Today I have repeated the expt for shot noise intercept current. Koji found that the Spectrum analyzer is going to saturation, so we have used one DC blocker (MCL - 15542 model) in PD signal.
I will analyze the data and report.
Ed by Koji: DC BLOCK is BLK-89-S
Summary: Measurement and plot of shot-noise-intercept-current for PDA255.
Motivation:It is to measure the shot noise intercept current for PDA255 - the MC transmission RF photodiode to get an idea for the noise current for the detector
Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 3.06mA
The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation
Vnoise = gdet* sqrt[ 2e (iDC+idet)] , where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).
On the other hand for DCcurrent calculation we must use the high-impedance value for the transimpedance i.e. 1e4 Ohm. idet is the shot noise intercept current.
For the rough calculation of the noise level we may use the following formulae:
Vnoise = gdet*sqrt[2e (iDC+idet)] = gdet*sqrt(2e in), when in=iDC+idet;
For say, in1=1mA; Vnoise1=gdet*sqrt(2e *in1)
and sqrt(2e *in1)~18pA/sqrt(Hz)
In current case dark noise is ~1.5e-7 V/sqrt(Hz)
Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 30pA/sqrt(Hz)
i.e. sqrt(2e *in2)=30pA/sqrt(Hz)
therefore, in2~3mA (since in1=1mA)
For, iDC=0, in=idet.
Therefore the shot-noise-intercept current will be ~3mA
Then Vdc = in2*1e4 = 30V
According to the experiment and also from the PDA255 manual the DC voltage level never goes beyond ~10V. Therefore following the photodiode characteristics(we work in reverse bias) we may infer that it can never become shot noise limited.
Also, from PDA255 manual, at 1650nm the dark noise is 30pW/sqrt(Hz) and the responsivity is 0.9A/W. Therefore the noise current level will be = noise power* responsivity ~27pA/sqrt(Hz). The value matches well with our expectation.
Today I have taken data for shot noise intercept current for PDA10CF. I will process the data and report.
Note: GPIB address changed, new command for AG4395A network/spectrum analyzer: ./netgpibdata.py -i 192.168.113.108 -d AG4395A -a 10 -f filename
Today I collected the data for shot noise intercept current for MC REFL PD. I didn't get many data points at higher DC voltage of the photodiode, cause the incandescent bulbs get burnt at that level; two bulbs I have burnt today. I will process the data and report.
Summary: Measurement and plot of shot-noise-intercept-current for PDA10CF.
Motivation:It is to measure the shot noise intercept current for PDA10CF.
Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.21mA
To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946
In the present case dark-noise is 4.3e-08 V/sqrt(Hz)
Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 8.6pA/sqrt(Hz)
Therefore the approximate shot noise intercept current ~ (8.6/18)^2=0.22mA
This value matches well with the fitted data.
From PDA10CF manual, NEP=1.2e-11W/sqrt(Hz) and responsivity~0.9A/W. Therefore the noise current level will be ~10pA.
Summary: Measurement and plot of shot-noise-intercept-current for MC REFL PD.
Motivation:It is to measure the shot noise intercept current for MC REFL PD.
Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.041mA
In the present case minimum noise value is 2.03e-08 V/sqrt(Hz)
Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 4.06pA/sqrt(Hz)
Therefore the approximate shot noise intercept current value is (4/18)^2 ~ 0.049mA, which is close to the fitted value.
... hard to believe these numbers. Wrong DC transimpedance? (KA)
Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 1.9mA
Vnoise = gdet* sqrt[ 2e (iDC+idet)] , where gdet= transimpedance of the PD in RF region ~600
In the present case minimum noise value is 1.46e-08 V/sqrt(Hz)
Therefore dark current(in2) ~dark noise voltage/RF transimpedance ~25pA/sqrt(Hz)
Therefore the approximate shot noise intercept current value is (25/18)^2 ~ 1.92mA, which matches well to the fitted value.
