I built a temperature sensor prototype for the 40m lab, which can be used for the PSL lab as well for temperature stabilization. It consists of an AD586 5V constant voltage output, an AD590 temperature sensor (I initially had 592 but they are very similar), and a LT1012 OP amp, along with a 10K resistor and a few capacitors (see first schematic). It uses the temperature of an object that touches the AD590, which is attached to a long cable, and converts it into a current (1microA/K), which is converted by the OP amp and resistor into a voltage. The AD586 is required because the sensor wants a constant input of 5V to accurately measure temperature. I used a 10K resistor on the OP amp so that the voltage should be around 3V when measuring room temperature. It requires an input of +15V and -15V to the OP amp, 15V to the input of the AD586 (this is shared with the +15V input to the OP amp), and a ground. The +15V (red) and -15V (black) inputs are given to the pins closer to LT1012 and the ground is farther away. The output voltage is read out through a BNC cable and can be converted into a temperature in K by multiplying the value by 100, but it shows a temerature that is about 2K higher than the actual temperature.

In addition, I used capacitors on the OP amp to stabilize the voltage input. I used a 100nF ceramic capacitor placed close to the pins of the OP amp and a 100microF electrolytic capacitor placed father away to achieve this. I have attached the schematic for this as well (second schematic), with 1 being the electrolytic capacitor and 2 being the ceramic capacitor.

Kira built the circuit below and and handed it off to Andrew and I at around noon today.  We tested it and found it was extremely noisy.  Andrew stuck a passive low pass filter on it and the circuit immediately calmed down and gave steady output.

I took Kira's circuit and soldered on an active low pass filter with an OP27.  The resistor is 10kΩ and capacitor is 22µF, so the corner frequency of the low pass is around 0.35 Hz. 

Hopefully this will calm down the temperature voltage monitor output of the circuit, and we can have at least an idea of the temperature fluctuations of our can.

I checked the temperature control servo for the vacuum chamber and found out that it was off. I could not turn it back on yet since there was some problems with the channel. I'll ask Peter to help me on this.

About a week ago, I tried to add another channel for controlling the second PMC servo card. I did not write an elog since it was not done yet.

I created PMC2.db in /usr1/epics/psl/db. It had only one channel for C3:PSL-PMC2_GAIN. I used #C6 S2. This channel might already be used for temp control. I'll try to remove the channel and see if the problem can be solved.

from   Measurements of Earth-station delay instabilities using a delay-calibration device  measured at 70MHz  

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=840746 

other data (e.g. for RG223/U) can be found here : http://tmo.jpl.nasa.gov/progress_report/42-99/99E.PDF

or here : http://ivs.nict.go.jp/mirror/meetings/v2c_wm1/phase_stability.pdf

or here: http://tesla.unh.edu/courses/ece758/Handouts/cable-specs.pdf

Type of cable             Temp coef (ppm/K)
RG-8A                          -85
RG-214                        -60
RG-223                        -40 to -100
Belden 9913               -21
Andrew FSJ4-50B      -2 to +6
Andrew LDF2-50        -8 to +6
Andrew LDF4-50A     +7 to +16

And for the LMR-240 which i would buy for future cable delay lines ~24ppm/K

http://www.haystack.mit.edu/tech/vlbi/mark5/mark5_memos/067.pdf

piezo is clamped between frame and side of table. More details see here

I'm optimizing the setup, and clearing the table a little bit.

• Self homodyne setup in ACAV path is removed. This is from Erica's setup and it is not used. The input part is left, since I might use it for fiber distribution system
• optics on RCAV path, all polarization are optimized. This includes, the input and output polarization for EOAM, and quarter wave plate before the periscope. The input polarization for sideband EOM is left intact after the last adjustment, and it should be good. With+/- 4V input, I can change the power by +/-10%, (1.0 +-0.1 mW is the current setup). For Evan: Do not touch anything before discussing with me!!!
• I replaced a new PBS for PDH locking in RCAV path. The old one is bad. The surface between the prisms is milky, see the pictures below for comparison. There is also beams from multiple reflection within the cube. The new one is much better. There is no ghost beam anymore.
• I blocked all the scattered light I could find in RCAV path with Irises and beam dumps. For ACAV, I just blocked the scattered lights from the laser to the PMC. I will finish the whole setup later.
• I rechecked the height of the beam through EOMs/EOAMs. Since it is a little tricky to center the beam through the openings. The EOMs in RCAV path are all checked. For ACAV, only those between the laser and the PMC are checked(BB for phase locking and 21.5 for PMC sideband). The 14.75Mhz sideband and EOAM will be done later. The EOAM and wave plates are removed temporarily.
• I modified the TTFSS for RCAV to have a gain reduction switch to help locking the laser. I tried to lock RCAV, but I cannot turn up the gain. I'm not sure what I did wrong but this has to be investigated.

