40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
 40m Log, Page 341 of 344 Not logged in
 New entries since: Wed Dec 31 16:00:00 1969
ID Date Author Type Category Subject
12061   Mon Apr 4 15:04:14 2016 gautamUpdateendtable upgradeCOMPONENT REMOVAL

I'm planning to start removing components from the X endtable tomorrow morning at ~10AM - if anyone thinks I should hold off and do some further checks/planning, let me know before this so that I can do the needful.

12063   Tue Apr 5 11:42:17 2016 gaericqutamUpdateendtable upgradeTABLE REMOVAL

There is currently no table at the X end!

We have moved the vast majority of the optics to a temporary storage breadbord, and moved the end table itself to the workbench at the end.

Steve says Transportation is coming at 1PM to put the new table in.

12065   Wed Apr 6 17:52:21 2016 gautamUpdateendtable upgradeFirst contact cleaning commenced

I've begun cleaning the optics that will eventually go back onto the newly installed X-endtable. We decided that First Contact was the way to go (as opposed to methanol drag wiping). Koji demonstrated the application of the (red) First Contact solution onto a 2" mirror - I then proceeded to work on the rest of the optics. We are broadly following the procedure in E1000079 - first one coat of First Contact solution is applied, then a small piece of PEEK is embedded by applying a second layer of solution over it (this will enable us to pull off the First Contact once we are ready - the plan is to do this after roughly placing the optic on the table. As of now, I've finished coating most of the optics that are part of the IR Transmon path - I will continue later in the evening.

The new endtable is almost ready for re-population. Steve just needs to shim the enclosure which will be done tomorrow morning. The game-plan as discussed at the meeting today is to first try and set up the IR Transmon path. This will allow us to verify that the endtable height is such that we can maintain a beam height of 4" everywhere on the table (I suspect we may have to compromise at some poing and do some fine adjustment of 1/4 to 1/2" somewhere though). It will also allow me to define the cavity axis relative to the table, which will be useful to place the green steering optics eventually. Doing this will be challenging though as right now, I can't see any of the arm flashes on the endtable using an IR card. Ideally, we want to somehow lock the X arm and then do the checks mentioned at the endtable, before beginning to put the endtable back together.

12066   Thu Apr 7 12:51:24 2016 gautamUpdateendtable upgradeBeam height differences

Steve has finished installing the enclosure on the new endtable. So Eric and I decided to try and lock the X arm and measure the beam height of the transmitted IR beam relative to the endtable. We initially thought of using POX DC as a the LSC trigger but this did not work as there was no significant change in it when the arm was flashing. Eric then tried misaligning the ITM and using AS110 as a trigger - this worked. We then recompiled the ASS model to take AS110 as an input, and ran the dither alignment. After doing so, I measured the beam height at two points on the new endtable.

Bottom line:

• The beam is roughly level across the table (along the North-South direction, within the precision to which I could place the irides and measure the height). The table has also been levelled pretty well...
• The beam height is ~4.7" across the endtable

So the beam is about 0.7" higher relative to the endtable than we'd like it to be. What do we do about this?

• Is it even possible to raise the table by 0.7" so we can have a level beam everywhere? Are there some constraints related to how the enclosure is attached to the window?
• Are we okay with tolerating a solution where we keep the beam level at 4", and use Y10 and Y11 (see layout in elog 12060) to raise the beam by 0.7", and then have slightly higher posts for the optics downstream of this point?

I've also placed two irides extending the cavity axis on the endtable. These should be helpful in aligning the green to the arm eventually.

12067   Thu Apr 7 14:30:58 2016 SteveUpdateendtable upgradeETMX table height

 Quote: Steve has finished installing the enclosure on the new endtable. So Eric and I decided to try and lock the X arm and measure the beam height of the transmitted IR beam relative to the endtable. We initially thought of using POX DC as a the LSC trigger but this did not work as there was no significant change in it when the arm was flashing. Eric then tried misaligning the ITM and using AS110 as a trigger - this worked. We then recompiled the ASS model to take AS110 as an input, and ran the dither alignment. After doing so, I measured the beam height at two points on the new endtable. Bottom line: The beam is roughly level across the table (along the North-South direction, within the precision to which I could place the irides and measure the height). The table has also been levelled pretty well... The beam height is ~4.7" across the endtable So the beam is about 0.7" higher relative to the endtable than we'd like it to be. What do we do about this? Is it even possible to raise the table by 0.7" so we can have a level beam everywhere? Are there some constraints related to how the enclosure is attached to the window? Are we okay with tolerating a solution where we keep the beam level at 4", and use Y10 and Y11 (see layout in elog 12060) to raise the beam by 0.7", and then have slightly higher posts for the optics downstream of this point? I've also placed two irides extending the cavity axis on the endtable. These should be helpful in aligning the green to the arm eventually.

The new TMC 4' x 3' x4" optical table and enclosure is installed - aligned- leveled.

Atm2,  Picture is taken ~42" from the window at 3.75 camera height. The leveled table height is wthin 1/4 at the center of the window.

I think this is close enough to move on with the installation of the optics.

We can raise the loaded table in the future if it is needed.

Atm4, Optical table height to floor 33" at the south west corner

Atm3, Enclosure top cover transmission at 1064 nm, 1mm beam size, power level 157 mW, 0 degree incident angle,   T 1.3% Metal shield is required above 100 mW hitting the wall of the enclosure!

Atm5, window to enclosure Kapton seal

12068   Fri Apr 8 09:13:20 2016 SteveUpdateendtable upgradeETMX-T beam height

X arm resonating after alignment, beam height on ETMX optical table ~4.75"

12073   Wed Apr 13 00:56:07 2016 gautamUpdateendtable upgradeX endtable repopulation

Over the last couple of days, I've been working on restoring the optical layout on the X-endtable. Some notes about the status as of today:

Lightwave NPRO output power

The output power from the lightwave NPRO is about 210mW (as measured with the calorimeter). This is significantly lower than the value of ~300mW reported in this elog. It may be that the laser crystal temperature has changed compared to that measurement, but the "ADJ" parameter is at 0, both today and in that measurement. The laser has also been on for more than a day now, that should be sufficient time for the crystal to equilibriate to its final operating state? Is such a large change in output power possible just because of a change in laser crystal temperature? Or did the laser really lose ~1/3rd of its output power over the last two months?

