The PSL Temperature Box (D980400-B-C, what kind of numbering scheme is that?) modified at LHO/LLO ~8 years ago to have better resolution on the in-loop temperature sensors.
I haven't been able to find a DCN / ECN on this, but there's an elog entry from Hugh Radkins here. I'm also attaching the PDF of the latest drawing (circa 2000) from the DCC.
The schematic doesn't show it, but I am guessing that the T_SENSE inputs are connected to the AD590 chips, and that 4 of these are attached somehow to the RefCav can. IF this is true, I don't understand why there are input resistors on the LT1125 of U1; the AD590 is supposed to be a current source ?
Peter King is supposed to be coming over to work on this today so whoever spots him should force/cajole/entice him to elog what he's done. Film him if necessary.
I also think R1-8 should be swapped into metal film resistors for stability. The datasheet says that it puts out 1 uA/K, so the opamps put out 10 mV/K.
J8 and JP1 should be shorted to disable both the tidal and VME control input. Both are unused and a potential source of drift.
I made the changes to the psl.db to handle the new Temperature box hardware. The calibrations (EGUF/EGUL) are just copied directly from the LHO .db file (I have rsync'd their entire target area to here).
allegra:c1psl>diff psl.db~ psl.db
< field(DESC,"TIDALOUT- drive to the reference cavity heater")
< field(SCAN,".5 second")
< field(INP,"#C0 S28 @")
< field(DESC,"TIDALINPUT- tidal actuator input")
< field(SCAN,".5 second")
< field(INP,"#C0 S3 @")
> field(DESC,"TIDALINPUT- tidal actuator input")
> field(SCAN,".5 second")
> field(INP,"#C0 S3 @")
> field(DESC,"TIDALOUT- drive to the reference cavity heater")
> field(SCAN,".5 second")
> field(INP,"#C0 S28 @")
Old -pre 6/2009 LLO DCPD 3 mm od GTRAN photodiode
Steve noticed the RGA was not working today. It was powered on but no other lights were lit.
Turns out the c0rga machine had not been rebooted when the file system on linux1 was moved to the raid array, and thus no longer had a valid mount to /cvs/cds/. Thus, the scripts that were run as a cron could not be called.
We rebooted c0rga, and then ran ./RGAset.py to reset all the RGA settings, which had been reset when the RGA had lost power (and thus was the reason for only the power light being lit).
Everything seems to be working now. I'll be adding c0rga to the list of computers to reboot in the wiki.
We measured the voltage noise of the heater used to control the RC can temperature. It is large.
The above scope trace shows the voltage directly on the monitor outputs of the heater power supply. The steps are from the voltage resolution of the 4116 DAC.
We also measured the voltage noise on the monitor plugs on the front panel. If these are a true representation of the voltage noise which supplies the heater jacket, then we can use it to estimate the temperature fluctuations of the can. Using the spectrum of temperature fluctuations, we can estimate the actual length changes of the reference cavity.
I used the new fax/scanner/toaster that Steve and Bob both love to scan this HP spectrum analyzer image directly to a USB stick! It can automatically make PDF from a piece of paper.
The pink trace is the analyzer noise with a 50 Ohm term. The blue trace is the heater supply with the servo turned off. With the servo on (as in the scope trace above) the noise is much much larger because of the DAC steps.
Rob found puddles of water very close to the chiller during lunch time. We raised the unit and took the side cover off. All surfaces were dry and the water level in the tub normal.
Later on we discovered that one of the Vons distilled water bottle was leaking. Jenne and I checked for excess amount of condensing water droplets inside the MOPA box.
On the bare,not insulated tubing and valve are loaded with droplets of water. Relative humidity is 44% at 24 C and HEPA filter speed set to 80 V in the enclosure.
we set the offsets for the MCWFS DC and for the MCWFS demod outputs and then turned off the lights put the MZ at half fringe and then centered the spots on the MCWFS heads.
The MCREFL beam looks symmetric again and the MC REFL power is low.
I took the pictures of all racks of electronics yesterday, and then uploaded these pictures on the wiki.
You can see them by clicking "pictures" in the wiki page.
Last night (Oct 07), I ran armLoss script in order to obtain the latest numbers for the arm cavity loss.
