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ID Date Authorup Type Category Subject
  4469   Wed Mar 30 20:50:43 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 3b: Non-circular? We can fix that...

A quick Beamscan sweep of the beam after the Faraday:

Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

25.8 503.9 478.8

25 477.5 489.0

24 447.1 512.4

21 441.6 604.5

20 476.3 645.4

19 545.4 704.1

18 620.3 762.8

 

After_Faraday.png

 

OK. It looks not too bad - doesn't look too different from what we had. Note that the x axis is in local table units - I found this useful for working out where things were relative to other things (like lenses and the FI) - but it means the beam propagates from right to left in the plot. in other words, the horizontal waist occurs first and is larger than the vertical waist. Also - they're not fitted curves - they're by-eye, best guesses and there's no solution for the vertical that doesn't involve offsets... discussion in a later part of the thread.

 

Anyway! The wonderful thing about this plot is that the horizontal and vertical widths cross and the horizontal focussing at this crossing point is shallower than the vertical. This means that we can put a lens in at the crossing point and rotate it such that the lens is stronger in the horizontal plane. The lens can be rotated until the effective horizontal focal length is right to fix the astigmatism.

 

 

I used a 200mm lens I had handy - a rough check sweeping the Beamscan quickly indicated should be about right though. Adjusting the angle until the beam size at a distant point is approx circular - I then move the profiler and adjust again. Repeat as required. Now… taking some data. with just that lens in:

 

Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

24 371.7 366.1

21 360.3 342.7

20 447.8 427.8

19 552.4 519.0

18 656.4 599.2

17 780.1 709.9

16 885.9 831.1

 

After_Faraday_and_Rotated_Lens.png

 

Well now. That looks quite OK. Fit's a bit rubbish on vertical but looks like a slight offset on the measurement again.

The angle of the lens looks awful, but if it's stupid and it works then it isn't stupid. If necessary, the lens can be tweaked a bit more, but there's always more tweaking possible further down the line and most of the astigmatic behaviour has been removed. It's now just a case of finding a lens that works to give us a 50 um beam at the oven position...

 

 

  4470   Wed Mar 30 21:21:15 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Step 4: Matching into the oven

 

 

Now that the astigmatism is substantially reduced, we can work out a lens solution to obtain a 50um waist *anywhere* on the bench as long as there's enough room to work with the beam afterwards. The waist after the Faraday and lens is at position 22.5 on the bench. A 50 mm lens placed 18 cm after this position (position 14.92 on the bench) should give a waist of 50 um at  24.57 cm after the waist (position 12.83 on the bench). This doesn't give much room to measure the beam waist in though - the Beamscan head has a fairly large finite size… wonder if there's a slightly less strong lens I could use…

OK. With a 66 mm lens at 23 cm (position 13.45 on the bench) after the waist we get a 50 um waist at 31.37 cm after the waist (position 10.15 on the bench). 

 

Oven_Lens_Solution_66mm.png

 

Closest lens I found was 62.9mm which will put the 50um point a bit further towards the wall, but on the X-arm the oven is at position 8.75 ish. So anything around there is fine.

 

Using this lens and after a bit of manual fiddling and checking with the Beamscan, I figured we needed a close in, fine-grained measurement so set the Beamscan head up on a micrometer stage Took a whoie bunch of data around position 9 on the bench:

 

 

Position A1_13.5%_width A2_13.5%_width

(mm) (um mean) (um mean)

-15 226.8 221.9

-14 210.9 208.3

-13 195.5 196.7

-12 181.0 183.2

-11 166.0 168.4

-10 154.0 153.1

-9 139.5 141.0

-8 127.5 130.0

-7 118.0 121.7

-6 110.2 111.6

-5 105.0 104.8

-4 103.1 103.0

-3 105.2 104.7

-2 110.9 110.8

-1 116.8 117.0

0 125.6 125.6

0 125.6 125.1

1 134.8 135.3

2 145.1 145.6

3 155.7 157.2

4 168.0 168.1

5 180.5 180.6

6 197.7 198.6

7 211.4 209.7

8 224.0 222.7

9 238.5 233.7

10 250.9 245.8

11 261.5 256.4

12 274.0 270.4

13 291.3 283.6

14 304.2 296.5

15 317.9 309.5

 

Matching_Into_Green_Oven_zoomed_out.pngMatching_Into_Green_Oven_zoomed_in.png

 

And at this point the maximum power available at the oven-waist is 298mW. With 663mW available from the laser with a desired power setting of 700mW on the supply. Should make sure we understand where the power is being lost. The beam coming through the FI looks clean and unclipped, but there is some stray light around.

 

Position A1_13.5%_width A2_13.5%_width

(bench) (um mean) (um mean)

7 868.5   739.9

6 1324 1130

5 1765 1492

4 2214 1862

 

The plot looks pretty good, but again, there looks to be an offset on the 'fitted' curve. Taking a couple of additional points further on to make sure it all works out as the beam propagates. I took a few extra points at the suggestion of Kiwamu and Koji - see the zoomed out plot.  The zoomed in plot has by-eye fit lines - again, because to get the right shape to fit the points there appears to be an offset. Where is that coming from? My suspicion is that the Beamscan doesn't take account of the any background zero offsets when calculating the 13.5% and we've been using low power when doing these measurements - very small focussed beams and didn't want to risk damage to the profiler head.

 

Decided to take a few measurements to test this theory. Trying different power settings and seeing if it gives different offset and/or a changed width size

 

7 984.9 824.0 very low power

7 931.9 730.3 low power

7 821.6 730.6 higher power

7 816.4 729.5 as high as I'm comfortable going

 

Trying this near the waist…

 

8.75 130.09 132.04 low power

8.75 106.58 105.46 higher power

8.75 102.44 103.20 as high as it can go without making it's saturated

 

So it looks like offset *is* significant and the Beamscan measurements are more accurate with more power to make the offsets less significant. Additionally, if this is the case then we can do a fit to the previous data (which was all taken with the same power setting) and simply allow the offset to be a free parameter without affecting the accuracy of the waist calculation. This fit and data coming to an e-log near you soon.

 

Of course, it looks from the plots above (well... the code that produces the plots above) that the waist is actually a little bit small (around 46um) so some adjustment of the last lens back along the beam by about half a cm or so might be required.

 
  4476   Thu Mar 31 14:10:00 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Quote:

 I went through the entries.

1. Give us a photo of the day. i.e. Faraday, tilted lens, etc...

2. After all, where did you put the faraday in the plot of the entry 4466?

3. Zoomed-in plot for the SHG crystal show no astigmatism. However, the zoomed out plot shows some astigmatism.
How consistent are they? ==> Interested in seeing the fit including the zoomed out measurements.

 OK. Taking these completely out of order in the easiest first...

2. The FI is between positions 27.75 and 32 on the bench - i.e. this is where the input and output apertures are. (corresponds to between 0.58 and 0.46 on the scale of those two plotsand just before both the vertical and horizontal waists) At these points the beam radius is around 400um and below, and the aperture of the Faraday is 4.8mm (diameter).

1. Photos...

Laser set up - note the odd angles of the mirrors. This is where we're losing a goodly chunk of the light. If need be we could set it up with an extra mirror and send the light round a square to provide alignment control AND reduce optical power loss...

P3310028.JPG

 

Faraday and angled lens - note that the lens angle is close to 45 degrees. In principle this could be replaced with an appropriate cylindrical lens, but as long as there's enough light passing through to the oven I think we're OK.

P3310029.JPG

3. Fitting... coming soon once I work out what it's actually telling me. Though I hasten to point out that the latter points were taken with a different laser power setting and might well be larger than the actual beam width which would lead to astigmatic behaviour.

  4477   Thu Mar 31 15:23:14 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Quote:

3. Zoomed-in plot for the SHG crystal show no astigmatism. However, the zoomed out plot shows some astigmatism.

How consistent are they? ==> Interested in seeing the fit including the zoomed out measurements.

Right. Fitting to the data. Zoomed out plots first. I used the general equation f(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c for each fit which is basically just the Gaussian beam width parameter calculation but with an extra offset parameter 'c'

Vertical fit for zoomed out data:

Coefficients (with 95% confidence bounds):

       c =   7.542e-06  (5.161e-06, 9.923e-06)

       w_o =   3.831e-05  (3.797e-05, 3.866e-05)

       z_o =       1.045  (1.045, 1.046)

 

Goodness of fit:

  SSE: 1.236e-09

  R-square: 0.9994

 
Horizontal fit for zoomed out data:
 

Coefficients (with 95% confidence bounds):

       c =   1.083e-05  (9.701e-06, 1.195e-05)

       w_o =   4.523e-05  (4.5e-05, 4.546e-05)

       z_o =       1.046  (1.046, 1.046)

 

Goodness of fit:

  SSE: 2.884e-10

  R-square: 0.9998

  Adjusted R-square: 0.9998

  RMSE: 2.956e-06

 

Zoomed_out_fitting01.png

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

 

OK. Looking at the plots and residuals for this, the deviation of the fit around the waist position, and in fact all over, looks to be of the order 10um. A bit large but is it real? Both w_o values are a bit lower than the 50um we'd like, but… let's check using only the zoomed in data -  hopefully more consistent since it was all taken with the same power setting.

