Valera pointed out the OPLEV SUM channels were incorrect. We changing the optical level sum channel to _OPLEV_SUM when it should have been OL_SUM. This has been fixed in the activateDAQ.py script.
I've modified the rc.local file to run the IOC codes as controls, which means they no longer write root permission log files on startup.
The awgtpman, which was the other permission issue with the start scripts, is started by a run script now. This new version seems to be content to keep the permissions of the current log file, which is set to controls.
This should prevent the issue of sudo wiping your path environment variable for just that command. (Try "sudo which burtwb" versus "which burtwb" for example). This apparently a security feature of sudo.
If you should happen to use sudo to run a start script, the easiest solution to fix the permissions is just got to the target directory (type "target") and run "sudo chown controls:controls -R *" on one of the workstations (the front ends don't handle the groups properly at the moment).
This should allow the scripts to properly use burtrb and burtwb to write and backup burt files.
I modified the core/advLigoRTS/Makefile to once again place the startc1SYS and killc1SYS scripts in the scripts/FE/ directory.
It had been reverted in the SVN update.
Could not load filters into the C1:SUS-ETMX_LOCKIN1_SIG filter bank.
Apparently the filter bank name was too long. I'm not sure why this isn't caught by the real time code generator, I'm planning on asking Alex and Rolf about it today.
Reduce the name of the components. Basically LOCKIN1 needs to become something like LOCK1 or LIN1.
In related news, it looks like the initial filters are hard coded to be 2048 Hz. Given that they start out empty they won't cause things to break immediately, and if you're editing the file you can update the rate as you add the filter. I'll also bring this up with Alex and Rolf and see if the RCG can't be more intelligent about its filter generation.
[Larisa, Kiwamu, Steve and Suresh]
We continued the labeling of video cables. All exiting cables which are going to be used used in the new scheme have been labeled.
We also labeled the cables running from the video mux to the TV monitors in the computer room. Some of these will be removed or reallocated.
We will continue next Wednesday (after the meeting) and will lay cables that are most urgently required.
The Distribution box is several steps nearer to completion.
1) Soldered capacitors and DC power lines for four units of the distribution box.
2) mounted all the components in their respective places.
3) Tomorrow we prepare the RF cables and that is the last step of the mechanical assembly.
4) we plan to test both the generator and distributon parts together.
Kevin took a transfer function of the newly assembled PD and noticed that the frequency has shifted to 14.99 freom 11. MHz.
We needed to find the current RLC combination. So we removed the ferrite core from L5 rendiring it to its aircore value of 0.96/muH. We then used this to find the Capacitance of the PD (117pF)
We used this value to compute the inductance required to achieve 11.065MHz which turned out to be 1.75microH.
This was not reachable with the current L5 which is of the type 143-20J12L (nominal H=1.4 micro Henry).
We therefore changed the inductor to SLOT 10 -3-03. It is a ferrite core, shielded inductor with a plasitc sleeve. Its nomial valie is 1.75 microH
We then tested the DC output to see if here is a response to light. There was nonel. l
The problem was traced to the new inductor. Surprisingly the inductor coil had lost contact with the pins.
I then replacd the inductor and checked again. The elecronics seems to work okay.. but there is a very small signal 0.8mV for 500microW.
There seems to be still something wrong with the PD or its electronics.
I worked a little bit more on optimizing the mode matching to the MC, but it's still not great. I've only gotten a visibility of ~45%, but Koji said that it used to be ~87%. So there is a long way to go. Kiwamu said he can work with the lower-power configuration for a few days, and so my next step will be to measure the beam profile (stick a window in the path, and look at the refl from the window....that way we don't get thermal lensing from transmission through an optic), and redo the mode matching calculation, to figure out where the last lens should actually sit.
So.... Kiwamu and I were concerned (still a little concerned) that ETMY is not damping as nicely as it should be. (It's fine, but the UL rms is ~5, rather than ~1 or less. BURT restores by Kiwamu didn't change anything.) Anyhow, I was heading out to push the annoying ribbon cables more firmly into the satellite adapter board things that are tied to the racks in various places (The back of 1X5 for the corner optics and the end station racks for the ETMs). The point was to push in the ETMY one, but while I was out in the lab and thinking about it, I also gave all of the corner connectors (MC1, MC2, MC3, ITMx, ITMY, BS, PRM, SRM) a firm push.
