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ID Date Authorup Type Category Subject
  3234   Fri Jul 16 12:36:00 2010 Katharine, SharmilaUpdateeloglevitation

After last night's challenge (or inspiration), we levitated our magnet this morning.  Since the nice Olympus camera is not currently in the 40m, we had to use my less stellar camera, but despite the poor video quality you can still see the magnet returning to its stable equilibrium position.  Once we recover the better camera, we will post new videos.  Also, we haven't yet figured out how to put videos in line in the elog entry, so here are the youtube links:


levitation 1

levitation 2


We adjusted the gain on coil 1 so that the resistance from the pots was 57.1k (maximum gain of 101.2,).

currents from power supply, pre-levitation: 0.08 A and 0.34 A

post levitation: 0.08 A and 0.11 A

note: we're not sure why changing the gain on coil 3 changes the current through the power supply, so we'd like to investigate that next.

Attachment 1: CIMG0649.AVI
  3256   Wed Jul 21 12:03:14 2010 Katharine, SharmilaUpdateWIKI-40M Updateweekly update

This past week, we levitated our small cylindrical magnet (with the flag made from heat shrink).  Though the levitated magnet didn't appear very jittery to the eye, we looked at the PD current on the scope and could see oscillations that corresponded to the flag hitting the sides of the OSEM.  The oscillations were more pronounced as we gently hit/vibrated the lab bench, and by pounding on the bench Rana knocked the levitated magnet completely out of the setup.  So, we're currently working on building a new, stabler mount.  The biggest challenge here is fixing the OSEM in place, but we're experimenting with different optics pieces to see which is the most stable for our purposes.   Jenne taught us how to make through holes using the drill press so we can add slats of aluminum to adjust the height of the OSEM mount.  We also plan to fix some heavy plates to the bottom of our system to decrease its vibration frequency.

We also calculated the transfer function of our circuit, which seems to match the measured frequency response to within a small factor.  We're playing with Rana's Simulink models and are currently modeling our own system to determine what gains we would expect to use and get a better understanding of our circuit.

Once our system is successfully mounted stably, we plan to experimentally observe the effects of changing the gain and integrator by looking at time series measurements of the PD current, as well as using the spectrum analyzer to compare the frequency response of our system at different gain settings.

  3111   Wed Jun 23 23:55:03 2010 Katharine, Sharmila, Rana, Steve and KiwamuUpdateVACwiped the BS

Some unused optics in the BS chamber were removed. 

After that the beam splitter has been drag wiped. 

So now the BS chamber is waiting for the installation of  the other core optics i.e. PRM, SRM and Tip-Tilts. 


-- removing of unused optics

      There were some unused optics, mainly 1.5 inch optics which had been used for the oplevs in the chamber. 

Kathaine, Shamila (Team Magnet) and Kiwamu took those optics out from the chamber.

And then we carefully wrapped each of them by aluminum foils and put them in some clear boxes.

In fact, before wrapping them, we gently attached lens papers on their HR surfaces such that aluminum foils can not damage it.

Now there are only three 1.5 inch optics in the chamber, and they are supposed to be used for the oplevs.

We didn't remove any of the 2 inch optics and the PZT mirrors because they are still going to be used.

These are the pictures of the BS chamber after we cleaned up them. 


-- wiping of the BS

        Rana and Kiwamu drag wiped the HR surface of the BS by using lens paper with the solvents.

The below is the procedure we did. You can find some details about the wiping technique for suspended optics in this entry.

In this time we could wipe the beam splitter without removing the front earthquake stops because the beam splitter was brought close enough to us. 


(1). put some blocks attaching the edge of the bottom plate of the tower in order to record the original position.

(2).  locked the beam splitter to the frame by screwing the earthquake stops.

(3). made sure if it is really locked by seeing the output signal of the OSEMs in dataviewer. If it's locked successfully, the resonant frequency gets higher and the Q-value gets lower.

(3).  moved the BS tower close to the door in order to reach the beam splitter easily.

(4). inspected the surface by using a fiber light. There were about 10 bright spots on the HR surface.

(5). wiped the surface three times by using the lens paper with Aceton.

(6). wiped it several times with Isopropyl.

(7). inspected the surface again, found there were no big bright spots near the center. Thumbed up 

(8). put the tower back to the original place and released the beam splitter from the earthquake stops.

  5470   Mon Sep 19 21:19:25 2011 KatrinUpdateGreen LockingBroadband photodiode characterization

Another Hamasutu S3399 photodiode was tested with the electronic circuit as described in LIGO-D-1002969-v.

RF transimpedance is 1k although the DC transimpedance is 2k.

The noise level is 25pA/sqrt(Hz) which corresponds to a dark current of 1.9mA or 1.7mA in the independent measurement.

At all frequencies the noise is larger compared to Koji's measurement (see labbook page 4778).


In file idet_S3399.pdf the first point is not within its error bars on the fitted curved. This point corresponds to the dark noise measurement

I made this measurement again. Now it is on the fitted curve. In the previous measurement I pushed the save button a bit too early. The

averaging process has not been ready while I pushed the 'save'  button.

Dark current is 1.05mA and noise is lower than in the previous measurement.

New file are the XXX_v2.pdf files







  5511   Thu Sep 22 01:05:28 2011 KatrinUpdateGreen LockingNew modulation frequency (Y arm)

[Kiwamu / Katrin]


On Wednesday, the green light was locked to the Y arm cavity.

Modulation frequency was changed from 279kHz to 178875Hz. The amplitude was changed from 10Vpp to 0.01Vpp to achieve a modulation index of 0.38. The modulation frequency was changed to minimize AM. With the new modulation frequency the laser light could still locked to the cavity.

The signal of the LO and the photodiode are multiplied by a ZAD-8 mini circuit mixer (Level 7). This mixer requires LO input is +7dBm = 1.4Vpp. Thus we put a 36dB attenuator between the LO and the PZT at the laser. PDH error signal shows lots of peaks that are most likely higher order sidebands. Thus, the next step is to work on the low-pass filter. However the SNR of the error signal has improved with the new modulation frequency. With the old mod. frequency the PDH signal was 4mVpp and the noise floor was 2mVpp.

Phase between the photodiode signal and LO is shifted by about 10 degrees. Step two is to work on a phase shifter.



  5531   Fri Sep 23 17:31:14 2011 KatrinUpdateGreen LockingStray light reduction (Y)

I inserted several beam blocks and iris on the Y arm Green table. There was/is lots of stray light because a lot of the mirrors are not under an angle of incident of 45°. Some stray light is left since couldn't find an appropriate beam block/dump due to lack of space on the table.


  5585   Fri Sep 30 15:22:17 2011 KatrinUpdateGreen LockingWhat happened on green YARM?


This is a kind of summary of what I have worked on this week.