To do lists

• put optics back in ACAV path and optimize them (alignment + polarization).
• fix RCAV TTFSS . Check by measuring the TF of the modified stage/ scanning laser + checking error signal

above: old PBS, bad inter surface can be seen.

above: new PBS: all surfaces are clear

 A tentative layout for almost symmetric layout for beat measurement. The double 1/4 objects  in the beam paths should be 1/4 and 1/2 waveplates.

Lenses might be used to focus the beam somewhere.

 I switched the RFPD between RCAV and ACAV, now the gain for FSS loop is set to 26 dB, but the beat signal does not change.

From previous elog entry, RCAV's RFPD does not have a peak at 35.5 MHz, and ACAV's RFPD has a peak ~36 MHz. And the FSS loop did not have enough gain,

so I switched RFPDs between both cavities. Attached pictures below show the error signal from RFPD when the cavities are scanned, before and after I switched them.

The power into the cavities are ~ 1mW for both cavities. 

The phase is adjusted to produce the best error signal.

Phase adj were 4.16 then changed to 5.67 V

I also inverted the phase on PDH box for ACAV. 

FSS gain can be reduced from 30(max) to 26 dB. 

Then I measured the beat noise, with 100 kHz input range, gain 5. There are no change compared to before.

i've suspended another cavity (very similar to the LIGO refcav) on an old stack which is a bit longer than the one we currently use. That shouldn't matter for the viton damping measurements of the wire suspension.
The suspension itself is not identical to the one we use. The posts are different, i had to make some springs which can handle the load, and i had to cut some new wire. Below pictures of the new one and the last picture is from the existing one for comparison. We don't have any spare parts from the original suspension.

Here the original suspension:

I measured Q factor for a few modes of refcav's suspension system, by shadow sensing technique, and found out that

The modes with high Q are associated with spring motion.

The vertical spring mode has Q ~ 1800 at 3.45 Hz.

Q from swing modes are not so high, ~ 150.

We will try to get rid of the springs later.

The setup is posted by Frank, see below. For sensing technique, A HeNe laser is used for

a light source and adjust so that half of the power is on the PD when the cavity is still.

Then each mode is excited, as the cavity moves, the power on the PD oscillates due to

part of the beam is sinusoidally blocked by the cavity. Then the voltage is monitored and recorded.

Details about how Q and amplitude relates is in 40m wiki page here.

The results are summarized below.

 mode                                             f0                  Q

swing (along the cavity axis)       2.25 Hz          144+/- 5

Vertical (spring)                           3.45 Hz            1800

Tilt                                                3.55 Hz       ~ 1500

Swing(left/right)/roll                     2.0 Hz            150+/- 10

Yaw                                              ~ 3Hz             N/A

1) For swing mode, the Q is low, it can be seen easily when the amplitude drops by a factor of 2 in 20 second span.

 2) However, for vertical spring it took ~ 2 mins before the amplitude decays by a factor of 2, so I measured the time

(~130 sec) and calculate Q, and plot it on a 20 second time span. I tried to excite only one mode, but it seems to excite

tilt as well, we can see the beat at ~ 0.1 Hz. Tilt is @ ~3.55 Hz, and its Q is might be about the same.

This 0.1 Hz beat also presents when I measured Q for tilt.

3) Left/Right swing and roll mode are hard to distinguish, so I treat them as one mode.

4) Yaw is really hard to measure alone, every time I excite Yaw, vertical

and tilt always couple in. I cannot get nice data out of Yaw yet, but Q seems to be pretty low.

and f0 is ~ 3Hz.