Here is the summary
Measured arm reflectivity R_cav: 0.875 +/- 0.005
Estimated round trip loss L_RT: 157ppm +/- 8ppm
Estimated finesse F: 1213+/-2
Data Points: 34
Measured arm reflectivity R_cav: 0.869 +/- 0.006
Estimated round trip loss L_RT: 166ppm +/- 8ppm
Estimated finesse F: 1211+/-2
Data Points: 26
TE=10ppm, LE=L_RT/2, RE=1-TE-LE
TF=0.005, LF=L_RT/2, RF=1-TF-LF
rcav = -rF +(tF^2 rE)/(1-rF rE)
R_cav = rcav^2
F = pi Sqrt(rF rE)/(1-rF rE)
I looked at the data of the day before yesterday (Oct 06) to know how much is the recycling gain.
X arm: (TRX_PRecycled) / (TRX_PRMmisaligned) * T_PRM = 83.1/0.943*0.07 = 6.17
Y arm: (TRX_PRecycled) / (TRX_PRMmisaligned) * T_PRM = 99.2/1.017*0.07 = 6.83
==> G_PR = 6.5 +/- 0.5 (oh...this estimation is so bad...)
From the recycling gain and the arm cavity reflectance, one can get the loss in the recycling cavity.
G_PR = T_PRM / (1-Sqrt(R_PRM * (1-L_PRC)*R_cav))^2
==> loss in the recycling cavity L_PRC: 0.009+/-0.009
(About 1% loss is likely in the recycling cavity)
Measured arm reflectivity R_cav: 0.875 +/- 0.005
Estimated round trip loss L_RT: 157ppm +/- 8ppm
Estimated finesse F: 1213+/-2
Measured arm reflectivity R_cav: 0.869 +/- 0.006
Estimated round trip loss L_RT: 166ppm +/- 8ppm
Estimated finesse F: 1211+/-2
Thermal lensing formula:
from (T090018 by A. Abramovici (which references another doc).
In the above equation:
w 1/e^2 beam radius
k thermal conductivity (not the wave vector) = 1.3 W / m/ K
alpha absorption coefficient (~10 ppm/cm for our glass)
NP power in the glass (alpha*NP = absorbed power)
dn/dT index of refraction change per deg (12 ppm/K)
d mirror thickness (25 mm for all of our SOS)
I'm attaching a plot showing the focal length as a function of recycling cavity power for both our current MOS and future SOS designs.
I've assumed a 10 ppm/cm absorption here. It may actually be less for our current ITMs which are made of Heraeus low absorption glass - our new ITMs are Corning 7980-A (measured to have an absorption of 13 ppm/cm ala the iLIGO COC FDD). I expect that our thermal lens focal length will always be longer than 1 km and so I guess this isn't an issue.
Awesome 5 hrs of locking Rob!
While measuring the Piezo Jena noise tonight we noticed that the LSC timing is setup strangely.
Instead of using the Fiber Optic Sander Liu Timing board, we are just using a long 4-pin LEMO cable which comes from somewhere in the cable tray. This is apparent in the rack pictures (1X3) that Kiwamu has recently posted in the Electronics Wiki. I think all of our front ends are supposed to use the fiber card for this. I will ask Jay and Alex what the deal is here - seems like to me that this can be a cause for timing noise on the LSC.
We should be able to diagnose timing noise between the OMC and the LSC by putting in a signal in the OMC and looking at the signal on the LSC side. Should be a matlab script that we can run whenever we are suspicious of this. This is an excellent task for a new visiting grad student to help learn how to debug the digital control system.
Could be this.
In ----o-------- | | --------o-------- Out
_ 1uF R 7.5 kOhms
David Nolting, chief LIGO Safety Officer and his lieutenants from LLO and LHO paid homage to the 40m lab this morning.
They give us a few recommendation: update safety documents, move optical table from the front of ETMX-rack and label-identify absorbent plastics on enclosure windows-doors.
We'll correct these short comings ASAP
Pump down #66 is 435 days old. RGA scan is normal. New maglev is fine. New UPS is in place but not hooked up to communicate.
V1 has bare minimum interlock. Pirani vacuum gauges PTP1 and PRP do not communicate with readout system.
There is no emergency dial out in case of vacuum loss. Our existing vacuum dedicated desk top computer is dead.
New cold cathodes, Pirani gauges and gauge controller should be added.
In general: vacuum system needs an upgrade !
This is a plot of the R and T of the existing ETM's HR coating. I have only used 1/4 wave layers (in addition to the standard 1/2 wave SiO2 cap on the top) to get the required T.
