ELOG 40m

IOO

MC_F calibrated spectrum

I updated the plots because I did not take into account the double path AOM effect, which doubles the frequency actuation efficiency. (2008/10/8)

I determined the MC_F counts to the PSL frequency change calibration.
The attachment 1 is the calibrated MC_F spectrum, which is, above the cross over frequency, equivalent to the frequency noise seen by the MC.

The calibration method is the following:

1) I picked spare AD and DA channels (C1:IOO-MC_TMP1 and C1:OMC-SPARE_DAC_CH_16_EXC). C1:OMC-SPARE_DAC_CH_16_EXC is labeled C1:OMC-OSC_FM on the cable.

2) C1:IOO-MC_TMP1 was calibrated by injecting a sine wave of known amplitude and measuring the amplitude in counts in dataviewer.
It was 63uV/cnt.

3) C1:IOO-MC_TMP1 was connected to the feedback BNC connector of the MC board, that is the direct monitor of the feedback voltage to the VCO.

4) C1:OMC-SPARE_DAC_CH_16_EXC was connected to the channel B excitation input of the MC board, which adds the signal to the fast feedback path.

5) Using DTT a swept sine signal was injected to the MC board through C1:OMC-SPARE_DAC_CH_16_EXC, and the transfer function from C1:IOO-MC_TMP1 to the
C1:IOO-MC_F was measured.

6) Using the calibration of C1:IOO-MC_TMP1, the transfer function from the MC_F count to the actual voltage applied to the VCO input was obtained.
(attm2)

7) Using the DC calibration of the VCO input voltage to the VCO frequency change (1.75MHz/V elog:993) and the fact that there is a 1.6Hz pole and a 40.8Hz zero between the VCO input connector and the actual input of the VCO chip, the final calibration transfer function from the MC_F count to the frequency change of the PSL (that is twice the frequency change of the VCO within the bandwidth of the FSS) can be obtained (attm3).

8) The analytic form of the calibration TF is, poles at [1.6Hz, 11.42Hz, 11.42Hz] and zeros at [40.8Hz, 113Hz, 113Hz] with the DC gain of 110Hz/cnt.

Attachment 1: MC_F-spectrum.png

Attachment 2: VCO_VoverMC_F.png

Attachment 3: PSL_FoverMC_F.png

1035

Wed Oct 8 21:26:20 2008

Attempt to replace the DC-DC converter (aborted)

Rich, Steve, Yoichi

We opened the MOPA box and inspected our NPRO.
We concluded that this NPRO is different from the ones at the sites.
At the sites, the NPROs have a connector on the board which accepts the output of the DC-DC converter.
Rich's replacement DC-DC converter has a matching connector to it. So replacement of the DC-DC converter is easy.
In our NPRO, there is no such a connector found. The cables coming from the external power supply are directly soldered
on to the PCB (see attm1).

We have to take out the PCB in order to work on it.
As shown in the second picture, there is a D-SUB connector sticking out of the box through the rear panel.
In addition, the PCB is connected to the metal box containing the crystal with an IDE style connector.
This means the PCB is tightly constrained.
To take out the PCB without applying too much stress on it, we have to take off the rear panel.
To do so, we have to remove the screws on the bottom of the NPRO box. That means we have to move the NPRO.
We did not want to do so, because it will screw up the alignment to the amplifier.

The model number of the DC-DC converter looks like NMH0512-something.
According to the datasheet of NMH0512S, the switching frequency is typically 95kHz. We saw 77kHz harmonics in the FSS error signal.
I'm not sure if this is the culprit. I will try to measure the EMI from this guy later.

Attachment 1: DCDC.JPG

Attachment 2: NPRO.JPG

1037

Wed Oct 8 23:18:23 2008

Correlation between the Sorensen switching noise and the FSS error signal

I took some spectra and coherence function of the FSS error signal and the +24V Sorensen power line.
The first plot shows spectra of the two signals. Looks like Sorensen is not responsible for most of the lines
in the FSS error signal.
The coherence function between the two signals supports it (second plot).
Slight coherence can be seen at 23kHz and 98.4kHz but not significant.

I will check the coherence of the power line with the ISS signal next.

Attachment 1: PowerLineSpe.png

Attachment 2: Coherence.png

1042

Mon Oct 13 11:32:50 2008

Yoixhi

MOPA is in trouble now

Steve, Alberto, Yoichi

A quick update.
The MOPA output went down to zero on Sunday early morning (00:28 AM).
We found that the NPRO beam is mis-aligned on the power monitoring PD (126MON).
We don't know yet if it is also mis-aligned to the power amplifier (PA) because the mechanical shutter is not working (always closed).
Most likely the beam is not aligned to the PA.
A mystery is that although the beam is terribly (more than a half inch) missing the monitor PD, the beam still goes through two faradays.
Another mystery is that the NPRO output power is now increased to 600mW.