After all the changes made last week, I could not manage to lock the green light to the cavity, but the PDH error signal looks nicer.....at least something.


Alignment of the light to the cavity:

  • DC level of green PD when light is non-resonating 100%
  • DC level of green PD when light resonates 75%
  • --> Not sure if this alignment is good enough
  • In comparision to last week the cavity mirrors seem to move more or my alignment is way worse than last week. The bright spot on ETMY could not be observed for more than let's say a second in the unlocked configuration.


Low-pass filter (LPF)

  • The PDH error signal was covered with oscillations of 3.3 kHz, 7.1 kHz and 35 kHz.
  • Measured cut-off frequency of the LPF used so far is 35 kHz
  • Designed and build a new LPF: second order, cut of frequency of 1.1 kHz (this is just the design value, haven't measured that so far)
  • With the new LPF the PDH error signal is free of the above mentioned oscillations.
  • Impedance should be checked


PDH error signal

  • Signal-to-noise ratio (SNR) could be improved to values between 7.8 and 11.1 (old SNR was 5 to 7)
  • Looks more like a PDH signal than with the old LPF (now just derivative of the carrier and the first order sidebands show up)
  • Amplitude of the first order sidebands are smaller than the zero order, but are still too high (about 80% of the first order), need to work on the proper value of the LO amplitude an the voltage averager


Phase shift between green PD signal and LO

  • Phase shift is about 1MHz
  • Tried to find a capacity that compensates the phase shift. This was not successful since the PD frequency changed every now and than by +/- 20 kHz
  5619   Tue Oct 4 20:34:20 2011 KatrinUpdateGreen Locking7kHz Peak in servo input YARM

[Kiwamu, Katrin]

As reported earlier an oscillation around 7kHz is an the PDH error signal. The lower spectrum show that there is a peak from 6-7kHz.

This peak is somehow dependent on the modulation frequency. This means the peak can be shifted to a higher frequency when the modulation frequency is increased (see for comparsion f_mod=279kHz).

If the power supply for the green PD is switched of the peak vanishes. The same happens if the LO is switched of.

servoinput.png servoinput2.png

  5623   Wed Oct 5 18:31:02 2011 KatrinUpdateGreen LockingExchanged mirror on YARM table

On the Green YARM end table the second mirror behind the laser has been exchanged.

Reason: The light is impinging on the mirror under an angle of  about 10 degrees, but the old mirror was coated for angle of incidence (aoi) of 45°.

Thus it was more like a beam splitter. The new mirror is a 1" Goock & Housego mirror which has a better performance for an aoi of 10 degree.

Realignment through Faraday Isolator and SHG cristall as well as 532nm isolator is almost finished.

  5631   Fri Oct 7 17:35:26 2011 KatrinUpdateGreen LockingPower on green YARM table

After all realignment is finished, here are the powers at several positions:



  5646   Mon Oct 10 18:53:04 2011 KatrinUpdateGreen LockingMirrors whose angle of incidence is not 45

The angle of incidence of light is for some mirrors on the YARM end table different from 45° even though the mirrors are coated for 45°.

The mirrors below are useful if there are plans to replace these mirrors by properly coated ones.


Angle of incidence (degree)
1st 1" mirror right after laser* 10
2nd 1" mirror right after laser 35
1st 2" steering mirror to vacuum system 15
2nd 2" steering mirror to vacuum system 28


* This is the new mirror as decribed on http://nodus.ligo.caltech.edu:8080/40m/5623


  5657   Wed Oct 12 18:54:02 2011 KatrinUpdateGreen Locking60 Hz oscillation due to broken BNC cable

There was a 60 Hz and 120 Hz oscillation on the green PDH photo diode output. After a long search, I could identify that

the source was a broken BNC cable which was connected to the photo diode. I exchanged that BNC cable and the 60 Hz

and 120 Hz are gone :-)

With the new cable the PD output was less noisy so that it was easier to achieve a better alignment of the light to the cavity.

The reflected power could be reduced from 40% to 30%. For perfect alignment the reflected power would be 20%.

  5658   Wed Oct 12 19:58:32 2011 KatrinUpdateGreen LockingPower splitter is unbalanced

The mini circuit power splitter ZFRSC-42S+ used at the YARM has no balanced output as it should have according to the data sheet.

@ 0.05MHz  the amplitude unbalance should be 0.03 dB

A quick measurement shows that there is a LO amplitude dependent unbalance:

LO amplitude input (Vpp)  unbalanced output (dB)
1.3 3.66
1.4 4.08
1.5 4.28
1.6 4.36

So my question is, shall I replace the power splitter just in case it is further degrading?

  5661   Thu Oct 13 20:25:32 2011 KatrinUpdateGreen LockingLPF transfer function YARM

It is a 4th order filter with cut of frequency of 120 kHz.







  5713   Thu Oct 20 16:33:24 2011 KatrinUpdateGreen LockingTransfer function YARM PDH box

Yesterday, I measured the transfer function of the YARM PDH box.



I tested the electronic board and couldn't find a frequency dependent behaviour. So I measured the TF again and it looked nice.


Today's nice measurement could is/was reproducible. I suppose yesterday's measurement is just an artefact.

The electronic board is modified according to Kiwamu's wiki entry http://blue.ligo-wa.caltech.edu:8000/40m/Electronics/PDH_Universal_Box


Btw. The light could be locked to the cavity for ~3min.

  5726   Fri Oct 21 16:59:14 2011 KatrinUpdateGreen LockingYARM PDH box broken

I could not improve the locking. So, I checked the transfer function of the PDH box again. The transfer function looks okay if the gain knob is <=2.0.

If the gain knob is >2.0 the 20dB step appears in the transfer function (see elog page 5713). This step is shifted to higher frequencies if the gain is

increased. The PZT drive out was not saturated at any time. Yesterday, I checked the electronic circuit with a gain of 2.0. Thus,  I couldn't find the broken

gain amplifier (AD8336). The amplifier is ordered in will arrive on Monday.

  5734   Tue Oct 25 11:48:02 2011 KatrinHowToElectronicssolder tiny smd op amps

Yesterday, I had the great pleasure to solder a tiny 4 x 4 mm op amp with 16 legs (AD8336).

I figured out that the best and fastest way to do it is

  1. to put solder with the soldering iron on every contact of the electronic board (top side)
  2. heat the bottom side of the electronic board with a heat gun
  3. use a needle to test if the solder is melted
  4. if it is melted place the op amp on the electronic board
  5. apply some vertical force on the op amp for proper contact and heat for 1 to 2 more minutes
  6. done


  5742   Wed Oct 26 11:35:08 2011 KatrinUpdateGreen LockingYARM PDH box


From time to time the 20 dB jump in the transfer function still occurs. The new AD8336 op amp did not change that issue. I am sure that the op amp was broken,

because the amplitude of the sine did not change when I turned the gain knob.

