noise is still present in the TRANS signal, seemingly discounting the beam jitter theory. I think I am too sad to ask Rana for the $5, though.

TRANS_with_PMC_10_19_11.pdf

 

  1570   Fri Nov 18 03:57:44 2011 KojiLaserGYROmore air noise testing

 

Quote:

To me, this suggests that there is almost certainly a strong external-FM-to-jitter coupling in the laser, which is very bad.

 It is also possible that there could be an offset to the locking point of the PMC.

 

Quote:

To me, this suggests that there is almost certainly a strong external-FM-to-jitter coupling in the laser, which is very bad.

Things worth doing:

  1. Swap out the laser head and see if that is the problem. It would be unfortunate if it is, but it is something we should definitely investigate.
  2. Optimize the PMC servo. Currently, it is just a single pole, which doesn't give us enough low-frequency gain.
  3. Find a HV solution. At the moment, every time the gyro unlocks, the integration of the gyro servo slams the laser frequency out of the range of the PMC servo. This leads to a pain-in-the-ass situation where we have to relock the PMC every time we change something. With a HV amplifier, the PMC would stay locked.

- The PMC servo should be packed in a NIM box. Proper low pass filtering after the mixer. This could be done with a prototype board rather than on a PCB.
In addition to the optimization mentioned above, we should implement the external adjustment of the gain as well as the external boost switching.

- The boost switch of the PDH box should be automated. Or, we should start using the new PDH2 board.

- Automation of the thermal path switching.

  1578   Fri Dec 9 17:56:07 2011 KojiLaserGYROnew box basic drawing

Looks nice.

18.5" x 45.5" x 0.75" ==> 1e7 mm^3 ==> 12kg for polycarbonate

This is heavy but still OK weight.

  1678   Sat May 26 15:27:18 2012 KojiLaserGYROno real improvement at vacuum

This is just a usual ringing...the freq sweep is to fast compared with the strage time.
As the intracaviy mode can't be (quasi) static, the dip/peak at the reflection/transmission don't reflect the actual cavity refl/trans in an equilibrium state.

 

  1694   Sat Jun 16 18:56:36 2012 KojiLaserGYRO(Dubious) linewidth measurement

By connecting the marconi output to the spectrum analyzer, you should directly be able to see how much you are shaking the marconi frequency.
This gives you the sanity check for the calibration of the AOM driving.

  1761   Thu Sep 6 12:33:46 2012 KojiLaserGYRONEW BEST gyro noise, without subtraction

Hamamatsu S3759 (5mm dia.) has a junction capacitance of 10pF with VR=100V. (c.f. FFD-100 8.5pF @15V)
This diode has high responsivity of 0.38A/W@1064nm. I tested this deiode with the BBPD. The bandwidth
of the PD is just 30MHz even with the bias of 100V. This can't be explained by the RC pole of the circuit.
Nevertheless thanks to the high responsivity, the noise performance (in terms of W/rtHz) is better than these with the other Si diodes (20pW/rtHz vs 150pW/rtHz).

I only have one S3759 in hand. If you like to try it, I can give it to you.

BTW, Newfocus 1611 has a bandwidth of 1GHz, responsivity of 0.78A/W, and noise level of 30pW/rtHz.
And PDA255 has 50MHz, 0.7A/W, and ~40pW/rtHz@1064nm.

Quote:

Since the subtraction test the other day, I have replaced the PDA255s with Koji's aLIGO BBPDs for the OOL RAM monitors. These should be better, but the lower responsivity of the diodes could mean that it is a wash. There is some low-frequency coherence that I may try to use for subtraction. Also, there is some coherence with the primary actuation signal.