The power drop was a very fast phenomenon (less than 1/16 sec).
We are trying to figure out what happened.
The first step is to fix the mechanical shutter. We have a spare in our hand.

Attachment 1: powerdrop.png

1044

Mon Oct 13 13:56:03 2008

MOPA is not that much in trouble now

The problem was found to be all to do with the shutter.
The shutter started to work again, after a while, apparently for no clear reason.
The alignment to the PA was actually not screwed, and the MOPA output is now slowly increasing.
We figured that the 126MON PD has been mis-aligned for a long time. It was just picking the
scattered light from the output of the PA. So when the shutter is closed, it is natural that 126MON also goes down to zero.
It is a bit difficult to center the beam on the PD because there is not much room for moving the PD.
However, Alberto came up with a configuration (flip the PD and reflect back the beam with a mirror to the PD), which seems to
be feasible. We will do this modification when the MOPA is confirmed to be ok.

Here is more detail about the shutter problem:
The shutter is controlled by the MOPA power supply. There are three ways to command the power supply.
The switch on the front panel of the power supply, the EPICS switch (through a XYCOM XY220), and the interlock.
The ribbon cable from the power supply's back is connected to J1 of the cross connect. The pin 59 of the cable is the one
controlling the shutter. It is then routed to J12 pin 36. The interlock and a XYCOM switch are both connected to this
pin.
Now what happened was, on the way tracking down those cables, I pushed some connectors, especially the ones on the XYCOM.
After that, I was able to open the shutter from the EPICS button.
Steve and Alberto tried the EPICS button many times in the morning without success.
My guess is that it was some malfunctioning of the XY220 accidentally fixed by my pushing of the cables.
But I cannot exclude the possibility of the interlock malfunctioning.

Quote:

1045

Mon Oct 13 18:59:39 2008

NPRO EMI and FSS error signal correlation

I made a simple loop antenna to measure the electro-magnetic inteference (EMI) around the master oscillator NPRO.

The first plot shows the comparison of the FSS error signal with the EMI measured when the antenna was put next to the NPRO (the MOPA box was opened).
There are harmonics of 78.1kHz which are present in both spectra. It is probably coming from the DC-DC converter in the NPRO board.

The second plot is the same spectra when the antenna was put far from the NPRO (just outside of the PSL enclosure).
The 78.1kHz harmonics are gone. So these are very likely to be coming from the NPRO.

The third plot shows the coherence functions between the signal from the antenna and the FSS error signal.
When the antenna was put near the NPRO, there is a strong coherence seen around 78.2kHz, whereas there is no strong coherence
when the antenna is far away from the NPRO.
This is a strong evidence that the 78.2(or 78.1)kHz harmonics is coming from the NPRO itself.

There are many peaks other than 78.1kHz harmonics in the FSS error signal spectrum. For most of them you can also find corresponding peaks in the EMI spectrum.
We have to hunt down those peaks to avoid the slew-rate saturation of the FSS.

Attachment 1: IMG_1692.JPG

Attachment 2: Spectrum.png

Attachment 3: SpectrumFar.png

Attachment 4: Coherence.png

1047

Tue Oct 14 19:18:18 2008

Rana, Yoichi

Most of the FE computers failed around the lunch time.
We power cycled those machines and now all of them are up and running.
I confirmed that the both arms lock.
Now the IFO is in "Restore last auto-alignment" status.

1049

Wed Oct 15 17:40:50 2008

I set the PMC servo input offset: closed the MOPA shutter, zeroed the mixer output with the offset slider,
relocked everything, and set the nominal to the new value of -6 V.

1051

Thu Oct 16 09:44:49 2008

Yesterday arount 1:30PM, we lost the LO signal for the FSS.
I found it was caused by a bad cable connecting from the peter's RF oscillator box to the LO of the FSS.
I temporarily replaced it with a BNC cable of comparable length.

1056

Fri Oct 17 21:41:09 2008

burtwb missing on Solaris but installed on linux64

c1lsc stalled this evening, so I powercycled it.
After that, I tried to lock arms to confirm the computer is working.
Then I realized that the restore alignment buttons do not work from any control room computer.
I found that it was because burtwb command was missing. For Solaris, looks like there used to be /cvs/cds/epics/extensions/burtwb but now
there is no /cvs/cds/epics directory. I thought there were directories other than "caltech" in /cvs/cds/, weren't there ?
Right now, there is only /cvs/cds/caltech.
Anyway, I installed burt for 64bit linux computer (under /cvs/cds/caltech/apps/linux64/epics/extensions/).
At this moment the alignment save/restore works on allegra (and probably on rosalba), but not on op440m yet.

