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  1210   Tue Jun 25 14:14:17 2013 ranaDailyProgressECDLNoise Calculations


 Its true that this approximation is valid for low frequencies, but we are interested in the total RMS frequency noise for cavity locking, not just the spectral density.

So you do have to take into account the frequency dependence. IF there is a lot of noise at 100's of MHz, these lasers will be totally useless to us.

  1211   Tue Jun 25 17:51:34 2013 ChloeDailyProgressECDLNoise Calculations

I spent this morning looking at the mounts and other mechanical parts necessary for the ECDL. This afternoon, I met with Tara to discuss how I should run some noise calculations for including a servo to reduce frequency noise. I will deal with the mechanical logistics later while we are waiting for the diode, etc. from Thorlabs. 


Its true that this approximation is valid for low frequencies, but we are interested in the total RMS frequency noise for cavity locking, not just the spectral density.

So you do have to take into account the frequency dependence. IF there is a lot of noise at 100's of MHz, these lasers will be totally useless to us.

I corrected this, since the paper did have an equation about how the power spectral density is reduced by frequency. This is in the updated noise pdf attached. We no longer have a low enough noise level to do the crackle experiment below 100 Hz or above 10 MHz using our original estimates. This makes running calculations including a servo important. 

I also played around in Mathematica trying to see what value of X would be sufficient to reduce the noise level. Uploading the notebook isn't working right now. It shows that in order to reduce the noise level to meet the requirements for the Crackle experiment, we need a parameter X of about 3000. This is quite large, and would require a cavity of length 30 m. Alternatively, we could reduce the noise by:

  • A different laser diode that had low enough noise to begin with, or a very small reflectivity
  • A diffraction grating that had a very high reflectivity
  • Finding a very good TEC, which would reduce thermal noise (most websites don't seem to offer this data...)
  • Note that at this time, it seems unfeasible to go with any current driver besides the one designed by Libbrecht and Hall, since the current noise limits how low the diode's noise can be at high frequencies

Tonight or tomorrow, I will try to shop around to see if other laser diodes have slightly nicer specs. I will also look to see if other papers encountered the same problem. 


Attachment 1: Noise2.pdf
Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf
  1214   Wed Jun 26 17:13:21 2013 ChloeDailyProgressECDLNoise Calculations

Today I spent the morning searching the literature on Web of Knowledge to see if anyone had ways to reduce the noise level of an ECDL further by tweaking the parameters of the Littrow configuration (our current plan, where first order beams coming off the diffraction grating go back into the laser diode). It may be worth examining configurations with more mirrors to lengthen the cavity, but otherwise my search was not particularly helpful. We may need to start looking at the Littman-Metcalf configuration??? This theoretically reduces linewidths more but has lower efficiency. The diffraction grating is immovable, and an adjustable mirror is used instead to reflect light back onto the diffraction grating. 

Tara got me the information for me to calculate how a servo would reduce the noise of the ECDL further. I worked most of the afternoon to understand the principle behind the feedback, and ran calculations after searching the literature for reasonable numbers. Using a piezoactuator, we can reduce the noise at low frequencies, but it does not solve our problem at high frequencies (above 10 MHz), where there is essentially no noise reduction. See the attached pdf with the updates included (pages 5-8). 

Tomorrow I will see if I can find a piezoactuator that has a large actuator gain, which would cause more noise reduction at higher frequencies. Otherwise, building an ECDL will not be very useful for us to use at LIGO... 

Attachment 1: Noise2.pdf
Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf Noise2.pdf
  1219   Sun Jun 30 22:58:45 2013 ChloeDailyProgressECDLNoise Calculations

I redid the plots from my meeting on Friday with Rana and Tara in Matlab, comparing different components. They are attached here. I'm still trying to get the minor gridlines to show up. 

Plot 1: Comparing noise levels of different experiments to determine which we will use as our standard. 

Plot 2: Comparing noise levels after the ECDL and servo of different diodes. Different diodes have different sizes, which affects the value of parameter X. They are all made of GaAs so other parameters are not affected. We have decided to order the Thorlabs and QPhotonics diodes. The Lumics diode has suspiciously low noise - perhaps the theoretical approximation breaks down in this case. 

Plot 3: Comparing noise levels after the ECDL and servo of different gratings. The gratings are only affected by the efficiency. We will go with the Thorlabs 1200/mm 1um blaze wavelength grating, since we want a blaze wavelength close to the wavelength of light we are selecting for (see Tara's ECDL note on the SVN), and we want as many grooves possible for maximum resolution. 

Plot 4: Comparing noise levels after the ECDL and servo of different cavity lengths. This plot is much better than the Mathematica one; we can see that longer cavities have lower noise, but a smaller FSR. We will likely go with 60-10 cm. 

Also attached is a sketch of our mechanical setup, agreed upon during the meeting on Friday with Rana and Tara. 

This week, I will get a draft of my first report done before the long weekend for Tara to look over. This will probably involve looking over some old concepts to write up something comprehensive. I will also be waiting for a response from QPhotonics and Thorlabs about preselecting diodes, and I need to talk to Dmass about using a current driver. Start looking at metal boxes in the 40m  and building the parts in Solidworks if I have time. 

Attachment 1: compare_experiments.png
Attachment 2: compare_diodes.png
Attachment 3: compare_gratings.png
Attachment 4: compare_length.png
Attachment 5: 100_0068.JPG
  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
  1228   Mon Jul 8 21:52:04 2013 taraDailyProgressopticmode matching to refcavs

 I redid the mode matching for both refcav, the visibilities are up to ~ 93% and 95% for RCAV and ACAV.

  • For RCAV (refcav with PMC), the visibility was ~ 80% before, now it is ~95%. (The numbers are measured from the reflected beam on the RFPD)
  • For ACAV (refcav without PMC), the visibility is now ~ 93%. This is pretty good, compared to ~ less than 85% from previous setup when we used an AOM.

I'll add the new layout for the current situation soon.



  • We care about mode matching because we already saw that any light that was not coupled into the cavity was reflected back to the laser and caused extra noise.
  • By changing the lens, the beams for fiber optic (both for Gyro and Erica's experiment) have to be re calculated. I'm sorry about that .
  1231   Tue Jul 9 19:35:20 2013 taraDailyProgressopticbeat board is back

I installed the beat board back behind the cavities. I still have not finished aligning both beams to the 1811.

