ELOG 40m

drum modes observable without excitation

The calibration of the MC_F feedback is posted in elog:1032.
I'm not sure where Caryn took MC signal, but if you take the signal from the servo out BNC on the MC board, it
directly corresponds to the voltage sent to the FSS VCO.
The DC calibration of the VCO is 1.75MHz/V. Since the AOM is the double-pass, the PSL frequency
change is 3.5MHz/V. At frequencies above 40Hz, the VCO calibration drops by a factor of 39/1000,
because of the pole/zero at 1.6Hz/40Hz in the VCO box.
So at the frequencies of interest (around 30kHz), the servo out voltage can be converted to the PSL frequency
change by 0.137MHz/V.
Since 30kHz is still within the bandwidth of the MC servo, the feedback signal should correspond to the actual
length change of the MC. So the above calibration factor can be used to calibrate Caryn's measurement and check
what Rana suggested.

1181

Fri Dec 5 20:40:38 2008

HowTo

Elog multi-keyword search

The current Elog search allows you to look for only one keyword in the text.
You cannot search for two keywords by simply separating them with a white space.
That is, a search term "abc def" matches a literal "abc def", not a text containing "abc" and "def".
This is extremely annoying. However, there are still some ways to search for multiple keywords.
The Elog search fields are treated as regular expressions.
In order to match a text containing "abc" and "def", you can use a search term "abc.*def".
A period (.) means "any character", and an asterisk (*) means "any number of repetition of the preceding character".
Therefore, ".*" matches "any number of any character" i.e. anything.
The search term "abc.*def" works fine when you know "abc" appears first in the text you are looking for.
If you don't know the order of appearance of the keywords, you have two choices: either to use,
"(abc.*def)|(def.*abc)"
or
"(abc|def).*(abc|def)"
The vertical bar (|) means "or". Parentheses are used for grouping.
The first example does exactly what you want. However, you have to list all the permutations of your keywords
separated by |. If you have more than two keywords, it can be a very very long search word.
(The length of the search word is O(n!), where n is the number of keywords).
In the second example, the length of the keyword is O(n). However, it can also match a text containing two "abc".
This means the search result may contain some garbages (entries containing only "abc").
I guess in most cases we can tolerate this.

To automatically construct a multiple keyword search term for the Elog, I wrote a bash script called elogkeywd
and it is installed in the control room machines.
You can type

elogkeywd keyword1 keyword2 keyword3

to generate a regular expression for searching a text containing "keyword1", "keyword2" and "keyword3".
The generated expression is of the second type shown above. You can then copy-and-paste the result to
the Elog search field.
The script takes any number of keywords. However, there seems to be a limit on the number of characters you can type
into the search field of the Elog. I found the practical limit is about 3 keywords.

1180

Fri Dec 5 14:13:41 2008

Summary

MC trend for the last 4 days

The MC has stayed locked for ~3 days! I just broke it to reset the MZ.

Attachment 1: g.png

1179

Fri Dec 5 09:29:59 2008

drum modes observable without excitation

Not sure what the y-scale is since there aren't any y axis labels in the plot, but it seems like we
now get an SNR of a ~few with a BW of 0.1 Hz. IN principle, the frequency noise out of the PSL ought
to be limited by the VCO phase noise at these frequencies (sort of) so the broadband MC_F level
is very roughly equal to 20-100 mHz/rHz.

Since dnu = dL*(c/lambda)/L_MC, the thermal peaks have a height of ~10^-15 m_RMS. We (Caryn) should check
that these numbers are true and then see if this is the correct amount of energy for thermally excited
mirror modes.

1178

Fri Dec 5 01:58:58 2008

tdscntr.pl now works at 40m

ASC

Tobin gave me the perl version of tdscntr some time ago.
Pinkesh and I modified and tested it at LHO.
I further modified it today and now it runs fine on the linux machines at the 40m. I haven't tested it with the Solaris machines.
My modifications include changing channel names to 40m ones, and using tdsavg to get QPD data rather than ezcaread.
The use of tdsavg is intended to avoid aliasing problem.
tdscntr.pl is installed in /cvs/cds/caltech/apps/linux/tds/bin

Now, the alignX runs on linux up to the centering of the QPDs.
However, ezcademod seems to behave wrongly on linux. I plan to investigate on this problem tomorrow.
I may try tdsdmd instead.