1057

Mon Oct 20 09:45:56 2008

The PSL HEPA filter was turned on.
It should be running all times.
The 0.5 micron particle count is up to 20,000 this morning.

1058

Mon Oct 20 12:18:38 2008

Alan

burtwb missing on Solaris but installed on linux64

Quote:

The automatic backup of /cvs/cds (and /frames/minute-trends ) to the LIGO archive in Powell-Booth,
which runs from fb40m using the scripts in /cvs/cds/caltech/scripts/backup ,
stopped when fb40m was rebooted on June 28, 2008,
and the check_backup script I run to send an email when this happens also failed due to a scripting error.

But we still have a backup of /cvs/cds from June 27.

The backup of /cvs/cds (excluding /cvs/cds/caltech and /cvs/cds/tmp)
circa June 27, 2008
has been restored to
/cvs/cds/recover_20081020 .

Please check to see that it has what we need.

Before moving it over to where it belongs,
it would be really nice to figure out what happened...

Meanwhile, I have fixed the check_backup script and restarted the backup, which will run this evening...
but maybe I should wait till the dust settles?

Now is also a good time to think about whether there is anything else besides for
/cvs/cds and /frames/minute-trends that should be backed up regularly.

- Alan

1062

Tue Oct 21 16:14:42 2008

divergence of He Ne 1035P

The ITM oplevs laser diodes are noisy.
They will be replaced by JDS 1035P
SN T8093307 was measured with the beamscanner.
This will able us to calculate the right lenses to get a small beam on the qpd.

**

The first column is distance from the front face of the laser in cm.
The second column is beam diameter in the horizontal direction in microns.
The third column is the beam diameter in the vertical direction in microns.

(edit by Rana)

Attachment 1: 1035p_divergence.png

1063

Tue Oct 21 16:17:45 2008

AD797 Oscillation in the FSS board

I checked each op-amp's output in the FSS board to see if any indication of slew-rate saturation can be found.
PA85, which was the most suspicious one, actually has a very large slew rate limit (1000V/usec).
Its output swing was about 5V/usec. So PA85 was ok in terms of slew rate.
However, I found that an AD797 used at the first stage of the PC path was oscillating by itself, i.e. even without the loop closed.
The frequency was about 50MHz and the amplitude was large enough to reach the slew rate limit of this chip (the steepest slope was 30V/usec whereas the slew
rate limit of AD797 is 20V/usec).

I replaced it and another AD797 right after the oscillating one with AD829s. Just replacing the chips caused oscillation of AD829.
It was because there were no phase compensation capacitors connected to the pin 5 of AD829s.
Since the PCB was designed for AD797, there is no pattern for compensation caps. So I ended up putting Mica capacitors (47pF) across the pin 5 and the nearest ground point.
It worked and the oscillation stopped.

As I reported in an earlier elog, stopping the oscillation did not solve the problem of low FSS bandwidth.

1067

Wed Oct 22 12:37:47 2008

Attached in open office format as well as excel format is spreadsheet containing all the devices with IP addresses at the 40m. Please contact me with any corrections.

Attachment 1: 40m_network_10-15-08.ods

Attachment 2: 40m_network_10-15-08.xls

1069

Wed Oct 22 17:48:58 2008

Lenses for focusing the optical lever laser (Re:divergence of He Ne 1035P)

Steve had difficulty in finding lenses for focusing the HeNe laser for the ITM op-lev.
Following his measurement of the beam divergence, I did some calculation to find a suitable set of lenses and positions.

First, I fitted Steve's data to get the waist size and location of the new HeNe.
The first plot shows the fitting result.
The size of the waist is 0.3mm at -367mm from the laser output (i.e. inside the laser).
(I only used horizontal beam size data.)

Then using the obtained beam parameter, I calculated the propagation of the beam through two lenses.
After playing with the focal length and location of the lenses, I found that with parameters {f1=-0.125m, f2=0.2m, d1=0.2m, d2=0.1m} we get about 1mm beam at the QPD (about 4m away from the laser). f1 and f2 are the focal lengths of the lenses, d1 is the distance from the laser to the first lens and d2 is the distance between the two lenses.
The second plot shows the beam size as a function of the distance from the laser.

The Mathematica notebook used to plot the beam propagation is attached.
By running it on Mathematica 6, you can dynamically change the parameters (focal lengths and locations) by sliders, and the plot (like the one shown in the second attachment) updates in real time. It is cool. Please try it.

Quote:

The first column is distance from the front face of the laser in cm.
The second column is beam diameter in the horizontal direction in microns.
The third column is the beam diameter in the vertical direction in microns.

