This Red Ladder movement also probably included some bumping of the MC2 stack (be more careful when working in the lab). Around 5 PM today, the MC lost lock.
When I came in later, I found that the MC was flashing the TEM17,9 mode and had been misaligned like this for ~1 hour. I looked through the MC SUS sensor trends and moved MC2 back to its old position to get the locking back. I disabled the WFS, tweaked the TEM00 mode alignment using only MC2 sliders, and then re-enabled WFS. Its been OK for the past 5 hours.
The PMC local oscillator is going a little weird dying. We need to check out why the level is fluctuating so much.
Here's a 6 month plot, where you can see that the lower level keeps getting lower (y-axis is dBm):
This LHO entry from 2008 shows where we first discovered this effect. As Rick Savage and Paul Schwinberg later found out, the ERA-5SM+ amplifier slowly degrades over several years and was replaced for both of the eLIGO interferometers. We have spares in the Blue box and can replace this sometime during the day.
Our PMC LO is made by this obsolete crystal oscillator circuit: D000419. There are many versions of this floating around, but they all have the ERA-5 issue.
The RF cables have been routed incorrectly. The cables run to the module from the front of the rack. We cannot close the doors to the racks if they are to remain this way.
I have asked Nichin to reroute the cables properly.
RF cables have been rerouted from the side of the rack, under the supervising eye of Manasa.
I moved the red ladder from near 1X4 to 1Y1 and back again.
Current list of RF cables:
REFL11, REFL33, REFL55, REFL165,
I have not connected them to the RF switch yet. ( until I figure out how to get both the switches working properly)
- Plots should be directly attached on the elog. (Attaching codes in a zip is OK.)
- Plot legends should not touch or hide any data points.
- Don't exclude data points.
- The model for the beam profile fitting is incorrect: zr and w0 are dependent
- The code needs to be reviewed by someone for refinement.
(EricQ, or possibly Jamie, Jenne while he is absent).
REFL33, AS55, REFL55,REFL165,REFL11,POX11,POP22
There were quite a few more demodulator units labelled with PD names. Do any of them need to be included in the automated frequency response measurement system? Please let me know so that I can include them to the RF switch and check them for proper illumination, which i will do for all the above PDs next week.
In the order that makes more sense to me, it looks like you have:
We don't really need POP22 right now, although we do want the facility to do both POP22 and POP110 for when we (eventually) put in a better PD there. Also, we want cabling for POP55, so that we can illuminate it after we re-install it. If we're working on 2f PDs, we might as well consider AS110 also, although I don't know that there was a fiber layed for it. The big one that you're missing is POY11.
A new RF cable has been included for POY11. Cabling for POP55 and POP110 might or might not exist. I will check and report it.
We observed one or two ants climbing over PMC optics without booties and safety glasses.
The floor was mopped with strong Bayer Home Pest Control solution in the Vertex area.
Do not work inside the 40m lab if you are sensitive to chemicals!
The floor is mopped again with strong PEST CONTROL SOLUTION in water in the Vertex area.
Do not plane to work in the IFO-room till noon if you are sensitive to chemicals!
Ants are back on the PSL table. We'll be mopping the floor with pest control solution tomorrow morning.
I moved stuff on the PSL table to accommodate the PMC ringdown setup.
I used the beam that leaks from the steering mirror at the PMC transmission that was dumped to a razor blade dump. I installed a Y1 to steer the beam to the ringdown PD. Power in the beam 75mW.
Results are in here elog
I was finally able to get a reasonable measurement for the beam waist(s) of the spare NPRO.
I used a razorblade setup, pictured below, to characterize the beam waist of the spare 1064nm NPRO after a lens (PLCX-25.4-38.6-UV-1064) in order to subsequently calculate the overall waist of the beam. The setup is pictured below:
After many failed attempts, this was the apparatus we (Manasa, Eric Q, Koji, and I) arrived with. The first lens after the laser was installed to focus the laser, because it's true waist was at an inaccessible location. Using the lens as the origin for the Z axis, I was able to determine the waist of the beam after the lens, and then calculate the beam waist of the laser itself using the equation wf = (lambda*f)/(pi*wo) where wf is the waist after the lens, lambda the wavelength of the laser, f the focal legth of the lens (75.0 mm in this case) and wo the waist before the lens.