The spec is a T = 15 ppm +/- 5 ppm. The calculation gives 8 ppm which is close enough. The calculated reflectivity for 532 nm is 3%. If the ITM reflectivity is similar, the signal for the 532 nm locking of the arm would look like a Michelson using the existing optics.
I found this interesting entry by Rana in the old (deprecated) elog : here
I wonder if Rolf has ever written the mentioned GUI that explained the rationale behind the test point number mapping.
I'm just trying to add the StochMon calibrated channels to the frames. Now I remember why I kept forgetting of doing it...
As far as I know, the EPICS channels have nothing to do with test points.
1) Turn off feedback to ETMY (the ETMY button on the LSC screen).
2) Put a 1 into the YARM->MC2 output matrix element on the LSC screen.
3) Turn off FM6 (comb), FM7 (0.1:10) on the MC2_MCL filter bank. This is to make the IOO-MCL loop more stable and to reduce the IOO-MCL low frequency gain.
4) Set the MC2-LSC gain to 0.5, turn the output ON, turn ON FM4 & FM5 & FM6 of the MC2-LSC filter bank.
5) Turn on the input of MC2-LSC and the arm should now lock.
6) After locking, set the MC2-MCL gain to zero. Hopefully with a few second ramp time.
(A comment by KA - c.f. this entry )
the inside temperature is alarming at the red level today - should check if the HIHI value is set correctly
It looked like the Busby Low Noise Box had too much low frequency noise and so I upgraded it. Here is a photo of the inside - I have changed out the 0.8 uF AC coupling cap with a big, white, 20 uF one I found on Rob's desk.
The Busby Box is still working well. The 9V batteries have only run down to 7.8V. The original designer also put a spare AD743 (ultra low current FET amp) and a OP27 (best for ~kOhm source impedances) in there.
Here's the noise after the fix. There's no change in the DC noise, but the AC noise is much lower than before:
I think that the AC coupled noise is higher because we are seeing the current noise of the opamp. In the DC coupled case, the impedance to ground from the input pins of the opamp is very low and so the current noise is irrelevant.
The change I implemented, puts in a corner frequency of fc = 1/2/pi/R/C = 1/2/pi/10e3/20e-6 = 0.8 Hz.
Overall, the box is pretty good. Not great in terms of current noise and so it misses getting an A+. But its easily a solid A-.
I've measured the voltage noise of the SR560's lead acid battery outputs; they're not so bad.
Steve ordered us some replacement lead-acid batteries for our battery powered pre-amps (SR560). In the unit he replaced, I measured the noise using the following setup:
SR560 Busby Box
(+12V/GND) -------------AC Input Out ---------------- SR785
The SR785 was DC coupled and auto-ranged. The input noise of the SR785 was measured via 50 Ohm term to be at least 10x less than the SR560's noise at all frequencies.
Its clear that this measurement was spoiled by the low frequency noise of the Busby box below 10 Hz. Needs a better pre-amp.
Steve is summarizing the Video Matrix choices into this Wiki page:
Price: < 5k$
Control: RS-232 and Ethernet
Interface: BNC (Composite Video)
Please check into the page on Monday for a final list of choices and add comments to the wiki page.
Composite video matrix switchers with 32 BNC in and 32 BNC channels out are listed.
I ramped the MZ PZT (with the loop disabled on the input switch) to calibrate it. Since the transmission has been blocked, I used the so-called "REFL" port of the MZ to do this.
The dark-to-dark distance for the MZ corresponds to 2 consecutive destructive interferences. Therefore, that's 2 pi in phase or 1 full wavelength of length change in the arm with the moving mirror.
Eyeballing it on the DTT plot (after lowpassing at 0.1 Hz) and using its cursors, I find that the dark-to-dark distance corresponds to 47.4 +/- 5 seconds.
So the calibration of the MZ PZT is 88 +/- 8 Volts/micron.
Inversely, that's a mean of 12 nm / V.
why am I calibrating the MZ? Maybe because Rob may want it later, but mainly because Koji won't let me lock the IFO.
Apparently, we haven't had a fast channel for any of the MZ board. So I have temporarily hooked it up to MC_DRUM at 21:13 and also turned down the HEPA. Now, let's see how stable the MZ and PMC really are overnight.
