I measured the power incident on REFL11 and REFL55. Steve was concerned that it is too high. If we consider this elog the incident power levels were REFL11: 30 mW and REFL55: 87 mW. (assuming efficiency of ~ 0.8 A/W @1064nm for the C30642 PD). However, currently there is a combination of Polarising BS and Half-waveplate with which we have attenuated the power incident on the REFL PDs. We now have (with the PRM misaligned):
REFL11: Power incident = 7.60 mW ; DC out = 0.330 V => efficiency = 0.87 A/W
REFL55: Power incident = 23 mW ; DC out = 0.850 V => efficiency = 0.74 A/W
and with the PRM aligned::
REFL11: DC out = 0.35 V => 8 mW is incident
REFL55: DC out = 0.975 V => 26 mW is incident
These power levels may go up further when everything is working well.
The max rated photo-current is 100mA => max power 125mW @0.8 A/W.
The WFS2 Transimpedance has been measured to determine if it also suffers from the same 200MHz oscillations seen in WFS1 sensor head
The attached plots (pdf attached) show that the 29.5 MHz peak needs tweaking in Q2 and Q1 seems to have a much lower transimpedance than other quadrants. The table below summarises the resonances and notches of the ckt
The peak at 10MHz is much sharper than the similar peak at 13MHz in the case of WFS1. Is this a matter for some concern?
The 200MHz oscillation once again exists in Q2, Q3 and Q4. This sensor head will also require the same treatment as WFS1.
I have shifted the Jenne laser back to the small table where we do RF PD characterisation (RFPD table). I found several 25pin D-type connector cables, connected them in tandem and am using that to power the WFS2 sensor head at the RFPD table.
The set up is ready for looking at the RF response of the WFS sensors. Will continue tonight.
What is the power level on MC_REFL_ PDs and WFS when the MC is not locked?
The measured change in the REFL DC power with and without PRM aligned seems unacceptably small. Something wrong ?
The difference in the power with and without PRM aligned should be more than a factor of 300.
[difference in power] = [single bounce from PRM] / [two times of transmission through PRM ]
= (1-T) / T^2 ~ 310,
where T is the transmissivity of PRM and T = 5.5% is assumed in the calculation.
Also the reflectivity of MICH is assumed to be 1 for simplicity.
We now have (with the PRM misaligned):
Today I wanted to investigate the MC Length path situation for obscure reasons.
Jamie has started to revert the "ALTPOS" effect on the MC mirrors. So far, the screens and SLOW channels have been fixed, but the fast channels still say "ALTPOS" in the dataviewer instead of "MCL".
I also noticed that all of our old ADCU channels for diagnosing the PSL, MC, ISS, PMC ,etc. are completely AWOL. Let's blame Joe.
I think that there are probably some ADC channels available and that we'll just have to figure out what Joe intended for this. We certainly need it if we want to diagnose our PMC, ISS, FSS, MC, etc. Kiwamu tells us that the old PSL/IOO AA chassis is being used for some of the GCV signals, so its likely that we just have to do the appropriate channel name mapping in the DAQCONFIG tool.
Forging ahead with no data, I made up some filters in the MC2-MCL filter bank so that there could be a stable crossover between the laser path. I was able to turn it on and get some suppression of the FSS-FAST control signal, but there's no way to be sure without the fast channels. We gotta get Jamie to help us out once he finished the ETM BO mess.
I measured the power in various beams on the AP table to check and see if any beam is having too much power.
I am uploading two pics one is in the "high power state" and the other is the "low power state". High power in the MC REFL PD occurs when the MC is unlocked. In addition the WFS also will see this hike in power. We wish to make sure that in either state the power levels do not exceed the max power that the PDs can tolerate.
Low Power state: MC locked, PRM not aligned. High Power state: MC unlocked, PRM aligned.
As noted before the resonances had to be tuned to the 29.5 MHz ( or rather 29.485 MHz to match with the Wenzel) and notches to twice that frequency (58.97 MHz).
I tuned these frequencies and remeasured the transimpedance curves . These are in the attached pdf file.
1) The variable inductances on the PCB have a ferrite core which is actually ferrite powder compacted around an iron screw. The screw serves to provide the adjustability. However, being iron, it seems to have rusted and so the cores are stuck. So several of the cores splintered when I tried to adjust the frequencies.
2) The WFS1 had a finger print/smudge on the face of the PD. I drag wiped it with methanol to get rid of it.
WFS1 is ready to go on the table. I am going to work on WFS2 today.
The framebuilder just needed to be restarted to pull in the fixed channel names. I restarted the framebuilder and now the channels (C1:SUS-MC2_MCL_*) are showing up properly.
