ID |
Date |
Author |
Type |
Category |
Subject |
2554
|
Fri Jan 29 13:14:49 2010 |
Alberto | Update | ABSL | Measurement running today at lunch time |
Quote: |
I just started a measuremtn that will be running for the next hour or so. Please be careful with the interferometer.
|
Done. IFO available |
2576
|
Mon Feb 8 14:13:03 2010 |
Alberto | Update | ABSL | PLL Characterization |
Lately I've been trying to improve the PLL for the AbsL experiment so that it could handle larger frequency steps and thus speed up the cavity scan.
The maximum frequency step that the PLL could handle withouth losing lock is given by the DC gain of the PLL. This is the product of the mixer's gain factor K [rad/V ], of the laser's calibration C [Hz/V] and of the PLL filter DC gain F(0).
I measured these quantities: K=0.226 V/rad; C=8.3e6 Hz/V and F(0)=28.7dB=21.5. The max frequency step should be Delta_f_max = 6.4MHz.
Although in reality the PLL can't handle more than a 10 KHz step. There's probably some other effect that I'm not.
I'm attaching here plots of the PLL Open Loop Gain, of the PLL filter and of a spectra of the error point measured in different circumstances.
I don't have much time to explain here how I took all those measurements. After I fix the problem, I'm going to go go through those details in an elog entry.
Does anyone have any suggestion about what, in principle, might be limiting the frequency step?
I already made sure that both cables going to the mixer (the cable with the beat signal coming from the photodiode and the cable with the LO signal coming from the Marconi) had the same length. Although ideally, for phase locking, I would still need 90 degrees of phase shift between the mixing signals, over the entire frequency range for which I do the cavity scan. By now the 90 degrees are not guaranteed.
Also, I have a boost that adds another 20 dB at DC to the PLL's filter. Although it doesn't change anything. In fact, as said above calculating the frequency step, the PLL should be able to handle 100KHz steps, as I would want the PLL to do. |
2577
|
Mon Feb 8 14:56:17 2010 |
Alberto | Update | ABSL | Suddenly a much better alignment of PRC |
I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.
Isn't anyone related to that? If so, may I please know how he/she did it? |
2578
|
Mon Feb 8 15:01:46 2010 |
rob | Update | ABSL | Suddenly a much better alignment of PRC |
Quote: |
I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.
Isn't anyone related to that? If so, may I please know how he/she did it?
|
oops, my bad. I cranked the 33MHz modulation depth and forgot to put it back. The slider should go back to around 3. |
2579
|
Mon Feb 8 15:41:51 2010 |
Alberto | Update | ABSL | Suddenly a much better alignment of PRC |
Quote: |
Quote: |
I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.
Isn't anyone related to that? If so, may I please know how he/she did it?
|
oops, my bad. I cranked the 33MHz modulation depth and forgot to put it back. The slider should go back to around 3.
|
I was actually hoping that the alignment got better. |
2581
|
Tue Feb 9 09:07:06 2010 |
Alberto | Update | ABSL | PLL Characterization |
Quote: |
Lately I've been trying to improve the PLL for the AbsL experiment so that it could handle larger frequency steps and thus speed up the cavity scan.
The maximum frequency step that the PLL could handle withouth losing lock is given by the DC gain of the PLL. This is the product of the mixer's gain factor K [rad/V ], of the laser's calibration C [Hz/V] and of the PLL filter DC gain F(0).
I measured these quantities: K=0.226 V/rad; C=8.3e6 Hz/V and F(0)=28.7dB=21.5. The max frequency step should be Delta_f_max = 6.4MHz.
Although in reality the PLL can't handle more than a 10 KHz step. There's probably some other effect that I'm not.
I'm attaching here plots of the PLL Open Loop Gain, of the PLL filter and of a spectra of the error point measured in different circumstances.
I don't have much time to explain here how I took all those measurements. After I fix the problem, I'm going to go go through those details in an elog entry.
Does anyone have any suggestion about what, in principle, might be limiting the frequency step?
I already made sure that both cables going to the mixer (the cable with the beat signal coming from the photodiode and the cable with the LO signal coming from the Marconi) had the same length. Although ideally, for phase locking, I would still need 90 degrees of phase shift between the mixing signals, over the entire frequency range for which I do the cavity scan. By now the 90 degrees are not guaranteed.
Also, I have a boost that adds another 20 dB at DC to the PLL's filter. Although it doesn't change anything. In fact, as said above calculating the frequency step, the PLL should be able to handle 100KHz steps, as I would want the PLL to do.
|
I might have found the problem with the PLL that was preventing me from scanning the frequencies by 100KHz steps. A dumb flimsy soldering in the circuit was making the PLL unstable.