(edit by Rana)

Attachment 1: BeamProfile.png

Attachment 2: BeamPropagation.png

Attachment 3: BeamPropagation.zip

1072

Thu Oct 23 15:27:19 2008

Here are the measurements I've got yesterday. The plot shows the transmitted power after the X arm while sweeping the frequency of the beat between the two lasers. That frequency is changed by scanning the frequency of the local oscillator of the PLL (that is the Marconi).
The X arm cavity has been locked to the TEM00 of the main beam. I tilted ITMX in order to enhance the higher modes of the secondary beam with the purpose of making them beat with the main beam.
Three traces are shown in the plot correspondent to three different measurements in which I clipped the transmitted beam at the X end with a razor blade from up and from the side of the photodiode.
Both the beats of the TEM00 mode of the main laser with the TEM01 and TEM10 modes of the secondary laser are expected to be at 6.2763 MHz. The plot has a candidate peak at 6.325MHz but it does not appear on both the measurements with the blade. the peaks at 3.897MHz and 7.795MHz are the first and the second longitudinal modes of the X arm cavity.

Attachment 1: TRX_aplot_03_04_05_together.png

1073

Thu Oct 23 18:23:47 2008

Quote:

Today I repeated the measurement and I'm attaching the resulting plot. Still, not clear and (and most of all) not nice.
It seems like tilting ITMX is introducing a lot of unwanted higher modes that don't let us to clearly identify TEM01 and TEM10.
I think I'm going to stop it to get back to technique in which the arm cavity is locked to the TEM01/10 of the main beam.

Attachment 1: TRX_plot_06_07_08_together.png

1074

Thu Oct 23 18:27:04 2008

Quote:

Here is the Matlab code I use to calculate the HOM frequencies.

Attachment 1: HOM_Frequencies.m

% FP Cavity HOM Frequencies Estimate
% Alberto Stochino, October 2008

R1 = 7280;      % Mirror1 radius of curvature
R2 = 57.57;     % Mirror2 radius of curvature
L = 38.458;     % Length of the FP Cavity
n = 1;          % X Order of the Mode
m = 0;          % Y Order of the Mode

c = 299792458;  % Speed of Light

... 11 more lines ...

1079

Thu Oct 23 21:52:27 2008

I measured the open loop transfer function of the FSS, for the first time after I mitigated the oscillation.
The attached plot shows the comparison of the OPLTF before and after the oscillation was mitigated.
Blue curves are when AD797 was oscillating, and the red ones are after AD797s were replaced by AD829s.
The FSS gain slider values are the same for the both measurements.
There is a notable difference in the shape of the TF.
Right now the UGF is around 450kHz with the phase margin of 50deg.
When the gain is increased by a few dBs in the common gain slider, the PC path becomes saturated.
This might be caused by the peak in the OPLTF at 1.7MHz sticking out of the 0dB line.
Another peak at 770kHz is also annoying.
Too bad that I did not take the TF above 1MHz before the oscillation was mitigated.
Also at 100kHz, the new TF has a lower gain than the old one, although it looks like the slope of the red curve is getting steeper and
it is catching up the blue one at lower frequencies.
I will measure the TF below 100kHz later.

With this bandwidth, I was able to increase the MC gain further.
I will report on the MC open loop measurements soon.

Attachment 1: FSS_OPLTF.png

1080

Thu Oct 23 23:09:18 2008

I measured three loop transfer functions of the MC servo.
The blue curve in the first attachment is the overall open loop gain of the servo measured using
the sum-amp A of the MC board (it is the sum-amp in the common part).
The red curve is the transfer function measured by the sum-amp B of the MC board, which is in the VCO path.
Mathematically the measured transfer function is G_vco/(1+G_L), where G_L is the loop gain of the length path
and G_vco is the loop gain of the VCO path.
The green curve is G_L/(1+G_vco) which was measured from dtt by using C1:SUS-MC2_MCL_EXC.
The UGF of the MC loop is 75kHz with the phase margin of 27deg.
The cross over frequency of the two loops is 43Hz. The phase margin there seems OK.

The second attachment is the comparison of the MC open loop TF measured on Sep. 4 (old) and today (new).
The increased bandwidth of the FSS gave us a slight gain in the phase margin and the elimination of
the slight bump in the gain around 150kHz existed in the blue curve.

Attachment 1: MC_Loop.png

Attachment 2: OldAndNew.png

1082

Fri Oct 24 11:09:08 2008

more lexan plates under cameras

SAFETY

The MC2, MC3&1 and BSC-SUS cameras were repositioned somewhat in the
process of placing lexan disks under neat them.
MC1&3 will have to be readjusted.

