40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 335 of 341  Not logged in ELOG logo
New entries since:Wed Dec 31 16:00:00 1969
ID Date Author Type Categorydown Subject
  4874   Fri Jun 24 00:13:24 2011 kiwamuUpdateABSLbeam 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 steveUpdateABSLI-P curve of LWE with serial numbers


 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 kiwamuUpdateABSLstatus 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 kiwamuUpdateABSLa 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 kiwamuUpdateABSLfine 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 kiwamuUpdateABSLsome 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 kiwamuUpdateABSLABSL 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.


  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 kiwamuUpdateABSLArm 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 ranaUpdateABSLArm length measurement : cavity kick technique


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 KojiUpdateABSLABSL Laser shutter closed

The shutter of the ABSL laser is closed for the vent work.

  8257   Fri Mar 8 12:57:57 2013 AnnalisaUpdateABSLBS 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 JenneUpdateABSLBS 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 AnnalisaConfigurationABSLABSL setup for g-factor measurement of PRC
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). 
  8361   Wed Mar 27 21:53:21 2013 AnnalisaUpdateABSLBeat 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.


  8369   Thu Mar 28 23:00:30 2013 AnnalisaUpdateABSLBeat 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. 



  8495   Fri Apr 26 10:50:07 2013 AnnalisaUpdateABSLATF 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   Thu May 16 08:32:05 2013 SteveUpdate40m upgradingETMY op table disabled


All ETMY optical table electronics- lasers-pds turned off, disconnected in order to remove enclosure.


  8594   Fri May 17 00:32:32 2013 AnnalisaUpdate40m upgradingETMY - progress

[Rana, Annalisa] 


 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).



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.

Attachment 1: IMG_0536.JPG
  8595   Fri May 17 15:38:51 2013 SteveUpdate40m upgradingETMY enclosure is on the way back


 It  will arrive around 10 am Monday morning.


  8596   Fri May 17 16:06:14 2013 ranaUpdate40m upgradingETMY op table disabled



  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  8597   Fri May 17 18:24:04 2013 AnnalisaUpdate40m upgradingETMY - 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   Thu May 23 00:16:32 2013 AnnalisaUpdate40m upgradingETMY - progress

 [Annalisa, Koji] 


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. 


Mode Matching calculation (tomorrow)

Fix the dumping situation

Replace some of the mounts with more solid ones (in the future)


 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.


(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.















Attachment 1: TransMonAndOplev.jpg
  8637   Fri May 24 02:12:50 2013 AnnalisaUpdate40m upgradingETMY - 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.



Attachment 1: ModeMatchingGreen.jpg
Attachment 2: ModeMatchingGreenZoom.jpg
Attachment 3: XYpath.jpg
  8638   Fri May 24 11:38:00 2013 KojiUpdate40m upgradingETMY - 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.


  8639   Fri May 24 12:50:25 2013 AnnalisaUpdate40m upgradingETMY - 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.


 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   Sat May 25 02:03:48 2013 AnnalisaUpdate40m upgradingETMY - 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. 


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. 





Attachment 1: ModeMatchingGreenNEW.jpg
Attachment 2: ModeMatchingGreenZoomNEW.jpg
Attachment 3: XYpathNEW.jpg
Attachment 4: photo1.JPG
Attachment 5: photo2.JPG
  8646   Mon May 27 21:38:53 2013 AnnalisaUpdate40m upgradingETMY - 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.


  8652   Tue May 28 22:11:23 2013 AnnalisaUpdate40m upgradingETMY - 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   Thu Aug 20 18:08:28 2015 IgnacioFrogs40m upgradingFatality. 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   Fri Nov 18 00:25:08 2016 JohannesOmnistructure40m upgradingAcromag 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.