 

 

Vertical data fit using only the zoomed in data:

 

Coefficients (with 95% confidence bounds):

       c =   1.023e-05  (9.487e-06, 1.098e-05)

       w_o =   4.313e-05  (4.252e-05, 4.374e-05)

       z_o =       1.046  (1.046, 1.046)

 

Goodness of fit:

  SSE: 9.583e-11

  R-square: 0.997

 

Horizontal data fit using only the zoomed in data:

 

Coefficients (with 95% confidence bounds):

       c =   1.031e-05  (9.418e-06, 1.121e-05)

       w_o =    4.41e-05  (4.332e-05, 4.489e-05)

       z_o =       1.046  (1.046, 1.046)

 

Goodness of fit:

  SSE: 1.434e-10

  R-square: 0.9951

 

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Zoomed_in_fitting01.png

 

The waists are both fairly similar this time 43.13um and 44.1um and the offsets are similar too  - residuals are only spread by about 4um this time.

 

I'm inclined to trust the zoomed in measurement more due to the fact that all the data was obtained under the same conditions, but either way, the fitted waist is a bit smaller than the 50um we'd like to see. Think it's worthwhile moving the 62.9mm lens back along the bench by about 3/4 -> 1cm to increase the waist size.

 

 

 

 

 

  4481   Fri Apr 1 18:54:41 2011 BryanConfigurationGreen LockingY end doubling oven

The doubling oven is now ready to go for the Y arm. The PPKTP crystal is mounted in the oven:

P4010036.JPG

Note - the crystal isn't as badly misaligned as it looks in this photo. It's just an odd perspective shot. I then closed it up and checked to make sure the IR beam on the Y bench passes through the crystal. It does. Just need to tweak the waist size/position a bit and then we can actually double some frequencies!

P4010041.JPG

  4485   Mon Apr 4 14:20:32 2011 BryanConfigurationGreen LockingThe wonderful world of mode-matching

Last bit of oven matching for now.

 

I moved the lens before the oven position back along the beam path by about 1cm - waist should be just above position 9 in this case. Note - due to power-findings from previous time I'm maximising the power into the head to reduce the effect of offsets.

 

From position 9:

Position A1_13.5%_width A2_13.5%_width

(mm) (um mean) (um mean)

-1 121.1 123.6

0 112.5 113.8

1 106.4 106.1

2 102.9 103.4

3 103.6 103.6

4 106.6 107.4

5 111.8 112.5

6 118.2 120.1

7 126.3 128.8

8 134.4 137.1

9 143.8 146.5

10 152.8 156.1

11 163.8 167.1

12 175.1 176.4

13 186.5 187.0

14 197.1 198.4

15 210.3 208.9

16 223.5 218.7

17 237.3 231.0

18 250.2 243.9

19 262.8 255.4

20 274.7 269.0

21 290.4 282.3

22 304.3 295.5

23 316.7 303.1

 

Note - had to reduce power due to peak saturation at 15mm - don't think scale changed, but be aware just in case. And saturated again at 11. And again at 7. A little bit of power adjustment each time to make sure the Beamscan head wasn't saturating. Running the fit gives...

 

Waist_Fits_from_laser.pngWaist_Fits_Bench_Position.png

 

OK. The fit is reasonably good. Residuals around the area of interest (with one exception) are <+/- 2um and the waists are 47.5um (vertical) and 50.0um (horizontal) at a position of 9.09 on the bench. And the details of the fitting output are given below.

 

-=-=-=-=-=-=-=-=-=-=-=-

Vertical Fit

 

cf_ =

 

     General model:

       cf_(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c

     Coefficients (with 95% confidence bounds):

       c =   5.137e-06  (4.578e-06, 5.696e-06)

       w_o =   4.752e-05  (4.711e-05, 4.793e-05)

       z_o =        1.04  (1.039, 1.04)

 

 

cfgood_ = 

 

           sse: 1.0699e-11

       rsquare: 0.9996

           dfe: 22

    adjrsquare: 0.9996

          rmse: 6.9738e-07

 

-=-=-=-=-=-=-=-=-=-=-=-

Horizontal Fit

 

cf_ =

 

     General model:

       cf_(x) = w_o.*sqrt(1 + (((x-z_o)*1064e-9)./(pi*w_o.^2)).^2)+c

     Coefficients (with 95% confidence bounds):

       c =    3.81e-06  (2.452e-06, 5.168e-06)

       w_o =   5.006e-05  (4.909e-05, 5.102e-05)

       z_o =        1.04  (1.04, 1.04)

 

 

cfgood_ = 

 

           sse: 4.6073e-11

       rsquare: 0.9983

           dfe: 22

    adjrsquare: 0.9981

          rmse: 1.4471e-06

 

 

 

  4486   Mon Apr 4 18:58:44 2011 BryanConfigurationGreen LockingA beam of purest green

We now have green light at the Y end. 

The set-up (with careful instructions from Kiwamu) - setting up with 100mW of IR into the oven.

Input IR power = 100mW measured.

 

Output green power = 0.11mW

(after using 2 IR mirrors to dump IR light before the power meter so losing a bit of green there light too)

 

And it's pretty circular-looking too. Think there might be a bit more efficiency to be gained near the edges of the crystal with internal reflections and suchlike things but that gives us an UGLY looking beam.  Note - the polarisation is wrong for the crystal orientation so used a lambda/2 plate to get best green  power out.

 

Efficiency is therefore 0.11/100 = 0.0011 (0.11%) at 100mW input power.

 

Temperature of the oven seems to be around 35.5degC for optimal conversion.

Took a picture. Ta-dah! Green light, and lots more where that came from! Well... about 3x more IR available anyway.

 

P4040042.JPG

 

 

  4495   Wed Apr 6 22:13:24 2011 BryanConfigurationGreen LockingResonating green light!

Every so often things just work out. You do the calculations, you put the lenses on the bench, you manually adjust the pointing and fiddle with the lenses a bit, you get massive chunks of assistance from Kiwamu to get the alignment controls and monitors set up and after quite a bit of fiddling and tweaking the cavity mirror alignment you might get some nice TEM_00 -like shapes showing up on your Y-arm video monitors.

So. We have resonating green light in the Y-arm. The beam is horribly off-axis and the mode-matching, while close enough to give decent looking spots, has in no way been optimised yet. Things to do tomorrow - fix the off-cavity-axis problem and tweak up the mode-matching... then start looking at the locking...

  4520   Wed Apr 13 16:56:08 2011 BryanConfigurationGreen LockingY-ARM Green-Locked!

 Locked!

The Y-arm can now be locked with green light using the universal PDH servo. Modulation frequency is now 277kHz - chosen because it seems to produce smaller offsets due to AM effects

To lock, turn on the servo, align the system to give nice circular-looking TEM_00 resonances, and wait for a good one. It'll lock on a decent mode for a few seconds and then you can turn on the local boost and watch it lock for minutes and minutes and minutes.

The suspensions are bouncing around a bit on the Y-arm and the spot is quite low on the ETMY and a little low on ITMY, but from this point it can be tweaked and optimised.

 

 

 

  4525   Thu Apr 14 17:45:59 2011 BryanConfigurationGreen LockingI leave you with these messages...

OK… the Y-arm may be locked with green light, which was the goal, and this is all good but it's not yet awesome. Awesome would be locked and aligned properly and quiet and optimised. So...  in order to assist in increasing the awesome-osity, here are a few stream-of-consciousness thoughts and stuff I've noticed and haven't had time to fix/investigate or have otherwise had pointed out to me that may help...

 

Firstly, the beam is not aligned down the centre of the cavity. It's pretty good horizontally, but vertically it's too low by about 3/4->1cm on ETMY. The mirrors steering the beam into the cavity have no more vertical range left, so in order to get the beam higher the final two mirrors will have to be adjusted on the bench. Adding another mirror to create a square will give more range AND there will be less light lost due to off 45degree incident angles. When I tried this before I couldn't get the beam to return through the Faraday, but now the cavity is properly aligned this should not be a problem.

 

A side note on alignment - while setting cameras and viewports and things up, Steve noticed that one of the cables to one of the coils (UL) passes behind the ETMY. One of the biggest problems in getting the beam into the system to begin with was missing this cable. It doesn't fall directly into the beam path if the beam is well aligned to the cavity, but for initial alignment it obscures the beam - this may be a problem later for IR alignment.

