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IDup Date Author Type Category Subject
  151   Fri Jul 3 21:26:13 2009 AidanComputingDAQDAQ Map medm screen - added channel frame acquisition status

Quote:

I've created an medm screen that displays the current data channels associated with each of the connectors on the front of the DAQ. Basically its supposed to make it really easy to figure out what each channel in the DAQ physically corresponds to. I've added a link (DAQ MAP button) to it on the main medm screen

Eventually this should be automatically generated every time we rebuild the front end. I'd also like to include an indication on there of the units of each channel and whether they are in the frame or not.

medm screen: /cvs/cds/caltech/medm/c2/atf/C2ATF_DAQ_MAP.adl

Please do not edit this screen in the medm editor. I've added some comments to the file and moved the definition of each of the channels to the end of the file. The comments get erased when the screen is edited and the channel definitions get moved back to different places in the file.

 

 

I've added some indicators to the DAQ_MAP medm that show whether channels are saved to frame ("SAVED") or not ("LOST"). I'll have to add a routine to the frame builder start up so that these are updated whenever the frame builder is rebooted.

Attachment 1: C2ATF_DAQ_MAP_v1.1.png
C2ATF_DAQ_MAP_v1.1.png
  152   Sat Jul 4 12:42:06 2009 Aidan ComputingDAQDAq Map screen complete - just need to work out how to generate it automatically now

I've finalized the DAQ_MAP screen. All the current channels are accounted for. I've added some standard LIGO medm screen paraphenalia, such as the information button and the title bar.

I'd like to incorporate this into the build of a front end so that this screen is generated automatically. I'm a bit stumped as to how to get the LOST/SAVED indicators to work automatically. Maybe we can write something that will run in the startup of fb0.

A couple of extra notes:

1. The names of the channels in the frame builder do not exactly match the names in EPICS. This makes it impossible to drag and drop channel names into data viewer. Example:

C2:ATF-QPD1_SEG1 is the  channel defined in Simulink. C2:ATF-QPD1_SEG1_INMON is the channel as it appears in EPICS and C2:ATF-QPD1_SEG1_IN1_32768 is the channel as it appears in the frame builder. Can we add a channel in the frame builder that has the same name as the corresponding EPICS channel?

2. There seems to be a problem with CH32. It's working, in the sense that the channel exists, but when I plug the signal generator into the corresponding BNC connector on the DAQ I don't see any response on EPICS. Need to triple check that I haven't done made a typo anywhere.

Attachment 1: C2ATF_DAQ_MAP_v1.11.png
C2ATF_DAQ_MAP_v1.11.png
  153   Mon Jul 6 15:31:07 2009 Aidan, AlastairMiscGeneralEquipment moved from 58C

The following equipment was from 58C (old mesa beam lab) into 58D during the clean out of the former lab.

2x SR560s ([Ligo Project Property (LPP) C20862, Caltech 44961], [LPP: n/a, Caltech 44782])

2x Phillips PM 5193 programmable function generators (0.1 - 50MHz): ([LPP: n/a, Caltech 9313], [LPP: C20365, Caltech: 1348])

1x SRS DS345 function generator (<30MHz): (no tag - serial # 36560)

1x Tektronix AFG3102: (no tag - serial# AFG3102 C020795)

1x HP 8656B signal generator 1-990MHz: (LPP: n/a, Caltech 23616)

These have all been labelled "John Miller Lab" to indicate where they came from. (None of the equipment was plugged in)

  154   Mon Jul 6 16:59:47 2009 Michelle Stephens, Connor MooneyLaser Power Output of 495 mW NPRO

We characterized the power output vs. drive current of the 495 mW NPRO laser for the gyro experiment. The current supply  goes up to 1.00 A. Here is our data:

C = [0.46 0.52 0.60 0.66 0.74 0.80 0.88 0.94 1.00];
Pd = [2 18 38 55 71 93 110 125 146];
Pu = [2 20 39 56 72 94 110 126 147];

C is drive current, Pd is lower limit on power output in mW, and Pu is upper limit.

We graphed the results and fit a line to it. The slope is 261.5 mW/A, and the intercept is -118.2 mW. The graph is attached.

directory is: \users\cmooney\Power495mW.m

Attachment 1: PowervCurrent495mW.pdf
PowervCurrent495mW.pdf
  155   Mon Jul 6 21:03:47 2009 DmassLaserFiberNPRO beam width divergence measurements

Quote:

We used the BeamScan to characterize the divergence of the NPRO laser as a function of distance. Measurements were taken at (1/e^2)*Imax. We then fit the data to the function characteristic of gaussian divergence to find the location and size of the waist. The results are shown graphically in the attached file. Extrapolating, we found that the waist is 21.5 cm behind the laser aperture, and the (virtual, assuming that the laser beam encounters a diverging lens before the aperture) waist size is 124 micrometers.

 

Here is our data:

The distances, measured in inches from the base of the laser, are

[0 0.5 1 3 5 7 9 11 13 15 17 19 21 23 25]. The distance from the aperture of the laser to the base is 0.75 inches.

The beam sizes, measured in micrometers along one axis, are

[1334 1399 1542 1655 1968 2234 2537 2785 3063 3359 3638 4001 4253 4561 4708]

 

The directories for each of the Matlab files used to generate a graph of the data and carry out a least-squares regression are

/users/cmooney/BeamScans.m

/users/cmooney/myfun.m

 In general, zip and upload your files and matlab code. You or someone like you may want it later, and may really want to be able to get it remotely.