  12634   Tue Nov 22 13:55:32 2016 JohannesOmnistructure40m upgradingAcromag Chassis

Current Acromag chassis status:

I found out that Acromag offers DIN rail mounting kits for the open boards, so we can actually fit both XT series and ES/EN series in the same boxes, depending on the signal needs. The primary design driver will be the ES footprint, but if we find we don't need that many channels in some of the units, it's interchangable. For the wiring to the front panel - for which we will have a standard front panel express design, but may order modified ones for the custom needs of the 40m, I will contract the same company that Rich used for the wiring in his DIO box (Panel mount connectors terminating in loose wires/pre-routed plugs for Acromag units). We will either run a single DIN rail along the length of the chassis, or have two in parallel across.

Lydia and I took close looks at the breakout arrangements on the rack sides, and determined that because of the many cross-connects between non-DAQ ports it is not possible to redo and debug this in a reasonable amount of time without essentially shutting down the interferometer. So instead, we will connect the chassis directly to the slots that were previously leading to the slow machines. They come in two different flavors: The ADC modules have 64 pins, while the DIO and DAC ones have 50. There are a couple things we can do:

  • For ADC: Put favorite 64+ pin connector on front panel. I would advocate for the 68 pin VHDIC (SCSI-5). This standard ist widely used, has a sturdy connector, and usually off-the-shelf cables have twisted pair leads.
  • For DAC+DIO: Either use favorite 50 pin connector (there are 50-pin DSUB connectors, and also 50-pin IDC connectors with backshell), or also send the signals through VHDIC connectors, tolerating a few unused lanes. I would prefer the second option, after all it all goes to some 64 pin VME-crate backplane connector in the end, so if we ever get rid of the rack-side breakouts the wiring will much more uniform.
  • For good measure, we will add a few (16 maybe) BNC connectors to the front panel.
  • A standardized front panel could have a variety of different connectors by default: DSUBs, BNCs, etc., to be used when needed with some initial default wiring.
  • Note that THEORETICALLY we could even connect all backplane EUROCARD ports to the Acromag chassis and do the cross-connect wiring entirely inside, although that would make the inside extremely messy.

Based on Rich's design I will get started on a parts list and wiring diagrams to send out to the cable company.

Attachment 1: acroplan.pdf
  10130   Sat Jul 5 04:18:45 2014 AndresUpdate40m Xend Table upgradeAdding Two Lenses After the Second Steering Mirror in Order Two Increase the Gouy Phase Difference Between the Sterring Mirrors

I had been working on the Xend table optical layout update. Since the two steering mirrors in the Xend green are too close to each, there is a very small Gouy Phase different between these two mirrors. It was suggested to place two lenses so that we can increase the Gouy Phase. I have been working with Nick on this problem, and we had found a solution by using a la mode. We had written an a la mode code that optimize the Gouy Phase and the Mode Matching at the same time. After trying different lenses, we found the following results: a mode matching of 0.9939 as it is show in the first attachment below, and we found a Gouy Phase different between the two mirrors of about 60 degrees. I took photos of the Xend Table. The first photo is the Xend table as we had it right now. In the second photo, I moved the 2nd lens, and I placed the two more lenses that we need it, with more or lenses the correct position where they will be placed. The three old lenses will be replaced by three lenses of different focal length as it can be seen in the first attachment below. The first lens and third lens will stay in the same position where the old first lens and old third lens are, and the second lens will be moved by about half of an inch. We might have one or two of the lenses that we need, but we will have to order the rest of the lenses that need. My plan is to verify the lenses that we already have. Then, I need to let Nick know with lenses we need to order. Hopefully, we will be able to update the table by the end of this week if everything turn out fine.

