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  2430   Fri Sep 20 18:34:19 2019 anchalNotesVacuumPossible reflected lights on upgrade

Attached is a first attempt at tracing the rays on reflection from the wedged and tilted window together with the cavity mirror.


I used Sean Leavey's zero and created a ray tracing module for simple purposes which is fast and easy to use. Check out the examples to see the capabilities.

To use, git pull labutils to update and keep labutils /traceit in your python path.

More info about each ray can be seen by layout['R4'] kind of statements. Or just write layout.rays to see info about all rays. This includes their vector positions, the origin phenomenon, and ray etc.

I know a lot can be done to make this look better. But I'm not going to dive into developing this module right now. However, suggestions on how to make the ray trace diagram more useful are welcome so that I can make it more informational.

Seems like most of the reflections would be bunched together in two directions where we should put the beam dumps.


Attachment 1: CTNPrompReflectionAfterUpgrade.pdf
CTNPrompReflectionAfterUpgrade.pdf CTNPrompReflectionAfterUpgrade.pdf CTNPrompReflectionAfterUpgrade.pdf CTNPrompReflectionAfterUpgrade.pdf CTNPrompReflectionAfterUpgrade.pdf
Attachment 2: CTNPrompReflectionAfterUpgrade.zip
  1047   Sun Sep 16 16:42:16 2012 taraDailyProgressfiber opticsetup for fiber optic distribution.

I'm setting up fiber optic so that I can send frequency stabilized laser to ATF. Right now the power coming out is small (0.8 mW from 20mW input). I'm working on better mode match for better efficiency.



Note: due to the space limitation, I cannot pick the beam after the broadband EOM used for frequency stabilized the laser. The beam is taken after the PMC, where it was used to dumped the excess power.

Collimator: http://www.thorlabs.com/thorProduct.cfm?partNumber=CFC-2X-C

optical fiber: nufern pm980

modematching: The focal length of the collimator is 2.0 mm, MFD of the fiber is 8 um. The beam diameter at the lens is then ~360 um.

The coupled power is quite small. I'll check the mode matching again to get more power coming out.


  1049   Mon Sep 17 20:59:15 2012 taraDailyProgressfiber opticsetup for fiber optic distribution.

 I adjusted the mode matching a bit ( changing lenses positions and rotate the lens on the collimator). The coupling efficiency was up to 66%. This should be enough for now.

The power input can go up to ~20mW, so the output is ~12mW which should be enough for gyro.  I also adjusted the polarization, so that the polarization of the input beam matched the fast axis of the cable. I tested the polarization of the output beam with a PBS and got the extinction ratio of ~ 670.

The fiber is polarization maintaining fiber, nufern pm980.IMG_1761.jpg

It has fast and slow axes, and we have to match the polarization of the input beam to the fast axis. To do that

  1. rotate the angle of the output state (B) to find the minimum and maximum transmitted beam behind the PBS. The extinction ratio is max/min.
  2. rotate the input stage (A) and repeat (1) until you find maximum extinct ratio

If the beam polarization matched the fiber axis, the output beam will have linear polarization which gives the maximum extinct ratio. Meanwhile if the beam polarization does not match the fiber axis, the output beam will have elliptic polarization and the extinction ratio will be lower, since certain amount of power will be transmitted and reflected no matter how you rotate the beam.



  • The output polarization is quite sensitive to the fiber motion/position. I could not really clamp it down because I had to rotate the fiber, and need to give it some slack. So the measured power changed a bit during the measurement. It could moved from 5 uW to ~ 30 uW for the minimum transmission. This increased the error by a factor of 6.
  • The reason for low extinction ratio may also come from the fact that the output beam angle changes with the rotation at B. So the beam did not always hit the PBS perpendicularly. I kept the PBS and PD close to output as much as possible to minimize any effects due to the beam position. This can be repeat by keeping the beam output stable, and rotate the PBS with a rotatable mount instead. I think Dmass mentioned that he had the stage. I'll ask him later.


  1201   Thu Jun 20 17:58:21 2013 EricaDailyProgressfiber opticMode matching

Tara showed me the lab, along with the needed booties and safety glasses.  We took off the plastic covering the table.   I took inventory of lenses in the lab so I know what I have to work with in order to mode match the laser to the collimater/fiber optic. Mode matching will prevent the laser from scattering and allow the most power through. 

We measured the distance from the PMC to the lens (8.2 in) and the total length from the PMC to the beam splitter that would come right before the lenses used to mode match (45 in). 

I will try to catch up on understanding the parameters needed to mode match and will copy the programs Beam Profile Simulator and Mode Matcher onto my laptop in order to determine which lenses are needed.  I also need to read up on various optical components used in the lab.



  1203   Fri Jun 21 18:02:49 2013 EricaDailyProgressfiber opticMode matching

I read more about various optical components used in the PSL lab, such as the half and quarter wave plate, electro-optic modulator, etc. 

Over lunch, Dr. Weinstein gave another talk for LIGO, this time focusing on the specific components on the interferometers, such as the mirrors and seismic isolators.  Also of interest, he explained why we have certain elements in our bodies, namely due to neutron star mergers and star core implosions. 

Another measurement was taken of the setup because I missed a lens in the beam path yesterday.  I copied the program Beam Profile Simulator and Mode Matcher onto my computer from one of the lab computers and spent the afternoon learning how to use it and what different parameters meant.  The programs allow you to enter certain parameters (beam waist, waist positions, lenses' focal lengths, total length, etc) and from those, determine needed ones, such as position of the lens.  For some reason, when I input the setup into both programs, it did not work in MM.  Then Tara and I tried entering the data into another program (I will ask for the name later) and that agreed with the BPS.  Even when I changed the overall length of the whole system to be at the beam waist, MM still did not work. 

I better understand how the collimator is set up, so I will obtain the needed information from Thorlabs, listed in the following link. 


The two collimators we are considering to use have focal lengths, f=2mm and f=4.6mm. 

Product numbers:  CFC-2X-C, CFC-5X-C

We want the beam waist to be located at the lens in the collimator.


For mode matching, one needs to match the spot size (beam radius, w) and position. 

Note: On the BPS, beam size means the beam radius, spot size, or w, as named in the paper by Kogelnik and Li, 1966.