Now all horizontal viewports are protected.

1084

Fri Oct 24 11:42:48 2008

Abs length: locking the X arm cavity in TEM01/10

I went back to lock the arm cavity in either TEM01 or TEM10 mode. Attached are the results. We still have several resonances which we can't clearly identify. I expect TEM01/10 to be at 6.276MHz but we don't have a peak exactly there. What we have is:
- a peak at 6.320MHz in the measurement of the TEM01 mode (the one with the lobes of the spot almost on the vertical axis)
- a peak at 6.590MHz in both the TEM01 and TEM10 measurements.

I'm either missing the real TEM01/10 mode or the peaks at 6.590MHz are those. If that were true, that would mean that the radius of curvature of ETMX is 49.29 m instead of 57.57 m as listed in the IFO data sheets. I think it's much more likely that the measurements are missing the right peaks.

Attachment 1: TRX_armTEM00-plot_09-10_together.png

1085

Fri Oct 24 15:05:13 2008

The old Dycor RGA is out of order.
I'm getting ready to purchase an SRS instrument.

1086

Fri Oct 24 17:21:13 2008

Abs length: the right amount of beam clipping

I found the reason why the peak at about 6.3MHz appeared only on the TEM10 mode: the blade was clipping the beam too much and it was probably totally killing the mode. I'm attaching a plot that shows that difference when I did that.

Attachment 1: 24OCT08_levels_of_clipping_comparison.png

1087

Fri Oct 24 18:05:01 2008

Abs length: transverse mode spacing measured for the X arm

The ETMX suffers of astigmatism. I measured the following frequencies for the higher order modes:
- f_01 = 6317500 +/- 500 Hz
- f_10 = 6305500 +/- 500 Hz

From

g2=1/g1*(cos(A*L*pi/c))^2

where A= (fsr-f_i), fsr=(3897654+/-15)Hz (see elog entry 956), L=(38.4580+/-0.0003)m, g1=0.9947 (from R1=7280m), I get the following values for the g-factor coefficients:

g2_x = 0.3164 +/- 0.0002
g2_y = 0.3209 +/- 0.0002

from which we have the radius of curvature of ETMX:

R_x = 56.26 +/- 0.01 m
R_y = 56.63 +/- 0.01 m

The specs for the mirror have R2= 57.57 m (unc).

So, they seem conditions similar of those of ETMY that Koji measured:

Rx = 56.1620 +/- 0.0013 [m]
Ry = 57.3395 +/- 0.0011 [m]

for which L_yarm: 38.6462 m +/- 0.0003 m

Attachment 1: 24OCT08_TEM10-01_comparison(file12-14).png

1090

Fri Oct 24 22:30:38 2008

Jenne,rana

Noise from Guralp Seismometer

PEM

Attached is a Power Spectrum of the noise on the Vert1 channel of the Guralp seismometer. The noise is in the several hundreds of nV/rtHz up near 50Hz and higher, but is in the several microV/rtHz range at lower frequencies. Our high frequency noise is almost definitely below the noise of the ADC, but the lower frequencies, where we actually care, it's not as clear.

To Do list:

Measure the noise of the ADC - is the Guralp Box lower for all frequencies?
Use conversion factors to convert this measured noise into the minimum ground motion that we can measure. Is this at least a factor of 100 lower than our regular ground motion?

** UPDATE: This is actually the noise of the Guralp breakout box, not the Guralp itself. It is the noise measured on the output of the box
with the input shorted. The board is configured to have a gain of 20 (10 from the AD620 and 2x for differential drive). We also measured
directly at the AD620 output and all of this noise comes directly from that chip. If Jenne calculates that this noise is too high we would
have to find a replacement with a better low frequency floor (e.g. LT1012 or LT1007 depending on the Guralps source impedance).

Attachment 1: Vert1_Noise_24Oct2008.png

1091

Sun Oct 26 21:02:18 2008

SVN medm problem

As we've seen in the past a few times, there's something wrong with the files in the trunk/medm area.
I get the following error message when doing a fresh checkout:

A    c1/lsc/help/C1LSC_LA_SET.txt
svn: In directory 'c1/lsc/help'
svn: Can't copy 'c1/lsc/help/.svn/tmp/text-base/C1LSC_RFadjust.txt.svn-base' to 'c1/lsc/help/.svn/tmp/C1LSC_RFadjust.txt.tmp.tmp': No such file or directory

It looks like that there are some .svn files which have been checked in as if they're some kind of source code instead of just maintenance files.
We probably have to go through and clean this out and then remove these excess files somehow.

1092

Mon Oct 27 10:02:16 2008

SVN medm problem

I tried to check out medm directory both from my laptop and nodus.
I did not get the error.
Have you already fixed it ? Or maybe it is to do with the version of the svn used to checkout ?