Attachment 1: OverlapAndComponentsOfTheSolution.png
Attachment 2: CloseLookToTheGouyPhaseBetweenMirr1AndMirr2.jpg
Attachment 3: EntireRangeOfBeamPath.jpg
Attachment 4: XendTableWithTwoNeedLensesAdding.JPG
Attachment 5: SchematicOfSolutionForTheLensesGouyPhase.jpeg
Attachment 6: XendGreenModeMatchingAndGouyPhaseOptimization.m
clear all
% In this code we are using a la mode to optimatize the mode matching and
% to optimatize the Gouy phase between mirror 1 and mirror 2. All the units
% are in meter

w0=2.943*1e-5; % The Waist of the laser measured before the faraday
z0_laser=-0.039; % position measured where the waist is located 
lamb= 532*10^-9; % wavelength of green light in mm
lFaraday=.0638; % Length of the faraday

... 148 more lines ...
Attachment 7: BeforeIncludingLensesORMovingLenses.JPG
  10191   Sun Jul 13 17:06:35 2014 AndresUpdate40m Xend Table upgradeXarm Table Upgrade Calculation and Diagrams of possible new table layout

 Current Mode Matching and Gouy Phase Between Steering Mirrors

We found in 40m elog ID 3330 ( http://nodus.ligo.caltech.edu:8080/40m/3330a documentation done by Kiwamu, where he measured the waist of the green. The waist of the green is about 35µm. Using a la mode, I was able to calculate the current mode matching, and the Gouy phase between the steering mirrors. In a la mode, I used the optical distances,which is just the distance measured times its index of refraction. I contacted someone from ThorLabs (which is the company that bought Optics For Research), and that person told that the Faraday IO-5-532-LP has a Terbium Gallium Garnet crystal of a length of 7mm and its index of refraction is 1.95. The current mode matching is 0.9343, and the current Gouy phase between steering mirrors is 0.2023 degrees. On Monday, Nick and I are planning to measure the actual mode matching. The attached below is the current X-arm optical layout. 



Calculation For the New Optical Layout


Since the current Gouy phase between the steering mirror is essentially zero, we need to find a way how to increase the Gouy Phase. We tried to add two more lenses after the second steering mirror, and we found that increasing the Gouy phase result in a dramatically decrease in mode matching. For instance, a Gouy phase of about 50 degrees results in a mode matching of about .2, which is awful. We removed the first lens after the faraday, and we added two more mirrors and two more lenses after the second steering mirror. I modified the photo that I took and I place where the new lenses and new mirrors should go as shown in the second pictures attached below. Using a la mode, we found the following solution:

 label                         z (m)            type                       parameters         

 -----                          -----              ----                        ----------         

 lens 1                       0.0800          lens                      focalLength: 0.1000

 First mirror              0.1550          flat mirror            none:            

 Second mirror         0.2800          flat mirror            none:            

 lens 2                      0.4275           lens                      focalLength: Inf   

 lens 3                     0.6549            lens                      focalLength: 0.3000

lens 4                      0.8968            lens                      focalLength: -0.250

Third mirror           1.0675            flat mirror            none:            

Fourth mirror         1.4183            flat mirror            none:            

lens 5                      1.6384            lens                     focalLength: -0.100

Fifth mirror            1.7351            flat mirror           none:            

Sixth mirror           2.0859            flat mirror           none:            

lens 6                     2.1621            lens                     focalLength: 0.6000

ETM                      2.7407            lens                    focalLength: -129.7

ITM                       40.5307          flat mirror          none:             

The mode matching is 0.9786. The different Gouy phase different between Third Mirror and Fourth Mirror is 69.59 degrees, Gouy Phase between Fourth and Fifth 18.80 degrees, Gouy phase between Fifth and Sixth mirrors is 1.28 degrees, Gouy phase between Third and Fifth 88.38 degrees, and the Gouy phase between Fourth and Sixth is 20.08 degrees. Bellow attached the a la Mode code and the Plots.



Plan for this week

I don't  think we have the lenses that we need for this new setup. Mostly, we will need to order the lenses on Monday. As I mention, Nick and I are going to measure the actual mode matching on Monday. If everything look good, then we will move on and do the Upgrade.