1177

Fri Dec 5 01:41:33 2008

MEDM screen snapshot now works on linux machines

As a part of my "make everything work on linux" project, I modified 'updatesnap' script so that linux machines can update MEDM screen snapshots.
Now, all 'updatesnap' in the subsystem directories (like medm/c1/lsc/cmd/updatesnap) are sym-link to /cvs/cds/caltech/medm/c1/cmd/updatesnap.
This script will take a window snapshot to a PNG file, and move the old snapshot to archive folders with date information added to the filename.
For compatibility, it also saves JPEG snapshot. Right now, most of 'view snapshot' menus in MEDM screens are calling 'sdtimage' command, which cannot display PNG files. I installed Imagemagick to op440m. We should change MEDM files to use 'display' command instead of 'sdtimage' so that it can show PNG files.
I've already changed some MEDM screens, but there are so many remaining to be modified.

PNG is better than JPEG for crisp images like screen shots. JPEG performs a sort of spacial Fourier transformations and low-pass filtering to compress the information. If it is used with sharp edges like boundaries of buttons on an MEDM screen, it naturally produces spacial aliasing (ghost images).

I also created several sym-links on the apps/linux/bin directory to mimic the Solaris-only commands, such as 'sdtimage', 'nedit' and 'dtterm'.
For example, nedit is symbolic linked to gedit. Many MEDM buttons/menus, which used to be incompatible with linux, now work fine on the linux machines.

1176

Thu Dec 4 17:42:23 2008

caryn

drum modes observable without excitation

So, the mode cleaner was evidently aligned better and now the drum modes are observable using DTT.
The Lock-In was set to 27.8kHz and the drum mode frequencies were previously observed to be 28.039kHz(MC2), 28.222kHz(MC3) and 28.221kHz(MC1). So, we might expect peaks at ~239Hz,421Hz,422Hz.
Peaks have been observed around the expected frequencies in channel IOO-MC-DRUM1.
Note that it is possible to resolve the separate MC1 and MC3 peaks which are so close together.
(sorry these are pdf's and not png's)

Attachment 1: drum_modes.pdf

Attachment 2: drum_modes2.pdf

1175

Thu Dec 4 16:29:20 2008

josephb

Error message on Frame Builder Raid Array

The Fibrenetix FX-606-U4 RAID connected to the frame builder in 1Y7 is showing the following error message: IDE Channel #4 Error Reading

1174

Thu Dec 4 13:49:39 2008

More of: Comparing Wiener subtraction using different sensors

Here is another version of the same type plot I put in the elog yesterday. This plot is looking at the 7200 seconds after 04Dec2008 08:45:00 UTC. This time was last night, when there was no crazy seismic activity, and well after the Ranger seismometer was moved to its new place under MC2.

This plot includes all possible combinations of the accelerometers, Guralp seismometer and Ranger seismometer (taking all 6 accelerometers as a set, and all 3 Guralp channels as a set). It is good to see that for the set of traces which do not include the accelerometers - brown, dark green and light blue - the subtraction at higher frequencies isn't all that great. Thus, the accelerometers are doing their job, and work well with the Wiener subtraction.

Still under investigation is why we don't see a whole lot of improvement at low frequency.

Attachment 1: Dec042008_c1wino_seisCombos.png

1173

Wed Dec 3 20:36:07 2008

Jenne, Rana

Comparing Wiener subtraction with different seismometers

The Ranger has now been moved over to sit underneath the MC2 tank (it was previously close to the PSL rack). It
is still pointed in the +Y direction (towards ETMY, aka south).

New spectra attached - looks like the coherence is still there between the Guralp and the Ranger which are now
seperated by the MC length (~12 m). At LLO, I have witnessed a coherence of less than 0.3 above 1 Hz for these
distances. Curious.

L960019-00-F describes measurements done at SLAC on seismic coherence. The iLIGO LSC PDD
(http://www.ligo.caltech.edu/docs/T/T970122-00.pdf) discusses in sec 4.2 how this was incorporated into the LSC design.

When we get our next Guralp, it will be interesting to move them around and determine what the cross-spectrum
is between different points in the lab during typical times.

In the second attachment, I have plotted the square of the quantity used in the LSC PDD (S_xy) which I think is
what we now plot in DTT as 'Coherence'.

The third attachment shows the coherences among the TM SUSPOS_INs. I've turned off the oplev servos for this but
the OSEM damping is still on. Its not quite the same as the theory, but we could probably measure/tweak the
seismic velocity and then get better agreement.

Attachment 1: d.pdf

Attachment 2: sco.png

Attachment 3: fly.pdf

1172

Wed Dec 3 20:10:09 2008

Jenne, Rana

Comparing Wiener subtraction with different seismometers

Attached is a plot of MC_L, and then the residual MC_L after static Wiener filtering, using different combinations of our accelerometers and seismometers.

This is the same type of plot that Rana has included in the past few weeks, using Wiener filters calculated with c1wino.m

This data is from GPS 912312914, duration = 7200 sec, sometime during the night last night.

Unfortunately, it doesn't look like adding the Guralp seismometer to the Accelerometers and the Ranger did much, especially at low frequencies (all sensors = black curve). We'll have to investigate why this is true, and what we can do to get some low-frequency subtraction going on.