  • Note about ACAV ( this path has PMC on it): After new mode matching with more visibility (from 80% to 95%), I can increase more gain and the error noise is getting lower. However, there is a problem with the beam reflected from the window of the tank. It overlaps with the main beam and cannot be blocked. I think this is the reason why we cannot suppress the error noise down to what we had before. I still need to convert the error noise back to frequency noise to see if it is below the estimated coating noise or not. If not, we have to reopen the chamber and tilt the cavity a bit. Rcav does not have this problem, the back reflection is away from the main beam and can be dump properly.
  • Note about RCAV: Erica and I plan to finish the EOM driver test tomorrow. After that I'll use it to drive the broadband EOM for locking RCAV to the cavity. The plan is to use one marconi to drive two EOM at the same frequency (14.75 MHz). We use a 4-way splitter for 2 EOM and 2 demodulations. I don't know how using same frequency for EOM will turn out (cross talk problem), but I want to see the first beat measurement within this week.
  • Note about beat setup: Evan calculated the mode matcing for beat setup, but I had to modify it. The first lenses were moved out of the board and mounted between the vacuum tank and the board due to space limitation. This might add some extra resonant peaks in the beat setup due to the long posts for lenses. The spot diameter on the PD is about 130um, which should be fine because 1811's diameter is ~300 um.
  1232   Wed Jul 10 17:54:58 2013 ChloeDailyProgressECDLSolidworks Design

I attached the Solidworks parts that I built. I put these together with the parts we are ordering from Thorlabs (they have the Solidworks parts on their website) and have an image of the assembly attached as well. 

 I spent today building the elements we want machined in Solidworks. We have a few pieces we need to get machined: 

  • Laser diode mount: This will hold the socket that Tara ordered (Thorlabs S8060), and we can easily replace the laser diodes in this socket since they are both the same package. 
  • Grating mount: The grating will be glued to the front of this, and a PZT will be used to adjust the distance. The PZT I am looking at is here (http://www.physikinstrumente.com/en/products/prdetail.php?sortnr=703300). Still need to check that this is our best choice, I'm shopping around more. 
  • Base/enclosure: We could either design our own base where the elements screw in solidly and put a lid on the structure, or we could use a commercial box (this one could work http://www.alliedelec.com/search/productdetail.aspx?SKU=70166638). Using a commercial box will only require minor modifications to the design. I want to talk to Tara about how easy it would be to modify a commercial box. The TEC will be attached to the base or box like the Birmingham group. 
  • I'm waiting on dimensions of the collimator so I can also build a collimator mount that the adjustable tube will sit in. 

We're seeing if the current driver Dmass uses is from Thorlabs. If it is, it means the commercial driver is good enough and we can purchase this. 

I haven't looked at tolerance values for shop processes yet because I'm not sure how important this is, or exactly how to do it. I know the general idea, but not sure how to deal with the actual calculations yet. I'll work on this more tomorrow once I talk to Tara again. 

Attachment 1: base.SLDPRT
Attachment 2: diode_mount.SLDPRT
Attachment 3: grating_mount.SLDPRT
Attachment 4: lid.SLDPRT
Attachment 5: sketch_with_lid.PNG
  1233   Thu Jul 11 00:19:52 2013 taraDailyProgressopticboth cavities are locked

Both cavities are locked (not optimized yet). Since it has been awhile that both are locked, here is a picture.


 Rcav is locked by Fast feedback only. I still have to check the polarity for PC feedback.  I adjusted the phase between the LO and PD for RCAV loop to get a nice error signal. I noticed that there is an offset in the error signal, I will try to adjust the polarization of the beam in front of the EOM to see if I can reduce this offset from RFAM.

To do:

  • lock rcav with both fast and PC feedbacks
  • optimize the setup ( reducing RFAM, minimize back reflection)
  • setup the beat path (mode match + alignment)
  • setup the ISS path
  • check the beat frequency
  • re organizing the wiring on the table.
  • replace the current SMA cables with the semi-rigid ones, once all the equipments are in place.




  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).
  1236   Thu Jul 11 17:51:12 2013 ChloeDailyProgressECDLSolidworks Design

 Tara got me the information about the adjustable collimator tube he ordered (http://www.thorlabs.us/thorproduct.cfm?partnumber=SM1L30C). I built a mount in Solidworks and added it to the assembly. I also contacted Thorlabs and am discussing how easy it will be to shorten the tube, since we don't need it nearly as long and the length gets in the way a bit. This should be doable. 

I decided that we would go for a box where everything is screwed onto a baseplate, and a lid is screwed to the sides of the baseplate. The reason for this is that the base plate will be much easier to build on than building on the bottom of a box. The screws are on the side instead of the top because this will be easier to have machined, and the design is more compact leaving less room for noise when the lid is disturbed. 

I'm currently looking at a few tasks that I will try and complete soon: 

  • How do we plan to mount the grating? Most literature uses Epoxy, but it may be less noisy to design something on the grating mount to hold the grating and clamp it in. I'm examining which will create less noise. 
  • Is the choice of PZT ok? This involves several things. We need to consider the distance the PZT needs to be able to move and whether it will fit inside the grating mount we have designed. 
  • Will we be using D-Sub or BNC connections? BNC is better for rf, but it only has one channel on each coaxial cable so it is bulker. D-Sub is much more compact, and we can wire several channels at once. Right now I am planning on using D-Sub for the TEC wiring, probably a 9 pin connector using 4 for the +/- thermistor and the +/- Peltier element connections. The current driver may be in the rf range if we want to create sidebands, in which case we will want to use BNC cables. I'm looking into this. 

Attached is a picture of the current setup, built in Solidworks and the lid built separately. I'm not going to bother attaching the Solidworks files until things are more finalized. 

Attachment 1: lid.PNG
Attachment 2: sketch_without_lid.PNG
  1238   Fri Jul 12 15:25:56 2013 ChloeDailyProgressECDLSolidworks Design




 Grating mount: I examined different ways to attach the grating to the grating mount. Our options are epoxy or some sort of actual mount the grating fits into. I finally decided that we should use epoxy for the following reasons:

  • Epoxy is much easier to align and attach than a mount would be, since a mount would rely on being machined extremely precisely
  • Epoxy has a much lower coefficient of thermal expansion (about 60 ppm/K) by about a factor of 4 than aluminum or any metal we would use to build the mount (about 230 ppm/K). This means that epoxy will be less affected by temperature, so it will affect our cavity length a lot less. 
  • It is impossible to design a stable mount that adjusts to clamp in the grating, while still being fixed solidly to the grating mount. I spent a long time brainstorming different designs, and looking at mounts from Thorlabs and Newport for ideas. Any mount that would clamp the grating in well would require some adjustability for small variations in the grating size, and as a result, cannot be fixed onto the grating mount without an excessive number of parts. 