After I fixed that problem and also after writing a cleverer data acquisition script in Python, I was able to scan continuosly the range 10-200MHz in about 20min (versus the almost 1.5-2 hrs that I could do previously). I'm attaching the results to this entry.
The 'smears' on the right side of the resonance at ~33MHz, are due to the PSL's sideband. I think I know how to fix that.
As you can see, the problem is that the model for the cavity transmission still does not match very well the data. As a result, the error on the cavity length is too big (~> 10 cm - I'd like to have 1mm).
Anyway, that was only my first attempt of scanning. I'm going to repeat the measurement today too and see if I can come out better. If not, than I have to rethink the model I've been using to fit. |
2582
|
Tue Feb 9 10:10:58 2010 |
Alberto | Update | ABSL | back to analog |
I want to try to do the measurement with the network analyzer used as local oscillator, instead of the Marconis that I'm using now. Tha could give me better noise rejection. It would also give me information about the phase.
Also I wouldn't dislike abandoning the GPIB interfaces to acquire data. |
2679
|
Thu Mar 18 10:46:51 2010 |
Koji | Update | ABSL | PLL reconstructed |
Last night (Mar 17) I checked the PLL setup as Mott have had some difficulty to get a clean lock of the PLL setting.
- I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
- The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
- Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
- In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.
Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...
Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc) |
2680
|
Thu Mar 18 12:27:56 2010 |
Alberto | Update | ABSL | PLL reconstructed |
Quote: |
Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.
- I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
- The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
- Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
- In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.
Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...
Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc)
|
I also had noticed the progressive change of the aux NPRO alignment to the Farady.
I strongly agree about the need of a good and robust PLL.
By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.
I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that? |
2681
|
Thu Mar 18 13:40:35 2010 |
Koji | Update | ABSL | PLL reconstructed |
We use the current PLL just now, but the renewal of the components are not immediate as it will take some time. Even so we need steady steps towards the better PLL. I appreciate your taking care of it.
Quote: |
Quote: |
Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.
- I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
- The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
- Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
- In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.
Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...
Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc)
|
I also had noticed the progressive change of the aux NPRO alignment to the Farady.
I strongly agree about the need of a good and robust PLL.
By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.
I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that?
|
|
2684
|
Thu Mar 18 21:42:26 2010 |
Koji | Update | ABSL | PLL reconstructed |
I checked the setup further more.
- I replaced the PD from NewFocus 1GHz one to Thorlabs PDA255.
- I macthed the power level of the each beam.
Now I have significant fraction of beating (30%) and have huge amplitude (~9dBm).
The PLL can be much more stable now.
Koji |
2696
|
Mon Mar 22 22:11:26 2010 |
Mott | Update | ABSL | PLL reconstructed |
It looks like the PLL drifted alot over the weekend, and we couldn't get it back to 9 dBm. We switched back to the new focus wideband PD to make it easier to find the beat signal. I replaced all the electronics with the newly fixed UPDH box (#17) and we aligned it to the biggest beat frequency we could get, which ended up being -27 dBm with a -6.3V DC signal from the PD.
Locking was still elusive, so we calculated the loop gain and found the UGF is about 45 kHz, which is too high. We added a 20 dB attenuator to the RF input to suppress the gain and we think we may have locked at 0 gain. I am going to add another attenuator (~6 dB) so that we can tune the gain using the gain knob on the UPDH box.
Finally, attached is a picture of the cable that served as the smb - BNC adaptor for the DC output of the PD. The signal was dependent on the angle of the cable into the scope or multimeter. It has been destroyed so that it can never harm another innocent experiment again! |
2697
|
Mon Mar 22 23:37:32 2010 |
Mott | Update | ABSL | PLL reconstructed |
We have managed to lock the PLL to reasonable stability. The RF input is attenuated by 26 dBm and the beat signal locks very close to the carrier of the marconi (the steps on the markers of the spectrum analyzer are coarse). We can use the marconi and the local boost of the pdh box to catch the lock at 0 gain. Once the lock is on, the gain can be increased to stabilize the lock. The locked signals are shown in the first photo (the yellow is the output of the mixer and the blue is the output to the fast input of the laser. If the gain is increased too high, the error signal enters an oscillatory regime, which probably indicates we are overloading the piezo. This is shown in the second photo, the gain is being increased in time and we enter the non-constant regime around mid-way through.
Tomorrow I will use this locked system to measure the PZT response (finally!). |
2703
|
Tue Mar 23 18:44:46 2010 |
Mott | Update | ABSL | PLL reconstructed |
After realigning and getting the lock today, I tried to add in the SR785 to measure the transfer function. As soon as I turn on the piezo input on the PDH box, however, the lock breaks and I cannot reacquire it. We are using an SR650 to add in the signal from the network analyzer and that has worked. We also swapped the 20 dB attenuator for a box which mimics the boost functionality (-20 dB above 100 Hz, 0 dB below 6Hz). I took some spectra with the SR750, and will get some more with the network analyzer once Alberto has finished with it.