I spent awhile today reading about op-amps and understanding what would be necessary to design a circuit which would directly give pitch and yaw of the QPD I am using. After getting an idea of what signals would be summed or subtracted, I opened up the QPD to take better pictures than last time (sorry, the pictures were blurry last time and I didn't realize). It turns out some of the connections have been broken inside the QPD, which would explain why we saw an unchanging signal in Ch2 on the oscilloscope yesterday when trying to test the laser setup.
I found a couple other QPDs, which I will be using to help understand the circuit (and what is going on). I will be trying to use the same QPD box since it has banana cable and BNC cable adapters, which is helpful to have in the lab. Once I have concluded what the circuitry is like and designed electronics to add and subtract signals, I will build and mount all the circuits within the box (more sturdily than last time) so as to have a quality way of measuring the mount vibrations when I get there.
I took better pictures of the circuits of the QPD and spent a couple of hours with a multimeter trying to figure out how all the connections worked. I will continue to do so and analyze the circuits over the weekend to try to understand what is going on. I also have an old SURF report that Eric sent me that is similar to the design I was planning to use to sum the pitch and yaw signals. I will try and look at this over the weekend.
I finished working out the circuit and figured out where the broken connections were. This is diagrammed in my notebook (will draw up more nicely and include in future elog post). Within the QPD circuitry, it seems like there are already opamps which regulate the circuit. I need to discuss the final diagram further with Eric.
I rewired the circuit inside the QPD box, which took awhile because it was difficult to solder the wires to such small locations without having multiple wires touch. This is completed, and on Friday I will begin to make the circuit to add/subtract signals to give pitch and yaw.
We turned IFO power back to 1.25W by removing the attenuator and forgot that the Y1 mirror before the REFL PD must be replaced with BS 10% before getting to full power. The PD is dead and now we are in the process of fixing it. Forgive us for all our sins!
On the other note, we have changed the mech shutter mode from N.O back to N.C. So the shutter now works as usual from the medm screen.
Today I tested the circuitry within the QPD to make sure I had put it back together correctly. The output was able to detect when a laser pointer was shone on different quadrants of the QPD when hooked up to the oscilloscope, so fixing the QPD worked!
Following this, I spent awhile understanding what was going on with the circuit reading from the QPD. I concluded that the opamp on the QPD circuit acted as a low pass filter, with corner frequency of about 17 kHz, which serves our purposes (we are only interested in frequencies below 1 kHz). I diagrammed the circuit that I plan to build to give pitch and yaw (attached). It will be necessary to make small modifications to the circuitry already built (removing some resistors), which I have started on.
Next time, I will construct the circuit that adds/subtracts signals on a breadboard and test it with the QPD circuit that is already built.
I corrected the circuit diagram I constructed last time - it would read 0 output most of the time because I made a mistake with the op amps. This will be attached once I discuss it with Eric.
I searched the 40m lab and ended up finding a breadboard in the Bridge lab. I then spent awhile trying to remove the QPD from the circuit board it was on, which was difficult since it had 6 pins. After that, I soldered wires to the QPD legs and began constructing the circuit on the breadboard. I also spent time showing Annalisa the setup and explaining my project.
On Friday I will try and reconstruct all of the circuitry from before for the QPD.
I took out a short (~12 cm) SMA cable from the "LO input" path into the MC demod board in an attempt to maximize the power in Q and minimize the power in I. The path might benefit from being shortened a little more, but it's hard to tell since I is noisy. (In the attached plots, channel 1 is Q and channel 2 is I.)
Should you find it necessary to restore the original path length, the cable I took out is in the "SMA ONLY" tupperware and has a printed label with "5" on it.
Here is the transimpedance for the other PD used for MC REFL
How much is the exact resonant frequency?
And what's the unit of the plot? The resonant "transimpedance" in the unit of Ohm can not be ~100.
The exact resonant frequency is 29.38MHz. I ve uploaded the other plot. It was the output of Vectfit.
Is the DC transimpedance now 10010 Ohm? I ve used 50 Ohm. Which one is correct?
