The script for running continuous scans on HP 8591E spectrum analyzer is located at scripts/general/netgpibdata/HP8591E_contdScan.py

Give the file HP8591E_param.yml as an argument when running the script. This contains the sweep parameters: Start and stop frequencies along with the place where the plot is stored as a PDF.

The default PDF is located on the Desktop and is named HP8591E_View.pdf     Open this using okular and then run the script.  (Okular pdf viewer automatically reloads the PDF as and when a new one is created)

What the script does:

1) Set the start and stop frequencies as given in the .yml file

2) Take a data trace and plot it in a PDF.

3) Repeat taking traces and update the PDF. Untill Ctrl+C is pressed (PDF refresh rate: approximately every 3 seconds )

4) Exit smoothly after the keyboard interrupt.

Other details:

This spectrum analyzer is connected to a GPIB - Ethernet controller that is configured as santuzza.martian (192.168.113.109)

I have currently stolen the wireless modem from the spectrum analyzer inside the lab (vanna.martian) and using it for this one. *poker face*

To improve:

Get the plot to show where the two biggest peaks are located. Currently it recognizes only the biggest one.

Possibly have makers on the two peaks.

PFA a sample pdf

From the last plot:

- Subtracting the offset of 0.0095, the modulation depth were estimated to be 0.20 for 11MHz, 0.25 for 55MHz

- Carrier TEM00 1.0, 1st order 0.01, 2nd order 0.05, 3rd order 0.002, 4th order 0.004

==> mode matching ~93%, dominat higher order is the 2nd order (5%).

Eric: now we have the number for the mode matching. How much did the cavity round-trip loss be using this number?

A test run was conducted on the PDFR system last afternoon and transimpedance plots were generated for 6 of the PDs. The laser was shut down after the test run.

I have not verified (yet) if the transimpedance values indicated by the plots are correct or not. The values mostly look INCORRECT. But the peaks are exactly where they need to be. *phew!*

Reasons: Incorrect calibration, Light other than from the PDFR system fibers on the PDs

Will have to work on debugging all this.

1) Debugging transimpedance calculations in the PDFR

Requires presence of an expert whenever I get inside the lab to take DC measurements or check the illuminating fibers.

2) Creating and incorporating canonical data plots with every measurement of PDFR.

3) Transfer function fitting for transimpedance

4) Improve the Spectrum analyzer scan scripts as mentioned in my elog.

Log-log ... 

Work Done:

• Solved all the timing issues pertaining to the R Pi and the FC.
• Took all the measurements for complete characterization of the frequency counter(Phase Plots to follow shortly).
• Finished  installation of the FC on the martian and created a channel  for the FC frequencies(will be tested in this week).

Plans for this Week:

• Testing of the EPICS soft IOC created for the FC as a channel access server and hence completing the installation of the FC.
• Placing the FC inside the lab( plan discussed in this elog: http://nodus.ligo.caltech.edu:8080/40m/10163) with proper supervision.
• Characterization of the temperature actuator.

Inside the 40m Lab:        

I will need to be inside the lab to place the FC . This will be done in the morning session (on thursday) with supervision of Manasa and Steve(if required).

 The fan is dying. It is changing speed erratically and stops for short time periods. It is very likely to stop rotating soon. It will halt all operations in the lab. We can not see the PMC-T power because Manasa is working on

 AOM alignment.

Updated script does the following:

1) Gets the highest 2 peaks

2) Puts a marker on the peaks. Now it looks very similar to the spectrum analyzer display.

3) The refresh rate is still 3 seconds. It might become better if the analyzer was hooked up to a wired martian LAN port rather than the wireless module I am using now.

PFA a sample pdf

 Purpose

To couple the spare NPRO into our Panda PM980 fibers, in order to carry out tests to characterize the fibers, in order to use them in FOL.

Design

 Manasa and I spent this morning building the setup to couple NPRO light into the fibers. We used two steering mirrors to precisely guide the beam into the coupler (collimator).

