Yesterday we had a meeting with Nick Lechocinski from Axiom Optics about InGaAs cameras. He went over various products they sell, which pretty much fall in the pixel count/noise/price range of the various other competitors. They have lent us a logarithmic response InGaAs camera.
I have been trying to get the camera to talk to the software on a windows laptop we have in the lab. It turns out that the interface HAS to be USB 3.0 or higher, which we don't have on any windows computers I know about (unless there is one at the 40m). I've spent a good chunk of time trying to get USB 3.0 ports on my Macbook pro to forward to an instance of Windows 7 on VirtualBox. It frustrating as USB 3 was supposed to be backward AND forward compatible but in this case the camera is not working for whatever reason.
Having tried various things with VirtualBox (including installing all the extra windows Guest Additions), I'm not sure its worth pushing on with that option. Mike and Christian don't have any PC laptops with USB 3.0 spare. I may repartition a spare MacMini of mine tomorrow to see if that works and maybe ask around more for a laptop.
Pictures of camera attached.
Today, Eric and I unboxed and inventoried the WOPO experiment components that Andrew had ordered.
Attached, is a pdf with pictures of the components with the packaging lists.
In order to collimate the 1064nm beam from the laser into the fibre, we are using the Thorlabs F240-APC-1064 fixed focus collimation package. The required beam diameter for this is 1.76mm. I used ABCD Propagation to try and come up with an optimal 3 lens solution to obtain a collimated beam of this size. The solution is as follows -
f1 = 30cm at z = 105cm ( z = 0 being the location of the Diabolo waist)
f2 = 20cm at z = 122.5cm
f3 =12.5cm at z = 146cm
I profiled the beam after the first and second lenses in order to correct my estimation of initial beam waist and location.
I have positioned the third lens in such a way that the spot size 43.5cm (waist location in ABCD prop) from the lens is around 880 microns as required by the collimator
I have also placed the collimator at the above mentioned location and have connected it to the 1064 single mode fibre. At the other end of the fibre, I have placed a photodiode and am attempting to get a signal from it in order to maximize coupling efficiency.
Note: The 400mW beam has been attentuated to 4mW by an HWP and PBS.
For the temperature control of the non linear waveguide, we will be using the Newport 3040 Temperature Controller. The phase matching temperature of the crystal is 62.3 C. The TEC will be run with the following settings -
Lower Lim Temp = 20 C
Upper Lim = 70 C
Max Current = 0.65A
Gain Mode = 10 Fast
C1 = 1.0445e-3
C2 = 2.5075e-4
C3 = 0
The waveguide has been mounted on a ThorLabs LM14S2 Universal Butterfly Pin Mount. The TEC Driver is a 9 pin input while the TEC output from the controller is a 15 pin output so I made an adapter for the two different configurations.
Upon testing the Temperature Control of the Waveguide, we found that the equilibrium temperature always falls about 1.1 C below the set temperature.
Plot phase matching curves of SHG in the crystal.
The WOPO experiment has been quite stagnant for the last two weeks because ineffective coupling of the 1064 light into the fibre (max 10%). Beam profiling says that the ABCD simulation results were correct, and there is no problem with the fibre collimation package. Yesterday, Andrew and I found a possible culprit. On examining the fibre with a microscope we found that the core of one of the ends is fine while the other has been damaged. I am attaching pictures of both the ends.
We will attempt to clean the fibre. If that doesn't work out, then we will order a new one.
I asked Koji if he had any hight QE photodiodes to use in a ballenced homodyne detector. None of the Ad LIGO ones can be used for this but Zach had a small stockpile in the ATF lab.
Pictures attached of the boxes (two in total). I need to track down the PO or part numbers to work out what they are. They look like they are ~1.5 mm^2 area, all with windows still on.
I beieve that they are Exelitas C30642.
FYI: There also is one on the former-gyro optical table. This one doesn't have the cap.
I've reordered fiber that was damaged.
Need to profile the beam actually going into the fiber after the third lens. If the slit profiler isn't large enough for the 1760 µm beam then maybe try the WinCamD CCD profiler. You might need to ask around to find which lab its in.
