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.
What is the Transfer Function of the suspension of the reference cavity? What were the design requirements? What is the Q and how well does the eddy current damping work? What did Wolfowitz know about the WMD and when? Who cooked the RTV in there and why didn't we use Viton??
To get to the bottom of these questions, today I shook the cavity and measured the response. To read out the pitch and yaw modes separately, I aligned the input beam to be misaligned to the cavity. If the beam is mis-aligned in yaw, for example, the transmitted light power becomes first order sensitive to the yaw motion of the cavity.
In the attached image (10 minute second-trend), you can see the second trends for the transmitted and relfected power. The first ringdown comes from the pitch or vertical mode. The second (shorter) one comes from the yaw misalignment and the yaw shake.
To achieve the up/down shake, I leaned onto the table and pumped it at its eigenfrequency. For the yaw shake, I put two fingers on the RC can's sweater and pushed with several pounds of force at the yaw eigenfrequency (2.6 Hz). For the vertical, I jumped up and down at half the vertical eigenfrequency (4 Hz).
I also made sure that the .SCAN field on these EPICS records were set to 9 so that there is no serious effect from a beating between the eigenfrequency and the EPICS sample rate.
f_vert = 4 Hz
tau_vert = 90 seconds
Q_vert = 1000 (yes, that number over there has 3 zeros)
f_hor = 2.6 Hz
tau_hor = 30 seconds
Q_hor = 250
This is an absurd and probably makes us very sensitive to seismic noise - let's make sure to open up the can and put some real rubber in there to damp it. My guess is that these high Q modes
are just the modes of the last-stage steel spring / pendulum.
This is the error point spectrum - it is filled with huge multiples of ~75 kHz as Yoichi noticed a couple years ago.
I tried to use the netgpib.py package to read out the Agilent 4395, but the SVN had been corrupted by someone saving over the netgpib.py package. To get it to work on rosalba I reverted to the previous version, but whoever is busy hacking on netgpib.py needs to checkin the original package and work on some test code instead.
I also noticed that the default output format for the AG4395.py file is in units of Watts. This is kind of dumb - we need someone to develop this package a little as Yoichi did for the SRS785.
I measured the open loop gain of the FSS (as usual, I have multiplied the whole OLG by 10dB to account for the forward loop gain in the box). I used a source level of -20 dBm and made sure this was not saturating by changing the level.
Its clear that the BW is limited by the resonance at ~1.7 MHz. Does anyone know what that is?
I measured the RF spectrum coming out the FSS RFPD to look for saturations - its close to the hairy edge. This is with the 8x power increase from my AOM drive increase. I will increase the FSS's modulation frequency which will lower the Q and gain of the PD to compensate somewhat. The lower Q will also gain us phase margin in the FSS loooop.
I put in a bi-directional 20 dB coupler (its only rated down to 30 MHz, but its only off by ~0.3 dB at 21 MHz) between the RFPD and the FSS box. I looked at the time series on the 300 MHz scope and measured the power spectrum.
The peak signal on the scope was 40 mV; that translates to 400 mV at the RFPD output. Depending on whether the series resistor in the box is 20 or 50 Ohms, it means the MAX4107 is close to saturating.
As you can see from the spectrum, its mostly likely to hit its slew rate limit (500 V/us) first. Actually its not going to hit the limit: but even getting within a factor of 10 is bad news in terms of distortion.
Besides the multiples of the modulation frequency, you can see that most of the RMS comes from the strange large peaks at 137.9 and 181.1 MHz. Anyone know what these are from?
On the middle plot above, I have enabled the 20 MHz BW limit so you can see how much the amplitude goes down when only the 21.5 MHz SB is included. You can also see from the leftmost plot that once in awhile there is some 400mV/10ns slewing. Its within a factor of 10 of the slew rate limit.
EO resonance in the RC path?
With a 30mm PPKTP crystal the conversion efficiency from 1064nm to 532nm is expected to 3.7 %/W.
Therefore we will have a green beam of more than 20mW by putting 700mW NPRO.
Last a couple of weeks I performed a numerical simulation for calculating the conversion efficiency of PPKTP crystal which we will have.
Here I try to mention about just the result. The detail will be followed later as another entry.
The attached figure is a result of the calculation.
The horizontal axis is the waist of an input Gaussian beam, and the vertical axis is the conversion efficiency.
You can see three curves in the figure, this is because I want to double check my calculation by comparing analytical solutions.