We also attached the lens to a moveable stage (in the z axis), so the setup could be fine tuned to put the beam waist precisely at the photodiode.

The fiber was attached to a fiber-coupled powermeter, so I would be able to tell the coupling efficiency.

Methods 

During alignment, the NPRO was operating at 1.0 amps, roughly half of nominal current (2.1A).

I first placed the coupler at the distance that I believed the target waist of 231um to be.

Using the steering mirrors and the stage that holds the couple, I aligned the axes of the coupler and the beam.

Finally, I used the variable stage that the lens is attached to to fine tune the location of the target waist.

Results

Once I was getting readings on the powermeter (~0.5nW), the laser was turned up to nominal current of 2.1A.

At this point, I and getting 120nW through the fiber.

While far from "good" coupling, it is enough to start measuring some fiber characteristics.

Moving Forward

Tomorrow, I hope to borrow the beam profiler once again so as to measure the fiber mode.

Beyond this, I will be taking further measurements of the Polarization Extinction Ratio, the Frequency Noise within the fiber, and the effects of a temperature gradient upon the fiber.

Once these measurements are completed, the fiber will have been characterized, and will be ready for implementation in FOL.

AOM removed from the beampath and PMC relocked. 

AOM alignment:

1. Measured the initial power after PMC as 1.30W and reduced it down to 130mW.
2. Checked the power in the AOM zero order transmission before touching it. For 0-1V modulation input, the power dropped from 125uW to 98.3uW.
3. Steered the mirror right before the AOM to increase AOM zero order transmission and then carefully moved the AOM around to obtain maximum power attenuation. I repeated this a few times and the maximum attenuation that I could obtain was 125uW to 89.2uW (~30% attenuation).
Although this is not the right way to align the AOM, we do not have much options with the current setup as there is not enough separation between the zero order and first order beams and the AOM is on a fixed rigid mount.
4. I tried to dump the first order beam from the AOM and it wasn't satisfactory as well. There is barely any separation between the zero order and first order beams.

PMC relocking:

1. SInce the alignment to the PMC was disturbed by moving the AOM and the steering mirror in front of it, the PMC alignment was lost.
2. I could not relock the PMC at low power or high power. Rana had to come to rescue and fixed the alignment so that we could see flashes of PMC on the trans camera (This was done by aligning refl beam to the PMC REFL PD while giving a triangular ramp to the PMC PZT voltage).
Also I should not have tried to lock the PMC at high power as I could have been steering the beam at high power to the edges of the PMC mirrors that way and burning stuff easily.
3. Before fine tuning the alignment, I decided to remove the AOM from the beam path as there needs some work done on it to make it useful.
4. I removed the AOM from the beam path and relocked the PMC. 
5. PMC is relocked with 0.79 counts in TRANS and I measured the power after PMC 1.30W

Attachment: picture showing AOM removed from the beampath.

[Koji, Manasa]

The air flow from the dying fan was kinda weak and we decided to give a help with an external fan.

Koji brought a fan taken from a junk found at EE shop in W.Bridge.
The fan has been tied to the cage of the existing fan using cable ties to provide air circulation.
So even if the existing one dies anytime, we still don't super-heat anything.
The power supply for the fan rests next to the controller. 

The air from the fan ventilation was hot, and now with the additional fan this hot air is actually sucked
out with stronger flow. So this is relieving for now.

I found the VCO driver, that Rana asked me to locate, inside the 40m. I already have one VCO from PSL lab. Now, I have kept both of them inside the 40m lab(one on the cart in the side of the Y-arm and the other near the X-arm electronics table).

Goal:

To estimate the transfer function and the noise in the FC that is a part of the FOL-PID loop.

Measurements Taken:

The setup used for the measurements is described in my previous elogs.

The input modulation signal and the FC output were recorded simultaneously for a certain period of time and the phase and gain are estimated from the data.