The SR750 spectra is posted below. The SR750 only goes up to 100 kHz, so I will have to use the network analyzer to get the full range. |
4832
|
Fri Jun 17 16:05:07 2011 |
kiwamu | Update | ABSL | LightWave out of MOPA box |
[Suresh / Kiwamu]
We did the following things :
- Took the LightWave NPRO out from the MOPA box
- Temporarily took out the laser controller which has been connected to the Y end laser.
- Put the LightWave on AP table and plugged the laser controller and confirmed that it still emits a beam

[Things to be done]
- measure the beam profiles and power
- get a laser controller, which will be dedicated for this laser, from Peter King
[Background and Motivation]
The PRC and SRC length have to be precisely measured before the vent.
In order to measure those absolute length we are going to use the Stochino technique, which requires another laser to scan the cavity profiles.
The LightWave NPRO laser in the MOPA box was chosen for the Stochino laser because it has a large PZT range of 5 MHz/V and hence allows us to measure a wider frequency range.
The laser in the MOPA box had been connected to home-made circuits, which are not handy to play with. So we decided to use the laser with the usual laser controller.
Peter King said he has a LightWave laser controller and he can hand it to us.
Until we get the controller from him we do some preparations with temporary use of the Y end laser controller. |
4840
|
Mon Jun 20 11:38:49 2011 |
kiwamu | Update | ABSL | I-P curve of LightWave M126-1064-700 |
The I-P curve of the LightWave NPRO (M126-1064-700), which was taken out from the MOPA box, was measured. It looks healthy.
The output power can go up to about 1 W, but I guess we don't want it to run at a high power to avoid any further degradation since the laser is old.

X-axis is the current read from the display of the controller. Y-axis is the output power, directly measured by Coherent PM10.
The measurement was done by changing the current from the controller.
Quote from #4832 |
[Things to be done]
- measure the beam profiles and power
- get a laser controller, which will be dedicated for this laser, from Peter King
|
|
4841
|
Mon Jun 20 13:48:25 2011 |
Koji | Update | ABSL | I-P curve of LightWave M126-1064-700 |
Hmm. Was the current within the operating range? (i.e. Is it a 700mW laser or a 1W one?)
You can obtain the nominal operating current from the old EPICS values (or some elog entries).
Note that NPROs are designed to be healthy only at around the nominal pumping power
(i.e. thermal gradient, and thermal lensing of the crystal, etc.)
ALSO:
Be aware that this laser should be used under the old SOP. So the appropriate interlocking is mandatory.
And probably we need to modify the SOP such that it reflects the latest situation.
Quote: |
The I-P curve of the LightWave NPRO, which was taken out from the MOPA box, was measured. It looks healthy.
The output power can go up to about 1 W, but I guess we don't want it to run at a high power to avoid any further degradation since the laser is old.
|
|
4842
|
Mon Jun 20 16:44:02 2011 |
steve | Update | ABSL | I-P curve of LightWave M126-1064-700 |
Put the serial numbers into the elog. So we can identify the laser and controller in the future.
The old days the NPRO ( inside the MOPA ) was running ~1.7A 500 mW |
4855
|
Wed Jun 22 15:24:10 2011 |
kiwamu | Update | ABSL | got a laser controller for LightWave |
Peter King came over to the 40m with a laser controller and gave it to us.
We will test it out with the LightWave NPRO, which was used for MOPA. |
4872
|
Thu Jun 23 22:59:45 2011 |
kiwamu | Update | ABSL | I-P curve of LWE |
The I-P curve was measured again, but this time in a lower current range of 1.0-1.9 [A].
The plot below is the latest I-P curve.

(Decision)
Based on the measurement and some thoughts, I decided to run this laser at about 1.8 [A] which gives us a middle power of ~ 360 [mW].
In the 40m history, the laser had been driven at 2.4 [A] in years of approximately 2006-2009, so it's possible to run it at such a high power,
but on the other hand Steve suggested to run it with a smaller power such that the laser power doesn't degrade so fast.
(notes)
The laser controller handed from PK (#4855) was used in this measurement.
The nominal current was tuned to be 1.8 [A] by tuning a potentiometer on the laser head (see page.18 on the manual of LWE).
There was a huge bump around 1.4 [A] and sudden power drop at 1.48 [A] although I don't know the reason.
Quote from #4842 |
The old days the NPRO ( inside the MOPA ) was running ~1.7A 500 mW
|
|
4874
|
Fri Jun 24 00:13:24 2011 |
kiwamu | Update | ABSL | beam profile measurement of LWE |
The beam profile of the LWE (LightWave Electronics) NPRO was measured.
Mode matching telescopes will be designed and setup soon based on the result of the measurements.