This was the WFS whose photodiode was repaced as the old one was found to be damaged.
I retuned the resonances and the notches of all the quadrant and have attached a pdf file of my measurements.
a) The variable inductor on WFS2Q2 quadrant may need to be changed. The ferrite code has come of the solinoid and is just held in place due to friction.. It may be easily disturbed. So though i chose to leave it in place for now, it will need to be replace in case the Q3 misbahaves..
b) In general the frequencies have shifted a bit when I closed the lid of tne WFS sensor head.
WFS1 and 2 have been installed on the AP table and are functional. I am shifting attention to the software.
What is implicit in Suresh's entry is that we decided to run the WFS with the 10 dB internal attenuation set to ON as the nominal. In the past, we have always had all the attenuation OFF for max gain. The layout of the WFS is such that we get that nasty 200 MHz oscillation due to crosstalk between the 2 MAX4106 opamps for each quadrant. The 10 dB attenuator is able to reduce the positive feedback enough to damp the oscillation.
In principle, this is still OK noise-wise. I think the thermal noise of the resonant circuit should be ~2-3 nV/rHz. Then the first opamp has a gain of 5, then the -10 dB attenuator, then another gain of 5. The noise going to the demod board is then ~10-15 nV.
The real noise issue will be the input noise of the demod board. As you may recall, the output of the AD831 mixer goes to a AD797. The AD797 is a poor choice for this application. It has low noise only at high frequencies. At 10 Hz, it has an input voltage noise of 10 nV/rHz and a current noise of 20 pA/rHz. If we wanted to use the AD797 here, at least the RC filter's resistor should be reduced to ~500 Ohms. Much better is to use an OP27 and then choose the R so as to optimize the noise.
We should also be careful to keep the filter frequency low enough so as not to rate limit the OP27. From the schematic, you can see that this circuit is also missing the 50 Ohm termination on the output. There ought to be the usual high-order LC low pass at the mixer output. The simple RC is just not good enough for this application.
As a quick fix, I recommend that when we next want to up the WFS SNR, we just replace the RC with an RLC (R = 500 Ohms, L = 22 uH, C = 1 uF).
Just tying up a loose end. The next day Kiwamu and I checked to see what the trouble was. We concluded that the PRM had not moved during my measurement though I had 'Misaligned' it from the medm screen. So all the power levels measured here were with the PRM aligned. The power level change was subsequently measured and e-logged
As a simple check of the gains on all the quadrants I hooked up the AM (Jenne) laser to put FM modulated light on to the WFS heads and observed the FM modulation frequency , 105 Hz, show up on a power spectrum of the RF outputs. The plots below show the peak at 105Hz in all the quadrants.
However I should have put in AM modulation rather FM modulation. I will do that using the digital system today. The first version above was done wth a Marconi driving the AM laser modulation.
The mode cleaner is not locking because the MC Trans QPD signal is not present. There is light on the QPD when the MC flashes and its position has not shifted. The cable is plugged in well into the sensor head. The signal cable is labled "MC2 Opt Lever" and it arrives on the 1X4 rack along with other Optical Lever cables. Pressing the connector in did not solve the problem.
It turns out that the MC_TRANS_SUM signal was being derived from the SUS-MC2_OL_SUM_INMON channel in the ioo.db file.
However, this channel name was recently changed to SUS-MC2_OLSUM_INMON (no underscore between OL and SUM) when
I added the new OL_SUM epics channel to the sus_single_control library model (I forgot to mention it in my previous log on this change,
apologies). This is why there appeared to be no signal. This was also what was preventing the mode cleaner from locking, since
the MC_TRANS_SUM signal is used as a trigger in the MC autolocker script.
We modified the ioo.db file at /cvs/cds/caltech/target/c1iool0/ioo.db [0,1] to change the name of the channel that the
C1:IOO-MC_TRANS_SUM signal is derived from. The diff on the ioo.db file is:
--- /cvs/cds/caltech/target/c1iool0/ioo.db 2011-07-21 11:43:44.000000000 -0700
+++ /cvs/cds/caltech/target/c1iool0/ioo.db.2011Jul21 2011-07-21 11:43:36.000000000 -0700
@@ -303,7 +303,7 @@
field(DESC,"MC2 Trans QPD Sum")
- field(INPA, "C1:SUS-MC2_OLSUM_INMON")
+ field(INPA, "C1:SUS-MC2_OL_SUM_INMON")
field(SCAN, ".1 second")
We then rebooted the c1iool0 machine, and when it came back up the MC_TRANS_SUM channel was showing the correct values.
