My previous eLog details how the noise in Hartmann Sensor defocus measurements appears to vary with ambient light. New troubleshooting analysis reveals that the rapid shifts in the noise were still related to the ambient light, sort of, but that ambient light is not the real issue. Rather, the noise was the result of some trouble with the centroiding algorithm.

The centroiding functions I have been using can be found on the SVN under /users/aidan/cit_centroid_code. When finding centroids for non-uniform intensity distributions, it is desirable to avoid simply using a single threshold level to isolate individual spots, as dimmer spots may be below this threshold and would therefore not be "seen" by the algorithm. The centroiding functions used here get around this issue by initially setting a relatively high threshold to find the centroids of the brighter spots, and then fitting a hexagonal close-packed array to these spots so as to be able to infer where the rest of the spots are located. Centroiding is then done within small boxes around each estimated centroid location (as determined by the hexagonal array). The functions "find_hex_grid.m" and "flesh_out_hex_grid.m" serve the purpose of finding this hexagonal grid. However, there appear to be bugs in these functions which compromise the ability of the functions to accurately locate spots and their centroids.

The centroiding error can be clearly seen in the following plot of calculated centroids plotted against the raw image from which they were calculated:

At the bottom of the image, it can be seen that the functions fail at estimating the location of the spots. Because of this, centroiding is actually being done on a small box surrounding each point which consists only of the background of the image. This can explain why these centroids were calculated to have much larger displacements and shifted dramatically with small changes in ambient light levels. The centroiding algorithm was being applied to the background surrounding each of these points, so it's very reasonable to believe that a non-uniform background fluctuation could cause a large shift in the calculated centroid of each of these regions.

It was determined that this error arose during the application of the hex grid by going through the centroiding functions step-by-step to narrow down where specifically the results appeared to be incorrect. The function's initial estimate for the centroids right before the application of the hex grid  is shown plotted against the original image:

The centroids in this image appear to correspond well to the location of each spot, so it does not appear that the error arises before this point in the function. However, when flesh_out_hex_grid and its subfunction find_hex_grid were called, they produced the following hexagonal grid:

It can be seen in this image that the estimated "spot locations" (the intersections of the grid) near the bottom of the image differ from the actual spot locations. The centroiding algorithm is applied to small regions around each of these intersections, which explains why the calculated "spot centroids" appear at incorrect locations.

It will be necessary to fix the hexagonal grid fitting so as to allow for accurate centroiding over non-uniform intensity distributions. However, recent experiments in measuring thermally induced defocus produce images with a fairly uniform distribution. It should therefore be possible to find the centroids of the images from these experiments to decent accuracy by simply temporarily bypassing the hexagonal-grid fitting functions. To demonstrate this, I analyzed some data from last week (experiment 72010a). Without bypassing the hex-grid functions, analysis yielded the following results:

However, when hexagonal grid fitting was bypassed, analysis yielded the following:

The level of noise in the centroid displacement vs. centroid location plot, though still not ideal, is seen to decrease by nearly two orders of magnitude. This indicates that bypassing or fixing the problems with the hexagonal grid fitting functions should enable a more accurate measurement of thermally induced defocus in future experiments.

This attachment is a Shockwave Flash animation of the iLIGO ETM getting a 1 W beam with a 3.5 cm radius getting fully absorbed onto the surface at t = 0.

 Here are some pictures of the ring heater segments destined for the H2 Y-arm this year.

 These still need to be put onto ResourceSpace.

Using some of the old data from James (attached below), I calculated the CCD conversion efficiency (CE) from electrons to bits (Counts).

Number of electrons(Ne) = QE*Number of Photons(Np)

noiseE = sqrt(Ne);

Number of Counts (NCo)= CE*Ne

Noise in Counts (noiseCo)= CE*sqrt(Ne)

noiseCo = sqrt(CE * NCo)

log(CE) = 2*noiseCo - NCo

Therefore CE = 10.0^(2*noiseCo - NCo)

From James's data on the intensity noise in the CCD, CE = 0.0269

Quote:

Using this function, I did the same analysis of the upper-left 200x200 pixels over all 200 images: (data from 200 images, over the upper-left 200x200 pixels)

 Around a year ago, Phil and I discussed the possibility of using an OPO to possibly generate our own laser beam at ~2 microns for TCS. This was to avoid all of the usual hassle of the 10 micron CO2 laser.

As it turns out, the 1.5-3 micron range doesn't have enough absorption in fused silica: the absorption depth would be basically the whole thickness of the optics and this is not so useful when trying to correct surface heating.

During my recent trip to JILA, Jan Hall mentioned to me that it should be possible to operate instead at ~5 microns, where laser technology may be solid state and where we can use Si:As detectors instead of the inefficient HgCdTe ones which we use now.