The above two curves were measured with different input amplitude of the sine from the spectrum analyzer. Nothing changed in between except that there was no

jump when Kiwamu was around. Very strange. Testing the electronic board led to no clue what is happening.

For now, I will just use the PDH box as it is, but one should keep this odd behaviour in mind.

  5743   Wed Oct 26 20:30:47 2011 KatrinUpdateLSCPOX11 and POP55 installed


RF photo diodes POP55 and POX11 are installed. The beams are aligned to the photo diodes.


PD DC out dark DC out bright light power calculated DC output  
POX11 0.1mV 1.3mV 0.09mW 3mV
POP55 35mV 55mV 3 to 4 µW 25mV

I used 0.7 A/W for the response and 50V/A for POP55 according to elog page #4576.


To install the third RF photo diode we need to order a plano-convex lens with a focal length of 750 or

maybe even better 1000

  5769   Mon Oct 31 14:01:56 2011 KatrinUpdateGreen LockingYARM locks for 2h

Today, I could lock the YARM laser for 2h to the YARM cavity. After to hours the output of the servo is saturated. I need to work on thermal feedback to the laser.

It is a nice TEM00 mode and the green light enters PSL table.


Measured with pin-ball machine spectrum analyzer (I forgot the real name, but it is the one that makes sounds like a pin-ball machine), source power10mVp, Lb1005 gain 2.05.




Input offset of LB1005 is zero


Locking history

On Thursday, Oct 27, lock for 3 min

On Friday, Oct 28, lock up to 18 min, improvements done by

  • finding the right adjustment of PI Corner frequency and gain
  • better alignment of the light to the cavity
  • I used a high-pass filter between LO and LB1005, but no improvement of lock. In contrast, it got worse.

On Monday,Oct 31, careful adjustment of summing box (rear of of LB1005), lock up to 2h, limited by saturated feedback signal --> work on slow control


Some more plots




Attachment 1: 20111031_OLTF.png
Attachment 2: YARM_setup.png
  5786   Wed Nov 2 17:29:10 2011 KatrinUpdateCDSc1scy.mdl compiled

Slight modification on that model:

  • terminated Q_out of Lockins to be able to compile the old model
  • assigned other ADC channels to GCY (green YARM)
  5787   Wed Nov 2 17:33:28 2011 KatrinUpdateGreen LockingADC channels for slow control

connector J9B of hardware ADC --> ch1 in software ADC --> GCY_ERR

connector J14 of hardware ADC --> ch11 in software ADC --> GCY_PZT

connector J15 of hardware ADC --> ch13 in software ADC --> GCY_REFL_DC



  5789   Wed Nov 2 20:56:49 2011 KatrinUpdateCDSdigital zeros at C1:X05-MADC0 (c1scy)

Channels C1:X05-MADC0_TP_XXX with XXX 2-9, 14-19, 21-27, 29-31 showed digital zeros.

Some of these channels are used in c1scy.mdl, e.g. for OSEM stuff. I guess this is not optimal...

  5790   Wed Nov 2 21:15:06 2011 KatrinUpdateCDSand again c1scy.mdl compiled

I changed an ADC channel for GCY_ERR and thus recompiled the c1scy model.

  5791   Wed Nov 2 21:49:59 2011 KatrinUpdateCDSc1iscey computer died again

while I was not doing anything on the machine.

  5797   Thu Nov 3 16:43:44 2011 KatrinUpdateGreen LockingSHG temperature (YARM)

Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.

The power emitted by the laser was the same as in the case without that cable. Note LT, i.e. measured crystal temperature, of the laser show a

different value when the BNC is connected, but the manual clearly states that this display does not work properly if a cable is connected to the

slow BNC plug, an offset is added.

The power of the 532nm light behind the SHG oven has been reduced from 1mW to 0.4mW. I changed the crystal temperature such that the power

of the green light is 1mW. With this new temperature setting the laser can be locked again.


  w/o BNC cable at slow plug w/ BNC cable at slow plug
T (°C) 29.776 29.776
LT (°C) 39.2 48.4
1064nm power (mW) 440 448
Temp. at TC200 (°C) 35.7 36.4
532nm power in front of Isolator (mW) 1.0 1.0




  5809   Fri Nov 4 13:53:33 2011 KatrinUpdateGreen LockingSHG temperature (YARM)


I must confess that I changed the temperature of the laser via the dial yesterday. I believe the initial (displayed) temperature was ~19o, whereas it is now probably in the high 20s. Sorry.


Changing the crystal temperature changes the laser frequency. This will causes the beat note missing at the vertex.

In other words, you will find the beat note at the vertex when the actual temperature of the crystal is reproduced as before,
no matter how the dial setting/temp voltage input is.


Okay, my elog entry was not clear I changed the temperature of the SHG which only changes the conversion efficiency. 



Anyhow, since the laser set temperature and thus the laser frequency has been changed by Zach and I couldn't find a note

of the original laser crystal temperature, my plan is to reset the SHG temperature to the old value, set the laser crystal temperature

around 19°C and do fine adjustment of that temperature by optimising the doubling efficiency. Okay?


  5815   Fri Nov 4 21:15:38 2011 KatrinUpdateGreen LockingNew fiber coupler (YARM)

63% coupling efficiency into the new fiber collimator (Thorlabs XXXX) and the blue fiber.This should be sufficient for a beat measurement with the PSL laser.

I think the coupling efficiency is not too bad with having no mode matching lenses and no adjustable collimator lens.


252mW in front of the fiber

159 mW fiber output

  5837   Mon Nov 7 17:38:18 2011 KatrinUpdateGreen LockingYARM length fluctuation


I measured the power spectrum of channel C1:GCY_SLOW_SERVO1_IN1, which is the PZT driving voltage.

I converted the output to a PSD. Next, I converted counts/sqrt(Hz) to volts/sqrt(Hz) by multiplying with 40 V / 2^16 counts.

Finally, I multiplied it with 5MHz/V for the PZT to end up with Hz/sqrt(Hz).


This corresponds to a cavity length fluctuation of


with lambda = 532nm and a YARM cavity length of 37.757m (elog # 5626).

All in one plot


  5846   Wed Nov 9 12:05:08 2011 KatrinUpdateGreen LockingYARM error signal and feedback signal

error signal = signal measured behind the low-pass filter

feedback signal = output of the gain servo, going to the PZT


First of all both signals in V/sqrt(Hz) just in case I mess up the next calibration step.