Quote:

As we've seen in the past a few times, there's something wrong with the files in the trunk/medm area.
I get the following error message when doing a fresh checkout:

A    c1/lsc/help/C1LSC_LA_SET.txt
svn: In directory 'c1/lsc/help'
svn: Can't copy 'c1/lsc/help/.svn/tmp/text-base/C1LSC_RFadjust.txt.svn-base' to 'c1/lsc/help/.svn/tmp/C1LSC_RFadjust.txt.tmp.tmp': No such file or directory

1094

Mon Oct 27 11:23:10 2008

new Olympus camera with IR vision

Photos

The IR blocker was removed from our new Olympus camera
SP 570UZ camera.
It has image stabilization, zoom 26-520 mm (20x optical)
and 10.7 Mpixel

Attachment 1: IRisin.JPG

1097

Tue Oct 28 11:10:18 2008

Higher Order Mode resonances in the X arms

LSC

Quote:

Recently we had been having some trouble locking the full IFO in the spring configuration (SRC on +166).
It was thought that an accidental higher order mode resonance in the arms may have been causing problems.

I previously calculated the locations of the resonances using rough arm cavity parameters(Elog #690). Thanks to Koji
and Alberto I have been able to update this work with measured arm length and g factors for the y arm (Elog #801,#802).
I have also included the splitting of the modes caused by the astigmatic ETM. Code is attached.

I don't see any evidence of +166MHz resonances in the y arm.

In the attached plot different colours denote different frequencies +33, -33, +166, -166 & CR.
The numbers above each line are the mn of TEMmn.
Solid black line is the carrier resonance.

I plugged the measures of the length of the X arm and radius of curvature of ETMX I made in to John's code to estimate the position of the resonances of the HOM for the sidebands in the X arm. Here's the resulting plot.

Attachment 1: HOM_resonances_Xarm.png

1100

Wed Oct 29 12:54:28 2008

Jenne

Calibrated Guralp Noise compared to average ground motion

PEM

Here is a calibrated noise plot of the Guralp seismometer box. This is the same noise measured on Friday, measured at TP3 (just after the first gain stage), with the inputs shorted.

The Guralp calibration is:

                TP3 noise
noise in m/s = -------------------
                 10 * 802(V/(m/s))

The 10 is from the gain of 10 between the output of the seismometer and the input of the breakout box, and the 802 V/(m/s) is from the calibration data that came with the seismometer.

From elog 881 by Rana, in the ~1-50Hz band, the calibration of the Ranger seismometer is 488*10^6 counts/(m/s). Using DataViewer, I estimated that the nighttime ground motion measured by the Ranger is ~3500 counts, and the max daytime ground motion is ~8000 counts. This is what was used for the nighttime/daytime lines in this plot.

It seems like the noise of the Guralp box is fine just as it is, and we don't need to worry about replacing the first gain stage (differential instrumentation amp) with a lower-noise op-amp, since at even the lowest freqs, we have almost a factor of 100 at night, and better than that at higher freqs.

NOTE about the plot: the legend isn't showing the correct colors for the night and day motion - obviously the nighttime motion is the lower RED line, and the day is the higher GREEN line.

Yet another note: When I was measuring the counts on the Ranger, I forgot to subtract the mean, so these numbers are overestimating the ambient ground motion. The blue curve is correct however.

Attachment 1: GuralpVert1Noise_mPERs_Ranger.png

1101

Thu Oct 30 11:07:25 2008

Computers

Wireless bridges arrived

Five wireless bridges for the GPIB-Ethernet converters arrived.
One of them had a broken AC adapter. We have to send it back.
I configured the rest of the bridges for the 40MARS wireless network.
One of them was installed to the SR785.
I put the remaining ones in the top drawer of the cabinet, on which the label printers are sitting.
You can use those to connect any network device with a LAN port to the 40MARS network.

1103

Fri Oct 31 08:52:19 2008

SUS

ETMY damping restored

ETMY watchdogs were tripped yesterday morning also. This is a problem that existed some months ago.(?)
Our seimo channels are inactive.

Attachment 1: etmy2d.jpg

1105

Sun Nov 2 20:44:58 2008

Wiener Filter performance over 5 hours

ASS

I took one 2 hour stretch of data to calculate a MISO Wiener filter to subtract the Ranger seismometer
and the 6 Wilcoxon accelerometers from the IOO-MC_L channel. I then used that static filter to calculate
the residual of the subtraction in 10 minute increments for 5 hours. The filter was calculated based upon
the first 2 hours of the stretch.