 

Attachment 1: noise_BBPD.pdf
noise_BBPD.pdf
  1778   Sat Oct 13 00:32:27 2012 KojiThings to BuyGeneralThings to buy
  • VWR While sticky mat (Large 25"x45") / VWR 18888-216 (30 layers x 8 sheets) -> delivered
  • VWR While sticky mat (Small 24"x36") / VWR 21992-042 (60 layers x 4 sheets) -> delivered
     
  • Thorlabs 8-32 screw kit / Thorlabs HW-KIT1 -> ordered newport equivalent
  • Pedestal Shims - Newport -> ordered (one kit and 10 additional pieces of PS-0.25, PS0.125)
SP-0.25-S-10	0.5" dia. 1/4in thick bag of 10 ($20.99)
SP-0.125-S-10	0.5" dia. 1/8in thick bag of 10 ($20.99)
SP-0.063-S-10	0.5" dia. 1/16in thick bag of 10 ($19.99)
SP-0.031-S-10	0.5" dia. 1/32in thick bag of 10 ($19.99)

PS-0.25		1" dia. 1/4in thick 1 ea. ($6.99)
PS-0.125	1" dia. 1/8in thick 1 ea. ($6.99)
PS-0.063	1" dia. 1/16in thick 1 ea. ($5.99)
PS-0.031	1" dia. 1/32in thick 1 ea. ($5.99)

Also you have a kit:
SP-KT ($199.99)
This contains
	5x PS-0.25
	5x PS-0.125
	5x PS-0.063
	5x PS-0.031
	10x SP-0.25-S-10
	10x SP-0.125-S-10
	10x SP-0.063-S-10
	10x SP-0.031-S-10

The kit is slightly more expensive than the individual ones.
Maybe due to the plastic case???

 

  1779   Fri Oct 19 18:07:10 2012 KojiLab InfrastructurePEMA huge current driver and coil magnet actuators are missing

I found some lab infrastructure like a huge current driver and coil magnet actuators went somewhere.

And a floppy disk drive too.

  1782   Tue Dec 18 19:01:29 2012 KojiMiscPMCImpact Hammaring of Gyro Metal PMC

Kristen and Norna have come to ATF for impact-hammering of metal PMC in the gyro setup.

  1784   Wed Mar 20 17:46:43 2013 KojiLaserDoublingMoved NPRO from ATF to the 40M

[Koji, Annalisa, Manasa]

NPRO with controller from ATF joins the 40m. We have put it on the POY table where we plan to use it for ABSL.

http://nodus.ligo.caltech.edu:8080/40m/8319

  1785   Mon Mar 25 20:11:26 2013 KojiMiscGeneralThorlabs power meter & WinCamD @56Lab

Borrowed Thorlabs power meter & WinCamD set for the use in the OMC setup.

==> Zach took the power meter back to ATF.

  1827   Mon May 20 22:44:04 2013 KojiMiscGeneralThorlabs power meter @56Lab

Borrowed Thorlabs power meter for the OMC test.

  1874   Thu Jun 19 00:51:54 2014 KojiLaserGYROGyro noise better by 10x *NOPE*

 

 Congratulations and I am looking forward to seeing the comparison plot to see how it is improved and how it is better than / close to the requirement.

  1927   Wed Jun 3 15:05:19 2015 KojiElectronicsSeismometerQPD matrix circuit

I made a QPD matrix circuit. We had a QPD head D980325-B and we needed a power supply & signal operation circuit.
The QPD head uses Centronic QD100 quadrant diode and OP497 for transimpedance.

The matrix circuit is built on a proto-SMD board with the eurocard size. It takes the supply voltage of +/-18V or higher.

Note that the circuit diagram is enclosed in the box.  The copy of the circuit diagram is attached here too.

Attachment 1: P6037723.jpg
P6037723.jpg
Attachment 2: P6037719.jpg
P6037719.jpg
Attachment 3: P6037720.jpg
P6037720.jpg
Attachment 4: P6037721.jpg
P6037721.jpg
  1930   Tue Jun 9 19:39:03 2015 KojiElectronicsGeneralNick Lockerbie's precision current driver

I need a current driver for the photosensor LEDs.

Nick Lockerbie@University of Strathclyde once taught us his precision current driver that is insensitive
to the temperature dependence of the transister bias current. The attachment is the circuit diagram.

The regulated current is given by Vref/RI. In the example case, the current is 50mA.
It is important to keep the retio R3/R1 = R2/RI for the Ib cancellation.
Vbias needs to be adjusted to make the transister work properly.
(i.e. Vi = ~Vref therefore Vbias needs to be higher than Vref as well as the transister voltage drop take into account.)

