It locked at almost 280 cts, and the transmitted power on the PSL table is about 40 uW.
To make it lock on the carrier I had to flip the sign of the error signal in the PDH loop, so I put a phase shifter (a Pomona box with a 23 uF capacitor) right before the LO input of the PDH box (on the model of the X arm).
Tomorrow I will put more details about the power budget and the phase shifter transfer function.
Koji tweaked the alignment sliders till we were able to get the Y arm locked to green in a 00 mode, GTRY ~ 0.5 which is the prevent number I have in my head. The green input pointing looks slightly off in yaw, as the spot on the ITM looks a little misaligned - I will fix this tomorrow. But it is encouraging that we can lock to the green, suggests we are not crazily off in alignment.
[Ed by KA: slider values: ETMY (P, Y) = (-3.5459, 0.7050), ITMY (P, Y) = (0.3013, -0.2127)]
While we were locked to the green, ITMY UL coil acted up quite a bit - with a large number of clearly visible excursions. Since the damping was on, this translated to somewhat violent jerking of ITMY (though the green impressively remained locked). We need to fix this. In the interest of diagnosis, I have switched in the SRM satellite box for the ITM one, for overnight observation. It would be good to narrow this down to the electronics. Since SRM is EQ-stopped, I did not plug in any satellite box for SRM. The problem is a difficult one to diagnose, as we can't be sure if the problem is with the LED current driver stage or the PD amplifier stage (or for that matter, the LED/PD themselves), and because the glitches are so intermittent. I will see if any further information can be gleaned in this regard before embarking on some extreme measure like switching out all the 1125 OpAmps or something...
Does anyone know if we have a spare satellite box handy?
After connecting the PD with the reflection from the arm to the PDH box, theY arm has been locked on the 01 mode. Maximizing the alignment, we obtained a 00 mode locking, but we couldn't maximize the power.
The size of the reflected beam was different with respect to the size of the incoming beam, so probably a bad mode matching was one of the issues.
Moreover, the reflected beam is very low power. We need to figure out why it is so (bad alignment? related to mode matching?)
After measuring better all the distances, I did a new mode matching calculation. I put the lenses after measuring the beam waist, so the size of the beam on the lenses was the same as expected from the calculation. Nevertheless, the beam size on the beam splitter looks bigger than expected, and also in this case green flashes into the cavity at some HOM (again 01).
I also tried to lock again the cavity and maximize the alignment, but I didn't get any improvement with respect to the previous mode matching.
Still no good locking!
After making the reflected beam size closer to the injected one, I maximized alignment. I locked again in 00 mode, but I couldn't maximize the power.
I just realized that maybe I'm not using the correct radius of curvature for the ETMY in the simulation. Tomorrow I will start checking from that.
Also make sure you are taking into account the substrate of the ETM.
For the mode matching calculation I was using the ETMY focal length that I found on Kiwamu's plot on the wiki page.
Taking into account also the substrate, the focal length turns out to be
fl = ((n-1)*(1/R1 - 1/R2 + (n-1)d/(nR1R2)))^(-1) = -125.81 m
with n = 1.46071 (refraction index of fused silica at 532nm)
R1 = 5625 m (radius of curvature of the first surface)
R2 = 57.37 m (radius of curvature of the second surface)
d = 25mm (thickness)
The value of the focal length is sligthly different from the one I was using before in the calculation, but maybe it is enough to change the coupling.
The mode matching solution I found is very sensitive to the lenses position.
The beam waist position can vary up to 20m varying by 1cm the first lens position, while it is slightly less sensitive to the second lens displacement.
As shown in the picture, along the green beam path there is also a 1m focal length lens. It's position is fixed, because it is along the IR transmetted beam path also. I tried to get a better solution without it, but I found that the waist position was still strongly dependent on one of the two lenses position, so it would not solve the problem to remove this lens.
