[Jenne, Manasa, Yuta]
We temporarily centered the beam on IPANG to see input pointing drift. From eyeball, drift was ~ 0.1 mrad/h in pitch.
What we did:
1. Aligned TT1/TT2 and aligned input pointing to Yarm.
2. Tweaked TT2 in pitch to center the beam on the first steering mirror of IPANG path. We still saw Yarm flash in higher order modes at this point. Before tweaking, the beam was hitting at the top edge.
3. Centered the beam on IPANG QPD.
4. Moved IPPOS first steering mirror because IPPOS beam was not on the mirror (off in yaw, on mirror edge). Also, IPPOS beam was coming out clipped in yaw.
5. Centered the beam on IPPOS QPD. We put lens in the path to focus the beam on the QPD.
6. Left input pointing untouched for 4 hours.
7. Restored TT2 again. We tried to align Y arm with IPANG available, but it was not possible without touching TRY path and AS was also clipped.
Below is the trend of IPANG sum, X, and Y. IPANG Y (IBQPD_Y) drifted by ~0.8 counts in 4 hours. IPANG is not calibrated yet, but Jenne used her eyeball to measure beam position shift on IPANG steering mirror. It shifted by ~2 mm. This means, input pointing drifts ~0.1 mrad/h in pitch.
Compared with yaw, pitch drift is quite large considering beam size at ETMY(~5 mm). We can monitor input pointing drift in weekends get longer trend.
- IPANG and IPPOS are both changed from the state before pumping.
I'm working on getting the input beam centered on the Yarm optics. To do this, I measured the spot positions, move the tip tilts, realign the cavity, then measure the new spot positions. While doing this, I am also moving the BS and Xarm optics to keep the Xarm aligned, so that I don't have to do hard beam-finding later.
Here is the plot of spot measurements today. The last measurement was taken with no moving, or realigning, just several hours later after speaking with our Indian visitors. I'm closer than I was, but there is more work to do.
Checking the drift in input pointing (TT2 is the main suspect)
I have centered IPPOS and the 2/3 part of IPANG that comes out of vacuum to the QPDs to see the drift in input pointing over the weekend or atleast overnight.
If anybody would be working with the IFO alignment over the weekend, do so only after recording the drift in IPANG and IPPOS or if you will be working later tonight, center them ion the QPDs before leaving.
I centered ipang and ippos on the QPDs (using only the steering mirrors) and wanted to see the drift over the weekend.
1. IPANG has drifted (QPD sum changed from -6 to -2.5); but it is still on the QPD.
2. IPPOS does not show any drift.
3. In the plot: The jump in IPANG on the left occured when I centered the beam to the QPD and that on the right is from the 4.7 earthquake and its aftershocks this morning.
1. Do we need to worry about this drift?
2. Which of the two TTs is resposible for the drift?
3. Do the TTs tend to drift in the same direction everytime?
P.S. The TTs were not touched to center on IPANG and IPPOS. The last time they were touched was nearly 6 hours before the centering. So the question of any immediate hysteresis is ruled out.
Spot centering on Y arm - DONE!
1. I went back to the IFO alignment slider positions from Friday. The Y arm was flashing in HOM because the earthquake this morning tripped all suspensions and the slider values were not real. X arm did not have any flashes.
2. Y arm aligned using TT1 and TT2. Spot centering measured using Jenne's A2L_Yarm script.
Pitch 6.48 4.39
Yaw -7.42 -3.135
3. I started centering in pitch. I used the same in-vac alignment method (down on TT1 and up on TT2 in pitch) and measured spot positions.
4. When the spot positions were centered in pitch, I started with yaw alignment.
5. I had to use TT1 to center on ITMY and move TT2 and ITMY to center on ETMY.
6. Spot positions after centering:
Pitch -1.22 -1.277
Yaw 0.42 -0.731
7. I wanted to go back and tweak the pitch cenetering; but framebuilder failed and dataviewer kept loosing connection to fb
AS seems clipped. Although it could be because of the misaligned BS.