The 60 Hz line (and its multiple) are a new feature. They show up as soon as the feedback loop is closed. So far, I couldn't find their origin.


For the next calibration step:

  • width of a typical error signal, i.e. the frequency band width of the carrier slope, ~1.4 kHz
  • height of a typical error signal 182 mV
  5872   Fri Nov 11 12:32:45 2011 KatrinUpdateGreen Lockingbeat PSL - YARM laser

[Suresh, Katrin]

Measured frequency fluctuation of the beat between PSL and YARM lasers.


Yesterday, it was very tricky to adjust the voltage offset to the slow YARM laser input to achieve the appropriate beat frequency. Today, it was much easier. During measurement beat around 25 MHz. Calibration factor 40 mV per 10 MHz.

  5874   Fri Nov 11 13:35:19 2011 KatrinUpdateGreen LockingFeedback to ETMY

[Kiwamu, Katrin]



Red and blue curves: frequency fluctuation of the beat node between PSL and YARM laser.

Green and broen curves: Actuation on ETMY.  In ALS_CONTROL.adl  ETMY filter bank 4 and 5 were switched on. Gain was 0.3


Nice reduction of the frequency fluctuation.


Y axis is in volts^2 per counts. In order to go to MHz/sqrt(Hz) you have to take the square root and then times [20Volts/(2^16)counts]*[10Hz/0.04V].


Started to scan the cavity, but this didn't work. Green light all out of lock. IR beam was badly aligned to cavity. Now, my time is over and I have to leave you.

Thanks, for your help and the nice time.

  12999   Fri May 19 19:18:53 2017 KaustubhSummaryGeneralTesting of the new Photo Detectors ET-3010 and ET-3040


I got some hands-on-experience on using RF photodetectors and the Network Analyzer from Koji. There were newly purchased RF photodetectors from Electro-Optics Technology, Inc.. These were InGaAs Photodetectors with model no.: 120-10050-0001(ET-3010) and 120-10056-0001(ET-3040). The User Guide for the two detectors can be found here. This is the first time we bought the ET-3010 model PD for the 40m lab. It has an operation bandwith >1.5GHz(not tested yet), much higher than other PDs of its kind. This can be used for detecting the output as we 'sweep' the laser frequency for getting data on the optical cavities and the resonating modes inside the cavity. We just tested out the ET-3040 model today but will test out the ET-3010 next week.

Tools and Machines Used:

We worked on the optical bench right in front of the main entrance to the lab. We put the cables, power chords, etc. to their respective places. We used screws, poles, T's, I's, multimeter, Network/Spectrum Analyzer(along with the moving table), a lab computer, Oscilloscope, power supply and the aforementioned PDs for our testing. We took these items from the stack of tools at the Y-arm and the boxes of various different labelled palced near the X-arm. We moved the Network Analyzer(along with the bench) from near the Y-arm to our workplace.


I will include a rough schematic of the setup later.

We alligned the reference PD(High Speed Photoreceiver model 1611) and the test PD(ET-3040 in this case) to get optimal power output. We had set the pump current for the laser at 19.5mA which produced a power of 1.00mW at the output of the fiber couple. At the reference detector the measured voltage was about 1.8V and at the DUT it was about 15mV. The DC transimpedance for the reference detector is 10kOhm and its responsivity to 1064 nm is around 0.75A/W. Using this we calculate the power at the reference detector to be 0.24mW. The DC transimpedance for the DUT is 50Ohm and the responsivity of about 0.9A/W. This amounts to a power of about 0.33mW. After measuring the DC voltages, we connected the laser input to the Network Analyzer and gave in an RF signal with -10dBm and frequency modulation from 100 kHz to 500 MHz. The RF output from the Analyzer is coupled to the Reference Channel(CHR) of the analyzer via a 20dB directional coupler. The AC output of the reference detector is given at Channel A(CHA) and the output from the DUT is given to Channel B(CHB). We got plots of the ratios between the reference detector, DUT and the coupled refernce for the Transfer Function and the Phase. We found that the cut-off frequency for the ET3040 model was at arounf 55 MHz(stated as >50MHz in the data sheet). We have stored the data using the lab PC in the directory .../scripts/general/netgpibdata/data.


The bandwidth of the ET-3040 PD is as stated in the data sheet, >50 MHz.


These PDs have an internal power supply of 3V for ET-3040 and 6V for ET-3010. Do not leave these connected to any instruments after the experiments have been performed or else the batteries will get drained if there is any photocurrent on the PDs.

To Do:

A similar procedure has to be followed in order to test the ET-3010 PD. I will be doing this tentatively on Monday.

Attachment 1: IMG_20170519_173247922.jpg
Attachment 2: IMG_20170519_173253252.jpg
Attachment 3: IMG_20170519_173300174.jpg
Attachment 4: PD_test_setup.png
  13005   Mon May 22 18:20:27 2017 KaustubhSummaryGeneralTesting of the new Photo Detectors ET-3010 and ET-3040

I am adding the text files with the data readings and paramater settings along with the Bode Plot of the data. I plotted these graphs using matplotlib module with python 2.7.



I got some hands-on-experience on using RF photodetectors and the Network Analyzer from Koji. There were newly purchased RF photodetectors from Electro-Optics Technology, Inc.. These were InGaAs Photodetectors with model no.: 120-10050-0001(ET-3010) and 120-10056-0001(ET-3040). The User Guide for the two detectors can be found here. This is the first time we bought the ET-3010 model PD for the 40m lab. It has an operation bandwith >1.5GHz(not tested yet), much higher than other PDs of its kind. This can be used for detecting the output as we 'sweep' the laser frequency for getting data on the optical cavities and the resonating modes inside the cavity. We just tested out the ET-3040 model today but will test out the ET-3010 next week...


Attachment 1: ET-3040_test.zip
Attachment 2: ET-3040_test.pdf
  13009   Tue May 23 18:09:18 2017 KaustubhConfigurationGeneralTesting ET-3010 PD

In continuation with the previous(ET-3040 PD) test.

The ET-3010 PD requires to be fiber coupled for optimal use. I will try to test this model without the fiber couple tomorrow and see whether it works or not.