Change of PZT: Our PZT choice relies on how much the PZT will need to be able to move. This changes the length of the cavity as well as the angle of the diffraction grating, and the screw on the PZT will be used to tune the angle. I calculated we will have a 400 nm change in wavelength per mm of the screw length changed, meaning we will only be making changes of less than a mm in the screw length. It made the choice of PZT from before seem a bit excessive. 

Instead, I was thinking of having a very short micrometer screw (http://eksmaoptics.com/opto-mechanical-components/adjustment-screws-870/micrometer-screws-870-0040/) with a chip piezoactuator (http://www.physikinstrumente.com/en/products/prdetail.php?sortnr=100800). I'm not sure how to build the threading into Solidworks or if this will be possible to mount, though. Need to keep looking into this... 

Shortening collimator tube: I have been corresponding with Thorlabs today about their collimator tube. It is made out of aluminum, and therefore we can probably saw off half of it and leave part of it threaded to mount in the collimator mount. Thorlabs also offers custom modifications, but this will likely take awhile and cost a lot more money. 


All of the changes I discuss above were implemented into the Solidworks figures. I just need to figure out the PZT and the parts should all be ready to be machined. I will also try to update the Wiki page this weekend since I haven't for a long time... 


  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.
  1244   Thu Jul 18 16:34:22 2013 ChloeDailyProgressECDLSolidworks Design

Sorry, I've been out for awhile since I had an extremely bad reaction to some medication. Only just starting to recover but I'll work during the weekend to make up for it. 

Today, I spent awhile looking at possible current drivers online. Dmass said that the Thorlabs one is not being used for any frequency sensitive measurements. After looking online, nothing seems to beat the Thorlabs driver in terms of noise level (<1 uA RMS), so maybe we will need to look into building our own current driver or buying the one online based on Libbrecht and Hall. That one is quoted at $4000-5000. 

I also spent awhile trying to figure out a new box design. I think we will want to purchase an AR coated window for the output beam, much like Birmingham. 1" diameter should be sufficient based on the size of the diode/collimator lens. Thorlabs and Newport have comparable products with regards to this (http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1117). It is also important that the box is airtight so no dust can accumulate on the grating or diode. I was thinking of having a 2 part box, with the metal folded, but I'm not sure how easily the machine shop can do this (fold thicker metal sheets, create rounded edges). Waiting to hear back from Tara about this. 

  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.
  1246   Mon Jul 22 18:30:20 2013 ChloeDailyProgressECDLSolidworks Design

Tara and I received the parts we ordered from Thorlabs. I will be working in the ATF lab on the corner of one of the optical tables. Tara showed me around a little; we will likely work there more tomorrow. 

I met with Tara and discussed the final mechanical design. In particular, 

  • Tara explained a way to design a mount to attach the window onto the wall of the box, and I built the mount. Although my design has the mount on the inside of the box, it is symmetric so it can go on the outside just as easily if we find that easier. 

  • We decided to have space for a 9 pin D-sub connector and 2 BNC cables (one for the current driver, one for the PZT) on our box. 

  • We decided to not make a collimator mount yet, since the focal length of the collimating lens will depend on the beam characteristics of the laser, which we will not know until we experiment with this. There aren't currently holes on the base plate for the collimator mount to screw in; we will add this later once things are more certain. 

  • For the PZT, we need to figure out how to make the grating angle/length adjustable. This can be accomplished with a screw and PZT element (based on what I've seen online, probably about 2 mm thick). We aren't sure whether the machine shop is able to make thread fine enough to put the screw directly on the grating mount (~80/inch), so Tara is emailing them to find out if they can. We can create a separate mount for a micrometer screw otherwise. This is the PZT I would like to order: http://www.physikinstrumente.com/en/products/prdetail.php?sortnr=100800 

  • The Mroziewicz paper discusses how to determine the ideal pivot point for a grating mount of an ECDL. I looked into this, and calculated that for a cavity of about 10 cm at 1064 nm (an angle of 39.7 degrees), we want the pivot point to be about 12 cm away from the center of the grating, so I modified the design slightly to accommodate for this. 

  • I'm adding an extra hole on the base so that if we decide to use a mirror mount with an adapter instead of the grating mount (in case the diode doesn't emit light straight in one direction). Everything is also at an appropriate height so if we decide we need to use a mirror mount, the rest of the design should still function. 

The changes have been implemented in Solidworks. The finalized pieces I want to have machined are on the 40m SVN in the ECDL folder. I've also attached a couple of pictures for a quick overview. 

Since we are trying to find a good enough current driver to use, Tara thinks I can start by configuring the TEC on a piece of copper to make sure it works. I will try to do this tomorrow now that the design is ready to be sent into the machine shop. I will also figure out a good time to go over to the machine shop and discuss the design with them. 

Attachment 1: final_3d.PNG
Attachment 2: final_top.PNG
  1250   Tue Jul 23 10:14:30 2013 EricaDailyProgressRefCavmeasurements of beam size, for calculations about setting up fiber

took some of the measurements for the refcav's beam path. Put in a polarizing BS and half wave plate to reduce the power going into the WinCam. Measured the output at various distances; the beam attenuated with an absorptive ND filters (OD 3 and 1.3).

I obtained a waist of 1170 um, which is rather large, about 2.26 m from the beam splitter.
Then calculating from this waist back to the laser, I get a waist of 220um about 0.5m away from the first lens (f = 171.9mm) which is rather long. I checked this with JamMT and my calculations were right... So maybe I should take data over a wider range.

I'll attach the diagram later with the measurements I took.
  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.

  1252   Tue Jul 23 11:43:00 2013 EvanDailyProgressElectronics EquipmentZach's op-amp recommendations
Zach wrote up his thoughts on how to choose the right op-amp in ATF:1752.

His recommendation for an AD743 replacement is the ADA4627. It has lower current noise and only slightly higher voltage noise compared to the AD743.

Apparently the AD743 was only discontinued in its 8-DIP form; it lives on as a 16-pin SOIC. According to the datasheet, the 8 extra pins do nothing, so I have no idea why they've chosen to manufacture it in this way (maybe they can't fit everything onto an 8-SOIC die?).
  1253   Tue Jul 23 17:59:47 2013 ChloeDailyProgressECDLSolidworks Design


Tara heard back from the machine shop, and they can do 1/4-80 threading. I finalized the design this morning. I was sure to check whether the frequency could be sufficiently tuned, and whether the screw on the grating mount would fit into the box. After making some changes, I printed out the designs and went to the machine shop with Tara to talk about our design. It should be ready sometime next week between Wednesday and Friday. Finalized designs are on the SVN. 