We put the razorblade, second lens (to focus the beam onto the photodiode (Thorlabs PDA255)), and the PD with two attenuating filters with optical density of 1.0 and 3.0, all on a stage, so that they could be moved as a unit, in order to avoid errors caused by fringing effects caused by the razorblade.
I took measurements at six different locations along the optical axis, in orthogonal cross sections (referred to as X and Y) in case the beam turned to be elliptical, instead of perfectly circular in cross section. These measurements were carried out in 1" increments, starting at 2" from the lens, as measured by the holes in the optical table.
Once I had the data, each cross section was fit to V(x) = (.5*Vmax)*(1-erf((sqrt(2)*(x-x0))/wz))+c, which corresponds to the voltage supplied to the PD at a particular location in x (or y, as the case may be). Vmax is the maximum voltage supplied, x0 is an offset in x from zero, wz is the spot size at that location in z, and c is a DC offset (ie the voltage on the PD when the laser is fully eclipsed.) These fits may all be viewed in the attached .zip file.
The spot sizes, extracted as parameters of the previous fits, were then fit to the equation which describes the propagation of the spot radius, w(z) = wo*sqrt(1+((z-b)/zr)^2)+c, w(z) = w0*sqrt(1+((((z-b)*.000001064)^2)/((pi*w0^2)^2))) where wo corresponds to beam waist, b is an offset in the z. Examples of these fits can be viewed in the attached .zip file.
Finally, since the waists given by the fits were the waists after a lens, I used the equation wf = (lambda*f)/(pi*wo), described above, to determine the waist of the beam before the lens.
note: I was not able to open the first measurement in the X plane (Z = 2in). The rest of the plots have been included in the body of the elog, as per Manasa's request.
The X Waist after the lens (originally yielded from fit parameters) was 90.8 27.99 ± .14 um. The corresponding Y Waist was 106.2 30.22 ± .11 um.
After adjustment for the lens, the X Waist was 279.7 907.5 ± 4.5 um and the Y Waist was 239.2 840.5 ± 3.0 um.
edit: After making changes suggested by koji, these were the new results of the fits.
Attached you should be able to find the razor blade schematic, all of the fits, along with code used to generate them, plus the matlab workspace containing all the necessary variables.
NOTE: Rana brought to my attention that my error bars need to be adjusted, which I will do as soon as possible.
TaraV - geology major undergrad - of Jenne's summer help received 40m specific basic safety training.
When I was trying to plot PSD of the measurements, I still couldn't get better resolution. There still seems to be a problem with timing and synchronization of the R Pi with the FC even after addition of the external trigger circuit. Now, I am looking to debug this issue. Attached are the plots showing missing data points and data from the FC at uneven spacing(zoomed in plot).
I'm not sure why the c1cal model didn't come up the last time c1lsc was rebooted, but I did an "rtcds start c1cal" on the lsc machine, and it's up and running now.
I managed to recover c1sus. It required stopping all the models, and the restarting them one-by-one:
$ rtcds stop all # <-- this does the right to stop all the models with the IOP stopped last, so they will all unload properly.
$ rtcds start iop
$ rtcds start c1sus c1mcs c1rfm
I have no idea why the c1sus models got wedged, or why restarting them in this way fixed the issue.
In addition to needing obnoxiously regular mxstream restarts, this afternoon the sus machine was doing something slightly differently. Only 1 fb block per core was red (the mxstream symptom is 3 fb-related blocks are red per core), and restarting the mxstream didn't help. Anyhow, I was searching through the elog, and this entry to which I'm replying had similar symptoms. However, by the time I went back to the CDS FE screen, c1sus had regular mxstream symptoms, and an mxstream restart fixed things right up.
So, I don't know what the issue is or was, nor do I know why it is fixed, but it's fine for now, but I wanted to make a note for the future.
All suspension damping restored. There had to be an earth quake.
PMC was relocked.
MC did not need any fixing to its alignment. I had to lock it manually and autolocker is set running now. So that should take care of things
The arms were aligned and ASS'd for IR PDH.
Green light PDH locks to the arms alright.