In the legend, "Residuals Accels, Guralp, Ranger" implies that the residual has been calculated using all of the sensors listed.

Attachment 1: Dec032008_c1wino_seisCombos.png

1171

Wed Dec 3 19:21:09 2008

I looked at the Ranger signals. Somehow it has a relative transfer function of 'f' between it and the Guralp.

      Ranger
i.e.  ------ ~ f
      Guralp

which is strange since according to their manuals, they should both be giving us a voltage output which is proportional
to velocity. I checked that the Ranger only has a load resistor and then an SR560 low pass at 300 Hz. Jenne assures
me that the Guralp breakout box shouldn't have any poles either (to be double checked). Its a mystery.

We made sure that the SR560 now is DC coupled, G = 100, & 1-pole low pass at 300 Hz. I moved it over next to the Guralp
(went through the mass recentering procedure after forgetting to lock it before moving). It is behaving as it was
before.

Attached is a 2 page PDF of the comparisons. The 'MC1' channels are Guralp and 'MC2' is Ranger.

The second attachment compares our seismometers (in counts) with the LHO Guralp seismometers. There's no high frequency
rolloff there like what we see here so I bet a dollar that there's a pole in the Guralp box somewhere.

Attachment 1: c.pdf

Attachment 2: wsnb.pdf

1170

Wed Dec 3 12:49:11 2008

jenne

something sketchy with NDS ... or something

Never mind...I had forgotten that you have to run mdv_config every time you open matlab, not just every time you boot a computer.

I am not able to get channels using get_data from the mDV toolbox on Allegra, Megatron or Rosalba.

The error I get while running the "hello_world" test program is:
hello_world
setting up configuration...
added paths for nds
added paths for qscan
couldn't add path for matapps_SDE
couldn't add path for matapps_path
couldn't add path for framecache
couldn't add path for ligotools_matlab
added paths for home_pwd
fetching channels for C...
Warning: get_channel_list() failed.
??? Error using ==> NDS_GetChannels
Failed to get channel list.

Error in ==> fetch_nds at 47
eval(['CONFIG.chl.' server ' = NDS_GetChannels(ab);']);

Error in ==> get_data at 100
out = fetch_nds(channels,dtype,start_time,duration);

Error in ==> hello_world at 6
aa = get_data('C1:LSC-DARM_ERR', 'raw', gps('now - 1 hour'), 32);

1169

Wed Dec 3 11:58:10 2008

Rana, Alberto,

more details on the MC alignment we did yesterday.

Last week Rana re-aligned the Mach Zender (MZ) on the PSL table to reduce the power at the dark port (see elog entry #1151). After that, the beam was aligned to the MZ but not properly aligned to the Mode Cleaner (MC) anymore. As a result the MC could not lock or did it on unwanted transverse modes. To fix that we decided to change the alignment of the MC input periscope on the PSL table.

The ultimate goal of the operation was to align the MC transmitted beam to the IFO and to maximize the power. Such a condition depends on:
a) a good cavity alignment and
b) input beam matching to the cavity TEM00 mode.

Since the MZ alignment had only affected the input beam, we assumed the cavity alignment was still good, or at least it had not changed, and we focused on the input beam.

The IOO computer, by the MC autolocker script, is able to change the cavity alignment and the length to match the input beam and lock the cavity. Although both the length servo (LSC) and the alignment servo (WFS) have a limited effective operating range. So for the script to work properly and at best, input beam and cavity matching have to be not far from that range.

The MC periscope has two mirrors which control the pitch and yaw input angles. By changing either yaw or pitch of both mirrors together (�two-knob" technique) one can change the input angle without moving the injection point on the cavity input mirror (MC1). So this is the procedure that we followed:

1) turned of the autolocker running the MC-down script
2) brought the reflected beam spot back on the MC-reflection camera and on the reflection photodiode (REFL-PD)
3) turned on the LSC servo
4) tweaked the periscope's mirrors until the cavity got locked on a TEM00 mode
5) tweaked the periscope aiming at ~0.3V from the REFL-PD and ~3V on the transmission photodiode (TRANS-PD).

Following the steps above we got ~0.5 V on the REFL-PD and ~2V on the TRANS-PD but no better than that.

Looking at the Drift Monitor MEDM screen, we found that the cavity was not in the reference optimal position, as we initially assumed, thus limiting the matching of the beam to the MC.

We restored the optics reference position and repeated the alignment procedure as above. This time we got ~3V on the TRANS-PD and ~0.5 on the REFL-PD. We thought that the reason for still such a relatively high reflection was that the beam was not well centered on the REFL-PD (high order modes pick-up?).