Measure the profile of the back propagation beam by injecting a beam from the other side.
This gives you how the input mode should be.
Do you recall if there are any fiber coupled 1064 nm lasers anywhere in the 40m or other bridge west labs?
Measure the profile of the back propagation beam by injecting a beam from the other side.
This gives you how the input mode should be.
Jenne's laser at the 40m PD testing table is a fiber coupled 1064nm DL.
But you just can couple 5~10% of the beam from the other side of the fiber to know the mode at the input side.
It does not require too much effort if you have the fiber testing illuminator to align the beam.
Correction: If the diode is 3mm x 3mm, it is Excelitas C30665.
I am attaching a schematic of the proposed design for the Homodyne detector. The damping capacitance in the two photodetectors has to be decided based on what we estimate the capacitance of the photodiode to be.
Please let me know if there's anything I can do to make this better suited for homodyne detection.
Using the 632nm laser provided by Gautam to back couple the 1064nm light into the fibre, I managed to finally get efficient mode matching. For 25.4mW of light going into the collimator, the fibre outputs 19.3mW (~76%). Now that efficient mode matching has been achieved, I finally managed to plot the SHG Phase matching curve for the PPKTP Waveguide (a plot of output power (532nm) against the temperature). I fit the data obtained to the function
Here, the normalised sinc(x) fiunction is given by
The optimised values are
Maximum SHG Power
Optimum Phase Matching Temperature.
That gives the FWHM as 2.32 C.
The maximum output is much lower than expected as that is because of loss at the fibre coupling at the waveguide. This loss is visible and I am attaching a couple of pictures.
These are the plots of the dark noise of the Thorlabs photodetectors lying in the ATF lab using the FFT network analyser. For higher frequency ranges, I have to configure the other network analyser.
These are the settings that the analyser was running on -
Measure Group: FFT
Measurement: FFT 1
Num of extracted Points: 401
FFT Lines: 400
Averaging Mode: RMS
Averaging Type: Exp. / Cont.
Overload reject: On
Edit : I've added a stiched plot of all the collected data. The noise from 10-100KHz is around the order of 40nV. We're hoping to see if we can do better by designing our own photodetectors. We also see a lot of peaks that correspond to the harmonics of the 60Hz mains.
Edit 2: The Photodetector is the Thorlabs PDA55 detector. We CANNOT use this detector as it is silicon and has a terrible quantum efficiency at 1064nm.
Ugh - I deleted those 1000 bad plots. Just give us 1 trace per PD, all on one plot. Each trace should also include the model # of the PD. Just 'stuff we have laying around' is not useful.
Also, what are the requirements on the PD? Describe how these are computed.
Yesterday, with a lot of help from Koji, we built the transimpedance circuit (Gain = 10k) for the photodetectors of the homodyne circuit.
While doing so, we encountered a most bizzare issue. The circuit shows a significantly larger amount of noise (especially in the 10-100kHz band) when it is on the table as opposed to when it is suspended in air. I'm attaching pictures if the setup as well as a comparative plot. We still cannot ascertain the reason behind this extra noise.
Yesterday, with a lot of help from Koji, we built the transimpedance circuit (Gain = 10k) for the photodetectors of the homodyne circuit.a
I connected the Excelitas C30665 photodiode to the above transimpedance circuit and measured the dark noise while suspended in air (please refer previous elog on table noise).
For a mW of light and a quantum efficiency of about 87%, we expect to see about 0.68mA of current. This gives the shot noise to be 14.7pA/sqrt(Hz) which corresponfs to about 147nV/sqrt(Hz) for a 10k gain which is significantly higher than the noise floor of the circuit between 10 and 100KHz.
I also made a op-amp subtractor circuit for the homodyne detector and measured the noise. It is significantly lower than the shot noise.
