I think you also should check the PZT's capacitance of the 700mW LightWave because 2.36 nF is the one for the 1W Innolight laser.
To combat this, I propose we simply change the resistor in the modulation path from 1M to 10k. This leaves the feedback path TF unchanged, and changes the mod path into a sort of bandpass filter for the modulation frequency. The fact that the phase is near zero at fmod means we don't have to come up with some way to phase shift the signal for demodulation.
A nice plot !
Can you put another y-axis on the right hand side of the same plot in terms of the cavity displacements ?
And can you also measure a more important spectrum, namely the suppressed error signal ?
Quote from #5837
I measured the power spectrum of channel C1:GCY_SLOW_SERVO1_IN1, which is the PZT driving voltage.
EDIT by KI:
The definition of the recycling gain is wrong here.
See the latest entry (#5875)
Here is a summary about the Power Recycled Michelson (PRMI).
It seems the mode matching is also one of the greatest contributor on the low recycling gain.
+ Loss = 5.3% (or effective reflectivity of 93.28% in Michleson) => Under coupling !!
+ Mode matching efficiency = 47.4 % => Really bad !!
With these values we end up with a recycling gain of 7 and a normalized REFLDC of 0.5 as observed (#5773).
Also according the incident beam scan measurement (#5773) the loss is NOT a local effect like a clipping, it is more like uniformly distributed thing.
As for the mode matching, the number indicates that approximately the half of the incident light is coming back to the REFL port without interacting with PRMI.
This is bad because the non-mode-matched light, which is just a junk light, is entering into the photo detectors unnecessarily.
In the worst scenario, those junk light may create a funny signal, for example a signal sensitive to the alignment of PRM.
The method to estimate the loss and the MM (Mode-Matching efficiency) is essentially the same as before (#5541).
One difference from the previous estimation is that the I used more realistic parameters on the transmissivity of ITMs and PRM :
PRM : T = 5.637 % (see the 40m wiki)
ITM : T = 1.384 % (see the 40m wiki)
In addition to the basic calculations I also made plots which are handy for figuring out where we are.
Quantities we can measure are the reflected light from PRMI and the recycling gain using the REFL PD and the POY PD respectively.
So I wanted to see how the loss and MM can be estimated from the measured REFL DC and recycling gain.
The plots below are the ones.
The first figure shows a contour map of the loss as a function of the measured REFL DC and recycling gain.
The white area is a place where no proper solutions can be found (for example MM can get to more than 100 or loss becomes negative).
The star mark in the plot corresponds to the place where we are now. Obviously the loss is about 5%.
If we somehow decrease the amount of the loss the star mark will mostly go up in the plot.
The second figure shows a contour map of the MM as a function of the measured REFL DC and recycling gain.
The X and Y axis are exactly the same as that of the first plot. Again the star mark represents the place where we are.
We are currently at MM=47%
Here are some solutions to bring the recycling gain higher.
We don't work on these things immediately since it requires opening of the chambers again and it will take some times.
But we should think about those options and prepare some stuff for a coming vent.
+ Refinement of the position of the mode matching telescopes. => The Recycling gain can go up to 15.
=> Assuming the loss in the cavity doesn't change, the star mark in the first plot will go to the left hand side along the "0.05" black solid line.
=> However PRMI will be still under coupled.
=> Needs an estimation about which way we move the telescopes.
+ Locate the place of the dominant loss source and reduce it somehow.
=> The recycling gain will be more than 18 if the loss reduces by a factor of more than 5.
=> Needs a clever way to find it otherwise we have to do it in the classical way (i.e. white light and trying to find dirty surfaces)
Goal of this week : ALS on the Y arm
Minimum success : Detection of the green beatnote between the freq-doubled PSL and the Y arm transmitted light
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.
[Katrin / Kiwamu]
The beat-note between the PSL green laser and the Y end green laser was successfully detected.
The detection was done by the new broad-band RFPD.