On the AS table we centered the REFL-PD by aligning a beam splitter in the optical path followed by the light to reach the photodiode.

We also centered the beam on the reflection Wave Front Sensors (WFS). To do that we halved the power on the MZ to reduce the sidebands power and prevent the WFS QPD from saturating. We then aligned the beam splitters on the QPD by balancing the power among the quadrants. Finally we restored the power on the MZ.

As a last thing, we also centered the transmitted beam on the TRANS-QPD.

The MC is now aligned and happily locked with 3V at the TRANS-PD and 0.3V at REFL-PD.

1168

Tue Dec 2 19:51:32 2008

half-micron particle count is alarming

The 0.5 micron dust monitor count is now pretty high (36000). I wandered around the lab to see if there was anything
nasty going on but I didn't see or smell anything in particular. Since today Alberto was sitting around where the
dust monitor is while aligning the PSL beam, we should blame him. Its either garlic, cologne, or time to bathe.

The 400 day hour trend shows that while the counts are not so unusual, the 40m is dirtier than it was last year.

Attachment 1: Untitled.png

Attachment 2: dust.png

1167

Tue Dec 2 19:18:10 2008

In entry http://dziban.ligo.caltech.edu:40/40m/881 and a follow up from Jenne I put in the Ranger calibration.
Since then, we've reduced the SR560 gain from 200 to 100 so the calibration factor is now:

1e-9 (m/s)/count and then 2 poles at 0 Hz, and a Q~1 zero pair at 1 Hz.

in DTT:
G = 1e-9
p = 0, 0
z = 0.7 0.7

1166

Tue Dec 2 17:56:56 2008

In the attempt to maximize the Mode Cleaner transmission and minimize the reflection from the steering mirrors of the MC periscope, we could not get more ~2 V at the MC Trans PD and ~ 0.5 V at MC REFL_DC. As it turned out from the SUS Drift Monitor, the reason was that the MC optics had been somehow displaced from the optimal position.

After restoring the reference position values for the mirrors and tweaking again the periscope, we got ~3V at the MC TransPD and 0.5V at the reflection.
The beam was then probably clipped at the REFL PD so that we had to adjust the alignment of one of the BS in the transmitted beam path on the AS table.
We also zeroed the WFS PDs, but not before reducing the power from the MZ, for their QPDs not to saturate.

After relocking, the transmission was 3V and the reflection ~0.3V.

The beam isnow centered on the Trans PD and REFL PD and the Mode Cleaner locked. More details on the procedure will follow.

1165

Mon Dec 1 15:09:27 2008

rob

half-micron particle count is alarming

1164

Thu Nov 27 22:56:42 2008

8-)

Attachment 1: mc.png

1163

Tue Nov 25 19:29:15 2008

Quote:

The PSL Room Temperature was alarming because it had gone above 23 C. This set off an unfortunate chain of events:

We found that the PSL HEPA was set low (20%). This is a fine setting for when no one is working in there but it
does raise the temperature since there are heat sources inside the blue box.

We tried to change the office area temperature to compensate and also the westmost sensor inside the lab area by 2 deg F.

The office area one was problematic - there was so much dust in it that the gas valve nipple was clogged. So we've
now blown it all clean with a compressed air can. We're now tuning the calibration screw to make our new
digital sensor agree with the setpoint on the controller.

Expect wild temperature swings of the office area for a couple days while Alberto and I tune the servo.

This morning Bob found 92F in the office area and in the control room of the lab. He turned down the thermostat and when I got in at about 9 I found 65. After a few hours of adjustment of the thermostat's calibration, I could stabilize the room temperature to about 72F. I also turned down the thermostats inside the lab of a couple of degrees F.

1162

Tue Nov 25 18:38:03 2008

Alberto, Rob

MC Periscope Alignment

This morning when I came in I found the MC cleaner unlocked and the autolocker script could not lock it. The reflected beam was quite off and showed in the bottom left corner of the IMCR camera. After turning off the WFS locking, I started slightly changing the alignment of the steering mirrors on the MC periscope, waiting for the LSC servo to lock the cavity. It didn't work. At some point I lost the beam from the IMCR camera and that is how someone might have found it when I left it for about one hour.

When I came back and tried again adjusting the steering mirrors, I noticed that the autolocker was working and was trying to lock the cavity. After just a bit of adjustment, the MC got easily locked.

After that, I spent a couple of hours trying to improve the alignment of the periscope to minimize the reflection and maximize the transmission. I started with a transmission of 0.4 V but, despite all the tweaking (I used the technique of turning both yaw knobs at the same time), I couldn't get more than 1.2 V (and 2.4 V at the reflection) if only the LSC servo was on. Looking at the camera, I moved the beam around to look for a more favorable spot but the MC wouldn't lock with the beam in other places. Maybe I could do better or maybe not because the cavity is not aligned. I'm going to try again tomorrow.