IPANG was centered on the QPD, but it is so clipped, that I'm not sure we can trust it. Max sum right now is -4, rather than the usual -8 or -9.
Once fb is fixed, we should align the X-arm which will be followed by green alignment.
Over the last few weeks, it has been observed that there is some strong seismic activity that starts at around 9PM everyday and goes on for a couple of hours. It seems unlikely that it is our geologist neighbour (Jenne met with the grad student who works on the noisy experiment).
Steve just told those of us in the control room that the custodian who goes into the IFO room regularly steps on the blue support beams to reach the top of the chambers to clean them. Since we have seen in the past that stepping on the blue tubes can give the tables a bit of a kick, this could help explain some of the drift, particularly if it was mostly coming from TT2. The custodian has promised Steve that he won't step on the blue beams anymore.
This doesn't explain any of the ~1 hour timescale drift that we see in the afternoons/evenings, so that's still mysterious.
Tega and I went in to adjust the POP being in the ITMX Table. The beam entered the table high, so we adjusted the this by adding mirrors (The highlighted in Turqoise are mirrors which adjust the pitch of the beam). All the mirrors are set and we are now in the process of adjusting the PD.
Got POP beam centered on camera and nominally on the two PDs. Attachment #1 shows "carrier" camera.
Yehonathan and I attempted to align the LO2 beam today through the BS chamber and ITMX Chamber. We found the LO2 beam was blocked by the POKM1 Mirror. During this attempt, I tapped TT2 with the Laser Card. This caused the mirror to shake and dampen into a new postion. Afterwards, when putting the door back on ITMX, one of the older cables were pulled and the insulation was torn. This caused some major issues and we have been able to regain either of the arms to their original standings.
[Yuta, Anchal, Paco]
As described briefly by JC, there were multiple failure modes going during this work segment.
Indeed, the 64 pin crimp cable from the gold sat amp box broke when work around ITMX chamber was ongoing. We found the right 64 pin head replacement around and moved on to fix the connector in-situ. After a first attempt, we suddenly lost all damping on vertex SUS (driven by these old sat amp electronics) because our c1susaux acromag chassis stopped working. After looking around the 1x5 rack electronics we noted that one of the +- 20 VDC Sorensens were at 11.6 VDC, drawing 6.7 A of current (nominally this supply draws over 5 Amps!) so we realized we had not connected the ITMX sat amp correctly, and the DC rail voltage drop busted the acromag power as well, tripping all the other watchdogs ...
We fixed this by first, unplugging the shorted cable from the rack (at which point the supply went back to 20 VDC, 4.7 A) and then carefully redoing the crimp connector. The second attempt was successful and we restored the c1susaux modbusIOC service (i.e. slow controls).
As we restored the slow controls, and damped most vertex suspensions, we noticed ITMY UL and SD osems were reading 0 counts both on the slow and fast ADCs. We suspected we had pulled some wires around when busy with the ITMX sat amp saga. We found that Side OSEM cLEMO cable was very loose on the whitening board. In fact, we have had no side osem signal on ITMY for some time. We fixed this. Nevertheless the UL channel remained silent... We then did the following tests:
DO NOT TRUST THE SATELLITE BOX TESTER 2.
It takes 18 months to double the computational power of microprocessors but it took man thousands of years to invent the zipper. I never really understood that till these days.
Here is a sample of my latest results from Optickle simulations of the locking signal for the Power Recycling Cavity.
Thanks also to Rob's revolutionary bidimensional rotating matrix idea (I can see entire books of linear algebra going to be rewritten now because of that) I could find the way to determine the optimal demodulation phases for the demod signals.
There were also an other couple of missing details. But that came easily along.
The parfor function for the parallel computation in Matlab sped up some loops by a factor of 100.
In these particular plots there's still no CARM offset scan. That's what I'm going to post next on the elog, together with the signals for the other degrees of freedom.
Just to show that I'm confident I'm getting reasonable results, I'll post two PRC scans for different CARM. One set of plots is for the current 40m with -19.78 deg of SRM detuning phase, the other is for the Old Upgrade (9 Mhz vs the 11 currently planned) with no detuning phase.