Here is a plot of the measured beam profile.

(some notes)
The measurement was done by using Kevin's power attenuation technique (#3030).
An window was put just after the NPRO and the reflected beam was sampled for the measurement to avoid the beam scan saturated. |
4877
|
Fri Jun 24 07:49:23 2011 |
steve | Update | ABSL | I-P curve of LWE with serial numbers |
Quote: |
The I-P curve was measured again, but this time in a lower current range of 1.0-1.9 [A].
Quote from #4842 |
The old days the NPRO ( inside the MOPA ) was running ~1.7A 500 mW
|
|
Lightwave Laser Head M126-1064-700 sn238, mounted on full size Al base and side heat sink on
Controller 125/126 Smart Supply sn 201M |
4917
|
Thu Jun 30 03:26:40 2011 |
kiwamu | Update | ABSL | status update |
Status update of the absolute length (ABSL) measurement:
- To accommodate the ABSL stuff, the AS path was relocated on the AP table.
(In this evening Jenne was able to lock MICH with AS55, so it's working fine.)
- On the AP table all of the necessary items, including the NPRO, a Faraday, some mirrors and etc., were in place
- The mode matching was coarsely done. The Rayleigh range looked reasonably long.
- Fine alignments will be done tomorrow
- Also a picture of the setup will be uploaded in the morning. |
4923
|
Thu Jun 30 14:11:55 2011 |
kiwamu | Update | ABSL | a photo of ABSL setup on the AP table |
Here is a picture of the latest ABSL setup at the east part of the AP table.

(Some notes )
- The ABSL laser is injected from the AP port.
- A 90 % reflection BS was installed just after the NPRO, this is for sampling a 10% of the laser to the PSL table.
However, I've just realized that this is not a nice way because the 10 % beam doesn't go through the Faraday. Whoops.
- A polarzser cell at the input side of the Faraday doesn't let any beam go through it for some reasons (broken ?).
Therefore instead of having such a bad cell, a cube PBS was installed.
- A room was left on the table for the AS165 RFPD (green-dashed rectangular in the picture).
Quote from #4917 |
- Also a picture of the setup will be uploaded in the morning.
|
|
4925
|
Thu Jun 30 21:00:20 2011 |
kiwamu | Update | ABSL | fine alignment done |
(Just a quick report)
The fine alignment of the ABSL laser injection was successfully done.
I was able to see the DRMI fringings at the AS camera. The ABSL beam is injected from the AS port, therefore what I saw on the camera was the reflection back from the interferometer.
(Things to be done)
- A beat-note setup on the PSL table.
- Refinement of the mode matching. The beam spot on the AS camera is a bit bigger, so I should more tightly focus the injected beam.
Quote from #4917 |
- Fine alignments will be done tomorrow
|
|
4939
|
Tue Jul 5 16:09:54 2011 |
kiwamu | Update | ABSL | some photos for ABSL setup |
Here I show two photos of the latest ABSL (ABSolute Length measurement) setup.

Figure.1 : A picture of the ABSL setup on the AP table.
The setup has been a little bit modified from the before (#4923).
As I said on the entry #4923, the way of sampling the ABSL laser wasn't so good because the beam, which didn't go through the faraday, was sampled.
In this latest configuration the laser is sampled after the faraday with a 90% beam splitter.
The transmitted light from the 90% BS (written in pink) is sent to the PSL table through the access tube which connects the AP and PSL table .

FIgure.2: A picture of the ABSL setup on the PSL table.
The 10% sampled beam ( pink beam in the picture) eventually comes to the PSL table via the access tube (the hole on the left hand side of the picture).
Then the ABSL beam goes through a mode matching telescope, which consists of a combination of a concave and a convex lens.
The PSL laser (red line in the picture) is sampled from a point after the doubling crystal.
The beam is combined at a 50 % BS, which has been setup for several purposes( see for example #3759 and #4339 ) .
A fast response PD (~1 GHz) is used for the beat-note detection. |
4940
|
Tue Jul 5 17:38:46 2011 |
kiwamu | Update | ABSL | ABSL laser frequency-locked |
In this past weekend the ABSL laser was successfully frequency-locked to the PSL laser with a frequency offset of about 100 MHz.
In the current setup a mixer-based frequency discriminator is used for detection of the beat-note frequency.
Setup for frequency locking
The diagram below shows the setup for the frequency locking.

(UGF)
According to a brief check of the loop oscillation it implies that the UGF is around 40 kHz.
Of course I will measure the open-loop over a wide frequency range at some point.
The lock was quite robust and it was able to stay locked for more than an hour as far as I observed.
(Beat-note detection and its amplification)
The fast RFPD, which is standing on the PSL table to detect the beat-note ( see the picture on #4939), showed the signal level of -16 dBm.