Today I finished building the adding/subtracting circuit for the QPD and tested that the QPD could see a laser moving across its visual field for both pitch and yaw. It didn't seem to behave weirdly (saturate) at the edges, but I need to test this more carefully to be sure.
However, this circuit uses many op amps, which will cause problems for building the actual circuit to fit into the QPD box. I am trying to figure out how to do this with fewer op amps (both with a quad op amp for amplifying the signals from the QPD and by summing/subtracting the signals with a single op amp instead of 3).
I finally got around to asking Steve to order more breadboards! Trying to determine what would be a good QPD to order for the final circuit, since we do not have any unmounted QPDs that aren't ancient. I'll read up on things I don't know enough about (namely op amps).
I have sketched out the circuit design for the QPD. However, it seems like even when using a different opamp configuration, which I talked to Eric about on Friday, space will be a problem. It may be possible to squeeze everything onto a single circuit board to fit in the QPD box but what I think is more likely is that I will need to have 2 separate circuit boards both mounted within the box, one which integrates the signal from the QPD and the other which adds/subtracts (this involves many resistors which will take up a lot of space). I will continue to think about the best design for this.
I will try to have the circuit built in the next week or so, which may be difficult since I just started finals which will take most of my time. I spent most of this week writing up an ECDL proposal for a SURF with Tara. I'll make up for whatever work I miss since I'll be here for my spring break and doing little besides working in lab.
This is the final version of the QPD circuit I'm going to build. After playing around with the spatial arrangement, this should fit into the box that I was planning to use, although it will be a rather tight fit. The pitch, yaw, and summing circuit will be handled with a quad op amp. Planning to meet with Eric tomorrow to figure out the logistics of building things.
In the meantime, I'm reading about designing the ECDL for my summer project with Tara. He sent me several papers to read so we can talk on Wednesday.
In order to test the mount vibrations, I will likely try and make a different circuit work (with the summing/subtracting on an external breadboard) and designing an optimal circuit will be a side project. This is the circuit with the power supply Rana came up with, and the design I had in mind for the rest of the circuit. In my free time, I will try to figure out what parts to get that reduce noise and slowly work on building this, since it would be useful to have in the lab.
I built the summing/subtracting circuit on the breadboard, and hooked this up with one of the other QPDs I found (image of setup attached). I wasn't able to get this to read the correct signals when testing with a laser pointer after a couple of hours of troubleshooting... I will hopefully get this working in the next day or 2...
I'm going to read up on ECDL stuff for Tara tonight and hopefully figure out what sort of laser diode we should purchase, since I'm meeting with Tara tomorrow. experimenting
Because we would like to get started on testing mount vibrations as soon as possible, I've been trying to get one of the other QPDs we found to work with the summing/subtracting circuit on a breadboard. I've been using a power supply that I think Jamie built 15 years ago... which seems to be broken as of today, since I no longer read any signal from it with an oscilloscope.
I tried using a different power supply, but I still can't read any change in signal with the QPD for any of the quadrants when using a laser pointer to shine light on it. I'll be working with Eric on this later this week. In the meantime, I'll try and come up with a shopping list for the nicer QPD circuit that'll be a longer term side project.
The voltage regulator on the QPD breadboard seems to be having problems... yesterday Eric helped me debug my circuit and discovered that the +12V regulator was overheating, so we replaced it. Today, I found that the -12V regulator was also doing the same thing, so I replaced it. However, it's still overheating. We checked all of the setup for the power regulators yesterday, so I'm not sure what's wrong.
I've also noticed that not all the connections on the breadboard that I've been using seem to work - I may search for a new breadboard in this case. Need to check I'm not doing something stupid with that.
Breadboards may not be suitable for a reliable work. Why don't you switch to any protoboard and real soldering?