The next step will be an extraction of the frequency fluctuation signal using the delay-line-mixer frequency discriminator.
(What we did)
+ Connected a BNC cable which goes from the c1iscey's DAC to the laser slow input
=> this enables a remote control of the laser frequency via the temeperature actuation
+ Realigned the beam pointing of the Y end green laser
+ Installed all the necessary optics on the PSL table
=> currently the PSL green light is adjusted to completely S-polarization
+ readjusted the mode matching telescopes
=> the Y green beam becomes the one with a long Rayleigh range
+ Health check on the broad-band RFPD to see if it is working
+ Installed the BB-RFPD with a +/-15V power supply
+ Fine alignment of the beam combining path
+ Fine tuning of the Y end laser temperature
=> T_PSL = 31.72 deg when the slow FSS feedback is zero.
=> Based on Bryan's measurement (see #elog) the Y end laser temperature was adjusted to 34.0 deg by applying an offset to the slow input.
+ Found the beat note at 100 MHz or so.
=> optimizing the alignment of the beam combining path by maximizing the peak height of the beat-note.
=> maximum peak height observed with an RF spectrum analyzer was about -36 dBm.
The recycling gain is determined by the optical configuration and the optical loss in the cavity.
How much is the actual recycling gain? And how does it affect the signal extraction?
As Koji pointed out I made a wrong definition on the recycling gain of PRMI (Power-Recycled Michelson Interferomter).
Reflectivity of PRMI (measured by REFLDC):
Power build up (measured by POY DC) :
Mode Matching (MM) efficiency :
Loss in the PRMI cavity :
(Results of Measurement and Estimation)
Estimated recycling gain = 15
Estimated MM efficiency = 47.4%
Estimated Loss = 5.3%
Measured power build Up = 7
Measured reflectivity of PRMI = 0.5
Goal of this week : Noise budgeting on the Y arm ALS
Minimum success : bring the Y arm to the resonance by using ALS NOISE BUDGETING!!!
=> as a preparation the incident beam pointing needs to be fixed by steering the MC suspensions.
Goal of this week : ALS on the Y arm (DONE)
Leaving a note on the ALS feedback before I forget:
The MC2 suspension needs to have an input for the ALS feedback in the realtime model like ETMs.
[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!!).
Locking activity last night :
The free run beat-note in 532 nm has been measured.
However I couldn't close the ALS loop somehow.
Every time I tried closing the loop it broke the Y end PDH lock in a couple of minutes.
(Things to be done)
1. Optimization of the Y end PDH servo loop
2. Refinement of the broadband RFPD setup
Dataviewer is not able to access to fb somehow.
I restarted daqd on fb but it didn't help.
Also the status screen is showing a blank white form in all the realtime model. Something bad is happening.
Some updates on the Y end green PDH lock
(Measurement of the Y arm fluctuation)
(Temporary servo setup)
I found that the temperature controller of the PSL doubling oven had been disabled.
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.
The noise budget on the Y arm ALS has begun.
Right now the fluctuation of the green beat-note seems mostly covered by unknown noise which is relatively white.
(Though I feel I made a wrong calibration ... I have to check it again)
[Suresh / Kiwamu]
The power switch button of the RF generation box is not properly working
For tonight we are leaving it as it is but it needs to be fixed at some point.
The temporary solution we decided is to leave it ON so that we can survive tonight.
The box was back in place. The MC is find and 11 MHz and 55 MHz seem okay.
Please be aware of it.
This is a picture showing the rear view of the RF generation box. The red arrow is pointing the blue LED switch button.
Jenne gave me a spare LED power switch .
I will replace the broken one on Monday.
By the way here is a picture album of the RF generation box which I took last night.
Recovery from the power shutdown
- Turned on the raid disk of linux1.
- Woke linux1 up. No fsck this time.
- Woke up all the lab machines.