I think that the main issue of this mode matching is related to the "space contraints", because the two lenses' positions can vary in a very small space, even though the green beam path on the table is quite long.
Eventually, I put the MM lenses found from this last simulation on the table, and it seems to work, since I've seen very strong 00 flashes. Unfortunately, while trying to maximize the alignment I broke it and I have to do it again, but I feel confident!
After restoring alignment I could see again strong 00 flashes (about 250-300 counts on ALS-TRY). So I locked the arm with IR and after enabling the PDH servo for the green locking, I also locked the green on the Y arm in 00 mode. Then I moved the two mode matching lenses to maximize the power into the 00 mode, but I didn't reach more than 30-35 counts.
Green power injected into the Y arm 0.680mW
Green power reflected back 0.090mW
Green power transmitted on the PSL few uW
I would expect more power on the PSL table (maybe 10x more).
Hmmm. You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement?
We should look at it with fresh eyes in the morning.
> Hmmm. You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement?
> We should look at it with fresh eyes in the morning.
Also, if you have been measuring the power of green refl at the rejection port of the green faraday, the polarization of the light entering the green faraday should be checked once again to make sure that you are measuring
only the reflected power from the arm cavity.
> > Hmmm. You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement?
> > We should look at it with fresh eyes in the morning.
> Also, if you have been measuring the power of green refl at the rejection port of the green faraday, the polarization of the light entering the green faraday should be checked once again to make sure that you are measuring
> only the reflected power from the arm cavity.
Sorry Sorrry Sorry!!
It was 0.090 mW, I just forgot a zero!!!
Is this reflection measured with the cavity locked or unlocked?
So what's the actual designed reflectivity of the ETM for green? No one seems to be able to give me a straight answer about this.
Looking at the reflected beam when the beam is misaligned makes it look like it's << 0.9. Is that expected given the coating spec?
You say the cavity scan goes as high as 300cts but you can only lock to 30cts, are you locked on the sideband?
-The reflection is measured when the cavity is unlocked. I measured it with the power meter in front of the PD, so I interrupted the PDH loop.
- From the specs of ETM we have:
T(S1,HR,532nm)=5.0%+/-3% (+/-1% target), R(S2,AR,532nm)<1000ppm
It means that I should have about 600-550 uW in reflection, but I don't. I can say that there are many losses, and maybe some power is clipping inside the Faraday. Nonetheless, the reflected beam looks less strong than the injected one, so most of the losses should be on the ETM table.
(- The reflected power is 0.090 mW, I just wrote it wrong yesterday, sorry!)
- The last question is actually very interesting. Maybe I was locking on the sideband when I locked to 30 cts, but if it is the case I cannot really explain why today I locked on the carrier (I locked the cavity to about 200-250 cts), and everything I changed was the PD gain and the amplitude on signal generator connected to the PDH box. It seems like there should be some sign flip somewhere, but I need to think about.
We aligned Y arm to Y green and tweaked TT1/TT2 to get IR locked in Y arm.
1. Align ETMY/ITMY to maximize TEM00 green transmission to PSL table. We reached ~240 uW.
2. Aligned PRM and TT2 so that PRM reflected beam go through FI and get ITMY-PRM cavity flashing. This is to coarsely align input pointing to Y arm. After this alignment, we got tiny Y arm flash. Input pointing to IPANG QPD was lost.
3. Aligned TT1/TT2 to maximize TRY in TEM00. We reached ~0.92.
I was struggling with finding Y arm flash. I was using IPPOS/IPANG as input pointing reference, and slider values (C1:SUS-(ITMY|ETMY)_(PIT|YAW)_COMM) or OSEM values (C1:SUS-(ITMY|ETMY)_SUS(PIT|YAW)_IN1) before pumping for Y arm alignment reference. But it was a lot more easier if Y arm is aligned to green and having Yarm cavity axis assured.