JWST, in partnerships with industry, have developed some Si:As detectors:  http://www.jwst.nasa.gov/infrared.html   

Some internet searching shows that there are now several laser technologies for the mid-IR or MWIR range. Some are <1 W, but some are in the ~10 W range.

Of course, its possible that we'll switch to Silicon substrates, in which case we need to re-evaluate the goals and/or existence of TCS.

- Had a meeting to talk about the basics of LIGO (esp. TCS) and discuss the project

- Created COMSOL model for the test mass with incident Gaussian beam.

- Added a ring heater to the previous file

- Set up SVN for the COMSOL repository

- Got access to and started working with SIS on Rigel1

- Fixed SVN issues

- Refined COMSOL model parameters and worked on a better way to implement the heating ring to get the astigmatic heating pattern.

 June 5

-Discussed the actual project outline 

-Installed Comsol on the system

-Learned the basics of Comsol with the help of tutorials available on 40m wiki

and others.

June 6

-Made few simple models in Comsol 

-Studied LIGO GWADW slides for a better understanding of the project.

-Setup SVN to access remote repository.

- Created a COMSOL model with thermal deformations

- Added non-symmetrical heating to cause astigmatism

- Worked on a method to compute the optical path length changes in COMSOL

-Created a COMSOL model for variation of temperature in two mass system.

-Used the above model for cryogenic conditions.

-checked it analytically.

- Tried to fix COMSOL error using the (ts) module, ended up emailing support as the issue is new in 4.3

- Managed to get a symmetric geometric distortion by fixing the x and y movements of the mirror to be zero (need to look for a better way to do this as this may be unphysical)

- Worked on getting the COMSOL data into SIS, need to look through the SIS specs to find out how we should be doing this (current method isn't working well)

-Created a COMSOL model for cryogenically shielded test mass with compensation plate.

-Analyzed the behavior of the model in different size configurations.

- Fixed the (ts) model, got strange results that indicate that the antisymmetric heating mode is much more prominent than previously thought

- Managed to get COMSOL data through matlab and into SIS

 -Continued with the same cryogenic model created and varied the length of  outer shield and studied the temperature variation inside.

-Compared the temperature difference given by COMSOL with manually calculated one.

- Realized that the strange deformations that we were seeing only occur on the face nearest the ring heater, and not on the face we are worried about (the HR face)

- Read papers by Morrison et al. and Kogelnik to get a better understanding of the mathematics and operations of the optical cavity modeled in SIS

- Read some of the SIS manual to better understand the program and the physics that it was using (COMSOL licenses were full)

-Derived formula for manual calculation of temperature due to total influx.

-Compared the results by COMSOL and by the formula.

- Plugged the output of the model with uniform heating into SIS using both modification of the radius of curvature, and direct importation of deflection data

- Generated a graph for asymmetric heating and did the same

- Aligned axes in model to better match with the axes in MATLAB and SIS so that the extrema in deflections lie along x and y (not yet implemented in the data below)

- Verified that the SIS output does match satisfy the equations for Gaussian beam propagation

- Investigated how changing the amount of data points going into SIS changed the output, as well as how changes in the astigmatic heating effect the output

     + The results are very dependent on number of data points (similar order changes to changing the heating)

     + Holding the number of data points the same, more assymetric heating tends to lead to more power in the H(2,0) mode, and less in the H(0,2)

 -Read about blue team design for maximum power budget.

-Read third generation talks to get a better understanding of the work. 

- Did more modeling for different levels of heating and different mesh densities for the SIS input.

- Lots of orientation stuff

- Started on progress report.

- Attended a lot of meetings (Safety, LIGO Orientation)

- Finished draft of week 3 report (images attached)

 -Attented LIGO orientation meeting and safety session.

-Prepared 3 week report

- Paper edits and more data generation for the paper (lower resolution grid data)

- Attended a talk on LIGO

 -Updated 3 week progress report with new additions and deletions.

-Attended LIGO lecture which was very interesting and full of information.

- Discussed the further project with Dr. Brooks.

-Tried to derive formula for the test mass inside cryogenic shield(infinitely long shield from one side)

Plan for building the model

- Find the fields that would be incident on the beam splitter from each arm (This is done already)

- Propagate these through until they get to the OMC using the TELESCOPE function in SIS

- Combine the fields incident on the OMC in MATLAB and minimize the power to get the input field for the OMC (Most of this is done, just waiting to figure out what kind of format we need to use it as an SIS input)

- Model the OMC as an FP cavity in SIS

    + Need to think about how to align the cavity in a sensible way in SIS (need to find out more about how they actually do it)

- Pick off the fields from both ends of the OMC-FP cavity for analysis

- Add thermal effects to one of the arms and see how that changes the fields, specifically how the signal to noise ratio changes

- Finished the MatLab code that both combines two fields and simulates the adjustment of the beamsplitter to minimize the power out (with a small offset).