  1209   Tue Jun 25 09:58:08 2013 EricaNotesfiber opticmode matching

for June 24, 2013

 I used MatLab and JamMT to mode match a laser beam coming from the PMC to the cavity for Tara (see diagram at post 1100).  It is for the lower or left PMC.   Used various equations from Kogelnik and Li, 1966, to determine the q value and beam waist at various points, particularly equations 16, 18,10 and 41.  The revised setup is in attachment 1.

I went to the LIGO laser safety training session led by Peter King. He discussed the importance of safety training, various biological effects lasers can have on the body, particularly the body, and how to work around lasers safely.  Safety glasses have an OD number for different wavelengths and should be checked at the door before entering a lab. We have two forms that we need to fill out. 

Then I went on to mode matching the fiber optic to the laser with the previously mentioned programs and will try coupling the fiber optic tomorrow.



Attachment 1: refcav_mm.JPG
  1213   Wed Jun 26 09:44:09 2013 EricaNotesfiber opticmode matching

June 25, 2013

Read some papers on noise due to fiber optics as well as cancellation of phase noise. 

We borrowed a fiber optic cable from 40m, that maintains polarization.  Realized that I did not include the collimator in calculations for mode matching, so I redid it.  The collimator I chose has f = 2mm, with the distance between the fiber and lens 3.5 um.  The lenses used to mode match have focal lengths f = 143.2mm and f= 74.9 mm. 



I have set this up on the table, but have yet to do alignment with the cable. Tomorrow (June 26), I'll try to get the laser beam into the cable. 

 Other tasks:

  • talk to ATF and crackle lab to understand what they are doing in the lab and what their noise budget is
  • look at how much noise a fiber adds and whether that level is under our noise budget
  • find out how noise is measured at end of fiber
  • finish filling out safety sheets

To clean lenses:

  • wear gloves,
  • work at the table with clean air. 
  • turn on the bright light (need to see what it's called) to better see particles on the lens
  • If there is dust, first spray with air cannister
  • if it's still dirty, use acetone, methanol, and then isoproponol to clean using tweezers and lens tissue.  make sure not to touch lens with tweezers
    • if it's very dirty, start w/ acetone and go down the solutions as stated above
    • if not, can start w/ methanol


Attachment 1: P1020393.JPG
  1215   Thu Jun 27 09:12:58 2013 EricaNotesfiber opticmode matching

June 26, 2013

Spent the day trying to mode match. 

First I used the power meter to measure the output of the fiber but its response was very slow so it was hard to align the beam and make adjustments so I hooked up a camera instead.  Then when the light could be seen on the camera, I would switch to the power meter to see if I could incrase the power and have a quantity for the power output. The whole process took a long time because there were many parameters and I trouble at times aligning the beam. 

Higher up in the beam path the power is 7mW.  The highest power output I have obtaned is about 850 uW, which is improvement from the intitial 7 nW. 


Note: Optimize one parameter before changing another (1 lens). 

  1222   Tue Jul 2 11:21:24 2013 EricaDailyProgressfiber opticmode matching
Sorry I type up my progress, but keep on forgetting to submit.

June 27, 2013

Talked to Evan to better understand GYRO. The goal of GYRO is to be able to differentiate between tilt and actual noise. There is a laser that is split and goes in opposite directions around a cavity which has mirrors on opposite corners and beam splitters on the other 2 corners; the laser is locked to the cavity. This setup uses the Sagnac effect. We are sending the CTN laser over because it has a lower noise, due to the shorter cavity, and will serve as reference for the noise level for the GYRO setup. I emailed Zach to ask about more specifics on the GYRO noise because he has a better idea but he has not yet replied.

I used a WinCam and a program called DataRay to look at the Gaussian profile of the beam at various differences from the output of the fiber(see setup here: http://nodus.ligo.caltech.edu:8080/PSL_Lab/1213). I took the radii from the two profiles at each distance, averaged them, and plotted that as a function of distance from the lens in the collimator and photodiode in the WinCam. This is to find the beam waist and its location because the current setup did not result in a beam waist at a location we predicted. See attachment 1.

I fit the equation 20 from Kogelnik and Li, 1966 to the graph and obtained a waist of 35um, at z = -0.0237 m. To check, I used equation 22, theta = lambda/(pi*w0) and the slope of the graph, to solve for w0. This ended up agreeing with the 35um.

June 28, 2013

Read papers Tara gave. Looked around for ones on related topics.

Took the new waist from yesterday's data and found a new setup. BPS program doesn't seem to work. After closing and reopening JamMT, 4 lenses show up on the diagram despite the fact I only chose 2 lenses, so I'm not sure what was going on. I ended up just doing trial and error in the program, until I got a setup that fit my parameters.

Setup is in attachment 2. The lens with f= 85.8mm is the lens that is already on the table. I added lenses with f=74.9mm and 143.2mm to mode match.

The beam waist and its location seems to match what was calculated.

I played around with different locations and got a maximum output of 48um. Unfortunately, I didn't look at the power further up the beam so I don't know what percentage. The power output at various locations seem rather strange because the data didn't converge to a single maximum, despite having made the most adjustments I could at each point.

July 1, 2013

Tried to find out more about self-homodyne detection and noise that the fiber optic contributes. Tried to find Eric Q but can't seem to ever find him so I emailed him to talk about crackle lab.

Went to Alan's talk today on the sources of gravitational waves. They include compact binaries, core collapses, spinning neutron stars, and cosmic gravitational wave background.

With 2 mW power, I was able to obtain 100uW from setup seen in attachment 1. I set up a half-wave plate, beam splitter, and mirrors to be able to recombine the beam tomorrow.
Attachment 1: snip_of_beam_profiling_6_27.JPG
Attachment 2: P1020518.JPG
  1224   Wed Jul 3 09:46:48 2013 EricaDailyProgressfiber opticmode matching
July 2, 2013

Started writing up the progress report due July 9. Need to find more papers about the different types of noise from a fiber.

I talked to Eric Q about the crackle lab. In the interferometer at LIGO, there are blade springs with mirrors that hang from them. The laser reflects off of these mirrors; a horizontal displacement of the mirror leads to a vertical displacement of the blade spring. Noise in the laser can lead to perturbations of the mirror, and therefore, perturbations of the blade springs, which can mask real signals. His setup is a Michelson interferometer with the mirrors placed at the end of masses hanging from blade springs. See attachment 1 for a diagram of the setup. His requirement for noise is 10^-15 m/sqrt(Hz) for the spring, with a displacement of about 1 cm, operating at a frequency of about 100 Hz. Using the equation in attachment, it says we need a frequency noise of 10^(-11) Hz/sqrt(Hz) which is much lower than what I expected so I will have to ask again to clarify.