- X arm flash in IR
- Steer X end green
- If X arm or AS looks bad, adjust IR input pointing and Y arm alignment. We have to steer Y end green afterwards.
That's good news. I was ready to give up and say we should vent and remove the baffles. It will be interesting if you can find out how much the sensors and OL and IPANG are off from their pre-pump values. We should think about how to have better references.
Also, what is the story with the large drift we are seeing in IPANG?
I implemented this today. For now, the LSC output matrix is set to actuate on MC2 for Y arm locking. As expected, the transmission was much more stable, and the PLL control signal RMS was also reduced by factor of ~3. MC2 control signal does pick up a large (~2000 cts) DC component over a few hours, so we need to relieve this periodically.
Now that we have a workable ASS for the Y arm as well, we should be able to have more confidence in returning to the same beam spot position on the ETM and staying there during a scan using this technique.
The main improvement to be trialled next in the scanning is to improve the speed of scanning. As things stand, my script takes ~2.5 seconds per datapoint. If we can cut this in half, that'd be huge. On Wednesday night, we were extraordinarily lucky to avoid MC3 glitching, EPICS/slow machine failures, and GPIB freezes. Today, the latter reared its head. Fortunately, since I'm dumping data to file for each datapoint, this means we at least have data till the GPIB freeze.
For future measurements, we should consider locking the IMC length to the arm cavity - this would eliminate such alignment drifts, and maybe also make the PLL control signal RMS smaller.
Not related to this work: Terra, Sandrine, Keerthana and I cleaned up the lab a bit today, and made better cable labels. Aaron and I have to clean up the OMC area a bit. Huge thanks to Steve for taking care of our mess elsewhere in the lab!
Ah. With MC2 feedback, we have about 3 times smaller "optical gain" for the ASS A2L. We have same dither, same actuator, but we need only 1/3 actuation of the MC2 compared to the ETMY case.
We had to reduce the ASS spot servo from 1 to 0.3 to make is stable, so this means that the ASS is really merginally stable.
I tried to lock the Y arm cavity length to the PSL frequency using POY11_I as an error signal. Even though I think the cavity alignment is good (I see TRY flashes ~0.8), I am unable to achieve a lock. I checked the signal conditioning, and as far as I can tell, all the settings are correct, but there may be some settings that have not been re-assigned correct values. The other possibility is that something is not quite right with the new c1iscaux. The PDH error signal and arm cavity flashes all seem good though (see Attachment #1), so I'm not sure what obvious thing I'm missing.
To be continued...
(Preparation of Y arm locking)
(A) The f2a filters were newly designed and applied to ETMY (see the attachment)
(B) Once the Y arm is aligned such that the TEM00 mode flashes, the transmitted light is visible on the ETMYT CCD camera.
(C) With the newly installed resonant EOM circuit the PDH signal from AS55 looks healthy.
(A) To design the f2a filters there is a handy python script called "F2A_LOCKIN.py" in /scripts/SUS.
The script measures the coil imbalance at high frequency and low frequency using a LOCKIN module and then gives us the information about the imbalance.
The script hasn't yet been completed, so it doesn't return the intuitive answers but returns something non-intuitive. I will modify it.
(B) To see the transmitted light from the Y arm I was going to align the CCD camera on the Y end table.
However I found that once the green light is blocked, the transmitted light can be visible on the camera without any re-alignment.
Therefore I haven't rearranged anything on the Y end table, but I just blocked the green light.
Perhaps we still need to align the photo diodes for the transmitted light.
(C) While Suresh was working on MC, I looked at the signal from AS55 with all the optics misaligned except for ITMY, ETMY and BS.
The signal from the Y arm looked very PDH signal, and the demodulation phase seemed to be about 45 deg to maximize the I signal.
I tried locking it by feeding the signal back to ETMY but failed due to a too much POS to angle coupling in the ETMY actuators.
I was momentarily able to capture a higher order mode with a negative gain in LSC-YARM_GAIN, but it was quite difficult to keep it locked.