We then found that the MC autolocker was not running, presumably because it had crashed after the channel rename?
In any event, we logged in to op340m and restarted the autolockerMCmain40m script.
The mode cleaner is now locked.
 Rana's log where this was initially defined
 All of the slow channel stuff is still in the old /cvs/cds/caltech path. This needs to be fixed.
I realigned the PSL beam going into the MC.
The MC beam was realigned so as to maximise the power in the MC. I minimised the MC_RFPD_DCMON dial on the MC_ALIGN screen while adjusting the two zig-zag mirrors at the end of the PSL table.
I restarted the fb twice during the last 15mins. This was after I added test points into the C1IOO/WFS1.mdl and C1IOO/WFS2.mdl.
This is part of the WFS activity. So far I have completed the following tasks:
1) I fixed the MEDM screens up to a point where they can be used for locking. There are still some buttons which invoke non-existing screens and some blank fields. But the basic filter banks and input and output matrices are fixed.
2) I copied all the old filter banks into the new screens both in the WFS head and in the WFS Master, where the servo filters are located. The I and Q filter banks in the WFS heads have been switched on.
3) I <=> Q phase settings in the WFS head for each quadrant: We have assumed that the I and Q are orthogonal so D=90 for all cases. I set the R phase to minimise the signal in all the Q lines. So the signal is largely in the I phase. I used Sine Response feature in DTT while supplying an excitation signal to MC2_ASCPIT_EXC. At times I used the YAW instead of PIT if I did not get enough coherence. This was set manually by watching the Q phase signal and minimising that by adjusting the R angle. It was in general possible to get this correct to a deg. There are several old scripts to do this in the MC/WFS but they do not work since most of them are based on the ezlockin or ezcademod functions. I will try to fix the ezWFS1phase and ezWFS2phase scripts to automate this. Some channel names have to be changed in these.
4) I measured the transfer function between the mirror motions [(MC1, MC2, MC3) x (PIT, YAW)] and the sensor DoF [(WFS1, WFS2) x (PIT, YAW)]. The measurements are reported below. The plan is to invert this matrix and use it as the Out_Matrix.
I list here the various steps I took in making this measurement.
a) Set the DC offsets on the individual quadrants to zero using an old script (which I updated with the new channel names). The script is called McWFS_dc_offsets and is located in the $scripts$/MC/WFS directory. Note that before doing this the PSL shutter was closed. This script sets a basic EPICS parameter called AOFF for each channel. These are listed in cvs/cds/caltech/target/c1iool0 .
b) Then the PSL beam into the MC was steered to optimise coupling into MC (described in my earlier post today). This is because we use the input beam as a reference while setting up the WFS.
c) Unlock the MC and center the directly reflected beam from the MC on the WFS. We use the DC monitors on the C1IOO_WFS_QPD.adl screen to center the spot on the WFS head.
d) Then used the WFSoffsets script to set the offsets in the I and Q filter banks to zero. This script uses the ezcaservo to look at the OUT16 channels and zeroes them by setting an appropriate offset. I took care to switch off all slow filters in the I and Q filter banks before this operation was carried out . Only the 60Hz comb filter was on.
e) Opened the PSL shutter and relocked the MC
f) Then I measured the transfer co-efs by oscillating the optic (exciting a specific degree of freedom) and observing the response in the WFS sensor degrees of freedom. These are tabulated above.
I plan to use this matrix and prepare the Output matix and then close the WFS servo loops.
[Suresh / Kiwamu]
The measurement of the spot positions on the MC mirrors are DONE.
Surprisingly the spot positions are not so different from the ones measured on May.
We used Valera's script senseMCdecenter to estimate the spot positions ( see his entry).
It returns so many EPICS error messages and sometime some measured values were missing. So we had to throw away some of the measurements.
Anyways we gave the resultant ASCII file to Valera's matlab file sensmcass.m to get the actual amount of off-centering in milli-meter.
The attached file is the resultant plot from his matlab code.
[Steve / Kiwamu]
An attenuator, consisting of two HWPs and a PBS, has been installed on the PSL table for the MC low power state.
Those items allow us to reduce the amount of the incident power going into the MC.
We haven't decreased the power yet because we still have to measure the arm lengths.
After we finish the measurement we will go to the low power state.
We have adjusted the polarization after the last HWP using another PBS. Now it is S-polarizing beam.
After the installation of the attenuator the beam axis has changed although we were immediately able to lock the MC with TEM00 mode.
I touched two steering mirrors on the PSL table to get the transmitted power of MC higher. At the moment the transmitted power in MC_TRANS is at about 30000 cnts.
The attached picture is the setup of the attenuator on the PSL table.