 

Next, the final lambda/2 waveplate is not yet in the beam. This will only become a problem when it comes to beating the beams together at the vertex, but it WILL be a problem. Remember to put it in before trying to extract signals for full LSC cavity locking.

 

Speaking of components and suchlike things, the equipment for the green work was originally stored in 3 plastic boxes which were stored near the end of the X-arm. These boxes, minus the components now used to set up the Y-end, are now similarly stored near the end of the Y-arm.

 

Mechanical shutter - one needs to be installed on the Y-end just like the X-end. Wasn't necessary for initial locking, but necessary for remote control of the green light on/off.

 

Other control… the Universal PDH box isn't hooked up to the computers. Connections and such should be identical to the X-arm set-up, but someone who knows what they're doing should hook things up appropriately.

 

More control - haven't had a chance to optimise the locking and stability so the locking loop, while it appears to be fairly robust, isn't as quiet as we would like. There appears to be more AM coupling than we initially thought based on the Lightwave AM/PM measurements from before. It took a bit of fiddling with the modulation frequency to find a quiet point where the apparent AM effects don't prevent locking. 279kHz is the best point I've found so far. There is still a DC offset component in the feedback that prevents the gain being turned up - unity gain appears limited to about 1kHz maximum. Not sure whether this is due to an offset in the demod signal or from something in the electronics and haven't had time left to check it out properly yet. Again, be aware this may come back to bite you later.

 

Follow the bouncing spot - the Y-arm suspensions haven't been optimised for damping. I did a little bit of fiddling, but it definitely needs more work. I've roughly aligned the ETMY oplev since that seems to be the mass that's bouncing about most but a bit of work might not go amiss before trusting it to damp anything.

 

Think that's about all that springs to mind for now…

 

Thanks to everyone at the 40m lab for helping at various times and answering daft questions, like "Where do you keep your screwdrivers?" or "If I were a spectrum analyser, where would I be?" - it's been most enjoyable!

 
  4532   Fri Apr 15 13:43:23 2011 BryanConfigurationGreen LockingI leave you with these messages...

Y-end PDH electronics.

The transfer function of the Y-end universal PDH box:

Y_End_Electronics_TF.png

 

  437   Tue Apr 22 17:08:04 2008 CarynUpdateIOOno signal for C1:IOO-MC_L
C1:IOO-MC_L signal was at zero for the past few days
  480   Thu May 15 14:39:33 2008 CarynSummaryPEMfiltering mode cleaner with mic
Tried filtering for mode cleaner data(C1:IOO-MC_L) using a siso-firwiener filter and microphone data(C1:PEM-AS_MIC) for noise input. The noise reduction in mode cleaner data using the microphone-filter is comparable to the noise reduction when an accelerometer(C1:PEM-ACC_MC1_X) filter is used. See attached graphs.
Attachment 1: MC_L_with_PEM-AS_MIC_filter.pdf
MC_L_with_PEM-AS_MIC_filter.pdf
Attachment 2: MC_L_with_PEM-ACC_MC1_X_filter.pdf
MC_L_with_PEM-ACC_MC1_X_filter.pdf
  494   Fri May 23 21:21:52 2008 CarynSummaryGeneralfiltering mode cleaner with wiener filter
I tried filtering some saved MC_L data (from Mon May19 4:30pm) with multiple MISO filters of different orders, with various sampling rates, at different times. Plotted the max rms error (where error is signal minus signal-estimate). 2min of data (around Mon May19 4:30pm) were used to calculate each filter. And each filter was applied to data at later times to see how well it performed as time progressed. Plots are attached. There appears to have been a disturbance during the 3rd hour. Rana pointed out perhaps it would be better to use data from the evening rather than during the day.
Attachment 1: error_vs_N_for_different_times_64Hz.pdf
error_vs_N_for_different_times_64Hz.pdf
Attachment 2: error_vs_N_for_different_times_128Hz.pdf
error_vs_N_for_different_times_128Hz.pdf
Attachment 3: error_vs_N_for_different_times_256Hz.pdf
error_vs_N_for_different_times_256Hz.pdf
Attachment 4: error_vs_N_for_different_times_512Hz.pdf
error_vs_N_for_different_times_512Hz.pdf
Attachment 5: error_vs_srate_for_different_times_256.pdf
error_vs_srate_for_different_times_256.pdf
Attachment 6: error_vs_srate_for_different_times_512.pdf
error_vs_srate_for_different_times_512.pdf
Attachment 7: error_vs_srate_for_different_times_1024.pdf
error_vs_srate_for_different_times_1024.pdf
Attachment 8: error_vs_time_for_different_srates_256.pdf
error_vs_time_for_different_srates_256.pdf
Attachment 9: error_vs_time_for_different_srates_512.pdf
error_vs_time_for_different_srates_512.pdf
Attachment 10: error_vs_time_for_different_srates_1024.pdf
error_vs_time_for_different_srates_1024.pdf
  518   Wed Jun 4 16:25:06 2008 CarynSummaryPEMmicrophone moved
The microphone 'C1:PEM-AS_MIC' has been moved right a bit. This change didn't seem to have much effect on filtering the 'C1:IOO-MC_L' signal, at least not compared to how the filter changes with time. Also used microphone data to filter MC_L data using firwiener filter/levinson. The N(order) and sample rate were varied to see how the filter changed. Attached are graphs of the max(rms(noise_estimate)) vs N or IR for varying srate. Note that filtered_signal=signal-noise_estimate. So, the larger the noise_estimate, the more the filter subtracts from the signal.
Green-filtered signal
blue-noise estimate
red-MC_L signal
note decreasing sample rate is more effective than increasing N (higher N takes more time to compute)
note sample rate doesn't change the max(rms(noise_estimate)) very much if impulse response time remains constant
note the 64hz, N=7000 (impulse response about 110s) filter is a better filter than the 512Hz, N=7000(impulse response about 14s)
Attachment 1: 1_MC_L.pdf
1_MC_L.pdf 1_MC_L.pdf 1_MC_L.pdf 1_MC_L.pdf
  522   Fri Jun 6 11:19:13 2008 CarynSummaryPEMFiltering MC_L and MC_F with PEM:ACC and microphone
Tried to filter MC_L and MC_F with acc/seis data and microphone data using wiener filter (levinson)

-Used get_mic_data.m and miso_filter_lev.m to make SISO filter for 2 minutes of IOO-MC_F data. Used PEM-AS_MIC signal as noise input data. Filters calculated at initial time were applied to later data in 1 hour intervals.
-microphone filter did not seem to filter MC_F very well in high frequency range using this filtering procedure.
-residual is larger than est (see MC_F pdf)
-Used do_all_time_lev.m to make graph of max(rms(residual)) to N(order) for different times.(note for each N, filter was calculated for initial time and then applied to data at other times).
-relation of max(rms(residual)) to N(order) is time sensitive (note-on graph, time interval is 1hour) (see MC_F pdf)
-Presumably, max(rms(residual)) should decrease as N increases and increase as time increases since the filter probably becomes worse with time. I think the reason this isn't always true in this case is that the max(rms(residual)) corresponds to a peak (possibly a 60Hz multiple) and the wiener filter isn't filtering out that peak very well.


-Used get_z_data.m and miso_filter_lev.m to make MISO filter for 2 minutes of IOO-MC_L used the following signals as noise input data
PEM-ACC_MC1_X
PEM-ACC_MC2_X
PEM-ACC_MC1_Y
PEM-ACC_MC2_Y
PEM-ACC_MC1_Z
PEM-ACC_MC2_Z
PEM-SEIS_MC1_Y
-Filter was applied to later data in 2hour intervals.
-Used do_all_time_lev.m to make graph of max(rms(residual)) to N(order) for different times.(note for each N, filter was calculated for initial time and then applied to data at other times).
-acc/seis filter seemed to filter MC_L OK for 128,256,512Hz srates. 64 Hz wasn't ok for certain N's after a period of time.
-residual is smaller than est for srates not 64Hz (see MC_L pdf)
-residual is larger than est for 64Hz at N=1448 for later times (see MC_L pdf)
-relation of max(rms(residual)) to N is not as time sensitive for higher sample rates (note-on graph, time interval is 2hours) (see MC_L pdf). Perhaps the levinson 64Hz sample rate filter doesn't do as well as time passes for these signals. When the filter didn't do well, the max(rms(residual)) seemed to increase with N.
-For 512Hz sample rate filter the max(rms(residual)) decreased with time. If the max(rms(residual)) were an indication of filter performance, it would mean that the 512Hz filter calculated at the initial time was performing better later as hours passed by! Perhaps max(rms(residual)) isn't always great at indicating filter performance.