Frank (from the Birmingham group) emailed us back about the ECDL. He said they used the $1000 current driver from Thorlabs (http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10), although he recommended the $4800 Vescent current driver (http://www.vescent.com/products/electronics/d2-105-laser-controller/). He also said that there was not a good way of predicting the noise budget beyond knowing what contributes to noise at different frequency ranges: 

  • temperature/environmental noise at low frequencies
  • acoustic vibrations at a few hundred Hz to kHz
  • current noise at kHz to MHz
  • relaxation oscillations of laser diode at a few MHz

Frank also said that he would be leaving the Birmingham in September and has discontinued the ECDL project, so they haven't gotten past making a working prototype. He was otherwise very willing to help. 

I'm currently talking to Thorlabs to see if they can give us the current noise density instead of an RMS noise on their current driver. It seems that if we use the Thorlabs 100 mA driver (instead of the Thorlabs 200 mA driver we had been planning on), the noise is reduced a lot. At 100 mA, we should get an output power of ~75 mW from the Thorlabs diode and ~50 mW from the QPhotonics diode. This actually is probably sufficient for what we need, so the lower current input should not be a huge problem. From a range of 10 Hz to 10 MHz we have the following values:

  • Vescent current driver (200 mA): 0.3 uA
  • Thorlabs current driver (200 mA): 1.5 uA
  • Thorlabs current driver (100 mA): 0.2 uA

Vescent current driver does much better at lower frequency ranges, and has RMS noise of 0.05 uA between 10 Hz and 100 kHz, but is comparable over a larger range with higher frequencies. While the RMS values are promising, we aren't sure how the noise density compares over the entire frequency range... I'm hoping to hear back from Thorlabs soon about this. It seems like the Thorlabs driver is an actual possibility though. 

Tomorrow Tara and I are going to get started in the lab. Tara will show me around, and I'll try to get the TEC working. 

  1256   Fri Jul 26 11:07:44 2013 EricaDailyProgressBEATcircuit for measuring temperature fluctations on CTN table
July 23, 2013
Went to a lecture Alan gave for the CGWAS on data analysis in the morning at Cahill (http://www.cgwas.org/index.php/Caltech_Gravitational-Wave_Astrophysics_School_2013). I had more data, signal from the recombined beam over different time periods that I took so I put those into graphs.

I practiced soldering stuff.
Wet the sponge below the iron. You can test to see if iron is hot if you hear the sizzle when you touch the iron to the sponge. A good idea is to cover the iron w/ new solder, since the old solder on the tip has oxidized.
Solder will go where it is hot, so you need to heat both the board and the wire to get a good connection. Good joints look like volcanoes.

Circuit design:
Evan figured out a circuit to for the AD590, as seen below.

The 20k resister determines the voltage that goes to the rest of the circuit. A high pass filter follows, with a capacitor on the order of 100 uF and resistor about 1 M ohm. This takes out the DC signal and AC couples the circuit. The filter will also ignore fluctuations that are slower than 100s. The two resistors connected to the op amp have a gain of 100. The op amp can only have an output up to 15V so with a gain of 100x, it can only take in 0.15 V before it saturates.

We used a breadboard where we can just plug in the components to see if the circuit works like it want it to. For the high pass filter, we used two 22 uF capacitors in parallel = 44 uF (22uF is the largest WIMA capacitor - film capacitor; anything higher will be ceramic and have a lot more noise; also they may be polarized which is a bit more hassle when wiring stuff up) and two 1 Mohm resistors to make a 2M ohm resistor.

We connected the circuit to a function generator and oscilloscope. The function generator was also connected to the oscilloscope (using T connector).
There was a 100x gain, as expected.
Note: make sure the oscilloscope is DC coupled, or else another capacitor will be put into the circuit in the oscilloscope and you won't get the correct signal.
Also, be careful about making the amplitude too large because that can saturate the op amp. If you do both of these things, then you get this weird signal that is trying to be a square wave but failing.

Note: AD590 has a polarization. The pin with the little bump sticking out should be connected to the positive side.
Attachment 1: P1030056.JPG
  1257   Fri Jul 26 11:22:45 2013 EricaDailyProgressBEATcircuit for measuring temperature fluctations on CTN table
July 24, 2013

Took the tour to JPL today. Got to see the twin of Curiosity that they assembled before the real one so they could adjust procedures for assembly and the Mars Yard where they drive the rover over various types of terrain. There is also the Scarecrow which is essentially just the frame and wheels, which is used to simulate the smaller gravity on Mars.

Soldered parts to the circuit board. I'll be putting both circuits onto the same board, using about half of the board total, so that we can attach more components later, if needed.
Only one side of the board has metal around the holes so we placed the components on the non-metalized side, and had the connects protruding to the opposite side.

Used scrap wire that was in the base of the stand to connect various joints that were close to each other. Also folded over excess wire from components to make connections. Any longer wires that weren't used were cut off.

Using red for positive, black for negative, and green wire for ground, as is standard.
  1258   Fri Jul 26 11:45:28 2013 EricaDailyProgressBEATcircuit for measuring temperature fluctations on CTN table
July 25, 2013

finished building the circuit today. Had the positive, negative, and ground wires running above the board, while the one jumper wire from the output to the negative input under.
Twisted the positive, negative, and ground wires together using a drill, as well as the positive and negative wires that will connect to the AD 590. We made these longer so we can connect to the power supply and place the AD590 at opposite ends of the table.

Tested the circuit, used an amplitude of 0.01Vpp and 0.1 Hz for frequency to drive circuit, which was what we did on Monday. The output signal is a square wave which was strange but found out the problem: the bnc cable driving the circuit was put in the sync output of the function generator, instead of the function output.
Fixed this, and the circuit behaves as we expect.

Discovered that I used a 36 kohm resistor instead of a 33 k ohm resistor, so now we have a gain of about 110, which is close to that of 100.

We used aluminum tape to connect the AD590 and insulating tape to prevent shorting. The output signal was at some DC voltage, which we expect at first due to the power supply turning on, and it should die away, but it didn't, or was very very slowly. So Evan placed a 15k Ohm resistor in parallel w/ the 2M ohm resistor in the high pass filter to lower the time constant, which brought the signal close to zero. Once he took the resistor away, then the signal would drift up to the previous DC level. The circuit was responding as expected when he placed a cooler object by it, so the signal went down, and the signal went up when we held the AD 590.