I'm going to put together the results and get some conclusion about the 3f locking scheme for the current 40m and the upgrade.
Today we found the green beam from the end was totally missing at the vertex.
- What we found was very weak green beam at the end. Unhappy.
- We removed the PBS. We should obtain the beam for the fiber from the rejection of the (sort of) dichroic separator although the given space is not large.
- The temperature controller was off. We turned it on again.
- We found everything was still misaligned. Aligned the crystal, aligned the Faraday for the green.
- Aligned the last two steering mirrors such that we hit the approximate center of the ETMX and the center of the ITMX.
- Made the fine alignment to have the green beam at the PSL table.
The green beam emerged from the chamber looks not so round as there is a clipping at an in-vac steering.
We will make the thorough realignment before closing the tank.
We extracted the fiber that Suresh and Sonali laid over the summer, for the IR beat for the Ygreen laser, and Frank took it back to Bridge to be used in the new fiber distributed reference laser setup.
In light of the Yend auxiliary laser's ill health, I think we should reconsider the possibility of changing out the Yend laser table next week.
My thinking here is that if whatever the new mode matching solution is for a replacement laser (Tara has borrowed our spare NPRO that used to sit on top of the fridge, or we could take Annalisa's) requires a rework of the table layout, we might as well put the new layout onto the new table. So, we need to figure out what laser we will put in as the new Ygreen, and what it's waist looks like. If it just requires a small movement of existing lenses or new lenses in similar positions to the current ones, we can keep living with our current table. But, if the mode matching solution requires enough changes to distances / lens placement / whatever, we should think seriously about putting in the new table next week.
Here's what I would like to see happen on / before Monday:
Annalisa - Mode matching solution for new laser. If we get the laser back from Tara, this will involve first measuring the waist, otherwise we already know the waist of the ABSL laser that Annalisa is currently using.
Annalisa and Steve - Find optics for new mode matching in the lab, or order them by Monday afternoon.
Manasa - List of every screw, washer, optic, mount, etc. that will go on the new Y end table, with a notation as to whether or not we have it in-hand, and if not, what needs to happen before we do. Also, for things that we don't have, I'd like to see a summary of temporary solutions (e.g. keep using current mount for doubling crystal while new one is being machined).
Manasa / Annalisa / Koji - will the new mode matching solution fit within the existing layout, or do we need to redo the table layout?
Zach has just replied, and said that we should feel free to take the laser from his iodine setup in the West Bridge subbasement, in the ATF lab.
Annalisa, please ask Koji or Tara to show you where it is, and help you bring it to the 40m. You should install it (temporarily) on the PSL table, measure the waist, and find the beat in IR. Elog 3755 and elog 3759 have some of the details on how it has been done in the past.
Ok, I'm going to contact Koji.
1) Annalisa is going to start working on mode profiling and beat note search for the old MOPA NPRO.
2) In the meantime, Manasa is working on the end table items. This will be reviewed by KA in the afternoon.
The laser at ATF is moved to the 40m when the status of 1) and 2) is determined by KA to be reasonable.
We also make the beat note measurement for the ATF laser too.
We also make the beat note measurement for the ATF laser too.
Today I installed mirrors to steer the pick-off from the main laser beam in a more free part of the PSL table and make the beat note measurement between it and the NPRO.
At the beginning I took the beam from the harmonic separator after the doubling crystal, and I was going to bring it in a less full part of the table . At the end I realized that there was already a beam steered up to a more free part of the table, and the beam is taken from the transmission of the PMC.
Tomorrow I'm going to use that beam to find the beat note with the NPRO.
I also removed almost all the steering optics that I used on the ITMY table to send the auxiliary beam for ABSL through the window parallel to the POY beam. The most important thing is that I removed the BS, which was on the same path of the POY beam (see elog 8257).
I moved the auxiliary laser from the ITMY table to the PSL table and installed all the optics (mirrors and lenses) to steer the beam up to a PDA55 photodiode, where also the pick-off of the PSL is sent.
Tomorrow I'm going to measure the beat note between the two.