EDIT: it railed the +/- 2V ADCwe have so I put in a 1:4 attenuator via Pomona box. The calibration of MC_DRUM in terms of MZ_PZT volts is 31.8 cts/V.
So the calibration of MC_DRUM1 in meters is: 0.38 nm / count
For the Laser Gyro, I wondered how much mechanical noise we might get with a non-suspended cavity. My guess is that the PMC is better than we could do with a large ring and that the MZ is much worse than we could do.
Below 5 Hz, I think the MZ is "wind noise" limited. Above 10 Hz, its just ADC noise in the readout of the PZT voltage.
I shorted the input to the box and then put its output into the SR560 (low noise, G = 100, AC). I put the output of the SR560 into the SR785.
*** BTW, the 2nd channel of the SR785 is kind of broken. Its too noisy by a factor of 100. Needs to go back for repair once we get started in the vac.
The attached PNG shows its input-referred noise with the short.
The picture shows the inside of the box before I did anything. The TO-5 package metal can is the meaty super dual-FET that gives this thing all of its low noise power.
In the spectra on the right are two traces. The BLUE one is the noise of the box as I found it. The BLACK one is the noise after I replaced R1, R6, R7, & R10 with metal film resistors.
The offset at the output of the box with either an open or shorted input is +265 mV.
I think we probably should also replace R2, R3, & R1, but we don't have any metal film resistors lower than 100 Ohms in the kit...but hopefully Steve will read this elog and do the right thing.
In this note, amplitude and power couplings of two astigmatic (0,0)-th order gaussian modes are calculated.
On Friday, Rana and I measured the scatter coming from the 35W beam dumps.
(These are the ones with big aluminum heat sinks on the back that kind of look like little robots with 2 legs...inside the horn is a piece of polished silicon at Brewster's Angle.)
For the measurement, we used the Scatterometer setup at the 40m on the small optical table near MC2.
We used a frequency of 1743 Hz for the Chopper, and this was also used as the reference frequency for the SR830 Lock-In Amplifier.
The settings on the Lock-In were as follows:
Time Constant = 1sec
'Scope reading Output A, Output A set to 'Display', and A's display set to "R" (as in magnitude).
Sensitivity changed throughout the experiment, so that's quoted for each measurement.
White Paper Calibration - white paper placed just in front of Beam Dump. Sensitivity = 500microVolts. Reading on 'scope = 7V
Laser Shuttered. Sensitivity = 500microVolts. 'scope reading = 9mV.
Black Glass at Beam Dump location. Sensitivity = 500microVolts. Reading on 'scope = 142mV. (DON'T touch the glass....measure the same setup with different sensitivity)
Black Glass at Beam Dump location (Not Touched since prev. measurement). Sensitivity = 10microVolts. Reading on 'scope = 6.8V
Laser Shuttered. Sensitivity = 10microVolts. 'scope Reading = 14mV +/- 10mV (lots of fluctuation).
Black Glass Wedge Dump at Beam Dump location. Sensitivity = 10microVolts. 'scope = 100mV.
Beam Dump with original shiny front plate. Sensitivity = 10microVolts. 'scope railing at 11V
Beam Dump with front plate removed. Sensitivity = 10microVolts. 'scope reading = 770mV
Beam Dump, no front plate, but horn's opening surrounded by 2 pieces of Black Glass (one per side ~1cm opening), BG is NOT flush with the opening...it's at an angle relative to where the front plate was. Sensitivity = 10microV. 'scope = 160mV +/- 20mV.
Beam Dump, no front plate, only 1 piece of Black Glass. Sensitivity = 10microV. 'scope reading = 260mV.
Beam Dump, no front plate, 2 pieces of Black Glass, normal incidence (the BG is flush with where the front plate would have been). Sensitivity = 10microV. 'Scope reading = ~600mV
Using our calibration numbers (Black Glass measured at 2 different sensitivities, not touching the setup between the measurements), we can find the calibration between our 2 different sets of measurements (at 500microV and 10microV), to compare our Beam Dump with regular white paper.
BG at 500uV was 142mV. BG at 10uV was 6.8V. 6.8V/0.142V = 47.9
So the white paper, which was measured at 500uV sensitivity, would have been (7V * 47.9) = 335 V in 10uV sensitivity units.
This is compared to the BG wedge dump at 10uV sensitivity of 100mV, and the Beam Dump reading of 770mV, and the Beam Dump with-black-glass-at-the-opening reading of 160mV.