So it seems that vertical motion is crucial. The peak in beatnote has a highest peak around 3.45 Hz.

I'll add the seismic from the spring mode in the nb.

 I add the effect from the suspension to the noise budget. Assuming no cross coupling among any modes, and

treat only seismic from vertical motion and horizontal motion along the cavity axis.

(vertical mode and along the axis swing mode)

In the model, seismic (acceleration) coupling to frequency noise via cavity's sagging. No

scattering is taken into account.

Originally, in the noise budeget we have

1)velocity data from the seismometer, v,

 2) times the transfer function through double stacks.

3) times (2 pi f) to convert velocity to acceleration

4) times a converting factor for acceleration -> frequency change ( obtaining from FEA)

I have to add:

5) multiplying the result with TF due to suspension = abs[ 1/ (f^2 + i*f*fo/Q +  fo^2)

6) multiplying again by (2*pi*f)^2  (since the TF is a conversion from F to mX, and we need acceleration)

I'm not sure if I did it correctly, I'll double check it.

emissivity coefficients - ε -  (300K)

Quartz, Rough, Fused  :  0.93
Stainless Steel, sandblasted : 0.38
Stainless steel: type 18-8, sandblasted : 0.44
Stainless Steel, polished : 0.075
Aluminum Foil, shiny side : 0.03
Electroplated Gold : 0.03
Gold: plated on stainless steel and polished : 0.028

  The drift in the demodulated signal (beat frequency x local oscillator) can be tracked by using ifr2023 and sr560. We successfully set the control loop, but

the detail about how ifr2023 works will be reviewed for clarity. The SR560 is set at gain -100, low pass at f = 10Hz. The power spectrum of the drift can be seen from the attachment.

Volts? What are Volts???

This plot should be converted into radians/rHz or Hz/rHz in order to be used.

Plots without physical units should almost never be used. Always Calibrate.

in order to get an idea about the part/subsystem causing the RF power modulation while sweeping the VCO frequency i changed the length of the cable to the AOM. I decided to just extend the existing cable using a cheap SMA cable, not one of those semi-rigid ones. Now i thought due to more losses, low quality cable, longer, more connection etc. the shifted power should be less, but it seems to be the opposite, see screenshot. The purple curve is the transmitted power through the refcav, red the VCO input signal, the rest unimportant. On the left third the old cable, then a short break where i extended the cable, the center part with the longer cable, another short break and then with the original length. First i thought it's some aligment related thing, touching the cable, changing the alignment of the AOM etc. But it's not. The PD behind the curved mirror (not shown) shows exactly the same. Any ideas?

Seem like a screwy AOM. I would take the double-passed beam and beat it with the initial beam (no cavities). Make sure the frequency shift is appropriate and make sure there is no amplitude change in the beat over the whole VCO range.  

we have probably some minor network problems which causes some channels not beeing available at all times even on the same computer.

example:
if you open the Striptool and Probe at the same time and access the same channel, one of the tools can see the channel, the other doesn't.
Or one tools sees a different value, e.g. if i change the setpoint of the temp loop, probe still sees the old value, but the Striptool already the new one.
Sometimes it helps if you close the application and after restarting it everything is fine. Same for the framebuilder. Sometimes some of the channels get lost.
I don't know where it comes from. It happens randomly to any of the channels. It's not the traffic on the network, but could be some routing problem.

i tried to figure out where the network problems come from. Looks like it's the fiber connection between fb1 and the switch in the PSL lab.

Here a result from a simple ping between fb1 and the other computers. It acrually doesn't matter which one.

--- 10.0.0.1 ping statistics ---
1000 packets transmitted, 817 received, 18% packet loss, time 201397ms
rtt min/avg/max/mdev = 0.169/0.233/0.381/0.025 ms

--- 10.0.0.2 ping statistics ---
1000 packets transmitted, 786 received, 21% packet loss, time 202036ms
rtt min/avg/max/mdev = 0.617/0.694/2.658/0.152 ms

--- 10.0.0.3 ping statistics ---
1000 packets transmitted, 796 received, 20% packet loss, time 201696ms
rtt min/avg/max/mdev = 0.410/0.453/2.655/0.081 ms

Pings between computers within the PSL lab but connected to the same switch are OK:

--- 10.0.0.1 ping statistics ---
1000 packets transmitted, 1000 received, 0% packet loss, time 202998ms
rtt min/avg/max/mdev = 0.000/1.092/13.755/1.340 ms

--- 10.0.0.2 ping statistics ---
1000 packets transmitted, 1000 received, 0% packet loss, time 203161ms
rtt min/avg/max/mdev = 0.200/1.719/13.230/1.545 ms

So i think it's the fiber connection.