Alignment into IR Faraday, and changes to the planned layout

I've set up the layout until steering the beam through the IR faraday. The input power into the IR Faraday is ~210mW. The output power is ~186mW, after optimizing the angle of the HWP. These numbers seem consistent with what I had reported in this elog (although this was for the Innolight NPRO). The alignment looks reasonably good to the eye as well.

I've made one change to the planned layout (latest version here). Y1 is now a 2" 99% reflective for S polarization beam splitter, instead of a 1" HR mirror. I made this change because we want some light from the NPRO to be transmitted through this optic to couple into the fiber eventually, for the IR beat. I measured the transmitted power to be ~1.5mW, which is around what we were coupling into the fiber before, and should suffice now. The Lightwave NPRO datasheet (page 4) suggests that the polarization of the output of the laser is S, and the measured power before and after this optic suggests that it is working as advertised. This means that HWP 1 also has to be moved downstream (to rotate the polarization so as to maximize transmission through the IR faraday). Space constraints meant that I could not mount HWP 1 on the baseplate+3/4" OD post assembly which is what we want where possible on the new table, so for this optic, I used a 1" OD post and a fork. There may be a couple of other optics in the final layout where space constraints dictate we compromise in this way.

I've also installed beam dumps for the rejected light from the Faraday. For now, these are the old beam dumps. They looked reasonably intact. I believe we have a bunch of new beam dumps on hand as well, so these can be swapped out if deemed necessary.

Cleaning of optics

All the optics are being cleaned using first contact before being installed on the table.

As I found out the hard way, it is not a good idea to clean small optics like half-wave plates while in their mounts. The first contact tends to bond to the frame while drying, and doesn't come off cleanly. Koji helped me clean the offending pieces (he used tweezers to manually remove the residual first contact, and then some acetone to clean up any remaining residue). Subsequently, he re-cleaned these optics, again using first contact, but this time being careful not to extend all the way out to the edge of the optic. The idea is to cover as much area as possible with first contact, while staying clear of the edge. This approach worked reasonably well.

The next major step is to achieve optimal alignment into the doubler. I've placed the doubler on the table in it's approximate final position, I wanted to make sure the enclosure support wasn't in the way (it isn't). The cable from the oven won't run all the way to the Thorlabs temperature controller in it's usual place, we need to either extend the cable, or figure out a new place where we can keep the temperature controller.

12074   Wed Apr 13 11:00:28 2016 SteveUpdateendtable upgradeX endtable repopulation

ETMX optical table is grounded to ETMX chamber through 1 Mohms

The doubling oven temp controller is installed to reach its cable.

12075   Wed Apr 13 18:25:07 2016 gautamUpdateendtable upgradeLightwave health check

[Koji,gautam]

Lightwave NPRO information:

Model: 126-1064-700

Serial Number: 337

Manufactured: December 1998!!

Details of checks performed:

Koji tuned the parameters on the laser controller and we observed the following:

1. Turning "ADJ" to +10 and the pumping current all the way up to the maximum (2.62A) allowed us to recover an output power of 300mW, at a laser crystal temperature of ~45degrees
2. The output power increased almost monotonically as a function of the laser crystal temperature - why? We were able to see powers as high as 250mW (at ADJ=0) for the maximum crystal temperature of ~60 degrees.
3. We checked that we could believe the readout of the power meter by measuring the power using the Scientech power meter - we saw ~270mW after the Faraday with this meter, accounting for ~10% loss through the Faraday, this corresponds to an output power of 300mW (all this was done at ADJ=+10, DC=2.62A). I suspect that the display is dodgy though, because changing the Diode Current from 2.52A to 2.62A increased the output power by almost 100mW, which seems hard to believe?
4. The Lightwave NPRO does not have heat dissipation fins attached - could this be affecting the power output somehow? In any case, this has to be rectified. So if we decide to keep the Lightwave NPRO, the layout will still need minor changes to accommodate the heat fins. Steve, do we have these in hand?

Way forward

Ericq has begun the characterization of the repaired Innolight. We checked that it outputs 1W of power. We will now have to perform the following measurements:

• Frequency noise using PLL
• AM/PM response of the PZT
• Laser power output as a function of diode current - this will be useful for diagnostic purposes in the future
• AUX temperature vs PSL temperature at which beatnotes can be found
• Waist measurement - the mode matching and optical layout upstream of the doubling oven at least will have to be modified significantly

All of these will have to be done before installing this laser at the endtable.

I believe the consensus as of now is to go ahead with carrying out the above measurements. Meanwhile, we will keep the Lightwave NPRO on and see if there is some miraculous improvement. So the decision as to whether to use the Innolight is deferred for a day or two.

12079   Fri Apr 15 18:38:12 2016 gautamUpdateendtable upgradeLightwave health check - NO IMPROVEMENT

I re-measured the power levels today.

We have ~205mW out of the NPRO, and ~190mW after the Faraday. It doesn't look like the situation is going to improve dramatically. I'm going to work on a revised layout with the Innolight as soon as I've profiled the beam from it, and hopefully, by Monday, we can decide that we are going ahead with using the Innolight.

12083   Tue Apr 19 18:37:29 2016 gautamUpdateendtable upgradeLaser swap + optical layout

Summary of work done over the last two days

1. Lightwave NPRO + controller moved to PSL table
• ​​The interlock is not connected to the controller
• Controller is not powered
2. Innolight NPRO + controller installed at endtable
• ​​​​Interlock has been connected
• For initial alignment purposes, I'm running it at an injection current of 1.000A (~50mW of IR out of the NPRO)
• Temperature of crystal set to 31.66 degrees in anticipation of operation in the nominal state
3. Laying out optics
• ​​Given that the mode out of the NPRO is different from that from the Lightwave, the mode-matching had to be re-done
• Attachment #1 shows the mode-matching solution being implemented
• Current state - I've placed all the optics up to and including the doubling crystal + oven. Alignment through IR Faraday is pretty good, QWP+HWP angles optimized to maximize transmission through the Faraday (<10% loss). Oven has been hooked up to temperature controller, and is currently set to 36.3 degrees. Coarse alignment into doubling crystal done at lower power. Even with the low IR power, I am able to see some green. It remains to turn the injection current up and do the fine alignment + lens position tweaking to maximize the green power from the doubling crystal - with ~1W of power, assuming 2%/W SHG efficiency, we should be seeing 20 mW of green (which is probably way too much)