- Added the signal recycling telescope to the SIS code that generates the fields

To Do: Make the OMC cavity in SIS

 -Discussed the project outline for next 6 weeks.

-made a write up for the tasks. (attached)

-Analyzed the variation of temperature of the test mass with input power for different lengths of the shield. 

Made a COMSOL model that can include CO2 laser heating, self heating, and ring heating

Figured out how to run SIS out of a script and set up commands to run the two SIS stages of the model

Borrowed thorlabs power meter on 21 Sep 2017.  It is on the south table of the ATF lab.

I've started an 80C cure of two materials bonded by EPOTEK 353ND. The objective is to see (after curing) how much the apparent glass transition temperature is increased over a room-temperature cure.

Ian and I moved some new hardware into the lab, shown in the below photos. It is from the shipment of loaned equipment recently returned by Whitman College. 

Attachment 1:

• ZnSe 1" dia. lenses (x2)
• ZnSe 38.1 mm dia. windows (x2)

Attachment 2:

• Synrad 20 W CO2 laser
• Synrad laser controller

Attachment 3:

• Intraaction Model GE modulator driver
• Intraaction AOM

Attachment 4:

• Second Intraaction Model GE modulator driver
• Unknown optical cavity (was packaged together with the driver)

The ZnSe lenses and windows were put in the CO2 drawer of the optics cabinet. The CO2 laser, AOM, and modulator drivers were left packaged in boxes underneath the large laser table.

Koji: QIL/TCS entrance flooding. Check your lab

Anchal: Can someone take a look at CTN too?

Koij: TCS needs more people @aidan

Koji: CTN ok

Aidan: On my way

Shruti: Cryo seems fine

Aidan: There was a leak in a pipe in the wall of B265A. It was coming from the building air conditioner condensation overflow. Facilities has fixed the pipe and is working on clean-up

I checked the lab this morning. It was dry and there wall was in the same state as yesterday.

11:29AM - Lab has flooded again this morning. I'm calling PMA. Looks to be the same issue as before.

Some photos of water and clean-up.

Summary: I came into the lab around 11:30AM and found water on the floor in the changing room outside QIL/TCS. Turns out the condesation overflow pipe from the AC blew out again. This time near the ceiling. Water was on the floor but also had sprayed a little onto the tool chest and East optical table. A few optics got wet on the table. Initial inspection looks like electronics were spared with the exception of the "broken" spectrum analyzer that was on the floor. 

Facilities came in and cleaned up the water. A small amount got into QIL but stayed near the door as the lab floor slopes up from the door area. They fixed the pipe and were looking into whether there was a blockage cuasing this problem. PMA was notified and John Denhart is coordinating follow-up.

Triage effort: given the AC was still active, John and I strung a temporary tarp across the two tables to block any spray.

http://www.thorlabs.com/thorProduct.cfm?partNumber=CPS180

I bought this laser diode from Thorlabs today to try the current modulation trick Phil and I discussed last Friday. 

That is:

1. Accept that there will be interference fringes on the Hartmann sensor probe beam with a laser diode source (especially if the probe beam is the retro-reflection from a Michelson interferometer with a macroscopic arm length difference)
2. Modulate the current of the laser diode source to vary its wavelength by a few hundreds on nm. Do this on a time scale that is much faster than the exposure time for a Hartmann sensor measurement
3. The contrast of the interference fringes should average out and the exposure should appear to be the sum of two incoherent beams.

It arrived on Friday.

The first pieces of the Bosch framing have arrived from Valin Corporation. These are just small pieces such as the fasteners and the gussets. There are no custom lengths of framing yet.

The details are in the attached Packing List. [1:25PM] I haven't verified that everything is there yet.

 Another box of Bosch stuff arrived in my office. The packing list is attached

 The custom pieces of the Bosch framing have arrived. Transportation is currently moving them downstairs to the lab. The packing list is attached.

 The Thorlabs MFF001 flipper mirror recommended by Bram has arrived. The delivery note is attached.

 Another box of Bosch framing parts arrived today. The delivery note is attached.

 See attached delivery note ...

 Given that the HWS requires several 2" optics to handle the big beam size, I've ordered the following items from Newport:

• 2x 2" 50/50 beam splitter: 20B20BS.2
• 6x 2" NIR mirrors: 5122
• 8x 2" Ultima mirror mounts: U200-A2K

Small/Medium size gloves need to be ordered in order to handle the optics carefully.

New gloves are ordered for the TCS and QIL labs. They arrive tomorrow (Friday).