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ID Date Author Type Category Subjectup
  4804   Fri Jun 10 12:04:57 2011 JenneUpdateRF SystemBad RF connections!!

I am in the process of calibrating AS55's shot noise, and I noticed that the AS55 PD input to the demod board was only finger-tight.  I then checked all of the other SMA connections in the set of RF PD demod boards, and found several more that were loose, including all of the REFL55 connections.  This is no good!!!! RF connections need to be tightened!  I went through and tightened all of the offending connections with my personal Snap-on SMA wrench. 

  1051   Thu Oct 16 09:44:49 2008 YoichiUpdatePSLBad cable for FSS
Yesterday arount 1:30PM, we lost the LO signal for the FSS.
I found it was caused by a bad cable connecting from the peter's RF oscillator box to the LO of the FSS.
I temporarily replaced it with a BNC cable of comparable length.
  3098   Tue Jun 22 18:56:32 2010 JenneUpdateEnvironmentBad placement of recycling bin

Someone has been moving the big blue recycling bin in front of the laser-chiller-chiller (the air conditioner in the control room).  This is unacceptable.  The chiller temp was up to 20.76C.  No good. 

You are free to move the recycling bin around so you can access drawers or the bike-exit-door in the control room, but make sure that it does not block air flow between the chiller-chiller and the chiller. 

The attached photo shows the BAD configuration.

  7354   Thu Sep 6 19:21:58 2012 ManasaConfiguration40m UpgradingBaffle problem

For the current baffle (dia. 40mm) centered along the beamline place at 1.77" from the test mass, the baffle will allow ~8.6mm visibility on the camera from the center of the test mass (in case of ETMY).

*assuming the pick off mirror is placed at the edge of the tunnel

  7359   Fri Sep 7 11:58:12 2012 ManasaConfiguration40m UpgradingBaffle problem

Quote:

The required diameter for the baffle if it sits on the cage at 1.77" from the test masses: the current baffle (dia. 40mm) centered along the beamline, will allow ~8.6mm visibility from the center of the test mass (in case of ETMY).

*assuming the pick off mirror is placed at the edge of the tunnel

Estimations of the visibility region (r1 on the test mass) with baffle (aperture size 40mm).

The baffle is installed on the cage at 1.125" from the test mass (distance changed from the previous elog after a double check).

The 40mm aperture is in no way going to help get clear view of the ITMs; 

  7361   Fri Sep 7 13:01:53 2012 ManasaConfiguration40m UpgradingBaffle problem

Quote:

Quote:

The required diameter for the baffle if it sits on the cage at 1.77" from the test masses: the current baffle (dia. 40mm) centered along the beamline, will allow ~8.6mm visibility from the center of the test mass (in case of ETMY).

*assuming the pick off mirror is placed at the edge of the tunnel

Estimations of the visibility region (r1 on the test mass) with baffle (aperture size 40mm).

The baffle is installed on the cage at 1.125" from the test mass (distance changed from the previous elog after a double check).

The 40mm aperture is in no way going to help get clear view of the ITMs; 

Required baffle diameter to have a visibility region r1 = 3 times the beam diameter

Picture1.png

  4178   Thu Jan 20 17:00:39 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

  4182   Fri Jan 21 11:45:01 2011 AidanConfigurationLockingBallpark figures for Green Locking PLLs (Digital vs Analogue)

Quote:

If we use a digital PLL for locking the frequency of the PSL and END green lasers then we can expect a UGF of around 1kHz (assuming a sampling rate of 16kHz). Let's assume a simple 1/f loop giving a loop gain of ~1000x at 1Hz. If the free-swinging ETM pendulum motion at 1Hz is of the order of 1 micron, then the residual motion at 1Hz, once we lock the digital PLL by actuating on the ETM position, will be of the order of 1nm. This is bordering on too high.

Alternatively, is we use an analogue PLL then we can expect a much higher UGF and many orders of magnitude more gain at 1Hz (see here). So we would expect the residual motion of the pendulum to be much smaller - probably limited by some other noise source somewhere in the system (I doubt it's going to be reduced by 12 orders of magnitude).

RA: I think ballpark's not good enough for this. To see what's good enough, we need to to an analysis similar to what Bram has for the ALS. Get the 40m seismic spectrum from the arm locking spectrum or the green laser feedback signal and then correct it for a realistic loop shape.

KA: For this purpose I have made the simulink model for the green locking more than a year ago, but the entire green team has consistently neglected its presence...
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/Green_Locking/Servo_modeling/091121/

 Agreed. It doesn't completely rule out the digital PLL. I'll check out Kiwamu's model.

  337   Fri Feb 22 16:47:54 2008 robUpdateElectronicsBaloney
Well I guess Rana didn't study too hard at Professor School, either. If he'd even bothered to actually read John's entry, he might have looked at the RF Out from the HP Analyzer. As it is, this experience so far has been like taking your car to a highly respected mechanic, telling him it's having acceleration problems, and then he takes a rag and wipes some dirt off the hood and then tells you "It's running fine. That'll be 500 bucks."

I make the current score:

Snarkiness: 2
Education:  0



I did RTFM, and it doesn't mention anything about crazy behaviour on the RF Output. So, I set up the analyzer to do a sweep from 500MHz to 1MHz, with output power of 0dBm, and plugged the output directly into the 300MHz scope with the input set to 50 Ohm impedance. The swept sine output looks totally normal from 500Mhz to 150MHz (measuring ~220mVrms below 300MHz -- 0dBm), where it abruptly transitions to a distorted waveform which the scope measures as having a frequency of ~25MHz and with 450mVrms (+6dBm). It then transitions again at some other part of the sweep to a cleaner-looking 25MHz waveform with ~1.2Vrms (+15dBm). See the attached Quicktime movie. The screeching in the background is the PSL door.

With this bizarre behaviour, it's actually possible that even someone who does everything carefully and correctly could break sensitive electronics with this machine. Let's get it fixed or get a new one.

Don't use the HP4195A anymore unless you want broken electronics.


Quote:
I'm not sure where Ward and Miller went to Analyzer school, but it was probably uncredited.
I turned it on and used 2 BNC cables and a T to hook up the source to the 2 inputs and measured the always-exciting TF of cable.

Score:  HP Analyzer  1
        Rob & John   0


I have left the analyzer on in this complicated configuration. RTFM boys.