 

I got PMC drawing from Dmass, this will be similar to gyro's steel PMC. I'll submit the work to machine shop soon.

The drawing is on svn full PMC assemble can be found at ATF:1543.There are spare mirrors in PSL that can be used. I still have to look for a PZT.

The round trip length is 0.33 cm. this corresponds to FSR = 454.45 MHz. If I want to be able to scan through 2 FSR, the displacement range of the PZT will be dL = 2*FSR * L / f, where L = 0.33m, f = c/lambda.  dL ~ 1um. 

[with Zach and Dmass] We discussed about the stainless steel pmc design  and here are the list of what should be modified.

The drawing can be found, on svn.

pmc_endcap_v2,

•  the hole for the beam exit can be larger (x1.3) so that the exit beam can pass without clipping. It should not be larger than the pzt
•  [Important]the thickness of the PZT, thickness of the back mirror, end cap,  will determine the optical path of the PMC (with the beam centered at the input/output mirrors), see pmc_spacer_v2. Make sure to get the thickness right, so the beam is centered on all mirrors.

 pmc_clamp

• the clamp for the input / output window can have a little larger opening to avoid clipping the beam. The through hole diameter can be 0.9 in stead of 0.8".

pmc_base

• The height should be corrected for 3" beam height, measured from the table to the center of the mirror (the previous one was designed for 4" beam height. The size of the ball bearing has to be specified (Dmass said it was for 3 mm radius).

Materials

• find the ruby/ sapphire bearings for the 3-point mount sapphire ball.
• Other parts of the PMC (spacer, pmc clamp, end cap) will be made from stainless steel, the base will be made from brass.
• press fit slot and press fit cone will be made from hardened steel dowel pin from McMaster

assembly

• make sure the assembly has the right beam height (3" for CTN)
• make sure to glue (with epoxy) the mirror, pzt, end cap carefully so all the parts are parallel, no tilt, no yaw.
• order ruby or sapphire ball

PZT can be ordered from www.pi.ws.

The requirements for PZT from (LIGO-xx), are (A) pzt range = 2.7 FSR, for 0 - 375 V, (B) resonant frequency at 10kHz or above.

Zach is using model P-016.10H. The displacement is 15 um (with 1000V), OD = 16mm, ID = 8mm, L = 15mm, resonant frequency = 67kHz.  Assuming the pzt is linear, the displacement will be 5.6 um for 375V, this corresponds to 11 FSR for our cavity (FSR = 454 MHz). I don't know if this will cause some locking problem or not, or it might just give us an extra gain in the pmc loop.

If I follow the requirement, the displacment of 5um @ 1000V will be enough for us (model P-016.00H), but the length of the PZT will be 7 mm, and I think we have to fix the drawing accordingly.

Above, an excerpt from the pzt catalog, the full one can be found HERE.

Kriten sent me solidwork part files for the steel pmc.  I'm checking all the parts and will decide what material we want to use.

She reported that a ss pmc will have the first body mode at 780 Hz, while an aluminum one will have the first body mode at 1kHz. But we have to take thermal expansion, stiffness into account. here are some material properties

I think the thermal expansion will be a problem, but their thermal expansion coefficients are not that different. I don't know about stiffness of the body. I'll ask someone about this. Otherwise Al might be a better material if we look for higher resonant frequency.

The PMC round trip is ~ 0.32m. The end mirror has ROC = 1.0m. The spotsize is 384 micron.  The end mirror has radius ~2.5 mm. The clipping loss will be ~ 1*10^-43 on the curve mirror, and much smaller at the flat mirrors. The number seems very small but I think it is correct.

 This is just a simple integration for power of the beam P(a) where a = radius of the mirror (2.5mm). The total loss on all three mirrors per one trip is definitely way below 1ppm.