Programming notes
-I had to modify values in do_all_time_lev.m to get the program to loop over the srates,N's,times I wanted
-do_all_time_lev.m is not as clean as do_all_lev.m
-for making the plots do_all_lev.m (which isn't really a procedure and is messy) has some examples of how to plot things from do_all_time_lev.m.
Attachment 1: MC_F.pdf
MC_F.pdf MC_F.pdf MC_F.pdf
Attachment 2: MC_L.pdf
MC_L.pdf MC_L.pdf MC_L.pdf MC_L.pdf MC_L.pdf MC_L.pdf MC_L.pdf MC_L.pdf
Attachment 3: miso_filter_lev.m
function [s] = miso_filter_lev(N,srate,rat,z)
%MISO_FILTER_LEV(N,srate,z) uses miso_firlev to get levinson
%   FIR Wiener filter of order N-1, using impulse response of 
%   N/srate. z is a structure gotten from the get_data function. 
%   z(end) is the signal which is filtered using z(i) for all i.
%   'rat' is the fraction of z which will be put into filter
%   funtion. The data from z is downsampled using srate and 
%   detrended. Let rat=1. I don't have that part working yet.


... 107 more lines ...
Attachment 4: get_mic_data.m
function[z,t0,duration]=get_mic_data(t,d_t,d)
%get_mic_data gets data for'C1:IOO-MC_F', 'C1:PEM-AS_MIC,
% Example:  z = get_mic_data('now',120,60)
%  start time is 't- d_t' so  d_t should be given in seconds. t should be given
%  as a number like 893714452. d is duration in seconds. get_mic_data saves
%  data to a file in current directory named 'temp_mic'. You will be asked to
%  save file as 'mic_(start_time)_(duration)'.

duration = d;

... 32 more lines ...
Attachment 5: do_all_time_lev.m
function[r] = do_all_time_lev(n,t0,int,duration,N,srate,rat,order,time,MC_L,MC_F,sample_rate)
%do_all_time explores how filter performance changes with time, sample rate,
%and order of filter. Outputs data,noise estimate, structure of max
%rms error and other info. It uses get_data, miso_filter_lev, and miso_filter_int and retrives
%MC_Ldata or MC_Fdata for multiple times, calculates a miso_filter for initial-time data
%file, applies filter to the other data files, and keeps track of the...
%max(rms(residual)) for each filter. n+1 is number of data files. int is time interval between
%data files, t0 is start time, duration is duration of each data file, srate
%is the sample rate for which filter is calculated, n_N is number of orders
%of the filter you want the program to calculate,int_N is interval by which N
... 215 more lines ...
Attachment 6: do_all_lev.m
function[r] = do_all_lev(n,t0,int,duration,n_N,int_N,n_srate,int_srate,rat,MC_L,MC_F)
%do_all_lev explores how filter performance changes with time, sample rate,
%and order of filter. Outputs data,noise estimate, structure of max
%rms error and other info. It uses get_data, miso_filter_lev, and miso_filter_int and retrives
%MC_Ldata or MC_Fdata for multiple times, calculates a miso_filter for initial-time data
%file, applies filter to the other data files, and graphs the rms of the cost
%function vs time. n+1 is number of data files. int is time interval between
%data files, t0 is start time, duration is duration of each data file, srate
%is the sample rate for which filter is calculated, n_N is number of orders
%of the filter you want the program to calculate,int_N is interval by which N
... 283 more lines ...
Attachment 7: do_all_plot.m
function[r] = do_all_plot(r,x,v)
 %do_all_plot plots variables contained in r(structure from
 %do_all_time_lev).Plots error(r.B.y) vs x. x can be
 %'s'(srate),'N'(order),'t'(time),'p'(impulse response). v can be 's','N','t'. 
 %example: do_all_plot(r,'s','t') makes a plot of error vs srate for
 %different times.

kk=1

err_N_srate=0
... 388 more lines ...
Attachment 8: miso_filter_int.m
function [s] = miso_filter_int(s,y)
%miso_filter_int inputs a filter and a structure array of data sets y, applies filter to data, and
%outputs a structure with fields: ppos(signal frequ spectrum),perr(cost
%function frequ spectrum),pest(signal estimate frequency
%spectrum),f(frequency),target(signal),est_darm(noise estimate),t(time).
%data file for which filter has been calculated is s (obtained using miso_filter). 
%y consists of data structures which will be filtered using
%filter from s. Then the power spectrum of the difference between signal and filtered-data is
%graphed for all the data files of y for comparison too see how well filter performs
%over time. Note if you want to create a y, take z1,z2,z3,etc. structures
... 120 more lines ...
  1130   Wed Nov 12 11:14:59 2008 CarynDAQPSLMC temp sensor hooked up incorrectly
MC Temperature sensor was not hooked up correctly. It turns out that for the 4 pin LEMO connections on the DAQ like J13, J14, etc. the channels correspond to horizontal pairs on the 4 pin LEMO. The connector we used for the temp sensor had vertical pairs connected to each BNC which resulted in both the differential pairs on J13 being read by the channel.
To check that a horizontal pair 4 pin LEMO2BNC connector actually worked correctly we unlocked the mode cleaner, and borrowed a connector that was hooked up to the MC servo (J8a). We applied a sine wave to each of the BNCs on the connector, checked the J13 signal and only one of the differential pairs on J13 was being read by the channel. So, horizontal pairs worked.
  1142   Mon Nov 17 20:47:19 2008 CarynSummaryGeneralDrove MC at 28kHz to excite drum modes
Rana, Alberto and I observed drum mode frequencies at 23.221kHz(MC1), 28.039kHz(MC2), 28.222kHz(MC3) while driving the mode cleaner. We observed no peaks when we didn't drive the mode cleaner. We used the SR785 to send a ~80mV noise signal in the 28-28.2kHz band to the mode cleaner mirrors via 1Y4-MC1,2,3-POSIN. Then we looked at 1Y2-Mode Cleaner-Qmon on the SR785 and saw peaks.
  1143   Tue Nov 18 13:28:08 2008 CarynDAQIOOnew channel for MC drum modes
Alberto has added a channel for the Mode Cleaner drum modes.
C1:IOO-MC_DRUM1
sample rate-2048
chnum-13648
  1158   Sat Nov 22 10:55:51 2008 CarynConfigurationIOODrum modes Lock-In settings changed
I unhooked the MC Demod Board's Qmon signal from the Lock-In. Set the demodulation frequency to 31.11Hz with 1V amplitude, and
put the output into MC_DRUM1. DTT showed a ~30Hz peak. Dataviewer showed signal with amplitude ~20,000.
Otherwise the settings were as Rana had them: Time Constant-100us,24dB/Sensitivity-200us/Low Noise
Want to check if Lock-In frequency drifts.
  1189   Tue Dec 9 10:48:17 2008 CarynSummaryGeneralcalibrating the jenne laser: impedance mismatch?

We sent RFout of network analyzer to a splitter, with one side going back to the network analyzer and the other to the laser modulation input. We observed a rippled transfer function through the splitter. The ripple is probably due to reflection due to an impedance mismatch in the laser.
Attachment 1: reflection.png
reflection.png
  1528   Tue Apr 28 12:55:57 2009 CarynDAQPEMUnplugged Guralp channels

For the purpose of testing out the temperature sensors, I stole the PEM-SEIS_MC1X,Y,Z channels.

I unplugged Guralp NS1b, Guralp Vert1b, Guralp EW1b cables from the PEM ADCU(#10,#11,#12) near 1Y7 and put temp sensors in their place (temporarily).

  11124   Mon Mar 9 16:50:35 2015 Champagne DuckFrogsTreasureCelebrating Lock

Attachment 1: 2015-03-09_16.35.47.jpg
2015-03-09_16.35.47.jpg
  7691   Thu Nov 8 22:04:43 2012 CharlesUpdateElectronicsEthernet Illuminator Control

Configured ethernet controlled power strips to have static IP addresses: 192.168.113.110, 192.168.113.111 and 192.168.113.112.

Wrote a python script to interact with the power strips that can turn individual sockets on or off via telnet.

This functionality will be implemented on the control room computer GUIs in short order.

  7695   Fri Nov 9 18:28:23 2012 CharlesUpdateSummary PagesCalendar

The calendar tab now displays calendars with weeks that run from Sunday to Saturday (as opposed to Monday to Sunday). However, the frame on the left hand side of the main page still has 'incorrect' calendars.

 

  7698   Mon Nov 12 23:38:50 2012 CharlesUpdateElectronicsEthernet Illuminator Control

Quote:

Configured ethernet controlled power strips to have static IP addresses: 192.168.113.110, 192.168.113.111 and 192.168.113.112.

Wrote a python script to interact with the power strips that can turn individual sockets on or off via telnet.

This functionality will be implemented on the control room computer GUIs in short order.