Quote:
The HP 4195A network analyser may be broken, measurements below 150MHz are not reliable. Above 150MHz everything looks normal. This may be caused by a problem with its output (the one you'd use as an excitation) which is varying in amplitude in a strange way.

Analyzer
  11416   Wed Jul 15 17:05:06 2015 JessicaUpdateGeneralBandpass Pre-Filter created

I applied a bandpass filter to the accelerometer huddle data as a pre-filter. The passband was from 5 Hz to 20 Hz. I found that applying this pre-filter did very little when comparing the PSD after pre-filtering to the PSD with no pre-filtering. There was some improvement though, just not a significant amount. For some reason, it also seemed as though the second accelerometer improved the most from pre-filtering the data, while the first and third remained closer to the unfiltered noise. Also, I have not yet figured out a consistent method for choosing passband ripple and stopband attentuation, both of which determine how good the filter is. 

My next step in pre-filtering will be determining a good method for choosing passband ripple and stopband attenuation, along with implementing other pre-filtering methods to combine with the bandpass filter. 

  13505   Fri Jan 5 19:19:25 2018 ranaConfigurationSEIBarry Controls 'air puck' instead of 'VOPO style' breadboard

We've been thinking about putting in a blade spring / wire based aluminum breadboard on top of the ETM & ITM stacks to get an extra factor of 10 in seismic attenuation.

Today Koji and I wondered about whether we could instead put something on the outside of the chambers. We have frozen the STACIS system because it produces a lot of excess noise below 1 Hz while isolating in the 5-50 Hz band.

But there is a small gap between the STACIS and the blue crossbeams that attache to the beams that go into the vacuum to support the stack. One possibility is to put in a small compliant piece in there to gives us some isolation in the 10-30 Hz band where we are using up a lot of the control range. The SLM series mounts from Barry Controls seems to do the trick. Depending on the load, we can get a 3-4 Hz resonant frequency.

Steve, can you please figure out how to measure what the vertical load is on each of the STACIS?

  4879   Fri Jun 24 17:04:25 2011 NicoleUpdateSUSBasic Laser Safety Training; Moved TT Mirror; Horizontal Displacement Mech Plan

Today Ishwita, Sonali, and I completed basic laser safety training with Peter King. I completed the Laser Safety Quiz and have turned in my certificate sheet.

I just need to turn in a signed copy of the Lab Safety Checklist to SFP (which I can now have signed by Koji after completing the course).

 

Steve and I have removed the TT mirror from the clean box. It is now on the small optical table in the lab that I have been working on.  Thanks to Steve, all of the mechanical components for the horizontal displacement measurement experiment are compiled and on the small optical table. Here is a photo of the small optical table with the gathered components. CompiledParts.JPG

The plan is to attach the slider and the shaker directly to the black mounting plate. On the slider, we we then place the smaller black mounting plate (with the lip). The lip will attach to the shaker. We know exactly where to drill and everything is lined up. The shaker will be placed on the smaller black mounting plate (with the lip).  The assembly will begin on Monday.

 

Here is a photo of the planned set-up for the shaker and the horizontal slider + mounting base.

 HorizontalDispMount.JPG

  13863   Fri May 18 14:18:03 2018 gautamConfigurationElectronicsBasic MEDM Control Screen setup

I setup a basic MEDM screen for remote control of the PLL.

The Slow control voltage slider allows the frequency of the laser to be moved around via the front panel slow control BNC.

The TTL signal slider provides 0/5V to allow triggering of the servo. Eventually this functionality will be transferred to the buttons (which do not work for now).

The screen can be accessed from the PSL dropdown menu in sitemap. We can make this better eventually, but this should suffice for initial setup.

  14568   Wed Apr 24 17:39:15 2019 YehonathanSummaryLoss MeasurementBasic analysis of loss measurement

Motivation

  • Getting myself familiar with Python.
  • Characterize statistical errors in the loss measurement.

Summary

​The precision of the measurement is excellent. We should move on to look for systematic errors. 

In Detail

According to Johannes and Gautam (see T1700117_ReflectionLoss .pdf in Attachment 1), the loss in the cavity mirror is obtained by measuring the light reflected from the cavity when it is locked and when it is misaligned. From these two measurements and by using the known transmissions of the cavity mirrors, the roundtrip loss is extracted.

I write a Python notebook (AnalyzeLossData.ipynb in Attachment 1) extracting the raw data from the measurement file (data20190216.hdf5 in Attachment 1) analyzing the statistics of the measurement and its PSD.

Attachment 2 shows the raw data. 

Attachment 3 shows the histogram of the measurement. It can be seen that the distribution is very close to being Gaussian.

The loss in the cavity pre roundtrip is measured to be 73.7+/-0.2 parts per million. The error is only due to the deviation in the PD measurement. Considering the uncertainty of the transmissions of the cavity mirrors should give a much bigger error.

Attachment 4 shows noise PSD of the PD readings. It can be seen that the noise spectrum is quite constant and there would be no big improvement by chopping the signal.

The situation might be different when the measurement is taken from the cavity lock PD where the signal is much weaker.

  13348   Mon Oct 2 12:44:45 2017 johannesUpdateCamerasBasler 120gm calibration

Disclaimer: Wrong calibration factors! See https://nodus.ligo.caltech.edu:8081/40m/13391

The two acA640-120gm Basler GigE-Cams have been calibrated. I used the collimated output of a fiber that carried the auxiliary laser light from the PSL table. With a non-polarizing beam splitter some of the light was picked off onto a PD, and I modified the RF amplitude of the AOM drive signal to vary the power coming out of the fiber. The fiber output was directed at a white paper, which was placed 1.06m from the front of the lens tube assembly, which is where the focal plane is. Using the Pylon Viewer App I made sure that the entirety of the beam spot was imaged onto the CCD. Since the camera sensor is 1/4" across, I removed the camera from the lens tube and instead placed the Ophir power meter head at the position of the sensor and measured the power reported versus PD voltage, which turned out to be 1.5 V/uW.

The camera was put back in place and I used the Pypylon package Gautam had stumbled upon to sweep the exposure time from 100us to 10ms at different light power settings including no laser light at all for background subtraction, and rather than keeping the full bitmap data for O(100s) of images I recorded only the quantities

  1. Pixel Max
  2. Pixel Sum
  3. Pixel Mean
  4. Pixel Standard Deviation
  5. Pixel Median

I performed this procedure for both the 152 and 153 cameras and plotted the pixel sum and the pixel max vs the exposure time. All the exposures were taken at a gain setting of 100, which is the smallest possible setting (out of 100-600). To obtain the calibration factor I use the input power Pin=75nW in the 'safe' region 1ms to 10ms where the pixel sum looks smooth and the CCD is reportedly not saturated.