Recombined the beams from the fiber and the laser and set up a photodiode. Placed the collimator from the fiber optic on a translational stage because it allows us to minutely change the length in order to more easily change the relative phase difference between the two beams. Talked to Evan about finding the beat frequency. We want to adjust the lengths of the two beams such that the phase between them is pi/2, so there is completely destructive interference => wL/c = (2n+1)pi/2.
Attachment 1: 130703-095332.jpg
  1235   Thu Jul 11 01:40:19 2013 EricaDailyProgressfiber opticmode matching
Tara changed the lenses in the beam path so I redid calculations for mode matching. Here is the setup.

I placed the lenses and obtained about 1% (1.54 uW out of 5.2 mW).
  1237   Fri Jul 12 00:51:39 2013 EricaNotesfiber opticmode matching
I finally got MatLab installed on my computer from Caltech.
You can get programs installed by being a Caltech student/faculty, through IMSS. Here is the website:

One of the things, I was unsure about and talked to Evan about mode matching where should the output waist be and how does one calculate it. Previously, I took the mode field diameter from the fiber, the focal length of the lens in the collimator, and then calculated the waist q parameters (from Kogelnik 1966), like I did calculating from the PMC. However, that leaves some questions - once the waist from the fiber is determined, when mode matching, should the incoming waist from the PMC be placed at the lens, or at the distance we calculated the waist to be from the lens in the collimator?

Other potential problems is possible change in the distance from the lens to the fiber in the collimator if one accidentally rotates it while attaching the collimator to the stand.

This can be resolved by looking the Gaussian profile and measuring the radii at various distances, to calculate the waist (see http://nodus.ligo.caltech.edu:8080/PSL_Lab/1222). Then when mode matching, one would try to place the waist at the lens in the collimator. I measured the Gaussian profile from the input side by switching the output and input sides of the beam so the laser was directed into the output end of the fiber, without altering the input end (distance from fiber to collimator, without removing fiber from stand and collimator, etc).

Then I measured the waist after the two fixed lenses from the PMC, to ensure the theoretical calculations for the waist were correct.

When checking the waist coming after the PMC, our calculations from the Gaussian profile did not agree with the location of the waist we observed with our eyes. Evan discovered that the lens we were using was not fused silica (UV) as most lenses are but BK7 (C), which for a given radius of curvature, has a different focal length than fused silica. So the lens we thought was f = 143.2mm had a focal length of f = 127.1 mm. Once this change had been made in the calculations, it agreed with our observations.
This means I'll have to redo the inventory because some of the lenses are fused silica, others are BK7.

Here is the final determination of the location of the waist coming from the PMC and the setup I used to determine it.

This is the new mode matching setup.

After setting it up, I obtained an output of 15%. 1.24mW out of 8.4mW.
  1240   Tue Jul 16 10:27:47 2013 EricaNotesfiber opticmode matching, beam recombination
July 14, 2013

We just went with the setup from yesterday.

We adjusted the input fiber so that one axis is vertical. If the lens of the collimator is as close to the fiber as possible, then the two screws on the side of the collimator are perpendicular to the little notch on the collimator, which is supposed to line up with one of the axes. Then we moved around the other knobs so we ended up getting the same maximum power output

At the output, we aligned everything up. After pol. beam splitter, there was a lot of power coming out of both s and p faces. This was confusing because we used a polarizing beam splitter to pick it off from the main beam.

We checked the beam going into the fiber was linearly polarized with a polarizing beam splitter - which it was, s-polarized.

We checked the output beam - took out the 45s beam splitter and then put pol beam splitter in there, rotated fiber until s- polarization was at a max (reflected beam)

We replaced the 45s beam splitter, still a lot of power not coming out in the direction we wanted - got transmitted rather than reflected. However, the power output from each beam after the 45s BS was about equal so didn't do anything about it.

After we checked the polarizations, we placed the polarizing BS to look at the beam recombination, and there was still light transmitted and reflected. This could be that the beam was really messy, and since the polarizing beam splitter is not 100%, there was still some p-polarization. This seems to be the reason why Tara had me place this second polarizing BS.

We placed a lens (f=70mm) placed in front of output to focus the beam, profile more like that from the laser

Using a OD2 filter, we used a photodiode (PDA100A) and an oscilloscope but could not see anything. Can't see fringes, just a DC line. Translating stage doesn't do much, we fiddled around with the knobs on mirrors and stage but not much change

Then we switched to looking at the Gaussian with DataRay, but - Gaussian from beam, not Gaussian from laser - clipping edge of mirrors so had to realign.

Here we can see fringes but the beams aren't very aligned. If they were exactly aligned, then you would see total destructive and total constructive interference. Even with moving knobs, it didn't really improve. Will work it more tomorrow.

Note: The power output from both beams should be about equal intensity.
  1241   Tue Jul 16 11:02:47 2013 EricaNotesfiber opticmode matching, beam recombination
July 15,2013

Asked Rana how to do the calculations for the noise.

Here is the picture of the explanation.

Rana suggested we place a lens (f=30mm to 200mm) to after the final polarizing BS so it would be easier to match the beams and so it is focusing into the photodiode. If the beam was 1-1.5mm at the mirror, then a lens shouldn't be needed before the BS. We placed a f = 30.6mm after the pol. BS but the beam profiles were not particularly alike, since the beam from the lens was diverging fairly quickly, but that definitely made it easier to see the beams because they weren't diverging. I replaced the other lens after the fiber, before the 45s BS, which made the beam profiles match a lot more.

I tried aligned the beams, but in a way that the beams really overlapped only where the photodiode was supposed to be, which was dumb. Could not read anything from it. So I redid the alignment for both beams, so they were about 3" from the table at all points and that definitely improved the matching, notably, giving a larger range over which the beams were overlapping very well.

We were able to detect some fringing just on the oscilloscope and were able to improve on by adjusting the knobs. The signal is at a certain DC level, with wiggles which are noise. However, whenever the stage, or table, or other components are touched, we can see it on the oscilloscope. Evan was concerned that the stage wasn't perfectly aligned with the beam, so translating the stage would ruin alignment ,but it didn't seem to much of a problem.

Note: Noise from laser is 10^4 (Hz/rt(Hz)).

task: need need need to find paper on fiber noise!!