 The ethernet power strips have been installed. 192.168.113.110 is on ETMX, 192.168.113.111 is on ETMY and 192.168.113.112 is on the vertex. I have also written an EPICS file "illuminator_control.adl" (currently stored in my named directory) that allows a user to turn individual sockets on and off at each of the three locations. Some short tests have indicated that everything is in working order.

Currently, no illuminators are hooked up to the power strips. However, the power control will most likely be ready for use tomorrow, granted I can find and use extension cords so that the illuminators might reach their respective power strips.

  7759   Wed Nov 28 23:18:35 2012 CharlesUpdatePEMDecreased RMS in Seismometers

The attached plots display RMS noise from various accelerometers and seismometers over the past 90 days. One can see how after the reinstallation of the seismometers in November, RMS from the GUR1Z and GUR1X channels decreases by a factor of about 100 from data in August. Additionally, the RMS over the course of the last 90 days has notably decreased in all instruments. In many cases, the RMS is only the result of inherent electronics noise, rather than from a signal.

Attachment 1: 8-31_11-29_PEM-RMS.jpg
8-31_11-29_PEM-RMS.jpg
  7770   Fri Nov 30 23:10:36 2012 CharlesUpdateElectronicsVertex Illuminators

 3 of the 4 remote controlled illuminators at the vertex are installed and can now be turned on via sitemap. There are a total of 15 controls for "Illum", but only the 3 labeled with MC, BS-PRM and ITMY-SRM are functional.

  7964   Wed Jan 30 14:00:02 2013 CharlesUpdateISSISS Design and Prototyping

Attached are both the circuit diagram and the liso formatted *.fil for the main branch of the ISS, as well as the resulting transfer function when analyzed. Unfortunately, as noted in the file, not all of the elements are possible to analyze in liso, such as any type of op-amp with more than two inputs and one output (AD602 used in this design has 16 pins with two distinct amplifiers contained within).

I have begun prototyping this circuit on a breadboard.

Attachment 1: ISS.fil
## ISS Main Branch
##
## All circuit elements are named according to the circuit diagram 
## "D020241-D2.pdf" by R. Abbott.

# Stages are separated by empty lines and elements between stages are
# also separated by empty lines for easy file navigation
# Before the first stage there is a 'fully differentiable' op-amp
# that I believe serves to isolate the device from the power supply
# However, liso does not have the capability to analyze such an op-amp,
... 79 more lines ...
Attachment 2: ISS_Transfer_Function.png
ISS_Transfer_Function.png
Attachment 3: D020241-D2.pdf
D020241-D2.pdf D020241-D2.pdf D020241-D2.pdf
  8110   Tue Feb 19 15:40:34 2013 CharlesUpdateISSISS Prototype

After spending a good deal of time learning how to use the SR785, I was able to characterize my prototype circuit. The transfer function from a swept sine measurement looks very similar to the theoretically calculated transfer function (both of which are attached). The frequency response of the circuit was considered over the range 10 Hz - 10 kHz, which contains the eventual working range of the ISS (at least to my knowledge).

Note that OP27 op-amps were used instead of the high-speed AD829 op-amps that will be implemented in the actual design. This was done as a result of the limitations and inherent noise characteristics of the breadboard on which the prototype was built.

Unfortunately, I saved the wrong dataset (i.e. phase of the transfer function, not magnitude) and thus the presented function here is image generated by the SR785.

RXA: One must learn to use the python-GPIB interface to not lose data in the future.

Attachment 1: Prototype_Transfer_Function.png
Prototype_Transfer_Function.png
Attachment 2: Theoretical_Transfer_Function.png
Theoretical_Transfer_Function.png
  8224   Mon Mar 4 19:38:21 2013 CharlesUpdateGeneralIntensity Stabilization and Control Systems

 I have been studying Jamies master's thesis concerning intensity stabilization of a solid-state laser (the 1064 nm specifically) to the ~10^-9 level, as well as relevant supporting material. I have also been reading about general control systems, photodiodes and acousto-optic modulators to help facilitate work on the ISS. 

Now that Altium has been properly installed, I have also begun familiarizing myself with the program and general libraries of boards and devices that have already been modeled with the program.

  8359   Tue Mar 26 20:20:10 2013 CharlesUpdateISSISS Design Plans - Servo Noise Analysis

In order to allow other individuals besides myself to consider the proposed design of the ISS, I have created a publicly available CircuitLab drawing, which can be found here: CircuitLab Drawing. For simplicity, I have used ideal op-amps without voltage rails or their associated power supplies. In the actual implementation of the ISS, we will most likely also have trim resistors to ensure a zero offset for each op-amp. We interpret the PD as a voltage source for simplicity and I will use an actual summing amplifier in place of the summing junction used in the diagram.

The diagram linked above is simply a naive copy of a design by Rich Abbott so there are most likely mistakes and/or unnecessary elements, but it is a work in progress. I began discussing, with Jamie, the relative use of the first few filter stages in the servo. As far as my understanding goes, the first 'stage' was part of cascade of op-amps that served to convert a differential input from the PD into a single DC signal referenced to ground. Indeed, the first stage of my diagram (U1) is simply a unity-gain low-pass filter with f~5 MHz. Additionally, the second filter 'stage', U2, is also a unity-gain low-pass filter although it introduces a phase shift of 180 deg as the input to the second stage is on the inverting input of the op-amp. These characteristics were determined using LISO and examining the transfer function.

Noise analysis was also performed for the above circuit. The noise from various elements is examined at the output of the servo (labeled as 'outU6' in my LISO file). In the attached diagram, we see the voltage noise at the output from each op-amp as well as the sum of all the various noises, which includes resistor noise and current noise from the inputs of each op-amp. These are LISO's standard considerations and it is also worthwhile to note that the result is not referred to the circuit input, but as we have the transfer function of the whole servo, referring the noise to the input is trivial.

I have also included the following output for the sake of completeness.

from 1 Hz onwards noise by OP:I+ (U3) dominates.

from 38.6812 Hz onwards noise by R(R24) dominates.

from 115.478 Hz onwards noise by R(R11) dominates.

 

 

Attachment 1: ISS.pdf
ISS.pdf
  8448   Fri Apr 12 10:33:42 2013 CharlesSummaryISSDC-Coupled ISS Servo Design

General ISS Design

Signals through the ISS are directed as follows:  an error signal is obtained by summing the ~5 V signal from the PD with a -5 V signal from a high precision voltage regulator (which is first filtered with an ~ 30 mHz low-pass Sallen-Key filter).  It is this signal that is processed/amplified by the servo. The output from the servo is then used to drive an AOM (it is not known exactly how this is done and whether or not any preamplifier/extra circuitry is necessary). The resulting modulation, hopefully, reduces fluctuations in the laser intensity incident on the PD, lowering the relative intensity noise.

Servo Design

Almost the entirety of my focus has been directed toward designing the servo portion of the ISS. Speaking in general terms, the currently proposed design consists of stages of active op-amp filters, but now the stages will have internal switches that allow them to switch between ‘flat’ gain buffers and more complicated filters with our desired behavior. Consider some Example Filter Stages where I have demonstrated a typical switching filter with the switch open and closed. When the switch is closed, the capacitor is shorted and we simply have a variable gain buffer (variable in the sense that its gain can be tuned by proper choice of the resistances) with no frequency dependence. When the switch is open, the capacitor introduces a pole at ~100 Hz and a zero at ~1 kHz.

CircuitLab has decent analysis capabilities and attached are plots generated by CircuitLab. The first plot corresponds to a frequency analysis of the voltage gain of op-amp U1 and the ‘flat’ ~20 dBV gain filter with the switch closed and the capacitor shorted. The second plot is the same frequency analysis, but now with op-amp U2 and the filter with the switch open and the capacitor introduced into signal processing. This particular combination of resistors and capacitors produce a DC gain of 60 dBV, a pole at ~100 Hz, a zero at ~10 kHz and high frequency behavior of ~constant gain of 20 dBV. In this simulation, the gain-bandwidth product of the simulated op-amp (the standard op-amp CircuitLab uses) was artificially increased in order to see more ideal behavior in the higher frequency domain.

Switches like the above can be used to add boosts to some initial filter state (which could be like the above or possibly a simple integrator to achieve high DC gain) and change it into a more complex and more useful filter state advantageous for desired noise suppression. Cascades of these switching filters could be used to create very complicated transfer function behavior. No general servo has yet been designed as the exact details of the intensity noise requirements are still being determined.

With regards to the implementation of the switches, some ‘smart’ signal will be used to trigger a switch opening and the boost being introduced to the signal processing. The switches will be opened (open corresponds to adding the boost) in a manner that maintains stability of the servo circuit. Essentially, some sort of time delay or power monitor induced signal (power from the PD output) will be used to modify the servo's behavior.

AOM

How exactly the signal will drive the AOM for correct noise suppression is unknown currently.