The MC lock stretch is from Oct 31 03:00 UTC (I think that we are -8 hours from UTC, but the DST confounds me).
So its from this past Thursday night.

I wrote a script (/users/rana/mat/wiener/mcl_comp.m) which takes the static filter and does a bunch of loops
of subtraction to get a residual power spectrum for each 10 minute interval.

In the attached PNG, you can see the result. The legend is in units of minutes from the initial t0 = 03:00 UTC.

BLACK-DASHED -- MCL spectrum before subtraction

I have also used dashed lines for some of the other traces where there is an excess above the unsubtracted data.
Other than those few times, the rest are all basically the same; this indicates that we can do fine with a very
slow adaptation time for the feed-forward filters-- a few hours of a time constant is not so bad.

After making the plot I noticed that the Ranger signal was totally railed and junky during this time.
This probably explains the terrible performance below 1 Hz (where are those Guralps?)

The second attached image is the same but in spectrogram form.

Attachment 1: f.png

Attachment 2: f1.png

1106

Sun Nov 2 21:37:22 2008

The ranger signal has been bad since around 11 AM on Oct 25 (last Saturday). There are no elog
entries from that day, but I am quite sure that someone must have been working around the PSL
rack area.

It looks like what happened is that someone moved the chair with the monitor on it and/or the wooden
stool next to it. That put tension on the cable connecting the SR560 and the seismometer. The SR560
connector now seems loose and I think probably the cable ground wasn't connected. I swapped the
cable over to the "B" side of the SR560 and the ranger signal is now reasonable (very small offset
and normal seismic signal).

Please be careful when working around there. Everyone always says "I didn't do anything" or "it doesn't
effect anything".

We need to clean up the cabling around there in addition to running a new power cable for the RF amplifier
on the POY table.

I have also reduced its sample rate from 2048 to 512 Hz. The data are OK after 909640694.

I also increased the sample rate of AS_MIC from 2048 to 16384 Hz but that one seems to be broken
---->> the microphone seems to be either disconnected or broken.

1107

Mon Nov 3 09:59:47 2008

The psl enclosure HEPAs were tuned on.

Loose paper drawing was found on the psl inside shelf.
This can fall down into the beam and ignite a tragedy.

Thanks for the color coded correction. My spell checker is not reliable

1108

Mon Nov 3 19:12:27 2008

alberto

Transverse mode spacing measurement for the X arm

I know a lot of expectations have been building up on these days in the scientific community at the 40m towards a conclusive elog entry about the g-factor measurement of the X arm cavity.
The reason of the delay is that the results are still under review by the author. It turned out that the measurements of the transverse mode spacing have been performed on the beat
of the TEM02/20 and TEM00 modes between the two laser beams instead of on the beat between 00 and 01/10. However, the results posted on the elog in the last weeks seem likewise correct,
in particular my plot of the HOM of the sidebands.

Anyways, lately I have been trying to repeat the measurement on the beat of TEM01/10 with 00 but, despite all the efforts and the countless configurations tried (on the locking of
the arm, on the tilt of the mirrors, on the injection of the secondary beams, on the chopping with the blade), only the beat of TEM10 has been measured - although quite clearly -
whereas that of TEM01 has so far hidden itself.

The search continues but even if it does not succeeds, a summarizing document is going to be posted soon.

Here I attach a plot that shows the kind of difficulties trying to detect TEM10. The red neat peak is the beat of TEM01 whereas the other curves are some of the resulting
resonances after trying to couple TEM10 with 00 (or vice versa, according to whether I'm locking the cavity to the 00 mode of the main laser or to that of the secondary beam).

Attachment 1: 2008-11-02_summarizingplot.png

1111

Mon Nov 3 22:35:40 2008

Wiener Filter performance over 5 hours

ASS

To speed up the Wiener filter work I defined a 256 Hz version of the original 16kHz IOO-MC_L signal. The
attached plots show that the FE decimation code works correctly in handling the anti-aliasing and
downsampling as expected.

Attachment 1: DAQ.pdf

1112

Tue Nov 4 00:47:53 2008

Wiener Filter performance over 5 hours

ASS

Same as before, but now with a working Ranger seismometer.

In the spectrogram, the color axis is now in dB. This is a whitened spectrogram, so 0 dB corresponds to
the average (median) subtraction. The color scale is adjusted so that the large transients are saturated
since they're not interesting; from the DV trend its some kind of huge glitch in the middle of the
night that saturated the MC1 accelerometers only (maybe a pump?).

The attached trend shows the 5 hours used in the analysis.