It took sometime to realize the circuit function in LTSpice as the circuit he taught us had wrong transister polarization.
(We have 4 polarity choises i.e. PNP vs NPN || Diode at emitter vs collector. For this voltage PNP & Emitter is the right choise)


The principle of the circuit is as follows:

- Vo = - (Vref-Vi) + Vb

- I_R2 = -(Vref-Vi)R3/(R1 R2)

- Ie + I_R2 + I1 = I2 + I1

- Ie = I2 - I_R2 = Vi/Ri + (Vref-Vi) R3/(R1 R2)

If R3/R1 = R2/RI, this is reduced to

Ie = Vref / RI

I checked the noise level by replacng the diode by a resister (and using an instrumentation amp).
When LT1128 is used, the current noise was 52, 30, 27, 27 pA/rtHz at 1, 10, 100, 1kHz (upper limit).
This corresponds to RIN of 1e-9 ~ 5e-10. If this is true, this is enough for the shotnoise level for 50mA (RIN 2.5e-9).
I initially thought an FET opamp gave us better performance, but the simulation denied it.

I think we should be able to modulate the current by modulating the reference voltage.

Attachment 1: current_driver.png
current_driver.png
  1954   Mon Jun 29 21:28:46 2015 KojiElectronicsGeneral2ch Photo Sensor circuit

Here the performance measurements for a 2CH reflective photo sensor circuit are presented.

Two sensor heads are driven by Nick's constant current driver. They are connected in series. Therefore the two heads need to be connected at the same time to make them work correctly.

The reflected light is detected by two photo diodes (per head) to cancel angular motion of the mirror. The photocurrent is amplified in the head and sent to the box.

It has a modulation input. One can connect a SYNC output of a signal generator to chop the LED current. The modulation freq of 3~5kHz gives the best result.
In order to use the modulation function, two internal jumpers should be removed to activate AC coupling cirucit.

The final outputs have 500Hz roll-off with 3rd order butterworth.

Attachment 1: Calibration of the photo sensor (CH1 only)

An Al mirror is placed in front of the photo sensor head1 on a sliding stage. When the sensor head is touch the mirror, the diplacement is marked zero. The sensor output depends on the distance of the sensor from the mirror. From the measured profile of the sensor, the near- and far-side calibrations were estimated to 2.6e3 V/m and 0.67e3 V/m, respectively. These numbers depends on the reflecting surface and if the modulation is used or not, as well as the modulation frequency. Therefore the calibration should be done everytime one sets the sensors up.

Attachment 2: Receiver performance

By disabling the current source, the dark noise level was tested. The PDs have the dark noise level of ~1pA/rtHz floor. This corresponds to the shot noise of 3uA DC current. This measurement has been done at the test points before the final roll off filters.

Attachment 3/4: DC RIN / AC RIN measurements

A head was positioned in front of the mirror with the distance where the response hit the maximum. This corresponds to the measurement of the RIN when there is no modulation. When the modulation is used, we can define a similar quantity to RIN, here we call this AC RIN. I don't see good suppression of the DC fluctuation. It might suggest that the DC amplitude of the LED current is changing this much and the ambient noise is not affecting the performance. So when an ambient noise is not an issue, DC meausrement gives us a better performance. When an ambient noise disturbs the displacement sensing, the modulation function should be used with the cost of noise floor level.

Attachment 5: Displacement noise without modulation

Finally, the displacement equvalent noise level was checked. This measurement has been done by placing Head1 in front of a fixed mirror with the distance about 1.5mm. This corresponds to the DC output of about 5V. The noise level is 0.2~0.5 nm/rtHz above 2Hz and 3/f^3 nm/rtHz below 2Hz. This noise curve actually includes the vibrational noise of the measurement setup.
 