Attachment 1: CurrentOpticalLayout.png
Attachment 2: NewSetUp.PNG
Attachment 3: AlaModeSolutionplots.png
Attachment 4: EntireScaleRangeAlaModeSolution.png
Attachment 5: NewXarmOptimizationFromFaraday.m
close all
clear all
% In this code we are using a la mode to optimatize the mode matching and
% to optimatize the Gouy phase between mirror 1 and mirror 2. All the units
% are in meter

w0=(50*1e-6)/sqrt(2); % The Waist of the laser measured after SHG
z0_laser=-0.0083; % position measured where the waist is located 
lamb= 532*10^-9; % wavelength of green light in mm
lFaraday=.0638; % Length of the faraday
... 209 more lines ...
  10195   Mon Jul 14 16:19:41 2014 AndresUpdate40m Xend Table upgradeTook the measurement for the Mode Matching

 Nick and I measured the reflected power of the green light in locked and unlocked. I'm working on the calculation of the mode matching. Tonight, I'll be posted my calculation I'm still working on it.

JCD:  Andres forgot to mention that they closed the PSL shutter, so that they could look at the green light that is reflected off the harmonic separator toward the IR trans path.  Also, the Xarm (and the Yarm) were aligned to IR using the ASS, and then ASX was used to align the green beam to the cavity.

  10207   Tue Jul 15 22:23:51 2014 AndresUpdate40m Xend Table upgradeScan the Xarm for the mode matching

 Nick and I with the help of Jenne scan the green light when the cavity is unlocked. Nick placed a Beam dump on the IR so that we can just scan the green, but it was removed as soon as we finished with the measurement. I'm working on the calculation, and i'll be posted solution tonight.

  10226   Thu Jul 17 02:57:32 2014 AndresUpdate40m Xend Table upgradeFInish Calculation on Current X-arm mode Matching

Data and Calculation for the Xarm Current Mode Matching

Two days ago, Nick, Jenne, and I took a measurement for the Green Transmission for the X-arm. I took the data and I analyzed it. The first figure attached below is the raw data plotted. I used the function findpeaks in Matlab, and I found all the peaks. Then, by taking close look at the plot, I chose two peaks as shown in the second figure attached below. I took the ratio of the TEM00 and the High order mode, and I average them. This gave me a Mode Matching of 0.9215, which this value is pretty close to the value that I predicted by using a la Mode in http://nodus.ligo.caltech.edu:8080/40m/10191, which is 0.9343. Nick and I measured the reflected power when the cavity is unlocked and when the cavity is locked, so we measured the PreflUnLocked=52+1µW and PreflOnLocked=16+2µW and the backgroundNoise=0.761µW. Using this information we calculated  Prefl/Pin=0.297. Now, since Prefl/Pin=|Eref/Ein|2, we looked at the electric fields component by using the reflectivity of the mirror we calculated 0.67. The number doesn't agree, but this is because we didn't take into account the losses when making this calculation. I'm working in the calculation that will include the losses.

Today, Nick and I ordered the lenses and the mirrors. I'm working in putting together a representation of how much improvement the new design will give us in comparison to the current setup.

Attachment 1: RawDataForTheModeGreenScan.png
Attachment 2: ResultForModeMatching.png
Attachment 3: DataAndCalculationOfModeMismatch.zip
  10237   Fri Jul 18 16:52:56 2014 AndresUpdate40m Xend Table upgradeFInish Calculation on Current X-arm mode Matching


Data and Calculation for the Xarm Current Mode Matching

Two days ago, Nick, Jenne, and I took a measurement for the Green Transmission for the X-arm. I took the data and I analyzed it. The first figure attached below is the raw data plotted. I used the function findpeaks in Matlab, and I found all the peaks. Then, by taking close look at the plot, I chose two peaks as shown in the second figure attached below. I took the ratio of the TEM00 and the High order mode, and I average them. This gave me a Mode Matching of 0.9215, which this value is pretty close to the value that I predicted by using a la Mode in http://nodus.ligo.caltech.edu:8080/40m/10191, which is 0.9343. Nick and I measured the reflected power when the cavity is unlocked and when the cavity is locked, so we measured the PreflUnLocked=52+1µW and PreflOnLocked=16+2µW and the backgroundNoise=0.761µW. Using this information we calculated  Prefl/Pin=0.297. Now, since Prefl/Pin=|Eref/Ein|2, we looked at the electric fields component by using the reflectivity of the mirror we calculated 0.67. The number doesn't agree, but this is because we didn't take into account the losses when making this calculation. I'm working in the calculation that will include the losses.