  156   Tue Jul 7 09:26:48 2009 AidanComputingDAQFrame builder not restarting ...

 

I tried to reboot the frame builder last night, as below, and now it won't restart and I can't log into it. If I can find the box then I can try to physically reset it.

[controls@ws1 ~]$ telnet fb0 8087
dadq> shutdown
  157   Tue Jul 7 15:16:35 2009 AidanComputingDAQFrame builder not restarting ... fixed!

Fixed!

The problem was a typo that had cropped up in /cvs/cds/caltech/chans/daq/C2ATF.ini when I was editing this file. I had to fix that file and reboot oms to get the frame builder working again. Now it appears to be fine - I can telnet into fb0 again.

 

Quote:

 

I tried to reboot the frame builder last night, as below, and now it won't restart and I can't log into it. If I can find the box then I can try to physically reset it.

[controls@ws1 ~]$ telnet fb0 8087
dadq> shutdown

 

 

 

  158   Tue Jul 7 16:49:05 2009 Michelle Stephens, Connor MooneyLaserGeneralNoise Measurements

We used an SRS Spectrum Analyzer in parallel with an oscilloscope to measure various sources of noise in the 495 mW NPRO laser. We sent the beam into a PDA10CS photodetector and fed that signal to the spec analyzer and the scope. We measured the dark noise, and then the total noise at 2 mW, 4 mW, 7mW, and 9mW. We then did a theoretical calculation for the shot noise, as follows:

N = (Po*dt) / (h*f)

dN = sqrt(Po*dt / h*f)

dE = sqrt(h*f*Po*dt)

dI = dE*(Responsivity of PD)

dV = dI*(Gain of PD)

We plotted all three of these noise sources in matlab. The plot and the code are attached. The directories are:

/users/mstephens/NPRONoise.m

/users/mstephens/495mW_NPRO_Noise.pdf

 

Attachment 1: 495mW_NPRO_Noise.pdf
495mW_NPRO_Noise.pdf
Attachment 2: NPRONoise.m
load -mat SRS003.MAT
load -mat SRS005.MAT
load -mat SRS006.MAT
load -mat SRS007.MAT
load -mat SRS008.MAT

h = 6.626E-34;
mu = 3E8/1.604E-6;
deltaT = 1.0;

... 94 more lines ...
  159   Wed Jul 8 10:36:44 2009 MichelleMisc Week 3 Update

We have mirrors! And clamps! And posts! In short, everything we need to actually put all the optics in their proper places. Thus, this week I have successfully placed the steering mirrors and the high reflectance mirrors into their mounts without touching/breaking any of them, and soon I'll be clamping them in their proper locations.

Connor and I  found out that Aidan's laser isn't behaving itself. The manufacturer specifies the waist as being in a different location than where we calculated it to be. We sent the beam through a half-wave plate and then a polarizing beam splitter and then measured the power along each axis, and the ratios are strange. We can't get the beam to be entirely transmitted along one axis by rotating the half-wave plate, like we should be able to if the beam is coming out linearly polarized. So the hypothesis is...it's not coming out linearly polarized. It may be elliptical. For the time being we're going to split the beam from the other NPRO and use it for both experiments, at least while the alignment is taking place. In the case of the gyro, we'll actually be feeding back to the laser and altering its frequency, so we'll definitely need separate lasers for each experiment at that time.

The 495 mW NPRO's SOP has finally been (mostly) approved and it first lased on Monday. This laser's power supply is a bit weird - the display for the power it thinks the laser is putting out doesn't match at all with what the powermeter actually says the laser is putting out. So we're not paying attention to the power display. The drive current goes up to 1.00 A, and at this maximum current, the laser is putting out ~150 mW. Apart from not being able to get a higher power than this, the laser is fairly well behaved - the power fluctuations as measured by the powermeter are small. The results of output power vs. drive currentmeasurements are on the eLog.

Connor and I also measured the electronics noise and intensity noise at various different powers, and then did a theoretical shot noise calculation for each of these. The setup and procedure are described in more detail in a recent eLog entry, which also includes graphs and the matlab code used to generate them.

Over the next week I'll be setting up the optics table for a simple PDH lock using a fabry-perot cavity, aligning the laser, and setting up the proper feedback using the DAQ. (Which I'll need to talk to Dmass about).

Oh, and we found out yesterday that Connor and I can't do any hazardous tasks in the lab without supervision, which includes aligning the lasers, even at low power. Aidan and Alastair will both be gone from tomorrow until next week Friday, so this poses a slight challenge. Hopefully Dmass will be around?

That's about it for now, I think.

  160   Wed Jul 8 10:46:58 2009 ConnorMiscGeneralWeekly Report #3

          The majority of this week has been spent learning about sources of intensity noise and the methods we use to characterize it.  The sources that I focused on were the "electronics noise" associated with various instruments (this week the instrument used was a photodetector, contributing fluctuations in intensity called "dark noise"), shot noise, and the noise produced by source itself (in our case, a 495 mW NPRO Laser).

          The theoretical method of characterizing a noisy time series is called a Power Spectrum, which is defined as the Fourier transform of the series' autocorrelation.  Intuitively, this is a frequency-domain representation of the extent to which a given frequency is represented in the time series.  Experimentally, it is more convenient to take advantage of a couple of theorems relating the Power Spectrum of a time series to its Fourier transform over a finite time interval;  The SRS spectrum analyzer that we used this week calculates the discrete Fourier transform of an input signal over a given time interval, squares that value, and divides by the time interval to get an estimation of the Power Spectrum.  Typically, we run the signal into the spectrum analyzer for many of these time intervals, and the values computed over each of these intervals are averaged.