[add calculation]

updated the stack TF using more accurate numbers for the RTV springs and masses and also updated the proposed TF for the stack using the modified RTV springs (see elog #762) (instead of SS springs). The updated model can be found on the svn.

Drilling the hole in the center of the existing springs reduces k to 19150N/m (RTV615 block, ~35Hz resonance (max value measured ~35Hz, minimum ~33Hz) with 0.396kg mass) from the original k=28900N/m (RTV615 block ~43Hz, resonance with 0.396kg mass). It should also be possible to reduce the number of springs from 8 to 4, at least for the top stack. For the bottom we have to check how much clearance we will have left between the two stack plates if we use softer springs and reduce the amount by a factor of two.

 estimated stack TF using measured RTV spring values

Ring-down measurement of modified RTV spring

moved the first 8 signals, the 4 individual sensors for each cavity, to the VME DAQ system.
Because i would have to open the foam box in order change the cables, i extended the existing ones for now to see if everything is working.
Once all channels are configured and everything is working i will open the box and make all the changes.
I also have to add the voltage reference for the second board and add the averaged channel from that board to the DAQ as well.
I need two more of the 9-pin D-SUB connector blocks or i have to make breakout cables instead.

Also added the VCO input monitor signal to the DAQ: channel name is C3:PSL-ACAV_VCOMON.
This channel can be used to keep the VCO signal centered in the range by feeding back to the temp setpoint of the cavity or the laser temp if locked alone (to match resonance of both cavities)

- personal notes -

J2  63/64  CH31  PSL-ISS_AOMRF

J2  45/46  CH22  PSL-FSS_LODET

J2  49/50  CH24  PSL-FSS_FAST

J2  51/52  CH25  PSL-FSS_PCDRIVE

J2  43/44  CH21  PSL-FSS_RFPDDC

J2  53/54  CH26  PSL-FSS_RCTRANSPD

J2  47/48  CH23  PSL-FSS_PCDET

J3  ?   CH34  PSL-PMC_TRANSPD

Found at least two (minor) problems:

1. So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
   For calibration i used the slope of the sine near the zero-crossing.
   As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
   Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
   

 

it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!

2. the channel which contains the calibrated VCO monitor signal uses a wrong sign.
   The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
   However, the frequency tuning curve i measured with the old (wrong) cable.
   I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
   This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
   Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
   
   so i think once the EPICS channel is fixed we can trust that channel

So, from the first plot, is the calibration factor for cable delay technique ~ 8MHz/Volt?

yes, for yesterdays measurements 7.435 MHz/V.

But that number changes from measurement to measurement as i'm changing the setup every time to improve SNR (or bring back stuff i've stolen from 40m)

Tom from the electrical workshop fixed the two sockets at the computer desk.
We also checked the other sockets as they were labeled wrong,so we didn't know which circuit breaker they go to.
Re-labeled the sockets.

All circuit breakers are located in the main panel in the ATF lab.

i've build a small baking chamber which we can use for small parts like posts, sensor and heater assemblies, wires, screws etc. It's a short (10" long) 6" CF reducer Tee with two heaters and a k-type thermocouple on it. We still don't have a RGA, but if we clean all parts carefully (made of materials we know that they are not a problem in general) and vacuum bake them for a few days we reduce the risk of contaminating our cavities by a lot. Current wait time for parts submitted for baking is ~2month. Would be great to find a slightly larger chamber to fit the larger parts in there as well (i don't want to use the (now) spare refcav chamber).

The medm screen for the 1st laser is completed, the servo is on an stable. Refcav has been locked for a few hours as of now.

• The output for slow feedback is on J9, slot 9/10 (VMIVME 4116 C2 S3). This is an unused channel previously assigned to PSL-ISS_ISET, I checked ISS.db file to look for the VMIVME address. For the slot number, I look up the channel name in D980535-C-C document.
• I added low pass filters (~100mHz) to both input and outputs of EPICS.
• All EPICS channels for slow feedback and perl scripts are in SLOW_LASER.db file.
• The startup.cmd file is updated accordingly.
• servo gain is optimized. ??? What does that mean??? How about some performance plots? (About the bode plot, I'm trying to get a transfer function of the NPRO slow input, with that I can estimate the bode plot of the loop. As of now I just adjust the PID gain so that the loop is stable)
  

fig1: FAST feedback to the laser is shown in blue plot, vertical axis:1V/div, horizontal axis:  4 sec/ div. I adjusted proportional gain first, to get only a few overshoots with acceptable rise time.

fig2: Then I adjusted integral gain to eliminate the offset, and Derivative gain to reduce overshoot. More about PID gain can be found here. Current Value KP = -0.0002, KI =-0.00015, KD = 0.