Also, talked to Evan about Gouy phase and how the PMC works, different kinds of polarization modes (including some weird cashew shaped ones), and PDH setup.
Sidebands = phase references.
  1242   Wed Jul 17 11:58:47 2013 EricaNotesfiber opticmode matching, beam recombination
July 16,2013
I tried improving mode matching by adjusting two knobs on the mirrors at once but that wasn't leading anywhere.
Evan suggested improving the polarization going into the input beam because we wanted the most linearly polarized light. So a half wave plate was placed right in front of the input collimator and another was placed before the final pol beam splitter before the photodiode. At each polarization on the first HWP, I would rotate the second HWP back and forth over a wide range of angles to get a feel for the eccentricity of the input light. At 5 degree intervals (of polarizer, so 10 degree intervals in polarization) over a 66 degree (for HWP) range, we changed the HWP in front of the input, and then oscillated the HWP at the output back in forth to see the fringing. The recorded pk-to-pk amplitude was noted using the cursors and by holding the fiber to bring about more drift.

The peak was at around 30 degrees for the HWP. I'm not sure why the two maximum do not have the same amplitude. We placed the polarizer at 30 degrees, removed the HWP at the output end, and then translated the stage. Now all the light coming out was S-polarized. We had to readjust the knobs on the input collimator stand because the power output was a little low; the half wave plate must have redirected the light a little bit.

So it turns out what I thought were fringes yesterday was just noise from the fiber, laser, etc., which we also want to detect. Something I should have noted yesterday was the drift of the DC level. Today we figured out that the drift was actually the fringing that occurred from a change in length. I could see the oscillations on the scope from when I translated the stage slowly or quickly. Then we optimized the alignment to increase the signal.

However, the length of the beam is fluctuating too much (due to temperature) so we can't keep it in the linear part of the cos^2 model for power. One thing to note is the noise seems to decrease at the max and min - not sure why.
  1243   Wed Jul 17 18:29:37 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
Went on a tour to 40m lab led by Jenne. It's basically a prototype of the ones in Livingston and Hanford. It allows LIGO to test coatings, control systems, etc. before AdvLIGO is even built.

I tried making the drift go away, but it seems to me it got better, and then got worse.
I tried turning off just one HEPA filter, then two. I couldn't really find that much stuff to insulate the fiber, so I used the bubble wrap that the coil came with to wrap around the coiled fiber. However, that didn't seem to really help at all.

With only 1 HEPA filter off (the one closest to the input), I was able to get a rise time of about 35s, which is pretty similar to what there was yesterday. With the 2 HEPA filters off, I got a rise time of about 5s.

For some reason, at one point the signal just started oscillating like crazy. I lowered the power coming from the output fiber (from 0.5 to 0.4mW) so it would be closer to the original beam (0.3mW) and there wasn't noise any more, but I'm not sure if it was because of the power differential at all.

How much drift is allowable? Does it have to be flat or is it okay if it is simply linear?

I can increase the output from the fiber to 1.3 mW.

  • A message has popped up on the oscilloscope that I've been using saying it needs to be recalibrated.
  • The wire connecting the probe to the power meter (PM100D, the red one) is coming out of the insulator.
  • Rana had me bring the SR620 to 40m so that's where it is.
  1245   Sat Jul 20 23:39:09 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
July 18
Redid inventory of the lenses and printed out a new sheet because there are fused silica and BK7 lenses, which have different focal lengths for a given radius of curvature. It only has the lenses in the box. Tara had like 6 to 8 other ones but I don't know where they are.

Looked for papers that give numbers for noise added... Like before, I'm having trouble.

got login for SVN to work

Evan helped come up with other solutions to try to reduce the drift on signal from the recombined beam. We put UHV aluminum foil on the coil of fiber to reduce the acoustic noise but it didn't seem to have much effect on the drift. Acoustic sound affected the fiber because the drift seemed to speed up a little bit when we closed the cabinet door and jumped around. When the lab door was closed, there was a spike in the signal but thing settled down fairly quickly. We turned off both Hepa filters but like yesterday, it also didn't seem to do much. We elevated the coil off the table by using the black rectangular clamps to dampen possible transfer of movement from the table to the coil.
We locked the laser to the cavity to reduce the laser noise. The error and control signals were very steady compared to the drift in the beam signal.

We calculated the change in frequency over 1 period of drift is about 5 MHz, and for the fiber to change by 1 wavelength, it would take a temperature change of 16 mK. Looking at Rana's graph of for noise calculations (http://nodus.ligo.caltech.edu:8080/PSL_Lab/1205), we calculated the rms temperature noise due to ambient air at 100 mHz (because the period of the drift was on the order of 10s) was 100mK rms, which is an order of 10 larger than the calculated change in temperature.

The fiber passes by the laser, which is emitting a bit of heat, which may be a part of what is causing the drift.
  1251   Tue Jul 23 10:29:12 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
July 22, 2013

We placed a plastic container from the GYRO lab over the spool of fiber. We wiped everything down w/ isopropanol. The cap is placed top side up and then the bottom is placed upside down on to the top of the cap. This is because the inside of the cap has ridges. There are two holes that the fiber is threaded thru. We used bubble wrap to cover it. It's not the most airtight but it should be okay. We left the aluminum foil surrounding the spool, to restrict air flow into the fiber. Then we left it there for awhile but coming back to it, there wasn't much improvement.

Evan suggested using a AD 590 to measure the temperature fluctuations of the table. Rana suggested we use the substitute for AD 743 that Zach found, which I need to find. Went to 40m to get a nicer circuit board and find a FET OpAmp with low current noise. We got a Vector Circboard 8015 and two OPA604's. We'll be building two setups so we can cross-correlate them and make sure the measurements are accurate.

tomorrow we will be soldering stuff.

  1266   Tue Jul 30 15:48:47 2013 EricaDailyProgressfiber opticnoise for GYRO


Talked to Evan to better understand GYRO. The goal of GYRO is to be able to differentiate between tilt and actual noise. There is a laser that is split and goes in opposite directions around a cavity which has mirrors on opposite corners and beam splitters on the other 2 corners; the laser is locked to the cavity. This setup uses the Sagnac effect. We are sending the CTN laser over because it has a lower noise, due to the shorter cavity, and will serve as reference for the noise level for the GYRO setup. I emailed Zach to ask about more specifics on the GYRO noise because he has a better idea but he has not yet replied.