So our Silicon/Steel horn dump is ~8x worse than a Black Glass wedge and (335 / 0.77) = 435x better than white paper.
We used regular white paper as a calibration because it has a Lambertian reflectance. For some general idea of how to do these kinds of scatter measurements, you can look at this MZ doc.
Assuming that our white paper had a BRDF of (1/pi)/steradian, we can estimate some numbers for our setup:
Sensitivity (signal with the laser shuttered) = (0.02 / 335 / pi) = 2 x 10^-5 / sr. This is ~3x worse than the best black glass surfaces.
Our wedge = (0.1 / 335 / pi) = 1 x 10^-4 / sr. Needs a wipe.
Our Silicon-Steel Horn = (0.75 / 335 / pi) = 7 x 10^-4 / steradian.
Our measurements were all made at a small angle since we are interested in scatter back along the incoming beam. We were using a 1" lens to collect the scatter onto a PDA55. The distance from the beam to the center of the lens was ~2" and the detector's lens was ~20" from the front of the horn. So that's an incident angle of ~3 deg.
* It seems that any front plate other than Black Glass is probably worse than just having no front plate at all.
* If we put in a front plate, it shouldn't be normal to the incident beam. Black Glass at normal incidence was almost at the same level as having no front plate. So if we're going to bother with a front plate, it should be about 30deg or 40deg from where the original front plate was.
* No front plate on the Dump is about 7x a Black Glass wedge dump.
* The silicon looks like it might have some dust on it (as well as the rest of the inside of the horn). We should clean everything. (Maybe with deionized nitrogen?)
* We should remeasure the Beam Dump using polished steel at a small (30-40deg) angle as the front plate.
* Photos taken with the Olympus camera, which has its IR blocker removed.
* In the photo you can see that we have a lot of reflection off of the horn on the side opposite from the silicon.
* The 2nd picture is of the scatterometer setup.
What was the power level, polarization and beam size at beam trap?
Rana noticed that recently the temperature inside the lab has been a little bit too high. That might be causing some 'unease' to the computers with the result of making them crash more often.
For the next hours I'll be paying attention to the temperature inside the lab to make sure that it doesn't go out of control and that the environment gets too cold.
Today the lab is perceptibly cooler.
The temperature around the corner is 73 F.
The main communications data structure is RFM_FE_COMMS, from the rts/src/include/iscNetDsc40m.h file. The following comments regard sub-structures inside it. I'm looking at all the files in /rts/src/fe/40m to determine how the structures are used, or if they seem to be unnecessary.
The dsccompad structure is used in the lscextra.c file. I am assuming I don't need to add anything fo the model for these. They cover from 0x00000040 to 0x00001000.
FE_COMMS_DATA is used twice, once for dataESX (0x00001000 to 0x00002000), and once for dataESY (0x00002000 to 0x00003000).
Inside FE_COMMS_DATA we have:
status and cycle which look to be initialized then never changed (although they are compared to).
ascETMoutput[P,Y], ascQPDinput are all set to 0 then never used.
qpdGain is used, and set by asc40m, but not read by anything. It is offset 114, so in dataESX its 4210 (0x00001072), and in dataESY its (0x00002072)
All the other parts of this substructure seem to be unused.
daqTest, dgsSet, low1megpad,mscomms seem unused.
dscPad is referenced, but doesn't seem to be set.
pCoilDriver is a structure of type ALL_CD_INFO, inside a union called suscomms, inside FE_COMMS_Data, and is used. In this structure, we have:
extData, an array of DSC_CD_PPY structures, which is used. Inside extData we have for each optic (ETMY has an offset of 9 inside the extData array):
Pos is set in sos40m.c via the line pRfm->suscomms.pCoilDriver.extData[jj].Pos = dsp[jj].data[FLT_SUSPos].filterInput; Elsewhere, Pos seems to be set to 1.0
Similarly, Pit and Yaw are set in sos40m, except with FLT_SUSPitch and FLT_SUSYaw, and being set elsewhere to 1.1, 1.2. However, these are never applied to the ETMX and ETMY optics (it goes through offests 0 through 7 inclusive).
Side is set 1.3 or 1.0 only, not used.
ascPit , ascYaw, lscPos are read by the losLinux.c code, and is updated by the sos40m.c code. For ETMY, their respective addresses are: 0x11a1c0, 0x11a1c4, 0x11a1c8.
lscTpNum, lscExNum, seem to be initialized, and read by the losLinux.c, and set by sos40m.c.
modeSwitch is read, but looks to be used for turning dewhitening on and off. Similarly dewhiteSW1R is read and used.