Immediate next steps:

1. Some optimization to be done with regards to beam dumps for rejected beam from IR Faraday. Also double check to make sure that the reflected beam from L1 doesn't go back directly to the laser (at the moment it doesn't, is there a standard way to do this? I was trying to have the lens as close to normal incidence as possible, but I may not have been entirely successful which is why the reflected beam is not going straight back at the moment).
2. Optimize mode-matching into the doubling crystal
3. Once the desired green mode is obtained, continue with the rest of the layout
4. Update CAD drawing to reflect new layout

12085   Thu Apr 21 14:25:52 2016 gautamUpdateendtable upgradeGreen light recovered

I've made progress on the new layout up to the doubling oven. After doing the coarse alignment with the diode current to the NPRO at ~1A, I turned it back up to the nominal 2A. I then rotated the HWP before the IR Faraday such that only ~470mW of IR power is going into the doubler (the rest is being dumped on razor beam dumps). After tuning the alignment of the IR into the doubling oven using the steering mirror + 4 axis translation stage on which the doubling oven is mounted, I get ~3.2mW of green after the harmonic separator and a HR mirror for green. The mode looks pretty good to the eye (see attachment #1), and the conversion efficiency is ~1.45%/W - which is somewhat less than the expected 2%/W but in the ballpark. It may be that some fine tweaking of the alignment + polarization while monitoring the green power can improve the situation a little bit (I think it may go up to ~4mW, which would be pretty close to 2%/W conversion efficiency). The harmonic separator also seems to be reflecting quite a bit of green light along with IR (see attachment #2) - so I'm not sure how much of a correction that introduces to the conversion efficiency.

While doing the alignment, I noticed that some amount of IR light is actually transmitted through the HR mirrors. With ~500mW of incident light at ~45 degrees, this transmitted light amounts to ~2mW. Turns out that this is also polarization dependant (see attachment #3) - for S polarized light, as at the first two steering mirrors after the NPRO, there is no transmitted light, while for P-polarized light, which is what we want for the doubling crystal, the amount transmitted is ~0.5%. The point is, I think the measured levels are consistent with the CVI datasheet. We just have to take care find all these stray beams and dump them.

I will try and optimize the amount of green power we can get out of the doubler a little more (but anyway 3mW should still be plenty for ALS). Once I'm happy with that, I will proceed with laying out the optics for mode-matching the green to the arm.

12089   Tue Apr 26 15:22:35 2016 SteveUpdateendtable upgradeCleaning ETMX vacuum dirty window

Gautom is progressing with the layout nicely. The X-arm transmission window have not seen cleaning for decades. This should be the time to do it. Here is picture of dirtiness.

It is not that simple... How much effort should we put in it? The hole table with 1W inno laser plus... set up now about ~500 lbs  We can pull it off carefully, but it is not risk free.

We should look at our other signal port windows! Gautom's long reach able him to do the first contact cleaning without moving anything. It is great!

12090   Tue Apr 26 23:19:42 2016 gautamUpdateendtable upgradeGreen aligned to arm - high order mode flashes seen

Attachment #1

Layout as of today. Most of the green path is done. The Green REFL PD + PZT mirrors have not been hooked up to their respective power sources yet (I wonder if it's okay to start laying cables through the feedthroughs on either end of the table already, or if we want to put whatever it is that makes it airtight eventually in first?). A rough power budget has been included (with no harmonic separator just before the window), though some optimization can be done once the table is completely repopulated.

Attachment #2

A zoomed-in version of the REFL path.

Some general notes:

1. I've tried to use the custom 3/4" O.D. posts + baseplate arrangement wherever possible (only 1 steering mirror is on a 1" post clamped with a fork to the table because of space constraints). Where the baseplates could not be bolted onto the table directly, I've used Newport SS Dogs to do the job.
2. I checked for continuity between the PZT outer case and the table top with a multimeter, and found none. So I chose to leave the Thorlabs baseplates in place. For the REFL PD, I've used an insulating baseplate given to me by Steve.
3. I've used some custom length 3/4" O.D. posts to get the beam up to the right height (~4.75") just before sending the green beam in. The beam height is 4" elsewhere.
4. I was playing around with positioning the harmonic separator immediately before the vacuum chamber window - I found that there is a substantial amount of green light that is reflected, though there doesn't seem to be any IR leaking through. The mirror was labelled Y1-1037-45P, which is a code for CVI mirrors, though I believe it is a LaserOptik product and that we have a couple of other such mirrors in the optics cabinet - though they are all 1". This document suggests that from the back side, there should be <0.1% reflection of green while on the front side it should be < 3%. I will have to hunt a little more for the specs, and measure the powers to see if they match the previously quoted numbers. In any case, I'll have to think of how to separate the (unwanted) reflected green and the transmitted IR from the cavity in the IR transmon path.
5. There are some minor changes to the planned layout posted here - I will update these in due course once the Transmon path and Oplev have been set up.

I am closing the PSL shutter and the EX laser shutters for the night as I have applied a layer of first contact to the window for cleaning purposes, and we don't want any laser light incident on it. It may be that the window is so dirty that we may need multiple F.C. cleaning rounds, we will see how the window looks tomorrow...

12094   Wed Apr 27 15:04:47 2016 SteveUpdateendtable upgradeCleaning ETMX vacuum dirty window

It looks very promising.