Camera IP Calibration Factor CF
192.168.113.152 8.58 W*s
192.168.113.153 7.83 W*s

The incident power can be calculated as Pin =CF*Total(Counts-DarkCounts)/ExposureTime.

  12617   Tue Nov 15 20:26:35 2016 JohannesUpdateCamerasBasler GigE-Camera on Optimus (+Mafalda dead)

I powered up the existing ace100gm GigE cam with the PoE injector and tried to interface with it as described in elog 4163. After a few initial problems with IP assignment and interfacing I connected it to one of the gigabit hubs and installed the most recent pre-compiled software suite on /opt/pylon5 on optimus, after which I was able to find it with the configuration software. I named it "c1gige_bas100-1" and gave it the static IP address 192.168.113.151.

Afterwards the image acquisition worked without problems.

It may be a good idea to leave the gigecam interfacing up to a dedicated machine. I was thinking I could use Mafalda for this, and also for developing the code for framegrabbing and imager settings, but found that it was dead, burnt at the stake so to say. I guess it wasn't running anything critical, since it wasn't even connected to the network and smelled like burnt electronics. I'll get a replacement desktop for it.

  12622   Thu Nov 17 12:14:21 2016 ranaUpdateCamerasBasler GigE-Camera on Optimus (+Mafalda dead)

Indeed. I suggest discussing with Joe B. I believe we should use a dedicated cam network to get the camera signals from the ends and corner all into one machine. Do not use the main CDS FE network for this since it might produce weird collissions. How about make a diagram, post it to elog, and send link to Joe?

It may be a good idea to leave the gigecam interfacing up to a dedicated machine.

  15448   Thu Jul 2 16:51:23 2020 JordanUpdateGeneralBathroom Science

As part of an ongoing effort to improve airflow in workspaces/bathrooms on campus, I have installed an air scrubber unit in each of the bathrooms at the 40m lab.

  7844   Mon Dec 17 21:41:30 2012 ranaSummarySUSBeCu wire

Just in case we want to retrofit the Tip/Tils with Beryllium Copper wire, here are links to a few sources which have a supply of the right composition and temper:

http://www.lfa-wire.com/Tempered-Alloy-25_C17200.htm

http://www.alloywire.com/beryllium_copper_CB_101.html

http://www.ngk.co.jp/english/products/electronics/berylliumcopper/wire/index.html

http://www.goodfellow.com/E/Copper-Beryllium-Wire.html

 

I don't think its worth it to do something to modify them unless we get a real reduction in the hysteresis - need a benchtop test setup ASAP.

  7855   Wed Dec 19 11:14:25 2012 SteveUpdateSUSBeCu wire in stock

Quote:

Just in case we want to retrofit the Tip/Tils with Beryllium Copper wire, here are links to a few sources which have a supply of the right composition and temper:

http://www.lfa-wire.com/Tempered-Alloy-25_C17200.htm

http://www.alloywire.com/beryllium_copper_CB_101.html

http://www.ngk.co.jp/english/products/electronics/berylliumcopper/wire/index.html

http://www.goodfellow.com/E/Copper-Beryllium-Wire.html

 

I don't think its worth it to do something to modify them unless we get a real reduction in the hysteresis - need a benchtop test setup ASAP.

 Be Copper in the lab is from Ca Fine Wire :  alloy 10 CDA 17 in sizes .008"  &  0.002"  There are other sus wire choices in the Drever lab

  2984   Tue May 25 17:04:37 2010 KevinUpdate Beam Profile After Mode Cleaner

I fit the data from the beam profile that Jenne measured on 5/21/2010. The distances are measured from halfway between MC1 and MC3 to the beam scanner. The fits give the following where w0 is the waist size and z0 is the distance from the waist to halfway between MC1 and MC3.

For the horizontal profile:

reduced chi^2 = 0.88

z0 = (1 ± 29) mm

w0 = (1.51 ± 0.01) mm

For the vertical profile:

reduced chi^2 = 0.94

z0 = (673 ± 28) mm

w0 = (1.59 ± 0.01) mm

I calculated the radius of curvature of MC2 using these values of w0:

horizontal: (16.89 ± 0.06) m

vertical:   (17.66 ± 0.07) m

For this calculation, I used the value of (13.546 ± .0005) m for the length of the mode cleaner measured on 6/10/2009. The specification for the radius of curvature of MC2 is (18.4 ± 0.1) m.

In the following plots, the blue curve is the fit to the vertical beam radius, the purple curve is the fit to the horizontal beam radius, * denotes a data point from the vertical data, and + denotes a data point from the horizontal data.

  2985   Tue May 25 17:09:22 2010 KojiUpdateIOOBeam Profile After Mode Cleaner

Very nice as usual. Can you add the curve to show the ideal mode of the MC on the profile plot?

Quote:

I fit the data from the beam profile that Jenne measured on 5/21/2010. The distances are measured from halfway between MC1 and MC3 to the beam scanner. The fits give the following where w0 is the waist size and z0 is the distance from the waist to halfway between MC1 and MC3.

For the horizontal profile:

reduced chi^2 = 0.88

z0 = (1 ± 29) mm

w0 = (1.51 ± 0.01) mm

For the vertical profile:

reduced chi^2 = 0.94

z0 = (673 ± 28) mm

w0 = (1.59 ± 0.01) mm

I calculated the radius of curvature of MC2 using these values of w0:

horizontal: (16.89 ± 0.06) m

vertical:   (17.66 ± 0.07) m

For this calculation, I used the value of (13.546 ± .0005) m for the length of the mode cleaner measured on 6/10/2009. The specification for the radius of curvature of MC2 is (18.4 ± 0.1) m.

 

  2986   Tue May 25 17:22:56 2010 KevinUpdateIOOBeam Profile After Mode Cleaner

Quote:

Very nice as usual. Can you add the curve to show the ideal mode of the MC on the profile plot?

Quote:

I fit the data from the beam profile that Jenne measured on 5/21/2010. The distances are measured from halfway between MC1 and MC3 to the beam scanner. The fits give the following where w0 is the waist size and z0 is the distance from the waist to halfway between MC1 and MC3.