          We measured the dark noise and the total intensity noise of a 495 mW NPRO laser using a PDA10CS photodetector, and made a theoretical prediction for shot noise based on the output power of the laser.  The data we collected is contained in yesterday's entry.

          Aidan has been working hard on getting the DAQ to its operating point, which will make measurements such as those described above easier to make.

          The plan of action for the upcoming days is to set up a Mach-Zehnder Interferometer for the same laser and characterize the phase noise its beam acquires, hopefully with the assistance of the DAQ.

 

  162   Wed Jul 8 17:29:46 2009 Connor Mooney, Michelle StephensLaserFiberBeam Divergence of 495mW NPRO

We made a set of beam width measurements of the 495 mW laser using the Beamscan. All values were taken at (1/e^2) of the peak intensity, in micrometers. The distances were taken in units of inches (no metric-based rulers).

Here is our data: 

Distances (in inches): [2 3 4 5 6 7 8 9 10 12 14 16 18 20 22]

Beam Diameters (in micrometers): [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999]

Again, we least-squared fit the data to the characteristic curve parametrized by the waist location and size, and found that the waist size is 178 micrometers, located 4.6 cm. in front of the aperture.

THINGS TO NOTE:

First, DMass mentioned he suspects that the beamscan is impaired, so we're not sure how well it is acting.

Second, Rana noted that the best indicators of the parameters of interest are data points taken far from the waist, where the beam width grows close to linearly with distance.  We took  lots of data points in the nonlinear regime, as seen on the attached plot. It might be a good idea to take more data points further away and refit our data.

Lastly, this laser is more stable than the 1W NPRO, with fluctuations of only 1-3 micrometers around the reported beam width values rather than the 40-50 we saw for the 1W.

The directory for our code is /users/cmooney/Beamscan_495mW.m

Here is the code:

%This is a graphical representation of beam width data taken for the 495 mW NPRO
%Laser, taken on July 8, 2009.

%W1 is the full width at 1/(e^2)*(peak intensity) taken at 1.00A driving
%current (around 150 mW) for the axis A1 as labelled on the BeamScan. Measurements are
%in micrometers.

W1 = [357 364 413 448 528 608 690 758 854 1043 1216 1403 1624 1812 1999];

%S1 is the standard deviation of the measurements given in W1.

S1 = [0.3 0.3 0.4 0.4 0.4 1.2 0.8 0.8 1 1 2.7 2.9 1.6 1.6 2.2];

d = 2; %distance from laser aperture to its base, from which it is easier to measure distance
D = [0 1 2 3 4 5 6 7 8 10 12 14 16 18 20]; %distances (in inches) at which measurements were taken
Ds = 2.54*(D+2)/100; %conversion to meters

W1s = 0.5*W1/(10^6);
S1s = S1/(10^6);

errorbar(Ds,W1s,S1s,'.')
title('Beam Width vs. Distance from Laser');
xlabel('Distance (m)');
ylabel('Beam Width (m)');

%This is a brief program to assist in the measurement of width of a
%Gaussian beam. Its wavelength is 1064 nm.

xdata = Ds;
ydata = W1s;
 
a0 = [.0001, .2]  % Starting guess
[a] = lsqcurvefit(@myfun,a0,xdata,ydata)

w_0 = a(1);
Zo = a(2)
L = 1064*10^(-9);
Dmax = 1;
sh = 0.35;
dt = (Dmax+sh)/10000;
Z = -sh:dt:Dmax;

Wt = w_0*(1+(((Z+Zo).*L)/(pi*w_0^2)).^2).^(1/2);

hold on;
plot(Z,Wt);

Attachment 1: beamdiv495mW.pdf
beamdiv495mW.pdf
  163   Wed Jul 8 19:05:49 2009 DmassLaserPSLMode Matching and the PMC

I measured the waist of the input beam to the PMC after putting the mode matching lenses back. In the process of this, I noticed some problems with the beamscan.

I played with the beamscan axis until I found something that looked gaussian to the eye, and took a series of measurements, and fit the data (see attached).

 

 

I calculated the expected power loss from mode mismatch a la Dana Anderson's paper on cavity (mis)alignment and got some results:

I get estimates for power losses of:

6% due to waist position mismatch

12% due to waist size mismatch

NOTA BENE: The formulas in the Anderson paper start to break down as the linear approximations break down, which is happening for us...

 

If b is my mismatch parameter in waist position, my condition for the linear approximation is:

lambda*b/(pi*waist^2) <<1          but the LHS quantity is .492

and if w0' and w0 are my input beam and cavity waists, respectively, my condition is:

w0'/w0 - 1 <<1                            but the LHS is .34 here

Summary: I don't know how bad the Anderson formulas are in this regime of mismatch, but I can clearly do better in my mode matching. Next step: mode match/fix lens positions

 

Attached Image:

RED is roughly the PMC waist and position (based on the 40m PMC's waist - we have no measurement of this PMC's waist size yet afaik: put this on to do list)

GREEN is weighted least squares fit

BLUE is the data

 

Attachment 1: PMCbeamwaist.pdf
PMCbeamwaist.pdf
  164   Thu Jul 9 02:24:07 2009 ranaLaserPSLMode Matching and the PMC
The Anderson formulas are sort of OK in this regime but should only be used to estimate the mismatch.
Of course, its easy just to do the overlap integral and get the exact number. Its of limited use, since
the cavity will often not lock at the right point of the mismatch is so big.