Kiwamu noticed that when I did this, the Mode Cleaner alignment got a little bit worse, as if the connection to the satellite adapter boards hadn't been great, I pushed the connectors in and the connection got better, but we also got a bit of a DC offset in the MC alignment. Anyhow, the MC_TRANS power went down by ~2, to about the place it had been before Kiwamu adjusted the position of the lens in between the zigzag mirrors. (I don't know if Kiwamu elogged it earlier, but he scooted the lens a teensy bit closer in the optical path to the Mode Cleaner).
To counteract this loss in MC transmitted power as a result of my connector actions, I went back to the PSL table and fiddled with the zigzag steering mirrors that steer the beam from the PSL table over to the mode cleaner. I got it a little better, but it's still not perfect.
Kiwamu has noted that to improve the mode matching into the Mode Cleaner with the new PMC in place, we might have to move the lens which is currently between the zigzag steering mirrors, and put it after the second mirror (so in between the last steering mirror and the pickoff window that sends a piece of the beam over to PSL_POS and PSL_ANG). This will make the waist between MC1 and MC3 tighter.
Moral of the story: To improve IMC mode matching we need to move the last lens closer in the optical path to the mode cleaner waist. Twiddle with zigzag steering mirrors to optimize.
This is the 140 ft. MFD measurement of the VCO phase noise. It is open loop and so should be a good measurement. The RMS is 30 Hz integrated down to 2 mHz.
I don't know why this doesn't agree with Suresh's measurements of the same thing which uses the PLL feedback method.
In BLUE, I also plot the frequency noise measured by using a Stanford DS345 30 MHz func. generator. I think that this is actually the noise of the FD (i.e. the SR560 preamp) and not the DS345. Mainly, it just tells you that the PINK VCO noise measurement is a real measurement.
I calibrated it by putting in a 5 kHz_pp triangle wave on the sweep of the DS345 and counting the counts in DV.
As one of the trouble shooting steps for the daqd (i.e. framebuilder) I rebuilt the daqd executable. My guess is somewhere in the build code is some kind of GPS offset to make the time correct due to our lack of IRIG-B signal.
The actual daqdrc file was left untouched when I did the new install, so the symmetricom gps offset is still the same, which confuses me.
I'll take a look at the SVN diffs tomorrow to see what changed in that code that could cause a 300000000 or so offset to the GPS time.
As one of the trouble shooting steps for the daqd (i.e. framebuilder) I rebuilt the daqd executable.
I talked to Alex today and had two things fixed:
First the maximum length of filter names (in the foton C1SYS.txt files in /chans) has been increased to 40, from 20. This does not increase EPICS channel name length (which is longer than 20 anyways).
This should prevent running into the case where the model doesn't complain when compiled, but we can't load filters.
Additionally, we modified the feCodeGen.pl script in /opt/rtcds/caltech/c1/core/advLigoRTS/src/epics/util/ to correctly generate names for filters in all cases. There was a problem where the C1 was being left off the file name when in the simulink .mdl file the filter was located in a box which had "top_names" set.
[Koji and Kiwamu]
We took transfer functions (TF) from the angle excitations at ETMX and ITMX to the green beat note signal (i.e. angle to length TF).
It turned out that the coupling from ETMX_PIT is quite large.
I wonder how f2p of the ETMX changes this coupling. We'll see.
The plot above shows a set of the transfer functions from the angle excitation to the green beat note.
Note that the y-axis has not been calibrated, it is just a unit of counts/counts.
You can see that the TF from ETMX_PIT to the beat (red cruve) is larger than the others by about a factor of 10 over most of the frequency range.
This means that any PIT motions on ETMX can be coupled into the green beat signal somewhat over the wide frequency range.
It looks having a resonance at 1.5 Hz, but we don't exactly know why.
At that time the coil gains on only ITMX were tuned by applying f2p filters, but ETMX wasn't because of a technical reason coming from epics.