The incident beam power going into MC was decreased down to 20 mW by rotating the HWP that we set yesterday.
A 10% beam splitter which was sitting before MCREFL_PD was replaced by a perfect reflector so that all the power goes into the PD.
And we confirmed that MC can be still locked by increasing C1IOO-MC_REFL_GAIN. Some modifications in the Autolocker script need to be done later.
Also we opened the aperture of the MC2F camera to clearly see the low power beam spot.
WE ARE READY FOR THE VENT !!
Power after the EOM = 1.27 W
Power after the HWPs and PBS = 20.2 mW
Power on MCREFL = 20 mW (MC unlocked)
MCREFL_DC = 0.66 V (with MC locked)
After we finish the measurement we will go to the low power state.
I measured the power transmitted from the PSL to the MC. It is 19mW.
The MC is now locked. The MC Autolocker script cannot be used now since the tigger conditions are not met. It has been disabled on the C1IOO-LOCK_MC screen. The boost switch also is set to zero. Increasing the boost results in MC unlocking.
The C1:IOO-MC_RFPC_DCMON was going from 1.4 (MC Unlocked) to 0.66 (MC_locked). I thought we ought to have a factor of ten drop in this since under high power conditions we used to have a drop of about 5.6 to 0.6. So I adjusted the zig-zag at the end of the PSL table to improve the alignment. It now goes from 1.4 to 0.13 when the MC is locked. The lock is also much more stable now. It still does not tolerate any boost though.
I checked to make sure that the beam centering on MC_REFL PD is optimal since I touched the zig-zag. The RFPD output is now 0.7V (MC unlocked). This matches well with the fact that we used to have 3.5V on it with the MC unlocked. And we have cut the down the power incident on this by a factor of 5. Because 1W -> 20mW at the PSL table and 10% BS -> 100% Y1-...
We attempted to minimise the A2L coupling in the MC mirrors (centering the beam spot on the actuation node on each optic). While it was easy to minimise the coupling in the pitch for all the three optics and yaw of MC2, the yaw alignment of MC1 and MC3 proved to be difficult. For one the adjustment required was quite large, so much so that PSL alignment into the MC is often lost during this adujstment. We had to align the PSL coupling several times in order to proceed. And the MC settles into a new position when the MC-PSL servo loop was disturbed by random denizens in the lab. Requiring us to start over again.
Kiwamu wrote a script to measure the MC(optic)(Pitch/yaw) -> Lockin(#1 to #6) matrix. Inverting this matrix gave us the linear combination of the offsets to put on the MC# PIT/YAW inorder to minimise a specific Lockin output. However the cross couplings were not completely eliminated. This made it very hard to predict what a given set of offsets were going to do to the Lockin outputs.
Net result: the spots are centered in vertical direction (pitch) but not in the horizontal (yaw)
Day time tasks have started so I am quitting now.
I modified a set of the automated MC locking scripts which are dedicated for the low power MC.
Currently there are three scripts like the usual MC locking scripts:
(1)mcup_low_power, (2) mcdown_low_power and (3) autolockMCmain40_low_power.
I ran those scripts on op340m as usual and so far they are running very well. The lock acquisition is quite repeatable.
I hope theses scripts always bring the lock condition to the same one and hence the LOCKIN signals don't change by every lock.
- To run the script
log into op340m and run autolockMCmain40m_low_power
And the MC settles into a new position when the MC-PSL servo loop was disturbed by random denizens in the lab. Requiring us to start over again.
We worked on the beam path from MC to BS this evening.
After the beam spots on MC1 and MC3 were close to the actuation nodes (<1mm away) we checked the beam position on the Faraday Isolator (FI) to make sure that it is passing through both the input and output apertures without clipping. The beam is slightly displaced (by about half a beam diameter) downwards at the input of the FI. The picture below is a screen shot from the MC1 monitor while Kiwamu held an IR card in front of the FI.
We then proceeded to check the beam position on various optical elements downstream. But first we levelled the BS table and checked to see if the reflection from PJ1 (1st Piezo) is landing on the MMT1 properly. It was and we did not make any adjustment to PJ1. However the reflection from MMT1 was not centered on MMT2. We adjusted the MMT1 to center the beam on it. We then adjusted MMT2 to center the beam on PJ2. At this point we noticed that the spot on IPPO (pick off window) was off towards the right edge. When we centered the beam on this it missed the center of the PRM. In order to decide what needs to be moved, we adjusted PJ2 such that the beam hits the PR2, bounces back to PR3, and becomes co-incident with the green beam from X-arm on the BS. Under this condition the beam is not in the center of PRM and nor is it centered on IPPO. In fact it is being clipped at the edge of the IPPO.