Attachment 1: f2.png

Attachment 2: f.png

1115

Wed Nov 5 12:41:36 2008

Absolute Length and g-factor measurements conclusions

LSC

Absolute Length and g-Factor Measurement for the 40m Arm Cavities, Summary of Results

MOTIVATION OF THE EXPERIMENT
Lately locking the interferometer in the so called spring configuration (SRC on +166 MHz sideband) has been difficult and a possible resonance of an higher order mode of the +166 MHz sideband in the arms was
hypothesized as the cause. We wanted to know the frequencies of the HOMs of the sidebands and see where they are, relatively to the carrier resonance.

THE EXPERIMENTAL TECHNIQUE IN BRIEF
A second laser beam from an NPRO is injected into the interferometer through the AS port. The beam is mode matched to the arm cavities so that it can resonate inside of these. The secondary beam interferes with
the PSL beam and the incident intensity on one end mirror, excluding by now any higher mode, is I(t)=I1+I2+(interference terms)*exp[-i*(f1-f2)*t]. The last term comes from the beat between the two fields at the
relative frequency of the two lasers. For beating frequencies multiple of the FSR of the cavity, the beat gets transmitted and appears at the trans PD.
Whereas the PSL has a constant frequency, the NPRO frequency fluctuates, so that the relative phase between the two is not constant. To prevent that, a PLL servo locks the phase of the NPRO to that of the PSL.
The result is a beat frequency at the steady and tunable value set by the local oscillator of the PLL.

Length Measurement
One arm at a time, the cavity is locked to the TEM00 mode of the main laser. The beat frequency is then scanned for a few cavity FSRs and the transmitted power is measured. A linear fit of the resonant frequencies gives
us the FSR of the cavity.

g-factor Measurement
For non-planar Fabry-Perot cavities, the HOMs of the laser are not degenerate and resonate in the cavity at frequencies different from the correspondent fundamental mode. The shift in frequency is measured by the
Transverse Mode Spacing (TMS) and it is a function of the g-factors of the cavity:

TMS=FSR*acos[sqrt(g1*g2)]/pi

with g1=1-L/R1, where L is the cavity absolute length and R1 the radius of curvature of the input mirror, and similarly for g2 for the end mirror.
We measured the TMS by means of the beat between an HOM of the main laser and the TEM00 of the secondary beam. To do that we locked the cavity to either TEM01/10 and looked at the transmitted power for frequencies
of the beat around the TMS expected from the design parameters of the cavity.
Since the phase of the intensity of the beat between TEM01/10 and TEM00 has only DC components if measured across a symmetric portion of the spot, it is necessary to brake the symmetry of the incident beam on the
PD by chopping it just before it hits the sensor.
We approximated g1=1 for the ITMs. The effect of an astigmatic ETM is to brake the degeneracy of the TEM10 and TEM01 modes and split their resonant frequencies. By measuring that shift, we can evaluate the radius
of curvature of the mirror for the axis of the two transverse modes.

EXPERIMENTAL RESULTS

X Arm
FSR     =  (3897627 +/- 5 )   Hz
L       = (38.45833  +/- 0.00005) m
g2x     =   0.31197  +/- 0.00004
g2y     =   0.32283  +/- 0.00004
R-ETM_x = (55.8957   +/- 0.0045) m
R-ETM_y = (56.7937   +/- 0.0038) m

Y Arm
FSR     = ( 3879252 +/- 30 )  Hz
L       = (38.6462   +/- 0.0003) m
g2x     =   0.31188  +/- 0.00004
g2y     =   0.32601  +/- 0.00004
R-ETM_x = (56.1620   +/- 0.0013) m
R-ETM_y = (57.3395   +/- 0.0011) m

CONCLUSIONS
The attached graphs,one for the X arm and the other for the Y arm, plot the distributions of the first HOMs of the sidebands near the carrier resonance in the arm cavities. As it appears, the resonances of
the +166 sideband are far enough for not resonating in the arm cavities if the arms are locked to the carrier.
We have to look for something else to explain the locking problem of the interferometer in the spring configuration.

Attachment 1: 2008-11-04_file_02-05.png

Attachment 2: HOM_resonances_Xarm.png

Attachment 3: HOM_resonances_Yarm.png

1116

Thu Nov 6 09:45:27 2008

head temp hick-up vs power

MOPA

The control room AC temp was lowered from 74F to 70F around Oct 10
This hold the head temp rock solid 18.45C for ~30 days as it shows on this 40 days plot.
We just had our first head temp hick-up

note: the laser chiller did not produce any water during this period

Attachment 1: htpr.jpg

1117

Thu Nov 6 10:06:41 2008

Locking

arms lock degradation

I have been locking the arms in the mornings lately.
The daily drift of LSC-TRX is ~ 15% and LSC-TRY ~5%

Attachment 1: arms.jpg

1120

Fri Nov 7 08:08:00 2008