12095   Thu Apr 28 00:41:08 2016 gautamUpdateendtable upgrademore progress - Transmon PD installed

The IR Transmon system is almost completely laid out, only the QPD remains to be installed. Some notes:

1. The "problem" with excessive green power reflected from the harmonic separator has been resolved. It is just very sensitive to the angle of incidence. In the present configuration, there is ~10uW of green power reflected from either side, which shouldn't be too worrisome. But this light needs to be dumped. Given the tiny amount, I think a black glass + sticky tape solution is best suited, given the space constraints. This does not reach the Transmon PDs because there is a filter in the path that is transmissive to IR only.
2. I aligned the transmitted beam onto the Thorlabs PD, and reconnected the signal BNC cable (the existing cable wasn't long enough so I had to use a barrel connector and a short extension cable). I then reverted the LSC trigger for the X arm back to TRX DC and also recompiled c1ass to revert to TRX for the dither alignment. At the moment, both arms are stably locked, although the X arm transmission is saturated at ~0.7 after running the dither alignment. I'm not sure if this is just a normalization issue given the new beam path or if there is something else going on. Further investigations tomorrow.
3. It remains to dump some of the unwanted green light from the addition of the harmonic separator...
4. We may want to redesign some (or all) of the Transmon path - the lens currently in use seems to have been chosen arbitrarily. Moreover, it is quite stubbornly dirty, there are some markings which persist after repeated first contact cleaning...

I feel like once the above are resolved, the next step would be to PDH lock the green to the arm and see what sort of transmission we get on the PSL table. It may be the polarization or just alignment, but for some reason, the transmitted green light from the X arm is showing up at GTRY now (up to 0.5, which is the level we are used to when the Y arm has green locked!). So a rough plan of action:

1. Install transmon QPD
2. PDH lock green to X arm
3. Fix the window situation - as Steve mentioned in an earlier elog, the F.C. cleaning seems to have worked well, but a little remains stuck on the window (though away from where any laser radiation is incident). This is resolved easily enough if we apply one more layer of F.C., but the bottle-neck right now is we are out of PEEK which is what we use to remove the F.C. once dried. Steve thinks a fresh stock should be here in the next couple of days...
4. Once 3 is resolved, we can go ahead and install the Oplev.
5. Which leaves the lst subsystem, coupling to the fiber and a power monitor for the NPRO. I have resolved to do both these using the 1% transmitted beam after the beamsplitter immediately after the NPRO rather than pick off at the harmonic separator after the doubling oven. I need to do the mode-matching calculation for coupling into the fiber and also adjust the collimating lens...
6. Clean-up: make sure cables are tied down, strain-relieved and hooked up to whatever they are supposed to be hooked up to...
12099   Fri Apr 29 00:55:46 2016 gautamUpdateendtable upgradegreen PDH locked to Xarm

Using the modulation frequency suggested here, I hooked up the PDH setup at the X-end and succeeded in locking the green to the X arm. I then rotated the HWP after the green Faraday to maximize TRX output, which after a cursory alignment optimization is ~0.2 (I believe we were used to seeing ~0.3 before the end laser went wonky). Obviously much optimization/characterization remains to be done. But for tonight, I am closing the PSL and EX laser shutters and applying first contact to the window once more courtesy more PEEK from Koji's lab in W Bridge. Once this is taken care of, I can install the Oplev tomorrow, and then set about optimizing various things in a systematic way.. MC autolocker has also been disabled...

Side note: for the IR Transmon QPD, we'd like a post that is ~0.75" taller given the difference in beam height from the arm cavity and on the endtable. I will put together a drawing for Steve tomorrow..

12100   Fri Apr 29 16:05:23 2016 gautamUpdateendtable upgradeCleaning ETMX vacuum dirty window

After a second round of F.C. application, I think the window is clean enough and there are no residual F.C. pieces anywhere near the central parts of the window (indeed I think we got most of it off). So I am going to go ahead and install the Oplev.

 Quote: It looks very promising.

12104   Mon May 2 19:14:18 2016 gautamUpdateendtable upgradeOptical layout almost complete

With Steve's help, I installed the Oplev earlier today. I adjusted the positions of the two lenses until I deemed the spot size on the QPD satisfactory by eye. As a quick check, I verified using the DTT template that the UGF is ~5Hz for both pitch and yaw. There is ~300uW of power incident on the QPD (out of ~2mW from the HeNe). In terms of ADC counts, this is ~13,000 counts which is about what we had prior to taking the endtable apart. There are a couple of spots from reflections off the black glass plate in the vacuum chamber, but in general, I think the overall setup is acceptable.

This completes the bulk of the optical layout. The only bits remaining are to couple the IR into the fiber and to install a power monitoring PD. Pictures to follow shortly.

Now that the layout is complete, it remains to optimize various things. My immediate plan is to do the following:

1. Maximize green transmission by tweaking alignment. I should also do a quick check using mirror specs to see that the measured transmitted green power compares favourably to what is expected.
2. Check the green PDH loop transfer function at the X end - this will allow me to set the gain on the uPDH box systematically.
3. Re-establish green beats, check noise performance.
4. There are possibly multiple beam dumps that have to be installed. For now, I've made sure that no high power IR beams are incident on the enclosure. But there are a couple of red and green beams that have to be accounted for.

I will also need to upload the layout drawing to reflect the layout finally implemented.

Not directly related:

The ETMx oplev servo is now on. I then wanted to see if I could lock both arms to IR. I've managed to do this successfully - BUT I think there is something wrong with the X arm dither alignment servo. By manually tweaking the alignment sliders on the IFOalign MEDM screen, I can get the IR transmission up to ~0.95. But when I run the dither, it drives the transmission back down to ~0.6, where it plateaus. I will need to investigate further.

GV Edit: There was some confusion while aligning the Oplev input beam as to how the wedge of the ETM is oriented. We believe the wedge is horizontal, but its orientation (i.e. thicker side on the right or left?) was still ambiguous. I've made a roughly-to-scale sketch (attachment #1) of what I think is the correct orientation - which turns out to be in the opposite sense of the schematic pinned up in the office area.. Does this make sense? Is there some schematic/drawing where the wedge orientation is explicitly indicated? My search of the elog/wiki did not yield any..

12105   Thu May 5 03:05:37 2016 gautamUpdateendtable upgradeALS status update

[ericQ, gautam]

Today we spent some time looking into the PDH situation at the X end. A summary of our findings.