For the horizontal profile:

reduced chi^2 = 0.88

z0 = (1 ± 29) mm

w0 = (1.51 ± 0.01) mm

For the vertical profile:

reduced chi^2 = 0.94

z0 = (673 ± 28) mm

w0 = (1.59 ± 0.01) mm

I calculated the radius of curvature of MC2 using these values of w0:

horizontal: (16.89 ± 0.06) m

vertical:   (17.66 ± 0.07) m

For this calculation, I used the value of (13.546 ± .0005) m for the length of the mode cleaner measured on 6/10/2009. The specification for the radius of curvature of MC2 is (18.4 ± 0.1) m.

Here is the plot with the ideal mode of the mode cleaner shown in brown. The ideal mode was plotted with the radius of curvature of 18.4. The blue curve is the fit to the vertical beam radius, the purple curve is the fit to the horizontal beam radius, * denotes a data point from the vertical data, and + denotes a data point from the horizontal data.

  6447   Mon Mar 26 23:47:54 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam

[Keiko, Suresh]

   Keiko and I measured the IPPOS beam profile.  The fit parameters  are :

  Vertical Horizontal
Waist (mm) 2.77 2.48
Rayleigh length (m) 23.5m 15.87
Waist location (m) 0.81 m 1.85

BeamProfile_IPPOS.png

 

The data files are attached. 

  6448   Tue Mar 27 02:05:40 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam

Quote:

[Keiko, Suresh]

  Vertical Horizontal
Waist (mm) 2.77 2.48
Rayleigh length (m) 23.5m 15.87
Waist location (m) 0.81 m 1.85

BeamProfile_IPPOS.png

 

 

If we assume the nominal wavelength of the IR light to be 1064nm and constrain the Rayleigh length to be zr = (pi w0^2)/lambda we obtain the following fit parameters: (these are compared with the beam profile measurements of June/18/2010 available in the wiki )

  Vertical

Vertical 

06/18/2010

Horizontal

Horizontal

06/18/2010

waist (radius) (mm) 2.77 2.81 2.47 2.91
Rayleigh length (m) (computed) 22.62   18.14  
Waist location w.r.t. to MM2 * 3.37 5.36 4.15 1.96

* I updated the waist waist location coz because I missed-out the distance in air from the vacuum port to the optic on the IPPOS table.

 

BeamProfile_IPPOS.png

 

 

  6449   Tue Mar 27 02:18:31 2012 keikoUpdateIOOBeam Profile measurement: IPPOS beam

Keiko, Rana, Suresh

Related to the beam profile of IPPOS today, we tried to measure the beam size at the ETMY point in order to estimate the input beam mode. We measured the beam size hitting at the suspension frame by a camera image, with two situations to see two "z" for beam profile.

(1) Input beam is slightly misaligned and the injected beam hits the end mirror frame. Assuming z=0 at the input mirror, this should be z=40m.

(2) Input beam hits the centre of the end mirror, and ITMY is slightly misaligned and the beam hits the end mirror frame after the one-round trip. Assuming z=0 at the ITM, this position should be z=120m.

text9149.png

The injected beam at the end point and the one round trip ligt at the end point should be the same size, if the input mode matches to the cavity mode. You can see if your injected light is good for the cavity or not. We compared and assumed the above two beam sizes by looking at the photo of the beam spot.

(1) first_cap.png (2) second_cap.png

 Assuming the zoom factor difference by the part below the beam (shown with allow in the photos. Arbitrary unit.), the beam in (2) is smaller than expected (roughly 40%?).

However this is a very rough estimation of the beam sizes! It is difficult to assume the beam size shown on the photos! It looks smaller only because the power of (2) is smaller than of (1). I don't think we can say anything from this rough estimation. One may be able to estimate better with CCD camera instead of this normal camera. 

 

  6451   Tue Mar 27 11:54:18 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

I'd like to know what we expect for these numbers.  I've added to Kiwamu's drawing some more distances, so I can calculate the expected beam size at the IPPOS port.

IPPOS_distances.pdf

 

Quote:

Quote:
 

  Vertical

Vertical 

06/18/2010

Horizontal

Horizontal

06/18/2010

waist (radius) (mm) 2.77 2.81 2.47 2.91
Rayleigh length (m) (computed) 22.62   18.14  
Waist location w.r.t. to MM2 * 3.37 5.36 4.15 1.96

 

  6452   Tue Mar 27 16:06:59 2012 keikoUpdateIOOBeam Profile measurement: IPPOS beam

I changed the ETMY CCD camera angle so that we can see the suspension frame in order to repeat the same thing as yesterday. The ETMY camera is not looking at the beam or mirror right now.

  6453   Tue Mar 27 17:19:02 2012 KojiUpdateIOOBeam Profile measurement: IPPOS beam

The mode looks quite terrible in the plot, but in reality it is an illusion of the plot.

The actual TEM00 content in this beam is ~99.7%


mode_coupling.pdf

Based on the above document, you can calculate power coupling between two elliptic gaussian modes.

Give the parameters of one beam as

zRy1 = pi*(2.77e-3)^2 / 1064e-9
z1y = 3.37
zRx1 = pi*(2.47e-3)^2 / 1064e-9
z1x = 4.15

Then, assume a round beam for the other.

zRx2 = zRy2 = zR
z2x = z2y = z0

Then run the optimizer to find the maximum for the quantity |C|^2

|C|^2 max: 0.9967
zR = 20.19
z0 = 3.804

  6456   Tue Mar 27 18:03:46 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

This is wrong!  See following elog for corrected plot (and explanation)

I'm not done meditating on what's going on, but here's what I've got right now:

BeamProp_usingMeas2012MMTnumbersLowRes.png

This is a beam profile, using the distances from the combined Kiwamu / Jenne sketch earlier today. 

0 meters along the horizontal axis is meters from the Mode Cleaner waist. (Yes, I was bad and forgot to label it.  Get over it.)

The pink and green dots to the left of the plot are the MC fitted waist measurements that we made in May 2010.

The pink and green dots in the ~center of the plot are the fitted waist measurements that Suresh and Keiko took yesterday, of the IPPOS path, so after the MMT.

The black dot is where we would like our non-astigmatic beam to be.  This is the calculated waist size of the cavity mode, using the new ~37.76m distance, after we moved the ETMs to their current positions.  The black dot indicates 3.036 mm at the ITM (averaged between the BS-ITMX and BS-ITMY distances).

The moral of the story that I'm getting from this plot:  something funny is going on.