- - - - measurement conditions
* PSL laser was locked to X arm by feeding back the IR PDH signal to MC2.
* the green laser was locked to Xarm as usual.
* took the green beat note signal (approximately 0 dBm) into Rana's MFD with the cable length of about 6 m.
* the output from the MFD was connected to XARM_COARSE channel without a whitening filter.
* excitation signal was injected into either ASC_PIT or ASC_YAW. The excitation was Gaussian noise with frequency band of 10 Hz and amplitude of 300 counts.
* only ITMY had the f2p filters, which balance the coil gains all over the frequency.
We updated the c1ass model to include the BS. We removed the dither excitation of the PZTs. PZT control goes to epics. To do this, modified the /cvs/cds/caltech/target/c1iscaux/PZT_AI.db file. We basically have it sum both the existing epics slider and our new output from c1ass.
More importantly we updated the color scheme.
We compiled and tested the Dolphin and RFM which work.
I should note we can't figure out why testpoints are not working properly with just this model. Alex and Joe spent well over an hour trying to debug it to no success. Current workaround is to add what channels you want from c1ass to the DAQ recording. Other testpoints on other models appear to be working.
Most of the RF cables required for the box are done. There are two remaining and we will attend to these tonight.
We expect to have finished the mechanical assembly by Sunday and start a quality test on Monday.
I restarted the elog using the script.
The mechanical assembly of RF distribution box is 99% complete. Some of the components may be bolted to the teflon base plate if needed.
All RF cables and DC voltage supply lines have been installed and tested. I removed the terminal block which was acting as a distribution box for the common zero voltage line. Instead I have used the threaded holes in the body of each voltage regulator. This allows us to keep the supply lines twisted right up to the regulator and keeps the wiring neater. The three regulator bodies have been wired together to provide a common zero potential point.
I did a preliminary test to see if everything is functioning. All units are functioning well. The output power levels may need to be adjusted by changing the attenuators.
The 2x frequency multiplier outputs are not neat sine waves. They seem to produce some harmonics, unlike the rest of the components.
I will post the measured power output at each point tomorrow. The RF power meter could not be found in the 40m lab. We suspect that it has found its way back to the PSL lab.
Frank is recommending these PhaseTrack-210 as phase stable low loss rf coax cables.
Larisa Thorne received 40m lab specific, basic safety training. She will attend P. King's Basic Laser Safety Training Session tomorrow.
As per Kiwamu's request I made a light touch to the input steering and the mode matching lens.
Here V_ref and V_trans are C1:IOO-MC_RFPD_DCMON and C1:IOO-MC_TRANS_SUM, respectively.
Result: Visibility = 1 - V_ref(resonant) / V_ref(anti_reso) = 1 - 0.74 / 5.05 = 85%
What has been done:
New noise spectra of the green locking have been updated.
The plot below shows the in-loop noise spectra when the beat signal was fedback to ETMX.
The rms noise integrated from 0.1 Hz to 100 Hz went down to approximately 2 kHz.
The red curve was taken when the beat was controlled only by a combination of some poles sand zeros on the digital filter banks. The UGF was at 40Hz.
This curve is basically the same as that Koji took few weeks ago (see here). Apparently the rms was dominated by the peaks at 16 Hz and 3 Hz.
The blue curve was taken when the same filter plus two resonant gain filters (at 16.5 Hz and 3.15 Hz) were applied. The UGF was also at 40Hz.
Due to the resonant gain filter at 16.5 Hz, the phase margin became less, and it started oscillating at the UGF as shown in the plot.
We wish to have roughly 2 dBm of output power on each line coming out of the RF distribution box. So I adjusted the attenuators inside the box to get this.
I also looked at why the 2x output looked so distorted and found that the input power was around 17 dBm whereas the maximum allowed (as per the datasheet of Minicircuits MK-2) is 15dBm. So I increased the attentuation on its input line to 5dBm (up by 2dBm) The input power levels are around 14.6dBm now and the distortion has come down considerably. However the net output on the 2x lines is now down to 0.7dBm. We will have to amplify this if we need more power.