I had been working on the Xend table optical layout update. Since the two steering mirrors in the Xend green are too close to each, there is a very small Gouy Phase different between these two mirrors. It was suggested to place two lenses so that we can increase the Gouy Phase. I have been working with Nick on this problem, and we had found a solution by using a la mode. We had written an a la mode code that optimize the Gouy Phase and the Mode Matching at the same time. After trying different lenses, we found the following results: a mode matching of 0.9939 as it is show in the first attachment below, and we found a Gouy Phase different between the two mirrors of about 60 degrees. I took photos of the Xend Table. The first photo is the Xend table as we had it right now. In the second photo, I moved the 2nd lens, and I placed the two more lenses that we need it, with more or lenses the correct position where they will be placed. The three old lenses will be replaced by three lenses of different focal length as it can be seen in the first attachment below. The first lens and third lens will stay in the same position where the old first lens and old third lens are, and the second lens will be moved by about half of an inch. We might have one or two of the lenses that we need, but we will have to order the rest of the lenses that need. My plan is to verify the lenses that we already have. Then, I need to let Nick know with lenses we need to order. Hopefully, we will be able to update the table by the end of this week if everything turn out fine.
To complete the characterization of the Mini Circuits UFC-6000 RF Frequency Counter to be used for beat note measurement as a part of frequency offset locking loop. The aim of this setup was to obtain the bode plots and PSD plots for the FC.
Detail about the Setup:
UFC RF Frequency Counter: Described in detail in one of my previous elog (http://nodus.ligo.caltech.edu:8080/40m/10020)
Raspberry Pi: Raspberry Pi will be running Raspbian which is a version of Linux, and not a RTOS. When sampling data at a certain frequency we want samples to occur at fixed time intervals corresponding to the sampling period. A normal operating system cannot provide us with this functionality, and there will be jitter (variation) in the time difference between consecutive samples. Whether this is an issue depends on how much jitter we have and what the specific application is. In our application(measuring phase and noise), the jitter has to be taken into consideration. Hence for data acquisition we need to sample with much more tightly defined sampling periods (reduced jitter) which can be done by providing an external timing standard(Like a square pulse of the frequency same as the sampling rate of the FC ).
ADC : The ADC serves for two different conversion processes in the setup:
1) For converting modulating analog signal(from SRS 30 MHz Wave Generator) into digital signal for data analysis on Raspberry Pi.
2) To provide an external clock reference to the Raspberry Pi.
Interfacing ADC(ADS1115) with Pi:
In order to set the modes of operation defined above we must set the config register within the ADS1115. A register is simply a memory location within the chip. Registers are made up of bytes (8 bits) of data. Registers are typically either one or two bytes long. The bits are:
Bit  This bit is used to start a conversion, by setting this bit to 1 a conversion is initiated. When reading the config register this bit remains equal to 0 while the conversion is carried out, and is set to 1 once the conversion is complete, we can monitor this bit to find the status of a conversion
Bits [14:12] These bits set which pin to use as input to the ADC. Note that we can choose either single ended or differential mode through setting these bits. Note that each configuration has two inputs AIN~p~ and AIN~n~. By setting AIN~n~ to GND we obtain a single ended input with AIN~p~ as the input.
Bits [11:9] These bits set which setting of the programmable gain amplifier to use
Bit  Continuous conversion / No Continuous conversion
Bits [7:5] Set the samples per second (sps) value
Bit [4:2] Comparator setup, we will not use the comparator so these bits are irrelevant
Bit [1:0] Comparator mode, set to 11 to disable the comparator.
Four channels are used in differential mode for A-D conversion of two analog signals, one the slow modulating signal input and the other for a square signal of 10 Hz (same as sampling rate of FC(0.1 s)).
The raspberry Pi reads the external trigger from ADC and starts reading input from the FC only when the square signal is 1. Thus in this way we can avoid the clock jitter and timing can be as accurate as the RTOS.
Three function generators are used in the setup:
The setup is attached as pdf. The computer scripts will follow this elog.
The input and output modulated signals are recorded and the delay and noise of the FC are to be estimated.
[ Nichin, Eric G]
RF cables have been installed between deomodulator output PD RF MON and the RF switch for the following PDs:
The cables are labelled on both ends and have been run on the overhead tray.