Attachment 1: PS_Calib.png
PS_Calib.png
Attachment 2: PS_Dark_noise.png
PS_Dark_noise.png
Attachment 3: PS_DC_OUT.png
PS_DC_OUT.png
Attachment 4: PS_AC_OUT.png
PS_AC_OUT.png
Attachment 5: PS_Disp_Noise.png
PS_Disp_Noise.png
  1979   Thu Jul 16 10:21:39 2015 KojiMiscSeismometerOptical lever installation (Re: Rhomboid motion)

Some supplimental info on Alessandra's entry

0. Suspension stopper: In order to make the work on the suspension easier, I made simple suspension stoppers.

1. Oplev layout: We decided to put all of the input-output optics on a single triangle platform so that the optical lever angle become small. However, this was a challenge as the x-z stage for the QPD calibration is bulky... Once the calibration is done, the stage can be replaced with a pole.

2. The laser: The bare outputs of the laser diodes are too dirty for the optical lever measurement. We decided to use a fiber pigtail laser as the mode quality is excellent.We needed to setup a collimation optics. I brought a bunch of fiber coupling optics including an aspherical collimation lens with f=10mm. It was adjusted to have the focus at ~1m from the collimator. The beam radius looked like ~0.5mm. Allessandra will check this this afternoon.

3. The reflection mirror: Since the beam height on the laser platform determines the optical height at the rhomboid that is higher than the middle plate of th rhomboid, we needed to use an optical mounts on the middle plate. In fact we installed two (almost) identical mirror assemblies for counter balancing. This actually made the rhomboid unstable as the center of mass became higher than the clamping point. We decided to add a balast mass at the bottom of the rhomboid. This also work as a tilt adjuster. The balast mass was attached to the plate using a double sided tape. As a result, we recovered a stable condition (positive spring constant) of the pendulum, however, the tilting (pitching) frequency is now not precisely tuned. Maybe this is what Alessandra can work on after the QPD calibration?

  1982   Fri Jul 17 11:51:46 2015 KojiMiscSeismometerQPD calibration

- The power supply was TEMMA triple power supply with dual 30V supplies and a fixed 5V supply. This was a long loan from ATF to the OMC lab.

- The 4ch color oscilloscope is a loan from the OMC lab to ATF. ATF seemed to have only one oscillocscope that is what Arjun is using.

- During the calibration, the suspension was stopped by the stoppers. Also we added a mass at the bottom so that the suspension is further stabilized by the increased pressue to the stoppers.

  1998   Sat Aug 8 19:05:38 2015 KojiMiscGeneralInverted pendulum 10mm rod holder

LIGO-D1500236

Attachment 1: 10mm_Rod_Holder.pdf
10mm_Rod_Holder.pdf
  2006   Fri Aug 21 22:59:00 2015 KojiMiscSeismometerStarted continuous data taking

This work was done at the 40m.


On Wednesday:

Alessandra and I jiggled the PID parameters in order to try some temperature stabilization. But the temperature kept going below the set temp and we were confused.


On Thursday (yesterday):

Alessandra and I succeeded to stabilize the box temperature. We used the PID setting of 250 250 0. Previously, the control gain was way too low and the final temp had significant deviation from the set temp. Now with the max I gain, the controller squishes the DC deviation better.


Today

In order to try to take the continuous temperature measurement, I picked up the Rapsberry Pi at the Yend.
It has the IP of 192.168.113.166 accoding to the log http://nodus.ligo.caltech.edu:8080/40m/8745

Initially I could not login to the host. After struggling with the HDMI cable and connected the display/keyboard/mouse to the host, I found that the user name is not "controls" but "pi". How can I know!

I could manage to change the password to the nominal 40m controls' one, and also created "controls" account by "adduser" command.


After played with Gautam's code a bit, I understood how to acess to the serial port.