Here is Zach's reply:

Because of common-mode rejection from the way the gyro works, the cavity length fluctuations only contribute to the gyro noise at the level of ~10^-7 or 10^-6. The gyro noise requirement for the beat frequency from the two counter-propagating beams is ~1 mHz/rtHz down to ~10 mHz or so, so this means the required stability of the light from the fiber is more like 1-10 kHz/rtHz at those frequencies.
  1267   Tue Jul 30 16:19:32 2013 EricaNotesfiber opticsetup for beam recombination
Diagram for newest setup with additional half wave and lenses:
  1271   Thu Aug 1 00:25:02 2013 EricaDailyProgressfiber opticinsulating foam

Wrote progress report

Fixed graphs from 7/21/13 because I had the wrong increments for the axes. The values the oscilloscope reads out is the exact value, no need to scale them.

Tara received the insulating foam today so we taped it around the fiber. We also enclosed the spool of fiber in the plastic container, but this time, without the aluminum foil around the spool. This time it was used to cover the hole in the corner allowing the fiber to still pass through. However, there doesn't seem to be much effect on the time scales. We do seem to be able to see the noise more easily though. See http://nodus.ligo.caltech.edu:8080/PSL_Lab/1251 for graphs.

  1276   Fri Aug 2 12:38:41 2013 taraDailyProgressfiber opticinsulating foam

I turned off the hepa fans over the table over the night. I came back this morning and the temperature (measured on the vacuum tank) was very stable(within 2mK) over 2 hrs.


above:BLUE Temperature measured on the can, the Y scale is in degree C. The temperature variation is within 2mK over 150 mins.


So I looked at the PD for Erica's fringe measurement, the fringe wrapping was slow, so with better temperature insulation, we should be able to hold the fringe for at least a minute.


above: The fringe signal from PD, the cursors show the max/min signal from the fringe. The signal drifts from min to max over ~ 60 seconds compared to ~10seconds as before.


So the drift we saw before was very likely to be from the temperature drift (1mK per second for 20second fringe wrap). More thermal insulation on the optic should reduce the temperature drift.

  1279   Mon Aug 5 12:21:00 2013 EricaNotesfiber opticcalculation: phase change for fiber

I'm not sure of the exact material of the fiber and therefore its index of refraction and coefficient of thermal expansion, so I'll have to email Thorlabs.

Right now I have
n = 1.5
alpha = 10^-6 /K
lambda = 1064nm
L = 60m

to give a deltaT of about 10 mK for the temperature changed needed to change the length of the fiber by one wavelength, or for the phase to change by 2pi.
Attachment 1: 130805-121449.jpg
  1280   Mon Aug 5 12:42:51 2013 EricaNotesfiber opticComponents


60m long

1064 nm PM FC/APC Patch Cable: Panda Style








  1282   Tue Aug 6 12:31:24 2013 EricaDailyProgressfiber opticinsulating foam
When we turned the laser back on today, the signal was oscillating pretty quickly. We taped white insulating
sheets of foam with scotch tape around the spool of fiber so that was sealed. We placed a thicker grey sheet of
foam underneath and on top of the spool. The top one was weighted down. Then we pulled down the drapes and let
the setup sit, so everything would settle down after we disturbed it.
After at least 30 minutes, the signal was oscillating even faster, a period was 7.5s.
However, around 6:30pm, the signal had slowed down, so the period was around 80s. We took some data with the
spectrum analyzer, pausing at the max and min and continuing whenever we hit a linear region so there was about
30 averages.

Will include graph

Once we have the noise budget, we'll have to measure various sources of noise and determine which sources cause
what part of the noise budget.
Types of noise:
  • Temperature -> length
  • Acoustic/Seismic
  • Laser frequency drift

We looked at possible circuits to measure the temperature fluctuations on the table, since the current circuit we have has an unaccounted DC value.
This is one possible one. AD 587 is a voltage reference. There a low pass filter to get rid of the noise. The potentiometer is to match the 2 voltages goign into the op amp.

The values are tentative as is the circuit itself.

Got a reply from Thorlabs but they weren't very helpful. The core is doped silica but the doping information is proprietary. They gave me the spec sheet that can be found online as well as a graph displaying the relation between wavelength and attentuation.
  1284   Wed Aug 7 13:27:00 2013 EricaDailyProgressfiber opticmore foam, calculations for convertion from voltage to frequency
august 6, 2013

We better insulated the exposed fiber by sandwiching it on both sides with foam. Instead of the aluminum foil, we used the bubble wrap that we used previously to cover the holes. We did this because the aluminum could be vibrating, which causes more noise.

I was able to take spectrum data since the drift was slow enough, at least 30s on the linear region.
The laser was not locked to the cavity when I took the data. I'll be putting it into matlab
The data was taken with the span at 400 Hz, 1.6 kHz, and 12.8 kHz. I took 50 averages
I tried to take the data so the pk-pk voltage would be the same but it still drifted a little bit.
For the data taken wtih the 1.6 kHz and 12.8 kHz, deltaV = 2.24V, Vmax = 2.7V, Vmin= 460 mV
For the 400 Hz, deltaV = 2.10V, Vmax = 2.56 V, V min = 460 mV.

The y-axis from the graph is in V/rt(Hz).
Here is the calculation done to calibrate between V and length change. see the correct calculation in 1286

*NOTE: I made an error in the calculations here. \phi = kx. But when I plugged in pi/4 to solve for dV/dx at pi/4, I did not multiply it by two. See

Here is the conversion from length to frequency.
  1286   Wed Aug 7 18:53:20 2013 EricaDailyProgressfiber opticnoise budget, Matlab notes.

pink is deltaV = 2.1 V for the 400 Hz. blue is deltaV = 2.24 V for each of the frequencies.
deltaV is the Vmax - Vmin of the signal, as seen below in my calculations. As stated in yesterday's post, the deltaV's aren't the same because the maximum drifted a little bit, probably due to alignment or slight changes in intensity. The different delta V's affect the calibration from voltage to length.
More details such as Vmax and Vmin values are in 1284. Laser was not locked to cavity.

I combined plots from yesterday taken at different frequencies. I used the concatenate command that Tara gave me.

Started thinking about presentation.

Reading up on the AD590 and potential circuits for measuring temperature. Evan mentioned doing one based off of Fig 13. from the AD 590 spec sheet.
We would use the AD 587 and put in a capacitor for a low pass filter, to get rid of noise.

Chloe pointed out an error in my calculations from yesterday for the calibration between voltage and length. Instead of calculating at pi/4, I was actually doing it at pi/8. so here is dV/dx at pi/4.