Analysis(Data and code attached):

The recordings must contain equal number of data points(around 6000 data points in my measurements) for analysis.

The steps I followed to generate these plots are:

• Took the FFT of both FC out data(from FC) and Modulation input(from SRS via ADC).
• Estimated the phase angles at the particular modulation frequencies from the FFT data(in Matlab using  angle(x) for phase at the frequency f(x);x: is the frequency bin)
• Then for the phase of the system at a particular modulation frequency, 

                              Phase(system) =Phase(FC Signal) - Phase(Input Signal)

• Plotted the acquired phase vs the modulation frequency on a Semi-log graph.

Results:

From the plots its can be inferred that :the delay of the FC is almost 0 until the modulation of 0.1 Hz. Then there are phase shifts of  +/- 180 degrees showing that the system has multiple poles and zeroes(will be estimated after I have phase plots at few more carrier frequencies).

To Do Next: 

Phase plots for varying carrier frequencies and different sampling times.

Installation of FC inside the 40m.

If I assume 1sample delay for 0.1s sampling rate, the delay is Exp[-I 2 pi f T], where T is the sampling period.

This means that you expect only 36 deg phase delay at 1Hz. In reality, it's 90deg. Huge!

Also there are suspicious zeros at ~1.6Hz and ~3Hz. This may suggest that the freq counter is doing some
internal averaging like a moving average.

It would be interesting to apply a theoretical curve on the plot. It's an intellectual puzzle.

[Rana, Jenne]

We had a look at the RIN of the transmission signals TRX and TRY, when the arms were individually locked on IR.  If the intensity noise is very bad, then the transmission signals aren't really a good option to use for locking.  So, if the RIN is bad, we need to work on our intensity stabilization. 

We need to understand what the situation is with the AOM, and why it isn't working as expected, so that we can reinstall it.  We also need to decide if we're going to use the SR560 setup, or if the Chas ISS is sufficiently characterized for us to use. 

The RIN is certainly bad.  Also, I don't know why the Xarm's RIN is worse between 10 Hz and a few hundred Hz than the Yarm.

MC loop is near unstable. Common gain reduced. Needs more loop tuning.

We've often seen that the MC gets into a state where it keeps losing lock and the EOM drive shows a large RMS. We've usually been looking at the noise spectrum to diagnose this.

Tonight we finally just measured the OLG. The attached plot shows the loop gain measured with the 4395 on the MC servo board

Although the phase margin is a healthy 45 degrees, its close to instability at 1 MHz. For this plot, I reduced the gain by 3 dB and now the margin is ~7 dB. So usually its pretty close to unstable and at least its always making a noise peak.

That whole TF above a few hundred kHz is weird. We should tune out whatever makes it so flat and also remove the resonance that makes the 1 MHz peak; maybe its from some post mixer low pass?

Anyone interested in helping in the investigation ought to measure the TF of the MC demod board, the MC servo board, and the FSS box.

Silver lining: if we fix this loop shape, we might be able to have a much more stable IMC and IFO.

Data and Calculation for the Xarm Current Mode Matching

Two days ago, Nick, Jenne, and I took a measurement for the Green Transmission for the X-arm. I took the data and I analyzed it. The first figure attached below is the raw data plotted. I used the function findpeaks in Matlab, and I found all the peaks. Then, by taking close look at the plot, I chose two peaks as shown in the second figure attached below. I took the ratio of the TEM00 and the High order mode, and I average them. This gave me a Mode Matching of 0.9215, which this value is pretty close to the value that I predicted by using a la Mode in http://nodus.ligo.caltech.edu:8080/40m/10191, which is 0.9343. Nick and I measured the reflected power when the cavity is unlocked and when the cavity is locked, so we measured the P_reflUnLocked=52+1µW and P_reflOnLocked=16+2µW and the backgroundNoise=0.761µW. Using this information we calculated  P_refl/P_in=0.297. Now, since P_refl/P_in=|E_ref/E_in|², we looked at the electric fields component by using the reflectivity of the mirror we calculated 0.67. The number doesn't agree, but this is because we didn't take into account the losses when making this calculation. I'm working in the calculation that will include the losses.