Then the signal goes through the RF amplifier stage to have an appropriate power level at the mixer in the frequency detection stage.
Before the signal goes into the amp. stage I put a power splitter so that I can see a signal on a spectrum analyzer.
(Frequency detection)
In the mixer-based frequency discriminator, the length difference between two coax. cable was chosen to be 1 m.
This length difference gives us a zero cross point (operation point) of ~100 MHz and linear range of ~ +/-100MHz, which can sufficiently cover the FSR of PRC: 22MHz.
(Control filter)
After the signal goes through the freq. discriminator, a low noise amplifier, ITHACO 1201 was installed as a control filter.
The reason I chose ITHACO 1201 was that it has a larger output range than that of SR560.
ITHACO 1201 can go to +/- 15V, which means the ABSL laser should be able to track the frequency by about +/- 65 MHz without a thermal actuation.
Right now a single pole was put at 1 Hz for an easy lock.
The output from 1201 goes directly to the laser PZT, whose input is on the front panel of the laser controller.
Temperature setpoints
During the work I found three temperature points, where we can observe the beat-note signal within a bandwidth of 1 GHz.
Here is a summary of the temperature set points :
PSL temperature = 31.71 deg
ABSL temperature = 44.19 deg (not good),
47.25 deg (chosen to be nominal set point),
50. 23 deg
The first one (44.19 deg) wasn't good because changing the temperature of the ABSL laser also changes the amplitude of the beat-note significantly.
In a worst case the signal completely disappeared when the ABSL laser was at a certain temperature close to 44.19 deg.
The other two temperature points seemed good. I eventually chose the second one (47.25 deg) for the nominal set point.
Note that the current readout has been 1.81 A on the laser controller. |
5079
|
Mon Aug 1 04:08:24 2011 |
kiwamu | Update | ABSL | Arm length measurement : cavity kick technique |
I made some attempts to measure the current length of the arm cavities by using the mass-kicking technique.
However unfortunately I am running out my energy to complete the measurement,
so I will finish the measurement at some time today.
I still have to set an appropriate kick amplitude. Right now I am injecting AWG into ETMY_LSC_EXC at 0.2 Hz with amplutde of 400 cnts.
I guess it needs a little bit more amplitude to get more psuedo-constant velocity.
Volunteers are always welcome !
(some notes)
The procedure was well-described in entry #555 by Dr.Stochino.
Here is just an example of the time series that I took today showing how the time series looks like.

|
5095
|
Tue Aug 2 16:55:21 2011 |
rana | Update | ABSL | Arm length measurement : cavity kick technique |
Quote: |
I made some attempts to measure the current length of the arm cavities by using the mass-kicking technique.
|
Why not just scan the Green laser to measure the arm lengths instead? The FSR of the arm is ~3.75 MHz and so all you have to do is lock the arm green and then sweep the PZT until the resonance is found at 3.75 MHz.

|
5117
|
Thu Aug 4 09:42:19 2011 |
Koji | Update | ABSL | ABSL Laser shutter closed |
The shutter of the ABSL laser is closed for the vent work. |
8257
|
Fri Mar 8 12:57:57 2013 |
Annalisa | Update | ABSL | BS installed on ITMY table |
Sendhil and I installed the S polarized BS on the ITMY table to steer the NPRO beam through the AR wedge and align it to the POY beam.
We took a shutter from the BSPRM table (which was not used) and a beam dump from the AS table (which was used by the auxiliary laser already removed and installed on the ITMY).
To do: do better alignment of the NPRO beam, maybe installing some iris after the BS and before the AS wedge, phase lock the two beams. |
8258
|
Fri Mar 8 13:42:35 2013 |
Jenne | Update | ABSL | BS installed on ITMY table |
Re: POY beam reduction.
We are able to lock the Yarm with the beam / gain as it is. I had thought we might need to increase the DC gain in the whitening board by a factor of 2, but so far it's fine. |
8303
|
Mon Mar 18 12:02:12 2013 |
Annalisa | Configuration | ABSL | ABSL setup for g-factor measurement of PRC |
Motivations
The ABSL technique has been already used in the past to measure the absolute length of the interferometer's optical cavities by means of an auxiliary laser source, as described in LIGO-P1200048-v3 and in Alberto Stochino thesis work.
Using the same technique it is possible to measure the g-factor of the power recycling cavity by measuring the cavity Transverse Mode Spacing.
Plan for experimental setup
The auxiliary laser is set on the POY table and is injected through the ITMY window in way to follow the same path of the POY beam. It hits the AR wedge of ITMY and is reflected back to the BS and the PRM.
Since the main beam is P-polarized, all the optics in the central IFO are P-polarization dependent, so it is useful to P-polarize the auxiliary beam before it enters the IFO.