This was because once I increased the gain to make it stable, the angle instability became more significant and lost the lock immediately.
This was the reason why I had to do the f2a filter redesign. Tomorrow we can try locking the Y arm.
The Y arm has been locked with AS55.
A next thing is to check the spot positions on the ETMY and ITMY mirrors so that we can evaluate the recent beam pointing.
- - - parameter settings - - -
C1:LSC-YARM_GAIN = -0.03
AS55 demod phase = 0.2
WF gains = 21 dB
C1:LSC-TRY_OUT = 0.57 (maximized by steering PZT2)
Although we did some of the Input Matrix diagonalization, we have not yet actually used this knowledge. As a result all of the optics are shaking all over the place.
There are still several data quality issues that can be improved. I think there is little point in reading too much into this until some of the problems outlined below are fixed and we get a better measurement.
As an interim fix, I'm going to try and use the Oplevs as a DC reference, and run the dither alignment from zero each time, as this prevents the runaway problem at least. Data run started at 11:20 pm.
Attachment #1 shows estimated systematic uncertainty contributions due to
In all the measurements so far, the ratio seems to be < 1, so this would seem to set a lower bound on the loss of ~35 ppm. The dominant source of systematic uncertainty is the 5% assumed fudge in the mode-matching
Bottom line: I think we need to have other measurements and simultaenously analyse the data to get a more precise estimate of the loss.
About Noise Budget
How to improve it ?
I was working around the PSL table and Y endtable today.
I modified the Y arm optical layout that couples the 1064nm light leaking from the SHG crystal into the fiber for frequency offset locking.
The ND filter that was used to attenuate the power coupled into the fiber has been replaced with a beam sampler (Thor labs BSF-10C). The reflected power after this optic is ~1.3mW and the trasmitted power has been dumped to a razor blade beam dump (~210mW).
Since we have a spare fiber running from the Y end to the PSL table, I installed an FC/APC fiber connector on the PSL table to connect them and monitored the output power at the Y end itself. After setting up, I have ~620uW of Y arm light on the PSL table (~48% coupling).
During the course of the alignment, I lowered the power of the Y end NPRO and disengaged the ETMY oplev. These were reset after I closed the end table.
Attached is the out of loop noise measurement of the Y arm ALS error signal before (ref plots) and after.
Prior to the works on the Y end setup I propose to perform the temperature scan business like Koji and Suresh did before (see this entry).
This business will allow us to easily find a beatnote at 532nm after the installation on the Y end.
I guess the right persons for this work are Bryan and Suresh.
Bryan will have a safety guidance from Steve in this after noon. So after that they can start working on it.
/* - - - coarse plan - - - */
* remove Alberto's laser from the AS table
* setup Alberto's laser on the PSL table
* put some stuff such as lenses, mirrors and etc. (Use the IR beam picked off after the doubling crystal for the main laser source)
* mode matching
Which laser are we going to use, Alberto's laser or MOPA laser ?
I found the beat note for the Y arm. Nothing was changed with respect to yesterday night, but the beat is back!
As I didn't have the green laser PZT feedback for the laser temp control, I went to the yend to check out what's the situation.
I found horrible and disgusting "remnants".
WHAT ARE THESE BSs AT THE Y END?
- The table enclosure was left open
- A (hacky) DB25 cable with clips was blocking the corridor and I was about to trip with the cable.
- This DB25 cable went to the table without going through the air tight feedthrough that is designed for this purpose.
- An SR560 (presumably for the openloop TF measurement) was left inserted in the loop with entangled cables connected to the servo box.
- Of course the laser PZT out mon was left unplugged.
Even after cleaning these cables (a bit), the end setups (including the X end too) are too amature.
Everything is so hacky. We should not allow ourselves to construct this level of setup everytime
we work on any system. This just adds more and more mysteries and eventually we can't handle
Beam colors: 1064 nm red, 514 nm green and 633 nm yellow.