Today, Nick and I ordered the lenses and the mirrors. I'm working in putting together a representation of how much improvement the new design will give us in comparison to the current setup.

I took back he VCO driver that Reetika brought over to the 40m from the PSL lab.  

In a attempt to debug the values of transimpedance generated by the PDFR system, I did a manual measurement for REFL11 PD.

• Took the tops off AS and POY tables. (REFL11 and REF PD) Under the supervising eye of Manasa
• Verify that no extra light is falling on REFL11.
• Retake DC voltage readings, power readings.
• Manually set the sweep parameters and record readings from network analyzer.
• Put the tops back on the tables
• Calculate transimpedance 

Results:

REF PD(1611):

Pinc = 1.12 mW                 T_dc = 10000 V/A (datasheet)

Vdc = 7.68 V                      T_rf = 700 V/A (datasheet)

Calculated Responsivity = 0.68 A/W (Which matches perfectly with the datasheet value of 0.68 A/W) 

REFL11:

Pinc = 0.87 mV             T_dc = 66.2 V/A (schematic)

Vdc = 32.5 mV      

Calculated Responsivity = 0.56 A/W

Network analyzer reading at 11 MHz : 0.42

Calculated RF Transimpedance = 460 V/A

40m Wiki : RF Transimpedance = 4 kV/A

I ran the same measurement using PDFR system and got the same results.

Attached: the automatic data and plot obtained.

Conclusion:  The PDFR system and manual measurements agree with each other. However the values do not match with 40m Wiki. I have no clue about which measurement is correct or any mistakes I might be making in the calculations. 

 Purpose

Steve and I moved some things around in the 1X2 rack in order to make room (roughly 6") for the electronics box that will contain rf frequency counters, ADC, and Raspberry Pi's for use in the Frequency Offset Locking apparatus

Picture

Occurrences

First, we killed power by removing the fuse that the boxes we were moving were running through.

Then, we moved the boxes. I dropped//lost a washer. It didn't seem to cause any problems, so no further attempts to locate it were made.

The fuse was reinstalled, and everything was reconnected.

Moving Forward

We are now working on putting together the electronics box, which will contain ADC, and raspberry pi's. The frequency counters will be mounted on the front of the box.

Once complete, it will be installed for use in FOL.

     PMC transmission as an indicator of laser controller with extra fan solution: 8 and 1day plot

What is the coupling factor between the RF in and the RF mon of the demodulator?
I don't assume you have the same amount RF power at those two points unless you have an RF amplifier in the mon path.

Additional comments:

This was done based on the earlier proposed setup plan for the frequency counters that will be used to measure the beat note frequencies [Akhil's elog]

I switched off the power supply to the green PDs so that we don't cause any damage while moving the amplifier panel for the beat signals and beatbox. 

It sounds like the work was done carefully. Even so, Jenne or Manasa have to run the ALS (X and Y) to check if they are still functional.

[Rana, Evan]

This morning we took several TFs of the MC servo board using the HP4395A.

The 4395 source was teed, with one output of the tee going to 4395 R and the other output going to the board's IN1. We then took TFs of (4395 A) / (4395 R), where 4395 A was one of the following four points on the servo board:

• OUT2
• A TEST1
• B TEST1
• SERVO

For each of these points, we took a TF at two gain settings: IN1 and VCO gains both at 0 dB, and then IN1 and VCO gains both at 20 dB.

Before doing these measurements, we calibrated out the cable delay. Additionally, SERVO was always loaded with 50 Ω—either from the 4395 or from a terminator.

The attached png shows the servo board settings when these TFs were taken with the 0 dB gain settings. The settings for the 20 dB measurements are identical, except for the higher IN1 and VCO gains.