I made a mode matching calculation with a la mode script, in order to mode match the auxiliary beam waist to the waist of the main laser.
However, before ordering and installing steering optics and mode maching lenses, I'm waiting to know whether someone has an NPRO laser to install on the END table in place of the broken one, otherwise the one I'm using could be taken.
In this case a possibility could be to take the auxiliary beam from the end table with an optical fiber, but it means to use the auxiliary laser alternately to lock the arm or make a measurement of TMS. If so, a new calculation for the mode matching needs to be done.
Anyway, I hope that another laser will be found!
In order to phase lock the auxiliary beam with the main beam, the latter will be taken from the PSL table after the PMC through a single mode fiber, which will be brought up to the POY table. This solution results to be more reliable then taking the POY beam to phase lock the two laser, because POY is related to the locking.
The signal with the beat note between the two lasers can be detected by the transmission from PR2 (POP).
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8361
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Wed Mar 27 21:53:21 2013 |
Annalisa | Update | ABSL | Beat note of ATF auxiliary laser |
After measuring the beat note, the "Alberto" NPRO auxiliary laser has been moved from the PSL table to the POY table. Its beam profile is going to be measured. It's going to be used as green laser on the END table, in place of the broken one.
The auxiliary laser borrowed form ATF lab (which will be used for the ABSL measurement) has been set on the PSL table to make a measurement of the beat note between it and the main laser.
The setup is mostly the same of the previous beat note measurement . In this case, laser input power is 326 mW, so I needed to replace one of the mirrors of the steering optics with a BS 50% reflecting in order to have less than 1 mW on the PD.
Now, the total power on the PD is less than 0.5 mW.
I didn't measure the beat note yet to leave the PSL table as quite as possible for the locking procedures.
To do:
Measure the beat note, fiber coupling the NPRO laser to bring it to the POY table.
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8369
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Thu Mar 28 23:00:30 2013 |
Annalisa | Update | ABSL | Beat note of ATF auxiliary laser found |
The beat note for the ATF lab laser has been found.
The measurement has been carried out in the same way as described in elog 8368.
The only difference is that in this case I started from a temperature of 35.2 degC, and I reduced it until the minimum which was 30.71 degC. No beat note in this range.
Then I rised on the temperature and I found the first beat note at 41.46 degC. It has been detected at a frequency of about 120 MHz with an RF power of -53 dBm and a frequency fluctuation of about +/- 5 MHz.
I tried to improve the alignment to have a stronger beat, but it was the maximum I could reach. Maybe I could increase the power hitting the photodiode, which was 0.453 mW.
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8495
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Fri Apr 26 10:50:07 2013 |
Annalisa | Update | ABSL | ATF laser on PSL |
The ATF NPRO auxiliary laser has been moved on the PSL table. All the optics for beat note measurement are in place and alignment has been done.
The setup for this measurement is the same as described in elog 8333. |
8590
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Thu May 16 08:32:05 2013 |
Steve | Update | 40m upgrading | ETMY op table disabled |
All ETMY optical table electronics- lasers-pds turned off, disconnected in order to remove enclosure.

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8594
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Fri May 17 00:32:32 2013 |
Annalisa | Update | 40m upgrading | ETMY - progress |
[Rana, Annalisa]
GREEN
The alignment for the green has been improved, so that we have much more green power.
The first lens position along the IR path has been changed in way to have the beam waist at the center of the first Faraday. In this way we had about 91% of the input power out from it.
The two cylindrical lenses which were used to correct the ellipticity of the beam have been replaced by a single lens. Its focal length is intermediate between the focal lengths of the two cylindrical.
Moving the position of the lens before the doubler crystal and improving the alignment we got about 1mW of green light (0.35% of the incoming IR beam).
TO DO
After aligning the green beam through the second Faraday, the beam waist of the outgoing beam has to be measured and the mode matching calculation has to be done to choose the two MM lenses. Then the steering mirrors will be placed to send the beam into the arm. |
8595
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Fri May 17 15:38:51 2013 |
Steve | Update | 40m upgrading | ETMY enclosure is on the way back |
It will arrive around 10 am Monday morning. 
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8596
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Fri May 17 16:06:14 2013 |
rana | Update | 40m upgrading | ETMY op table disabled |
TODO:
- We need to replace all of the floppy anodized Al dumps with clean razor blade dumps on stiff mounts. BOTH of the rejected ports of the 1064 FI need some kind of custom dump.
- All of the leakthrough beams of the HR mirrors also need razor dumps. A good rule of thumb is that your first notion of how to implement the beam dump is NOT good enough.
- The whole lens / modematching situation for the 1064 and 532 paths will have to be redone so as to put the beam waists inside the Faraday crystal (NOT outside). The beam waist in the 4.7 mm diameter Faraday should be ~0.3-0.4 mm.