Another possible method is to turn the power way down (less than 1 mW) and then scan it and fit
for the modes in transmission. The low power is to avoid thermal self-locking distortion of the fringe.

One can use knowledge of the PZT coefficient and the wavelength of the laser and modulation frequencies
to determine the cavity's g-factors and therefore the waist sizes. The cavity g-factor is defined as
g = 1 - L/R.
  165   Thu Jul 9 10:45:16 2009 AidanComputingDAQAlex's frame builder problem diagnosis ...

 

This from Alex: 

 

The filesystem is full. If you look at the log messages:

[controls@oms fb]$ pwd
/cvs/cds/caltech/target/fb
[controls@oms fb]$ tail -5 logs/daqd.log.19816 
[Thu Jul  9 10:07:51 2009] Couldn't open full frame file
`/frames/full/data38/.C-R-931194464-16.gwf' for writing; errno 28
[Thu Jul  9 10:07:51 2009] Couldn't open full trend frame file
`/frames/trend/second/data2/C-T-931194420-60.gwf' for writing; errno 28
[Thu Jul  9 10:08:07 2009] Couldn't open full frame file
`/frames/full/data38/.C-R-931194480-16.gwf' for writing; errno 28
[Thu Jul  9 10:08:23 2009] Couldn't open full frame file
`/frames/full/data38/.C-R-931194496-16.gwf' for writing; errno 28
[Thu Jul  9 10:08:39 2009] Couldn't open full frame file
`/frames/full/data38/.C-R-931194512-16.gwf' for writing; errno 28
[controls@oms fb]$ df -h /frames/
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                     275G  261G     0 100% /frames


I stopped the frame builder for now until we figure out the data
directories. Can I delete all the data in /frames/full and recreate a new
set of directories? Otherwise this is too messy to rearrange. Let me know.

-alex


On Wed, 8 Jul 2009, Aidan Brooks wrote:


Hi Alex,

I fixed the problem with being able to telnet into fb0. There was just a typo in the file:
/cvs/cds/caltech/chans/daq/C2ATF.ini
Once I fixed that the frame builder rebooted just fine.

The problem at the moment is that the data does not appear to be writing to file. If I rebuild the front end from the start, so I go to oms and run the following commands:

cd /cvs/cds/advLigo
make realclean
make atf
make install-atf
make install-daq-atf
make install-screens-atf

And if I edit the file C2ATF.ini so that a single channel, e.g. C2:ATF-CTRL_PMC_REFL_IN1_DAQ is set to acquire. 

and killatf, followed by startatf and reboot the frame builder

Then: the front end starts okay and I can see signals in the EPICS screen that make sense. I can run StripTool and see the real time time series of a channel, I can start dataviewer and see C2:ATF-CTRL_PMC_REFL_IN1_DAQ in the list of fast channels. I can run the realtime viewer in dataviewer and see that channel realtime in a Grace window. However, I cannot get a playback of that channel to work and if I run dtt I can only get a spectrum if I specify a start time for that spectrum within the last (approximately) 30s in the past.

The data rate in the .mdl simulink model is 16K, the data rate in the C2ATF.ini files is 16K, the data rate in the file:
/cvs/cds/caltech/target/fb/daqdrc is set to 16K and there are 120 data directories in the /frames/full directory.

I can't think of any reason why the data is not being written to file. Can you log in and figure out what's wrong? You should be able to get access via controls@131.215.114.183

Thanks for your help,
Aidan.
 

  166   Thu Jul 9 10:46:52 2009 AidanComputingDAQDeleted old /frame/full directories and rebuilt directory structure ...

 

This was also from Alex:

 

Too late, I deleted /frame/full data already, sorry.

So I changed the number of full frames dirs from 120 down to 60 and
restarted the frame builder and c2atf front-end. Looks like the data is
written out to disk now. Please check it out.

Alex

  167   Thu Jul 9 10:48:03 2009 ConnorLaserFiberBeamscan for 1w NPRO

Aidan suggested that we try to characterize the beam width of the 1W NPRO again, this time operating the laser at high power and attenuating the beam with a half-wave plate and a polarizing beam splitter.  I aligned the optics such that at full output power (~1.19W), the power incident on the BeamScan is 145 mW.

There are a number of things I noticed about the beam profile around 10" from the laser aperture that I don't know how to deal with, so I decided not to make measurements until working things out.

While the profile of the beam is much cleaner now than it was before when we measured beam width at low power output, the width of the beam seems to depend on the driving current to the laser.  At 1.2A driving current, the beam diameter was roughly 1650 micrometers.  The width dropped down to around 1300 micrometers at 2A driving current, and then climbed back up to 1500 micrometers at full power output with 2.38A driving current.

Also, as David noted, the beam width fluctuated by up to 40 micrometers when moved to different places on the head.

  168   Thu Jul 9 13:29:08 2009 AidanComputingDAQMore from Alex on frame builder disk being full

 Hey Alex,


I've got a couple of questions (just for my own understanding).

- I thought the frames were supposed to overwrite old data. Why then  
did the disk appear full? And is it likely to appear full in future?  
If so how do we deal with it?

I reduced the total number of data directories from 120 to 60. I think the
frame size has increased and  so the disk filled up. daqd program, the
version you have there, erases old frames based on total number of
directories, it doesn't look at the disk full percentage. I have a new
version which doesn't do that, so we may want to install that new version
at some point, especially when you guys decide to upgrade to the latest
real-time code generator software. The new version of daqd/nds is not
erasing anything but simply relies on a cron job to erase old files.

- why did you reduce the number of directories in /frame/full to 60?