  13011   Wed May 24 18:19:15 2017 KaustubhUpdateGeneralET-3010 PD Test


In continuation to the previous test conducted on the ET-3040 PD,  I performed a similar test on the ET-3010 model. This model requires a fiber couple input for proper testing, but I tested it in free space without a fiber couple as the laser power was only 1.00 mW and there was not much danger of scattering of the laser beam. The Data Sheet can be found here


The schematic(attached below) and the procedure are the same as the previous time. The pump current was set to 19.5 mA giving us a laser beam of power 1.00mW at the fiber couple output. The measured voltage for the reference detector was 1.8V. For the DUT, the voltage is amplified using a low noise amplifier(model SR-560) with a gain of 100. Without any laser incidence on the DUT, the multimeter reads 120.6 mV. After alligning the laser with the DUT, the multimeter reads 348.5 mV, i.e. the voltage for the DUT is 227.9/100 ~ 2.28 mV. The DC transimpedance of the reference detector is 10kOhm and its responsivity to 1064 nm is around 0.75 A/W. Using this we calculate the power at the reference detector to be 0.24 mW. The DC transimpedance for the DUT is 50Ohm and the responsivity is around 0.85 A/W. Using this we calculate the power at the DUT to be 0.054 mW. After this we connect the the laser input to the Netwrok Analyzer(AG4395A) and give an RF signal with -10dBm and frequency modulation from 100 kHz to 500 MHz.The RF output from the Analyzer is coupled to the Reference Channel(CHR) of the analyzer via a 20dB directional coupler. The AC output of the reference detector is given at Channel A(CHA) and the output from the DUT is given to Channel B(CHB). We got plots of the ratios between the reference detector, DUT and the coupled refernce for the Transfer Function and the Phase. I stored the data under the directory.../scripts/general/netgpibdata/data. The Bode Plot has been attached below and seeing it we observe that the cut-off frequency for the ET-3010 model is atleast over 500 MHz(stated as >1.5 GHz in the data sheet).


The bandwidth of the ET-3010 PD is atleast 500MHz, stated in the data sheet as >1.5GHz.


The ET-3010 PD has an internal power supply of 6V. Don't leave the PD connected to any instrument after the experimentation is done or else the batteries will get drained if there is any photocurrent on the PDs.

To Do:

Caliberate the vertical axis in the Bode Plot with transimpedance(Ohms) for the two PDs. Automate the procedure by making a Python script for taking multiple set of readings from the Netwrok Analyzer and aslo plot the error bands.

Attachment 1: PD_test_setup.png
Attachment 2: ET-3010_test.pdf
Attachment 3: ET-3010_test.zip
  13016   Sat May 27 10:26:28 2017 KaustubhUpdateGeneralTransimpedance Calibration

Using Alberto's paper LIGO-T10002-09-R titled "40m RF PDs Upgrade", I calibrated the vertical axis in the bode plots I had obtained for the two PDs ET-3010 and ET-3040.

I am not sure whether the values I have obtained are correct or not(i.e. whether the calibration is correct or not). Kindly review them.

EDIT: Attached the formula used to calculate transimpedance for each data point and the values of other paramaters.

EDIT 2: Updated the plots by changing the conversion for gettin ghte ratio of the transfer functions from 10^(y/10) to 10^(y/20).

Attachment 1: ET-3040_test_transimpedance.pdf
Attachment 2: ET-3010_test_transimpedance.pdf
Attachment 3: Formula_for_Transimpedance.pdf
  13077   Fri Jun 23 02:43:43 2017 KaustubhHowToComputer Scripts / ProgramsTaking Measurements From AG4395A


I have written a code(a basic one which needs a lot of improvements, but still does the job) for taking multiple measurements from the AG4395A. I have also written a separate code for plotting the data taken from the previoius code along with the error bars upto 1 standard deviation.


Details on How To Operate AG4395A:

  1. Under 'Measurement' tab, press the 'Meas' button and select the Analyzer Type (Network Analyzer or Spectrum Analyzer).
  2. Then under the same options select which 'ratio' needs to be measured (A/R, B/R or A/B).
  3. Then press the 'Format' button to select what needs to be measured (Eg - Log|Mag|, Phase, etc.).
  4. In order to measure and see two channels at the same time (Eg - Log|Mag| and Phase), press the 'Display' button and select 'Dual Channel'.
  5. Using the 'Scale' button we can set the scale/div or use autoscale and also set the attenuator values of the different channels.
  6. The 'Bw/Avg' option gives us an averaging option which averages few sets of data to produce the result. In doing this we lose quiet a lot of data and the resulting plot isn't able to give us the information on the statistical errors.
  7. This option also allows us to set the 'Intermediate Frequency' Bandwidth. This basically dictates the sampling rate of the Analyzer. The lower the IF bw, the higher is lesser is the noise (due to less uncertainty in Frequency).
  8. The 'Cal' button helps us calibrate the Analyzer to the current connections and signals. This is done because there is usually a difference in the 'cable lengths' for the two channels which introduces an extra phase term depnding upon the rf frequency. The calibration can be simply done by removing the Device Under Test (DUT) and diectly connecting the coaxial cables to the channels. After this the 'Calibrate Menu' allows us to calibrate the response using the short, open and thru methods.
  9. Now, under the 'Sweep' tab, the 'Sweep' button allows us to select various sweep options such as 'Sweep Time' (Auto, or set a time), 'Number of Points' (b/w 201-801) and 'Sweep Type' (Linear, Log, List Freq. etc.).
  10. Using the 'Source' button we can set the source power in dBm units (Usually kept as -20 to -10 dBm).
  11. The Scan Range can be set in a few ways such as using the start and end points or using the center and span range/width.
  12. After setting up all of the above, we can take the measurement either from the analyzer itself or using one of the control PCs. The command to download the data from AG4395A is netgpibdata -i -d AG4395A -a 10 -f [filename].


Brief Details on How the 'AGmeasure' command works:

AGmeasure is a python script developed by some of the people who work at 40m. It is set as a global command and can be used from within any directory. The source code is in the scripts folder on the network, or else it can also be found in Eric Quintero's git repository. This command accepts at the very least a parameter file. This is supposed to be a .yml file. A template (TFAG4395Atemplate.yml) can be found in the scripts folder or in Eric's repo. There are some other options that can be passed to this command, see the help for more details.


The Multi_Measurement Script:

This script calls the 'AGmeasure' command repetitively and keeps storing the data files in a folder. Right now, the script needs to be fed in th template file manually at prompt.


The Test_Plotting Script:

This script plots the a set of data files obtained from the above mentioned script and produces a plot along with the errors bands upto 1 standard deviation of the data. The format (names) and total number of text files need to be explicitly known, for now at least.



  1. The output test files and the two scripts.
  2. This is the 'Bode Plot' for a data set made using the above two scripts.


To Do:

  • Improve upon the two scripts to be as compatible as the AGmeasure function itself.
  • Try and incorporate the whole script into AGmeasure itself along with improving upon the templates.
  • The above details, with some edits perhaps, can go into the 40m wiki too(?).


Update: Increased the font size in the plot. Added a few comments to the two scripts

To Do: Need to consider the transfer function as a single physical quantity (both the magnitude and phase) and then take the averages and calculate the standard deviation and then plot these results. 