The cabling looks neat on 1Y2, but not so much in 1Y1(RF switch). I will better organize them later.
I tested the RF switch selection code and then the data acquisition code for the NWAG4395A network analyzer and they both seemed to work fine. I selected the channel to which AS55 is hooked up to and then remotely got its transfer function.
There is quite some noise in the system as the plot shows. Especially the phase. Maybe my driving power was a bit too low. Have to figure out the reason behind this.
Never mind. This is just the low pass filter that Den put in to try to deal with the moving cavity pole.
Before I realized this, just in case it was a computer quirk, Koji and I rebooted the end station front end machines. This had no effect other than to keep me searching and measuring until I figured it out. If I turn off the low pass, the phase pops back up to very close to the reference. The low pass currently comes on automatically as part of the carm_cm_up script.
I need to figure this out before it's worth trying any acrobatic AO path turn-on scenarios.
Also this evening, I went to the Yend and did another tweak-up of the green beam alignment.
After the meeting, I aligned the IFO to the IR, and then I aligned the Ygreen to the Yarm. I then found the beatnotes and used ALS to hold the arms with CARM/DARM, locked the PRMI, and reduced the CARM offset until I had arm powers of about 3. Given that this was at 3pm, and people were tromping all over inside the IFO room, I feel positive about tonight.
So, IFO seems ready, carm_cm_up script was successful, and got me to arm powers of 1, and then I further reduced the offset by a bit to go a little higher.
[Nichin, Eric Q]
We added a new LAN wire from Rack 1Y4 to 1Y1 to connect the RF switch at 1Y1 to the martian network. The wire is labelled "To RF Switch (1Y1)"
The wire was run along the Y arm in the tray right next to the vaccum chamber, not the one on top.
Koji has provided a 2TB USB3 external hard drive that will get daily backups of chiara:/home/cds, the idea being that if the internal HD at /dev/sdb1 fails, we can physically open the external up, and swap the hard drive into chiara.
We're running an rsync job on it right now, which should be done in a few hours. (USB3 is fast!)
I've also written a backup script at scripts/backup/rsync_chiara.backup which keeps its books in scripts/backup/rsync_chiara.backup.log
I'm adding a entry to the root crontab on chiara to execute the script every day at 7am.
Ophir power meter gets new filter with calibration. This is not cheap. It was the second time we lost it.
Filter leash is attached.
This morning valve condition: V1, VM1, V4 and V5 valves were closed. IFO pressure rose to 1.3 mTorr
It was caused by low N2 pressure. Our vacuum valves are moved-controlled by 60-70 PSI of nitrogen.
When this supply drops below 50-60 PSI the interlock closes V1 valve. This is the minimum pressure required to move the large valves.
It is our responsibility to check the N2 cylinder pressure supply.
The vacuum valve configuration is back to VAC. NORMAL, CC1 4.8E-6 Torr
PS: Bob says that the second cylinder was full this morning, but the auto-switch over did not happen.
The TESCOM automatic changeover regulator [ model ACS 012-1011 ] manifold is most likely clogged. The new one will arrive 8-8-2014
This means that the IFO pressure may go up to a few mTorr when we change cylinder or V1 valve triggered because there is no nitrogen supply.
We had a look this morning at the status of the seismometer array, so that we can get it all put together. While we were looking at the Guralp at the Yend, we noticed that it was pointing the wrong way. The North-South nubbins were pointed East-West, so X and Y coming out of the seismometer were backward.
To fix the Yend's Guralp, we powered off the Guralp readout box, rotated the seismometer, re-leveled it, and then turned the power back on. Now X from the seismometer lines up with the X data channel, and similarly for Y.
The Yend Guralp has all of the cabling needed, and is installed on the granite slab. This seismometer doesn't need any more work for now. When we get around to it, we'll need to do some kind of thermal insulation, but other than that, it's good to go.
The Xend will also have a Guralp (Zach still has it in the Gyro lab for now). We have the long cable that should go from the readout box to the slab that we'll need to put into the cable tray. The short cable from the slab's plate to the seismometer is already in place. For this seismometer, we should just need to plop the instrument in place and lay the cable in the overhead cable trays. We should also remove the now obsolete STS-2 cable while we're doing that. So, the Xend seismometer station doesn't need too much work.