Matlab Notes:
can't load excel files into Matlab.

first number indicates direction of combination the matrices, 1 is vertical concatenation, 2 is horizontal.
the numbers in the parentheses indicate the elements wanted from each file.

Also, I attended the Wednesday lecture at lunch. It was about modeling polar ice caps. They seem to be using techniques that are similar to some people in the data analysis group, using hypothetical data, plugging those parameters in, and seeing the result, though they seem to know even less about the constraints that are going into the simulation.
  1296   Tue Aug 13 12:39:36 2013 EricaDailyProgressfiber opticrewrote calculations for converting from voltage noise to frequency noise
The equation for voltage is derived here: 1241
Attachment 1: P1030458.JPG
Attachment 2: P1030459.JPG
Attachment 3: P1030460.JPG
  1302   Fri Aug 16 10:40:20 2013 EricaDailyProgressfiber opticSpectra Data Locked and Unlocked Laser

 Tara improved the alignment so we got a little over 1V coming from the fiber alone. We took another run of data of the recombined beam:

laser not locked to cavity:

deltaV = 3.64V

Vmin = 880mV

Vmax = 4.52V


laser locked to cavity:

deltaV = 0.17V



This matches up with the original data taken.


We also took data for the noise of the spectrum analyzer.

This can be approximated at a straight line.  I took an average of the points so the noise level is at 1.9*10^-6 Hz/rtHz.


Then we took data with the laser locked to the cavity.  The power is much lower because we accidentally misaligned the beam.

As seen in the graph below, the fiber seems to be okay; the plots of the laser unlocked to the cavity match up.

deltaV = 0.17V




We took data for the error signal from the servo. The slope of the error signal for ACAV path is 200kHz/V (see elog entry  1920) .  We are using this to convert from voltage noise to frequency noise.  The shape of the spectrum from the recombined beam follows the shape of the error signal.




Attachment 2: 0815error.fig
  1303   Fri Aug 16 15:11:32 2013 EricaNotesfiber opticNoise Budget for 60m fiber


Attachment 2: NoiseBudget.fig
  1419   Mon Mar 31 17:44:52 2014 EvanDailyProgressfiber opticGyro fiber pickoff now on north cavity transmission

I removed the 90% reflector from the north transmission path on the ISS breadboard and then installed the fiber launcher.

The ThorLabs power meter says 440 uW going into the fiber on the CTN side; the ThorLabs fiber power meter says 260 uW coming out on the ATF side.

  1427   Mon Jun 9 20:42:21 2014 EvanDailyProgressfiber optic60 m PM980-XP fiber

I used the 633 nm fiber illuminator and the ThorLabs power meter (set to 633 nm) to test the 60 m polarization-maintaining fiber that we have.

Power right out of the illuminator was 1.25(2) mW, and the power out of the fiber was 0.45(1) mW. Since this fiber is only specked to work above 980 nm, I'm not sure how to interpret this number.

I'd like to compare to the 35 m PX980-XP fiber we have strung from CTN to Crackle.

I performed the same test with the 1060XP fiber (50 m, not polarization maintaining). I got 0.12(1) mW transmission.

  1434   Tue Jun 24 10:49:27 2014 Emily, EvanDailyProgressfiber opticFiber mode-matching, PMC tune-up

Installation of optics for fiber phase noise measurement

To couple CTN light into the fiber, we decided to pick off using the reflected port of the PBS directly after the south EOAM. In order to mode-match into the fiber, we installed two lenses (and a steering mirror) between the PBS and the fiber.

Mode matching details are as follows: the round trip length of the PMC is 42 cm and the radius of curvature of the concave mirror is 1 m; this gives a waist of 370 microns.  From there, we calculated the proper lenses needed: PLCX-25.4-64.4-UV-1064 (lens 1, focal length 124 mm) and a PLCX-25.4-128.8-UV-1064 (lens 2, focal length 250 mm). Between the two lenses is a mirror, Y1-1037-45-S, which is tilted at a ~45 degree angle to guide the light from lens 1 to lens 2.  Lens 1 and Lens 2 are roughly 2 inches away from each other. There is a fiber coupler placed 4 inches away from the second lens.

Currently, is about 1.4 mW going into the fiber, and about 150 uW coming out.

Edit: We did some more aligning and found that there is 2.2 mW going into the fiber and .7 mW coming out.

PMC alignment tune up, FI power adjustment

Coupling through the PMC was very bad today; we saw 12 mW incident and ~1 mW transmitted. I (Evan) touched the three steering mirrors before the PMC and brought the transmission up to 5 mW.

In order to have more power incident on the fiber, we changed the angle of the HWP immediately after the PMC from 306.5 degrees to 338.0 degrees.

  403   Fri Nov 19 01:24:03 2010 taraDailyProgressopticchanging Faraday Isolator's mount/ TF from ACAV path

I switched the post to V-block for Faraday Isolator mount, for better stability, and adjusted the Faraday isolator to minimize back reflection to the laser.

I also measure the TF from ACAV path,  The UGF is ~65 kHz.


  The faraday isolator was installed on a standard pillar post, so I use a V block to mount it instead.

After adjusting the FI, I remeasured the beat note frequency, and the signal did not change from yesterday measurement.

(no differences between red and green plots)

blue: beat signal before fixing the ACAV opening

red: beat signal after fixing the ACAV opening

green : beat signal after re installing the FI



ACAV TF: I connect the signal output after the PDH servo box to SR560 A and SR785 B (resp)

                 Then source out from SR785 is connected to SR560 B

                 The output of SR560 is connected to SR785 B (ref) and to the VCO


The setup for SR560 is DC coupling for A and B, select A - B, gain 1, no filter.


Attachment 1: beat.png
Attachment 2: ACAV_TF.png
Attachment 3: data.zip
Attachment 4: code_2010_11_18.zip
  437   Mon Dec 20 19:55:11 2010 taraDailyProgressopticrearraging optics for beat measurement

I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.

  440   Thu Dec 23 22:41:28 2010 taraDailyProgressopticrearraging optics for beat measurement

Beat measurement optics' height is changed to 3". I cleaned all optics already, but I couldn't really clean 1/2 and 1/4 wave plates, one of the f =200 mm lens is quite hard to clean.

I'll wait and ask someone before trying to clean again. I cannot lock both cavities at the same time, once I can, I'll align the beam on the PD.