It is clear that both IPPO and the PRM need to be moved. To be sure that the beam is centered on PR2 we plan to open the ITMX chamber tomorrow.
The spot positions on the MC mirrors were adjusted by steering the MC mirrors, resulting in 1 mm off-centering on each optic.
One of the requirements in aligning the MC mirrors is the differential spot positions in MC1 and MC3.
It determines the beam angle after the beam exists from MC, and if it's bigger than 3 mm then the beam will be possibly clipped by the Faraday (#4674).
The measured differential spot positions on MC1 and MC3 are : PIT = 0.17 mm and YAW = 1.9 mm, so they are fine.
(Measurement and Results)
Suresh and I aligned the MC cavity's eigen axis by using MCASS and steering the MC mirrors.
Most of the alignment was done manually by changing the DC biases
because we failed to invert the output matrix and hence unable to activate the MCASS servo (#5167).
Then I ran Valera's script to measure the amount of the off-centering (#4355), but it gave me many error messages associated with EPICS.
So a new script newsensedecenter.csh, which is based on tdsavg instead of ezcaread, was made to avoid these error messages.
The resultant plot is attached. The y-axis is calibrated into the amount of the off-centering in mm.
In the plot each curve experiences one bump, which is due to the intentional coil imbalance to calibrate the data from cnts to mm (#4355).
The dashed lines are the estimated amount of off-centering.
For the definition of the signs, I followed Koji's coordinate (#2864) where the UL OSEM is always in minus side.
After the beam spots on MC1 and MC3 were close to the actuation nodes (<1mm away)
This morning Steve and I opened the doors on the IOO and OMC chamber to let the IR beam go to MC.
And found the MC flashing is way far from TEM00, there were very higher order modes.
The MC suspensions were realigned based on an assumption that the incident beam didn't change recently.
Anyways we should check the leveling of the IOO table and the spot positions on the MC mirrors again to make sure.
The leveling was still okay. The MC mirrors were realigned and now they all are fine.
We will go ahead for the vertex alignment and extraction of the pick-off beams.
Here is a summary of the spot measurement.
Light into the MC is 20 mW at atm, MC_Transmitted ~10 MW = 400 count
The PMC_T is OK but something else is drifting.
After the MC1 and MC3 OSEMs were repositioned MC had to be realigned and the beam spots had to be recentered on the actuation nodes.
To do that I had to change the input beam direction into the MC and the coil offsets.
I also measured the resultant spot positions
spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
0.1354 -0.2522 -0.1383 -1.0893 0.7122 -1.5587
The MC1 and MC3 yaw can be improved further after the chambers are closed and evacuated. The PZT adjustments needed to realign the input beam pointing are quite small and should not pose a problem.
We wanted to continue the work with WFS servo loops. As the current optical paths on the AP table do not send any light to the WFS, I changed a mirror to a 98% window and a window to a mirror to send about 0.25mW of light towards the WFS. The MC locking is unaffected by this change. The autolocker works fine.
When the power to the MC is increased, these will have to be replaced or else the WFS will burn.
1) To see if there are significant dark-offsets on the WFS sensors we closed the PSL shutter and found that the offsets are in the 1% range. We decided to ignore them for now.
2) To center the MC_REFL beam on the WFS we opened the PSL shutter, unlocked the MC and then centered the DC_PIT and DC_YAW signals in the C1IOO_WFS_QPD screen.
3) We then looked at the power spectrum of the I and Q signals from WFS1 to see if the spectrum looked okay and found that some of the quadrants looked very different from others. The reason was traced to incorrect Comb60 filters. After correcting these filters we adjusted the R phase angle in the WFS1_SETTINGS screen to suppress the 1Hz natural oscillation signal in the Q channels of all the four quadrants. We repeated this process for WFS2
4) To see if the relative phase of all four quadrants was correct we first drove the MC_length and tried to check the phase of the response on each quadrant. However the response was very weak as the signal was suppressed by the MC servo. Increasing the drive made the PMC lock unstable. So we introduced a 6Hz, 50mVpp signal from an SR785 into the MC_servo (Input2) and with this we were able to excite a significant response in the WFS without affecting the PMC servo. By looking at the time series of the signals from the quadrants we set the R phase angle in WFS_Settings such that all the quadrants showed the same phase response to the MC_length modulation.
Using the larger response were were able to further tweak the R angle to supress the Q channels to about 1% of the I phase signals.