The corner station will need more work. Zach made for us the long cable, although he still has it in the Gyro lab, so when we get the seismometer and cable back, we'll need to lay that cable in the overhead trays. The short cable from the slab's plate to the seismometer does not exist yet. We want to make sure that we can feed the finished cable and connector through the hole in the slab, and then we'll solder it up out here on the EE bench. I think this is how Den was doing things. If not, we'll have to do the soldering in-situ, which we don't want. So, for the corner station, we need to make the short cable, lay the long cable, get the T-240 back from Zach and put it on the slab, re-install the readout box that Zach has, etc, etc. We should also make sure that the spaghetti pot fits on the slab, underneath the piece of metal that's sticking out over the slab. We think that it's the same amount of clearance that the Yend pot has, so it should be okay, but we'll check. The O-ring seems to be sitting on the MC2 chamber, so we should remember that.
Neither the Xend nor the corner station had the yellow dog clamps, so we'll have to figure out where Den / Steve have hidden them.
EDIT: We have checked, and the Guralp connector, which is larger than the Trillium connector, fits through the hole in the slab (with some disassembly), so we can solder together the short cable out here on the EE bench, and install it separately. Eeeeexxxxxcelllent.
The attached are the gain plots at carrier frequencies of 100 MHz, 500 MHz and 1 GHz measured using IFR 2023B (Marconi).
EDIT: The script and template file have been moved to /opt/rtcds/caltech/c1/scripts/general/netgpibdata/
The NEW and IMPROVED script for remotely getting data from Agilent 4395A network analyzer is located at /users/nichin
This script is quite different from the one in Elog 10108 and fetches us both magnitude and phase. There is an added feature of setting the IF Bandwidth.
The network analyzer is located at crocetta.martian (192.168.113.108)
> python NWAG4395A_data_acq.py [filename.yml]
I connected a simple 2MHz Low pass filter between the modulation output and signal input of the NA and ran a scan from 100KHz to 20MHz. The script was run from Ottavia.
The expected plot was obtained and is attached here.
Setting up the RF switch in rack 1Y1 to select between required PDs and scripts to tell it which channel to choose over the Ethernet.
Just a quick update on the status of the auto locker:
sudo initctl start MCautolocker
This was pretty simple to set up, once I figured out how to provide the necessary environment variables in AutoLockMC.init
I would like to measure the switching time of the AOM. So I have disconnected the modulation input to the AOM that comes from the ISS. I have also turned OFF the SR560's and the AWG that belong to ISS.
Pics and cable connections of the state in which the ISS setup was left at, will be updated soon.
I installed a fast PDA10CF along the path of a leaking beam from one of the steering mirrors that direct the main beam to the PMC. This beam was dumped to a razor blade. I removed the razor blade and installed a Y1 to steer this beam through a lens on the PD.
Pics of the layout post-installation will be updated.
Also, I tested the AOM by giving it 0-1V modulation input from the AWG. This has been disconnected after the test. So everything should be as it was pre-testing.
Edit/manasa/ Data has not been fit correctly in here. A proper fit will follow this elog.
Proper fits and numbers are here :elog
Earlier last week I had tried to measure the AOM ringdown and concluded I could not make one.
I was proved wrong and I was able to make a measurement. I am still not sure why I was not able to make the measurement earlier with the very same settings and configuration.
What I did:
I gave the AOM a 0-1V modulation input using the signal generator (50 ohm feedthrough bnc was used to impedance match the AOM driver's modulation input). For the measurement here I used a 1Hz square wave. I used a 300MHz oscilloscope to look at the falling edge of the ringdown PD output installed.
I recorded a few ringdown samples. To get a quick number, I fit one such sample to find the AOM switching time as 1.48us (Plot attached).
The Yarm ASS is now working (as is the Xarm ASS). Both of the TT's pitch servos had a sign flip. We don't know why.