Summary: Routing Fibers on AP table for Photo Diode Frequency Response Measurement System
Objective: We are to set-up one simultaneous transfer-function measurement system for all the RF-PDs present in 40m lab. A diode laser output is to be divided by 1x16 fiber splitter and to be sent to all the PDs through single-mode fiber. The transfer function of the PDs will be measured using network analyzer. The output of the PDs will be fed to network analyzer via one RF-switch.
Work Done So Far: We routed the fibers on AP table. Fibers from RF PDS - namely MC REFL PD, AS55, REFL11, REFL33, REFL55, REFL165, have been connected to the 1x16 fiber splitter. All the cables are lying on the table now, so they are not blocking any beam.
We will soon upload the schematic diagram of the set up.
Missing Component: Digital Fiber Power Meter, Thorlab PM20C
Here I am attaching the first schematic diagram of the PD frequency response set-up, I will keep updating it with relevant informations with the progress of the work.
Description: Our objective is to set-up one simultaneous transfer-function measurement system for all the RF-PDs present in 40m lab. A diode laser will be used to illuminate the PDs. The diode laser output will be divided by 1x16 fiber splitter and will be sent to all the PDs through single-mode fiber. The transfer function of the PDs will be measured using network analyzer(Agilent 4395A). The output of the PDs will be fed to network analyzer via one RF-switch. The diode laser will be controlled by the controller ILX LDC 3744C. The scanning frequency signal will be fed to this controller from network analyzer through its external modulation port. The output of the controller will be splitted into two parts: one will go to laser diode and the other will be used as reference signal for network analyzer.
Today we have routed the fibers from 1x16 fiber splitter to POX table for POX11 PD and POP55 PD. Also we labeled the fibers on AP table, they have been fixed on the table. The photo of the table after work is attached here. We will do it for POX table tomorrow.
No.... what I told was to put the roll next to the splitter, not on the table.
The table area is more precious than the rack space.
Koji> The slack of the fibers should be nicely rolled and put together at the splitter side.
No.... what I told was to put the roll next to the splitter, not on the table.
The table area is more precious than the rack space.
Ok, will do it on the coming week.
Annalisa and I met yesterday and fixed the voltage regulator on the breadboard so the QPD circuit is working. We will meet with Eric on Thursday to determine the course of action with measurements.
Koji spent some time earlier this evening exploring where the excess RIN that we see in the PRC is coming from.
He did this by locking the PRMI (MICH on AS55Q, PRCL on REFL33I, Pnorm for MICH = sqrt(POP110) with 0.1, Pnorm for PRCL = sqrt(POP110) with 10, MICH gain = -30, PRCL gain = 8), and then exciting each relevant optic, one at a time, in yaw. The excitation was always using the ASCYAW excitation point on each of the optics (BS, PRM, ITMX, ITMY), with a frequency of 4.56 Hz, and an amplitude of 30 counts.
He also took reference traces with no optics excited.
Here, I plot (for each excited optic separately) the reference traces and traces during excitation for POP110_I_ERR, POPDC, and the OPLEV_YERROR for the optic that is being excited.
What we are looking for (only in yaw, since we see on the cameras that the dominant motion is in yaw) is an increase in POPDC and POP110 at the same frequency as an optic's excitation.
We see that neither ITM is contributing a noticeable amount to either POPDC or POP110. BS is contributing a little bit, but PRM is clearly contributing. No this entry should be read. (KA)
A week or two ago, I calculated in elog 8489 that the angular motion that we see does not explain the RIN that we're seeing, unless our cavity is much more unstable than Jamie calculated in elog 8316.
I think that I need to install one of the T240's on the new granite slab, and see what kind of coherence we have between seismic and PRM yaw motion, and if FF can get rid of it.
There was an issue with running the new summary pages, because laldetchar was not included (the website I used for instructions doesn't mention that it is needed for the summary pages). I figured out how to include it with help from Duncan. There appear to be other needed dependencies, though. I have emailed Duncan to ask how these are imported into the code base. I am making a list of all the packages / dependencies that I needed that weren't included on the website, so this will be easier if/when it has to be done again.