1. There is something that I don't understand with regards to the modulation signal being sent to the laser PZT via the sum+HPF pomona box - it used to be that with 2Vpp signal from the function generator, we got ~5mVpp signal at the PZT, which with the old specs resulted in a modulation of ~0.12rad. Now, however, I found that there was a need to place a 20dB attenuator after the splitter from the function generator in order to realize a modulation depth of ~0.25 (which is what we aim for, measured by locking to the TEM00 modes of the carrier and sidebands and comparing the ratio of powers). It could be that the PZT capacitance has changed dramatically after the repair. Nevertheless, I still cant reconcile the numbers. We measured the transfer function from the LO input of the pomona box to the output with the PZT connected, and figure there should be ~70dB of attentuation (with the 20dB additional attenuator in place). But this means 1Vpp*0.0003*70rad/V = 0.02rad which is an order of magnitude away from what the ratio of powers suggest. Maybe the measurement technique was not valid. In any case, this setup appears to work, and I'm also able to send +7dBm to the mixer which is what it wants (function generator output is 3Vpp).
2. In addition to the above, I found that the demodulated error signal had a peak-to-peak of a few volts. But the PDH servo is designed to have tens of mV at the input. Hence, it was necessary to turn down the gain of the REFL PD to 10dB and add a 20dB attenuator between mixer output and servo input.
3. While Johannes and I were investigating this earlier in the afternoon, we found that the waveform going to the laser PZT was weirdly distorted (still kind of sinusoidal in shape, but more rounded, I will put up a picture shortly). This may not be the biggest problem, but perhaps there is a better way to pipe the LO signal to the PZT and mixer than what is currently done.
4. We then looked at loop transfer function and spectrum of the control signal. Plots to follow. They look okay.
5. I measured the green power coming onto the PSL table. It is ~400uW. After optimizing alignment, the green transmission is ~0.4 according to whatever old normalization we are using.
6. We then recovered the X green beatnote and looked at the ALS noise spectrum. Beatnote amplitude at the beat PD is ~ -27dBm. The coherence in the region of a few hundred Hz suggests that some improvements can be made to the PDH situation (the gain of the PDH servo is maxed out at the X end at the moment...). But the bottom line is this is probably good enough to get back to locking...
12108   Thu May 5 14:05:01 2016 ranaUpdateendtable upgradeALS status update

All seems very fishy. Its not good to put attenuators and filters in nilly-willy.

1. Once the post-PD bandpass has been designed and constructed, you should be able to use whatever PD gain setting gives you the best SNR. There's no need to use more PD gain than necessary; it just reduces the PD bandwidth. What is the input referred current noise of the PD at the different gain settings?
2. The open loop mixer output *should* be very large. It should be reduced to mV only when the loop is closed.
3. The better way to estimate the modulation depth is to lock the arm on red as usual and then scan the EX laser and look at the green transmission. The FSR is 3.7 MHz, so the SBs should show up well in a narrow scan around the carrier.
4. I guess its going to be tough to impedance match the splitter box to the NPRO PZT, since its impedance is all over the place at 200-300 kHz, but you could put a 50 Ohm in-line terminator in there somewhere?
5. The Bode plot seems to indicate that we could easily get a 10 kHz UGF and then switch on a Boost. Is the remote Boost switch disabled or always ON? I am suspicious of the plot and think that the coarse trace is probably missing some sharp resonances which will sneakily bite you.
12109   Thu May 5 21:28:44 2016 gautamUpdateendtable upgradeInnolight PZT capacitance

I suggested in an earlier elog that after the repair of the NPRO, the PZT capacitance may have changed dramatically. This seems unlikely - I measured the PZT capacitance with the BK Precision LCR meter and found it to be 2.62 nF, which is in excellent agreement with the numbers from elogs 3640 and 4354 - but this makes me wonder how the old setup ever worked. If the PZT capacitance were indeed that value, then for the Pomona box design in elog 4354, and assuming the PM at ~216kHz which was the old modulation frequency was ~30rad/V as suggested by the data in this elog, we would have had a modulation depth of 0.75 if the Function Generator were set to output a Signal at 2Vpp (2Vpp * 0.5 * 0.05 * 30rad/V = 1.5rad pp)! Am I missing something here?

Instead of using an attenuator, we could instead change the capacitor in the pomona box from 47pF mica to 5pF mica to realize a modulation depth of ~0.2 at the new modulation frequency of 231.25 kHz. In any case, as elog 4354 suggests, the phase introduced by this high-pass filter is non-zero at the modulation frequency, so we may also want to install an all-pass filter which will allow us to control the demodulation phase. This should be easy enough to implement with an Op27 and passive components we have in hand...

12122   Thu May 19 16:29:20 2016 SteveUpdateendtable upgradeOptical layout almost complete

12526   Fri Sep 30 19:53:07 2016 gautamUpdateendtable upgradeX end IR pickoff fiber coupled

[johannes, gautam]

Today we re-installed the fiber coupler on the X-endtable to couple some of the PSL light into a fiber that runs to the PSL table, where it is combined with a similar PSL pickoff to make an IR beat between the EX AUX laser and the PSL. The main motivation behind this was to make the process of finding the green beatnote easier. We used JAMMT (just another mode matching tool) to calculate a two lens solution to couple the light into the collimator - we use a +200mm and -200mm lens, I will upload a more detailed mode matching calculation + plot + picture soon. We wanted to have a beam waist of 350um at the collimator, a number calculated using the following formula from the Thorlabs website:

$d =4\lambda (\frac{f}{\pi*MFD})$

where d is the diameter of the output beam from the collimator, f is the collimating lens focal length and MFD is 6.6um for the fiber we use.

There is ~26mW of IR light coming through the BS after the EX AUX - after playing around with the 6 axis stage that the coupler is mounted on, Johannes got the IR transmission to the PSL table up to ~11.7mW. The mode matching efficiency of 45% is certainly not stellar, but we were more curious to find a beat and possibly measure the X arm loss so we decided to accept this for now - we could probably improve this by moving the lenses around. We then attenuated the input beam to the fiber by means of an ND filter such that the light incident on the coupler is now ~1.3mW, and the light arriving at the PSL table from the EX laser is ~550uW. Along with the PSL light, after the various couplers, we have ~500uW of light going to the IR beat PD - well below its 2mW threshold.

The IR beat was easily found with the frequency counter setup. However, there was no evidence of a green beat. So we went to the PSL table and did the near-field-far-field alignment onto the beat PD. After doing this, we were able to see a beat - but the amplitude was puny (~-60dBm, we are more used to seeing ~-20dBm on the network analyzer in the control room). Perhaps this can be improved by tweaking the alignment onto the PD while monitoring the RF output with an oscilloscope.