1161

Mon Nov 24 19:15:16 2008

Mon Nov 24 17:14:44 2008

It looks like the MZ has gotten less drifty after the alignment on Friday.

Attachment 1: Untitled.png

1159

Mon Nov 24 16:43:34 2008

Alex and Jay took away some computers from the racks

I was over at Wilson house and saw Jay and Alex bring in 3 rackmount computers. One was a Sun 4600 and
then there were 2 3U black boxes. I got the impression that these were the data concentrators or
data collectors or framebuilder test boxes. They said that they got these from the 40m and no one was
in the lab to oppose them except for Bob and he didn't put up much of a fight.

Everything looks green on the DAQ Detail and RFM network screens so perhaps everything is OK. Beware.

1158

Sat Nov 22 10:55:51 2008

Caryn

Drum modes Lock-In settings changed

I unhooked the MC Demod Board's Qmon signal from the Lock-In. Set the demodulation frequency to 31.11Hz with 1V amplitude, and
put the output into MC_DRUM1. DTT showed a ~30Hz peak. Dataviewer showed signal with amplitude ~20,000.
Otherwise the settings were as Rana had them: Time Constant-100us,24dB/Sensitivity-200us/Low Noise
Want to check if Lock-In frequency drifts.

1157

Fri Nov 21 21:28:32 2008

A few minutes after restarting fb0 for the Guralp channels, the DAQAWG lights went red on the DAQ screens.
Why?? I chose revival procedure #3 for c0daqawg from the Wiki and it came back in a couple minutes.

1156

Fri Nov 21 21:20:24 2008

Guralp noise measurement

This is the spectra and time series of the Guralp channels along with the Ranger (MC2). Looks like we could reduce the gain
on the ranger. The Guralp channels run into ADC noise around 40 Hz (which is OK). We'll have to look at the weekday trends
to see if they saturate.

Attachment 1: a.png

1155

Fri Nov 21 20:29:43 2008

rana, alberto, rob

Mach Zender alignment

Quote:

So now the MZ alignment seems good; Alberto is on the MC periscope alignment like a cheap suit.

And alignment is now mostly done - MC locks on the TEM00.

                 REFL_DC

Unlocked           4.50  V
Locked noWFS       1.30  V
Locked + WFS       0.42  V

and the 29.5 MHz modulation depth is really small.

We should be able to rerun the Wiener analysis on this weekends MC data.

I don't know what our nominal StochMon numbers now are, but after Alberto tweaks up the alignment he can tell us if the RFAM has gotten any better.

1154

Fri Nov 21 19:47:26 2008

Guralp noise measurement

and here's the spectra with them connected - from the coherences, it looks like it needs to be rotated by 90 deg.

I'll next rename the channels to fix this so that we get good seismic data over the weekend with the MC.

Attachment 1: a.png

1153

Fri Nov 21 17:27:47 2008

Guralp noise measurement

Here is the data from the Guralp Seismometer for the past day or so, before I fixed the VERT-1 channel. The NS and EW show what's going on in the world, and VERT is measuring essentially the noise of the box, through the ADC, in counts.

Attachment 1: guralp_vert_shorted.jpg

1152

Fri Nov 21 16:52:48 2008

Guralp seismometer's Channel Problems are solved

PROBLEM noticed earlier this week: It looked like one of the seismometer channels (VERT-1) wasn't working, no matter how I put which channel into which input of the PEM ADCU. Watching the channel on Dataviewer, it looked like the ADC was measuring VERT-1 to be zero (actually measuring zero, not digital noise-type zero). I had checked the ADC by putting in a sine wave with a function generator, and saw on Dataviewer the wave I expected, so I knew that I had the correct channel, and that the channel was good.

SOLUTION: This afternoon I took the box out of the rack and opened it up. As soon as I opened it, I saw that I had left something inside the box which was causing the problem. Back when we were measuring the noise of the box, to ensure that it is lower than the ADC's noise, Rana and I had shorted the test points on the input of the VERT-1 channel with a little piece of wire. It turns out that I had closed up the box without remembering to remove the wire.

CONCLUSION of the story: I took out the piece of wire, and now all three seismometer channels (VERT-1, N/S-1, E/W-1) all work, and all detect me jumping around near the BSC. Since the seismometer breakout box reads a differential measurement, and since the input test points were connected, it was indeed measuring zero. Zero equals zero is all well and good, but it's even better now that it's measuring actual seismic motion.

1151

Fri Nov 21 16:11:26 2008

rana, alberto, rob

Mach Zender alignment

The Mach Zender's dark port DC voltage had gone up too high (~0.5 V)and was turning yellow
on the screen. I re-aligned by touching the knobs on the 166 MHz path. Doing alignment after the
166 EOM had very little effect. The main improvement came from doing yaw on the turning mirror
just ahead of the 166 MHz EOM; this is the one which as no adjustment knobs (duh).