[Koji, Annalisa, Manasa]
NPRO with controller from ATF joins the 40m. We have put it on the POY table where we plan to use it for ABSL.
The beat note between the main PSL and the auxiliarly NPRO has been found!
The setup didn't change with respect to the one described on the previous note on the elog. A multimeter has been connected to the laser controller diagnostic pin to read out the voltage that indicated the laser crystal temperature.
The connector has been taken from the Yend table laser controller.
The voltage on the multimeter gave the same temperature shown by "Laser temperature" on the display of the controller, while "set temperature" was wrong.
The temperature has been varied using the laser controller with reference to the voltage read on the multimeter display.
Starting from 35.2 °C, the temperature has been first lowered until 20 °C and no beat note has been found, then temperature has been increased up to 35.2 °C and the first beat note has been found at 38.0 °C.
It has been detected at a frequency of about 80 MHz with an RF power of -27 dBm and a frequency fluctuation of about +/- 4 MHz.
I made more measurements slowly varying the laser temperature, to see how the beat note frequency changes with it. I'll make the plot and post it as soon.
I plot the variation of the beat note frequency as a function of "Alberto" NPRO laser's temperature.
After some discussion, now I'm going to vary the PSL temperature and find the auxiliary NPRO temperature matching to have the beat note between the two.
"Alberto"NPRO laser has been moved again on PSL table in order to make a measurement of the beat note varying also the PSL temperature.
It is useful because if the PSL temperature would drift we have to know which is the NPRO temperature that returns the beat.
I'm going to measure it tomorrow.
I measured the beat note between the "Alberto" NPRO laser and the PSL varying the PSL temperature and find the matching NPRO temperature that gave the beat.
I first switched off the FSS loop for the PSL, then I varied its temperature and switched on the loop back.
PSL temperature has been varied starting from 31.88 °C (its starting temperature) down to 23.88 by 1°C step, and then from 31.88 °C up to 36.92 °C, always with a 1°C step.
For each PSL temperature, the NPRO temperature was varied as well, in way to find the temperature to have a beat note between the two.
The trend of the NPRO laser temperature reminds the frequency change of the laser as a function of the crystal temperature continuous tuning.
I made measurements only for the first temperature of the NPRO laser which gave me the beat note. Tomorrow I'm going to find the beat note also for higher frequencies of the NPRO laser.
The beat note between the PSL laser and the "Alberto" NPRO laser has been measured. In particular, for each PSL temperature, more than one Aux laser frequency has been found.
The second of the three curves seems to be more stable than the other two, even if a "step" trend can be found in all of them (maybe due to the frequency change of the NPRO laser as a function of the crystal temperature continuous tuning, as mentioned in the previous elog). This is the reason why the points are not perfectly aligned, and the errors on the fit parameters are so big.
Attachment #1 shows the RIN and phase noise requirements for the 40m BHD for measuring Ponderomotive squeezing.
I did some more calculations based on our discussions at the meeting yesterday. Posting preliminary results here for comments.
Attachment #1 - Schematic illustration for the scattering scenarios. For all three scenarios, we would like for the scattered field to be lower than unsqueezed vacuum (safety factor to be debated).
Attachment #2 - Requirements on a fraction of the counter-propagating resonant mode of the OMC scattering back into the antisymmetric port, as a function of RIN and phase noise on this field (y-axis) and amount of field (depends on the amount of contrast defect light which can become resonant in the counter propagating mode). I don't encode any frequency dependence here.
Attachment #3 - Requirements on the direct scatter from the arm cavity resonant field (assumed to dominate any contribution from the PRC) onto the OMC DCPDs, for some assumed phase noise (y-axis) and fraction of the field that makes it onto the OMC DCPDs. This is a pretty stringent requirement. But the probability is low (it is the product of three presumably small numbers, (i) probablity of the beam scattering out of the TEM00 mode, (ii) BRDF of the scattering surface, (iii) probability of scattering back towards the DCPDs), so maybe feasible? I didn't model any RIN on this field, which would be an additional noise term to contend with. The range of the y-axis was chosen because I think these are reasonable amplitudes for chamber wall / other scattering surface motion at acoustic frequencies.