Today, Nick and I ordered the lenses and the mirrors. I'm working in putting together a representation of how much improvement the new design will give us in comparison to the current setup.

We want to be able to graphically see how much better it is the new optical table setup in comparison to the current optical table setup. In other words, we want to be able to see how displacement of the beam and how much angle change can be obtained at the ETM from changing the mirrors angles independently. Depending on the spread of the mirrors' vectors we can observe whether the Gouy phase is good. In the plot below, the dotted lines correspond to the current set up, and we can see that the lines are not spread from each other, which essentially mean that changing the angles of the two mirrors just contribute to small change in angle and in the displacement of the beam at the ETM, and therefore the Gouy phase is not good. Now on the other hand. The other solid lines correspond to the new setup mirrors. We can observe that the spread of the line of mirror 1 and mirror 4 is almost 90 degrees, which just implies that there is a good Gouy phase different between these two mirrors. For the angles chosen in the plot, I looked at how much the PZT yaw the mirrors from the elog http://nodus.ligo.caltech.edu:8080/40m/8912. In this elog, they give a plot in mrad/v for the pitch and yaw, so I took the range that the PZT can yaw the mirrors, and I converted into mdegrees/v and then I plotted as shown below. I plot for the current setup and for the new setup in the same plot. The matlab code is also attached below.

Attachment 1: OldAndNewSetupPlotsOfDisplacementAndAngleAtTheETM.png
Attachment 2: OldSetUpDisplacementAndNewSetup.m.zip
  10290   Tue Jul 29 20:14:08 2014 AndresUpdate40m Xend Table upgradeXarm Green steering mirror upgrade

 Xarm Green Steering Mirror Upgrade

Nick and I did the upgrade for the green steering mirror today. We locked in the TEM00 mode.
We placed the shutter and everything. We move the OL, but we placed it back. Tonight, I'll be doing a more complete elog with more details.

  10291   Tue Jul 29 20:14:10 2014 KojiUpdate40m Xend Table upgradeXarm Green steering mirror upgrade

That was super fast! Great job, Andres and Nic!

  10296   Wed Jul 30 10:16:54 2014 AndresUpdate40m Xend Table upgradeGreen Steering Mirror Upgrade completed

Green Steering Mirror Update

Yesterday, Nick and I completed the green steering mirrors upgrade. I attached the file that contained the procedure that we plan before we did the upgrade. We placed an iris at the input of the OL and we place another iris before the harmonic separator. We did not use the beam scanner because someone was using it, so what we did was to assume that the cavity is well align and place the iris so that we can recover the alignment. We used the measuring tape to approximate as close as we could the position where the lenses were supposed to go. I did a measurement of the derivative of the waist size in terms of the position of the lens and the derivative of the waist Position in terms of the lenses position at the optimum solution that a la mode give us. Because of this plot, we decide to mount lens 3 and lens 5 into translational stages. After mounting each lenses and mirrors we worked on the alignment of the beam into the cavity. We were able to align the green into the cavity and we were able to locked the cavity to the TEM00 mode. We started to work on the optimization of the mode matching. However, the maximum mode matching that we got was around 0.6, which we need to work a little bit more on the tuning of the mode matching. We leave the iris mounted on the table. I took a picture of the table, and I attached below. For the OL, we just make sure that the output where somehow hitting the QPD, but we didn't really I aligned it. We need to work a little bit more on the alignment of the OL and the tuning of the mirror to maximize the green mode matching.