- Turned on all the electronics racks' AC powers
- Woke up fb and then front end machine (the raid for fb had been already up as I turned on the AC powers)
- Turned on all the electronics racks' DC powers (Sorensens, Kepcos, and etc.)
- Turned on the Marcnois which is driving the RF generation box.
- Woke up all the lasers (PSL and End lasers)
- Some burtrestoring (c1ioo, c1sus, c1susaux, c1msc, c1psl, c1iool0, c1auxey, c1auxex, c1oaf, c1pem)
- Ran autolockMC scripts on op340m => After relocking of PMC a lock of MC was acquired immediately.
- Turned on the PZT HV drivers.
- One of the Sorensens in 1X8 rack is showing the current limit sign. This is exactly the same situation as we saw before (#5592).
Currently it's off. It needs an investigation to find who is drawing such a large amount of current.
- C1SCX is not properly running. Rebooting the machine didn't help. This needs to be fixed.
The symptom is : (1) all the values are frozen in the screens. (2) the c1scx status screens shows NO SYNC sign. (3) however the timing board looks blinking happily.
- One of the VME rack on 1X3 is not showing the +/-15V green LED lights.
This is the one on very upper side of the rack, which contains the old c1lsc machine and c1iscaux2. If we are still using c1iscaux2, it needs to be fixed.
DO NOT CHANGE THE IFO ALIGNMENT UNTIL TOMORROW MORNING OR FURTHER NOTICE.
Plus, MC has to be kept locked with the WFS.
An RFAM measurement is ongoing
This is a trend for a day long showing the REFL11/55 demod signals, REFLDC (corresponding to the MC transmitted power) and the PSL booth temperatire.
There are sudden jumps in the REFL55_I and REFL11_Q signals around 5:00 AM this morning, also at the same time the temperature suddenly went up.
But the quality of the signal turned out to be not so good because the fluctuation is still within 1 bit of the ADCs,
we have to try it again with a bigger gain in the analog whitening circuit.
The 2nd trial of the Y arm ALS noise budgeting :
(Removal of broad band noise)
I will add the dark noise of the broad-band beat-note PD and the MFD read out noise on the budget.
I found that the slow machine c1auxey, which controls and monitoring the ETMY suspension things, were not responding.
The machine responded to ping but I wasn't able to telnet to it.
I went down there and power-cycled it by keying the power of the VME rack, and then it came back and seems working properly.
I have no idea why it ran into such condition.
I have changed the MC2_YAW DC bias because the PZT1_YAW was railing.
I also realigned the steering mirrors in zig-zag path since the mode cleaner tended to resonate with higher order modes after I have changed the MC2 bias.
C1:SUS-MC2_YAW_COMM = -1.1548 => -1.1208
(The broad-band noise vs. gain of the Y end green PDH)
Last night I was trying to identify the broad band noise which is white and dominant above 20 Hz (#5970).
I found that the level of the noise depended on the servo gain of the Y end green PDH loop.
Decreasing the servo gain lowers the noise level by a factor of 2 or so. This was quite repeatable.
(I changed the gain knob of the PDH box from the minimum to a point where the servo starts oscillating)
(Malfunction in the comparator)
However I had to give up further investigations because the comparator signal suddenly became funny: sometimes it outputs signals and sometimes not.
It seems the comparator circuit became broken for some reason. I will fix it.
[Rana / Kiwamu]
As a part of the ALS noise budgeting we took a look at the Y end PDH setup to see if we are limited by an effect from the Amplitude Modulation (AM).
(AM transfer function)
(Y table setup needs more improvements)
[Rana / Mirko / Kiwamu]
The watchdogs on the MC suspensions are not working.
Switching off the watchdogs doesn't stop feeding signals to the suspensions.
For tonight, we will leave the controller of the MC suspensions switched off so that the computer won't smash the optics accidentally.
The 1X8 Sorensen's issue has been solved somehow.
