I have run Kiwamu's length tolerance code (in CVS iscmodeling, ArmTolerance.m & analyseArmTorelance.m ) for the vertex ifo.
In his previous post, he monte-carlo-ed the arm lengths and saw the histogram of the sensing matrix and the demodulation phase between POP55 MICH and POP55 SRCL. From these plots, he roughly estimated that the tolerance is about 1 cm (sigma of the rondom gaussian) and in that case POP55 MICH and SRCL is separated by the demodulation phase 60-150 degrees.
This time I put the length displacements of random gaussian on PRC, SRC, MICH lengths at the same time (Fig.1).
Fig. 1. History of random walk in PRC, SRC, MICH lengths parameter space. Same as Kiwamu's previous post, The position of the three degrees are randomly chosen with a Gaussian distribution function in every simulaton. This example was generated when \sigma = 1 cm for all the three lengths, where \sigma is the standard deviation of the Gaussian function. The number of simulation is 1000 times.
When the sigma is 1 cm, we found that the sensing matrix is quite bad if you look at Fig. 2. In Fig.2 row POP55, although the desired degrees of freedoms are MICH and SRCL, they have quite a bit of variety. Their separation in the demodulation phase is plotted in Fig.3. The separation in the demodulation phase varies from 40 degrees to 140 degrees, and around 270 degrees. It is not good as ideally we want it to be 90.
Fig. 2 Histgram of the sensing signal power in the matrix when 1 cm sigma rondom gaussian is applied on PRC, SRC, MICH lengths. x axis it the signal power in log10.
Fig.3 POP55 MICH and POP55 SRCL separation with the displacement sigma 1 cm.
Kiwamu suspected that PRC length as more strict tolerance than other two (SRC, MICH) for POP55, as 55MHz is fast and can be sensitive to the arm length change. So I ran the same monte-carlo with SRC, MICH displacements but no PRC displacements when sigma is the same, 1cm. The results were almost same as above, nothing obvious difference.
With 2mm sigma, the signal power matrix and the POP55 MICH and POP55 SRCL separation in the demodulation phase look good (Fig. 4 and Fig. 5).
Fig.4 Signal power matrix when PRC, SRC, MICH lengths fractuate with random gaussian distribution with 2mm sigma. The signal powers are shown in log10 in x axis, and they do not vary very much in this case.
Fig.5 POP55 MICH and POP55 SRCL separation with the displacement sigma 2 mm. The separation of the two signal is 60-90 degrees, much better than when sigma is 1 cm. We may need to check 60 degree separation is really ok or not.
PRC SRC MICH lengths tolerances of 2 mm in the real world will be very difficult !
Next I will check what happens on 3f signals.
Required arm length = 37.7974 +/- 0.02 [m]
This is a preliminary result of the estimation of the Arm length tolerance.
We noticed that we have used wrong code for MICH degree of freedom for both of the ELOG entries on this topic (cavity lengths tolerance search). It will be modified and posted soon.
Length tolerance of the vertex part is about 5 mm.
Sorry for my procrastinating update on this topic. In my last post, I reported that the length tolerance of the vertex ifo would be 2mm, based on Kiwamu's code on CVS. Then we noticed that the MICH degrees of freedom was wrong in the code. I modified the code and ran again. You can find the modified codes on CVS (40m folder, analyzeDRMITolerance3f.m and DRMITolerance.m)
In this code, the arm lengths were kept to be ideal while some length offsets of random gaussian distribution were added on PRCL, SRCL and MICH lengths. The iteration was 1000 times for each sigma of the random gaussian distribution. The resulting sensing matrix is shown as histogram. Also, a histogram of the demodulation phase separation between MICH and SRCL is plotted by this code, as these two length degrees of freedom will be obtained by one channel separated by the demodulation phase. We check this separation because you want to make sure that the random length offsets does not make the separation of these two signals close.