Changed the setup for LabJack testing so that we can better isolate problems with the DAC and ADC (if they exist). The previous setup consisted of passing two signals through the LabJack and comparing their outputs using the Rayleigh statistic. Since there are problems activating two DACs and two ADCs on the LabJack at once, we needed a different design that would only use one of these at a time. The new design (Figure 1) inputs a digital signal which is stored as a control signal to compare against. Next, the digital signal is passed through the DAC and comes out as an Analog signal through terminal DAC0. Since only the DAC or the ADC can run at one time, the DAC is then paused until the ADC converts the signal back to digital, at which point the ADC is paused and the DAC resumes functioning. Theoretically, this conversion should be happening at 100 Hz, and in practice, this number will be very close to 100 Hz. With this setup, problems occur after running the LabJack where either the DAC or the ADC stops passing through data. This doesn’t happen immediately but will happen seconds to minutes after the test begins. This seems to occur because the DAC and ADC are being turned on and off too quickly. However, if we run the DAC and ADC at too low of a rate then we lose resolution on the test wave and it becomes harder to run statistics on the data set. I believe I can get this setup to work by tuning the sampling frequency of the DAC and ADC so we're in a spot that allows the LabJack to both pass through data but also allows us to have a high enough resolution to run other tests on the data set.
I will attempt to get the first setup to work. However, if I can’t resolve the issues with the DAC or ADC not passing through data, we could also attempt a different setup that moves the Analog to Digital conversion out of the LabJack so that the DAC doesn’t need to be switched on and off (Figure 2). With this setup, we would need to purchase an ADC that can be soldered onto a Raspberry Pi (MCP3008).
We have received the SHI cryocooler CH-104 (figure attached), which has been moved to the QIL. I have inspected all the components after unboxing it. Cold head test report supplied by SHI is attached below.
The cryocooler comes with a HC-4A Zephyr air cooled helium compressor. This compressor is a single stage, air cooled and designed to deliver high pressure helium gas to the cryocooler.
There are 2 helium supply/return (although both the hose says supply, which I am not sure why, hence will check it out) hose along with a kit to install it. This is currently charged with helium pressure of 280 psi, however, once it is installed then the helium pressure has to be adjusted (I am currently reading the manual to assemble the system).
The cryoocoler cold head will be finally placed on a bench which we have bought. I plan to use a breadboard to clamp it down. The compressor will be placed a few feet (based on hose length) away from it. Typically the compressors are noisy, hence later on we can get longer hose to keep the compressors further away.
The vacuum chamber (collar) will be moved in the lab and on the optical bench this Thursday (although this was supposed to be moved in last week, however due inadequate communication by the Caltech moving service this couldn't happen).
The top and bottom flange covers for the vacuum chamber (fabricated by Kurt Lesker) has been shipped on 24 Oct and we should be receiving it this week.
We have our shiny new vacuum chamber (fabricated by Nor-Cal), now sitting on the optical bench.
SHI Cryocooler – Vacuum chamber assembly
The attached picture shows a schematic of the assembly/connection of SHI cryocooler to the vacuum chamber. The cryocooler has warm flange mounting holes. Using a mating flange – hose/bellows will be connected to the cryocooler. The mating flange will have a port for roughing pump and vacuum gauge connection. The hose/bellows will be connected to the flange reducer which will be bolted to the CF (4-5/8 size) flange of the cryostat.
I will upload a CAD model of the mating hose and will also look for an appropriate size hose and flange reducer.
The top (seen with several threaded holes along with 16 through holes) and bottom (only 2 threaded holes for lifting and 16 through holes) plate for the vacuum chamber has arrived and I have moved them into the QIL optical bench/table. Using some aluminum struts/bosch, I am making a simple 3’’ tall spacer on top of which the bottom plater will be resting. After wiping them with solvents, I will start assembling the chamber and the plates.
The schematic of the homodyne configuration is shown below.
Following is the component list
This afternoon Chris and I installed the ADC and DAC cards in fb4.
We may want to start with a fresh install of Debian 9 and just reinstall the LIGO binaries.
I know there is some CTN slow channel data on the disk. Is it at all possible to boot so that can be recovered?
This afternoon Chris and I installed the ADC and DAC cards in fb4. We connected them to the timing card adapters (left external to the computer chassis for now).