There should be room for lens in front of the pd at red3 and a mirror for alignment in the new layout.
This picture may help you how to improve the new ETMX 4' x 3' optical layout.
[Tomotada / Kiwamu]
The open loop transfer function of the Y end PDH loop was remeasured : the UGF was found to be at 17 kHz.
The phase margin at the UGF was about 27 deg.
While the measurement we noticed that the modulation onto the laser PZT was too big
and it was creating a big AM on the reflected light with an amplitude of a few mV.
So we put a 20 dB attenuator to decrease the modulations and the reflected light became much quitter.
Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).
As promised, I will get on this this week.
The doubling oven is now ready to go for the Y arm. The PPKTP crystal is mounted in the oven:
Note - the crystal isn't as badly misaligned as it looks in this photo. It's just an odd perspective shot. I then closed it up and checked to make sure the IR beam on the Y bench passes through the crystal. It does. Just need to tweak the waist size/position a bit and then we can actually double some frequencies!
The Y arm green PDH servo is working fine with a sufficient amount of suppression.
And the servo configuration looks like this :
(the Error signal)
I took a spectrum of the error signal when the laser was locked to the Y arm and found that it meets the requirement.
Another way to make a 1:100 pole:zero boost is to use resistors and capacitors in a Pomona box
mixer -> LB box -> Pomona box -> PZT
Pomona Box = R1 = 7.2 kOhm, C2 = 22 uF, R2 = 72 Ohms (sr560 = $2400, pomona ~ $50)
For the RMS calculation, it would be good to notch out the harmonics. They don't matter since our ALS feedback will have notches at those frequencies.
I wouldn't bother...
I measured the PZT actuator gain for the Lightwave NPRO at the Y-end to be 3.6 +/- 0.3 MHz/V. This is somewhat lower than the value of 5 MHz/V reported here, but I think is consistent with that measurement.
In order to calibrate the Y-axis of my Aux PDH loop noise budget plots, I wanted a measurement of the end laser actuator gain. I proceeded to measure this as follows:
The attached plot shows the measured data. The X-axis is shown after the conversion mentioned in the last bullet point. The error bars are the standard deviations of the averaging at each DC offset.
After the discussions at the Wednesday meeting, I redid this measurement using a sinusoidal excitation summed at the error-point of the PDH servo as opposed to a DC offset. From the data I collected, I measured the actuator gain to be 2.43 +/- 0.04 MHz/V. This is almost half the value we expect, I'm not sure if I'm missing something obvious.
I redid this measurement and have now determined the actuator gain to be 4.61 +/- 0.10 MHz/V. This is now pretty consistent with the expected value of ~5MHz/V as reported here.
I made the following changes to the old methodology:
I also took spectra of the phase tracker output and error signal to make sure I was choosing my excitation frequencies in regions where there were no peaks already present (Attachment #1).
The scatter of measured actuator gains at various excitation frequencies is shown in Attachment #2.
Indeed it is strange. I took a quick look at it.
In order to recover the same condition (e.g. the same amount of the reflected DC light and the same temperature readout),
it needed to have +8.9V in the slow input from the DAC through EPICS.
Obviously applying an offset in the slow input to maintain the same condition is not good.
It needs another solution to maintain the sweet frequency where the frequency of the PSL and the Y end laser is close in a range of 200 MHz.
Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.
Currently, the y end plant is yep.mdl. In order to compile it properly (for the moment at least) requires running the normal makefile, then commenting out the line in the makefile which does the parsing of the mdl, and rerunning after modifying the /cds/advLigo/src/fe/yep/yep.c file.
The modifications to the yep.c file are to change the six lines that look like:
"plant_mux = plant_gndx" into lines that look like "plant_mux = plant_delayx". You also have to add initialization of the plant_delayx type variables to zero in the if(feInt) section, near where plant_gndx is set to zero.