As a part of the ALS noise budgeting we took a look at the Y end PDH setup to see if we are limited by an effect from the RF Amplitude Modulation (AM).
The AM transfer function of the Y end laser has been measured again, but using the frequency-doubled laser this time.
Here is the latest plot of the AM transfer function. The Y-axis is calibrated to RIN (Relative Intensity Noise) / V.
IFBW (which corresponds to a frequency resolution) was set to 100 Hz and the data was averaged about 40 times in a frequency range of 100 kHz - 400 kHz.
Also the zipped data is attached.
It is obvious that out current modulation frequency of 179 kHz (178850 Hz) is not at any of the notches.
It could potentially introduce some amount of the offset to the PDH signal, which allows the audio frequency AM noise to couple into the PDH signal.
Currently I am measuring how much offset we have had because of the mismatched modulation frequency and how much the offset can be reduced by tuning the modulation frequency.
I have restarted the c1sus machine around 9:00 PM yesterday and then shut it down around 4:00 AM this morning after a little bit of taking care of the interferomter.
c1sus has been shutdown so that the optics dont bang around. This is because the watch dogs are not working.
However I couldn't close the ALS loop somehow.
Locking activity last night:
It became able to close the ALS loop (beat-note signal was fed back to ETMY).
The UGF was about 60 Hz, but somehow I couldn't bring the UGF higher than that.
Every time when I increased the UGF more than 60 Hz, the Y end PDH was unlocked (or maybe ETMY became crazy at first).
Perhaps it could be a too much noise injection above 60 Hz, since I was using the coarse frequency discriminator.
Anyway I will try a cavity sweep and the successive noise budgeting while holding the arm length by the beat-note signal.
Another thing : I need a temperature feedback in the Y end green PDH loop, so that the PZT voltage will be offloaded to the laser temperature.
I have restarted the c1sus machine and burt-restored c1sus and c1mcs to the day before Thank giving, namely 23rd of November.
I have restarted the c1sus machine around 9:00 PM yesterday and then shut it down around 4:00 AM this morning after a little bit of taking care of the interferometer.
I reset the modulation frequency to 11065910 Hz (#5530). It had been at 11065399 Hz probably since the power shut down.
Here is a 48 hours trend of the RFAM monitor (a.k.a StochMon):
The upper plot is the DC output from the StochMon PD and the lower plot shows the calibrated RIN (Relative Intensity) at each modulation frequency.
I have downloaded minutes trends of StochMon for 48 hours staring from 6:00AM of Nov/24.
I followed Koji's calibration formula (#6009) to get the actual peak value (half of the peak-peak value) of the RF outputs and then divided them by the DC output to make them RIN.
It looks the RINs are hovering at ~ 4 x 10-4 and fluctuate from 1x10-4 to 1x10-3. Those numbers agree with what we saw before (#5616)
So it seems the StochMon is working fine.
New RFAM mon calibration
I have shut down the c1sus machine at 3:30 AM.
[Zach / Kiwamu]
Woke up the c1sus machine in order to lock PSL to MC so that we can observe the effect of not having the EOM heater.
I left the EOM stabilization running overnight, so we can finally see how the EOM temperature stabilization does over long periods of time.
The controller was turned on at ~8:40 UTC, and you can see that the Stochmon signals quiet down a lot right at that time.
Indeed the fluctuation of the RFAM became quieter with the temperature control ON.
However the absolute value of the RFAMs stayed at relatively high value.
I guess we should be able to set the right temperature setpoint such that the absolute value of the RFAM is smaller.
Here is the calibrated RFAM data (for 5 hours around the time when Zach activated the temperature control last night):
Okay I have turned ON the temperature control at 2:40 AM and will leave it ON for a while.
I was hesitant to claim that this is definitely true without the control data we were taking after the heater was turned off today. This is because before I replaced the malfunctioning op amp last night, the heater was actually ON and injecting temperature noise into the system that would not be there with it off. I think the best idea is to compare the data from today (heater on vs. heater off, but with functioning circuit).