 I had some syntax errors in the script that prevented the script from doing the right thing. The backup is now up to date, and the cronjob should work. 

We want to be able to graphically see how much better it is the new optical table setup in comparison to the current optical table setup. In other words, we want to be able to see how displacement of the beam and how much angle change can be obtained at the ETM from changing the mirrors angles independently. Depending on the spread of the mirrors' vectors we can observe whether the Gouy phase is good. In the plot below, the dotted lines correspond to the current set up, and we can see that the lines are not spread from each other, which essentially mean that changing the angles of the two mirrors just contribute to small change in angle and in the displacement of the beam at the ETM, and therefore the Gouy phase is not good. Now on the other hand. The other solid lines correspond to the new setup mirrors. We can observe that the spread of the line of mirror 1 and mirror 4 is almost 90 degrees, which just implies that there is a good Gouy phase different between these two mirrors. For the angles chosen in the plot, I looked at how much the PZT yaw the mirrors from the elog http://nodus.ligo.caltech.edu:8080/40m/8912. In this elog, they give a plot in mrad/v for the pitch and yaw, so I took the range that the PZT can yaw the mirrors, and I converted into mdegrees/v and then I plotted as shown below. I plot for the current setup and for the new setup in the same plot. The matlab code is also attached below.

Rack 1Y2, I took transfer function measurements for each of the following demodulator boards: REFL11, REFL33, REFL55, REFL165, AS55, POP22, POX11 and POY11.

What I did:

1) Removed the wire at PD Input to demodulator board.

2) Put the MOD output from network analyzer into PD input of board.

3) Ran a sweep from 100kHz to 100MHz.

4) Measured the transfer function between PD RF MON and PD Input. (The PD RF MON signal came out of the RF multiplexer, so the mux is included as well )

5) Put the original wire back at PD Input.

Results:

The plots clearly show an attenuation of 20dB (factor of 10) for all the demodulator boards. This explains why my transimpedance measurements are off by 10 times.

Note: for REFL 165, there was an extra 100MHz high pass filter installed at PD Input. I did not remove this and made my measurements along with this.

To Do:

a) Modify the PDFR system to calibrate out this attenuation.

b) Measure the transfer function between the input and output of RF mux, so that we can have just the transfer function between PD input an PD RF MON (for documentation's sake)

 Thanks Koji , for your  hint for the brain teasing puzzle. I was looking into Filters that are usually used in devices like counters, DSO and other scopes. I found that , to improve the quality of the measurement one of the best approach  is averaging. I looked deeper into averaging and found out this:

There are two general use-cases for averaging . The first, successive sample averaging, takes a single acquisition and averages between its samples. The second, successive capture averaging, combines the corresponding  samples of multiple captures to create a single capture. Successive sample averaging is also called boxcar filtering or moving average filtering. In an implementation of this type of averaging each output sample represents the average value of M consecutive input samples. This type of averaging removes noise (one of the reasons the noise level was not bad: http://nodus.ligo.caltech.edu:8080/40m/10151) by decreasing the device's bandwidth(could be one of the reasons why the FC operates in 4 different frequency ranges). It applies an LPF function with a 3dB point approximated by  0.433 * s / M, where M is the number of samples to be averaged, and s is the sample rate in samples per second. 

Now I tried verifying the 3 dB points in the gain plots I generated :

For 1 s Sampling time : the 3 dB point for such a Boxcar filter should be at 0.433* 1/M. If we assume that it averages for 2 samples, M=2 which gives the 3dB point at 0.288 Hz but occurs somewhere between 0.3 and 0.4 Hz.  (http://nodus.ligo.caltech.edu:8080/40m/140619_120548/GainVsFreq.png)

For 0.1s Sampling time: the 3dB point should be at 2.17 Hz and in reality is 2.5 Hz(http://nodus.ligo.caltech.edu:8080/40m/140701_211904/gain.png).