 

Attachment 1: Example_Switching_Filter_Transfer_Function_-_Switch_Closed.png
Example_Switching_Filter_Transfer_Function_-_Switch_Closed.png
Attachment 2: Example_Switching_Filter_Transfer_Function_-_Switch_Open.png
Example_Switching_Filter_Transfer_Function_-_Switch_Open.png
  8474   Mon Apr 22 20:17:05 2013 CharlesUpdateISSNew Servo w/switching filters

 

In my previous post here, a new servo design was discussed. Although the exact design used will depend on the particular noise requirements for the 40m and the Bridge Labs (requirements will be considered separately for each application), I still have to yet to see those formalized. Despite this, I have been simulating an example servo circuit with three switchable stages. The design can be found at: New Servo.

Essentially, this circuit consists of three unity gain buffers that can be switched into different filtering states. Attached is a plot of the transfer function of this particular circuit with successive stages turned on. The curve (0) corresponds to all of the filters being switched off, so the total behavior is that of a unity gain buffer. The curve (1) corresponds to the first stage being turned on with the 2nd and 3rd still acting as unity gain buffers. This first state has a gain of ~80 dB at DC and a pole at ~10 Hz which sets the unity gain crossing at ~100 kHz. The curves (2) and (3) correspond to the second and third stage being turned on, respectively. Each of these stages has a pole at DC (i.e. ~infinite gain) and a zero at 10^4 Hz. For f > 10^4 Hz, these stages have gain ~ 1, as we can see in the transfer function below.

I have also performed some noise analysis of this circuit. Attached are a few plots produced by LISO showing the resistor and op-amp noise separately (it was too cluttered on one plot) at the output node of the servo. Both of these plots have a "Sum Noise" trace, which is the sum for every circuit element and is thus identical between plots. The third noise spectrum included is simply the noise at the output referenced to the input with the previously computed transfer function. I'm not sure if there is a simple method embedded in LISO to reference the noise at the output node to the input, but it should be as simple as numerically dividing the noise spectrum by the transfer function between input and output. 

Next, I will be attempting time-dependent simulations of this simple circuit using delayed switches instead of manually controlled ones.

Attachment 1: Servo_v0.1.png
Servo_v0.1.png
Attachment 2: Example_Filter_-_Transfer_Function_(mag).png
Example_Filter_-_Transfer_Function_(mag).png
Attachment 3: Example_Filter_-_Transfer_Function_(phase_in_final_state_only).png
Example_Filter_-_Transfer_Function_(phase_in_final_state_only).png
Attachment 4: New_Servo_-_Op-Amp_Noise.jpg
New_Servo_-_Op-Amp_Noise.jpg
Attachment 5: New_Servo_-_Resistor_Noise.jpg
New_Servo_-_Resistor_Noise.jpg
Attachment 6: New_Servo_-_Total_Noise_Input-Referenced.png
New_Servo_-_Total_Noise_Input-Referenced.png
  8748   Tue Jun 25 22:57:01 2013 CharlesUpdateISSProposed ISS for CTN Experiment

Following Tara's noise budget, I have developed the following ISS, whose transfer function was computed with LISO and is also displayed below. The transfer function was computed from the output of the differential amplifier circuit (i.e. it does not include the portion of the schematic in the dashed box). The differential amplifier is included for completeness. Essentially, the resistor values of this portion (and even the voltage reference if need be) can be modified to handle various signals from PDs in different experiments. Some filtering may also be applied to the signal from the voltage reference. In previous designs for the ISS, a ~30 mHz low-pass filter applied to the output of the voltage reference has also been proposed.

Screen_Shot_2013-06-25_at_10.24.07_PM.png

TF_Mag-CTNServo_v2.png

LISO was also used to compute the input-referred noise of this circuit. Using the response function of Tara's PD the noise spectrum was converted from [V / sqrt(Hz)] to [W / sqrt(Hz)] and then subsequently converted to a frequency noise spectrum, specifically [W / sqrt(Hz)] to [Hz / sqrt(Hz)], using the following transfer function which couples RIN to frequency noise in the CTN experiment. In these particular units, we can make a direct comparison between the inherent noise contribution from the servo itself and other more significant noise contributions shown earlier in Tara's noise budget. Indeed, the servo contributes significantly less noise.

Input_Noise-Freq-CTNServo_v2.png

This servo has been prototyped on a breadboard and will soon be characterized with the SR785. Additionally, schematics will be drawn up in Altium and eventually put on PCB.

Additional servos for other experiments can be designed once various requirements for noise suppression are explicitly formalized.

  8759   Wed Jun 26 21:52:55 2013 CharlesUpdateISSCTN Servo Prototype Characterization

Following the circuit design in elog 8748, I constructed a prototype for the servo portion of the ISS (not including the differential amp) to be used in the CTN experiment. The device was built on a breadboard and its transfer function was measured with the Swept Sine measurement group of an SR785. For various excitation amplitudes, the transfer function (TF) was not consistent.

TF_Mag-CTNServo_v2_Prototype.png

Recall the ideal transfer function for this particular servo and consider the following comparisons.

  • The unity gain frequency is consistent, and the measured TFs all exhibit some amount of 1/f behavior up to this point, but there is no zero around f~10^3 and individual low-frequency poles/zeros are not visible.
  • For each of the inputs, there is a feature that is not exhibited in the ideal TF. We see a large drop in gain a little past 10^3 Hz for a 100mV input, just past 10^2 Hz for a 10 mV input and around 10^1 Hz for a 1 mV input.
  • The ideal TF also goes as 1/f for f < 10 Hz, so I believe the low-frequency behavior of each of the above transfer functions is simply a physical limitation of the breadboard or the SR785, although I don't think this is caused by the circuit elements themselves. I used OP27 op-amps in the prototype as opposed to AD829 op-amps which are must faster and end up amplifying noise. To ensure that these op-amps were not the source of the gain limitation, I also tried using AD829 op-amps. The resulting transfer functions are shown below.
  • Both the frequency at which we see the anomalous feature and the maximum gain increase nearly proportional to the increasing input excitation amplitude.

This gain limitation is problematic for characterizing prototypes as my particular servo has very large gain at low frequencies. 

TF_Mag-CTNServo_v2_Prototype_AD829s.png

At the risk of looking too deeply into the above data,

  • It appears there is a slight change in slope around f ~ 10^3 Hz which would be consistent with the ideal TF.
  • For f > 10^3 Hz, one can easily see the TF goes as 1/f. The slope for f < 10^3 Hz is not as clear, although it obviously does not show 1/f^2 behavior as we would expect from the ideal TF.
  • We see the same gain limitation around G ~ 55 as we did with OP27 op-amps.

Unfortunately, the noise was too large for lower excitation amplitudes to be used to any effect. I'll try this again tomorrow, just as a sanity check, but otherwise I will proceed with learning Altium and drawing up schematics for this servo.

 

  8771   Thu Jun 27 18:24:25 2013 CharlesUpdateISSCTN Servo Prototype Characterization - Done Correctly

As I showed in [elog 8759], measuring the transfer function of my prototype servo was difficult due to physical limitations of either some portion of the construction or even the SR785 itself. To get around this, I tried using lower input excitation amplitudes, but ran into problems with noise.

Finding a TF consistent with theoretical predictions made by LISO was easy enough when I simply measured the TF of each of the two filter stages individually and then multiplied them to obtain the TF for the full servo. I still noticed some amount of gain limitation for 100 mV and 10 mV inputs, although I only had to lower the input to 5 mV to avoid this and thus did not see significant amounts of noise as I did with a 1 mV input. The individual transfer functions for each stage are shown below. Note that the SR785 has an upper cutoff frequency of 100 kHz so I could analyze the TF beyond this frequency. Additionally, the limited Gain Bandwidth Product of OP27 op-amps (used in the prototype) causes the magnitude and phase to drop off for f > 10^5 Hz approximately. The actual servo will use AD829 op-amps which have a much larger GBWP.

TF-CTNServo_v2_Prototype-Individual_Stages.png

The measured TFs above are very close to ideal and agree quite well with theoretical predictions. Based on the [circuit schematics],

  • Stage 1 should have Gain ~ 10^3 until the pole at f ~ 10 Hz  
  • Stage 2 should exhibit a DC pole, a zero at f ~ 10^3 Hz and then unity gain for f > 10^3 Hz

Indeed, this is exactly what we can see from the above two TFs. We can also multiply the magnitudes and add the phases (full_phase = phase1 + phase2 - 180) to find the TF for the full servo and compare that to the ideal TF produced by LISO,

TF-CTNServo_v2_Prototype-Calc_vs_Meas.png

And we find exceptionally consistent transfer functions, which speaks to the functionality of my prototype 

As such, I'll proceed with designing this servo in Altium (most of which will be learning how to use the software)

Note that all TFs were taken using the netgpibdata python module. Measurement parameters were entered remotely using the TFSR785.py function (via control room computers) and following the examples on the 40m Wiki.