The result is a bit different from the previous post, in the better way! The length tolerance is about 5 mm for the vertex ifo. Fig.1 shows the sensing matrix. Although signal levels are changed by the random offsets, only few orders of magnitude is changed in each degrees of freedom. Fig.2 shows that the signal separation between MICH and SRCL at POP55 varies from 55 to 120 degrees, which may be OK. If you have 1cm sigma, it varies from 50 degrees to 150 degrees.
Fig. 1 Histgram of the sensing matrix including 3f channels, when sigma is 5mm. Please note that the x-axis is in long 10.
Fig. 2 Histogram of the demodulation phase difference between MICH and SRCL, when sigma is 5 mm. To obtain the two signals independently, 90 is ideal. With the random offsets, the demodulation phase difference varies from 55 degrees to 120 degrees.
My next step is to run the similar code for LLO.
Here are the results of the arm loss measurements, which I have done before the vent.
I ran the existing matlab script, called 'armLoss.m', to estimate the loss. The script resides in /scripts/LSC.
Round trip loss = 154.668624 +/- 11.343204 ppm
The figure above is a time series of the measurement.
In the lower plot the power in the ASDC_PD are plotted. The green dotted-curve is the power when the Y arm is unlocked.
The blue dotted-curve is the one when the Y arm is locked.
In the upper plot the estimated loss from each combination of locked/unlocked power are plotted.
Round trip loss = ????? 50 ppm ?????
The obtained time series looked wired because difference in the ASDC power when the arm was locked/unlocked were small.
This small difference results in such a small loss.
To see what was going on I will look at the trend data.
I did the measurement of the arm loss on both X and Y arm by running the armLoss script.
The results will be posted later.
The measurement itself wasn't good.
I looked at the full 2 kHz data which was taken during the time when I was running the arm loss script on the X arm.
The plot below shows the raw data. The X arm was locked and unlocked sequentially several times.
The ASDC power didn't show a significant difference between the state where it is locked and unlocked.
I am not sure why, but It could be because of a misalginment or some kind of mode-mismatching, which can decrease the coupling efficiency of light going into the cavity.
The raw data were analyzed.
I split the ASDC data into two data, (1) low power state, when the cavity is locked (2) high power state, when the cavity is unlocked.
Then each state was averaged to estimate the averaged ASDC power in each case.
The number I obtained are :
ASDC when X arm was locked = 54.77755 cnts
ASDC when X arm was unlocked = 55.45830 cnts
Those numbers correspond to a round trip loss of 78.780778 ppm, which sounds too small for me.
To see what was going on I will look at the trend data.
To check the demodulation boards for REFL33 and REFL165, a long cable from ETMY (SUS-ETMY-SDCOIL-EXT monitor) is pulled to the rack on Y side.
(1) A filter just after the RF input and (2) transfer function from the RF input to the demodulated signal will be checked for the two 3f demod boards to confirm that they are appropriate for 33 and 165 MHz.
There is a LP filter just after the RF input of an demodulation board (its schematic can be found as D990511-00-C on DCC). I have checked if the 3f freq, 33MHz, can pass this filter. The filter TF from the RF input to RF monitor (the filter is between the input and monitor) on REFL33 demo-board was measured as shown in Fig. 1. At 33MHz, the magnitude is still flat and OK, but the phase is quite steep. I am going to consider if it is ok for the PDH method or not.
Fig. 1 Transfer function from the RF input to RF monitor on the REFL33 demodulation board. At 33MHz, a very steep phase is applied on the input signal.
The phase delay due to the RF input filter on the demodulation board will not bother the resulting PDH signals.
I quickly calculated the below question (see the blue sentence in the quote below). I applied an arbitrary phase delay (theta) due to the filter I measured, on the detected RF signal by the photo detector. Then the filtered RF signal is multiplied by cos(omega_m) then filter the higher (2 omega_m) freqency as the usual mixing operation for the PDH signal. As a result, the I signal is delayed by cos(theta) and the Q signal is delayed by sin(theta). Therefore the resulting signals and its orthogonalitity is kept ok. From the sideband point of view, theta is applied on both upper and lower and seems to make the unbalance, however, as it is like a fixed phase offset on both SBs at the modulation frequency, the resulting signals is just multiplied by cos or sin theta for I and Q, respectively. It won't make any strange effect (it is difficult to explain by sentence not using equations!).