Thanks for your help,
Aidan.
 

  169   Mon Jul 13 13:59:19 2009 MichelleLaserGeneralNPRO acting up

I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out.

The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure.

So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

  170   Mon Jul 13 21:39:11 2009 MichelleLaserGeneralNPRO acting up

Quote:

I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out.

The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure.

So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

 We should get back to trending the lab temperature. I think there are some long standing problems with the HVAC setup. It would help to quantify this.

  171   Tue Jul 14 15:08:07 2009 Connor MooneyLaserPSLBeam Divergence of PSL

A while ago, Dmass made some beamscans of the PSL beam after it passed through two lenses. Here is a link to the Dmass Modematching elog.

We wanted to make sure that these measurements are consistent with what we think the incoming beam parameter is.  I wrote a matlab file which works backwards from his data to find the incoming beam parameter using ABCD matrices.  I used the focal lengths indicated on the lenses.

I found a disagreement of 20cm in the PSL waist location with a yesteryear elog entry  Dmass checked to see if my computation matched with his, and got the same result.

The first thing that we thought might have been wrong is that the focal lengths need to be switched, but switching them didn't significantly our change our results (in fact, it made them worse).

We also suspected that the engineering tolerance of the lenses might allow for the difference. I tried changing the focal lengths of the lenses by 10% for both lens orientations, but the computations made only small changes to our original result, so this is probably not the culprit.

 

 

 

  172   Wed Jul 15 10:47:55 2009 MichelleLaserGeneralNPRO acting up

Quote:

I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out.

The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure.

So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

 I took the power supply over to the 40m to see if Alberto's laser would work when hooked up to it. It did, so I suspect that the problem lies with the laser rather than the power supply. Alberto was able to get double the drive current that we were getting, so that is also suspect. He said the "ADJ" readout (power adjustment) on the supply was usually set to zero, but when the "Pwr" readout (supposedly the power coming out of the laser) is changed, it changes the ADJ and drive current and anything else which would obviously be associated with power. I hooked up the power supply to my laser again and here's what I found:

-It lases for short periods of time, usually <5 mins, before it stops.

-It lases for longer periods of time at higher drive currents.

-I still can't get more than 1.02 A and less than 0.30 A out of the power supply.

-The "Pwr" display on the supply still doesn't correspond to the power as measured by the Ophir powermeter.

My next steps are to see if Alberto can come and take a look, in case I'm doing something on the operator side which is obviously wrong. I will also consult with Rana.

  173   Wed Jul 15 12:36:17 2009 Connor MooneyMiscGeneralWeekly Report #4

     Aidan was in Hanford this week, so I switched gears and worked mostly on modematching the 35W PSL with Dmass.  This requires passing the beam through a couple of lenses to alter the waist size and location before it enters the PMC. Last year, he took some beamscans post-lenses. We wanted to see if this data matched with the pre-lens beam parameter. I used ray transfer matrices to perform the inverse calculation. We found a mismatch between the calculated and expected waist location, which could not be fully explained by the engineering tolerance of the lenses or by the lens orientation.

     Dmass also noticed something funny about the head of one of the lenses, so he made some changes to that and made more beamscans that we will look at.

     There are a number of objectives for the upcoming week:

     1) We believe that the 1W NPRO is elliptically polarized. I learned about Jones vectors and Jones matrices, which are a convenient linear-algebraic representation of a beam's polarization and how it changes as it passes through various optics. The beam can be linearly polarized by passing it through a quarter-waveplate (QWP) whose fast axis is correctly angled. To test this, I will pass the beam through a QWP, and aligned a half-waveplate (HWP) and polarizing beamsplitter (PBS) to find its extinction ratio for various QWP angles. (The extinction ratio is the ratio of the minimum to maximum transmitted powers of the beam as the HWP is rotated.)

     2) I'll work on coupling the 1W NPRO into a 50m fiber.

     3)I'll align a Mach-Zehnder interferometer to measure the phase noise of the 1W NPRO, and also single pass the beam in one arm through the 50m fiber and characterize the phase noise it acquires.

    

 

  174   Wed Jul 15 14:40:44 2009 MichelleLaser NPRO ... fixed?

Alberto came over to have a look at the laser and discovered that the diode temperature was continuously increasing the longer the laser was kept on. The crystal temperature remained constant. He turned off the laser and shut the shutter, jiggled the cable connected to the laser a bit, and turned it back on. Lo! The temperature no longer increased...

So for the time being the laser seems to be fixed. If these problems start happening again, however, I may have to do some more rigorous troubleshooting/actually find out what's causing the problem.

  175   Wed Jul 15 16:05:53 2009 DmassLaserPSLPSL Realigned, now better

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

  176   Wed Jul 15 22:13:09 2009 ranaLaserGeneralGyro NPRO
I just came down and got the same behavior. With the diode current cranked up all the way, the output power was 700 mW.
This is good, since this is supposed to be a 700 mW NPRO.

I recommend that we pick a diode current (whatever we get with ADJ = 0) and stick with it. Use a PBS for changing the power and not the diode current.

In order to actually run the NPRO for extended periods of time we need a heatsink mounted on its side. Otherwise these things get too hot and the TEC for the diode can't keep up. I'll ping Peter King for one, but if he doesn't have one we'll just buy one from a catalog.

The lab temperature also seemed warm, like Michelle noted. The AC controller had the right setting so I think its that the valve in the overhead ducting has gone bad again. It failed twice in the first couple weeks that the lab was opened. I have replaced the battery in the digital temperature sensor and put it on the gyro table. After I lowered the temp. setpoint on the wall by a couple degrees it came down to 72 F. I also re-activated the circular paper temp. recorder and put it on the First Aid kit. Its in 24-hour mode so we can get a trend.