During this procedure, I had the MC off, the ISS off, and the MC autolocker off. After finishing
the alignment, the power on the ISS PDs had railed and the dark port power was ~0.29 V. So we
put in a ND0.2 on the ISS path and now the voltages are OK (~2 V on each PD). We have to remove the
ND filters and change the first ISS turning mirror into a ~10-20% reflector.

So now the MZ alignment seems good; Alberto is on the MC periscope alignment like a cheap suit.

Attachment 1: PB210051-1.JPG

1150

Fri Nov 21 16:03:50 2008

I found some black & red "Ninja" alkaline AA batteries in the battery charger. This is dangerous. Please
do not put alkaline batteries in there, only Nimh. If you need help with the battery charger you can
come and talk to me or Rob and we can help you out getting started.

1149

Thu Nov 20 09:37:39 2008

This 12 days plot shows that it can hold lock if the daily temp variation is not more than 3/4 of a degree C
The MZ is happy if it's HV is above 100V

Attachment 1: mztemp.jpg

1148

Wed Nov 19 18:12:35 2008

new channel for MC drum modes

I set up the lockin to take the MC Demod Board's Qmon signal, demodulate it at 27.5 kHz, and
put the output into a DAQ channel (I think its either MC_DRUM1 or MC1_TEMPS). However,
the MC_DRUM channel doesn't look like its getting anything in the DTT although it looked fine
on a scope. I used the 'sensitivity' setting of the lockin to make the demodulated signal
large enough but not so large that it would saturate the ADC (+/- 2V).

1147

Wed Nov 19 18:02:18 2008

All the Marconi Set to the Rubidium Frequency Standard

Not sure what was going on before. I changed the frequency counter to use an AC coupled input, and had it average
for 50 seconds. The output now agrees with the Marconi front panel to less than 1 Hz. Its still not 0.000 Hz,
but not bad.

1146

Wed Nov 19 10:32:11 2008

Alberto

All the Marconi Set to the Rubidium Frequency Standard

I placed the SRS Rubidium FS275 over the PSL rack, next to the frequency counter. This one and the Marconi on the PSL rack have been connected to the 10MHz output of the frequency standard. I set also the first Marconi, the one that used to drive the others, to external, direct frequency reference. Now it reads 166981718 Hz versus 166981725 Hz measured by the frequency counter: 8 Hz difference.

1145

Tue Nov 18 19:44:53 2008

Alberto

X Arm Cavity "Negative" FSRs Measured

General

Previous measurements on the X arm cavity revealed a shift of the frequencies of the cavity resonances from where one would expect these to be by just looking at integer multiples of the cavity FSR. In particular, plotting the resonant frequencies versus the order of their occurrences while sweeping the laser frequency (in our case that of the beat between the two lasers), the linear fit of the data contained an unwanted offset:

resonant_frequency = n x FSR + offset

In part, we attributed this offset to the local oscillator of the PLL, the Marconi, which was not referred to an absolute frequency clock.
For that reason, I connected the Marconi to the RS FS275 which uses the 1PPS from the GPS to generate a 10 MHZ reference signal, and then scanned the cavity again. This time I started from negative beat frequencies, that happen when the frequency of the secondary laser is smaller than the main laser's, to positive frequencies. The way I made sure of the sign of the frequency was looking at the effect of changing the temperature of the NPRO. I decided that negative frequencies where those for which an increase in temperature lowered the beat frequency and positive frequencies those for which increasing the temperature made the beat frequency go up.
I then plotted the data and obtained the attached plot.

The offset was reduced to about 80 Hz (from more than 200 in the previous measurements). I think the residual offset has to do with something that happens in the cavity, something, as Koji found out, related to the alignment of the mirrors.

Thanks to the more data points, the measurement of the FSR improved to (3897627 +/- 5) Hz, which would let us know the measure of the cavity length with an error of 50um, if it weren't for the offset. I have to understand whether and how to take this into account to determine the precision in the cavity length. I guess it depends on whether it is real or it is still a systematic error due to the measurements.

Attachment 1: 2008-11-17_Linear_Fit.pdf

1144

Tue Nov 18 19:37:23 2008

MC1 OSEM signals sign flipped and c1susvme1 restart problem

Around 2PM, MC1 started to swing crazily.
The damping feedback was not working and it was actually exciting the mirror wildly.
It turned out that the sign of the UR and UL OSEM signals flipped at that time.
Restarting c1sosvme fixed the problem.