The distances Kiwamu quoted on the sketch are very close to the ones that I used for designing and checking the MMT in the first place, which were based off of measurements using rulers etc to measure distances.  Steve said he looked at photos today, and agreed that Kiwamu's numbers looked reasonable also.

Something that we haven't done lately is measure the position of each optic from every other optic, along the beam path.  I propose we come up with a clever way to put a target on top of / next to mirrors, and then a way to hold the laser distance measure-er at an optic, so that we can go thorough systematically and measure the actual path that our beam is seeing.  Maybe this is too much work, and not worth it, but it would make me happier.  In my head, these 'fixtures' are just small pieces of cleaned aluminum, one that can sit on a mirror mount, and one which we can use to align the laser ruler to approximately the front of an optic.  Nothing fancy.

  6457   Tue Mar 27 21:20:32 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

Quote:

The moral of the story that I'm getting from this plot:  something funny is going on.

 Yup, something funny was going on.  Nic's MM code that I used, "a la mode", calls for the focal length of the optics, whereas the code that I wrote and used for ages called for the radius of curvature.  f = R/2.  Fixing that factor of 2 I get something more like:

BeamProp_usingMeas2012MMTnumbersLowRes.png

This is obviously much better, in that the beam profile goes through (within some error) both of the measured sets of points - the MC waist measured in May 2010, and after the MMT measured yesterday.

So, what does it all mean?  That I'm not sure of yet.

  6459   Tue Mar 27 23:37:35 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam

Quote:

Quote:

The moral of the story that I'm getting from this plot:  something funny is going on.

 Yup, something funny was going on.  Nic's MM code that I used, "a la mode", calls for the focal length of the optics, whereas the code that I wrote and used for ages called for the radius of curvature.  f = R/2.  Fixing that factor of 2 I get something more like:

.....

So, what does it all mean?  That I'm not sure of yet.

 In an attempt to estimate the errors on the fit parameters I upgraded my Mathematica code to use the function 'NonlinearModelFit', which allows us to define weights and also reports the errors on the fit parameters.   The plots have been upgraded to show the error bars and residuals.

Beam-Profile_IPPOS_wError.png

 

The parameters determined are given below and compared to the earlier measurements of 06/18/2010

Vertical Profile:

Parameter Estimate Standard Error 95% Confidence interval 06/18/2010 measurement
Waist (mm) 2.768 0.005 2.757 -- 2.779 2.81
Waist location from MMT2 (m) 5.85 0.12 5.625-- 6.093 5.36

 

 

Horizontal Profile:

Parameter Estimate Standard Error 95% Confidence Interval 06/18.2010 measurement
Waist (mm) 2.476 0.009 2.455 -- 2.496 2.91
Waist Location from MMT2 (m) 4.935 0.145 4.645 -- 5.225 1.96

 

There is a significant change in the beam waist location (as compared to previous report) because I corrected a mistake in the sign convention that I was using in measuring the distances to the waist from the zero-reference.
 

  6460   Wed Mar 28 01:17:29 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

As I was a little dissatisfied with the inaccuracy in the distance numbers in Kiwamu's sketch, I went back to the 18 Dec 2010 table layout drawing for more accurate numbers.  These are now included in this round of plots.

Also, I include astigmatism due to the incident angles on MMT1 (~3.5 deg) and MMT2 (~1 deg).

First plot, IPPOS path, using the recent (fixed) measurements from Suresh to fix the beam width.  Note that the old 2010 measurements of the MC waist are consistent with this measurement.

Second plot, Main IFO path all the way to the ITM (average) position, using the 2010 MC waist measurements to fix the beam width.

Third plot, Main IFO path all the way to the ITM position, but with PRM flipped (negative RoC), using the 2010 MC measurement to fix beam width.

With the PRM correctly oriented (2nd plot), I get beam waists of (x = 2.529 mm, y = 2.646 mm), which corresponds to a mode matching to the arm cavity of (eta = 97.43%, PRM correct).

With the PRM flipped (3rd plot), I get beam waists of (x = 3.176 mm, y = 3.3 mm), which corresponds to a mode matching to the arm cavity of (eta = 99.55%, PRM flipped).

 

First plot:

BetterDistances_IPPOSLowRes.png

Second plot (this is how the MMT was designed to be, before the ETMs were moved, which made the ideal waist larger):

BetterDistances_MainIFO_PRMnormalLowRes.png

Third plot:

BetterDistances_MainIFO_PRMflippedLowRes.png

For both the 2nd and 3rd plot, we can't look at the post-MMT waist measurements, since that distance on the plots is after the PRM, which is a curved optic.  So the fact that the post-MMT measurements match the correct-PRM plot better than the flipped-PRM plot can't be taken to be meaningful.

Moral of the story:  I'm not sure how to interpret any of this to tell us if the PRM is flipped or not, since the measurements are all of the beam profile before the beam sees the PRM.  We'd have to measure the profile after the PRM somehow in order to get that information.  We have okay but not great mode matching to the arm if the PRM is correct, but I don't know that we readjusted the MMT after we moved the ETMs.  I don't remember recalculating any optimal telescope lengths after the arm length change.  If we need better mode matching, I can do that calculation, although given how much space we don't have, it would be hard in practice to move the MMT mirrors by much at all.

  6461   Wed Mar 28 18:26:47 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

More calculations....

Game Plan:  Using MC waist measured beam as the starting point of beam propagation, move MMT mirrors around until the beam profile fits with the IPPOS measurements from Monday.

Plot 1:  Allow MMT mirrors to move as much as they want to.  Note that the Y-beam goes through the IPPOS measured point. (This implies we put the MMT in the wrong place by ~half a meter.  Unlikely)

Plot 2: Using MMT locations from plot 1, what does the beam look like at the ITMs? 

Plot 3:  Allow MMT mirrors to move as much as 2cm.  Note that the Y-beam doesn't quite go through IPPOS measured point.

Plot 4: Using MMT locations from plot 3, what does the beam look like at the ITMs?

For all of the above, I was optimizing the propagation of the Y-beam profile.  Since the X-beam profile measurement is so different, if I want to optimize to X and let the MMT mirrors move as much as they want, MMT1 ends up inside the MC.  Unlikely.  So I'm just looking at Y for now, and maybe Suresh or someone needs to rethink the error bars on their measurements or just remeasure.