I will call up PMA and tell them we need a temperature consult again.


Also, the lab is not your personal trash receptacle. Please don't store empty cardboard boxes or drinks in there. Put tools back where they go when you're done and don't leave a pile of booties and hats laying on the floor.
  177   Thu Jul 16 04:59:38 2009 DmassLaserPSLRazor Blades!

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Attachment 1: Photo_1.jpg
Photo_1.jpg
Attachment 2: Photo_3.jpg
Photo_3.jpg
  178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

  179   Thu Jul 16 17:43:59 2009 DmassLaserPSLRazor Blades!

Quote:

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

 

I got about a .002" error using a micrometer with my other setup, I expect this will suffice. If the errors in position end up too large I will use the new setup.

  180   Thu Jul 16 17:46:41 2009 DmassLaserPSLPSL Realigned, now better

Quote:

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

 

I will add pictures of what knobs we touched and how much each was turned by here

  181   Thu Jul 16 23:21:40 2009 DmassLaserPSLPSL Diode Powers and temperatures

At Anamaria's request, I recorded the diode powers (and temperatures) of the PSL.

~5 min after power up they were:

temp/power

20C  / 29.8W

23.8C / 28.6W

24C / 25.2W

25C / 27.8W

6 hours later they were

20C / 29.0W

23.8C / 28.1W

24C / 24.8W

25C 27.3W

  182   Fri Jul 17 15:39:31 2009 DmassLaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 Using the setups in the quoted post, I took manual beamscans 23" in front of the PSL enclosure, before the first steering mirror, and fit P = A erf(B*x + C)

 I measured the relative position of my razorblade with a micrometer and calculated the error from an estimated uncertainty of it's angle. This seemed to agree with repeatability of measurements for a given experimental state. Uncertainty < .002"

I watched the Power meter for ~ 60 seconds for each measurement, it fluctuated around some point and seemed to not be drifting @ DC, so the upper and lower error bars of each point included are the bounds of the fluctuation of the power meter. These were less than +/- 5mW about my points, so a fractional uncertainty of about 2% at my maximum power.

 

I got waists of:

Vertical: 799 +/- 4.5 microns

Horizontol 827 +/- 1.2 microns

Attached plot includes data w/ error and functional form of fit

 

As expected, my Chi^2 is "bad" since I am fitting the input beam to the PMC with a 00 mode description of the waist, which ignores all higher order modal content.

Attachment 1: RazorScans.pdf
RazorScans.pdf
  183   Sun Jul 19 09:44:09 2009 AidanComputingGeneralAliases added for standard LIGO tools

 

I've updated the /home/controls/.bashrc file to include some aliases to standard ligo tools. These should now be accessible anywhere from the command line.

alias dtt="/bin/diaggui"
alias dmt="/bin/dmtviewer"
alias foton="/bin/foton"
alias dv="dataviewer"
 
StripTool is already accessible from the command line.

  184   Mon Jul 20 23:19:49 2009 ranaLaserPSLRazor Blades!
Yeah, real micrometer with a reading is > plain screw.
  185   Tue Jul 21 02:09:45 2009 DmassLaserPSLPSL Realigned, now better

Quote:

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

 The following image contains approximations of the changes we made to the PSL steering mirrors (~5 degree accuracy)

Attachment 1: PSLRealignment.png
PSLRealignment.png
  186   Tue Jul 21 18:45:26 2009 ConnorLaserFiberalignment of optics

The 1W NPRO is, for the moment, being used for both the FS and Gyro experiments. Aidan and I began aligning the optics for the FS experiment today.

The beam is first passed through a quarter-waveplate to linearize its polarization. A 50-50 beamsplitter picks off the beam for the Gyro experiment. The transmitted beam (for FS) is then attenuated by a half-waveplate and PBS. We steer the transmitted beam through a lens, a Faraday Isolator, and another lens to collimate it.

A photograph of the setup is attached.

We plan to direct the beam through an AOM and couple it to the fibre so we can characterize the acquired phase noise.

Attachment 1: FSprelimsetup.jpg
FSprelimsetup.jpg
  187   Tue Jul 21 20:39:18 2009 DmassLaserPSLPSL Beam Scans

I took a bunch of scans of the PSL with the Beamscan and compared them with some razorblade occlusion measurements

The first steering mirror after the beam exits the PSL was removed, and data was taken at this point in the beam path.

The numbers for the waist derived from my razorblade measurements are on the plot in green. The disagreement seems not horrible to me.

 

We should still fix the beamscan, and think about buying another (newer) one.

 

I am told that the beamscan axis drawn on the head (labeled "1" and "2"), not the slit axis is what sets the direction of the field you are sampling. Data for both vertical and horizontal spatial modes of the beam are included. There is some ellipticity to the beam that I will have to account for in choosing my (new?) mode matching solution.

 

Error bars are included on the green point, they are just small.

Attachment 1: VertPSLScan.pdf
VertPSLScan.pdf
Attachment 2: HorPSLScan.pdf
HorPSLScan.pdf
  188   Tue Jul 21 20:41:56 2009 DmassLaserPSLRazor Blades!

Quote:
Yeah, real micrometer with a reading is > plain screw.