While I was looking for the cause of the problem, c1susvme1 and c1susvme2 failed several times.
I don't know if it is related to this problem.
Now it is not trivial to restart c1susvme1. It fails to restart if you just power cycle it.
Alberto and I had to connect an LCD and a keyboard to it to see what was going on. After pushing the reset button on the front panel,
I had to press Ctrl+x. Otherwise, the state LED of c1susvme1 stays red and nothing happens.
After Ctrl+x, the boot screen came up but the boot sequence failed and an error message something the following was shown:
"PXE Boot failed, check the cable"
So I swapped the network cable with c1susvme2, which was already up and running.
This time, c1susvme1 started fine and surprisingly, c1susvme2 stayed alive.
Currently, both c1susvme1 and c1susvme2 are up and running with the LAN cables swapped.
We have to check the LAN cables.

1143

Tue Nov 18 13:28:08 2008

Caryn

DAQ

new channel for MC drum modes

Alberto has added a channel for the Mode Cleaner drum modes.
C1:IOO-MC_DRUM1
sample rate-2048
chnum-13648

1142

Mon Nov 17 20:47:19 2008

Caryn

Summary

General

Drove MC at 28kHz to excite drum modes

Rana, Alberto and I observed drum mode frequencies at 23.221kHz(MC1), 28.039kHz(MC2), 28.222kHz(MC3) while driving the mode cleaner. We observed no peaks when we didn't drive the mode cleaner. We used the SR785 to send a ~80mV noise signal in the 28-28.2kHz band to the mode cleaner mirrors via 1Y4-MC1,2,3-POSIN. Then we looked at 1Y2-Mode Cleaner-Qmon on the SR785 and saw peaks.

1141

Mon Nov 17 16:59:22 2008

Seismometer hooked up, reading channels on DataViewer

Alberto, Jenne

The Guralp Seismometer is (finally) hooked up to the PEM ADCU. Alberto helped me make channels in the c1pem1 .ini file, which correspond to:

Guralp1 VERT = channel 9 on PEM ADCU = C1:PEM-SEIS_MC1_VERT
Guralp1 NS = channel 10 on PEM ADCU = C1:PEM-SEIS_MC1_NS
Guralp1 EW = channel 11 on PEM ADCU = C1:PEM-SEIS_MC1_EW

We also renamed the Ranger seismometer's channel to C1:PEM-SEIS_MC2_Y from C1:PEM-SEIS_MC1_Y, since tomorrow I'll move the Ranger Seismometer to be underneath MC2's chamber (it's currently sitting somewhere in the middle of the Mode Cleaner).

I can see the VERT and NS channels with dataviewer, but EW looks dead. I need to figure out if this is a bad cable thing, or if the ADC channel is no good, or if something in the box on that channel is no good. All 3 channels were tested and working after all the soldering was completed by Caryn, but something may have come undone while putting the box into its new place in the top of 1Y1. (In dataviewer, it looks like the EW channel is just floating, and not connected to anything.)

Plan of Attack:
* figure out why EW looks dead on Dataviewer
* redo Rana's static Wiener filter analysis, now that we have 2 seismometers (1 Ranger and 1 Guralp)
* work on adaptive Wiener filtering with the Guralp

1140

Mon Nov 17 15:07:06 2008

I used MATLAB's system identification tool box to estimate the response of the reference cavity, i.e. cavity pole.
What I did was basically to estimate a model of the RC using the time series of the measured input and output power.

First, I prepared the input and output time series for model estimation.
The input is the input power to the RC, which I produced by inverting the PBS reflected light power and adding an offset
so that the signal is zero at t=0. Offset removal was necessary to make sure that the input time series does not give an
unintentional step at t=0.
The output time series is the transmission power of the RC. I also added an offset to make it zero at t=0.
Then I commanded MATLAB to compute the response of a first order low-pass filter to the input and try to fit
the computed response to the measured output by iteratively changing the gain and the cut-off frequency.
("pem" is the name of the command to use if you are interested in).

The result is shown in the attachment.
Blue curve is the input signal (I added a vertical offset to show it separately from the output).
The green curve is the measured output (RC transmission). The red curve is the response of the estimated model.
The estimated cut-off frequency was about 45kHz.

You can see that the red curve deviates a lot from the green curve after t=15usec.
By looking at this, I realized that the bandwidth of the RC cavity servo was too high.
The time scale we are looking at is about 50kHz whereas the FSS bandwidth is about 400kHz.
So when the input light was cut off, the error signal of the FSS becomes meaning less and the
input laser frequency was quickly moved away from the resonance. This is why the green curve does not
respond to the large peaks in the blue curve (input). The cavity was already off-resonance when the input power
showed bumps.

Since the red curve matches nicely with the green curve at the very beginning of the ring down, the estimated 45kHz
cavity pole is probably not that a bad estimate.