I drew out some idea of how we might use a single OMC to clean both paths of the BHD after mixing, without being susceptible to polarization-dependent effects within the OMC. Basically, can we send the two legs of the BHD into the OMC counterpropagating. I've attached a diagram.
I think one issue would be scattered light, since any backscatter directly couples into the counterpropagating mode, and thus directly to the PD. However, unless the polarization of the scattered light rotates it would not scatter back to the IFO. And, since the LO and signal mix before the OMC, this scattered light would not directly add phase noise.
Maybe more problematic would be that if the rejection at the PBS (or the polarization rotation) isn't perfect, light from the LO directly couples into the dark port. Can we get away with a Faraday isolator before the OMC?
I think a Faraday rotator rotates the polarizations in a same way for both forward and backward beam, and it's not like in this figure.
And the transmission through multiple faradays will also be a big issue.
A question was raised as to how much passive filtering we benefit from if we pick off the local oscillator beam for BHD from the PRC. I did some simplified modeling of this. For the expected range of arm cavity round trip losses (20-50 ppm), I think that the 40m CARM pole will be between 75-85 Hz. The corresponding recycling gain will be 40-50, with the current PRM. I assumed 1000 ppm loss inside the PRC. The net result is that, assuming the single pole coupled cavity response, we will get ~8-9 dB of filtering at ~200 Hz of the intensity noise of the input laser field to the interferometer if we pick the LO beam off from the PRC (e.g. PR2 transmission), instead of picking it off before.
The next questions are: (i) can we do a sufficiently good job of achieving the required RIN stability on the LO field for BHD without relying on the passive filtering action of the PRC? and (ii) is the benefit of the PRC filtering ruined in the process of routing the LO field from wherever the pickoff happens to the BHD setup?
We need to determine the geometry (= round-trip length and RoC of curved mirrors) of the OMC cavities for the 40m BHD experiment. Sticking to the aLIGO design of a 4 mirror bowite cavity with 2 flat mirrors and 2 curved mirrors, with a ~4deg angle of incidence, we need to modify the parameters for the 40m slightly on account of our different modulation frequencies. I've setup some infrastructure to do this analytically - even if we end up doing this with Finesse, it is useful to have an analytic calculation to validate against (also not sure if Finesse can calculate HOMs up to order 20 in a reasonable time, I've only seen maxtem 8).
Attachment #1: Heatmap of the OMC transmission for the following fields:
The code used for the ABCD matrix calcs have been uploaded to the BHD modeling GIT (but not the one for making this plot, yet, I need to clean it up a bit). Some design considerations have also been added to our laundry list on the 40m wiki.
4 deg is not an optimized number optimized for criteria, but to keep the cavity short width to 0.1m. But the justification of 4deg is found in Section 3 and 4 of T1000276 on Page 4.
Question for Koji: how is the aLIGO OMC angle of incidence of ~4 degrees chosen? Presumably we want it to be as small as possible to minimize astigmatism, and also, we want the geometric layout on the OMC breadboard to be easy to work with, but was there a quantitative metric? Koji points out that the backscatter is also expected to get worse with smaller angles of incidence.
The requirement on the phase noise on the direct backscatter from the OMC back into the SRM is that it be less than @ 100 Hz, for a safety factor (arbitrarily chosen) of 10 (= 20dB below unsqueezed vacuum). Assuming 5 optics between the OMC and SRM which contribute incoherently for a factor of sqrt(5), and assuming a total of 1 ppm of the LO power to be backscattered, we need the suspensions to be moving @ 100 Hz. This seems possible to realize with single stage suspensions - I assume we get f^4 filtering from the pendulum at 100 Hz, and that there is an additional 80 dB attenuation (from the stack) of the assumed 1 micron/rtHz motion at 100 Hz, for an overall 160 dB attenutaiton, yielding 10^-14 m/rtHz at 100 Hz.