We tried this in the CTN lab but it didn't seem to work; there was a lot of noise. I'll test it again tomorrow.
A possibility is the power supply could be noisy.
  1261   Mon Jul 29 13:30:26 2013 EricaDailyProgressBEATadding resistor, capacitor, and sockets
July 26, 2013

Was able to place the 24k ohm resistor in parallel with the 2Mohm resistor to make the time constant shorter, and see the response on the oscilloscope. The signal is way way high, because even w/ the shortened time constant, it takes awhile for the signal to actually reach zero.

Took out the 36k resistor. Attached sockets to the circuit board so we can easily remove and replace resistors. The new one we used was 1 kOhm resistor.

Had crazy noise - with spikes, due to extra capacitance from the additional sockets. We decided to add a capacitor to filter out the high frequency noise from feeding back to the negative input of the op amp.

Added more sockets so we can easily remove and attach the capacitor .
I tried out different capacitors, centered around 1 nF but this kind of helped. There were no longer giant spikes. However, now the signal in general is noisier.

Note: if soldering something to another component that is only attached at that 1 pin, make sure you hold that piece so that it doesn't drop. OR else, you need to solder that one-piece again, while making sure the other component gets connected to it as well.
  1264   Tue Jul 30 00:01:22 2013 EvanDailyProgressISSRelative intensity noise with south cavity locked

Chas has been building an ISS and needs a spec for suppression of relative intensity noise for Tara's 1.45″ silica/tantala cavities.

I measured the RIN of the south cavity with the cavity locked. The common and fast gains were both set to 400 on the TTFSS frequency servo box. I placed a PDA100A at the transmission of the south cavity. The DC power incident on the PD was 0.370 mW and the DC voltage was 0.439 V. I plugged the PD output into the SR785 and recorded the PSD of the voltage, both for light incident on the PD and for no light incident on the PD (i.e., the noise floor). To get the amplitude spectral density (ASD) of relative intensity noise, I've taken the square root of the voltage PSD and divided by 0.439 V.

I've attached a figure showing the RIN (and the noise floor of the measurement), as well as the data and code used to generate the plot.

Both the shape and overall amplitude of the RIN are roughly consistent with what has been measured earlier (e.g., PSL:986 and PSL:736). I'm unsure whether this is the same laser that was used for the previous iteration of the CTN experiment, but it is the same model (Lightwave NPRO 126). [Edit: I've talked to Tara, and this is the same laser as was used in the previous measurements.]

Attachment 1: rin_southcav.pdf
Attachment 2: rin_2013-07-29_data_code.zip
  1265   Tue Jul 30 12:23:41 2013 EricaDailyProgressBEATaddressed noise problem, DC signal
july 29, 2913

Worked on progress report due Friday.

Tried using the power supply from the electronics lab and that was much better. Switched back to the old one and used shorter wires to connect the ground, so random magnetic fields don't induce current in the wires and this helped immensely. There were still random little noise but not like before. This was tested using the function generator giving a sinusoidal wave.

With the AD 590 connected, like before, the signal was well above 0V. However, it did not saturate, even when it not on the CTN table, but out in the open air.
The signal was pretty linear so we looked at the slope over a region where there were three peaks and calculated the corresponding input. This gave 1.39 uA, which is much smaller than the 13mA required just for the wire to change one wavelength.

We're not sure where the DC signal is coming from because the high pass filter is supposed to filter it out. This has been done with only one circuit so we don't have much to compare to. Perhaps need to rethink a different circuit...

Also, I put insulating foam underneath the exposed fiber. Tara has ordered more, which are wider, so that will cover the whole exposed area of the fiber.
  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.
  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.

  1272   Thu Aug 1 03:34:35 2013 ChloeDailyProgressECDLAssembling ECDL

Today I worked on updating my progress report and abstract. Posted to the SVN. 

Our machined parts were finished by the machine shop. I picked them up, and Tara and I washed them in a sonicator for an hour to get the oil and metal shavings off. I tried assembling things to see how things look. It seems like the laser diode mount will have enough adjustability with the diode that we will not need to have vertical adjustment ability on the grating mount. We will need to make modifications on the plate with the D-sub and BNC holes because we will need 2 D-sub connectors, and there needs to be a better way to mount the male-to-solder connectors on the plate so they don't move. 

I went to Rana's electronics talk. I'm trying to get LISO on my own computer but encountering some problems with Linux. 

Tara found a 1/4-80 screw from a mirror mount to put into the grating mount. It was long enough that we'll have adjustability. We may need to get springs to put in the grating mount slit to offset the force from the screw. 

Tara and I took apart a 5 mm focal length lens from a fiber optic and added it to our temporary setup from yesterday to test if a shorter focal length lens helps with collimating the beam. It works very well - we can get the beam to be essentially parallel at up to at least 50 cm with the right adjustments. 

I put together a shopping list tonight of things we need to get checking Thorlabs and Newport: 


  • http://www.physikinstrumente.com/en/products/prdetail.php?sortnr=100800 - price requires quote, but Tara referred me to this website.
  • http://www.thorlabs.us/thorproduct.cfm?partnumber=AE0203D04F - Thorlabs has a product, $72.80, seems like it would also serve our purposes but I don't know which manufacturer is preferred for PZTs. 
  • Newport doesn't have anything that would fit in our setup

Optical window: 
Collimating lens: 
Collimating lens mount: I can't seem to find a good lens mount that can hold such a small lens, offers adjustability in enough directions so we can focus the beam, and is at the right optic height for our setup (1 inch). Thorlabs can't deal with such small lenses. I found something fixed from Newport that we could use if we figure out how to focus the beam in advance (http://search.newport.com/?x2=sku&q2=LH-0.25). I like this mount (http://search.newport.com/?q=*&x2=sku&q2=LFM-1A) although it is about 3 mm too tall, but there's not really an adapter to hold a lens our size. I could maybe design something with a similar idea to this mount? Not sure until I discuss with Tara... 
I'll try looking again tomorrow to see if I have better success with the collimating lens mount. Will try to put TEC on the box. 

  1273   Thu Aug 1 18:33:12 2013 ChloeDailyProgressECDLAssembling ECDL

Today I tried to set up the TEC on the actual assembly. When doing so, Tara pointed out that I needed to have a separate temperature sensor to monitor the TEC, and to use to calibrate the PID gain on the TEC controller. 