Most dependencies are met. The next issue is that matplotlib.basemap is not installed, because it is not available for our version of python. We need to update python on megatron to fix this.
I'm not sure what's going on today but we're seeing ~80% packet loss on the 40MARS wireless network. This is obviously causing big problems for all of our wirelessly connected machines. The wired network seems to be fine.
I've tried power cycling the wireless router but it didn't seem to help. Not sure what's going on, or how it got this way. Investigating...
I'm still seeing some problems with this - some laptops are losing and not recovering any connection. What's to be done next? New router?
Mike and Christian brought over a Mac laptop for surf Alex.
They power cycled the wireless router of 40Marsh and labtops are working. Seeing 75-80% signals on all 3 Dell lab top sisters at both end of the lab
We characterized Koji's BBPD MOD for REFL165 (see attachment).
First, we calibrated the Agilent 4395 Network Analyzer (NA) to account for differences in cable features between the Ref PD and Test PD connections. This was done using the 'Cal' softkey on the NA.
Then we performed transimpedance measurements for the test PD and reference PD relative to the RF output of the NA and relative to each other (see 2nd attachment. Note that the NA's RF output is split and sent to both the IR Laser and the NA's Ref input).
Next, we made DC measurements of the outputs of the photodetectors to estimate the photocurrent distribution of the transimpedance setup (like the 2nd attachment, but with the outputs of the PDs going to a multimeter). By photocurrent distribution, we mean how the beamsplitter and respective quantum efficiencies/generalized impedance/etc. of the PDs influence how much current flows through each PD at with a DC input.
Finally, we measured the output noise as a function of photocurrent (like the 2nd attachment, but with a lightbulb instead of the IR Laser). Input voltages for the lightbulb ranged from 0mV to 6V. Data was downloaded from the NA using netgpibdata from the scripts directory. Analysis is currently in progress; graphs to come soon.
Alex and Eric
For the photodetector frequency response automation project, we plan to add modules to rack 1y1 as shown in the attached picture (Note: boxes are approximately to scale).
The RF switch will choose which photodetector's output is sent to the Agilent 4395A Network Analyzer.
The Diode Laser Module is powered by Laser Power Supply, will be modulated by the Network Analyzer and will be output to a 1x16 optical splitter which is already mounted in another rack (not pictured).
The Transformer Module has not been built yet.
We would like to install the power supply and the laser module tomorrow and will not begin routing fibers and cables until we post a drawing in the elog.
Also, our reference photoreceiver arrived today.
We mounted our Laser Module and Laser Power Source in rack 1y1. We plan to add our RF Switch and Transformer Module to the rack, as pictured. (Note: drawn-in boxes in picture are approximately to scale.) Note that the panel of knobs which the gray boxes overlap is obsolete and will soon be removed.
Continued with tests on the PZT driver board. I made a few changes to replace defective components and also to modify the gain of the HV amplifier stage. I believe the board has been verified to be satisfactory, and is now ready for a piezo to be connected, tested and calibrated.
Revised Wiring Diagram:
DAC Max. Output Trace on Oscilloscope
We are planning to add our reference PD to the southern third of the AS Table as pictured in the attachment. The power supply will go under the table.
I installed 'nfs-client' on zita (the StripTool terminal). It now has mounted all the shared disks, but still can't do StripTool since its a 32-bit machine and our StripTool is 64.
The PSL HEPA stopped working while it was running at 80%. I have closed the PSL enclosure.
Steve is working to fix this.
I measured the transfer functions in the delay line cables, and then calculated the time delay from that.
The first cable had a time delay of 1272 ns and the second had a time delay of 1264 ns.
Below are the plots I created to calculate this. There does seem to be a pattern in the residual plots however, which was not expected.
The R-Square parameter was very close to 1 for both fits, indicating that the fit was good.
I tried to recompile the modbusApp binary for linux-arm acrhitecture since I suspected someting wrong with it. But still the problem persists; I can connect to acromag but cannot access the channels. I have also reconfigured new acromag bus works terminal XT 1221-000 and I want to test if I could access its channels. My target is to complete this acromag setup work before sunday morning so that I can focus towards having some useful results for my presentation.