To start, we lowered the matrix elements that push on the TTs by a factor of 3, to compensate for the new factor of 3 in the slider gains: ezcastep C1:ASS-YARM_OUT_MTRX_5_5 /3 C1:ASS-YARM_OUT_MTRX_5_7 /3 C1:ASS-YARM_OUT_MTRX_6_6 /3 C1:ASS-YARM_OUT_MTRX_6_8 /3 C1:ASS-YARM_OUT_MTRX_7_5 /3 C1:ASS-YARM_OUT_MTRX_7_7 /3 C1:ASS-YARM_OUT_MTRX_8_6 /3 C1:ASS-YARM_OUT_MTRX_8_8 /3
ezcastep C1:ASS-YARM_OUT_MTRX_5_5 /3 C1:ASS-YARM_OUT_MTRX_5_7 /3 C1:ASS-YARM_OUT_MTRX_6_6 /3 C1:ASS-YARM_OUT_MTRX_6_8 /3 C1:ASS-YARM_OUT_MTRX_7_5 /3 C1:ASS-YARM_OUT_MTRX_7_7 /3 C1:ASS-YARM_OUT_MTRX_8_6 /3 C1:ASS-YARM_OUT_MTRX_8_8 /3
We turned off all 4 tip tilt ASS servos (in the Yarm ASS servo screen), and turned them on one at a time. By doing this, we discovered that the pitch servos for both TT1 and TT2 needed to have the opposite sign from what they used to have. However, the yaw servos kept the original signs. It really doesn't make sense to me why this should be, but this is the way the ASS servo works. We left both Xarm and Yarm ASSs on for several minutes, and saw that they didn't push any mirrors out of alignment.
The ASS_DOTHER_ON burt snapshot has been resaved with the new values.
Also, earlier this evening, I aligned the Yarm green beam to the cavity, although the cavity was not optimally aligned, so this needs to be re-done.
On our to-do list should be to add the tip tilt slider values to the DAQ channels list.
Arms and PRC hold well, powers are within normal ranges. (TR[X,Y] >.9, POP110I > 400)
Then, Jenne took over, worked some alignment magic, and did the hard part of getting the Yarm locked and ASS'd.
Green no longer locks to 00 on the Y-arm, and the X-arm green transmission isn't the best despite PZT fiddling (~.6). Also, when green is locked to the Xarm, I see a distinct circular spot on the GTRY camera, with Y green and PSL green shutters closed.
While Jenne used Yarm ASS successfully, when I run it now, it slowly pushes things out of alignment, and two of the traces (YARM_ETM_YAW_L_DEMOD_I_OUTPUT, and the same for ITM) have a reasonable constant offset that doesn't move away.
Sorry Rana for not giving much attention to the plot. I will definitely change the way they are being plotted.
I was more focused on getting the data acquisition to work. Also, the current script gets only the magnitude and not the phase... I still have to work on that.
The IR beam was found on the PRM surface, some CCDs, and in the X arm. The TTs are not aligned well yet.
I'm leaving the IFO with the following state.
ITMY/ETMY - aligned to the given green beam. GTRY (no PSL green) 1.0~1.1
ITMX/ETMX - aligned to the green beam. The end PZT for the green beam was steered to have maximum GTRX (0.76 without PSL green)
TT1/TT2 - unknown alignment, TT1/TT2 are related such that the spot is on the POP CCD
PRM - aligned to the given IR beam (i.e. PRM spot on the REFL CCD)
BS - aligned to the given IR beam (i.e. ITMX spot on the AS CCD, The X arm is flashing)
- ITMX was stuck in the suspension. it was caused by the EQ.
- When the X arm was aligned to the green beam, there was no green hitting on the GTRX PD. That's why the end PZT was adjusted.
- In order to earn more range for TT1, C1:IOO-TT1_YAW_GAIN and C1:IOO-TT1_PIT_GAIN were increased to 300 (100 nominal) and the limiter (at 500) were removed.
- The HeNe laser for BS/PRM does not emit the beam even with the driver turned on. Is there a hidden shutter or something? ==> Jenne
- Find the Y arm fringe by moving TT1 and TT2 without loosing the PRM/AS/POP spots.
I came in the lab. Found bunch of white EPICS boxes on ottavia.
It turned out that only ottavia was kicked out from the network.
After some struggle, I figured out that ottavia needs the ethernet cable unplugged / plugged
to connect (or reconnect) to the network.