I lined up the Y Arm for locking and then centered the oplevs for ETMY and ITMY.
* The ITMY OL has still got the old style laser. Steve, pleaes swap this one for a HeNe. Also the optical layout seems strange: there are two copies of the laser beam going into the chamber (??). Also, the QPD transimpedance needs to be increase by a factor of ~10. We're only getting ~500 counts per quadrant. Its worth it for someone to re-examine the whole ITMY OL beam layout.
* The ETMY OL beam was coming out but clipping on the mount for the ETMY OL HeNe. This indicates a failure on our part to do the ETMY closeout alignment properly. In fact, I get the feeling from looking around that we overlooked aligning the OL and IPPOS/ANG beams this time. If we're unlucky this could cause us to vent again. I undid part of the laser mount and changed the height on the receiving mirror to get the beam back onto the QPD.
I noticed that there is significant green light now getting into some of the IR PDs; beacuse of this there are weird offsets in the TRY QPD and perhaps elsewhere. We had better purchase some filters to tape over the front of the sensitive IR sensors to prevent the couplling from the green laser.
* There is a beam on IPPOS, but its too big for the detector (this has always been the case). We need to put a 2" lens with a weak focusing power on this path so as to halve the beam size on the detector. Right now its clipping and misleading. There is also a 0.9V offset on the SUM signal. I'm not sure if this readout is working at all.
* I couldn't find any beam on IPANG at all. Not sure what's changed since Kiwamu saw it.
* ITMY OL: Also the optical layout seems strange: there are two copies of the laser beam going into the chamber (??).
* The ETMY OL beam was coming out but clipping on the mount for the ETMY OL HeNe. This indicates a failure on our part to do the ETMY closeout alignment properly.
The 2nd beam from this laser is for the SRM's OpLev, so that shouldn't be changed.
For better or worse, we didn't do anything to the ETM OpLevs, because they don't have any in-vac steering optics. We did however go through and check on all the corner OpLevs.
A comment :
Since the LSC RFPD have a long cable of more than 6 m, which rotates a 33 MHz signal by more than 360 deg, so the delay has always existed in everywhere.
The circuit you measured is a part of the delay existing in the LSC system, but of course it's not a problem as you said.
In principle a delay changes only the demodulation phase. That's how we treat them.
RA: Actually, the issue is not the delay, but instead the dispersion. Is there a problem if we have too much dispersion from the RF filter?
Filters at the RF inputs of REFL33 and REFL165 demodulation boards were measured again. The filters will be totally fine for 33MHz and 165MHz.
Last time I forgot to calibrate the cable lengths, therefore the phase delay of the measurement included the cable lengths. This time the measurements were done for REFL33 and REFL165 demod board with calibration. As the cable lengths were calibrated, the shown plots (Fig.1 and Fig.2) do not include the phase delay dues to measurement cables. Please note that the x-axis is in linear. The phase delays of both boards seems to be not too steep (it will not affect anyway, as Kiwamu pointed out in his comment on the previous post). You can see that the two filters do not filter 33MHz and 165MHz component out.
Fig.1 A response of a filter which is placed just after the RF input of the demodulation board for REFL33. X-axis is shown in linear (~50MHz).
Fig.2 A response of a filter which is placed just after the RF input of the demodulation board for REFL165.
I also quickly checked the orthogonality of the demodulation board for REFL33 and REFL165 using function generators and oscilloscope. I checked the frequencies at 1,10,100,1K,10KHz of the demodulated signals. They are fine and ready for 3f signal extraction.
Wait. I am checking the whitening filters of the 33 and 165 demodulation boards.