The attachment with the test files and the code now also contains a pdf with all the relations/equations I have used to calculate the averages and errors.

Attachment 1: Test_Files_and_Code.zip
Attachment 2: Bode_Plot_with_Error_Bands.pdf
  13078   Fri Jun 23 02:55:18 2017 KaustubhUpdateComputer Scripts / ProgramsScript Running

I am leaving a script running on the Pianoso for the night. For this purpose, even the AG4395A is kept on. I'll see the result of the script in the morning (it should be complete by then). Just check so before fiddling with the Analyzer.

Thank you.

  13086   Thu Jun 29 00:13:08 2017 KaustubhUpdateComputer Scripts / ProgramsTransfer Function Testing

In continuation to my previous posts, I have been working on evaluating the data on transfer function. Recently, I have calculated the correlation values between the real and imaginary part of the transfer function. Also I have written the code for plotting the transfer function data stream at each frequency in the argand plane just for referring to. Also I have done a few calculations and found the errors in magnitude and phase using those in the real and imaginary parts of the transfer function. More details for the process are in this git repository.

The following attachments have been added:

  1. The correlation plot at different frequencies. This data is for a 100 data files.
  2. The Test files used to produce the abover plot along with the code for the plotting it as well as the text file containing the correlation values. (Most of the code is commented as that part wasn't needed fo rhte recent changes.)



Seeing the correlation values, it sounds reasonable that the gaussian in real and imaginary parts approximation is actually holding. This is because the correlation values are mostly quite small. This can be seen by studying the distribution of the transfer function on the argand plane. The entire distribution can be seen to be somewhat, if not entirely, circular. Even when the ellipticity of the curve seems to be high, the curve still appears to be elliptical along the real and imaginary axes, i.e., correlation in them is still low.


To Do:

  1. Use a better way to estimate the errors in magnitude and phase as the method used right now is a only valid with the liner approximation and gives insane values which are totally out of bounds when the magnitude is extrmely small and the phase is varying as mad.
  2. Use the errors in the transfer function to estimate the coherence in the data for each frequency point. That is basically plot a cohernece Vs frequency plot showing how the coherence of the measurements vary as the frequency is varied.


In order to test the above again, with an even larger data set, I am leaving a script running on Ottavia. It should take more than just the night(I estimate around 10-11 hours) if there are no problems.

Attachment 1: Correlation_Plot.pdf
Attachment 2: 2x100_Test_Files_and_Code_and_Correlation_Files.zip
  13109   Mon Jul 10 21:31:15 2017 KaustubhHowToComputer Scripts / ProgramsDetails on Cavity Scan Analysis


The following elog describes the procedure followed for generating a sample simulation for a cavity scan, fitting an actual cavity scan and calculating the relevant paramaters using the cavity scan and fit data.


1. Cavity Scan Simulation:

  1. First, we define the sample cavity parameters, i.e., the reflectivitie,transmissivities of the mirrors, the RoCs of the mirrors and the absolute cavity length.
  2. We then define a frequency range using numpy.linspace function for which we want to take a scan.
  3. We then define a function that returns the tranmission power output of a Fabry-Perot cavity using the cavity equations as follows: P_{t} = \frac{t_{1}t_{2}}{1-r_{1}r_{2}\exp({\frac{4\pi Lf}{c}+(n+m+1)\phi_G)}} where Pt is the transmission power ratio of the output power to input power, t1,t2,r1,r2 are the transmissivities and reflectivities of the two mirrors, L is the absolute cavity length, f is the frequency of the input laser, c is the speed of light, \phi_G = \arccos{g_{1}g_{2}} is the gouy phase shift with g1,g2 being the g-factors for the two cavity mirrors(g=1-L/R). 'n' and 'm' correspond to the TEMnm higher order mode.
  4. We now obtain a cavity scan by giving the above defined function the cavity parameters and by adding the outputs for different higher order mode('n', 'm' values). Appropriate factors for the HOMs need to be chosen. The above function with appropriate coefficients can be used ti also add the modulated sidebands to the total transmission power.
  5. To this obtained total power we can add some random noise using numpy modules random.normal function. We need to normalise the data with respect to the max. power transmission ratio.
  6. We can now perform fitting on the above data using the procedure stated in the next section and then plot the two data sets using matplotlib module.
  7. A similar code to do the above is given here.


2. Fitting a Cavity Scan:

  1. The actual data for a cavity scan can be found in this elog entry or attached below in the zip folder.
  2. We read this data and separate the frequency data and the transmission data.
  3. Using the peakutils module's indexes function, we find the indices of the various peaks in the data set.
  4. These peaks are from the fundamental resonances, sideband resonances(both 11MHz and 55MHz) as well as a few HOMs.
  5. Each of these resonances follows the cavity equations and hence can be modelled as Lorentzian within small intervals around the peak frequencies. A detailed description of how this is possible is given here and is in the atached zip folder('Functionsused.pdf').
  6. We define a Lorentzian function which returns the fo\frac{a}{1+(\frac{\nu - \nu_0}{b})^{2}}llows:  where 'a' is the peak transmission value, 'b' is the 'linewidth' of the Lorentzian and \nu_0 is the peak frequency  about which the cavity equations behave like a lorentzian.
  7. We now, using the Lorentzian function, fit the various identified peaks using the curve_fit function of the scipy module. Remember to turn the 'absolute_sigma' parameter to 'True'.
  8. The parameters now obtained can be evaluated using the procedure given in the next section.
  9. The total transmission power is evaluated by feeding in the above obtained parameters back into the Lorentzian function and adding it for each peak.
  10. We can plot the actual data set and the data obtained using the fit of different peaks in a plot using matplotlib module. We can also plot the residuals for a better depiction of the fit quality.  
  11. The code to analyse the above mentioned cavity scan data is given here and attached below in the zip folder.