I built a simple temperature sensor with a 10k thermistor. The temperature can be determined by measuring Vout and determining RT. Once RT is determined, this can be converted into a temperature using the information on the data sheet for the 10k thermistor. The schematic is attached. I chose the value for R0 based on what would maximize the difference in Vout for a 1 degree C fluctuation about room temperature (25 C) which is what will be used to tune the PID gain. I chose Vin based on what would make the signal have fluctuations of about 500 mV, which is what is needed to be readable on an oscilloscope. Once I built this circuit, I tested it. It is sensitive to temperature changes, since the output voltage changed when I covered the thermistor with my hand.

Tonight I am going to incorporate changes Tara suggested for my progress report. The updated version will be put on the SVN. Tomorrow I will try to the temperature sensor I built today to calibrate the PID gain on the TEC controller. 

Attachment 1: tempsensor.PNG
  1274   Thu Aug 1 21:19:57 2013 taraDailyProgressBEATsearching for beat

I locked both cavities and trying to search for the beat signal, I have not succeeded yet.

I used lenses that could get the two transmitted beam to be close and small enough for the beat PD (new focus 1811) (we ordered  what we need but they are not here  yet).

I locked ACAV at a fixed SLOW DC level (1.207 V), and varied RCAV's SLOW DC level from 1.199V, 0.33V, -0.554V, -1.477V (1FSR ~ 4GHz is about 1 V). The slider for RCAV slow is set to +/- 2V so I have not tried other values yet. It can be changed to -2V to 9 V, but I have to restart the crate which will disturb the temperature servo, so I'll try to adjust RCAV slow value using a voltage calibrator instead.

I talked to Evan about the beat measurement in GYRO lab, the SLOW DC for both lasers can be different up to 6 V (for ~100MHz beat). see gyro1832

I varied RCAV's SLOW DC first because this path does not have a PMC, so I don't have to worry about locking the PMC.

From PSl:1124 ,the beat frequency should be ~60-100 MHz, without the heater on any cavity.  I'll try the same method to check the beat frequency between the two cavities one more time. If it is still ~ 100 MHz, I'll increase the range of SLOWDC, and see if the beat will show up of not.  The setpoint was not changed that much (31.2 to 31.25), So I expect the beat frequency should still be close.

If the beat still not show up, I'll try to realign the beam.


Current setup

Vac chamber Setpoint = 31.25

Vheat for RCAV =  0

Vheat for ACAV = 0



  1275   Fri Aug 2 12:18:16 2013 taraDailyProgressBEATsearching for beat

Found the beat @ 116 MHz. RCAV SLOW =5.762V, ACAV SLOW = 1.209 V.



beat 1kHz input range, calibration  = 718 Hz/V


above, beat signal with 1kHz input range on Marconi.

Plenty of things that I need to optimize and add:

input optics (ACAV/RCAV):

  • beam alignment
  • optimizing quarter wave plates in front of the cavities.
  • block all the reflected beams properly
  • fixing the back reflection from vac window for ACAV.
  • measure error point noise from both servos and compare them with beat
  • optimizing TTFSS servo gain

Beat setup:

  •  mode matching lens
  • power on beat PD
  • optimizing PLL servo
  • implementing ISS

Seismic isolation

  • new table legs ( I have not ordered the new set yet). The current set is broken
  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.

  1277   Fri Aug 2 18:15:06 2013 ChloeDailyProgressECDLAssembling ECDL

Today I calibrated the PID gain on the TEC. In order to do this, I used a silicone heat sink compound to help the thermal conductivity between the Peltier element/thermistors and the TEC. Then, I held things together using aluminum tape.

I calibrated the TEC so it reaches the correct resistance after only overshooting the value once. It is usually able to reach the correct temperature within about 30 seconds. I had the temperature sensor I built yesterday hooked up to an oscilloscope so that I can monitor the fluctuations in voltage across the thermistor (directly related to resistance). However, my flash drive doesn't work and I didn't have a spare on me today so I will try and record the oscilloscope output either this weekend or on Monday morning. This will be used to estimate the transfer function of the TEC controller. 

Important: there is a directionality to the TEC element. There is a hot side and a cold side. The cold side is attached to the laser diode mount, and the hot side is attached to a piece of aluminum we found around the lab to act as a temporary heat sink. Because of this we need to rework some of the design to thermally isolate the diode mount from the box, and let the box act as a heat sink. My proposed design is attached (I made a quick sketch of it in Solidworks). I'm still thinking about the best way to incorporate the Peltier element. 

Tara will order the collimator lens, window, and PZT this weekend. Still trying to figure out if it's possible to build a collimator mount that will be sufficient to serve our purposes. 

Attachment 1: possible_tec_mount.PNG
  1281   Mon Aug 5 18:47:04 2013 ChloeDailyProgressECDLAssembling ECDL

 I brought in a different USB drive to get data off of the oscilloscope. It took awhile to figure out how to capture the data with the best settings. I have a sample graph of the heating and cooling of the diode mount attached (converted to temperature using datasheet for 10k thermistor). Notice that I took data over about 4 degrees, so that it was possible to see the change in voltage as the temperature changed. Even then, it would be nice to have more resolution on this data. I cannot make the voltage increments smaller than 500 mV because the offset of the oscilloscope isn't enough to still see the data (I tried). I will talk to Tara tomorrow about if I can get better data on this to analyze, since this data has poor resolution. 



 Tara asked me to try to calculate the free running noise of the laser diode to have an estimate for when we actually collect this data. We will be using a Michelson interferometer with different arm lengths. I used Erica's past elog entry as a starting point (1241) and wrote a bit more explanation into my own calculations so it will be clear to me in the future and to make sure I understood everything. However, I'm unsure of how to incorporate the noise levels after calculating the power received by the photodiode, and I need to talk to Tara about how to do this tomorrow if he's around. The calculations that I have done are attached. 



  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.
  1283   Tue Aug 6 19:48:19 2013 ChloeDailyProgressECDLAssembling ECDL

 I calculated a way to convert our spectrum measurement of voltage from the photodiode to the frequency noise of the laser in the Michelson interferometer setup. I still need to check this calculation to make sure it works, and determine the ideal differential arm length to use tomorrow. 

Today I also took a measurement of the relationship between power and voltage of the photodiode at 20dB gain. The result for that is also included in the attached file. I will clean all of the calculations up tomorrow; I suspect I've made a mistake or 2. 

Attachment 1: 100_0079.JPG
  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.
  1285   Wed Aug 7 18:13:21 2013 ChloeDailyProgressECDLAssembling ECDL


 I calculated a way to convert our spectrum measurement of voltage from the photodiode to the frequency noise of the laser in the Michelson interferometer setup. I still need to check this calculation to make sure it works, and determine the ideal differential arm length to use tomorrow. 