Also, LSC-REFL33-I-IN1(IN2, OUT) and LSC-REFL165-Q-IN1(IN2,OUT) channels may not be working??
LSC-REFL33-I-IN1(IN2, OUT) and LSC-REFL165-Q-IN1(IN2,OUT) channels are back!
We disconnected and connected again the AA filters then the channels are fixed. Apparently the AA filters just before the digital world were somhow charged and not working... Thank you Kiwamu!
Before we install the REFL 3f PDs I made a drawing of the current table layout, since there has been no update lately. Once I've incorporated the two extra PDs (now seen sitting bottom left), I will update the drawing and post in the wiki as well.
(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.
Whitening filters for the REFL33 & 165 demodulated channels were measured and confirmed that they are working. They can be turned on and off by un-white filter switches on the MEDM screen because they are properly linked. The measured filter responses are showen below. (Sorry, apparentyl the thumbnails are not shown here. Please click the attachments.)
Attachments: (top) Whitening filter for REFL33 demodulation board. (bottom) Whitening filter response for REFL 165 demodulation board.
Old Coherent diode laser was replaced by Uniphase HE/NE 1125P at ITMX.
Newport 10B20NC.1 broadband beam sampler set up as beamspitter to dump 90% of the light into beam trap. Beam in to test mass 0.7 mW , returning to qpd 0.07 mW = ~ 3,700 counts
f 1.5 m lens placed into ingoing beam path to reduce the spot size on the qpd. ITMY oplev will be done in this manner tomorrow.
* IP-ANG is lost with the Piezo Jena PS
* IP-POS cable have to be found at the LSC rack
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)
Keiko, Jamie , Kiwamu
The I and Q orthogonalities of REFL33 and 165 demodulation board were measured by "orthogonality.py" Python package scipy were addied on Pianosa to run this code. Please note that "orthogonality.py" can be run only on Pianosa.
The results were:
ABS = 1.070274, PHASE = -81.802479 [deg]
if you wanna change epics values according to this result, just copy and execute the following commands
ezcawrite C1:LSC-REFL165_Q_GAIN 0.934340 && ezcawrite C1:LSC-REFL165_PHASE_D -81.802479
- - - - - - - - - - - - - - - - - -
ABS = 1.016008 , PHASE = -89.618724 [deg]
ezcawrite C1:LSC-REFL33_Q_GAIN 0.984244 && ezcawrite C1:LSC-REFL33_PHASE_D -89.618724
Fig.1 and 2 are the resulting plots for 33 and 165 MHz demod baoards, respectively.You should look at the 3Hz in x axis, as the demodulated signal frequency was set as 3 Hz.
Fig. 1 REFL33 I and Q orthogonality at 3 Hz.
Fig. 2 REFL165 I and Q orthogonality at 3 Hz.
The spot positions on ITMY and ETMY were measured using the LOCKIN modules in C1ASS when the Y arm stayed locked.
The beam was successfully aligned such that it hits the center of the ETMY mirror.
However on the other hand the angle of the beam is pitching and it's going upward as the beam propagates to ETMY.
/***** RESULTS ******/
Here is a summary of the measurement :
Also a cartoon is shown below.
The scale is not quite true, but at least it gives you a 3D information of how the beam is pointing down to the Y arm.
/***** MEASUREMENT *****/
In order to measure the spot positions the standard technique, namely A2L, was used.
Since the C1ASS model was made for doing the A2L measurements on each arm cavity, the LOCKIN modules in C1ASS were used.
First the Y arm was locked with AS55 (#5398), and then the C1ASS was activated by calling some scripts from C1ASS_QPDs.adl.
In order to calibrate the signals from LOCKINs, an intentional coil imbalance was introduce.
This is the same calibration technique as Valera explained before (#4355) for measurement of the MC spot positions.