This ends the DSC_CD_PPY structure.
lscCycle, which is used, although it seems to be an internal check.
dum is unused.
losOpLev is a substructure that is mostly unused. Inside losOpLev, opPerror, opYerror, opYout seem to be unused, and opPout only seems ever to be set to 0.
Thats the end of ALL_CD_INFO and pCoilDriver.
After we have itmepics, itmfmdata, itmcoeffs, rmbsepics,...etymyepics, etmyfmdata,etmycoeffs which I don't see in use.
We have substructure asc inside mcasc, with epics, filt, and coeff char arrays. These seem to be asc and iowfsDrv specific.
lscIpc, lscepics, and lscla seems lsc specific,
The there is lscdiag struct, which contains v struct, which includes cpuClock, vmeReset, nSpob, nPtrx, nPtry don't seem to be used by the losLinux.c.
The lscfilt structure contains the FILT_MOD dspVME, which seems to be used only by lsc40m.
The lsccoeff structure contrains the VME_COEF pRfmCoeff, which again seems to only interact in the lsc code.
Then we have aciscpad, ascisc, ascipc, ascinfo, and mscepics which do not seem to be used.
ascepics and asccoeff are used in asc.c, but does not seem to be referenced elsewhere.
hepiepics , hepidsp, hepicoeff, hepists do not appear to be used.
I made a wiki page dedicated for the photos of the optical tables.
The current layouts were uploaded.
Now the lock with megatron is pretty easy. Really. It's very cool.
As we saw the oscillation of the YARM servo, we temporalily increased the gain of TRY filter by a factor of 2 (0.003->0.006). Also decreased the gain of YARM servo by the factor of 2 (1->0.5). This makes the servo gain reduced by a factor of 4 in total. This change seemed to come from the change of the ADC/DAC range.
We finally fixed the hi-gain pd transmission communications from Megatron to the c1lsc by tracking down the correct RFM memory location (which is unhelpfully labeled as a qpd channel in both losLinux and lsc40.m). The memory location is 0x11a1e0, and is refered to as qpdData.
We were able to lock the Y-arm using Megatron and the RCG generated code, with nothing connected to c1iscey.
All relevant cables were disconnected from c1iscey and plugged into the approriate I/O ports, including the digital output. Turns out the logic for the digital output is opposite what I expected and added XOR bitwise operators in the tst.mdl model just before it went out to DO board. Once that was added, the Y arm locked within 10 seconds or so. (Compared to the previous 30 minutes trying to figure out why it wouldn't lock).
The upgrade's input mode matching telescope design is complete. A summary document is on the MMT wiki page, as are the final distances between the optics in the chain from the mode cleaner to the ITMs. Unless we all failed kindergarden and can't use rulers, we should be able to get very good mode matching overlap. We seem to be able (in Matlab simulation land) to achieve better than 99.9% overlap even if we are wrong on the optics' placement by ~5mm. Everything is checked in to the svn, and is ready for output mode matching when we get there.
In the middle of the last month, Kiwamu and I went to Garilynn's lab to measure the phase maps of the new ITMs and SRMs.
Analysis of the phase map data were posted on the svn directory:
The screen shots and the plots were summarized in a PDF file. You can find it here:
The RoCs for all of the PRMs are turned out to be ~155m. This is out of the spec (142m+/-5m) although the actual effect is not understand well yet..
These RoCs are almost independent from the radus of the assumed gaussian beam.
In deed, I have checked the dependence of the RoC on the beam spot position, and it turned out that the RoCs vary only little.
(In the SRMU01 case, for example, it varies from 153.5m to 154.9m.)
The beam radius of 3mm was assumed. The RoCs were calculated 20x20mm region around the center of the mirror with a 2mm mesh.
Sun Feb 28 18:23:09 2010
Hi. This is Alberto. Its Sun Feb 28 19:23:09 2010
Monday, March 1, 9:00 2010 Steve turns on PSL-REF cavity ion pump HV at 1Y1
I have measured a wideband response of the fast PZT in the LWE NPRO 700mW in the Alberto's setup.
This is a basic measurement to determine how much phase modulation we can obtain by actuating the fast PZT,
primarily for the green locking experiment.