I set the output to be between -2 V to 9 V. Since we need to lock it to GYRO later, it has to be able to be tuned to match the gyro laser. Currently, Gyro laser is operated around 35 Deg C which is similar to 8V input to slow feedback.

I'm trying to draw a cartoon for DAQ wiring in CTN lab for future reference. This is what I have so far. I'll add it in WIKI page.

Slow feedback for 2nd laser is ready.

EPICs channel:

• C3:PSL-RCAV-FMON was created for fast mon to laser.
• C3:PSL-RCAV_SLOWOUT was created for SLOW feedback. The channel was originally named C3:PSL-FSS_VCOMODLEVEL J9 input 11 and 12, VMIVME-4116, C2 S4.

The output of EPICS channels have capacitors installed in parallel for low pass filter.

 - personal notes -

slow actuator values

RCAV : 0.1915ACAV : 0.2050

(.1915 V - .2050 V) * 1180 MHz/V = -15.93 MHz difference

both cavities @35 degrees +/- 5mK

slow actuator values

RCAV : 0.1890
ACAV : 0.1993

(.1890 V - .1993V) * 1180 MHz/V =  12 MHz difference

• temperature of one cavity has to be tuned about ~12MHz with 6mK/MHz, so ~70mK
• loosing lock @~+3V input to the VCO which should go up to at least 5V

anyway, the tuning range is only 10MHz in that direction, so can't lock both at the same time right now

frequency see here: VCO tuning

slow actuator settings for being resonant:

update @1pm:

refcav2: 0.4649
refcav1: 0.4469

heater refcav1: programming voltage 1.95V
heater refcav2: power supply voltage 16V

ACAV 0.2602 V

RCAV 0.1102 V

Software feedback to laser temp didn't work correctly. Fixed it.

Script is located in /usr1/epics/psl/scripts

Hey,

So I'm done-ish with the simulink file that models the loop that locks the laser to the reference cavity. I will ask Frank/Tara for a second opinion to see if I am missing any details or if I need to change something.

So over the whole summer, I've put together, little by little, the simulink model for the path that locks the laser to the reference cavity. I'm going to attach the matlab files in a zip folder. I've tried my best to comment as best as possible and to make the programs as robust as I could possibly think of.

I am also attaching the LISO models to the TTFSS paths and for the fits to the measured PZT and EOM Actuator transfer functions. I'm going to list the links of past elogs that refer that mention these fits. I'm also going to attach the fits themselves.

LISO TTFSS

EOM Actuator Measurement Procedure

PZT and EOM Actuators Fit

A more complete description of my measurements can be found in my surf report

I am still not satisfied with these fits and would like some feedback in improving them. I am most worried about my measured EOM Actuator transfer function fit.

to test how much insulation we need to reduce our acoustic noise (or air currents) problem we've added a simple aluminum-foil plated styrofoam box around the beat breadboard.
There are plenty of holes for all the beams and cables :

• two for incoming beams
• two for the power stabilization
• aux beam from combining beam splitter
• reflected beam from beat PD
• video, power, PD cables,...

Even with all those holes we can already see a reduction with a simple lid on top of it. Due to power outage yesterday we still have no stable system yet, so waiting until tomorrow for measurements.

not all amps are good for use as a comparator

https://www.analogictips.com/faq-use-op-amp-comparator/

Here is the characterization of the shot noise.

I ended up with two different answers for the shot noise intercept. When I fitted it to Z(2e(i_{dc}+i_{int})^{1/2}, where Z is the transimpedance, i_dc is the measured data, and i_int is the shot noise intercept, I got 0.27mA.  When I fit two lines for the input referred noise level and the shot noise, the shot noise intercept is at 0.17mA.