The schematic and the power output are now like this:
Alex and I updated the open mx drivers from 1.3.3 to 1.3.901 (1.4 release candidate). We downloaded the drivers from: http://open-mx.gforge.inria.fr/
We put them in /root/open-mx-1.3.901 on the fb machine (and thus get mounted by all the front ends.). We did configure and make and make install.
We did a quick check with /opt/mx/bin/mx_info on the fb machine at this point and realized the MAC addresses and host names were all messed up, including two listings for c1iscex with different mac addresses (neither of which was c1iscex).
We then brought all the front ends mx_streams down, brought the fb down, then cleared all the peer names with mx_hostname. We then brought the fb up, and the front end mx_stream processes.
/opt/mx/mx_info now shows a clean and correct set of hostnames and mac addresses. Testpoints and trends are working.
Having finished labeling the existing cables to match their new names, we (Steve, Kiwamu and Larisa) moved on to start laying new cables and labeling them according to the list.
Newly laid cables include: ETMXT (235'), ETMX (235'), POP (110') and MC2 (105'). All were checked by connecting a camera to a monitor and checking the clarity of the resulting image. Note that these cables were only laid, so they are not plugged in.
The MC2 cable needs to be ~10' longer; it won't reach to where it's supposed to. It is currently still in its place.
The three other cables were all a lot longer than necessary.
[Kevin, Rana, Koji]
I calculated the dark noise of POX and POY due to Johnson noise and voltage and current noise from the MAX4107 op-amp using nominal values for the circuit components found in their data sheets. I found that the dark noise should be approximately 15.5 nV/rtHz. The measured dark noise values are 18.35 nV/rtHz and 98.5 nV/rtHz for POX and POY respectively. The shot noise plots on the wiki have been updated to show these calculated dark noise sources.
The measured dark noise for POY is too high. I will look into the cause of this large noise. It is possible that the shot noise measurement for POY was bad so I will start by redoing the measurement.
Just in case anyone else wants to access it, we now have 30 days of H1 S5 DARM data sitting on Rossa's harddrive. It's in 10min segments. This is handy because if you want to try anything, particularly Wiener Filtering, now we don't have to wait around for the data to be fetched from elsewhere.
Cheater cables for SRM sus tied up. They were dangling aimlessly on the floor.
I did a quick calculation to determine the amount of sideband transmission through the FP cavity.
The modulation frequency of the end PDH is 216kHz. The FSR of the cavity is about 3.9MHz. So the sidebands pick up about 0.17 radians extra phase on one round trip in the cavity compared to the carrier.
The ITM reflectance is r_ITM^2 = 98.5% of power, the ETM reflection is r_ETM^2 = 95%.
So the percentage of sideband power reflected from the cavity is R_SB = r_ITM*r_ETM*(exp(i*0.17) - 1)^2 / (1 - r_ETM*r_ITM exp(i*0.17) )^2 = 0.85 = 85%
So about 15% of the sideband power is transmitted through the cavity. The ratio of the sideband and carrier amplitudes at the ETM is 0.05
So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.
Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.
Two different measurement have been performed for a test of the green locking last night.
Everything is getting better. yes. yes.
[ measurement 1 : IR locking]
The X arm was locked by using the IR PDH signal as usual (#4239, #4268) .
The in-loop signal at from the IR path and the out-of-loop signal at from the green beat note path were measured.
Let us look at the purple curve. This is an out-of-loop measurement by looking at the green beat note fluctuation.
The rms down to 0.1 Hz used to be something like 60 kHz (see here), but now it went down to approximately 2 kHz. Good.
This rms corresponds to displacement of about 260 pm of the X arm. This is barely within the line width. The line width is about 1 nm.
[ measurement 2 : green locking]
The motion of the X arm was suppressed by using the green beat signal and feeding it back to ETMX.
After engaging the ALS servo, I brought the cavity length to the resonance by changing the feedback offset from epics.
Then took the spectra of the in-loop signal at the beat path and the out-of-loop signal at the IR PDH path.
Here is a time series of TRX after I brought it to the resonance.