5) I then edited the c1ioo.mdl so that we can use the six lockins just as they are used in MC_ASS. However we can now set elements of the SEN_DMD_MATRX (sensor demod matrix) to select any of the MCL, WFS PIT and YAW channels (or a linear combination of them) for demodulation. The change is shown below. While compiling and model on C1IOO FE machine there were problems which eventually led to the FB crash.
I reverted the C1IOO model to the last working version and restarted the fb at this time..Tue Aug 30 17:28:38 PDT 2011
The triple resonant box was checked again. Each resonant frequency was tuned and the box is ready to go.
Before the actual installation I want to hear opinions about RF reflections because the RF reflection at 29 MHz isn't negligible.
It might be a problem since the reflection will go back to the RF generation box and would damage the amplifiers.
(Frequency adjustment and resultant reflection coefficient)
In order to tune the resonant frequencies the RF reflection was continuously monitored while the variable inductors were tweaked.
The plot below shows the reflection coefficient of the box after the frequency adjustment.
In the upper plot, where the amplitude of the reflection coefficient of the box is plotted, there are three notches at 11, 29.5 and 55 MHz.
A notch means an RF power, which is applied to the resonant box, is successfully absorbed and consequently the EOM obtains some voltage at this frequency.
These power absorptions take place at the resonant frequencies as we designed so.
A good thing by monitoring this reflection coefficient is that one can easily tune the resonant frequency by looking at the positions of the notches.
Note that :
If amplitude is 0dB ( =1), it means all of the signal is reflected.
If a circuit under test is impedance matched to 50 Ohm the amplitude will be ideally zero (= -infinity dB).
at 11 MHz = -15 dB (3% of RF power is reflected)
at 29.5 MHz = -2 dB (63% of RF power is reflected)
at 55 MHz = -8 dB (15% of RF power is reflected)
What are the reflected RF powers for those frequencies?
Is the 29.5MHz more problem than the 55MHz, considering the required modulation depth?
The reflected RF power going back to the RF generation box will be :
Power at 11MHz = 2 dBm
Power at 29.5 MHz = 3 dBm
Power at 55 MHz = 9dBm
Assuming the input power at 11 and 55 MHz are at 27 dBm (40m wiki page). And 15 dBm for 29.5 MHz.
Since there is an RF combiner in between the generation box and the resonant box, it reduces the reflections by an additional factor of 10 dB (#4517)
In the estimation above, the reduction due to the RF combiner was taken into account.
Besides the reflection issue, the circuit meets a rough requirement of 200 mrad at 11 and 55 MHz.
For the 29.5 MHz modulation, the depth will be reduced approximately by a factor of 2, which I don't think it's a significant issue.
So the modulation depths should be okay.
Assuming the performance of the resonant circuit remains the same (#2586), the modulation depths will be :
Mod. depth at 11 MHz = 280 mrad
Mod. depth at 29.5 MHz = 4 mrad (This is about half of the current modulation depth)
Mod. depth at 55 MHz = 250 mrad
What are the reflected RF powers for those frequencies?
Is the 29.5MHz more problem than the 55MHz, considering the required modulation depth?
Free swing of ITMY started at
Tue Sep 6 17:41:43 PDT 2011
I think Kiwamu accidentally restarted this kick at 17:48:02 PDT.
We did the following things in the ITMY chamber today:
1) We tried to get the ITMY stuck again by adjusting the coil gains so that it goes into the orientation where it used to get stuck. We (reassuringly) failed to get it stuck again. This, as we came to know later, is because kiwamu had rotated the side OSEM such that the optic does not get stuck . However the OSEM beam is at about 30 deg to the vertical and the SD is sensitive to POS motion now resulting in the poorer separation of modes as noted by Jenne earlier (5439)
2) We checked the earthquake stops and repositioned two at the bottom (towards the AR side of the optic) which we had backed out earlier.
3) We took pics of all the OSEMS.
4) Checked to see if there are any stray beams with an IR card. There were none.
5) I obtained the max values of the OSEMS by misaligning the optic with the coil offsets. These values are in good agreement with those on the wiki
OSEM UL UR LR LL SD
Max 1.80 1.53 1.68 1.96 2.10
Current 0.97 0.79 0.83 0.97 1.02
We can close the heavy doors tomorrow morning.
After Steve pointed out the 'deep hoop' issue, we decided to examine putting an RF Amp on the PSL table, between the RF combiner and the triple resonant box.
This will reduce the chances of standing waves in the cables and reduce the radiation induced pick-up in the RF PD and Demod electronics.
We would like to send ~10 dBm from the distribution box to the combiner. We also want to able to get as much as ~33 dBm of drive at 11 and 55 MHz. So the amp should have a gain of ~20-30 dB and an operating range of 10-100 MHz.