For some unknown reason, ottavia was isolated from the martian network and couldn't come back.
This caused the MC autolocker frozen.
I logged in to megatron from ottavia, and ran at .../scritpt/MC
nohup ./AutoLockMC.csh &
Now the MC is happy.
The updated script for remotely getting data from Agilent 4395A network analyzer is located at /users/nichin
This network analyzer device is located at crocetta.martian (192.168.113.108)
> python NWAG4395A_modified.py [filename.yml]
I connected a simple 2MHz Low pass filter between the modulation output and signal input of the NA and ran a scan from 0Hz to 20MHz. The script was run from Chiara.
I now have to work on setting up the RF switch in rack 1Y1 to select between required PDs and also on the code that chooses which channel is being selected.
There is also a problem of 2 8x1 RF switches being present, instead of one 16x1. Alex's code for RF switching does not take this into account.
Finally, the 0.1s sampling rate of the frequency counter(FC) has been achieved. For this I had to :
Send in byte codes to set a particular range of the frequency counter.
I was digging in to find how exactly the circuit inside the frequency counter works and how the processor inside is able to read and write bytes through a HID-USB interface. I found out that the 'AutoRange' setting (which I have been using so far) has an independent multiplexing circuit which consumes some time(that varies with the drift in frequencies) and thus, the the processor waits for some specific time for this process and cannot reach the minimum 0.1 s sampling time. To mitigate this issue, I set the range bytes to the appropriate range of frequencies so that I can bypass the MUX delay. Here is the list of Range and frequencies for the FC:
Range 1: 1 - 40 MHz
Range 2: 40 - 190 MHz
Range 3: 190 - 1400 MHz
Range 4 : 1400 - 6000 MHz
I then took measurements for sampling time of 0.1 s at carrier frequencies of 5 MHz and 25 MHz from SRS DS345 and plotted the improvised gain plots(attached) to those in my previous elog(10070) with the same procedure mentioned before.
To do Next:
Plot the gain plots for higher carrier frequencies till range 3 using Marconi Function generator.
Write the data from FC into C1: ALS-Y_SLOW_SERVO1_OFFSET EPICS channel.
To use a razorblade to measure beam waist at four points along the optical axis, so as to later extrapolate the waist. This information will then be used to effectively couple AUX laser light to fibers for use in the frequency offset locking apparatus.
1) Step the micrometer-controlled razorblade across the beam at a given value of Z, along optical axis, in the plane orthogonal to it (arbitrarily called X).
2) At each value of X, record the corresponding output of a photodiode, (Thorlabs PD A55) here given in mV.
3) Repeat in Y plane at the same value of Z
4) Repeat process at multiple points along Z
Data from each iteration were fitted to the error function shown below.
y(x) = (.5*P)*(1-erf((sqrt(2)*(x-x0))/wz))
'P' corresponds to peak power, 'x0' to the corresponding value of x (or y, as the case may be), and 'wz' to the spot size at the Z value in question.
The spot sizes from the four Z values were then fit to:
y(x) = w0*sqrt(1+((x*x)/(zr*zr)))
Where 'w0' corresponds to beam waist, and 'zr' to Rayleigh Range.
This yielded a Y-Waist of 783.5 um, and an X-Waist of 915.2 um.
The respective Rayleigh ranges were 2.965e+05 um (Y) and 3.145e+05 um (X).
I will do the same analysis with light from the optical cables, which information I will then use to design a telescope to effectively couple the beams.
I finally did carry out a measurement on the network analyzer. This proves that the previous system will work properly. Just the optical splitter problem is to be taken care of.
For this, after Elog 10102, I did not touch any of the tables or photodiodes. Only turned on the laser at 1Y1 and took readings from the NA located nearby. I switched off the laser after measurements. The power to REF PD remains on.
I plotted transimpedence plots in the usual way and got ridiculous values of 15 ohms at 55MHz. Obviously there is the problem of varying amount of power illuminating the REF PD and AS55.