3. Calculating Physically Relevant Parameters:

  1. The data obtained from the fitting the peaks in the previous section now needs to be analysed in order to obtain some physically relevant information such as the FSR value, the TMS value, the modulation depths of the sidebands and perhaps even the linear caliberation of the frequency.
  2. First we need to identify the fundamental, TEM00 resonances among all the peaks. This we do by using the numpy.where function. We find the peaks with transmission values more than 0.9(or any suitable value).
  3. Using these indices we will now calculate the FSR and the Finesse of the peaks. A description of the correlation between the Fit Parameters and the FSR and Finesse is given here.
  4. We define a Linear fitting function for fitting the frequency values of the fundamental resonances against the ith fundamental resonance. The slope of this line gives us the value of FSR and the error in it.
  5. The Finesse can be calculated by fitting the linewidth with a constant function.
  6. The cavity length can be calculated using the FSR values as follows: L = \frac{c}{2\nu_{FSR}}.
  7. Now, the approximate positions of the sideband frequncies is given by 11*106%FSR and 55*106%FSR away from the fundamental, carrier resonances.
  8. The modulation depth, 'm', is given as \sqrt{\frac{P_{c}}{P_{s}}} = \frac{J_{0}(m)}{J_{1}(m)} where Pc is the carrier transmission power, Ps is the transmission power of the sideband and Jv is the Bessel Function of order 'v'.
  9. We define a function 'Bessel Ratio' using which we'll fit the transmission power ratio of the carrier to the sideband for the multiple sideband resonances.
  10. We also check for the Linearity in frequency data by plotting Fitting the frequencies corresponding to peaks in the actual data to ones obtained after fitting.
  11. After this we attempt to identify the other HOMs. For this we first determine a rough estimate for the value of TMS using the already known parameters of the mirrors,i.e., the RoC. We then look in small intervals (0.5 MHz) around frequencies where we would expect the HOMs to be, i.e., 1*TMS, 2*TMS, 3*TMS... away from the fundamental resonances. These positions are all modulo FSR.
  12. After identifying the HOMs, we take the difference from the fundamental resonance and then study these modulo the FSR.
  13. We perform a Linear Fit between these obtained values and (n+m).  As 'n','m' are degenerate, we can simply perform the fit against some variable 'k' and obtain the value of TMS as the slope of the linear fit.
  14. The code to do the above stated analysis is given here.


Most of the above info and some smaller details can be found in the markdown readme file in this git repo.

Attachment 1: Attachments.zip
  13116   Thu Jul 13 16:10:34 2017 KaustubhSummaryComputer Scripts / ProgramsCavity Scan Simulation Code

The code to produce a cavity scan simulation and then fitting the data and re-evaluating the initiallt set parameters can be found in this git repo.

The 'CavitScanSimulation' python script now produces a cavity scan with custom parameters which can be easily modified. It also introduces the first TEMs(n+m=0,1,2,3,4) to the laser with power going as (1/(2(n+m)+1))^2 {Selected carefully}. The only care that needs to be taken is that the frequency span should be somewhere near an integral multiple of the FSR so that there are equal number of resonances for all modes and sidebands. This code, as of now also calls the 'FitCavityScan' script which performs the fitting procedure on the data generated above{This data is actually written in a '.mat' file} and generates the Fit parameter data files. The Simulation code then calls the 'CalculatingPhysicalParameters' script which evaluates the data based on the Fit parameters and outputs some physically relevant results like the FSR, Finesse, Modulation Depths, TMS{Current Output is the Estimated RoCs of the two mirrors which isn't something we want directly, so it can be modified a bit to output TMS based on the HOMs}. The scripts do some 'Linearity' checks which might not really be of much significance but can be seen as a reference. Also, the ipython notebook will show all intermediate plots for the actual data and data with custom noise, fit data, FSR fitting, linearity checks, Bessel Ratio plot with mod_depths.


Note: The scripts should be run using either an IDE like 'spyder'{for .py files}{Comes with Anaconda} or using an ipython notebook{for .ipynb files}.
  13065   Thu Jun 15 14:24:48 2017 Kaustubh, JigyasaUpdateComputersOttavia Switched On

Today, I and Jigyasa connected the Ottavia to one of the unused monitor screens Donatella. The Ottavia CPU had a label saying 'SMOKED''. One of the past elogs, 11091, dated back in March 2015, by Jenne had an update regarding the Ottavia smelling 'burny'. It seems to be working fine for about 2 hours now. Once it is connected to the Martian Network we can test it further. The Donatella screen we used seems to have a graphic problem, a damage to the display screen. Its a minor issue and does not affect the display that much, but perhaps it'll be better to use another screen if we plan to use the Ottavia in the future. We will power it down if there is an issue with it.

  13067   Thu Jun 15 19:49:03 2017 Kaustubh, JigyasaUpdateComputersOttavia Switched On

It has been working fine the whole day(we didn't do much testing on it though). We are leaving it on for the night.


Today, I and Jigyasa connected the Ottavia to one of the unused monitor screens Donatella. The Ottavia CPU had a label saying 'SMOKED''. One of the past elogs, 11091, dated back in March 2015, by Jenne had an update regarding the Ottavia smelling 'burny'. It seems to be working fine for about 2 hours now. Once it is connected to the Martian Network we can test it further. The Donatella screen we used seems to have a graphic problem, a damage to the display screen. Its a minor issue and does not affect the display that much, but perhaps it'll be better to use another screen if we plan to use the Ottavia in the future. We will power it down if there is an issue with it.


  13068   Fri Jun 16 12:37:47 2017 Kaustubh, JigyasaUpdateComputersOttavia Switched On

Ottavia had been left running overnight and it seems to work fine. There has been no smell or any noticeable problems in the working. This morning Gautam, Kaustubh and I connected Ottavia to the Matrian Network through the Netgear switch in the 40m lab area. We were able to SSH into Ottavia through Pianosa and access directories. On the ottavia itself we were able to run ipython, access the internet. Since it seems to work out fine, Kaustubh and I are going to enable the ethernet connection to Ottavia and secure the wiring now.  


It has been working fine the whole day(we didn't do much testing on it though). We are leaving it on for the night.


Today, I and Jigyasa connected the Ottavia to one of the unused monitor screens Donatella. The Ottavia CPU had a label saying 'SMOKED''. One of the past elogs, 11091, dated back in March 2015, by Jenne had an update regarding the Ottavia smelling 'burny'. It seems to be working fine for about 2 hours now. Once it is connected to the Martian Network we can test it further. The Donatella screen we used seems to have a graphic problem, a damage to the display screen. Its a minor issue and does not affect the display that much, but perhaps it'll be better to use another screen if we plan to use the Ottavia in the future. We will power it down if there is an issue with it.



  13071   Fri Jun 16 23:27:19 2017 Kaustubh, JigyasaUpdateComputersOttavia Connected to the Netgear Box

I just connected the Ottavia to the Netgear box and its working just fine. It'll remain switched on over the weekend.


Kaustubh and I are going to enable the ethernet connection to Ottavia and secure the wiring now.  


  5273   Sat Aug 20 00:42:22 2011 KeikoUpdateLSCTolerance of PRC, SRC, MICH length = 2 mm ?

 Keiko, Kiwamu

 I have run Kiwamu's length tolerance code (in CVS iscmodeling, ArmTolerance.m & analyseArmTorelance.m ) for the vertex ifo.

In his previous post, he monte-carlo-ed the arm lengths and saw the histogram of the sensing matrix and the demodulation phase between POP55 MICH and POP55 SRCL. From these plots, he roughly estimated that the tolerance is about 1 cm (sigma of the rondom gaussian) and in that case POP55 MICH and SRCL is separated by the demodulation phase 60-150 degrees.