The watchdogs' issue has been solved and they are now working fine.
It was just because one of the Sorensens had been off.
Tonight we noticed that, in fact, the watchdogs don't work for any of the corner optics (I confirmed that they do work for the ETMs).
I am going to try handing off the ALS servo to the IR PDH servo on the Y arm and measure the noise.
- first I need to investigate why the Y end PDH servo becomes unstable when the ALS is engaged with a high UGF.
So far I still kept failing to increase the UGF of the ALS servo for some reason (see #6024).
Every time when I increased the UGF more then 50 Hz, the Y arm PDH lock became unlocked. It needs an explanation and a solution.
Another thing: During several trials in this evening I found the ETMY_SUSPOS_GAIN had been set to 1, so I reset it to 20, which gives us the damping Q of about 5.
(Temperature feedback activated)
As planed in #6024 I have activated the temperature feedback, so that the PZT control signal is offloaded to the temperature. And it seems working fine.
Currently the gain is set to 0.03, which gives us a time constant of ~30 sec for offloading the control signal.
The signal observed by the coarse frequency discriminator was actually dominated by the ADC noise above 30 Hz.
It means that once increasing the UGF more than 30 Hz the servo will feed the ADC noise to the test mass and shake it unnecessarily.
I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071).
(But still it doesn't fully explain the instability).
To improve the situation I am going to do the following actions:
(1) Installation of a whitening filter (probably use of SR560s)
(2) Redesign of the servo filter
Here is a brief noise budget of the coarse sensor.
Gray curve: free running noise when no servo is applied
Green curve : in-loop noise when the ALS loop is closed with the coarse frequency-discriminator. The UGF was at 30 Hz.
Red curve : ADC noise of the coarse discriminator
Eventually the instability in the Y end PDH servo turned out to be some kind of an alignment issue.
After carefully realigning the green beam to the Y arm, the UGF of the ALS loop became able to be at more than 50 Hz.
With this UGF it became able to suppress the arm motion to the ADC noise level (few 100 pm in rms).
Now I am scanning the arm length to look for a TEM00 resonance.
I have noticed that the spatial fringe pattern of the reflected green light was very sensitive to the pitch motion of ETMY when the green light was locked to the Y arm.
So I realigned the last two launching mirrors to minimize the reflected light. Indeed the misalignment was mainly in the pitch direction.
I basically translated the beam upward by a couple of mm or so.
The amount of the DC reflection is about 2.4 V when it is unlocked and it is now 0.77 mV when the green light is locked.
I guess this could be one of the reasons of the unstable behavior in the Y end PDH lock (#6071). (But still it doesn't fully explain the instability).
I succeeded in handing off the servo from that of the ALS to IR-PDH.
However the handing off was done by the coarse sensor instead of the fine sensor because I somehow kept failing to hand off the sensor from the coarse to the fine one.
The resultant rms in the IR-PDH signal was about a few 100 pm, which was fully dominated by the ADC noise of the coarse sensor.
Tomorrow I will try :
(1) Using the fine sensor.
(2) Noise budgeting with the fine sensor.
Here is the actual time series of the handing off.
Next step: Kiwamu needs to find his happy mode cleaner place, and we'll realign the PSL beam to the MC. The PSL-MC axes were mismatched pretty badly according to Suresh anyway, so this had to be done no matter what.
No real progress.
Probably I spent a bit too much time realigning the beat-note optical path.
(what I did)
Since the c1lsc machine became frozen I restarted the c1lsc machined and daqd.
Then I burtrestored c1lsc, c1ass and c1oaf to this evening. They seem running okay.
Status update of the Y arm green lock:
+ Recent goal : automation of the single arm green lock
(Things to be done)
+ Recent goal : automation of the single arm green lock
I have restarted the daqd process at 1:01 PM since I have added some new ALS's daq channels.