This is the same calculation as I had posted a couple of months ago (see elog that this is a reply to), except that Koji pointed out that the LO power is expected to dominate the (carrier) power incident on the OMC cavity(ies). So the more meaningful comparison to make is to have the x-axes of the plots denote the backscatter fraction, rather than the LO power. One subtlety is that because the phase of the scattered field is random, the displacement-noise induced phase noise could show up in the amplitude quadrature. I think that in these quadrature field amplitude units, the RIN and phase noise are directly comparable but I might have missed a factor of 2*pi. But in the worst case, if all the phase noise shows up in the amplitude quadrature, we end up being only ~10dB below unsqueezed vacuum (for 1 ppm backscatter).
For the requirement on the noise in the intensity quadrature - I think this is automatically satisfied because the RIN requirement on the incident LO field is in the mid 10^-9 1/rtHz regime.
I did some more investigation of what the appropriate cavity geometry would be for the OMC. Unsurprisingly, depending on the incident mode content, the preferred operating point changes. So how do we choose what the "correct" model is? Is it accurate to model the output beam HOM content from NPROs (is this purely determined by the geometry of the lasing cavity?), which we can then propagate through the PMC, IMC, and CARM cavities? This modeling will be written up in the design document shortly.
*Colorbar label errata - instead of 1 W on BS, it should read 1 W on PRM. The heatmaps take a while to generate, so I'll fix that in a bit.
Update 230pm PDT: I realize there are some problems with these plots. The critically coupled f2 sideband getting transmitted through the T=10% SRM should have significantly more power than the transmission through a T=100ppm optic. For similar modulation depth (which we have), I think it is indeed true that there will be x1000 more f2 power than f1 power for both the IFO AS beam and the LO pickoff through the PRC. But if the LO is picked off elsewhere, we have to do the numbers again.
Attachment #1: Two candidate models. The first follows the power law assumption of G1201111, while in the second, I preserved the same scaling, but for the f1 sideband, I set the DC level by assuming a PRG of 45, modulation depth of 0.18, and 100 ppm pickoff from the PRC such that we get 50 mW of carrier light (to act as a local oscillator) for 10 W incident on the back of PRM. Is this a reasonable assumption?
Attachment #2: Heatmaps of the OMC transmission, assuming (i) 0 contrast defect light in the carrier TEM00 mode, (ii) PRG=45 and (iii) 1 W incident on the back of PRM. The color bar limits are preserved for both plots, so the "dark" areas of the plot, which indicate candidate operating points, are darker in the left-hand plot. Obviously, when there is more f1 power incident on the OMC, more of it is transmitted. But my point is that the "best operating point(s)" in both plots are different.
Why is this model refinement necessary? In the aLIGO OMC design, an assumption was made that the light level of the f1 sideband is 1/1000th that of the f2 sideband in the interferometer AS beam. This is justified as the RC lengths are chosen such that the f2 sideband is critically coupled to the AS port, but the f1 is not (it is not quite anti-resonant either). For the BHD application, this assumption is no longer true, as long as the LO beam is picked off after the RF sidebands are applied. There will be significant f1 content as well, and so the mode content of the f1 field is critical in determining the OMC filtering performance.
I've started a spreadsheet for the BHD optics specifications and populated it with my best initial guesses. There are a few open questions we still need to resolve, mostly related to mode-matching:
The spreadsheet is editable by anyone. If you can contribute any information, please do!
Last night Yehonathan and I located the two steel PMCs in the QIL, with help from Anchal. They are currently sitting on my desk in Bridge, inside a box that also contains optics and other OMC parts. I will bring them over to the 40m the next time I come.
To supplement the material presented during the BHD review, I've put together a projected noise budget for the 40m. Note these are the expected interferometer noises (originating in the IFO itself), not BHD readout noises. The key parameters for each case are listed in the figure title. Also attached is a tarball (attachment 4) containing the ipython notebook, data files, and rolled-back version of pygwinc which were used to generate these figures.
Attachment 1: Phase quadrature readout.
Attachment 2: Comparison to aLIGO design sensitivity (phase quadrature).
Attachment 3: Amplitude quadrature readout.