Also, This type of filter will have very sharp nulls at frequencies corresponding to signals whose periods are integer sub-multiples of M/s. As seen my previous plots (http://nodus.ligo.caltech.edu:8080/40m/10118 , http://nodus.ligo.caltech.edu:8080/40m/10070) there are sharp nulls at frequencies

0.4 Hz for 1S sampling time and

at 1.5 Hz,3 Hz for 0.1 S sampling time as correctly predicted.

The moving average filter is  L-sample moving average FIR, with the frequency response as:   H(ω) = (1/L) (1 − e^{− jω L})/(1 − e^{− jω})..

There is an overall delay of (M - 1)/2 samples from such a length-M causal FIR filter. 

The expected bode plots for such a filter with L= 5 is attached(attachment 2).

Purpose 

We wanted to measure the mode coming out of the fibers, so we can later couple it to experimental setups for measuring different noise sources within the fiber. i.e. Polarization Extinction Ratio, Frequency Noise, Temperature Effects.

Methods

I used the beamscan mounted on a micrometer stage in order to measure the spot sizes of the fiber coupled light at different points along the optical axis, in much the same way as in the razorblade setup I used earlier in the summer.

Analysis

I entered my data (z coordinates, spot size in x, spot size in y) into a la mode to obtain the beam  profile (waist size, location)

Code is attached in .zip file.

Moving Forward

After I took these measurements, Manasa pointed out that I need points over a longer distance. (These were taken over the range of the micrometer stage, which is 0.5 inches.)

I will be coming in to the 40m early on Monday to make these measurements, since precious beamscan time is so elusive.

Eventually, we will use this measurement to design optical setups to characterize Polarization Extinction Ratio, Frequency Noise, and temperature effects of the fibers, for further use in FOL.

I looked at what the RIN contribution of the sqrtInv sensor is by locking the arms individually on IR using POX and POY.  I then took spectra of the sqrtInv channels.  For the Xarm, I had forced the triggering so that the QPD was being used as the transmission PD, while the Yarm was using the regular Thorlabs PD.  I also had the green lasers locked to the arms, and took beatnote spectra to see what the sensing noise of the beatnotes is, all at the same time.

For the sqrtInv channels, I used the Optickle calibration from elog 10187. For today's plot, I am using the calibration at about 1nm, since that is about where we are when we transition to the sqrtInv Thorlabs signal usually.

For the ALS channel, I was using the _FINE_PHASE_OUT signal, which is in units of degrees of phase for a single green wavelength.  So, since k * x = phi, I want the phase data to be converted to radians (2*pi/360), and use k = 2*pi / lambda_green.  So, doing some algebra, this gives me x = phi_degrees * lambda / 360 for my calibration. 

What I see in the plot is that the ALS sensing noise is pretty bad compared to the sqrtInv channels, so maybe we don't have to work so hard on the ISS this next week.  Also, the Thorlabs PD is much better than the QPDs, which maybe isn't so surprising since we have them set so that they have good SNR at higher power.

Anyhow, here's the plot:

Also, here is the Thorlabs PD only, with single arm locked on RF, with the noise calibrated to different CARM offsets:

Your calibration of the ALS signal should be revised.

The phase for the ALS is not an optical phase of the green but the phase of the phase tracker servo output.

The calibration of the phase tracker depends on the cable length of the delay line in the beat box.
It seems that we are based on this calibration. Which gives up ~19kHz/deg.

Or, equivalently, use C1:.....PHASE_OUT_HZ instead.

Patient One for this new system will be the MC servo card. The DCC number is D1400242. Currently, v1 is just the original drawing with no modifications. I've updated the DCC document tree at E1400326 accordingly.

It looks like we can use Jenne's information in 40m:9892 to deduce the modifications that have been made (alternatively, someone can just pull the board and examine it on the bench).

 Purpose

The idea was to measure the profile of the light coming out of the fiber, so we could have knowledge of it for further design of measurement apparatuses, for characterization of the fibers' properties.