Also ACAV's PD for ACAV_trans_PD is broken. It gives out 11 V regardless of the beam falling on the PD, so I replace it with a PD that is used for NPRO_PWRMON.



I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.


  441   Sun Dec 26 02:42:47 2010 taraDailyProgressopticrearraging optics for beat measurement

Both cavities are locked at the same time. The temperature setting are, RCAV = 34.95, ACAV = 37.2.

I realigned the beam onto the PD to get maximum contrast. I'll readjust the setting back to the original value

and see if the beat noise is improved.

I just notice that one of the beam on the mirror on ACAV's path behind the cavity is almost clipped. I'll readjust it tomorrow.


Beat measurement optics' height is changed to 3". I cleaned all optics already, but I couldn't really clean 1/2 and 1/4 wave plates, one of the f =200 mm lens is quite hard to clean.

I'll wait and ask someone before trying to clean again. I cannot lock both cavities at the same time, once I can, I'll align the beam on the PD.

Also ACAV's PD for ACAV_trans_PD is broken. It gives out 11 V regardless of the beam falling on the PD, so I replace it with a PD that is used for NPRO_PWRMON.



I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.



  442   Mon Dec 27 02:51:33 2010 taraDailyProgressopticrearraging optics for beat measurement

I measured the beat noise after I realigned all optics behind the cavities. The power has not been reduced to 1 mW yet.

This is just a quick measurement to see where we stand (red curve). The noise gets worse compared to the best measurement (green) before the optics behind the

cavities are rearranged, but the mechanical peaks around 1kHz are suppressed significantly.

Attachment 1: beat_2010_12_27.png
  599   Wed May 4 01:20:00 2011 taraDailyProgressopticminimizing RFAM/ aligning 35.5 MHz EOM

I minimized the RFAM by aligning the 35.5 MHz EOM and remeasured the RIN coupling coefficient.

The upper limit is 5 [Hz/uW (fluctuation of input power = RIN x Pin) ]@ 10 Hz

(This entry is approved by Kiwamu and is written in his style)Tue May 10 19:20:22 2011

  As pointed out in the LIGO-X meeting that my setup might suffer a lot from RFAM, so I came back to:

  • 1. minimize the RFAM by aligning the 35.5 MHz EOM,
  • 2. determine how much Vmod I can apply to amplitude modulation without exciting the RFAM noise above the background, and
  • 3. remeasure RIN coupling coefficient again with the allowed maximum Vmod.



The power input was 1mW as usual.

The frequency of Vmod is 10Hz. The amplitude of Vmod to EAOM for amplitude modulation was varied from 2 to 10 Vpkpk. Common/Fast gain was 500/900. I had to reduce it so the signal is not too large. I measured the spectrum of FASTMON and tried to observe the peak at 10Hz  with 12.5 mHz linewidth. The background level was ~10mV.

I do this to determine what is the maximum driving voltage where the effect from RFAM is still small compared to the background.


Drive Vpkpk     FASTMON peak(Vrms/rtHz)

10                   74.7

8                     48.17

5                     29.6

3                    23.02

2                  ~comparable to BG level ~ 10mV/rtHz


[ 1. aligning EOM ]

I picked up the beam after EOM on RCAV path and sent it to a PD (Thorlabs PDA10A.)  There were 35.5 MHz pick up on the table, so I had to choose where the peak from pickup was minimum. Then I adjusted the half wave plate before the EOM and EOM's pitch/yaw position to minimize the peak.

[ 2. determine max Vmod ]

 Although we want to modulate the power as small as possible to have a good linear approximation, we also need the signal to be large enough to be able to see the effect. However, the alignment of the EOM is not perfect, there will be RFAM effect adds into the signal. If the modulation is too large, the RFAM will mask the real signal.  I need to determine what is the maximum Vmod I can use without having the RFAM effect excited above the background.

     To see the effect of RFAM, I kept the setup similar to what I did with RIN coupling coefficient measurement, but without locking the cavity, and the laser frequency off from the resonance. This will tell us how much "fake signal" is produced by RFAM.

     When the cavity is not locked, all the carrier and sidebands will be incident on the RFPD. The signal should be flat (beat between the carrier and both sidebands cancel each another,) and after it is demodulated by 35.5 MHz from LO, the level should be zero. However, if the amplitude is modulated at 35.5 MHz due to misalignment of the EOM, this will appear as DC signal at the error point. Hence, any power modulation at f0 (for this case, 10 Hz) will multiply up the error signal and cause offset fluctuation and slope change at f0. Slope change is not a problem, but the offset is. It will change the point where the laser will be locked, as the error signal moves up and down. Thus the system will interpret it as frequency noise of the laser and try to fight against it. This will appear as a peak in the FASTOUT spectrum at the modulation frequency, f0.

     I measured the spectrum of FASTOUT (MIXER OUT is another option) to see the effect of RFAM 

[ 3. remeasure RIN coupling coefficient ]

So I used 2Vpkpk drive, locked the cavity, and measured FASTMON again to see if I can measured the RIN coupling or not. The gain was set back to optimum value (common = 970 fast= 900.)  However, there was no observable peak at 10Hz from FASTMON signal. It was quite flat ~100 uVrms/rtHz.

 I made sure that the amplitude was really modulated by checking RCTRANSPD. It had a 5.37 Vrms/rtHz peak at 10Hz with 200mV DC level. Therefore, the laser noise is higher than the thermo-optic effect at this modulation level. I cannot increase modulation depth because the RFAM will mask the signal. 

If I use this number to calculate the coupling coefficient, (flat level of FASTOUT, and peak from RCTRANSPD)

it will be ~ 8 [Hz/ uW of fluctuation of the input power into the cavity] still larger than 1[Hz/uW] as measured at 40m, but it's getting smaller than the last entry (60 [Hz/uW] of input power)

       I still can change the power input, but I think the RFAM will scale up by the same amount and mask the signal again. I'll try that later.


 Let's check what does this value give us in the noise budget @10Hz. The input power is 1mW, RIN = 10^-4. Frequency noise will be

8 [Hz/uW] x 1000 [uW] x 10^-4 [RIN] = 0.8 [Hz/rtHz] which is higher than coating noise (10 [mHz/rtHz]@10Hz) So we still cannot ignore the effect.

[Take II]

 I tried 16 mW input power, there was signal from RFAM when I measured FASTOUT with unlocked cavity, the peak was 46 m[Vrms/rtHz] above 10m[Vrms/rtHz] background. Vmod = 1Vpkpk.