TRX was hovering around at the maximum power, which is 144 counts.
Since I put one more 10:1 filter to suppress the noise around 3 Hz, the rms of the in-loop beat spectrum went to about 1 kHz, which used to be 2 kHz (see #4341).
But the out-of-loop (IR PDH signal) showed bigger noise by a factor of 2 approximately over frequency range of from 2 Hz to 2 Hz. The resultant rms is 2.7 kHz.
The rms is primarily dominated by a peak at 22 Hz (roll mode ?).
I calibrated the IR PDH signal by taking the peak to peak signal assuming the finesse of the cavity is 450 for IR. May need a cooler calibration.
I forgot to mention about the whitening filter for the ALS digital control system.
As usual I used a whitening filter to have a good SNR against ADC noise, but this time our whitening scheme is little bit different from the usual our systems.
I used two ADC channels for one signal and put a digital summing point and digital filters to keep good SNR over the frequency range of interest.
It's been working fine but it's still primitive, so I will study more about how to optimize this scheme.
The diagram above shows our scheme for the signal whitening.
Basically the SNR at DC is bad when we use only a whitening filter as shown on the bottom part of the diagram because the signal is quite tiny at DC.
On the other hand if we take raw signal into ADC as 'DC path' shown above, the SNR is better at DC but not good at intermediate frequencies (30 mHz - 1kHz).
So the idea to keep the good SNR over the frequency range of interest is to combine these 'DC path' and 'AC path' in a clever way.
In our case, the 'DC path' signal is not as good as the 'AC path' signal above 30 mHz, so we cut off those high frequency signals by using a digital low pass filter.
In addition to it, I put a gain of 1000 in order to match the relative gain difference between 'DC path' and 'AC path'.
Then the resultant signal after the summing point keeps the good SNR with a flat transfer function up to 1 kHz.
In this past weekend I replaced a summing amplifier for the end green PDH locking by a home-made summing circuit box in order to increase the control range.
It's been working well so far.
However due to this circuit box, the demodulation phase of the PDH locking is now somewhat different from the past, so we have to readjust it at some point.
However due to this circuit box, the demodulation phase of the PDH locking is now somewhat different from the past, so we have to readjust it at some point.
At the X end station, the voltage going to the NPRO PZT had been limited up +/- 4 V because of the summing amplifier : SR560.
Therefore the laser was following the cavity motion only up to ~ +/- 4 MHz, which is not wide enough. (it's okay for night time)
So we decided to put a passive circuit instead of SR560 to have a wider range.
We made a passive summing circuit and put it into a Pomona box.
The circuit diagram is shown below. Note that we assume the capacitance of the 1W Innolight has the same capacitance as that of the PSL Innolight (see #3640).
The feedback signal from a PDH box goes into the feedback input of the circuit.
Then the signal will be low passed with the corner frequency of 200 kHz because of the combination of RC (where R is 681 Ohm and C is capacitance of the PZT).
Because of this low pass filter, we don't drive the PZT unnecessarily at high frequency.
On the other hand the modulation signal from a function generator goes into the other input and will be high passed by 50 pF mica capacitor with the corner frequency of 200 kHz.
This high pass filter will cut off noise coming from the function generator at low frequency.
In addition to it, the 50 pF capacitor gives a sufficient amount of attenuation for the modulation because we don't want have too big modulation depth.
Here is a plot for the expected transfer functions.
You can see that the modulation transfer function (blue curve) has non-zero phase at 216 kHz, which is our modulation frequency.
I made several scripts to handle the mcass configuration and sensing measurements:
- The scripts and data are in the scripts/ASS directory
- The mcassUp script restores the settings for the digital lockins: oscillator gains, phases, and filters. The MC mirrors are modulated in pitch at 10, 11, 12 Hz and in yaw at 10.5, 11.5, and 12.5 Hz. The attached plot shows the comb of modulation frequencies in the MCL spectrum.