Attachment 3: TF-CTNServo_v2_Prototype-Individual_Stages.fig
Attachment 4: TF-CTNServo_v2_Prototype-Calc_vs_Meas.fig
  8786   Fri Jun 28 16:19:06 2013 CharlesUpdateISS40m Noise Budget - Seismic Contribution

 I'm working on developing a full noise budget for the 40m. To that end, I'll use measurements from the GUR1 seismometer to characterize seismic noise. Without any unit calibration, I found the following spectrum,

seismic_noise_6-28-13_raw.png

To extract useful information from this data, I first used the calibration from "/users/Templates/Seismic-Spectra_121213.xml" to obtain the spectrum in [m / s / sqrt(Hz)].

calibrated_data = raw_data * 3.8e-09

I then divided each point in the power spectrum by the frequency of said point to obtain [m / sqrt(Hz)]. I don't think we can simply divide the whole spectrum by 40 meters to obtain [RIN / sqrt(Hz)], although that was my immediate intuition. Having power spectra of all the major noise contributions in units of [RIN / sqrt(Hz)] would make designing an appropriate filtering servo fairly straightforward.

 seismic_noise_6-28-13_meters.png

 

Attachment 2: seismic_noise_6-28-13_raw.fig
Attachment 4: seismic_noise_6-28-13_meters.fig
  8791   Tue Jul 2 12:59:46 2013 CharlesUpdateISSGeneral Design for ISS Applicable to Multiple Applications

 While attempting to develop a somewhat accurate noise budget for the 40m, I reasoned that while the shape of the transfer function for the ISS is important, the degree to which we can 'tune' it to a particular experiment/application is limited.

  • Since we're using a DC-coupled servo, the TF magnitude will go like f^k with k < 0 for low frequency.
  • The UGF will be somewhere around 10 kHz to 1 MHz (most likely right around 100 kHz) as beyond 1 MHz, the gain of our servo is limited by the GBWP of the op-amps.
  • We need around 3 or 4 orders of magnitude of gain in the 1-100 Hz range based on this, with gain > 10 for f < 10 kHz

Beyond that, we're sort of limited by the desired high and low frequency behavior as well as the general principle that more electronics = more noise so we probably don't want more than 3 or 4 filter stages, if that. Additionally, the ISS can be over-engineered so that it suppresses the laser noise to levels well below other fundamental noise sources over the important regime ~10 - 10^3 Hz without particular regard to a noise budget.

The design I propose is very similar to a previous design, with a few adjustments. It consists of 3 filter stages that easily be modified to increase gain for higher frequencies if it is known/determined that the laser being stabilized has a lot of high frequency noise.

40mServo_v1.png

Stage 1: Basic LP Filter + Establish UGF (each stage 'turning on' will not change the UGF),  Stage 2: Integrator with zero @ 10 kHz,  Stage 3: Optional extra gain if necessary

40mServo_v1-Stage1.pdf40mServo_v1-Stage2.pdf40mServo_v1-Stage3.pdf

With the full TF given by,

 40mServo_v1.pdf 

As usual we consider the noise caused by the servo itself. Noise analysis in LISO is done with a 1 V input excitation.

40mServo_v1-Input_Noise.pdf

This servo should function sufficiently for the 40m.

  8799   Wed Jul 3 20:51:43 2013 CharlesUpdateISSProposed ISS for CTN Experiment - Altium Schematic

 After familiarizing myself with Altium, I drew up the attached schematic for the ISS to be used in the CTN experiment. The filename includes 'abbott-switch' as I am using an Altium component (the switch, in particular), that he created. The MAX333A actually has 20 pins on a single component, but the distributed component that he created is useful for drawing uncluttered schematics. I won't be using all of the pins on this switch, but for completeness, I have included the 3rd and 4th portion of the full component in the upper right hand corner.

Currently, the schematic includes the voltage reference (AD586), a LP filter for the reference signal, the differential amplifier stage to obtain the error signal and then finally all of the filter stages. The schematic does not include the RMS detection and subsequent triggering of each filter stage. The TRIGGER 1 signal is a user input (essentially the on button) while the TRIGGER 2 signal will flip the second switch when the RMS noise has decreased sufficiently after the first filter stage has been turned on. 

PCB layouts will be done once I understand that part of Altium 

 

NOTE THAT I HAVE DELETED ELOG 8798 AS IT WAS A DUPLICATE OF THIS ONE.

I wanted this elog to be in reply to a previous one and I couldn't figure out how to change that in an elog I already submitted.

 

 

 

Attachment 1: CTNServo_v2_abbott-switch.pdf
CTNServo_v2_abbott-switch.pdf
  8830   Thu Jul 11 13:52:51 2013 CharlesUpdateISSRMS threshold detection and triggering

There are essentially two major portions of the ISS I am designing. One system has the voltage reference, differential amplifier and filtering servo (schematic attached) while the other has a comparator circuit and a triggering mechanism. The first system amplifies an error signal obtained from the PD output and the voltage reference, which is then fed back through the AOM. I've done a lot of work designing/prototyping this first half and now I'm starting to design the second half.

The second system's main purpose is to maintain loop stability as the ISS is engaged. Let's assume a user has decided they want noise suppression. They would first close the ISS feedback loop and an error signal would pass through three unity-gain buffers, providing minimal noise reduction. The user can then send a signal to theTRIGGER 1 port to switch the first stage from its unity-gain position to its filtering position and reduce the intensity noise further. This signal will most likely be digital in origin. Alternatively, when the user first closes the ISS loop, the first stage can already be in its filtering position rather than necessitating two commands.

A test channel (not drawn in the included schematic) will monitor the RMS level of the incoming signal from the PD. This noisy AC signal will first be amplified and then passed through an RMS-to-DC converter. The resulting DC signal is used as a part of the triggering mechanism for later stages. Once the first stage has been switched manually, and the DC signal corresponding to RMS noise of the PD output drops below a certain threshold, stages 2 and 3 will be internally triggered with a short delay between them. Toward being able to detect this threshold, I have designed a simple comparator circuit with an LT1016. The circuit has a fairly low-level output when the input voltage is larger than the threshold (about 1.6 V for my simple prototype), but when the input passes below the threshold, the comparator puts out almost 4 V, a number limited by the supply voltage. The schematic is shown below.

Simple_Comparator_Circuit.png

The component V2 and the various voltage dividers serve to establish the reference/threshold voltage. Note that although the LT1016 is not powered in the schematic, it requires ±5 V (a max of 7 V). The above circuit was also prototyped on a breadboard and I characterized it with an oscilloscope. Using a CFG253, I made a low frequency (~0.3 Hz) triangle wave with an amplitude and DC offset such that it oscillates between 0 and 5 V. This was applied to the IN node in the above schematic. The input waveform and the circuit's response (voltage at the OUT node) are shown below. As expected, R2 serves to establish hysteresis. The comparator switches to 'high' output until the input drops below 1.6 V, and then it doesn't switch back to the 'low' output until the input goes up to ~3.4 V.

F0001TEK.JPG

This behavior is ideal for our application as we can detect when the DC signal from the RMS-to-DC converter drops below a certain level (i.e. the first stage that has been activated does some amount of filtering to lower RMS noise), and then we can trigger subsequent filter stages off of the comparators high-level output. 

This circuit could easily be used to drive the MAX333a switches shown in the first schematic attached. I believe the low-level output is not sufficient to switch the MAX333a although the ~4 V high-level output is quite sufficient. Regardless, these exact values (thresholds, outputs etc) will be determined after I have a better idea of the RMS noise of the laser without any intensity stabilization as well as a solid understanding of how the AD8436 RMS-to-DC converter works. This was simply a proof of concept for lower threshold detection using basic Schmitt trigger topology.

Attachment 1: 40mServo_v1.pdf
40mServo_v1.pdf
  8836   Fri Jul 12 12:51:13 2013 CharlesUpdateISSRMS Noise from PMC Transmission

I went out on the floor to look at the transmitted signal from the PMC to get a rough idea of the noise of the unstabilized laser. There was already a scope hooked up so I just used the measurement features to find the following:

Signal average = 875 mV.  Peak-to-Peak noise = 45 mV

Assuming the noise can be approximated as Gaussian noise, the heuristic for converting to RMS noise of the signal is RMS = Peak-to-Peak / 8 (or Peak-to-Peak / 6, I've used both...)

-> RMS Noise ~ 6.5 mV

When designing my filtering stages and RMS detection/triggering, I'll use relative RMS, i.e. 6 mV / 875 mV = 0.007, as a measure of unstabilized laser noise.

  8839   Fri Jul 12 18:30:20 2013 CharlesUpdateISSRMS Noise from PMC Transmission

Quote:

It would be better to measure the power spectrum density of the fluctuation.
The RMS does not tell enough information how the servo should be.
In deed, the power spctrum density gives you how much the RMS is in the entire or a specific frequency range.