This is necessary to get the position feedback within the plant model to work properly.
#NOTE by Koji
#NOTE by Koji
This entry means that Makefile was modified not to parse the mdl file.
This affects making any of the models on megatron.
#NOTE by Koji
This entry means that Makefile was modified not to parse the mdl file.
This affects making any of the models on megatron.
To prevent this confusion in the future, at Koji's suggestion I've created a Makefile.no_parse_mdl in /home/controls/cds/advLIGO on megatron. The normal makefile is the original one (with correct parsing now). So the correct procedure is:
1) "make yep"
2) Modify yep.c code
3) "make -f Makefile.no_parse_mdl yep"
Attachments #1 is the current setup of AUX Y Green locking and it has to be improved because:
About the above two:
One of the example for improvement is just adding a new lens (f=10cm) soon after the doubling crystal. That will make mode matching better (100%) and also make separation better (85 deg) (Attachments #4 and #5). I'm checking whether we have the lens and there is space to set it. And I will measure current power of transmitted main laser in order to confirm the improvement of alignment.
About the last:
I am considering what component is needed.
[ Yuki, Gautam ]
The setup I designed before has abrupt gouy phase shift between two steering mirrors which makes alignment much sensitive. So I designed a new one (Attached #1, #2 and #3). It improves the slope of gouy phase and the difference between steering mirrors is about 100 deg. To install this, we need new lenses: f=100mm, f=200mm, f=-250mm which have 532nm coating. If this setup is OK, I will order them.
There may be a problem: One lens should be put soon after dichroic mirror, but there is little room for fix it. (Attached #4, It will be put where the pedestal is.) Tomorrow we will check this problem again.
And another problem; one steering mirror on the corner of the box is not easy to access. (Attached #5) I have to design a new seup with considering this problem.
[ Yuki, Steve ]
With Steve's help, we checked a new lens can be set soon after dichroic mirror.
We want to remotely control steeing PZT mirrors so its driver is needed. We already have a PZT driver board (D980323-C) and the output voltage is expected to be verified to be in the range 0-100 V DC for input voltages in the range -10 to 10 V DC.
Then I checked to make sure ir perform as we expected. The input signal was supplied using voltage calibrator and the output was monitored using a multimeter.
But it didn't perform well. Some tuning of voltage bias seemed to be needed. I will calculate its transfer function by simulation and check the performance again tommorow. And I found one solder was off so it needs fixing.
diagram --> elog 8932
Plan of Action:
Interim Procedure Report:
The current setup of AUX Y-arm Green locking has to be improved because:
What to do
Final Procedure Report for Green Locking in YARM:
To do for Green Locking in YARM:
The auto-alignment servo should be completed. This servo requires many parameters to be optimized: demodulation frequency, demodulation phase, servo gain (for each M1/2 PIT/YAW), and matrix elements which can remove PIT-YAW coupling.
The MON outputs of the Y end QPD whitening board were hot earlier today while pulling it out of the crate. After swapping the 4 pin lemo connector with an isolated panel mount bnc connector, I stuck the board back into the crate and this immediately kicked the ETMY suspension. Jenne and I went to the Y end to look at what was going on. We removed the board from the crate after smelling something burning. The MON output ports of the whitening board were super hot this time. There is no sign of any components melting on the board (comparing the board with its pictures that were taken earlier) and a tester board stuck into the crate lights up just fine.
So the back panel is still ok. We need to troubleshoot or replace the whitening board.
Edit, JCD: The attached photos are from right after I replaced the "Rgain" resistor, elog 9823. What they show is that it looks like some of the melting / burning may have already been happening before I pulled the board, and I just never noticed :( In particular, look at the resistors on the main board above the blue "G" sticker. There isn't a difference that I can tell between this photo from last week, and today's situation.
maybe the tantalum caps on the daughter board power supply lines are blown? If so, replace with 35V+ ceramic.