I have reconfigured the refl beam path on the AP table to include REFL33 and REFL165. Would be done if we hadn't prepared P BSs instead of S, which required some serious digging to find two others. And if someone hadn't stolen our two 3m SMA cables that Keiko and I made on our previous visit and I had left with the 3f PDs. I don't expect them to reappear but if they do, it would be grand.
Note: Refl beam from ifo looks a bit high, ~1cm on the lens 20'' from output port. Not sure what that means about ifo alignment change, I've left it as is. When we know we have a good alignment, we should be able to easily realign the beam path if necessary. If it remains the same, we might want to change the lens height.
1) REFL11 and REFL55 are now hooked up and aligned in a low power beam. (I set the power as low as I could by eye to not risk burning the PDs during alignment)
2) The required BSs and REFL33 and REFL165 are in place, powered.
3) I have set them in a configuration such that the beam is the same distance from the main beam, to adjust beam size easily for all 4.
4) Camera has been moved from main beam to behind a steering mirror, ND filters removed, centered on camera.
1) Find one more longish SMA cable.
2) Align beam on REFL33 and REFL165.
3) Check beam size carefully. (I get a plateau on the scope, and I can "hide" the beam on the PD, but it could be better. The path has become longer by ~5-8inches.)
4) Adjust power.
5) Redo layout diagram, post in wiki.
Forgot to attach a picture of the ITMY's face camera when it was locked.
The horizontal position of the spot looks good, but the vertical position is apparently too low, which agrees with the A2L result.
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.
In addition to REFL 33 ans 165, I checked the orthogonality for the other existing three channels.
ABS = 1.025035 PHASE = -93.124929 [deg]
ABS = 0.920984 PHASE = -88.824691 [deg]
ABS = 1.029985 , PHASE = -90.901123 [deg]
The demodulated signal was set as 50 Hz (for example LO 11MHz and RF 11MHz+50Hz from function generators.) These AS11, REFL11, REL55, REFL33m REFL165 are the current available channels in terms of the connection to the data system from the demodulation board. I am going to estimate the error next.
- We aligned MICH and were successfully locked MICH using AS55Q. The other mirrors were misaligned so that the other degrees of freedom didn't exist. AS55 was fed back to BS. The f2a filters on BS suspension were required to lock, because the pos feedback was unbalanced to angle degrees of freedom.
- We tried to lock PRCL next, however, because we aligned the MICH and the REFL beam paths were changed, REFL PDs didn't have the light anymore. The REFL paths were modified now, so we will try the PRCL locking next.
- We couldn't confirm REFL55 signals although we alined the REFL paths to REFL55 PD.
Kiwamu, Keiko, Anamaria
We were able to lock PRC using REFL11I after improving the MICH dark fringe a bit (moving BS) and rotating AS55 and REFL11 such that the signal was maximized in the phases we were using. The dark port is not so dark... but the lock is stable.
I had finished the whole REFL path alignment, but I didn't have a good input beam reference at the time, which is why we had to realign the PDs and the camera. We only had strength to realign 11 and 55. Otherwise, we just need to tweak and center beam on 33 and 165, figure out what's up with 55 and be done with the AP table mods. I hope.
Put up a temp. setup on the laser table to measure the RF modulation depths using the optical spectrum analyzer. First with a pickoff beam with about 2mW => SNR of 8 of 1 peak per FSR.
Then with a beam with about 100mW. Much better SNR on the single peak but still no sidebands visible. Modematching not too good in either case. Shouldn't matter.
Just to give some heads up on how the setup on the PSL table does / will look. We start out with one of the two reflections of a window. Power about 2mW.
I started today with a different input beam, so I had to realign the REFL path again. Then we measured the RF signal out of the 4 REFL PDs and found them to be too low. We increased the power to around 10mA for each diode, and we can see the right modulation frequency on each diode, though REFL165 is way too weak so we might need an RF amplifier on it. We will measure demod board noise tomorrow.