Plot 1:

OptimizedMMT_halfMeterChange_IPPOSviewLowRes.png

Plot 2:

OptimizedMMT_halfMeterChange_IFOviewLowRes.png

Plot 3:

OptimizedMMT_pt2cMeterChange_IPPOSviewLowRes.png

Plot 4:

OptimizedMMT_pt2cMeterChange_IFOviewLowRes.png

  6462   Wed Mar 28 20:54:02 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

I fitzed by hand with the numbers for the incident angles on MMT1 and MMT2, and then let the code optimize the position of MMT1 and MMT2.

Here I have set the incident angle for MMT1 = 25deg, and MMT2 = 12deg (should be 3.5deg, 1deg by design).  The length of the telescope doesn't want to change by more than 7mm, but the position of the telescope wants to change by 1.3meters.  Is it possible that the distances on the Monday IPPOS measurements aren't actually correct?

MMT_moved_by_1pt3meters_MMT1th_25_MMT2th_12_LowRes.png

  6476   Mon Apr 2 18:58:32 2012 JenneUpdateIOOBeam Profile measurement: IPPOS beam

Suresh noted that I never wrote down the waist positions of the beam propagated through the MMT (based on where we think it is from ruler-based measurements).  This uses the MC waist measured beam as the starting point, and just propagates through the MMT, out to the IPPOS port.

Yq:

  Properties:
                    q: 2.2488 +23.8777i
               lambda: 1.0640e-06
            waistSize: 0.0028  (at z = 13.2676 meters)
               waistZ: 2.2488    (relative to z = 13.2676 meters)
      divergenceAngle: 1.1910e-04
    radiusOfCurvature: 255.7849
            beamWidth: 0.0029
        rayleighRange: 23.8777

So, to sum up, the vertical beam waist is 2.8438 mm at 11.0188 meters from the MC waist.

 

Xq:

  Properties:
                    q: 5.1953 +24.7342i
               lambda: 1.0640e-06
            waistSize: 0.0029   (at z = 13.2676 meters)
               waistZ: 5.1953    (relative to z = 13.2676 meters)
      divergenceAngle: 1.1702e-04
    radiusOfCurvature: 122.9525
            beamWidth: 0.0030
        rayleighRange: 24.7342

So, to sum up, the horizontal beam waist is 2.8943 mm at 8.0723 meters from the MC waist.

In pictorial form,

NonOptimized_propagatedWaistPlotted_LowRes.png

  6477   Mon Apr 2 23:06:38 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam: Mystery deepens

Quote:

I fitzed by hand with the numbers for the incident angles on MMT1 and MMT2, and then let the code optimize the position of MMT1 and MMT2.

Here I have set the incident angle for MMT1 = 25deg, and MMT2 = 12deg (should be 3.5deg, 1deg by design).  The length of the telescope doesn't want to change by more than 7mm, but the position of the telescope wants to change by 1.3meters.     Is it possible that the distances on the Monday IPPOS measurements aren't actually correct?

 

I am trying to track down possible errors in our measurements. 

So as a first step I am recomputing the IPPOS waist location with respect to the MC waist, using the same optical layout diagram as the one used by Jenne in her calculations.  Pic of Jenne's lab notebook showing location of optics is attached.  

IPPOS: measurement elog 6459: Vertical Std.Error Horizontal Std.Error
Waist  2.768 mm 5 microns 2.476 mm 10 microns
Waist location from MC waist  12.411 m  17 mm  9.572 m 54 mm

Std Dev of residuals from fit function

  37 microns   54 microns

 Let us compare it with the old measurement of the IPPOS beam from June/18/2010.

IPPOS: measurement June 18th 2010 Vertical Std.Error Horizontal Std.Error
Waist  2. 812mm 8 microns 2.909 mm 20 microns
Waist location from MC waist  9.265 m  224 mm  5.869 m 415 mm

Std Dev of residuals from fit function

  ~ 25 microns   ~25 microns

Note that there is a discrepancy of about 3.2 m in the waist location for the vertical profile and about 3.5 m for the horizontal profile between these two measurements. 

Let us compare these measurements with what is expected from calculations.  Jenne uses the known parameters of MC waist and the locations of the MMT optics to compute the parameters for the IPPOS beam:

IPPOS: Jenne's Calculations elog 6476:

Vertical Std.Error Horizontal Std.Error
Waist  2.844 mm   2.894 mm  
Waist location from MC waist  11.019 m   8.072 m  

 As the 2010 measurements are reported wrt to MMT2 and calculations are wrt MCwaist, I have used the distance between the MCwaist to MMT2 = 3.910 m to shift the reference from MMT2 to MC waist. Refer to the attached diagram from Jenne's notes for this MMT2 <--> MC waist distance.

There is a discrepancy of 1.5 meters between the calculations and recently measured waist location.  The discrepancy with the 18Jun2010 measurement is much larger, about 3 meters in both v and h.

Are such variations to be expected between two successive measurements?  I looked at another case where we have two measurements of a beam to see what to expect.

I looked at the REFL (Reflection from PRM) case, where we repeated a measurement, to see how much variation could happen in w0 and zr, between repeated measurements. This was a particularly bad case as our first attempt had problems due to OL servo loop oscillations in the PRM suspension damping.  We fixed that later and measurement 2 has smaller residuals. And I think we are doing okay in IPPOS case as seen by the reduced scatter of the residuals.

 These are the fits from the REFL beam measurement 1

REFL: Reflection from PRM: measurement 1 Vertical Error Horizontal Error
Waist 1.662 mm 4 microns 2.185 mm 4 microns
Waist location from MMT2 after reflection at PRM 1.781 m 17 mm 4.620 m 53 mm
Std.Dev. of residuals from fit function   61 microns   98 microns

 I have also recomputed the fits to the data from REFL beam measurement 2.  They match the earlier fits reported by kiwamu in his elog 6446

REFL: Reflection from PRM: measurement 2 Vertical Error Horizontal Error
Waist 1.511 mm 3 microns 2.128 mm 3 microns
Waist location from MMT2 after reflection at PRM 1.281 m 9 mm 3.211 m 37 mm
Std. Dev of residuals from fit function   58 microns   61 microns

 

Note that between these two measurements the beam waist location has shifted by 0.5 m for the vertical and about 1.3 m for the horizontal cases.  So variations of 1.5 m in the waist locations are possible if we are not careful.  But this is a particularly extreme example, I think we are doing better now and the measurement is unlikely to change significantly if we repeat it.

Some notes:

Fits for IPPOS and both REFL measurements 1 and 2 are attached. 