Also desirable are low distortion (high IP3) and good reverse isolation ( > 40 dB).
Some possibilities so far (please add your RF Google Results here):
1) Mini-Circuits ZHL-1-2W-S: G = +32 dB, Max Out = +33 dBm, NF = 6 dB, Directivity = 25 dB
2) Mini-Circuits TIA-1000-1R8: G=+40 dB, Max Out = +36 dBm, NF = 15 dB (AC Powered, Inst. Amp), Directivity = 58 dB.
3) Mini-Circuits ZHL-2-8: G = +27dB, Max out = +29 dBm, NF = 6dB, Directivity = 32 dB
4) RFbay MPA-10-40: G = +40dB, Max Out = + 30 dBm, NF = 3.3 dB, Rev Iso = 23 dB
5) No proper stuff from Teledyne Couger
The attenuator was removed and now the MC is happily locked with the full power of 1.2 W.
(what we did)
+ replaced the perfect reflector, which was before the MCREFL_PD, by a 10% beam splitter like it used to be.
+ removed the attenuator (combination of HWP and PBS).
+ realigned the beam path on the AP table, including the MCREFL path and WFS path.
+ made the aperture of the MC2F camera narrower in order to avoid a saturation.
+ aligned the MC suspensions so that it resonates with the TEM00 mode.
+ put a ND filter on the AS camera
C1:IOO-MC_RFPD_DCMON = 0.98 (locked)
C1:IOO-MC_TRANS_SUM = 17500 (locekd)
(next things to do)
+ measurement of the spot positions on each MC mirror.
+ centering of the beam spot by steering the input mirrors on the PSL table
Last night I noticed that PZT1 didn't work properly
I am not sure what is going on. Today I will try localizing the cause of the problem.
As far as I remember it was perfectly working at the time just after we readjusted the OSEMs on MC1 and MC3 (Aug 23th)
The symptoms are :
+ No response to both pitch and yaw control from EPICS (i.e. C1:LSC-PZT1_X and C1:LSC-PZT1_Y)
+ When a big value (-3 or so) from EPICS was applied, the PZT1 mirror suddenly jumped.
However it turned out it just corresponded to a state where OOR (Out Of Range) LED lights up.
I did some brief checks :
+ checked the voltage going into the HV amplifiers' "MOD" input. Those are the voltage coming out from DACs and controlled from EPICS.
--> looked healthy. They went from -10 to 10 V as expected (although the HV amp takes up to only +/-5V).
+ swapped the ''MOD" input cables such that C1:LSC-PZT1 controls the PZT2 HV and vice versa.
--> The PZT2 mirror was still controlable, but the PZT1 mirror still didn't move. So the DAC and EPICS are innocent.
+ swapped the D-dub cables, which are directly going into the feedthroughs, such that the PZT1 HV drives the PZT2 mirrors and vice versa.
--> the PZT2 mirror became unable to be controlled. For the PZT1 mirror, only PITCH worked smoothly.
Something happened about 8 years ago.
Old iLog entry by AJW (2003/Sep/8)
Old iLog entry by AJW (2003/Sep/9)
The spot positions on the MC mirrors were measured in the vacuum condition.
The obtained spot positions are quite bad and roughly at 2-3 mm level. We have to realign the beam axis and the MC mirrors.
Aug 23 2011 (in air)
By looking at what Daniel used in the low noise EOM Driver for aLIGO, we found the A2CP2596 from Cougar.
G = +24 dB, NF = 5 dB, Max Out = +37 dBm. It comes in a 2-stage SMA connector package. I've asked Steve to order 2 of them with the appropriate heatsinks.
The spot positions on the MC mirrors were readjusted.
All the amount of the off-center became smaller than 2 mm, which meet requirements of the beam clearance on the Faraday.
In order to improve the MC1-YAW and MC3-YAW spot positions, the angle of the incident beam has to be shifted by approximately 1/100 rad.
However it turned out to be very difficult to introduce such amount of angle only with the steering mirrors on the PSL table since we have to keep the same translation while changing the angle.
I re-aligned the beam onto the MC TRANS QPD since Kiwamu had centered the spots on the mirrors. However, I then inspected the MC2F camera. After coming back into the control room I noticed that the MC transmission had gone down by 50% and that the MC2 OSEMs showed a large step. My guess is that somehow the opening and closing of the can shifted the suspension. So I adjusted the MC2 alignment biases to recover the transmitted power (its now ~50000 instead of the ~33000 from Friday).
[Mirko / Kiwamu]
The resonant box has been installed together with a 3 dB attenuator.
The demodulation phase of the MC lock was readjusted and the MC is now happily locked.