1. Locked the PLL of for the PSL-NPRO beating at 20MHz.
2. Added the modulation signal to the NPRO PZT input.
I used the output of the network analyzer sweeping from 100kHz to 1MHz.
3. Measured the transfer function from the modulation input to the PLL error signal.
The PLL error is sensitive to the phase fluctuation of the laser. Found that the first resonance is at 200kHz.
The TF is not valid below 3kHz where the PLL suppresses the modulation.
4. Single frequency modulation: Disconnected the PLL setup.
Plug Marconi into the fast PZT input and modulate it at various frequencies.
Observing with the RF spectrum analyzer, I could see strong modulation below 1MHz.
It turned out later that the TF measurement missed the narrow peaks of the resonances due to the poor freq resolution.
Also the modulation depth varies frequency by frequency because of the resonances.
Scanned the frequency to have local maximum of the modulation depth. Adjusted the
modulation amplitude such that the carrier is suppressed (J0(m)=0 i.e. m~2.4). As I could not obtain
the carrier suppression at above 1MHz, the height of the carrier and the sidebands were measured.
The modulation frequency was swept from 100kHz to 10MHz.
5. Calibration. The TF measured has been calibrated using the modulation depth obtained at 100Hz,
where the resonance does not affect the response yet.
The responce of the PZT was ~10MHz/V below 30kHz. Looks not so strange although this valure is
little bit high from the spec (2MHz/V), and still higher than my previous experience at TAMA (5MHz/V).
Note that this calibration does not effect to the modulation depth of the single freq measurement as they are independent.
In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.
Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.
They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.
For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.
Then the question is; which can achieve better modulation efficiency ?
Volker and I talked about it and maybe found an answer,
We believe our EOM can be potentially better because we use full length of the EO crystal.
This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.
The people in University of Florida just used one of three separated parts of the crystal for each frequency.
Did you find what is the merit of their impedance matching technique?
Yes, I found it.
Their advantage is that their circuit is isolated at DC because of the input capacitor.
And it is interesting that the performance of the circuit in terms of gain is supposed to be roughly the same as our transformer configuration.
It took too long to get this box ready for action. I implemented all of the changes that I made on the previous one (#1437). In addition, since this one is to be used for phase locking, I also made it have a ~flat transfer function. With the Boost ON, the TF magnitude will go up like 1/f below ~1 kHz.
The main trouble that I had was with the -12V regulator. The output noise level was ~500 nV/rHz, but there was a large oscillation at its output at ~65 kHz. This was showing up in the output noise spectrum of U1 (the first op-amp after the mixer). Since the PSRR of the OP27 is only ~40 dB at such a high frequency, it is not strange to see the power supply noise showing up (the input referred noise of the OP27 is 3.5 nV/rHz, so any PS noise above ~350 nV/rHz becomes relavent).
I was able to tame this by putting a 10 uF tantalum cap on the output of the regulator. However, when I replaced the regulator with a LM7912 from the blue box, it showed an output noise that went up like 1/f below 50 kHz !! I replaced it a couple more times with no benefit. It seems that something on the board must now be damaged. I checked another of the UPDH boxes, and it has the same high frequency oscillation but not so much excess voltage noise. I found that removing the protection diode on the output of the regulator decreased the noise by a factor of ~2. I also tried replacing all of the 1 uF caps that are around the regulator. No luck.
Both of the +12 V regulators seem fine: normal noise levels of ~200 nV/rHz and no oscillations.
Its clear that the regulator is not functioning well and my only guess is that its a layout issue on the board or else there's a busted component somewhere that I can't find. In any case, it seems to be functioning now and can be used for the phase locking and PZT response measurements.
For your reference: Voltage noise of LM7815/LM7915 (with no load)
Just before working on the FSS today, I noticed that the VCO RF output level was set incorrectly.
This should ALWAYS be set so as to give the maximum power in the first order diffracted sideband. One should set this by maximizing the out of lock FSS RFPD DC level to max.
The value was at 2.8 on the VCOMODLEVEL slider. In the attached plot (taken with the FSS input disabled) you can see that this puts us in the regime where the output power to the FSS is first order sensitive to the amplitude noise on the electrical signal to the AOM. This is an untenable situation.
For adjusting the power level to the FSS, we must always use the lamba/2 plate between the AOM and the RC steering mirrors. This dumps power out to the side via a PBS just before the periscope.