Moreover, the green PDH problems with the X end persist - even though the arm readily locks to a TEM00 mode, it frequently spontaneously drops lock. I twiddled around with the gain on the uPDH box while looking at the error signal while locked on a oscilloscope, but was unable to mitigate the situation. Perhaps the loop shape needs to be measured and that should tell us if the gain is too low or high. But ALS is getting closer to the nominal state...

Johannes is running his loss measurement script on the X arm - but this should be done by ~10pm tonight.

12532   Wed Oct 5 16:28:10 2016 gautamUpdateendtable upgradeEX laser power monitor PD installed

I installed a 10% BS to pick off some of the light going to the IR fiber, and have added a Thorlabs PDA55 PD to the EX table setup. The idea is to be able to monitor the power output of the EX NPRO over long time scales, and also to serve as an additional diagnostic tool for when ALS gets glitchy etc. There is about 0.4mW of IR power incident on the PD (as measured with the Ophir power meter), which translates to ~2500 ADC counts (~1.67V as measured with an Oscilloscope set to high impedance directly at the PD output). The output of the PD is presently going to Ch5 of the same board that receives the OL QPD voltages (which corresponds to ADC channel 28). Previously, I had borrowed the power and signal cables from the High-Gain Transmon PD to monitor this channel, but today I have laid out independent cabling and also restored the Transmon PD to its nominal state.

On the CDS side of things, I edited C1SCX to route the signal from ADC Ch28 to the ALS block. I also edited the ALS_END library part to have an additional input for the power monitor, to keep the naming conventions consistent. I have added a gain in the filter module to calibrate the readout into mW using these numbers. The channel is called C1:ALS-X_POWER_OUT, and is DQed for long-term trending purposes.

The main ALS screen is a bit cluttered so I have added this channel to the ALS overview MEDM screen for now..

438   Tue Apr 22 22:19:02 2008 robMetaphysicslorejiggling sliders

In the interests of tacit communication of scientific knowledge, I here reveal a nugget of knowledge which may or may not prove useful to new LIGOites: sometimes when front-end machines are rebooted, the hardware they control can wind up in a state which is not accurately represented by the EPICS values you may see. This can be easily rectified by momentarily changing the EPICS settings in question. For reference, this came up tonight in the context of the whitening gain sliders for the TransMon QPDs.
1104   Sun Nov 2 20:21:58 2008 ranaConfigurationloreHP 5550dtn (Grazia) set up on allegra
I set up printing to grazia from allegra. The CUPS interface was not as straightforward as Tobin had made it seem in the Wiki. I had to type in the IP address and port number by hand.

The steps (AFAIR):
1) Goto http://localhost:631/
3) Choose HP JetDirect
4) Use the correct address (socket://131.215.115.220:9100)
5) Choose HP and the 5550 postscript driver as the options
6) Try to only print useful stuff and not kill too many trees.
1217   Thu Jan 8 16:49:37 2009 ranaConfigurationloreHP 5550dtn (Grazia) set up on allegra

 Quote: I set up printing to grazia from allegra. The CUPS interface was not as straightforward as Tobin had made it seem in the Wiki. I had to type in the IP address and port number by hand. The steps (AFAIR):1) Goto http://localhost:631/ 2) Click on "Add Printer" 3) Choose HP JetDirect 4) Use the correct address (socket://131.215.115.220:9100) 5) Choose HP and the 5550 postscript driver as the options 6) Try to only print useful stuff and not kill too many trees.

It ought to be root to do that.
1579   Wed May 13 02:53:12 2009 robSummaryloreChannel Hopping: That ancient enemy (MC problems)

We were stymied tonight by a problem which began late this afternoon.  The MC would periodically go angularly unstable, breaking lock and tripping the MC2 watchdogs.  Suspicion fell naturally upon McWFS.

Eventually I traced the problem to the MC3 SIDE damping, which appeared to not work--it wouldn't actually damp, and the Vmon values did not correspond to the SDSEN outputs.  Suspicion fell on the coil driver.

Looking at the LEMO monitors on the MC3 coil driver, with the damping engaged, showed clear bit resolution at the 100mV level, indicating a digital/DAC problem.  Rebooting c1sosvme, which acquires all the OSEM sensor signals and actually does the side damping, resolved the issue.

1582   Wed May 13 14:43:29 2009 robSummaryloreChannel Hopping: That ancient enemy (MC problems)

 Quote: We were stymied tonight by a problem which began late this afternoon.  The MC would periodically go angularly unstable, breaking lock and tripping the MC2 watchdogs.  Suspicion fell naturally upon McWFS. Eventually I traced the problem to the MC3 SIDE damping, which appeared to not work--it wouldn't actually damp, and the Vmon values did not correspond to the SDSEN outputs.  Suspicion fell on the coil driver. Looking at the LEMO monitors on the MC3 coil driver, with the damping engaged, showed clear bit resolution at the 100mV level, indicating a digital/DAC problem.  Rebooting c1sosvme, which acquires all the OSEM sensor signals and actually does the side damping, resolved the issue.

Lies!  The problem was not resolved. The plot shows a 2-day trend, with the onset of the problem yesterday clearly visible as well as the ineffectiveness of the soft-reboot done yesterday.   So we'll try a hard-reboot.

2138   Fri Oct 23 15:02:00 2009 robUpdateloremarconi phase

So, it appears that one doesn't even have to change the Marconi set frequency to alter the phase of the output signal.  It appears that other front panel actions (turning external modulations on/off, changing the modulation type) can do it as well.  At least that's what I conclude from earlier this morning, when after setting up the f2 Marconi (166MHz) for external AM, the double-demod handoff in the DRMI no longer worked.  Luckily this isn't a real problem now that we have the setDDphases and senseDRM scripts.

2139   Sat Oct 24 04:57:33 2009 ranaUpdateloremarconi phase

 Quote: So, it appears that one doesn't even have to change the Marconi set frequency to alter the phase of the output signal.  It appears that other front panel actions (turning external modulations on/off, changing the modulation type) can do it as well.  At least that's what I conclude from earlier this morning, when after setting up the f2 Marconi (166MHz) for external AM, the double-demod handoff in the DRMI no longer worked.  Luckily this isn't a real problem now that we have the setDDphases and senseDRM scripts.