Also, everytime I get more data, I end up with a different answer :(

While I'm at it, I will post the transfer function of the PD.

detailed CAD drawings for the short cavities, mirrors, cavity mount, radiation shields, adapter plates and modified top stack  can be found in the drawings folder on the SVN. Need latest version (2011/2012) of Solidworks to open files.
Also included detailed drawing with all tolerances for the spacer which i used to ask for quotes as a pdf.

ordered new shoe covers. Will try those below as they seem to be better than the ones we had but are much cheaper. Come in packs of 300, so 150 pairs for <$30.

AMD8007/CS		Shoe Cover		1	$23.60	$23.60
DYN2134		Disposable Shoe Covers	Features: X-Large Non-Conductive / Nonskid	1	$28.00	$28

we had several shutdowns of the laser within the last days. A couple of times the well known "HT error", today we had an "PS error" for the first time. When does this happen? The other error is related to a malfunction of the chiller as we found out by luck. The chiller temp readout jumps from 26 down to 15 or so within a fraction of a second (so it's not real). This causes the PS to start heating even if the temp is high enough. This screws up the stabiliy of the laser and sometimes causes a chiller error as well. But the "PS error" ? Any idea?

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.

 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.

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.

==Note==

• 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.

I'm in the process of locking the 2nd cavity. The work is in progress. 

•  The 2nd TTFSS is working fine. I tested it by using the 2nd TTFSS to lock the first refcav. The error signal was similar to what I got from the first TTFSS.
•  Mode matching was revised (See Erica's entry).
• Heatsink for the 2nd laser was ready, I added it on the laser.

To Do:

• prepare for the 2nd EOM, I need to think about an oscillator driving and EOM. Since there is no resonant EOM, I'll use Rich's EOM driver on a BB EOM for sideband.

I'm setting up a scattered light measurement for AlGaAs samples. The methods are summarized below.

I discussed with Manasa about the setup and how to do the measurement. The goal is to measure  scattered losses from AlGaAs samples from a normal incident beam. The setup is shown below.

==setup==

The setup is in the ATF lab, on the unused optical table. It is too crowded on CTN table. So I will need a to borrow a 1064 laser from somewhere. 

The incident beam will have to be slightly angle from the normal angle in order to dump the beam properly. 

The arm holds the camera, it can rotate to change the angle to cover the measurement from around 10 degrees to ~70 degrees.

==calibration method==

• We can take a picture from a diffuser plate, make sure it is not saturated. 
• Then use a power meter, measure the power fall on the camera.
• compare the output of the camera and the measured power
• I have to think about how to make sure the solid angle of the camera aperture and the power meter are the same.

==measurement and data analysis==

• For each position, take one picture without the beam on the mirror and one with the beam on the mirror. The first one will be used for subtracting the ambient noise from a picture when the beam is on the mirror. 
• Make sure that no pixel is saturated
• For each pair of picture, we will use Matlab to count the output, then use the calibration to convert to power.
• integrate over half the sphere. I have to think about this to make sure I get it right.

I'm testing the setup and a code for extracting scattered light from the images. 

I used a red laser pointer to test the scattered light setup. Then took a picture with no light (fig1) and a picture with the incident light (fig2). The scattered light can be extracted by subtract fig1(background) from fig2.

The snapshots saved by SampleViewer are in .bmp file. When it is read by MATLAB, the file will contain 480x752x3 matrix element, Each are varied between 0 and 255. The values are proportional to the brightness (how many photons hit the cell). 480x752 is the resolution of the image, x3 are for R G B color. In our case, the image is greyscale and the values are identical. The code can be found in the attached file.  

fig1: The test mirror without incident beam taken as a background image. The image is enhanced by a factor of 5 (by matlab).

fig2: The test mirror with a red incident beam around the center. The image is enhanced by a factor of 5.

fig3: the image is created by subtracting data of fig1 (background) from fig2 (scattered light) and enhanced by a factor of 100. The scattered light on both surfaces can be seen clearly around the center.

 ==To do next==

• From fig 3, the background can be seen even after subtraction, so some black curtains and beam dumps should be added behind the mirror.
•  A room light filter should be installed in front of the camera.
• I'll see if we can find a sample with known scattering loss, so that we can compare how accurate the measurement is.