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

[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The two cylindrical lenses which were used to correct the ellipticity of the beam have been replaced by a single lens.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.

 It  will arrive around 10 am Monday morning.

 TODO:

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.

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.

 [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.

 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.

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.

 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. 

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.

 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.

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.

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.

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.

In the revival of the experiement length measurement for the recycling cavities, I turned the auxiliary NPRO back on. The shutter is closed.

I also recollected all the equipment of the experiment after that during the summer it had been scattered around the lab to be used for other purposes (Joe and Zach's cameras and Stephanie and Koji's work with the new EOM).

I'm working on the PSL table to set up the PLL setup for the AbsL experiment.

I turned the auxialiary NPRO for the AbsL Experiment on. Its shutter stays closed.

Aligning the beam for the PLL of the AbsL Experiement I rotated the polarizer along the path of the MC Input pick off beam (= the pick off coming from the MC periscope).

I've been trying to lock the PLL for the AbsL Experiment but I can't see the beat (between the auxiliary NPRO and the PSL).

I believe the alignment of the PLL is not good. The Farady Isolator is definitely not perfectly aligned (you can see it from the beam spot after it) but still it should be enough to see something at the PLL PD.

it's probably just that the two beams don't overlap well enough on the photodiode. I'll work on that later on.

I'm leaving the lab now. I left the auxiliary NPRO on but I closed its shutter.

All the flipping mirrors are down.

I've opened the AP table and I'm working on it.

I re-aligned the Faraday on the AP table. I also aligned the beam to the periscope on the PSL and all the other optics along the beam path.  Now I have a nice NPRO beam at the PLL which overlaps with the PSL beam. The alignment has to be further improved because I see no beat yet.

I wonder if the all the tinkering on the PSL laser done recently to revive the power has changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat. So maybe the misalignment is the casue.

Not feeling very well right now. I need to go home for a while.

AP table closed at the moment.

NPRO shutter closed

 We definitely changed the PSL NPRO temp while fiddling around, trying to increase the laser power.  I think it's noted in the elog both times that it's happened in the last few months (once when Rana, Koji and I worked on it, and then again when it was just Koji), but we opened up the side of the MOPA box so that we could get at (and change) the potentiometer which adjusts the NPRO temp.  So you may have to search around for a while.

Yes it did.

For long time, the crystal temperature C1:PSL-126MOPA_LTMP was 43~46deg. Now it is 34deg. Try ~10deg lower temperature.

I've opened the AP table and I'm working on it.

Also auxiliary NPRO turned on and mechanical shutter opened.

 Beat found at 30MHz with auxiliary NPRO temperature of 37.19 degrees, vs. ~48 deg as it used to be.

The beat is small (-70dBm). PLL alignment has to be improved.

 PLL alignment improved. Beat amplitude = -10dBm. Good enough.

DC readouts at the PLL photodiode:

V_NPRO = -4.44V

V_PSL = -3.76V

The NPRO beam is attenuated by a N.D.=1 attenuator just before going to the photodiode.

Something strange happened at the last. Right before -10dBm, the amplitude of the beat was about -33dBm. Then I was checking the two interfering beams with the IR card and saw that they overlapped quite well. I then turned my head back to the spectrum analyzer and suddenly the beat was at -10dBm. Not only, but a bunch of new peaks had appeared on the spectrum. Either I inadvertently hit the PD moving it to a better position or something else happened.

Like if someone was making some other modulation on the beam or the modulation depth of the PSL's sidebands had gone up.

I locked the PLL and made some first measuremtns of the spectrum of the error signal. I'll post them later.

I closed the shutter of the NPRO.

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

 Closing the AP table and the NPRO shutter now.

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.

The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.

Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.

Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.

It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.

Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.

I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.

 I confirm what I said earlier. The amplitude of the beat is -10 dBm at 300MHz. It goes down at lower frequencies. In particular it gets to-60 dBm below 20 MHz. For some strange reason that I couldn't explain the beating efficiency has become poorer at low frequencies.

 NPRO shutter closed

Problem found. Inspecting with Koji we found that there was a broken SMA-to-BNC connector in the BNC cable from the photodiode.

I measured the open loop gain of the PLL in the AbsL experiment.

I repeated the measurement twice: one with gain knob on the universal PDH box g=3.0; the second measurement with g=6.0

The UGF were 60 KHz and 100 KHz, respectively.

That means that one turn of the knob equals to about +10 dB.

I closed the shutter of the NPRO for the night.

 Plots don't really make sense. The second one is inherently unstable - and what's g?

The way the filter's transfer function has been measured is by a swept sine between the "SERVO INPUT" and the "PIEZO DRIVE OUTPUT" connection on the box front panel. The spectrum analyzer used for the measurement is the SR785 and the source amplitude is set at 0.1V.

The two transfer functions are clearly different. In particular the old one looks like a simple integrator, whereas the new one already includes some sort of boost.

That probably explains why the new one is unable to lock the PLL. Indeed what the PLL needs, at least to acquire lock, is an 1/f filter.

I thought the two boxes were almost identical, at least in the filter shapes. Also the two schematics available in the DCC coincide.

Yesterday I measured the Open Loop Gain of the PLL in the absolute length experiment. The servo I used was that of the old Universal PDH box.

The OLG looks like this:

The UGF is at 10 KHz.

 To me, they both look stable. I guess that the phase has to go to -180 deg to be unstable.

Why does the magnitude go flat at high frequencies? That doesn't seem like 1/f.

How about a diagram of what inputs and outputs are being measured and what the gain knob and boost switch settings are?

I opened the auxiliary laser's shutter.

I'm currently working on the AP table.

 I finished working on the table.

I closed the AUX NPRO's shutter.

 I'm done for the moement.

I realized that I need to take into account somehow the DC power from the photodiode. By now the measurement of the transmitted beat's power is affected by the total power circulating inside of the PRC and thus it depends on the cavity alignment.

I closed the laser shutter and turned down the flipping mirrors.

I'm planning to restart measuring by 2.30pm today. Till then the interferometer is available.

I'm currently running a measurement on the PRC.

Please don't interfere with the IFO until it is done. Talk with Alberto if you've been intending to work inside the lab.

Thank you.

Leaving for dinner. Back in ~1hr.

I left a measurement running. Please don't interfere with it till I'm back. Thanks.

 Per Alberto's instructions, I have closed the shutter on his laser so that the Adaptive Team can play with the Mode Cleaner.