The real problem is that we are using frequency synthesizers to make the beat signals (133 and 199) instead of mixers. Luckily, the future 40m will not use beat signals (?) or synthesizers.

2414   Mon Dec 14 15:18:18 2009 JenneUpdatelorearmLoss script ran....results confidential

I ran the armLoss script for both Xarm and Yarm.  The results are confidential, pending the completion of Alberto's cavity pole/finesse measurement due to the 'bet' as to what the new losses are after the drag wiping.

If you're the kind of person who likes to look at their Chrismas presents, the log files with the results are in the usual place for this script: /scripts/LSC/loss-ARM-GPStime.log  (loss-Y-944865071.log and loss-X-944865946.log)

2566   Wed Feb 3 09:01:42 2010 robUpdateloreIFO isn't playing nice tonight

Quote:

I checked the situation from my home and the problem was solved.

The main problem was undefined state of the autolocker and the strange undefined switch states, being associated with the bootfest and burtrestore.

- MC UP/DOWN status shows it was up and down. So I ran scripts/MC/mcup and scripts/MC/mcdown. These cleared the MC autolocker status.

- I had a problem handling the FSS. After mcup/mcdown above, I randomly pushed the "enable/disable" buttons and others, and with some reason, it recovered the handling. Actually it acquired the lock autonomously. Kiwamu may have also been working on it at the same time???

- Then, I checked the PSL loop. I disconnected the loop by pushing the "test" button. The DC slider changes the PZT voltage only 0~+24V. This is totally strange and I started pushing the buttons randomly. As soon as I pushed the  "BLANK"/"NORMAL" button, the PZT output got back under the control.

- Then I locked the PMC, MZ, and MC as usual.

Alberto: You must be careful as the modulations were restored.

 Quote: [Jenne, Kiwamu] It's been an iffy last few hours here at the 40m.  Kiwamu, Koji and I were all sitting at our desks, and the computers / RFM network decided to crash.  We brought all of the computers back, but now the RefCav and PMC don't want to lock.  I'm a wee bit confused by this.  Both Kiwamu and I have given it a shot, and we can each get the ref cav to sit and flash, but we can't catch it.  Also, when I bring the PMC slider rail to rail, we see no change in the PMC refl camera.  Since c1psl had been finicky coming back the first time, I tried soft rebooting, and then keying the crate again, but the symptoms remained the same.  Also, I tried burt restoring to several different times in the last few days, to see if that helped.  It didn't.  I did notice that MC2 was unhappy, which was a result of the burtrestores setting the MCL filters as if the cavity were locked, so I manually ran mcdown.  Also, the MC autolocker script had died, so Kiwamu brought it back to life. Since we've spent an hour on trying to relock the PSL cavities (the descriptive word I'm going to suggest for us is persistent, not losers), we're giving up in favor of waiting for expert advice in the morning.  I suppose there's something obvious that we're missing, but we haven't found it yet......

This is a (sort of) known problem with the EPICS computers: it's generally called the 'sticky slider' problem, but of course it applies to buttons as well.  It happens after a reboot, when the MEDM control/readback values don't match the actual applied voltages.  The solution (so far) is just to twiddle' the problematic sliders/button.  There's a script somewhere called slider_twiddle that does this, but I don't remember if it has PSL stuff in it.  A better solution is probably to have an individual slider twiddle script for each target machine, and add the running of that script to the reboot ritual in the wiki.

2598   Fri Feb 12 14:19:28 2010 rana, steveHowToloreInternational Fax

Steve showed me how to send an international fax today:

2. Dial:   011 - (country code) - number
3. Press START (either the black or color option)
4. wait for the screaming fax noise
5. Done

3660   Wed Oct 6 14:49:54 2010 ranaSummaryloreSteve on the sea

4960   Mon Jul 11 14:03:37 2011 steveHowTolorehow to visit your old lab

Alberto is visiting us from Australia. He brought some terrific presents. It is going to be very demanding task to wait for the rest of the 40m team

to return from Wales to taste coffee:  PNG Peaberry of Wagonga, Monsooned Malabar of Jindebah and Signature Blue Blend of Cosmorex.

6694   Sun May 27 17:19:27 2012 ranaSummaryloreStrawberries

We have placed some sweet giant strawberries in the fridge; free for eating for anyone working in the lab today or tomorrow:

8887   Mon Jul 22 03:10:41 2013 ranaSummaryloreAngel of the Y End Table?

Trying to take an image or movie of the ETMY Transmon cam, we got instead this attached image.

I think it is just some scattered green light, but others in the control room think that it is a message from somewhere or someone...

8888   Mon Jul 22 06:58:17 2013 LisaSummaryloreAngel of the Y End Table?

 Quote: Trying to take an image or movie of the ETMY Transmon cam, we got instead this attached image. I think it is just some scattered green light, but others in the control room think that it is a message from somewhere or someone...

It is not an angel, it is clearly a four leaf clover (also known as "quadrifoglio"). It is very rare, it brings good luck!

9966   Fri May 16 20:55:18 2014 JamieFrogsloreun-full-screening Ubuntu windows with F11

Last week Rana and I struggled to figure out how to un-full-screen windows on the Ubuntu workstations that appeared to be stuck in some sort of full screen mode such that the "Titlebar" was not on the screen.  Nothing seemed to work.  We were in despair.

Well, there is now hope: it appears that this really is a "fullscreen" mode that can be activated by hitting F11.  It can therefore easily be undone by hitting F11 again.

12915   Wed Mar 29 09:24:28 2017 SteveUpdateloresummery pages

The summery pages are working at a slow motion speed. It's response time 12 minutes.

1020   Thu Oct 2 16:44:28 2008 steveSummaryoplevsoptical levers
The idea is to push the UGF to 10 Hz of the TM oplev servos with quiet HeNe laser.
We measured good intensity noise of JDS 1103P in May 2007 and converted most of the TM oplevs to it.
The ITMs still have the noisy 670nm , 1 mW, diode lasers to begin with.
In order to get 1 mW power returning to the qpds I measured the power going to TMs
and returning on qpds ...so we can select the appropriate laser power for the conversion.