We had an issue with REFL165 not giving the right DC level, low by a factor of 10, even though it was receiving the same optical power as the others. We fifteen-checked clipping and alignment, then pulled it out and measured it on the test stand - found it to be ok. So I uplugged its power cable at the rack and connected it to the AS165 slot. Problem sloved. Not sure what was wrong with the other power slot.
Then we found REFL55 to be clipping on its black glass, we fixed that. But the REFL55 DC power still changes a lot with seemingly not huge motions of the PRM. We'll investigate more tomorrow.
We added a lens in the path to REFL165 because unlike the others it is a 1mm diode. All diodes have about half a turn to a full turn flatness of maximum (on tiny steering mirror).
We set the whitening gain on all four diodes to 21 db.
Not sure if we should set the power to be different on these diodes since their sensitivity is different to RF, and now REFL11 sees huge signal.
We continued the DRMI locking attempt and brought in the SRC, using AS55I to control it. It kind of works/stays locked. We did manage to get MICH and PRC better controlled than last night, but with SRC in the mix, something is wrong. We have to redo f2a filters on SRM and hopefully things will be better after Jenne's suspension work tomorrow. Oplevs not optimized yet either.
We intend to realign POY beam path so we can monitor power in cavities.
The demodulation phases and gains for the all existing channels, AS11, REFL11,REFL55, REFL165, and REFL33, were adjusted by the command "ezcawrite" commands.
REFL165 ezcawrite C1:LSC-REFL165_Q_GAIN 0.934340 && ezcawrite C1:LSC-REFL165_PHASE_D -81.802479
ezcawrite C1:LSC-REFL33_Q_GAIN 0.984244 && ezcawrite C1:LSC-REFL33_PHASE_D -89.618
New channels, POP55 and POY11 are connected to the rack and now available on the data system.
POX11 I is not working. I didn't investigate what was wrong. Please make sure when you come to need POX11.
The orthogonalities of POY11 and POP55 were measured and already adjusted. The results are below:
ABS = 0.973633
PHASE = 92.086483 [deg]
ezcawrite C1:LSC-POY11_Q_GAIN 1.027081 && ezcawrite C1:LSC-POY11_PHASE_D 92.086483
ABS = 1.02680579
PHASE = 88.5246 [deg]
ezcawrite C1:LSC-POP55_Q_GAIN 0.973894 && ezcawrite C1:LSC-POP55_PHASE_D 88.524609
Keiko, Paul, Kiwamu
We found that POP beam is clipped by the steering mirrors inside the tank. POY beam is also likely to be clipped inside. Also the hight of POY beam is too high (about 5 cm higher than the normal paths) at the first lens. These imply the input pointing is bad.
[Anamaria / Kiwamu]
The incident beam pointing was improved by using PZT1 and PZT2.
With some triggers the lock of PRMI became smoother.
For the DRMI lock, the MICH and SRCL signals on AS55 are not quite decoupled, so we should find cleaner signals for them.
(what we did)
+ locked the Y arm
+ aligned incident beam by using PZT1(#5450) and PZT2. The spot positions on ITMY and ETMY are now well-centered.
+ tried activating C1ASS but failed. It needs some gain changes due to the new PZT1 response.
+ locked the X arm
+ aligned the TRX PD (Thorlab signal PD) and set the trigger.
+ C1ASS also doesn't work for the X arm
+ realigned the PRM and BS oplevs. the PRM oplev was clipped at a steering mirror on the optical bench
+ locked PRMI and aligned the PRM mirror such that the optical gain was maximized
+ optimized the demod phase of AS55 and REFL11
+ checked the UGF of the MICH and PRCL lock. The UGF of MICH is about 100Hz with gain of -20, and the UGF of PRCL was 85 Hz with gain of 0.1
+ adjusted the output matrix such that the MICH control doesn't couple into the PRCL control.
+ set the triggers for the MICH and PRCL control to make the lock acquisition smoother.
+ tried locking DRMI and it was sort of locked. However the SRCL signal showed up a lot in AS55_Q, where the MICH signal is extracted.