The zero reference for the z axis of the IPPOS beam plot is at a distance of 6.719 m from MC waist for a beam propagating towards the IPPOS QPD.

The zero reference for the z axis of the REFL beam plots is at a distance of 5.741 m from the MMT2 in the direction of a beam reflected by PRM and propagating towards the REFL port.

 

  6526   Thu Apr 12 01:17:56 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam: Possible Clipping

[Suresh, Jenne]

  The input beam is most probably being clipped at the Faraday Isolator.  

Evidence: 

a)  The beam scan of the IPPOS beam showed a nongaussian beam in the horizontal direction.  This was visible in the beam scan since it overlays a gaussian-fit over the data.

b)  I was able to remove this departure from gaussian profile by introducing an offset of 5 into the C1:IOO-WFS2_YAW_OFFSET.  

c)   We made a few measurements of the beam diameter as a function of distance at an offset of 7.  At a distance of beyond 3 m the deviation from gaussian profile was once again apparent. 

d)  We increased the offset to 14 to remove this deviation. 

e)  When we measured the beam diameter again with this new offset the horizontal diameter and vertical diameters dropped by 2.sigma.  Indicating there the beam was clipped till then.

f)   We increased the offset to 16 and the beam diameter did not change further (within 1.sigma). Implying no more clipping, hopefully. 

And then the earthquake stopped us from proceeding further. 

We plan to investigate this further to be sure..  Data attached.

 

Subsidiary effects to keep track of:

1) Introducing an offset into the WFS loops decreases the coupling from PSL into MC. 

2) If the beam is being clipped at the Faraday Isolator then the REFL beam would also show lesser clipping with WFS offsets.

  6531   Thu Apr 12 23:12:16 2012 SureshUpdateIOOBeam Profile measurement: IPPOS beam: Possible Clipping

WiQuote:

[Suresh, Jenne]

  The input beam is most probably being clipped at the Faraday Isolator.  

Evidence: 

.....

We plan to investigate this further to be sure.. 

.....

 

I tried to determine an optimal WFS2YAW offset to be used so that we may avoid clipping.

Initially, I just measured the beam diameter as a function of offset.  If the beam diameter would become independent of offset if it is not clipped.  However a systematic effect became apparent when I shifted the beam on the detector to a slightly different location.  So I repeated the measurements while recentering the beam to the same location everytime  (centered at -1650+/- 50 for both H and V directions).

I have attached plots of the scans for both cases, with recentering and without.    I have not been able to figure out what is going on since the beam diameter does not become independent of the offset.  While the beam profile becomes more gaussian beyond offsets of about 7 or so, the beam diameter does not seem to follow a clear pattern.  The measurements are repeatable (within one sigma) so the experimental errors are smaller than 1 sigma.

The photographs below show the improvement of Horizontal beam profile with WFS2Yaw offset.  These seem to indicate a good gaussian beam for offsets beyond 7 or so.  At offsets more than 12 the MC unlocks.

 

Hor_OSet-2.png Hor_OSet0.png Hor_OSet2.png Hor_OSet8.png
 Offset = -2   Offset = 0   Offset = 2   Offset = 8

 

 

HorizontalNoRecenter.png  HorizontalRecentered.png
  This seems to indicate that the beam diameter does not vary for WFS2Yaw offset > 8  But if we recenter the beam for each measurement this effect seems to vanish

        

 Will continue tomorrow.   Jenne wants to do some IFO locking now.

 

  6458   Tue Mar 27 21:37:51 2012 keikoConfigurationIOOBeam Profile measurement: IPPOS beam

 From the mode measurement I and Suresh have done yesterday, I calculated what beam size we expect at ETM ((1) upper Fig.1)  and at ETM after one bounce ((2) lower Fig.1).

expsche.png

Fig.1 (Yarm)

In case of (1), we expect approximately w=6300 um (radius), and w=4800 um for one-bounce spot (2) from the measured mode, see Fig.2.

drawing.png

Fig.2

This roughly agree with what we observed on CCD camera. See, pic1 for (1) and pic2 for (2). The spot at the ETMY (1) is larger than the one-bounced spot (2). From the monitor it is difficult to assume the radius ratio. The observed spot of (2) is a bit smaller than the prediction. It could happnen when (A) the ETMY (as a lens) is slightly back of the ideal position (= the distance between the ITM and ETM is longer than 40m) (B) the real waist is farer than ITM position toward MC (I assumed roughly 5 m from Jenne's plot, but could be longer than that).

P3270007-s.jpg  P3270008-s.jpg

pic1 (left): beam spot hitting on the suspension frame. pic 2 (right): the one-bounced beam spot hitting on the suspension frame.

 

  6441   Fri Mar 23 05:10:46 2012 SureshUpdateIOOBeam Profile measurements: Errors too large to yield good fits.

[Kiwamu, Suresh]

   Today we attempted to measure the beam profile of the REFL beam under two conditions:

              (a) with PRM aligned and ITMs misaligned 

              (b) with PRM misaligned and ITMs aligned

 

The raw data is shown below.  In each of the above conditions we measured in both the vertical (v) and horizontal (h) directions.   The measurements in the vertical direction were better than the ones in the horizontal direction because the optics had a horizontal oscillation which gave larger errors in measurement.

rawdataplot.png

 

Looking at the general trend of these lines it is clear that modes are not matched since the beam reflected by the PRM has a different divergence than that reflected from ITMs.  The beam is also astigmatic as the vertical and horizontal directions have different divergences.

I could find beam parameters only for the Blue line above (Profile in the vertical direction while PRM was aligned).   The fit is quite sensitive to the data points close to the waist, so we need to make better (lower St.Dev.) measurements near the AP table closer to the beam waist.  The intensity with only one ITM aligned is too low and also contributes to the errors.   The beam size is close to 6mm in the horizontal direction, this coupled with yaw oscillations give large errors in this measurement.

Here is the only reliable fit that could be obtained, which is for the prompt reflection from the PRM in the vertical direction

PRM-to-REFL-profile.pdf

The fit function I used is  Beam Dia = Waist { Sqrt [ 1+  ((z + z0)/zr)^2). The fit parameters we get for this data are

z0 = 7.7 m 

Waist = 2.4 mm

zr = 6.9 m

 

Will make another attempt later today...

 

 

 

 

  15529   Mon Aug 17 15:18:26 2020 gautamUpdateEquipment loanBeam Profiler + peripherals --> 40m

Gabriele left the DataRay beam profiler + peripherals (see Attachment #1) in his office. I picked them up just now and brought them over to the 40m.