Today I also took a measurement of the relationship between power and voltage of the photodiode at 20dB gain. The result for that is also included in the attached file. I will clean all of the calculations up tomorrow; I suspect I've made a mistake or 2. 

 I fixed my calculations from last time and wrote it up in LaTex. It seems that we can use a differential arm length of somewhere around 10cm and it should work well for our purposes. 


Tara: I removed the pdf file, as I have warned you about this  for several times. 

Chloe: I put the PDF on the SVN. I won't make this mistake again. 








  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.
  1287   Wed Aug 7 20:55:47 2013 EvanDailyProgressopticPreparing the EOAM

In preparation for getting the ISS up and running, Tara and I have been fooling around with the EOAM and associated half waveplates. Additionally, Tara inserted a quarter waveplate (mounted horizontally, for space reasons) after the EOAM in order to get linear amplitude modulation. The HWP before the EOAM is at 99 degrees and the QWP after the EOAM is at 51 degrees.

There's currently 8.0 mW going into the EOAM and 4.0 mW coming out after the EOAM + QWP + PBS. When 10 V dc is applied to the EOAM, the power drops to 3.7 mW. This gives a conversion factor of 3.0×10−5 W/V. The value expected from the manual is (π/2)(8 mW / 300 V) = 4×10−5 W/V, so we're not too far off. 

For those who prefer the status quo, the original HWP angles are as follows. The HWP after the PMC was at 336 degrees, the HWP before the EOAM was originally at 150 degrees, and the HWP before the cavity (which Erica is using as a pickoff for her fiber) was at 236 degrees. Restoring these angles will not restore the previous power configuration unless the quarter waveplate is removed.
  1288   Thu Aug 8 18:31:14 2013 EvanDailyProgressISSCTN ISS plant transfer function

Tara and I have taken a measurement of the transfer function which takes volts the EOAM and produces volts at the ISS PD.

The EOAM is driven with a 4 Vpp swept sine from the SR785. Approximately 1 mW of light is incident on the south cavity, and 0.5 mW is incident on the PDA10CS positioned at the cavity transmission. The spot size is a little bigger than the PD area, since I'm unsure of the damage threshold of the PD and don't want to fry it. The PD has its internal preamp set to 20 dB of gain (1.5×104 V/A) and has a quantum efficiency of about 0.6 A/W. The DC voltage of the PD is about 5.9 V. The inputs of the SR785 are dc coupled. Each data point on the transfer function is integrated over 20 cycles.

As a control, there is a second PDA10CS set up before the cavity input to capture the transfer function without the filtering effect of the cavity and associated optics. The input power is about 0.4 W and the gain is also 20 dB. In the attached plot, I've normalized this transfer function to have the same amplitude as the transmission transfer function.

Evidently, the magnitude of the plant transfer function is (more or less) 0.057 V/V.  Based on the calculation in PSL:1278 I'd expect something more like 0.024 V/V (with a = 0.5), and I'm not sure where the extra factor of 2 is coming from. I've measured the PD gain to be 11 V/W at 20 dB (by putting an OD2.0 filter in front of the PD, and then making the spot size small enough that all the light falls on the PD), which is close to what I'd expect (9 V/W, given a quantum efficiency of 0.6). We've measured the EOAM gain to be 3×10-5 W/V. There's definitely 0.5 mW going towards the PD. So something's not adding up.

Attachment 1: eoamtopd.pdf
Attachment 2: eoamtopd_data.zip
  1289   Thu Aug 8 18:43:44 2013 ChloeDailyProgressECDLAssembling ECDL

 Today I designed a better circuit to measure the TEC's response with the oscilloscope. It is called a bridge circuit, and allows for the output voltage to be centered around 0 instead. This type of circuit is often used for different sensors, and seems to fit our purposes well here. The schematic is attached here. 


After I built this circuit (modified the circuit I was previously using), I tested it with the TEC to see how the PID gain calibration looked. This took awhile to get a signal, because it seems like the oscilloscope I was using had some problems. I took data of heating and cooling shown below (didn't bother converting to temperature since we're mostly interested in how the temperature or voltage settles right now). 



A lot of the data I tried to take today had the same sort of oscillations as for the cooling data shown above (about 0.04 Hz). However, I didn't see such oscillations when I hooked the circuit up to a multimeter and monitored the voltage changes over time. In fact, the voltmeter suggested that the voltage stabilized much more quickly. I'm going to look at this again tomorrow to see if I can figure out the cause of these oscillations, and perhaps tune the PID gain on the TEC better now that I can see how the temperature settles much more easily and quantitatively. 

Today, I also finalized the Solidworks drawings for the insulator that will be used to thermally isolate the laser diode from the rest of the setup, as well as the heat sink that will be in contact with the Peltier element. These files are on the SVN, and I will try to go to the machine shop with these soon. I should have done this earlier. 

I will be presenting my project at the end of August, so Tara wants me to put together a talk so we can rehearse next week. I am going to start doing this in my free time. 

  1292   Fri Aug 9 18:01:47 2013 ChloeDailyProgressECDLAssembling ECDL

 I spent awhile reading about PID controllers in order to understand how to tune the TEC. P represents proportional gains, and deals with the present error from the set value. I represents integral gains, and deals with past errors. D represents derivative values, and uses the current data to predict future errors. They each affect how the TEC overshoots/oscillates about the correct temperature in different ways. I figured out that the oscillations that I saw yesterday in the heating and cooling data were due to improper tuning of the PID gain. I decreased the integral gain and it seemed to fix the problem. 

I also discovered that the oscilloscope was on the wrong setting, with 10x attenuation. I noticed this when converting the data from output voltage to temperature. I changed the settings to 1x attenuation and took data for heating and cooling, shown below. There only seems to be one slight overshoot when changing the temperature by about 1 degree, which is entirely reasonable. The correct temperature settles after about 1 minute. 


While these measurements were useful in tuning the PID gain so that the temperature settles quickly, there was a discrepancy in the measured resistance across the thermistor and the resistance calculated from the measurement of Vout. Using the TEC controller, I brought the resistance of the feedback thermistor to 10k, but this resulted in a Vout that predicted a thermistor resistance of 9.91k (0.2 degrees K difference). In order to zero Vout, I had to bring the thermistor resistance down to 9.892k. I'm trying to think of a way to calibrate this difference, but I'm not sure which thermistor is reading more accurately right now. I'm going to read more about using thermistors as temperature sensors to see if there is anything I can try to do for this. 