- The mcassOn and mcassOff scripts turn on and off the dither lines by ramping up and down the SUS-MC1_ASCPIT etc gains
- The senseMCdecenter script measures the response of the MCL demodulated signals to the decentering of the beam on the optics by imbalancing the coil gains by 10% which corresponds to the shift of the optic rotation point relative to the beam by 2.65 mm (75mm diameter optic) and allows calibration of the demodulated signals in mm of decentering. The order of the steps was MC1,2,3 pitch and MC1,2,3 yaw. The output of the script can be redirected to the file and analyzed in matlab. The attached plot shows the results. The plot was made using the sensemcass.m script in the same directory.
- The senseMCmirror script measures the response of the MCL demodulated signals to the mirror offsets (SUS-MC1_ASCPIT etc filter banks). The result is shown below (the sensemcass.m script makes this plot as well). There is some coupling between pitch and yaw drives so the MC coils can use some balancing - currently all gains are unity.
- The senseMCdofs scripts measures the response to the DOF excitation but I have not got to it yet.
- The next step is to invert the sensing matrix and try to center the beams on the mirrors by feeding back to optics. Note that the MC1/MC3 pitch differential and yaw common dofs are expected to have much smaller response than the other two dofs due to geometry of this tree mirror cavity. We should try to build this into the inversion.
The beam of IR for doubling is clipping on bnc cable to green beam transmitted pd.
This experiment deals with measuring the total harmonic distortion (THD) contribution of mixers in a circuit.
(a circuit diagram is attached) where:
Mixer: ZFM-3-S+ at +7dBm
Attenuator: VAT-7+, at +7dB
Low-pass filter: SLP-1.9+, which is set to DC-1.9MHz
The total harmonic distortion can be calculated by the equation:
where Vn represents the voltage of the signal at a certain harmonic n.
In this experiment, only the voltages of the first three harmonics were measured, with the first harmonic at 400Hz, the second at 800Hz, and the third at 1.2kHz. The corresponding voltages were read off the spectrum analyzer after it had time averaged 16 measurements. (picture of the general shape of the spectrum analyzer output is attached)
(results for this mixer's particular configuration are on the pdf attached)
There really isn't that much correlation between the modulations and the resulting THD.
We won't know how good these numbers are until more experiments on other mixers are done, so they can be compared. Since the rest of the mixers are relatively high levels (+17dBm, +23dBm in comparison to this experiment's +7dBm), an RF amplifier will need to be hooked up first to do any further measurements.
[Rana / Koji]
The MC servo loop has been investigated as the MC servo was not an ideal state.
With the improved situation by us, the attached setting is used for the MC and the FSS.
The current UGF is 24kHz with phase margin is ~15deg, which is unbearably small.
We need to change the phase compensation in the FSS box some time in the next week.
- We found the PD has plenty of 29.5MHz signal in in-lock state. This was fixed by reducing the LO power and the modulation depth.
- The LO power for the MC demodulator was ~6dBm. As this was too high for the demodulator, we have reduced it down to 2dBm
by changing attenuator to 12dB (at 6 oclock of the dial) on the AM stabilization box.
- The RF power on the MC PD was still too high. The PD mush have been saturated. So the modulation slider for 29.5MHz was moved
from 0.0 to 5.0. This reduced the 29.5MHz component. (But eventually Koji restored the modulation depth after the servo shape has been modified.)
- The openloop gain of the loop has been measured using EXC A/TEST1/TEST2. The UGF was ~5kHz with the phase mergin of ~10deg.
- This quite low phase margin is caused by the fact that the loop has f^-2 shape at around 4k-100kHz. The reference cavity has
the cavity pole of 40kHz or so while the IMC has the pole of ~4kHz. Basically we need phase lead at around 10-100kHz.
- We decided to turn off (disable) 40:4000 boost of the MC servo to earn some phase. Then MC did not lock. This is because the LF gain was not enough.
So put Kevin's pomona box in the FAST PZT path (1.6:40). By this operation we obtain ~75deg (max) at 560Hz, ~35deg at 5kHz, ~20deg at 10kHz.
- In this setup the UGF is 24kHz. Still the phase margin is ~15kHz. This phase lag might be cause by 1) the MC servo circut 2) PMC cavity pole
- Put/modify phase lead in the FSS box.