  13002   Mon May 22 10:53:02 2017 DhruvaUpdateOptical LeversBeam Profiling Results

 

Quote:

Andrew and I set up the razor blade beam profiling experiment for He-Ne lasers on the "SP" table.  Once I receive the laser safety training, I will make power measurements and fit it to an erfc curve from which I will calculate the gaussian profile of the beam. I'm attaching some pictures of the setup. 

Least count of the micrometer - 2 microns 

Laser  : Lumentum 22037130:1103P

Photodetector : Thor Labs PDA100A

I had measured the y-profile of the beam of Friday at 5 axial locations and fit them to an erfc function using the lsqcurvefit function of MATLAB. 

The results were as follows - 

z(cm)    w (in)

4          0.0131

10        0.0132

15        0.0137

20       0.0139

25        0.0147

I left w in inches in the intensity plots as MATLAB gave more accurate fits for those values.

I converted these to S.I while making the spot-size vs z plot and the corresponding values in microns were 

332.74, 335.28, 347.98, 353.06, 373.38.

On fitting these values to the formula for the spot size of a Gaussian beam, the beam waist came out to be 330.54 microns and the location of the beam waist was at z=-2cm, where z=0 marks the head of the laser. 

 

TO-DO : Measure the spot size of the beam at more axial points to obtain a better fit. 

              Measure the x-profile of the beam. 

              Analyse the error in the spot sizes and corresponding error in the beam waist. 

 

 

  13006   Tue May 23 10:27:24 2017 DhruvaUpdateOptical LeversBeam Profiling Results

I have attempted to calculate the instrument error (micrometer least count) using the values of the spot size obtained by the least squares fitting method. This error is large towards the centre of the beam as the power varies significantly between adjecent markings of the micrometer. Using the new values of error obtained, I used the chi-square fitting minimisation method to further optimise the waist size. 

The modified values are - 

z(cm)    w (in)

4         0.0134

10        0.0135

15        0.0140

20        0.0142

25        0.0150

 

And the revised values for the beam waist and location are 338.63 microns and -2.65 cm respectively. 

I will now try to use the chi-square stastitic to estimate the error in spot size. 

  13007   Tue May 23 15:22:04 2017 ranaUpdateOptical LeversBeam Profiling Results
  1. Include several sources of error. Micrometer error is one, but you should be able to think of at least 3 more.
  2. There should be an error bar for the x and y axis.
  3. Also, use pdftk to put the PDFs all into a single file. Remove so much whitespace.
  4. Google 'beautiful plots python' and try to make your plots for the elog be more like publication quality for PRL or Nature.
  13008   Tue May 23 16:33:00 2017 SteveUpdateOptical LeversBeam Profiling Results

You may compare your results with this.

RXA: please no, that's not the right way

  13021   Tue May 30 18:31:54 2017 DhruvaUpdateOptical LeversBeam Profiling Results

​Updates in the He-Ne beam profiling experiment. 

  1. I've made intensity profile plots at two more points on the z-axis. The additition of this plots hasn't affected the earlier obtained beam waist significantly. 
  2. I have added other sources of error, such as the statisitical fluctuations on the oscilloscope(which is small compared to the least count error of the micrometer) and the least count of the z-axis scale.
  3. I have also calculated the error in the parameters obtained by fiiting by calculating the covariance matrix using the jacobian returned by the lsqcurvefit function in MATLAB. 
  4. I have also added horizontal error bars to all plots. 
  5. All plots are now in S.I. units 

 

 

  13053   Thu Jun 8 12:43:42 2017 DhruvaUpdateOptical LeversBeam Profiling Results

 

Quote:

​Updates in the He-Ne beam profiling experiment. ​

New and improved plots for the He-Ne profiling experiment 

Font size has been increased to 30. 

The plots are maximum size (Following Rana's advice, I saved the plots as eps files(maximized) and converted them to pdf later).

There is a shaded region around the trendline that represents the parameter error. 

Function that I fit my data to (should have mentioned this in my earlier elog entries) 

P = \dfrac{P_0}{2}\Bigg[1+erf\Big(\dfrac{\sqrt2(X-X_0)}{w}\Big) \Bigg]

Description of my error analysis -

1. I have assumed a 20% deviation from markings in the micrometer error. 

2. Using the error in the micrometer, I have calculated the propogated error in the beam power :

\delta P = \sqrt{\dfrac{2}{\pi}}{P_0}\dfrac{\delta x}{w}\exp\Bigg({\frac{-2(X-X_0)^2}{w^2}}\Bigg)

I added this error to the stastistical error due to the fluctuation of the oscilloscope reading to obtain the total error in power. 

3. I found the Fisher Matrix by numerically differentiating the function at different data points P_b with respect to the parameters p_i =  P_0, X_0 and w.

F_{ij} = \sum_{b} {\frac{\partial P_b}{\partial p_i}\frac{\partial P_b}{\partial p_j}}\frac{1}{\sigma^2_b}

I then found the covariance matrix by inverting the Fisher Matrix and found the error in spot size estimation. 

EDIT : Residuals added to plots and all axes made equal 

  12997   Wed May 17 18:08:45 2017 DhruvaUpdateOptical LeversBeam Profiling Setup

Andrew and I set up the razor blade beam profiling experiment for He-Ne lasers on the "SP" table.  Once I receive the laser safety training, I will make power measurements and fit it to an erfc curve from which I will calculate the gaussian profile of the beam. I'm attaching some pictures of the setup. 

Least count of the micrometer - 2 microns 

Laser  : Lumentum 22037130:1103P

Photodetector : Thor Labs PDA100A

  1724   Wed Jul 8 18:46:56 2009 DmassAoGElectronicsBeam Scan Funky

The beam scan (which has been living in the bridge subbasement for a bit now) is in a state of imperfection.

I noticed that:

  • The waist reading seems to change by not insignificant amounts as you move the spot across the head, even for just small perturbations about the center.
  • None of the features which require two slits seem to be working (unsure if this is software or hardware related)

I took some pictures to try and illuminate the situation - The inverted images are included to make it easier to see the flecks (?) in the slits

I am not sure how to figure out if any bit of the scan is/has been fried.

 

Pending further investigation, enjoy large error bars in your scan measurements!

 

PICTURES OF BOTH SLITS ON THE BEAMSCAN HEAD:

ELOG V3.1.3-