The curve named (A) is one of the simplest solution, which assumes that the incident beam is a cylindrical plane wave.
The other curve (B) is also analytic solution, but it assumes different condition; the power profile of incident beam is a Gaussian beam but propagates as a plane wave.
The last curve (C) is the result of my numerical simulation. In this calculation a focused Gaussian beam is injected into the crystal.
The numerical result seems to be reasonable because the shape and the number doesn't much differ from those analytical solutions.
Why does the small spot size for the case (A) have small efficiency as the others? I thought the efficiency goes diverged to infinity as the radius of the cylinder gets smaller.
Therefore we will have a green beam of more than 2mW by putting 700mW NPRO.
Good point. There is a trick to avoid a divergence.
Actually the radius of the cylindrical wave is set to the spot size at the surface of the crystal instead of an actual beam waist. This is the idea Dmass told me before.
So that the radius is expressed by w=w0(1+(L/2ZR)2)1/2, where w0 is beam waist, L is the length of the crystal and ZR is the rayleigh range.
In this case the radius can't go smaller than w0/2 and the solution can not diverge to infinity.
We tested out the functionality of the EG&G 113 preamp that I found in one of the cabinets. This is one of the ancestors of the SR560 preamp that we are all used to.
It turns out that it works just fine (in fact, its better than the SR560). The noise is below 3nV/rHz everywhere above 30 Hz. The filter settings from the front panel all seem to work well. And the red knob on the front panel allows for continuous (i.e. not steps) gain adjustment. In the high-bandwidth mode (low pass filter at 300 kHz), there is ~35 deg of phase lag at 100 kHz. So the box is pretty fast.
I would easily recommend this above the SR560 for use in all applications where you don't need to drive a 50 Ohm load. Also the battery is still working after 17 years!
There's several more of the this vintage in one of the last cabinets down the new Y-arm.
The beams from the Innolight and Lightwave NPROs were both incident on a 1GHZ New Focus PD. Mott and I swept the temperature of the Lightwave and tracked the change in frequency of the beatnote between the two. The Innolight temperature was set to 39.61C although the actual temperature was reported to be 39.62C.
Freq. vs temperature is plotted below in the attached PDF. The slope is 2.8GHz/K.
The data is in the attached MATLAB file.
% plot the data from the Lightwave Temperature sweep
% Lightwave temperature
LWTemp = [0.2744
Same thing for the Innolight Mephisto.
Not unexpected values with dn/dT around 11E-6 K^-1 and coefficient of thermal expansion = 8E-6 K^-1 and a laser resonator length of order 10cm.
% plot the data from the Innolight Temperature sweep
% Innolight temperature
InnTemp = [0.60
.65] + 39;
Please put those numbers onto wiki somewhere at the green page or laser characterization page.
Jenne, Koji and I assembled the Covesion Oven today, inserted a PPKTP crystal from Raicol, aligned the crystal to a 50mW focus and
got some green beam coming out.
Covesion Oven assembly
The oven contains a brass clip that can clamp a crystal up to 10mm wide x 0.5mm high x 40mm long (according to the instructions). According to the correspondence from Covesion the clip can accomodate a crystal up to 1.5mm high. Our crystal is 1mm x 1mm x 30mm.
Alignment of the crystal to the focus
The oven was mounted on a 4-axis Newport translation stage. We plonked the assembly onto the table, removed the lid and adjusted the rough position so that a focus of the 1064nm beam, from a 100mm lens, was positioned near the center of the crystal - then it was clamped down to the table. From here we adjusted the alignment of the stage, using an IR card and a viewer to guide us, until we eventually saw some green beam coming out. We were all very excited by this! We optimized the alignment as best we could using the IR card and then we replaced the lid on the oven. At this point the temperature of the PPKTP was around 26.5C and the green beam coming out look quite dim. We turned the oven up to around 36 degC and observed the beam getting much brighter and we approached the optimum phase-matching condition.
We haven't done anyway quantitative measurements yet but we were pleased with how easy this first stage was.
[Edit by Koji] More photos are on Picasa album
I liked to know quantitatively where the spot is on a mirror.
With an interferometer and A2L scripts, one can make the balance of the coil actuators
so that the angle actuation does not couple to the longitudinal motion.
i.e. node of the rotation is on the spot
Suppose you have actuator balancing (1+α) f and (1-α) f.