- Measure the PMC cavity pole
- Measure and put notch in the PZT path
- Increase the UGF / measure the openloop TF
The power ratio of the beatnote signal vs. the 216kHz sideband has been measured.
The measured ratio was -55 dB, which is smaller by about 20 dB than Aidan's estimation.
To confirm this fact we should check the modulation depth of the end PDH somehow.
The below is a picture showing the sidebands around the beatnote locked at 66.45 MHz.
Other than the +/-216 kHz sidebands, we can see some funny peaks at +/- 50 kHz and +/-150 kHz
I wonder if they come from the servo oscillation of the MC servo whose UGF is at 24 kHz. We can check it by unlocking the MC.
Can we set up a fiber-PD on the end table to look at the beat between the "end laser IR beam" and the "PSL IR beam fiber-transmitted end beam"?
We should see the same thing on that PD that we see on the green PD (plus any fiber noise and I'm not really sure how much that'll be off the top of my head). If we unlock the lasers from the arm cavity then the free-running noise of the lasers wrt to each other will probably swamp the 50kHz and 150kHz signals. Maybe we could lock the end laser to the free-running PSL by demodulating the beat note signal from the fiber-PD and then we could look for the extra sidebands in the IN-LOOP signal. Then we could progressively lock the PSL to the MC and arm cavity and see if the sidebands appear on the fiber-PD at some point in that process.
It's possible that the 216kHz drive of the PZT on the Innolight is somehow driving up some sub-harmonics in the crystal. I think this is unlikely though: if you look at Mott's measurements of the Innolight PZT response, there are no significant PM resonances at 50 or 150kHz.
Other than the +/-216 kHz sidebands, we can see some funny peaks at +/- 50 kHz and +/-150 kHz.
When Koji and I were massaging the MC, we noticed that the oscillations were at 48.5 kHz. They were pretty huge and are probably what you're seeing on the beat. My guess is that they are the PZT resonances of the PSL 2W NPRO; we need to put a notch in the FSS box - it still has the notch from the old NPRO.
The elog was dead this morning. I reanimated it. It is now undead.
[Koji / Rana]
- Since the MC servo had UGF up to ~20kHz and huge servo bump at 50kHz, we needed more phase between 20kHz to 100kHz.
- Today a phase compensation filter in a Pomona box has been inserted between the MC servo box and the FSS box.
This is a passive filter with zero@14kHz and pole@140kHz. We obtain ~60deg at around 50kHz.
- After the insertion, the lock of the MC was achieved immediately. The overall gain as well as the PZT fast gain was tweaked
such that the PC feedback is reduced down to 1~2.
- The OLTF has been measured.
The insertion of the filter change increased the UGF to 130kHz even with "40:4kHz" and double super boost turned on.
The phase margin is 54deg. Quite healthy.
- Rana modified the existed Auto Locker script.
It is now continuously running on op340m!
We made a couple of testsif it correctly relock the MC and it did. VERY COOL.
- Measure the PMC cavity pole
- Measure the circuit TF and try to shave off the phase lag.
- Measure the PZT resonance of the NPRO and put notch in the PZT path
- Increase the UGF / measure the openloop TF
Kiwamu and I noticed that there is a ghost beam on the green beam going into the ETM. What we see is some interference fringes on the edge of the transmission of the green beam through the dichroic beam splitter (DCBS). If we look at the reflection from the dichroic beam splitter these are much more pronounced.
The spacing of the fringes (about 2 per 10mm) indicates an angle between the fields of around 0.1 mrad.
We were able to cause significant motion of the fringes by pushing on the knobs of the steering mirrors that steer the beam into the DCBS. A rough calculation of the derivative of optical path difference between the ghost and the primary beam as a function of input angle gives about 15 microns per mrad. What filtering the effect the arm cavity will have on the ghost beam is not immediately clear, but the numbers shouldn't be too difficult to determine.
The previous measurement for the shot noise of POY had the dark noise at ~100 nV/rtHz. I redid the measurement and got 26 nV/rtHz for the dark noise. I think that when I made the previous measurement, the spectrum analyzer had automatically added some attenuation to the input that I failed to remove. This added attenuation raised the noise floor of the measurement making the dark noise of POY appear larger than it is.