Actually the clipping of POP wasn't in the chamber but it was on the first lens on the optical bench.
So I repositioned the lens to avoid the clipping and now there are no clipping on POP.
We found that POP beam is clipped by the steering mirrors inside the tank.
Earlier measurements of the modulation index were less than optimal because we had too low transmission through the cavity. Contrary to what was believed you actually need to modematch onto the cavity.
Earlier transmitted power was about 8.5uW.
With a 250mm lens we archived 41uW.
Impinging power on the cavity is 1.7mW.
PD TF approx 0.1V / uW.
Carrier power: 4.1V => 41uW
41uW/1.7mW = 2.4 % transmission. Manufacturer clain for peak transmission: 20-30%.
11MHz SB: 28.8mV => m=0.17
55MHz SB:36mV => m=0.19
As you can see on the pic the SNR of the SBs is not too good.
The gain of whitening filters on AS55 was decreased from 21 dB to 0 dB for the Y arm locking.
- - (Background)- -
Since the modulation depths became bigger from the past (#5462), the PDH signal from Y arm was saturated in the path of AS55.
Due to the saturation the lock of the Y arm became quite difficult so I decreased the gain of of the whitening filter from 21 dB to 0 dB.
In this condition, a required gain in C1:LSC-YARM_GAIN is about -0.3, which is 10 times bigger from the default number.
For the MICH locking tonight, it may need to be back to a big gain.
Here I note the procedure for the demodulation board orthogonality check for the future reference.
1. prepare two function generators and make sure I an Q demodulation signals go to the data acquisition system.
2. sync the two generators
3. drive the function generator at the modulation frequency and connect to the LO input on the demod board
4. drive the other function generator at the modulation frequency + 50Hz the RF in
5. run "orthogonality.py" from a control computer scripts/demphase directory. It returns the amplitude and phase information for I and Q signals. If necessary, compensate the amplitude and phase by the command that "orthogonality.py" returns.
If you want to check in the frequency domain (optional):
1. 2. 3 are the same as above.
4. drive the function generator at the LO frequency + sweep the frequency, for example from 1Hz to 1kHz, 50ms sweep time. You can do it by the function generator carrier frequency sweep option.
5. While sweeping the LO frequency, run "orthogonality.py"
6. The resulting plot from "orthogonality.py" will show the transfer function from the RF to demodulated signal. The data is saved in "dataout.txt" in the same directory.
I have made some cleaning up of the LSC-related MEDM screens.
- LSC overview screen: ADC OVFL and WFAA indicators are now correctly matched to it associated PD signals.
- Whitening screens now have the correct indication of the associated PD signals.
- LSC Ctrl screen, which is invoked from the overview screen by clicking the servo filters, now has the switches of the servo filters.
- LSC tab of the sitemap was cleaned up by removing the broken links.
Keiko, Anamaria, Koji
We were not able to establish the stable DRMI tonight. We could lock MICH and PRCL quite OK, and lock the three degrees of freedom at somewhere strange for several seconds quite easily, but the proper DRMI lock was not obtained.
When MICH and PRC are locked to the carrier, REFL DC PD reading dropps from ~3000 counts to 2600~2700 counts as REFL beam is absorbed to PRC. We'll try to lock PRC to sidebands - but flipping gain sign didn't work today, although it worked a few days ago.
POP beam (monitor) is useful to align PRM.
As promised, I have made a final AP table drawing, including the MC camera relocation changes by Kiwamu. I have posted it in the wiki on the tables list, and on the AP table page I've attached the inkscape .svg I used to make it, if someone needs to do small modifications.
Attached is a pdf version of it.
1) REFL beam has been split into 4, to go in equal powers and equal beam size to the now 4 REFL RFPDs, 11, 33, 55 and 165. A lens had to be added for REFL165 because it's a 1mm PD instead of 2mm like the other 3.
2) MC camera has moved.
3) I've cleaned up most of the random components on the table, put them away, and tidied up the cabling.