So, I just plotted the bode plots of transfer function got from the NA to check if the characteristics of AS55 looks as it was supposed to be and Yes! I got a nice peak at 55MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
2) Number of Points sampled in the range: 801
3) Type of sweep: Linear
The experimental values obtained were:
The experimental values obtained were:
DC output voltage of REF PD: 7.48V
DC output voltage of AS55: 53.7mV
Power incident on REF PD and AS55 respectively: 2.4mW and 1.6mW
Taking the DC transimpedence of AS55 as 66.2 ohms (from schematic given at D1300586-v1) and for REF PD as 1E04 ohms
Hence, Responsivity for REF PD and AS55 respectively are: 0.312 A/W and 0.51 A/W
The data and code used are in the zip file.
I have been trying to use an ADC with the Raspberry Pi to be able to measure the phase difference between FC input and output signals.I had a hard time interfacing the ADC with the Pi (setup attached) even after trying to debug the issue for last two days. So I and Eriq Q performed a system reboot on the Pi and tried all the possible ways for the Pi to detect the ADC but we were not able to. At the end we decided to order another IC(Microchip MCP 3008) which we hope can be interfaced with the Pi. Till then I will finish to write data from the FC into pipes so that the control computers can access the real time data. I will also look the correctness of the sampling time that is provided by the spec of the MCL-Mini circuits that is if we could really achieve 0.1 s sampling time with the FC.
Reconfigured razorblade analysis setup on the PD table as per instructions. Used it to collect data to calculate beam waist with, analyses to follow.
See attached schematic for optical setup.
I wanted to make sure Alex's system of Diode laser + laser controller + optical splitter was working fine and then make a manual measurement for AS55 PD. Manasa was supervising my work and helping me with unhooking the fibers and taking power meter readings. I have tuned on the power to REF DET from under the POY table.
I switched on the laser sitting in the 1Y1 rack and turned up the driving current to 240mA. On checking the laser power readings at AS55 (AS table) and REF DET (POY table) simultaneously, we got readings of 1.6mA and 2.4mA respectively. This much difference in readings was not expected and I did not continue taking the readings for transimpedence measurement.
I will rectify if this unequal splitting of power by the 1x16 optical splitter is going to cause any difficulties for the automated PDFR system measurement technique and resolve it if needed.
I was asked to calculate the lenses that we need in order to obtained a Gouy phase close to 90 degrees between the two mirrors that are in the Xend green. Yesterday, I measured the distances between the mirrors, and the distance between the mirror relative to the cavity as illustrate in the image attached below. I looked in to the 40m elog and Manasa did the last update on the length of the cavity. She measured 37.7 + 0.05m. The waist size of the beam that was measured by Annalisa in ID 8637 after the Faraday was w0=2.943e-5m @ -0.039m. I calculated the waist size inside the cavity, and I found a waist of w0=2.2 mm. My plan this week is to keep working in the calculation and finish all the calculation this week so that next week I can go inside and place the lenses.
See attached weekly update
Harry will update this elog with details about his beam waist measurements for the old NPRO on the SP table.
see http://nodus.ligo.caltech.edu:8080/40m/10098 for the update
To use a razorblade to measure beam waist at multiple points along the optical axis, so as to later extrapolate the modal profile of the entire beam. This information will then be used to effectively couple AUX laser light to fibers for use in the frequency offset locking apparatus.
1) Step the micrometer-controlled razorblade across the beam at a given value of Z, along optical axis, in the plane orthogonal to it (arbitrarily called X).
3) Repeat process at multiple points along Z
Data from each iteration in the X were fitted to the error function shown below.
V(x) = A*(erf((x-m)/s)+c)
In the Y, they were fitted to:
V(x) = -A*(erf((x-m)/s)+c)
'A' corresponds to an amplitude, 'm' to a mean, 's' to a σ, and 'c' to an offset.
(Only because in Y measurements, the blade progressed toward eclipsing the beam, as opposed to in the X where it progressively revealed the beam.
These fits can be solved for x = (erf-1((V/A)-c)*s)+m1 which can be calculated at the points (Vmax/e2) and (Vmax*(1-1/e2)). The difference between these points will yield beam waist, w(z).
Calculations yielded waists of: X1=66.43um, X2=67.73um, X3=49.45um, Y1=61.20um, Y2=58.70, Y3=58.89
These data seem suspect, and shall be subjected to further analysis.
Attached is the weekly work plan / equipment requirement / lab expert's presence needed for the upcoming week.