I'm also still trying to think if there's a way to adjust the P, I, and D controls so that I can actually go back to previous values. The controls are unlabeled on the TEC controller we have, so they cannot be accurately returned to specific settings. It seems well calibrated for the moment, though. 

  1294   Mon Aug 12 18:21:03 2013 ChloeDailyProgressECDLSURF Presentation

 Tara would like me to present at the SURF Seminar Day in August (either on the LIGO field trip to the Livingston Observatory or at Caltech), so I spent yesterday and today putting together my presentation and trying to organize the work I have done/plan out what to say. The entire presentation will have to be focused on the noise calculations and design, since we are still waiting on parts to arrive (namely, the collimating lens so we can focus the beam to make a free running noise measurement). The presentation for right now is on the SVN: https://nodus.ligo.caltech.edu:30889/svn/trunk/ecdl/documents

  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
  1297   Tue Aug 13 18:13:35 2013 ChloeDailyProgressECDLAssembling ECDL

Made some modifications to the Solidworks design. All of these have been changed on the SVN. 

  • Made heat sink for TEC adjustable so it can clamp the TEC element between the heat sink and the laser diode mount, with no risk of it touching the laser diode mount. This was achieved by making a longer hole on the base plate so the heat sink can be screwed on anywhere. The heat sink will be copper because this is very thermally conductive compared to aluminum or other metals. 
  • The laser diode will be thermally isolated from the rest of the setup using a piece of plastic (most likely delrin). 
  • Tara and I found a lens mount we can use which allows for small height adjustments (Newport LA1V-XY, http://search.newport.com/?x2=sku&q2=LA1V-XY). This is at an optic height of 1 inch which works well with our setup. We are going to purchase this (http://search.newport.com/?q=*&x2=sku&q2=LPLH-25T) which is an adapter so that it can hold the 0.25" optic. The collimating lens' distance from the laser diode will be adjustable by the same method as the heat sink - there is a longer hole on the base plate so that the lens mount can be screwed down anywhere. 
  • Added 2 D-sub holes that are properly sized (last time was a bit too small) so that we can plug in the TEC and current driver onto the ECDL box. 

Tomorrow morning I will go to the machine shop to get the base plate and left plate modified, and get them to machine a heat sink and plastic insulator. 

  1298   Tue Aug 13 21:45:51 2013 taraDailyProgressNoiseBudgetTransfer Functions (RIN to Frequency noise via photothermal)

I rechecked the TF between power fluctuation and frequency noise in beat measurement that I did last year. The estimated result agrees more with the measured result. This can be used to estimate the requirement for ISS for SiO2/Ta2O5 and AlGaAs coatings.

The calculation is taken from Farsi etal 2012 (J. Appl. Phys. 111, 043101), and compared with the measurement from 8" cavities, SiO2/Ta2O5 QWL with SiO2 1/2 wave cap. The code I wrote before has several mistakes, so I fixed them.

Mistakes in the original code:

  1.  Beta effective was for 1/4 cap of nL: I changed it to the right one (1/2 cap of nL). This can be done by GWINC or an analytical result.
  2.  Cut off frequency ws, wc in the paper, I divided by a factor of 2*pi make them in Hz.
  3. Missing a factor of imaginary in thermoelastic in coatings calculation.
  4. r0 in the paper is where the power is dropped by 1/e, so r0 = w0/sqrt(2) where w0 is the radius of the beam when the power is dropped by 1/e^2.


Above: Measurement(purple) from SiO2/Ta2O5 coatings and analytical result (cyan) in comparison. Finesse = 7500 (old ACAV), absorbtion = 5ppm.  The slope at high frequency seems to be real TO noise. Notice that phases from TE and TR have different sign and cancel one another.


==for TO optimized AlGaAs coatings==


Above: Calculation for RIN induced thermo noise for optimized AlGaAs coatings in Hz/Watt unit. The calculation is for 200 ppm transmission,-> Finesse ~14 000. 1.45" cavity. The cancellation in coatings will reduce the noise. The estimated effect is plot against the measurement from 8" cavity, T=300ppm, SiO2,Ta2O5 cavity.

We might have to make sure that RIN is small enough, since this time we will have no common mode rejection like what we had with just a single laser. I'll add the estimated requirement later.

Attachment 2: farsi_2013_08_13.fig
Attachment 4: RIN_TO_algaas.fig
  1299   Thu Aug 15 18:53:45 2013 ChloeDailyProgressECDLAssembling ECDL


Made some modifications to the Solidworks design. All of these have been changed on the SVN. 

  • Made heat sink for TEC adjustable so it can clamp the TEC element between the heat sink and the laser diode mount, with no risk of it touching the laser diode mount. This was achieved by making a longer hole on the base plate so the heat sink can be screwed on anywhere. The heat sink will be copper because this is very thermally conductive compared to aluminum or other metals. 
  • The laser diode will be thermally isolated from the rest of the setup using a piece of plastic (most likely delrin). 
  • Tara and I found a lens mount we can use which allows for small height adjustments (Newport LA1V-XY, http://search.newport.com/?x2=sku&q2=LA1V-XY). This is at an optic height of 1 inch which works well with our setup. We are going to purchase this (http://search.newport.com/?q=*&x2=sku&q2=LPLH-25T) which is an adapter so that it can hold the 0.25" optic. The collimating lens' distance from the laser diode will be adjustable by the same method as the heat sink - there is a longer hole on the base plate so that the lens mount can be screwed down anywhere. 
  • Added 2 D-sub holes that are properly sized (last time was a bit too small) so that we can plug in the TEC and current driver onto the ECDL box. 

Tomorrow morning I will go to the machine shop to get the base plate and left plate modified, and get them to machine a heat sink and plastic insulator. 

 Today I got the newly machined parts. I put together the TEC element and stuff again and will calibrate the next time I get a chance. 

Erica and I practiced our presentations in front of Tara. I got a lot of feedback and I'm going to edit my presentation in my free time outside of lab. It was also useful to see someone else's work to get an idea of how to present. 

I'm working on putting together a Michelson interferometer to measure the laser diode free running noise. I don't have the actual collimating lens, so I'm using a f=5mm lens from a fiber optic. I have mirrors and I borrowed a beam splitter from the GYRO experiment. Picture below. I'm working on getting the beams to combine by adjusting the mirrors. Will continue doing this tomorrow. 

Attachment 1: 100_0104.JPG
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