DRMI team needs to use at least three lockins on LSC
I created 3 kinds of LSC matrices, PRMI condition with carrier resonant in PRC, PRMI condition with SB resonant in PRC, and DRMI with SB resonant in PRC. The matrices are with AS55 and REFL11 which are used for locking right now. The signal numbers are written in log10, and the dem phases are shown in degrees.
From CR reso PRMI to SB reso PRMI, demodulation phases change ----
PRMI - Carrier resonant in PRC
PRCL MICH SRCL
PRMI - SB resonant in PRC
SB reso PRMI
DRMI - SB resonant in PRC
- The code was modified, compiled, and installed.
- The code is now running. FB was restarted to deal with the change of the channel names.
- Now we have LOCKIN1, 2, and 3. This required the change of the names from C1:LSC-LOCKIN_.... to C1:LSC-LOCKIN1_...
- The LSC screen has also modified. It has three lockins on the screen.
- The corresponding matrix screens have been modified/created and linked from the main screen.
- I need to make the screens more cool but the locking team can start to use those lockins.
Tonight we want to measure the LSC matrix for PRMI and compare the simulation posted last night (#5495).
First. we locked MICH and PRCL, and measured the OLT to see how good the locking is. The following rough swept sine plots are the OLTs for MICH and PRCL. The gain setting was -10 and 0.5 for MICH and PRCL, respectively. Integrators were off. Looking at the measured plots, MICH has about 300 Hz UGF, when the gain is -20, and PRCL has about 300 HZ UGF, too, when the gain is 0.8.
As these lokings seemed good, so we tried the LSC matrix code written by Anamaria. However it is not working well at this point. When the script add excitations to the exc channels, they kick the optics too much and the lockings are too much disturbed...
Also, we have been trying to lock PRC with the SB resonant, it doesn't work. Looking at the simulated REFL11I (PRCL) signal (you can see it in #5495 too), the CR and SB resonances have the opposite signs... But minus gain never works for PRCL. It only excites the mirror rather than locking.
The scripts I wrote can be found in /users/anamaria/scripts/sensemat/
]There are two of them:
- one that sets all the switches, gains, frequencies, etc, then cycles through the various RFPDs I and Q into the LOCKIN signal, so as to see the sensing matrix.
- the second one is a matlab script that takes the crappy file tdsavg outputs and makes it into a cute mag/phase matrix.
They're quite primitive at this point, I've forgotten a lot of tcsh... may improve later. But could be useful later to someone else at least.
I don't think it's particularly the fault of the script that we can't measure the sensing matrix. We can slam on the excitation by hand, and it holds for a little while. I set a wait time for lock to adjust, and most times it just oscillates a bit for a few seconds. Also, the script turns on the excitation and it's done, the rest is just measurement, then turns it off at the end. So during the script, there's not much to deal with, except keeping the lowpass filters quiet when switching the signal to demod; but that doesn't go anywhere, so it definitely doesn't disturb the ifo. Turns out pressing the RSET clear history button needs a 2 to make it happen.
I think I might prefer to set the excitation to run, and then do the old retrieve-data-later-nds-matlab thing. I do not trust these measurements without coherence and a bit of variance study, given instabilities.
Point is... Even on carrier, the PRC lock is not stable by any means. Can barely turn on low freq boosts, every other lock. Until we fix the lock stability issue, there's not much to measure I guess.
Unfortunately, I don't know how to make that happen. Before we leave on Friday we could do a few sanity checks such as measuring the noise of the RFPDs vs ADC+whitening, which I may have said I would do; and perhaps setting up a couple OSAs, one on REFL, one on AS, to make sure we know what the sidebands are doing. Both of which Rana suggested at some point.
(There used to be a quote here from Keiko here but I got mad when it reformated my entire log to be one cluster- hence the look)
Found some LSC scripts didn't run on pianosa. Particularly all the scripts on the C1:IFO_CONFIGURE screen don't run.
They need to be fixed.