Converting from flemish ells was hard. I'll just use a mic next time.
  189   Wed Jul 22 09:43:53 2009 ConnorMisc Weekly Report #5

Most of this week has been spent aligning optics for the fiber stabilization experiment.  Part of the setup is shown here

The next step is to couple the beam into the fiber, single pass it and interferometrically beat it with the original signal so we can characterize the acquired phase noise.

Mode matching to various optical elements involves changing the beam parameter (i.e., beam width and radius of curvature) to fit specifications. We do this using lenses. Given the incoming beam parameter, the desired outgoing beam parameter, and lens focal lengths, we can find solutions (lens positions) to the problem.

  190   Wed Jul 22 11:09:45 2009 MichelleMisc Weekly Update 5

Over the course of the past week I've done a few things. When I began alignment I discovered that our laser was periodically shutting itself down. This was a very perplexing problem for about 2 days before Alberto came in with the diagnosis: the diode was overheating. We'll be sending that in to get it fixed, and we'll also put a heat sink on its casing. Hopefully that will be up and running by the time we really need it.

Right now, Aidan's laser is set up with a 50/50 beamsplitter, and then a half wave plate at each output of that. That way we can run the laser at full power, and each of us can independently adjust the power going into our respective experiments. This is working well while we're aligning things, but it clearly won't work long-term - we need to act directly on the laser's frequency to lock it to a cavity. This may not fare so well for fiber noise suppression.

We have our setup mostly aligned. The beam is going through some steering mirrors, through a lens, into the Faraday Isolator, through another set of steering mirros and a lens, and into the EOM. There is very little loss inside the isolator (putting in ~35 mW and getting out 33-34 mW), however I have not been able to get the power at the output of the EOM higher than ~ 24 mW. I don't think this is normal, but I will check that with people who know better than I do. I think it is probably the fault of poor alignment - the aperture is ~ 2mm and it's about 2 cm from the lens in the middle of the table, so it's hard to reach it or even view it properly to see what needs tweaking.

Over the next week I plan to finish the alignment and hopefully get a lock. I'll get a picture up once the rest of the setup is in place and aligned.

 

Oh, and I also helped clean the lab this week. It's pretty shiny, except for the heaps of garbage boxes now sitting in the hallway. We'll take care of that soon.

  191   Wed Jul 22 20:36:37 2009 Aidan, ConnorLaserFiberAligned beam into fiber ... mode-matching needs a little work

Connor and I got the beam aligned into the fiber today. After a little optimization of the fiber coupled XYZ I'd estimate we were getting maybe 10-15% transmission. I'm pretty sure we can improve this with some work. We caculated the input mode (which I will reproduce elsewhere) but it's looking for a mode size of approximately 6.6 microns diameter. With a 10X microscope objective (f = 16.5mm) we want the intput beam to the coupler to be around 3.4mm diameter - which we have.

We mounted the AOM and inserted it into the setup. We should be able to get an 80MHz frequency shifted beam through the fiber tomorrow measure the fiber noise. That same setup can be used in a PLL to suppress the fiber noise.

 

  192   Wed Jul 22 20:40:13 2009 AidanLab InfrastructurefubarFiling cabinet lock engaged ... with no key

This happened mysteriously and had absolutely nothing to with me. The fact that I was the last person to open the filing cabinet before this happened is circumstantial and beside the point.

Will get the lockshop onto this in the next couple of days. In the meantime, just try and exercise your clairvoyance.

  193   Thu Jul 23 07:22:35 2009 AidanComputingCDSChecked out the 40m MEDM screens from SVN to /cvs/cds/caltech/medm/c1

 

As title says ...

  194   Thu Jul 23 07:33:41 2009 AidanComputingCDSAdded C2 MEDM screens to 40m SVN.

 

I've added our medm screens from the ATF to the 40m SVN. They can be found in 

https://nodus.ligo.caltech.edu:30889/svn/trunk/medm/c2/atf/

  195   Thu Jul 23 13:14:03 2009 Aidan, ConnorLaserFiberAOM Aligned, beam matched into fiber, pick off from beam splitter correct size

 

Connor and I have been assembling the FS experiment. The following diagram shows the layout of everything that is aligned at the moment.

We've got the AOM installed and have it aligned to give -1 order when driven at 80MHz (attached image shows main 0th order and -1 order to the right. Not sure what spot up the top is).

Attachment 1: FS_layout_2009_07_23.png
FS_layout_2009_07_23.png
Attachment 2: photo.jpg
photo.jpg
  196   Thu Jul 23 16:05:48 2009 DmassLaserPSLMore Mode Matching

Our lens positions for mode matching into the PMC seem to be based ON LIES. I cannot locate my old data on the first PSL scans and fitting. I have now learned a very important lesson in imitating Aidan.

Since my old "measurement" (quoted number) seems to disagree with what I have found by roughly a sign, I am operating under the assumption that I was simply wrong in the linked entry.

I have plotted our old mode matching solution with the new beam parameters.

I have also found 2 mode matching solutions for the "average" mode coming out of the PSL, one with two 500mm lenses, and an alternative in case we don't have them around.

 

If these do not suffice for our locking needs, we will need to deal with the ellipticity of the beam. I think it will be fine for now based on this.

 

I have included plots of the two offered mode matching solutions, as well as the picture of what we were using for coupling into the cavity.

Attachment 1: OldMMSol.pdf
OldMMSol.pdf
Attachment 2: MMSol500500.pdf
MMSol500500.pdf
Attachment 3: MMSol1000400.pdf
MMSol1000400.pdf
  197   Thu Jul 23 16:31:28 2009 MichelleLaser I've done some things in lab.