The updated measurement can be found on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.
I somehow screwed up the PDH box at the X end station.
Right now it's not working, so I am going to check and fix it today.
In the last evening I found that one of the gain stages on the PDH box wasn't fully functional.
So I started investigating it and I though it was going to finish soon, but actually it wasn't so easy.
The PDH box has several gain stages. So an input signal goes through a buffer, a filter, a boost and an output buffer stages sequentially.
The boost stage is supposed to have gain of 10, but I found it didn't have such gain.
In fact the gain was something like -30dB which is pretty small. Plus this boost stage was imposing an wired bump on the transfer function around 50 kHz.
I checked the voltages on some components around the boost stage and confirmed there were no strange voltage.
Then I suspected that the op-amp : LF356 had been broken for some reason. So I replaced it by LT1792 to see if it fixes the issue.
Indeed it did make it functional. However after few minutes of the replacement, it went back to the same bad condition.
I have no idea about what was going on at that time. Anyway it needs more careful investigations.
I temporarily put a jumper cable on the board to skip this stage, but now the PDH lock is not healthy at all.
Finished calculations for harmonic distortion at each of the 10 outputs of the RF distribution box. The diagram can be found on Suresh's post http://nodus.ligo.caltech.edu:8080/40m/4342
THD calculation consisted of gather data on the dBm at harmonics of the fundamental frequency. These dBm values were converted into units of power and plugged into the appropriate THD equation pulled from Wikipedia:
On the table, the number 1-6 correspond to the harmonic number of the input frequency used. For example, the first five PD's listed used an 11MHz source, while the second set of five PD's listed used a 55MHz source. Values listed under certain harmonics are dBm measurements at the corresponding frequency. The P-subscript values are essentially the dBm measurements converted to units of power (Watts) for ease of calculation in the equation above. THD is then calculated using these power units; I have converted the ratios to percentages.
It should be noted that as with all THD calculations, the more data points collected, the more precise the THD % will be.
By the way, the outputs on the physical RF distribution box for REFL165 and AS165 are actually labeled as REFL166 and AS166.
I made a noise budget for the ALS noise measurement that I did a week ago (see #4352).
I am going to post some details about this plot later because I am now too sleepy.
Fast work indeed! It would be nice if we could have the following details filled in as well
a) A short title and caption for the table, saying what we are measuring
b) the units in which this physical quantity is being measured.
It is good to keep in mind that people from other parts of the group, who are not directly involved in this work, may also read this elog.
Here I explain how I estimate the contribution from the differential noise shown in the plot on my last entry (#4376) .
According to the measurement done about a week ago, there is a broadband noise in the green beatnote path when both Green and IR are locked to the X arm.
The noise can be found on the first plot on this entry (#4352) drawn in purple. We call it differential noise.
However, remember, the thing we care is the noise appearing in the IR PDH port when the ALS standard configuration is applied (i.e. taking the beatnote and feeding it back to ETMX).
So we have to somehow convert the noise to that in terms of the ALS configuration.
In the ALS configuration, since the loop topology is slightly different from that when the differential noise was measured, we have to apply a transfer function to properly estimate the contribution.
(How to estimate)
It's not so difficult to calculate the contribution from the differential noise under some reasonable assumptions.
Let us assume that the MC servo and the end PDH servo have a higher UGF than the ALS, and assume their gains are sufficiently big.
Then those assumptions allow us to simplify the control loop to like the diagram below:
Since we saw the differential noise from the beatnote path, I inject the noise after the frequency comparison in this model.
Eventually the noise is going to propagate to the f_IR_PDH port by multiplying by G/(1+G), where G is the open loop transfer function of the ALS.
The plot below shows the open loop transfer function which I used and the resultant G/(1+G).
In the curve of G/(1+G), you can see there is a broad bump with the gain of more than 1, approximately from 20 Hz to 60 Hz.
Because of this bump, the resultant contribution from the differential noise at this region is now prominent as shown in the plot on the last entry (#4376).
I am going to post some details about this plot later