When I lock the cavity and measure the coupling:

FASTMON peak = 278.6 uVrms/rtHz

RCTRANSPD peak = 30.82 mV, DC level = 2.57 V, Pin = 16mW. Linewidth = 12.5mHz.

Common/Fast gain = 480/906

Use the calculation from here.

The upper limit for coupling coeffiicient is ~ 5 [Hz/uW]. It is only the upper limit because RFAM effect is still present.

  602   Wed May 18 20:51:35 2011 taraDailyProgressopticoptic layout for new fss setup

I planned the layout for new fss setup.

The new setup has 1) both cavities placed in the same vacuum chamber, 2) two AOMs used in both RCAV and ACAV paths, 3) more compact beat path.

 In the layout, I assumed that

  • Two cavities in the chamber are 3 inches apart.
  • Two AOMs are of the same model, have the same setup
  • There is no change of plan for the layout between PMC and the laser

This is just a plan, no mode matching has been calculated yet.

I am concerned  that the mode matching lens might block the beam in ACAV path where the incoming beam and reflected beam cross, but this can be adjust later.

The outer foam box will be smaller, but it should have enough space to keep some electronics inside like we have now.

I should find two similar sets of beam splitters/ mirrors for beams in the beat path behind the cavity. So the pick up beams from two cavities can have same power.

Right now the power going into two PDs for RCTRANSPD are not the same because the splitter are not the similar.

Note that we might install a platform  behind the cavities so that we don't need the periscopes to lower the beam, and get rid of their associated mechanical peaks.


  603   Thu May 19 11:32:46 2011 taraDailyProgressopticoptic layout for new fss setup

I added more details on the layout, and necessary half wave plates in the beam path.


  605   Wed May 25 18:29:09 2011 taraNotesopticpurchases

I ordered a few opto mechanical components to replace the current shaky periscopes.

The new  periscope is shown here, elog:574. Currently we have only one set, so I ordered a post clamp to complete another set. 

I also ordered 4 mirror mounts that can be mounted on 45 degree mounting adapters. The thickness of these mounts are thinner than a regular mirror mount, so it can be fit on the adapter. I plan to use these in Crackle experiment as well. 



  606   Mon May 30 15:23:53 2011 ranaNotesopticpurchases

The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.


  607   Tue May 31 11:31:18 2011 taraNotesopticpurchases

I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .


The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.



  609   Wed Jun 1 01:50:35 2011 KojiNotesopticpurchases

They are found in DCC. Some comments

- You can not steer the beam. The beam should be steered before or after the periscope.

- The side plates were too thick. It can be 1/2" thickness to reduce the total weight.

D1001446-v1 40m Vertex Green Locking Periscope A Base Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001447-v1 40m Vertex Green Locking Periscope A Sidebar Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001448-v1 40m Vertex Green Locking Periscope A Mirror Holder Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001613-v1 40m Vertex Green Locking Periscope A PTFE Post Koji Arai Auxiliary Optics
Basic R&D
15 Jul 2010


I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .


The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.




  610   Wed Jun 1 21:00:05 2011 FrankNotesopticpurchases

we have to design our own. The 40m one has 2" mirrors (too large, we don't have the space), wrong height for incoming/outgoing beam and is clamped to the table, which i think is bad in terms of stability.
The design principle does not look much different compared to the original refcav periscope design, except for the mirror holder itself. That was bad designed for the old one.



They are found in DCC. Some comments

- You can not steer the beam. The beam should be steered before or after the periscope.

- The side plates were too thick. It can be 1/2" thickness to reduce the total weight.

D1001446-v1 40m Vertex Green Locking Periscope A Base Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001447-v1 40m Vertex Green Locking Periscope A Sidebar Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001448-v1 40m Vertex Green Locking Periscope A Mirror Holder Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001613-v1 40m Vertex Green Locking Periscope A PTFE Post Koji Arai Auxiliary Optics
Basic R&D
15 Jul 2010


I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .


The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.





  614   Tue Jun 14 23:07:03 2011 taraDailyProgressopticoptic layout for new fss setup

The mode matching for new FSS is calculated. The plan is shown below.


Note for the setup:

1) the spotsize in the AOM is 200um, the specsheet says 550 um (I might have to correct this).

2) Two AOMs are of the same model.

3) For mode matching to the AOM in acav path, I used only a single lens.

4) focal lengths of the lenses are in mm, We have to order the one with * (f = 57.4 mm)

5) Both cavities are 1" apart (3" from center to center)

6) Mistake in the drawing: the x2 QWPs just before the beams enter the vacuum chamber should be placed before the periscopes, not after.


  628   Mon Jul 18 02:20:01 2011 taraDailyProgressopticoptic layout for new fss setup

  The new mode matching for optics in front of the cavities is done.  The rest (for beat measurement) will be finished soon.

A few changes in this layout are:

1) spotsize for AOM is 500 um, as specified by the datasheet.

2) Mirrors behind the AOMs will be changed to R= 2.0 m instead of 0.3 m.

3) Spot size in the 35.5 MHz EOM is ~300um which is good for the model.

4) More mirrors (for steering the beam) for the AOMs are added.


I'm a bit worried about using f=57.4mm lenses because they are quite sensitive when we have to move the lenses around, but the space is very limited this time.

I'll let Raphael double check my calculation so he can learn how to do mode matching.




  629   Mon Jul 18 11:41:22 2011 ranaDailyProgressopticoptic layout for new fss setup

There's no need to use such a large spot size on either the AOM or the EOM.

When using high power this could be an issue, but you can use a beam radius of more like 100-200 microns for the AOM to get fast response time.

  631   Wed Jul 20 15:54:21 2011 taraDailyProgressopticoptic layout for new fss setup

  I edited the layout so that the spots in both AOMs are 200 um. I'll list what optics we might have to buy.


Most of the optics are already used on the table. I need to find:

  •  a lens with f = 343.6 m (plcx R =154.5mm)
  •  one more curve mirror with R = 0.3m for the second AOM.
  • aom adaptor plate (need to submit this to the work shop to have it done
  • periscope sets for both ACAV and RCAV (we need 4 in total, but we have only 2 sets)
  • second VCO

The optics on ACAV path have been removed, I left the optics on RCAV path for now because Raphael might want to remeasure EOM TF.

Once the measurement is done, all optics will be removed. We will clean the table, clean the optics before put them back on the table.





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