Gautam and I were able to get the Raspberry Pi up and running today, including being able to ssh into it from the control room.
Below are some details about the setup/procedure that might be helpful to anyone trying to establish Ethernet connection for a new RPi, or a new operating system/SD card.
Here is the physical setup:
The changes that need to be made for a new Raspbian OS in order to communicate with it over ssh are as follows, with links to tutorials on how to do them:
1. Edit dhcpcd.conf file: https://www.modmypi.com/blog/how-to-give-your-raspberry-pi-a-static-ip-address-update
2. Edit interfaces file: https://www.mathworks.com/help/supportpkg/raspberrypi/ug/getting-the-raspberry_pi-ip-address.html
3. Enable ssh server: http://www.instructables.com/id/Use-ssh-to-talk-with-your-Raspberry-Pi/
The specific addresses for the RPi we set up today are:
IP Address: 192.168.113.107
Gateway/Routers/Domain Name Servers: 192.168.113.2
GV: I looked through /etc/var/bind/martian.hosts on chiara and decided to recycle the IP address for Domenica.martian as no RPis are plugged in right now... I'm also removing some of the attachments that seem to have been uploaded multiple times.
1064 nm Semiconductor Laser Fiber Distribution System and Mirror Tomography
Below threshold these Semiconductor Fabry-Perot lasers have an axial mode structure with a spacing of about a THz. As you turn up the current to above threshold the first mode to oscillate saturates the gain down on all the modes and only it oscillates. The laser I have here in my office (a backup for the one you have at the 40 meter) has a wavelength of 1064.9 nm at 70 Degrees C. We should be able to temperature tune it down to 1064.3 nm although this could be a bit tedious the first time we do it. The specifications claim a "spectrum width" of 1.097 nm which I believe is the temperature tuning range. I don’t know what the line width is but it will be single frequency and we shouldn’t have mode hoping problems. So we should be able to use it in the “Mirror Tomography” experiment. You might want to use some sort of polarization diversity to avoid the problems of fiber polarization drift.
There have been 2 student projects on using the fiber distributed PD frequency response at1064 nm laser.
“Automated Photodiode Frequency Response Measurement System,” Alexander Cole - T1300618
“Final Report: Automated Photodiode Frequency Response Measurement System for Caltech 40m lab,” Nichin Sreekantaswamy - P140021
I’ll look up a few more references and add include them in the next elog.
I am currently working on an optical arrangement consisting of a QPD that measures the fluctuations of an incoming HeNe laser beam that is reflected by a mirror. The goal is to add a second QPD to the optical arrangement to form a linear combination that effectively cancels out the (angular) fluctuations from the laser beam itself so that we can only focus on the fluctuations produced by the mirror.
In order to solve this problem, I have written a program for calculating the different contributions of the fluctuations of the HeNe laser and fluctuations from the mirror, for each QPD (program script attached). The goal of the program is to find the optimal combination of L0, L1, L2, and f2 that cancels the fluctuations from the laser beam (while retaining solely the fluctuations from the mirror) when adding the fluctuations of QPD 1 and QPD 2 together.
By running this program for different combinations of distances and focal lengths, I have found that the following values should work to cancel out the effects of the oscillations from the HeNe laser beam (assuming a focal length of 0.2 m for the lens in front of the original QPD):
L0 = 1.0000 m (distance from laser tube to mirror)
L1 = 0.8510 m (distance from mirror to lens in front of QPD 1)
L2 = 0.9319 m (distance from beamsplitter to lens in front of QPD 2)
f2 = 0.3011 m (focal length of lens in front of QPD 2)
Based on these calculations, I propose to try the following lens for QPD 2:
1’’ UV Fused Silica Plano-Convex Lens, AR-Coated: 350 - 700 nm (focal length 0.3011 m). https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6508