Update:

Today I aligned the laser beam through the EOM with something resembling a normal shape at the output. This was tricky. The powermeter isn't giving me very reasonable readouts, the aperture on the EOM is impossible to see with the IR viewer, the EOM is in the middle of the table where I can't really reach it, and it's very close to a focusing lens. The point being that I may have to tweak it a bit, but I really don't want to have to redo the alignment of that particular optic. So no earthquakes for a while.

A note on the power meter: It's been registering anywhere between -6 mW and 11 mW with no beam on it at all. I've been zeroing it before putting it in the beam before each use, but I don't know how much I trust it.

The beam shape coming out of the EOM  is still a bit funny - with one bright beam, and then a very faint ring, so it looks like a ring you would wear on your finger with a diamond on top. I am attributing this to the fact that the beam is slightly larger than the EOM's aperture; I have set it up so the center of the EOM coincides with the beam's waist. I'm also (according to the power meter) getting a high attenuation inside the EOM, but whether this is correct or normal I haven't yet figured out.

We need another mount for a beam splitter, this will go at the input to the cavity. We are also still in need of a quarter waveplate, and Aidan says he has a spare that he won't need to use for a few weeks. Also, CVI doesn't specify the damage threshold for the cavity mirrors for cw lasers, only for pulsed sources. Alastair has sent them an email requesting this information, and once we know that we can send the beam into the cavity at appropriate power levels.

  198   Thu Jul 23 16:55:24 2009 Aidan, ConnorLaserFiberFiber coupling dominance - 19% transmission.

10:10AM : need to align AOM and check RF drive into it.
    AOM - wants < 2W RF Power Level
    Amplifier gain [ZHL-1A http://www.minicircuits.com/pdfs/ZHL-1A.pdf] - 16dB
    Maximum power output (dBm) = +28dBm = 630mW

14:00: Have AOM aligned. 3Vpp amplitude 80MHz signal to power amp gives ~63% diffraction efficiency [-1 order: 100+/-3mW, total: 160+/-3mW]

16:40: -1 order is aligned into fiber - coupler is very touchy and sensitive to misalignments. looks to be good transmission though. 37mW incident, 7mW transmitted - about 19%!

  199   Fri Jul 24 16:59:10 2009 ConnorLaserFiber1W NPRO minimum extinction ratio

The 1W NPRO beam is elliptically polarized. We use a quarter-waveplate (QWP) to linearize the polarization.

7 days ago, I made some measurements of the extinction ratio of the beam for various orientations of the QWP (attenuating the beam with a half-waveplate and polarizing beamsplitter) to find the QWP orientation at which the light is linearly polarized. The minimum ratio occured when the fast axis was between 10 and 15 degrees from the vertical. I've attached a plot of the data, and I will fit it to a curve as soon as I work out which function should describe the data.

Attachment 1: ExtRatio1WNPRO.pdf
ExtRatio1WNPRO.pdf
  200   Fri Jul 24 19:00:37 2009 ranaLaser I've done some things in lab.
Make sure to use only ~5 mW to do all of the alignment.

Turn off the room lights if the power meter is not sitting well at zero.

Instead of the IR viewer, you can use a CCD camera to look at the input to the EOM and its output. You want to just center the beam in the EOM's apertures and then we will do the fine alignment by monitoring the RF AM.

Don't run the cavity with high power yet. Just 5 mW is easily high enough.
  201   Mon Jul 27 17:57:55 2009 DmassLaserPSLMore Mode Matching

Quote:

Our lens positions for mode matching into the PMC seem to be based ON LIES. I cannot locate my old data on the first PSL scans and fitting. I have now learned a very important lesson in imitating Aidan.

Since my old "measurement" (quoted number) seems to disagree with what I have found by roughly a sign, I am operating under the assumption that I was simply wrong in the linked entry.

I have plotted our old mode matching solution with the new beam parameters.

I have also found 2 mode matching solutions for the "average" mode coming out of the PSL, one with two 500mm lenses, and an alternative in case we don't have them around.

 

If these do not suffice for our locking needs, we will need to deal with the ellipticity of the beam. I think it will be fine for now based on this.

 

I have included plots of the two offered mode matching solutions, as well as the picture of what we were using for coupling into the cavity.

 I checked the relative stability of each of the two mode matching solutions here by perturbing the lens positions and focal lengths.

 I used the Anderson formulas <add link> to calculate the power lost to first order into higher order modes. I then altered parameters (lens positions and focal lengths) as noted in the following tables and compared changes in power loss.

 

Solution with f1 = 0.5m   x1 = 0.42m     f2 = 0.5m    x2 = 0.62m    with positions relative to PSL enclosure
Change in Power Loss dx1 = 5mm dx2 = 5mm df1 = 1% df2 = 1% Absolute Loss
Red (Horizontal)  1.9%  0.29%  0.34%  1.4% 10.7%
Green (Average)  0.02%  0.02%  ~0%  ~0% 0.01%
Blue (Vertical)  0.44% 0.09%  0.3% 0.38% 3.38%
Solution with f1 = 1.0m   x1 = 0.47m     f2 = 0.4m    x2 = 0.55m    with positions relative to PSL enclosure
Red (Horizontal) 1.15% 0.76% 0.43% 1.4% 10.07%
Green (Average) 0.02% 0.02% 0.01% 0.06% 0.01%
Blue (Vertical) 0.31% 0.09% 0.14% 0.46% 3.67%

 

 

 

 

 

 

 

 

I choose the .5m and .5m solution.

 For lenses, I plan on using a plano-convex lens for as lens 1, and a biconvex lens as lens2.

 

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