40m optical lever lasers:

HeNe laser JDS 1103P, 633nm, linear polarization 500:1,

ETMX: qpd 0.12 mw (4%) reflected of 3 mW,
ETMY: qpd 0.1o (3.8%) " 2.6
BS: qpd 0.02 ( 2.5%) " 0.8
PRM: qpd 0.01 (1.3%) " 0.75
SRM: qpd 0.08 (10%) " 0.8

Coherent 670 nm Diode Lasers VLM-tm, 0.95 mW, linear polarization 100:1,

ITMX: qpd 0.1 mW (11%) reflected back from TM of 0.9 mW
ITMY: qpd 0.04 (7%) " " 0.6

It seems that JDS HeNe laser 633 nm, linear polarization 500:1, 10 mW will do the job
1245   Thu Jan 22 12:08:59 2009 peteUpdateoplevsoplev calibration
Following the procedure described in Royal Reinecke's 2006 SURF report, I've calibrated the ETMY yaw oplev DOF. The idea is to sweep the mirror tilt, measuring the transmitted cavity power and the oplev error signal. The cavity power can be related to the mirror tilt in radians following D. Anderson APPLIED OPTICS, Vol. 23, No. 17, 1984.

I've made a simple matlab script which spits out the final number; it calls Royal's perl script to do the sweep. I get 420 microrad/ct for ETMY yaw. In 2006 Royal got 250 microrad/ct. Could something have changed this much, or is one of us wrong? I'll double check my procedure and do the other arm cavity oplevs, and describe it in detail when I have more confidence in it.

Kakeru and I plan to extend this to handle the PRM, SRM, and BS. One script to rule them all.
1247   Thu Jan 22 23:36:50 2009 peteHowTooplevsarm cavity oplev calibration
calibrated the y-arm oplevs. the procedure is contained in a matlab script. the whereabouts of this script will be revealed in a future log entry.

procedure:

1) Start with a single arm aligned and locked. Dither the mirror tilt in a DOF. Measure arm cavity power and oplev error signal. See the first attached plot.

2) Fit the plot to a gaussian and determine mu and sigma.

3) For a spherical ETM optic, the power in the cavity P(a), as a function of translational beam axis displacement a=R*sin(theta), is proportional to exp[-a^2/(2*x^2)] where x is the waist size (D. Anderson APPLIED OPTICS, Vol. 23, No. 17, 1984). The power as a function of mirror tilt in cts, P(tilt) is proportional to exp[-(tilt-mu)^2 /(2*sigma^2)]. So if R is the mirror radius then theta = arcsin(a/R) = arcsin[(1/R)*(tilt-mu)*x/sigma)].

4) Fit theta versus mirror tilt to get the calibration. See the second attached plot.

5) For a flat ITM optic, mirror tilt causes an angular displacement of the beam. The math for this case is given in Anderson.
1249   Fri Jan 23 12:48:12 2009 KakeruUpdateoplevsarm cavity oplev calibration
I calibrated optlevs of x and y arm cavity, indipendently from Peter's work.

This result is similar to Royal's one (within 30% difference except for ETMX pit), but different from Peter's in ETMY.

The attached figure is the data and fitted curve of ITMX pit.
I took this data for 8s, with 4 Hz excitation.
1251   Fri Jan 23 16:33:27 2009 peteUpdateoplevsx-arm oplev calibrations

As with y-arm, my ITM measurements agree with Kakeru and Royal, but my ETM measurements are not quite a factor of 2 higher. Kakeru and I are investigatin.
1259   Thu Jan 29 17:24:41 2009 KakeruUpdateoplevsarm cavity oplev calibration
I calibrated optlevs again. My previous work has a lot of mistakes, so ignore it.

(For ITMY, the data is low quality)

My calcuration and Peter's(based on Royal's report) is different in two point.
i) Royal uses some geometrical factor to calibrate ITM.
ii) Royal fits data to exp(-a^2/(2*w0^2)), and I fit data to exp(-a^2/w0^2).

When I calculate with modification of these differences, my result became almost same value of Peter's one.
Now we are discussing which equation is correct.

But we must do some laser works before it...
1377   Mon Mar 9 17:11:38 2009 AlbertoConfigurationoplevsoptical levers centering

Yoichi, Alberto

this afternoon we centered the optical levers for all the optics.

To do that we first ran the alignment scripts for all the cavities.

1403   Sat Mar 14 22:53:12 2009 KakeruUpdateoplevsarm cavity oplev calibration
I finished a calibration of optical levers.

To calibrate oplevs, I locked appropriate cavity and tilted a mirror.
A cavity with tilted mirror decrease its arm power. So I can know how much the tilt is.
For calibration of ITMX and ETMX, I locked X arm and measured TRX.
For ETMX, ETMY and BS, I locked Y arm and measured TRY
For PRM, I locked PRC and measured SPOB
For SRM, I locked SRC and measured REFL166

I used, for example, C1:SUS-ITMX_OPLEV_PERROR as an oplev signal.

The calibration factors for each mirror is below. The attachment is figures of my fitting.
I used modified equation for ITM calibration from my last calibration, so the value become small around 30%.

ITMX Pitch: 142   microrad/counts

SRM Yaw:    146   microrad/counts`

It looks strange that ITMY, BS and SRM has different value. I think this is a fitting problem.
These data have some asymmetry and cause these 20%-30% difference.
Actually, PRM Yaw has a little asymmetry but the value doesn't differ from Pitch.
This means that this calibration factor potentially has below 30% error.
(These data are the most fine data. I think we must adjust Y arm yaw alignment. The beam spot of ETMY looks too low!)
For SRM, I couldn't get fine data because it was very sensitive to tilt and easily lose its lock.
When I tuned cavity enough, The data become almost flat, so I used detuned cavity.

It is also strange that ITMX and ITMY is different. I guess that this is caused by the difference of the QPD input. The sum of QPD is around 10000 for ITMX and around 4500 for ITMY.
The difference between BS or PRM and SRM is same, I guess. The sum of QPD input for BS and SRM is around 1500, but for SRM, it is around 10000.

I will write more detailed document and upload it with my calibration code.
ELOG V3.1.3-