=> d = 0.016 x α [m]
Full Imbalance α = 1 -> d = 15 [mm]
10% Imbalance α = 0.1 -> d = 1.5 [mm]
1% Imbalance α = 0.01 -> d = 0.15 [mm]
Eq of Motion:
I ω2 θ = 2 R f
(correction) - I ω2 θ = D f cos(arctan(L/2/D))
(re-correction on Sep 26, 2017) - I ω2 θ = D f
m ω2 x = 2 α f ,
(correction) - m ω2 x = 2 α f ,
where R is the radius of the mirror, and D is the distance of the magnets. (kinda D=sqrt(2) R)
d, position of the node distant from the center, is given by
d = x/θ = α I / (m R) = 2 α β / D,
where β is the ratio of I and m. Putting R=37.5 [mm], L=25 [mm], β = 4.04 10-4 [m2], D~R Sqrt(2)
i.e. d = 0.015 α [m]
Oh, but it gets even better: in order to trust the A2L script in this regard you have to know that the coil driver - coil - magnet gain is the same for each channel. Which you can't.
But we have these handy f2pRatio scripts that Vuk and Dan Busby worked on. They use the optical levers to balance the actuators at high frequency so that the A2L gives you a true spot readout.
But wait! We have 4 coils and the optical lever only gives us 2 signal readouts...
Yes, of course. But so far I am trusting that the coils are inheretly balanced.
Probably you are talking about the dependence of the nodal position on the frequency...I need to check if 18Hz is sufficiently high or not for 0.1mm precision.
Also I am practicing myself to understand how I can adjust them by which screws as we probably have to do this adjustement many times.
(i.e. removal of the MZ, move of the table, PSL renewal and so on)
For the actuator calibration, we may be able to calibrate actuator responses by shaking them one by one while reading the OPLEV P/Y signals.
Oh, but it gets even better: in order to trust the A2L script in this regard you have to know that the coil driver - coil - magnet gain is the same for each channel. Which you can't.
i tried to commit something this afternoon and got the following error message:
Error: Commit failed (details follow):
Error: Server sent unexpected return value (405 Method Not Allowed) in response to
Error: MKCOL request for '/svn/!svn/wrk/d2523f8e-eda2-d847-b8e5-59c020170cec/trunk/frank'
anyone had this before? what's wrong?
As per Steve's request I checked the MC incident power as a function of time.
The output is negative: the lower voltage, the higher power.
Before I put the attenuator the incident power was 1.1W. It appear as -5V.
Now the output is -0.1V. This corresponds to 22mW.
So I finished writing a script which takes an .ipc file (the one which defines channel names and numbers for use with the RCG code generator), parses it, checks for duplicate channel names and ipcNums, and then parses and .mdl file looking for channel names, and outputs a new .ipc file with all the new channels added (without modifying existing channels).
The script is written in python, and for the moment can be found in /home/controls/advLigoRTS/src/epics/simLink/parse_mdl.py
I still need to add all the nice command line interface stuff, but the basic core works. And already found an error in my previous .ipc file, where I used the channel number 21 twice, apparently.
Right now its hard coded to read in C1.ipc and spy.mdl, and outputs to H1.ipc, but I should have that fixed tonight.
This IPC stuff looks really a nice improvement of CDS.
Please just maintain the wiki updated so that we can keep the latest procedures and scripts to build the models.
After the recent removal of the old IMMT and the relocation of the Faraday isolator, the MC table was tilted a bit (southward and slightly westward---as of when I opened the chamber this afternoon). I re-leveled it by putting an extra two rectangular ballast blocks on the stack that was already hanging off the NNE edge of the table (there are a total of 4 in the stack now). I also screwed down the circular block that Koji and I put between the Faraday and SM1 on Tuesday, and re-mounted the two wire harness towers onto the table.
Needless to say, this threw the MC way out of alignment. I spent the rest of the afternoon reacquiring alignment and getting it to lock robustly. Here is a summary:
After that, I shut off the loops, blocked the beam, and put the light doors back on the tanks. Then I went to the parking lot, then I got in my car, etc, etc, etc.
Thanks Zach.This was a great job.
It was not mentioned but: was the Faraday clamped down on the table?
Ah... no, I didn't. That explains why there were loose dogclamps on the table. I wrapped them in foil and put them on the clean cart. Can this wait until the next time we open the tank (i.e. to measure the beam profile), or should I go over there and clamp it down today?