To make a better measurement, I will try to reduce the bandwidth of the RC servo by using only the PZT actuator.
If there were no ringing in the input light power, we wouldn't have to worry about the bandwidth of the servo because our
feedback is all made to the laser, not the cavity length.
In order to reduce the ringing in the input power, I asked Bob to make new HV cables using HV grade coax cables.

Attachment 1: Fit.png

1139

Mon Nov 17 11:01:15 2008

Alberto

HowTo

Calibrating the Frequency Standard of the Marconi

I locked the SRS Rubidium Frequency Standard FS275 to the the 1pps from the GPS. The specs from the manual provide a frequency accuracy of 5x10^-11, that is 5x10-4 @ 10 MHz, since this is the reference signal frequency we're are going to use.
The Marconi internal frequency standard is provided by a TCXO oscillator. The instrument can be set in either one of these ways: 1) Indirect Synchronization, by which the internal TCXO is phase-locked to the external frequency standard (i.e. the SRS FS275 in our case) 2) Direct Sync, in which the internal TCXO is bypassed and the frequency standard is the external one.

I checked the specs of both frequency standards and found:

SRS FS275: 5x10^-11 -> 5x10^-10 Hz @ 10 MHz

Marconi: here what the data sheet says is that "the temperature coefficient is 7 in 10^7 in the temperature range between 0 and 55 C" and so should be also the frequency accuracy.

The SRS FS275 seems more accurate than the TCXO therefore I'm going to set the Marconi on the direct external mode.

Attachment 1: 2023ASeriesOperatingManual.pdf

Attachment 2: SRS_FS275_Rubidium_Frequency_Standard.pdf

1138

Fri Nov 14 22:40:51 2008

Quote:

I'll check it with Bob.

Quote:

2) the EO has to have a resistor on it to prevent ringing due to the impedance mismatch.

Did you use a shunt or series resistor ?
If shunt, I guess it has to have a huge heat sink.
Actually, DEI says the pulser does not require any external shunt/series resistors or impedance-matching network.
Looks like it is not true ...

Quote:

3) We needed ~3.5 kV to get the EO shutter crystal to flip the light by 90 deg.

Yes, I adjusted the voltage to maximize the power change and it was about 3.5kV.

1137

Fri Nov 14 20:35:47 2008

To make the DEI pulser make a fast pulse on the EO shutter EOMs, we had to make sure:

1) the cable had a high voltage rated dielectric. cheap dielectrics show the 'corona'
effect, especially when there is a bend in the cable.

2) the EO has to have a resistor on it to prevent ringing due to the impedance mismatch.

3) We needed ~3.5 kV to get the EO shutter crystal to flip the light by 90 deg.

1136

Fri Nov 14 19:20:42 2008

Thanks to Bob making the high-voltage BNC cables for the HV pulse generator, I was able to operate the EOM in front of
the reference cavity.

The conceptual setup is the following:

[HV pulse] ----+           +-->-- [PD2]
               V           |
->--[HWP]->-- [EOM] -->-- [PBS] --<->-- [QWP] --<->-- [Reference Cavity] -->-- [PD1]
                           |
                [PD3] --<--+

The high voltage pulse rotates the polarization of the light after the EOM. When the HV is applied, the PBS reflects most of the light
into PD2 (Thorlabs PDA255), shutting down the incident light into the cavity.
The transmitted light power of the reference cavity is monitored by PD1 (PDA255). The reflected light from the reference cavity
is monitored by the DC output of the RF PD (PD3). PD3 is low-passed so the response is not fast.
Thorlabs says PDA255 has 50MHz bandwidth.

The attached plot shows the time series of the above PD signals when the HV was applied.
Input Pulse (blue curve) is the input to the HV pulse generator. When it is high, the HV is applied.
"PBS reflection" (red) is PD2. "Reflection" (green) is PD3. "Transmission" (light blue) is PD1.

The red curve shows huge ringing. At first I thought this was caused by the bad response of the PD.
However, the same ringing can be seen in the PD3 and the peaks match very well.
When red curve goes down the green curve goes up, which is consistent with the energy conservation.
So it looks like the light power is actually exhibiting this ringing.
May be the HV pulse is distorted and the voltage across the EOM is showing this ringing.
I will check the input voltage shape to the EOM using a high impedance probe, if possible.

The green curve shows a slow decay because it has a long time constant. It is not an actual
trend of the reflected light power.

The RC transmission power shows some peaks, probably due to the ringing in the input power.
So just fitting with an exponential would not give a good estimate of the cavity pole.
Even though, we should be able to de-convolute the frequency response of the reference cavity
from the input (red curve) and output (light blue curve) signals.

Attachment 1: RingDown.png

1135

Fri Nov 14 17:41:50 2008

Omnistructure