Some tips
- python library "serial" is installed only for python3.
- In order to use the USB port, the user must be in "dialout" group

I made a little bit of coding to have constant but slow sampling rate. Now I started to log the temperature data with the rate of 10sec.
This program changes the set temp from 22degC to 23 degC and continuously take the data.

controls@raspberrypi ~ $ cat 150821_222610.log
1440221170  21.9   : 08/21/15 22:26:10
1440221180  21.9   : 08/21/15 22:26:20
1440221190  21.9   : 08/21/15 22:26:30
1440221200  21.9   : 08/21/15 22:26:40
1440221210  21.9   : 08/21/15 22:26:50
1440221220  21.9   : 08/21/15 22:27:00
1440221230  21.9   : 08/21/15 22:27:10
1440221240  21.9   : 08/21/15 22:27:20
1440221250  21.9   : 08/21/15 22:27:30
1440221260  21.9   : 08/21/15 22:27:40
1440221270  21.9   : 08/21/15 22:27:50
controls@raspberrypi ~ $ cat 150821_222802.log
1440221290  21.9   : 08/21/15 22:28:10
1440221300  21.9   : 08/21/15 22:28:20
1440221310  22.0   : 08/21/15 22:28:30
1440221320  22.0   : 08/21/15 22:28:40
1440221330  22.0   : 08/21/15 22:28:50
1440221340  22.0   : 08/21/15 22:29:00
1440221350  22.0   : 08/21/15 22:29:10
1440221360  22.1   : 08/21/15 22:29:20
1440221370  22.1   : 08/21/15 22:29:30
1440221380  22.1   : 08/21/15 22:29:40
1440221390  22.1   : 08/21/15 22:29:50
1440221400  22.1   : 08/21/15 22:30:00

Unfortunately this program stopped when I logged out. It was fixed by running the command via nohup (no hangup):

nohup ./TC200scan.py &

The previous attempt injected the heat to the system, I'll let the system cooled down for several hours and then run the step rise to log the data.

BTW: TC200 doesn't allow us to observe the data below 0.1 degC level. The other temp controller we brought from WB read the thermister resistance with the precision of 0.001 Ohm.

  2010   Wed Sep 16 04:43:35 2015 KojiMiscSeismometerIP test at the 40m

Alessandra and I have constructed the IP at the 40m.

The lowest resonant freq I could obtain was 132mHz when 1613g additional mass is placed on the top plate.

It is very tilt sensitive and the bottom plate has three screws to adjust the leveling.

 

Attachment 1: IMG_20150914_181922982.jpg
IMG_20150914_181922982.jpg
Attachment 2: IMG_20150914_182024785_HDR.jpg
IMG_20150914_182024785_HDR.jpg
Attachment 3: IMG_20150914_182037693.jpg
IMG_20150914_182037693.jpg
Attachment 4: IMG_20150914_182550377.jpg
IMG_20150914_182550377.jpg
Attachment 5: IMG_20150914_181825903_HDR.jpg
IMG_20150914_181825903_HDR.jpg
  2021   Thu Feb 18 13:39:33 2016 KojiMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

Can you calculate the IQE from EQE and reflectivity (by ignoring scatter loss)?

Can you measure the EQE/IQE/reflectivity at the angle where the EQE goes maximum for the P pol?

Can you use larger fonts in the plots?

  2044   Fri Mar 4 16:18:45 2016 KojiMiscGeneralPhotos of the experiment

https://goo.gl/photos/FaqFC7tuxz76m2236

  2046   Sun Mar 6 02:25:47 2016 KojiMiscGeneral PD glass reflections

OMC_Lab/252

  2127   Wed Jun 28 20:05:02 2017 KojiUpdateWOPOPDs for homodyne detector

I beieve that they are Exelitas C30642.
FYI: There also is one on the former-gyro optical table. This one doesn't have the cap.

  2129   Fri Jun 30 12:17:07 2017 KojiUpdateWOPOMode Matching Woes - Fibre issues

Measure the profile of the back propagation beam by injecting a beam from the other side.
This gives you how the input mode should be.

  2131   Sun Jul 2 21:21:39 2017 KojiUpdateWOPOMode Matching Woes - Fibre issues

Jenne's laser at the 40m PD testing table is a fiber coupled 1064nm DL.

But you just can couple 5~10% of the beam from the other side of the fiber to know the mode at the input side.
It does not require too much effort if you have the fiber testing illuminator to align the beam.

  2132   Wed Jul 5 16:44:34 2017 KojiUpdateWOPOPDs for homodyne detector

Correction: If the diode is 3mm x 3mm, it is Excelitas C30665.

  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.

ELOG V3.1.3-