This time I put the length displacements of random gaussian on PRC, SRC, MICH lengths at the same time (Fig.1).



Fig. 1. History of random walk in PRC, SRC, MICH lengths parameter space. Same as Kiwamu's previous post, The position of the three degrees are randomly chosen with a Gaussian distribution function in every simulaton. This example was generated when \sigma = 1 cm for all the three lengths, where \sigma is the standard deviation of  the Gaussian function. The number of simulation is 1000 times.

When the sigma is 1 cm, we found that the sensing matrix is quite bad if you look at Fig. 2. In Fig.2 row POP55, although the desired degrees of freedoms are MICH and SRCL, they have quite a bit of variety. Their separation in the demodulation phase is plotted in Fig.3. The separation in the demodulation phase varies from 40 degrees to 140 degrees, and around 270 degrees. It is not good as ideally we want it to be 90.


Fig. 2 Histgram of the sensing signal power in the matrix when 1 cm sigma rondom gaussian is applied on PRC, SRC, MICH lengths. x axis it the signal power in log10.




  Fig.3 POP55 MICH and POP55 SRCL separation with the displacement sigma 1 cm. 


 Kiwamu suspected that PRC length as more strict tolerance than other two (SRC, MICH) for POP55, as 55MHz is fast and can be sensitive to the arm length change. So I ran the same monte-carlo with SRC, MICH displacements but no PRC displacements when sigma is the same, 1cm. The results were almost same as above, nothing obvious difference.


With 2mm sigma, the signal power matrix and the POP55 MICH and POP55 SRCL separation in the demodulation phase look good (Fig. 4 and Fig. 5). 


 Fig.4 Signal power matrix when PRC, SRC, MICH lengths fractuate with random gaussian distribution with 2mm sigma. The signal powers are shown in log10 in x axis, and they do not vary very much in this case.


 Fig.5 POP55 MICH and POP55 SRCL separation with the displacement sigma 2 mm. The separation of the two signal is 60-90 degrees, much better than when sigma is 1 cm. We may need to check 60 degree separation is really ok or not.


PRC SRC MICH lengths tolerances of 2 mm in the real world will be very difficult ! 

Next I will check what happens on 3f signals.




 Required arm length = 37.7974 +/- 0.02 [m]

This is a preliminary result of the estimation of the Arm length tolerance.

This number was obtained from a simulation based on Optickle.
Note that the simulation was done by considering misplacements in only the arm lengths while keeping PRCL, SRCL and MICH at the ideal lengths.
Therefore the tolerance will be somewhat tighter if misplacements in the central part are taken into account.

Next : check 3f signals, and include misplacements in PRCL, SRCL and MICH.



Figure.2  A sensing matrix of the 40-m DRFPMI while changing the position of ETMX/Y by \sigma = 2 cm.
For convenience,  only REFL11, AS55, POP11 and POP55 are shown. They are the designed signal ports that
mentioned in the aLIGO LSC document (T1000298). In all the histograms, x-axis represents the optical gain in log scale in units of [W/m].
The y-axis is the number of events. The diagonal ports are surrounded by red rectangular window.
(Results2 : demodulation phase of MICH and SRCL on POP55)
Now a special attention should be payed on the MICH and SRCL signals on POP55.
Since MICH and SRCL are designed to be taken from POP55, they must be nicely separated in their demodulation phases.
Therefore the demodulation phase of MICH and SRCL has to be carefully examined.
The plot in Figure.3 is the resultant phase difference between MICH and SRCL on POP55 when \sigma_x = \sigma_y = 2 cm.
As shown in the plot the phase are always within a range of 60 - 120 deg, which satisfies my requirement (2) mentioned in the last section.
 Figure.3 Difference in the demodulation phase of MICH and SRCL on POP55.
x-axis is the difference in the demodulation phase of MICH and SRCL, and y-axis the number of events.



  5292   Tue Aug 23 17:51:37 2011 KeikoUpdateLSCTolerance of PRC, SRC, MICH length = 2 mm ?

Keiko, Kiwamu

We noticed that we have used wrong code for MICH degree of freedom for both of the ELOG entries on this topic (cavity lengths tolerance search). It will be modified and posted soon.

  5334   Fri Sep 2 04:41:35 2011 KeikoUpdateLSCTolerance of PRC, SRC, MICH length = 5 mm ?

 Keiko, Kiwamu

Length tolerance of the vertex part is about 5 mm.

Sorry for my procrastinating update on this topic. In my last post, I reported that the length tolerance of the vertex ifo would be 2mm, based on Kiwamu's code on CVS. Then we noticed that the MICH degrees of freedom was wrong in the code. I modified the code and ran again. You can find the modified codes on CVS (40m folder, analyzeDRMITolerance3f.m and DRMITolerance.m)

In this code, the arm lengths were kept to be ideal while some length offsets of random gaussian distribution were added on PRCL, SRCL and MICH lengths. The iteration was 1000 times for each sigma of the random gaussian distribution. The resulting sensing matrix is shown as histogram. Also, a histogram of the demodulation phase separation between MICH and SRCL is plotted by this code, as these two length degrees of freedom will be obtained by one channel separated by the demodulation phase. We check this separation because you want to make sure that the random length offsets does not make the separation of these two signals close.

The result is a bit different from the previous post, in the better way! The length tolerance is about 5 mm for the vertex ifo. Fig.1 shows the sensing matrix. Although signal levels are changed by the random offsets, only few orders of magnitude is changed in each degrees of freedom. Fig.2 shows that the signal separation between MICH and SRCL at  POP55 varies from  55 to 120 degrees, which may be OK. If you have 1cm sigma, it varies from 50 degrees to 150 degrees.


Fig. 1 Histgram of the sensing matrix including 3f channels, when sigma is 5mm. Please note that the x-axis is in long 10.


 Fig. 2 Histogram of the demodulation phase difference between MICH and SRCL, when sigma is 5 mm. To obtain the two signals independently, 90 is ideal. With the random offsets, the demodulation phase difference varies from 55 degrees to 120 degrees.

My next step is to run the similar code for LLO. 

  5377   Sat Sep 10 14:55:28 2011 KeikoUpdateLSC3f demodulation board check

 To check the demodulation boards for REFL33 and REFL165, a long cable from ETMY (SUS-ETMY-SDCOIL-EXT monitor) is pulled to the rack on Y side.

(1) A filter just after the RF input and (2) transfer function from the RF input to the demodulated signal will be checked for the two 3f demod boards to confirm that they are appropriate for 33 and 165 MHz.

ELOG V3.1.3-