I wanted the RMS noise simply to establish a very rough estimate of thresholds on RMS detectors that will be part of my device. If you refer to elog 8830, I explain it there. Essentially, when the ISS is first engaged, only one of the 2 or 3 filter stages will be active. Internal RMS threshold detection serves to create a logic input to switch subsequent filters to their 'on' stage.

  8876   Thu Jul 18 21:45:36 2013 CharlesUpdateISSISS - Full Schematic

 Here I have included the full schematic (so far) of the proposed ISS. There are two sheets: the first schematic details the filter stages and their accompanying circuitry while the second schematic details the RMS threshold detection and subsequent triggering.

The first schematic is fairly self explanatory as to what different portions do, and I have annotated much of the second schematic as there are some non-traditional components etc.

I have not yet included some mechanism to adjust the threshold voltage in real time or any of the power regulation, but these should follow fairly quickly.

Attachment 1: 40mServo_v1.pdf
40mServo_v1.pdf 40mServo_v1.pdf
  8920   Wed Jul 24 22:58:03 2013 CharlesUpdateISSISS - Full Schematic - Updated

 I have made significant changes to the ISS schematic, mostly in the form of adding necessary subsystems.

Some changes I have made:

  • Added a front page with sheet symbols that are representations of the other schematic sheets.
  • Added an 'Excitation' subsystem for use in determining the closed-loop transfer function
  • Added an instrumentation amplifier (with ADA4004s at Rana's recent suggestion) to handle the differential input from the PD
  • Included a switchable inverting amplifier (Gain of 1 or -1) to ensure we have the correct polarity
  • Made it so the first filtering stage is immediately active when the ISS loop is closed
  • Added LP filters with large time constants to buffer/delay trigger signals
  • Added test points all over the board
  • Refined a few buffer amplifiers

On the front page, all inputs and outputs are currently BNC ports, although this is most likely not the final design that will be used. For instance, the ports ENABLE, INPUT GND and INVERT are supposed to be logic inputs for a MAX333a switch. These will most likely be front panel switches that either connect the switch's logic pin to GND (Logic 0) or something like a +5 V supply (Logic 1).

I also have not included power regulation for my board although I have some of the actual D1000217 Chasis Power Regulator boards and I'll incorporate those in my design soon.

Attachment 1: 40mServo_v1.pdf
40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf
  8922   Thu Jul 25 12:53:45 2013 CharlesUpdateISSComparator + Triggering Prototype

 I realized I totally forgot to post this last week, but I prototyped the comparator and boost triggering portion of the ISS, at least in part. Below is a schematic that shows the prototype circuit I made. Note that it includes ports for the oscilloscope channels that appear in the second image included. Essentially, I was able to verify that the output from the LT1016, as it's currently constructed in the ISS schematic, would be sufficient logic to switch the MAX333a.

Comparator_Prototype.png

Below, we can first see that the comparator is switching its output as desired. When the DC level of the input drops below a certain threshold (~1.6 V) the output of the comparator switches on to ~4 V. When the DC level of the input goes back up above the upper threshold (~3.2 V), the comparator switches off to ~0.3 V. The exact values of the threshold voltages can be determined/tuned at a later date, but this is the basic behavior that the comparator circuit will have.

To detect whether or not the MAX333a was switching properly, I connected the common terminal of one of the switches to a +5 V supply, and looked at the voltage coming off both the 'open' and 'closed' terminals of said SPDT switch. We can see that with Logic 0 (comparator output ~0.3 V) Channel 4 exhibits a ~5 V signal, just as we would expect from the above schematic. With Logic 1 (comparator output ~4 V), Channel 3 exhibits the characteristic 5 V signal.

Comp_Triggering_Behavior.jpg

  8927   Fri Jul 26 14:39:08 2013 CharlesUpdateISSPower Regulation for ISS Board

I constructed a regulator board that can take ±24 V and supply a regulated ±15 V or ±5 V. I followed the schematics from LIGO-D1000217-v1.

I was going to make 2 boards, one for ±15 V and one for ±5, but Chub just gave me a second assembled board when I asked him for the parts to construct it 

 

  8928   Fri Jul 26 22:19:24 2013 CharlesUpdateISSISS - Full Schematic - Updated

Quote:

 I have made significant changes to the ISS schematic, mostly in the form of adding necessary subsystems.

Some changes I have made:

  • Added a front page with sheet symbols that are representations of the other schematic sheets.
  • Added an 'Excitation' subsystem for use in determining the closed-loop transfer function
  • Added an instrumentation amplifier (with ADA4004s at Rana's recent suggestion) to handle the differential input from the PD
  • Included a switchable inverting amplifier (Gain of 1 or -1) to ensure we have the correct polarity
  • Made it so the first filtering stage is immediately active when the ISS loop is closed
  • Added LP filters with large time constants to buffer/delay trigger signals
  • Added test points all over the board
  • Refined a few buffer amplifiers

On the front page, all inputs and outputs are currently BNC ports, although this is most likely not the final design that will be used. For instance, the ports ENABLE, INPUT GND and INVERT are supposed to be logic inputs for a MAX333a switch. These will most likely be front panel switches that either connect the switch's logic pin to GND (Logic 0) or something like a +5 V supply (Logic 1).

I also have not included power regulation for my board although I have some of the actual D1000217 Chasis Power Regulator boards and I'll incorporate those in my design soon.

 More changes that I've made:

  • Added daughter boards for power regulation. Currently I have ±24V going into two boards, with ±15V coming out of one and ±5V coming out of the other. Again, these are based off of LIGO-D1000217
  • Added an optional Dewhitening filter (with p=1Hz and z=100Hz, although these can easily be changed) to accommodate any PD's that have whitening
  • Added a bypass to allow the boosts (stages 2 and 3 of the filtering servo) to be enabled/disabled by a front panel switch
  • I also put in jumpers that can be used to provide Logic 1 (boost enabled) to both Boost 1 and Boost 2 without depending on the internal RMS detection/triggering
  • Changed the input grounding switch so that it's set up correctly. Before, it was taking the PD signal and sending it to GND, not actually grounding the input to the rest of the ISS 
Attachment 1: 40mServo_v1.pdf
40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf 40mServo_v1.pdf
  8959   Thu Aug 1 22:58:45 2013 CharlesUpdateISSCTN Servo - Explicit Requirement and Proposed Servo

 In PSL elog 1270, Evan elucidated the explicit requirements for the CTN ISS board. Essentially, the transfer function of the ISS should be something like:

     TF_mag = (Unstabilized RIN) / (Calculated RIN Requirement)

I took Evan's data and did exactly this. I then designed a servo (using the general design I proposed here) to meet this requirement with a safety factor of ~10. By safety factor, I mean that if the ISS operates exactly according to theory, it should suppress the noise by a factor of 10 more than what is necessary/set out by the requirement. Below is a plot of the loop gain obtained directly from the requirement (the above expression for TF_mag) and the transfer function of the servo I am proposing.

CTN_Servo_TF_-_Proposed_v_Req.png

I don't have the actual schematics attached as I was working with a LISO file and have yet to update the corresponding Altium schematic. The LISO file is attached and I will add the schematics later, although one can reference the second link to find a simple drawing.

Attachment 2: CTNServo_v3.fil
# Stage 1
r R31 1.58k in n_inU3
op U3 ad829 p_inU3 n_inU3 outU3
r R35 1k p_inU3 gnd
c C33 1u p_inU3 gnd
c C32 10n n_inU3 outU3
r R34 158k n_inU3 outU3

# Stage 2
#r R41 15.8 outU3 n_inU4U5
... 24 more lines ...
  8961   Fri Aug 2 21:59:36 2013 CharlesUpdateISSFinalized ISS Schematic (hopefully)

Attached is the finalized schematic. The general circuit topology should remain the same from this point forward, although individual component values are subject to change. I will also be adding some more annotations to ensure everything on the board is clear.

In general, I have finally included all of the correct components (i.e. front panel switches are now actually switches and front panel LEDs are now included). I also added an external 'Boost' switch, which can be used to enable or disable the boosts. The motivation for including this switch is that one might want to test functionality of the ISS without using the 'fancy' RMS detection and triggering circuitry. Additionally, one can disable the boosts when all the circuitry is stuffed in order to troubleshoot, so it essentially grants the board some flexibility in its operation.

I am now working on the PCB layout and I should hopefully have that done next week. 

Attachment 1: ISS_v3.pdf
ISS_v3.pdf ISS_v3.pdf ISS_v3.pdf ISS_v3.pdf ISS_v3.pdf
Attachment 2: ISS_v3-Power_Reg.pdf
ISS_v3-Power_Reg.pdf
ELOG V3.1.3-