Attachment 1: XarmUpgrade.pdf
XarmUpgrade.pdf XarmUpgrade.pdf XarmUpgrade.pdf XarmUpgrade.pdf XarmUpgrade.pdf XarmUpgrade.pdf
Attachment 2: dWaistSize_dlensVsdWaistPosition_dlens.png
Attachment 3: XarmNewOpticalSetup.PNG
  2653   Wed Mar 3 18:32:25 2010 AlbertoUpdate40m Upgrading11 MHz RFPD elctronics
** Please add LISO file w/ component values.
I designed the circuit for one of the 11 MHz photodiodes that we're going to install in the 40m Upgrade.

This is a simple representation of the schematic:

#          |
#          Cw2
#          |
#          n23
#          |
#          Lw2
#          |
#           n22
#          |
#          Rw2                
#                 |                   |\            
#           n2- - - C2 - n3 -  - -  - |  \          
#            |    |      |   |        |4106>-- n5 - Rs -- no
# iinput    Rd   L1     L2 R24    n6- |  /     |           |
#      nin - |    |      |   |    |   |/       |         Rload    
#           Cd   n7     R22 gnd   |            |           |          
#            |    |      |        | - - - R8 - -          gnd              
#           gnd  R1     gnd      R7 
#                 |               |
#         gnd               gnd

I chose the values of the components in a realistic way, that is using part available from Coilcraft or Digikey.

Using LISO I simulated the Tranfer Function and the noise of the circuit.

I'm attaching the results.

I'll post the 55MHz rfpd later.

Attachment 1: rfpd11_v2_TF.pdf
Attachment 2: rfpd11_v2_Noise.pdf
  2655   Thu Mar 4 08:43:35 2010 AlbertoUpdate40m Upgrading11 MHz RFPD elctronics

** Please add LISO file w/ component values.

oops, forgotten the third attachment...

here it is

Attachment 1: rfpd11_v2.fil
# Resonant RF diode front end
#		  gnd
#		  |
#		  Cw2
#		  |
#		  n23
#		  |
#		  Lw2
#		  |
... 60 more lines ...
  2656   Thu Mar 4 19:53:56 2010 AlbertoUpdate40m Upgrading11MHz PD designed adjusted for diode's resistance; 55 MHz RFPD designed
After reading this study done at LIGO MIT in 1998 I understood why it is difficult to define an effective impedance for a photodiode.

I read a few datasheets of the C30642GH photodiode that we're going to use for the 11 and 55 MHz. Considering the  values listed for the resistance and the capacitance in what they define "typical conditions" (that is, specific values of bias voltage and DC photocurrent) I fixed Rd=25Ohms and Cd=175pF.

Then I picked the tunable components in the circuit so that we could adjust for the variability of those parameters.

Finally with LISO I simulated transfer functions and noise curves for both the 11 and the 55MHz photodiodes.

I'm attaching the results and the LISO source files.


Attachment 1: rfpd55_Noise.pdf
Attachment 2: rfpd55_TF.pdf
Attachment 3: rfpd11_v2_TF.pdf
Attachment 4: rfpd11_v2_Noise.pdf
Attachment 5: rfpd11_v2.fil
Attachment 6: rfpd55.fil
  2657   Thu Mar 4 22:07:21 2010 ranaUpdate40m Upgrading11MHz PD not yet designed

Use 10 Ohms for the resistance - I have never seen a diode with 25 Ohms.

p.s. PDFs can be joined together using the joinPDF command or a few command line options of 'gs'.

  2704   Tue Mar 23 22:46:43 2010 AlbertoUpdate40m UpgradingREFL11 upgraded
I modified REFL11 according to the changes lsited in this schematic (see wiki  / Upgrade 09 / RF System / Upgraded RF Photodiodes ).
I tuned it to be resonant at 11.06MHz and to have a notch at 22.12MHz.
These are the transfer functions that I measured compared with what I expected from the LISO model.