- The efficiency that we got for the doubling shows that we don't need the cylindrical lenses - they are nice, but not needed to get 90% of the max power.
- The lenses between the 1064 FI and the doubler should be put onto a base that can be used to adjust the lens position for MM optimization. Nothing fancy, just something slideable.
- For this iteration of the table, we can do as Annalisa has written so as to get the green MM lenses ordered ASAP. After next week we can come up with a new plan before dismantling the EX table.
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8597
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Fri May 17 18:24:04 2013 |
Annalisa | Update | 40m upgrading | ETMY - progress |
I aligned the green beam into the Faraday. I needed an HWP to have the right polarization for the light entering the Faraday itself.
I tried to dump as much beams as possible with razor dumps, but eventually I had to use some "temporary solutions" for higher beams, because I didn't find the right mounts for razor dumps.
I measured the beam waist after the Faraday with the beam scan. Analysis and MM calculation to follow. |
8622
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Thu May 23 00:16:32 2013 |
Annalisa | Update | 40m upgrading | ETMY - progress |
[Annalisa, Koji]
GREEN
I aligned back the beam (we lost part of the alignment after we put back the box and after the posts were installed). The green beam out from the crystal is still low, but anyway I get about 1.2 mW of green out from the Faraday.
TO DO
Mode Matching calculation (tomorrow)
Fix the dumping situation
Replace some of the mounts with more solid ones (in the future)
TRANSMON PATH
QPD, PD and Camera have been rotated as Rana suggested last Wednesday. A 1m focal length lens is on the main beam transmitted path (before the harmonic separator), and the beam diameter on the QPD is about 5mm. We put another lens with a shorter focal length to put the PD very close to the beam waist and in way to have a reasonable beam size on the camera. Tomorrow I will write down all the correct sizes of the beams.
OPLEV
(for Steve) I marked a possible beam path for the Oplev (the laser is not in the right place in the picture, but I left it in the correct place on the table). I also put the QPD for the IP-ANG, so we know in which part of the table the beam can be steered.
The space in the red rectangle (right corner) has to be left empty to put a PD for the rejected beam from the green Faraday.
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8637
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Fri May 24 02:12:50 2013 |
Annalisa | Update | 40m upgrading | ETMY - Mode Matching for green |
Mode Matching calculation for green beam - Yarm
After measuring the beam radius out from the Faraday for the green, I made the calculation to match the green beam mode with the IR mode inside the arm.
The beam waist after the Faraday is elliptical, and I found the following value for the waist:
w0x = 3.55e-5 m @ z0x = -0.042 m
w0y = 2.44e-5 m @ z0y = -0.036 m
(the origin of the z axis is the output of the Faraday, so the waist is inside the Faraday itself)
I did the calculation using a la mode, using as beam waist and its position the following values:
w0 = sqrt(w0x*w0y) = 2.943e-5 m @ z0 = (z0x+z0y)/2 = -0.039 m
The results are shown in the attached plots.
Focal length (m) position (m)
lens1 0.125 0.1416
lens2 0.100 0.5225
L 1.000 1.5748 (fixed lens used to focus transmitted beam)
As the first plot shows, the green beam size on the ETMY is about 6mm. My concern is that it could be too big.
The third plot shows the X and Y section of the beam. It is strongly elliptical, but nevertheless the coupling factor calculated with Koji's formula gives C=0.936 for the astigmatic beam, and C=0.985 for the non astigmatic beam, so it seems to be still ok.
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8638
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Fri May 24 11:38:00 2013 |
Koji | Update | 40m upgrading | ETMY - Mode Matching for green |
I got confused. Is the mode calculation in the cavity correct?
Are you sure the wavelength in the code is 532nm?
The first plot says "the waist radius at ITMY is 2.15mm". This number is already very close to
the waist size of the cavity mode (2.1mm@ITM, 3.7mm@ETM), but the spot radius at ETMY is 6mm.
They are inconsistent.
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8639
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Fri May 24 12:50:25 2013 |
Annalisa | Update | 40m upgrading | ETMY - Mode Matching for green |
Quote: |
I got confused. Is the mode calculation in the cavity correct?
Are you sure the wavelength in the code is 532nm?
The first plot says "the waist radius at ITMY is 2.15mm". This number is already very close to
the waist size of the cavity mode (2.1mm@ITM, 3.7mm@ETM), but the spot radius at ETMY is 6mm.
They are inconsistent.
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Jenne and I just realized that a la mode has 1064e-9 m as default value. I'll change it and make the calculation again. |
8645
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Sat May 25 02:03:48 2013 |
Annalisa | Update | 40m upgrading | ETMY - Mode Matching for green - new calculation |
Mode matching calculation for green - Yarm
I did again the mode matching calculation. The previous one was using 1064nm as wavelength, so it was wrong.