Methods

The method was the same as the last time I tried to measure the fiber mode.

This time I moved the beam profiler in a wider range along the z-axis.

Additionally, I adjusted the coupling until it gave ~1mW through the fiber, so the signal was high enough to be reliably detectable.

Measurements were taken in both X and Y transections of the beam.

The range of movement was limited by the aperture of the beam profiler, which cuts off at 9mm. My measurements stop at 8.3mm, as the next possible measurement was beyond the beam profiler's range.

Analysis

I entered my data into A La Mode, which gave me a waist of 5um, at a location of z = -0.0071 m, that is to say, 7.1mm inside the fiber.

Note that in the plot, data points and fits overlap, and so are sometimes hard to distinguish from each other.

Code is attached.

Moving Forward

Using this data, I will begin designing setups to measure fiber characteristics, the first of which being Polarization Extinction Ratio.

Eventually, the data collected from these measurements will be put to use in the frequency offset locking setup.

Interlock closed valve V1, V4, V5 and VM1 when the nitrogen supply run out. The IFO pressure rose to P1 1 mTorr

In order to recover Vacuum Normal valve configuration I did the following:

Replaced both nitrogen cylinders. Confirmed pneumatic nitrogen pressure 70 PSI.   Opened valves V4 and V5

At P2 < 1 mTorr, Maglev rotation 560 Hz , V1 was opened.

VM1 was opened when CC1 pressure dropped below < 1e-5 torr

Please  take a look at the N2 cylinders pressure on Friday to insure that there is enough for the week end.

The daily consumption is 600-700 PSI

The expected bode plots for such a filter with L= 4 is attached and compared with the measured.

RXA: When comparing two things, please put them onto the same plot so that they can be compared.

The autolocker claimed it was running and blinking, but not doing anything (i.e. lock bit was not updating and no switches or sliders being touched)

After stopping and starting it a number of times, it began working again, through no real changes of my own. I'm a little mystified as to what the problem was... keep an eye out.

Using these numbers for both arms (Modulation takes away .2*.25 = 5% power, mode matching takes away 7% after that), I get the following from my data from March:

Xarm loss is 561.19 +/- 14.57 ppm

Yarm loss is 130.67 +/- 18.97 ppm

Obviously, the Xarm number looks very fishy, but its behavior was qualitatively very different when I took the data. ASDC would change from ~0.298 to ~0.306 when the Yarm was locked vs. misaligned, whereas the xarm numbers were .240 to .275. 

In any case, I'll do the measurement again tomorrow, being careful with offsets and alignment; it won't take too long. 

 Edit

The previous data were flawed, in that they were taken in groups of three, as I had to move the micrometer stage which held the beamscan between holes in the optical table.

In order to correct for this, I clamped a straightedge (ruler) to the table, so I could more consistently align the profiler with the beam axis.

These data gave a waist w_o = 4um, located 6mm inside the fiber. While these figures are very close to what I would expect (3.3um at the end of the fiber) the fitting still isn't as good as I would like.

The fit given by ALM is below.

Moving Forward

I would like to get a stage//rail so I can align the axes of the beam and profiler more consistently.

I would also like to use an aperture the more precisely align the profiler aperture with the beam axis.

Once these measurements have been made, I can begin assembling the setup to measure the Polarization Extinction Ratio of the fiber.

The attached zip file has a modified schematic of the MC servo card (011/MC), as deduced from Jenne's photos. Someone should go through and verify that the schematic is correct. Then it can go on the DCC as D1400242-v2.

To modify the schematic, I used Inkscape (the svg files for each sheet are included in the zip file). Then to generate the pdf, I ran

for i in sheet*.svg; do inkscape -A "${i/svg/pdf}" "$i"; done

pdftk sheet*.pdf cat output D1400242

Using the modified schematic (40m:10250), I've made a plot of the TFs I expect for G_IN1 = G_VCO = 0 dB, taking into account our 50 Ω loading of the board.