The electronics transfer function is measured directily between the "Test Input" and the "RF Out" connector of the box. the optical transfer function is measured by means of a AM laser (the "Jenne laser") modulated by the network analyzer.
The AM laser's current was set at 20.0mA and the DC output of the photodiode box read about 40mV.
The LISO model has a different overall gain compared to the measured one, probably because it does not include the rest of the parts of the circuit other than the RF out path.

I spent some time trying to understand how touching the metal cage inside or bending the PCB board affected the photodiode response. It turned out that there was some weak soldering of one of the inductors.

  2711   Wed Mar 24 14:57:21 2010 AlbertoUpdate40m UpgradingREFL11 upgraded


 Hartmut suggested a possible explanation for the way the electronics transfer function starts picking up at ~50MHz. He said that the 10KOhm resistance in series with the Test Input connector of the box might have some parasitic capacitance that at high frequency lowers the input impedance.

Although Hartmut also admitted that considering the high frequency at which the effect is observed, anything can be happening with the electronics inside of the box.

  2715   Thu Mar 25 17:32:42 2010 AlbertoUpdate40m UpgradingREFL55 Upgraded

I upgraded the old REFL199 to the new REFL55.

To do that I had to replace the old photodiode inside, switching to a 2mm one.

Electronics and optical transfer functions, non normalized are shown in the attached plot.


The details about the modifications are contained in this dedicated wiki page (Upgrade_09 / RF System / Upgraded RF Photodiodes)

Attachment 1: 2010-03-25_REFL55_model_to_meas_comparison.png
  2761   Sat Apr 3 19:54:19 2010 AlbertoUpdate40m UpgradingREFL11 and REFL55 PDs Noise Spectrum

These are the dark noise spectrum that I measured on the 11MHz and 55MHz PD prototypes I modified.

The plots take into account the 50Ohm input impedance of the spectrum analyzer (that is, the nosie is divided by 2).

2010-04-03_REFL11_darknoise.png 2010-04-03_REFL55_darknoise.png

With an estimated transimpedance of about 300Ohm, I would expect to have 2-3nV/rtHz at all frequencies except for the resonant frequencies of each PD. At those resonances I would expect to have ~15nV/rtHz (cfr elog entry 2760).


  1. For the 55MHz PD the resonance peak is too small
  2. In the 55 MHz: noise is present at about 7MHz
  3. In the 11MHz PD there's a lot of noise below 10 MHz.

I have to figure out what are the sources of such noises.


  2767   Mon Apr 5 10:23:40 2010 AlbertoUpdate40m UpgradingREFL11 Low Frequency Oscilaltion Reduced

After adding an inductor L=100uH and a resistor R=10Ohm in parallel after the OP547A opamp that provide the bias for the photodiode of REFL11, the noise at low frequency that I had observed, was significantly reduced.

See this plot:


A closer inspection of the should at 11MHz in the noise spectrum, showed some harmonics on it, spaced with about 200KHz. Closing the RF cage and the box lid made them disappear. See next plot:


The full noise spectrum looks like this:


A big bump is present at ~275MHz. it could important if it also shows up on the shot noise spectrum.

  2782   Thu Apr 8 10:17:52 2010 AlbertoUpdate40m UpgradingREFL11 Noise Vs Photocurrent

From the measurements of the 11 MHz RFPD at 11Mhz I estimated a transimpedance of about 750 Ohms. (See attached plot.)

The fit shown in the plot is: Vn = Vdn + sqrt(2*e*Idc) ; Vn=noise; Vdn=darknoise; e=electron charge; Idc=dc photocurrent

The estimate from the fit is 3-4 times off from my analsys of the circuit and from any LISO simulation. Likely at RF the contributions of the parassitic components of each element make a big difference. I'm going to improve the LISO model to account for that.


The problem of the factor of 2 in the data turned out to be not a real one. Assuming that the dark noise at resonance is just Johnson's noise from the resonant circuit transimpedance underestimates the dark noise by 100%.

ELOG V3.1.3-