We needed more modulation depth on each modulation frequency and so for the reason we installed the resonant box to amplify the signal levels.
Since the resonant box isn't impedance matched well, the box creates some amount of the RF reflections (#5339).
In order to reduce somewhat of the RF reflection we decided to put a 3 dB attenuator in between the generation box and the resonant box.
+ attached the resonant box directly to the EOM input with a short SMA connector.
+ put stacked black plates underneath the resonant box to support the wight of the box and to relief the strain on the cable between the EOM and the box.
+ put a 3 dB attenuator just after the RF power combiner to reduce RF reflections.
+ readjusted the demodulation phase of the MC lock.
(Adjustment of MC demodulation phase)
The demodulation phase was readjusted by adding more cable length in the local oscillator line.
After some iterations an additional cable length of about 30 cm was inserted to maximize the Q-phase signal.
So for the MC lock we are using the Q signal, which is the same as it had been before.
Before the installation of the resonant box, the amplitude of the MC PDH signal was measured in the demodulation board's monitor pins.
The amplitude was about 500 mV in peak-peak (see the attached pictures of the I-Q projection in an oscilloscope). Then after the installation the amplitude decreased to 400 mV in peak-peak.
Therefore the amplitude of the PDH signal decreased by 20 %, which is not as bad as I expected since the previous measurement indicated 40 % reduction (#2586).
The shift of MC2 which Rana noted caused the beam spots on the MC mirrors to decenter. I used the mcassUp and mcassOn scripts and checked the output of the C1IOO lockins to get the spot positions. I first tried to realign just the MC2 to recenter the spots. But this was not sufficient. I then worked on the pitch of all three optics since it is easier to align. By the time this was done the offset in yaw also reduced, probably due to cross coupling between pitch and yaw in the coils. At the end of the process I obtained all decentering around 1.5mm or less, then I went over to adjust the MC2TransQPD beam path so that we center the spot on the QPD. This action shifted the stack, I had to iterate this two more times before the successive corrections grew sufficiently small. I think it may shift again if we touch the chamber (the image of MC2Face is still inverted).
The new spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
1.3212 -0.8415 0.6795 -1.4292 -0.3574 -1.5208
- Further improvement of beam centering can be done but first I would like to be sure that the MC is stable. The MC2Trans light is centered on the QPD as a reference.
- We have checked the situation of the broken Piezo Jenna PZT (called PZT1)
- Tested PZT1 by applying a dc voltage on the cables. Found that pitch and yaw reasonably moving and the motions are well separated each other.
The pitch requires +20V to set the IPPOS spot on the QPD center.
- Made a high-voltage (actually middle voltage) amp to convert +/-10V EPICS control signal into -5 to +30V PZTout. It is working on the prototype board and will be put into the actual setup soon.
- The Piezo Jenna driver box has 4 modules. From the left-hand side, the HV module, Yaw controller, Pitch controller, and Ben abbot's connector converter.
- We checked the voltage on Ben's converter board. (Photo1)
It turned out that the red cable is the one have the driving voltage while the others stays zero.
- We hooked a 30V DC power supply between the red cable and the shield which is actually connected to the board ground.
- Applying +/-10V, we confirmed the strain gauge is reacting. If we actuated the pitch cable, we only saw the pitch strain gauge reacted. Same situation for yaw too.
- Kiwamu went to IPPOS QPD to see the spot position, while I change the voltage. We found that applying +20V to the pitch cable aligns the spot on the QPD center.
- I started to make a small amplifier boards which converts +/-10V EPICS signals into -5V to +30V PZT outs.
- The OPAMP is OPA452 which can deal with the supply voltages upto +/-40V. We will supply +/-30V. The noninerting amp has the gain of +2.
- It uses a 15V zener diode to produce -15V reference voltage from -30V. This results the output voltage swing from -5V to +35V.
The actual maximum output is +30V because of the supply voltage.
- On the circut test bench, I have applied +/-5V sinusoidal to the input and successfully obtained +5V to +25V swing.
- The board will be put on Ben's board today.
The PZT driver is now in place. The actual PZTs are not connected yet!
It is accommodated on Ben's connector adapter board.
The panel has additional connectors now: two inputs and a power supply connector.
The supply voltage is +/-30V (actual maximum +/-40V), and the input range is +/-10V
which yields the output range of -5V to 30V. The gain of the amplifier is +2.
It is confirmed that the HV outputs react to the epics sliders although the PZT connector is not connected yet
so as not to disturb the locking activity.
When we engage the PZT connector, we should check the HV outputs with an oscilloscope to confirm they
have no oscillation with the capacitances of the PZTs together with the long cable.