Evidently I'm somehow missing a factor of 2 in the gain of the overall TF, but the shapes of the expected vs. measured magnitudes agree quite well.

At 1 MHz, I expect we should have accumulated about 80 degrees of phase going through the servo board. In reality, we appear to have lost more like 105 degrees.

I repeated the exact steps above and made sure everything was back where it should be after I was done.

Reason I had to retake the measurements:

My script for acquiring data from the AG4395A network analyzer was such that it first acquired the magnitude data from channel 1 and then recorded phase data from channel 2 without holding its trace. Hence the phase and magnitude data were not exactly in sync with each other. So, when I tried to fit the data to a model using vector fitting, I ended up with very bad results.

I have now changed every single script relating to the network analyzer to just get the real and imaginary data in one go and then calculate the phase using this data.

The fitting process is now in progress and results will be up shortly.

 ITMY oplev was nearly clipping in yaw, causing wonky behavior (POY lock popping in and out frequently). I recentered it and the arm is locking fine now. 

I repeated this process once more, this time using the computer controlled stage that the beam profiler is designed to be mounted to.

These data//fitting appears to be within error bars. The range of my measurements was limited when the beam width was near the effective aperture of the profiler.

This latest trial yielded a waist of 4um, located 2.9 mm inside the fiber for the X profile, and 3.0mm inside the fiber for the Y profile.

Code is attached in fiberModeMeasurement4.zip. Note that the z=0 point is defined as the end of the fiber.

 The Past Week

I spent the past week coupling NPRO light into the fibers, and subsequently measuring the fiber mode profile using the beam profiler.

The Next Week

In the next week, I plan to at least do measurements of the Polarization Extinction Ratio of the fibers.

Materials

My current optical setup, plus an additional polarizing beam splitter (have it).

 Work Done:

• Created a Channel Access Server on the Raspberry Pi  to write data from the FC into EPICS Channel.
• Completed characterization and noise estimation of the FC counter with improved timing.
• Started installation of FC inside the 40m.

Plans for this Week:

• Testing how well the FC can replace the spectrum analyzer which is in the control room. For this I have asked Steve to order  an RF adder/combiner to see how frequency counter responds to two RF signals at different frequencies(much like the RF signal fed to the spectrum analyzer) .
• Complete the installation of FC insode the 40m and start initial testing.
• Characterization of the Temperature Actuator and initial PID loop design.

Inside the 40m Lab:

• I will have to go inside the 40m lab this week for routing the RF mon cables to the FC box(in detail:http://nodus.ligo.caltech.edu:8080/40m/10163) .
• Also to setup for characterization of the temperature actuator, I will be required to go inside the lab in this week.

As Koji pointed out, I messed up the calibration.  However, fixing it doesn't change things that much.

From this calibration by Yuta, the Xarm ALS calibration is 54 deg / MHz, or 19.17 kHz / deg.  So, I multiply my data which is in these degree units by 19.17e3 to get Hz.  Then I use delta_f / f = delta_L / L to convert to meters.  f = c / lambda_green, and L = 37.5 meters. 

This only changes the calibration by about 10-15%.  It still looks like the ALS noise is well above the RIN level of the sqrtInv signal.

Quad processor 2 & 3 were replaced.

To do:

1. Measure and calibrate out  attenuation and phase changes due to RF cables in the PDFR system.
2. Create a database of canonical plots for comparison each time new data is acquired.
3. Vector fitting or LISO fitting of transimpedance curves.

Does not require time from a lab expert.

 As a part of installation of two(X-ARM and Y-ARM) frequency counters in the 40m, I have tested their performance when using them both on a single Raspberry Pi. The timing plots are attached. There are almost no timing issues in this configuration and it can be said that there is no harm using both of the FCs on the same platform.

We will be installing the FC box inside the lab and carry out few tests with RF mon beat note inputs.