The seed beam waist and its position are the same as in elog 8637. The new results are shown in the attached graphs.
I got the following values for focal lengths and positions of the two Mode Matching lenses:
Focal length (m) Distance from the Faraday output (m)
lens1 0.125 0.1829
lens2 -0.200 0.4398
L 1.000 1.4986 (fixed)
The position of the lens L has changed because the path lengh has been slightly reduced.
The Coupling factor for he astigmatic beam is C = 0.959 (it is C = 0.9974 if we consider the beam as non astigmatic).
I put the lenses and aligned the beam up to the shutter, which has been moved from its initial position because the beam size on it was too large.
TO DO
The green beam needs to be aligned and sent into the arm cavity.
Polarization has to be checked.
Many beams still have to be dumped, both in IR and Green paths.
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8646
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Mon May 27 21:38:53 2013 |
Annalisa | Update | 40m upgrading | ETMY - Beam Dumps |
I put many razor dumps along the IR/green path. The rejected beam from the IR Faraday needs to be dumped (about 1.5 mW). I used all the new razor blade I had, so I need one more for that beam.
The IR reflection of the Harmonic separator right after the doubler needs to be dumped in a better way. At the moment there is a black screen, but we need something suitable to dump more than 300 mW.
After the second steering mirror along the green beam path there is a very small transmission (about 6 uW), which is difficult to dump because there is no space enough. Can it be dumped with a black screen?
The Oplev has a lot of reflection hitting the central BS (The BS for the transmitted beam). It is very difficult to dump them without intercepting the main beam path. Maybe we have to slightly change the Oplev beam angle to avoid so many reflections.
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8652
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Tue May 28 22:11:23 2013 |
Annalisa | Update | 40m upgrading | ETMY - Yarm shutter cable |
For some strange reason the Yarm shutter cable runs up to the POY table, where it is connected to another cable going to the rack. It has to be put off from the table, at least. It would be better to have only one cable going directly to the rack.
I roughly aligned the green into the Yarm and I've seen the green beam flashing on the PSL table, but the mode matching is not so good and I get an higher order mode, so I'm going to fix the mode matching tomorrow. |
11521
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Thu Aug 20 18:08:28 2015 |
Ignacio | Frogs | 40m upgrading | Fatality. Something broke. |

So I made coffee at 1547 and was astonished to find the above. Its a sad, very sad day.
At first I thought that something (a gravity wave?) or someone, accidentally hit the thing and it fell and broke. But Koji told me that the janitor was cleaning around the thing and it did indeed fell accidentally. |
12625
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Fri Nov 18 00:25:08 2016 |
Johannes | Omnistructure | 40m upgrading | Acromag Chassis Development |
I had Rich show me his approach to a chassis for the Acromag modules. The document tree for his design can be found on the DCC. Note that he's using the high densitymodel ES series, which is available as a bare board variant with pluggable screw terminals:

He can fit up to 4 of these in a 2U chassis and has outsourced the wiring from front panel Dsubs to the board connectors to an external company. At the 40m (and in West Bridge) we currently only have the rail mounted XT series

At first glance the specs are very similar. Both A/D and D/A flavors have 16-bit precision in both cases. The high density ES series with Rich's layout can achieve 128 A/D per 2U, 64 D/A per 2U, or 384 DIO per 2U. Into a 4U chassis of the type we have currently we can fit ~32 XT modules (assuming two rows), which results in very similar numbers, except for the DAC, of which we could fit more.
XT1221-000 (8 diff. channel 16-bit ADC) $495.00 $61.88/ch
XT1541-000 (8 channel 16-bit DAC and 4 discrete I/O ) $525.00 $65.63/ch
XT1120-000 (16 channel DIO) $320.00 $20.00/ch
ES2162-0010 (32 diff. channel 16-bit ADC) $2050.00 $64.06/ch
ES2172-0010 (16 channel 16-bit DAC) $1400.00 $87.50/ch
ES2113-0010 (96 channel DIO) $1100.00 $11.46/ch
It's cheaper to stick with the current XT models, but they need the bulkier 4U chassis. The good news is that actually all these models have 16 bit precision, which wasn't clear to me before. Lydia and I will work out what connectors we want on the boxes, and how many modules/channels we need where. Rich also got me in touch with Keith Thorne, who handles the analog I/O Acromag at LLO, and I will ask him for advice. From his documents on the DCC it seems that he is using yet another series: EN. The 968EN-4008 for example is a rail-mounted ADC with pluggable connections, but looses quite clearly in price per channel.
For a generic multipurpose DAQ interface box the ES series is the best approach in my opinion, because it offers a more compact design. We could for example fit 1 ADC, 2 DAC, 1 DIO in a 2U chassis for 32/32/96 channels. The combined price tag for this scenario would be ~$6k.
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