We found fb4 to be running Debian 8 so first attempted to upgrade to 9, as that is the version supported by Jamie's cymac binaries. However, we encountered problems during the upgrade, apparently with gdm (the linux GUI). By switching to consol mode and killing gdm, were able to proceed to the point of updating all the packages. It completed successfully, but then the system failed to reboot, even in recovery mode. During boot, the advligo-rts kernel fails to start, and then boot hangs completely at the point the graphical interface is started.
OK...but how will the amplitude stabilization be done? How about a diagram showing the feedback loop and electronics?
Attachment #1 shows the schematic of the experimental setup for amplitude stabilization using AOM. The proposed idea is as follows
Following are the results from RF driver and AOM characterisation.
Attachment #1 shows the results from characterisation of Brimrose RF driver . The RF power and frequency are measured on Agilent spectrum analyser. A 30 dB attenuator was also used in the path from RF driver to spectrum analyser. This attenuation value is taken care in RF power output calculation. The RF driver has two BNC connectors labelled as “Modulation” and “Frequency” , located on the front panel. Varying the modulation input (in the range 0 V to 1 V) changes the RF output power from the RF driver as shown in attachment #1 (a). The maximum RF output power is about 0.6 W and the input RF power to the AOM is limited to this value as exceeding the same might cause damage to the AOM. Varying the frequency input (in the range 0 V to 10 V) changed the RF frequency from the RF driver as shown in attachment #1 (b). The AOM centre frequency is at 80 MHz with a frequency shift range of 8 MHz.
Attachment #2 and #3 shows the output power from the zeroth order and first order port of the AOM when the frequency input voltage to the RF driver (thus the RF frequency from the driver) is varied. The output power from the first order port is maximum (output power from zeroth order is minimum) when the frequency is about 78.8 MHz. As expected, the power in the zeroth order port is completely transferred to the first order port. This happens when the frequency input voltage to the RF driver is about 8.8 V.
Attachment #4 and #5 shows the output power from the zeroth order port of the AOM when the Modulation input voltage to the RF driver (thus the RF power from the driver) is varied. The output power from the first order port is maximum (output power from zeroth order is minimum) when the RF power to the AOM is maximum. This happens when the modulation input voltage to the RF driver is 1 V.
Attachment #5 shows the diffraction efficiency to the first order port (we use output power from first order port for the heterodyne measurement) as a function of frequency and RF power. The diffraction efficiency is calculated from the ratio of Power in first order port to the input power to the AOM.The power at the input end of AOM is 1.29 mW. So the percentage value calculated includes the insertion loss ( as per data sheet : 3-4 dB for the first order port ) as well . So the conclusion is , inorder to get maximum diffraction efficiency to the first order port of AOM, we should supply RF power of about 0.6 W at 78.8 MHz . If we are using the Brimrose driver, this can be set by giving modulation input voltage of 1 V and frequency input voltage of 8.8 V.
We then attempted to measure the band width. To do that, the source output from SR785 was fed into input B of SR560. Part of the source output was fed into channel 1 of SR 785, through T connector, for the transfer function measurement. We also used a T connector at the input A port of SR 560 and one of the ports of this T connector was fed into channel B of SR785. I still must interpret most of the results that we got.
Attachment # 2: Closed loop transfer function (a) Magnitude (b) Phase, at different gain values in SR 560 when the Marconi actuation slope is 10 kHz/V.
Attachment # 3: Closed loop transfer function at different actuation slope value in Marconi when the gain is 7 dB. The increase in noise at lower frequency in phase plot (b) may indicate that the phase/frequency noise of the Marconi increases if the actuation slope value is increased.
Attachment # 4: Closed loop transfer function at different actuation slope value set in Marconi when the gain is 10 dB. The transfer function measured for the case of gain = 10 dB and actuation slope = 100 kHz/V (that is the product of gain and actuation slope is larger) shows significantly different characteristics.
Using the SSUserFn option in SR785, we tried to get the open loop transfer function as well from SR 785. The functional form was
Attachment # 5: Open loop transfer function at different gain values set in SR 560 when the Marconi actuation slope is 10 kHz/V. The unity gain band width are 0.9 kHz, 2.8 kHz and 5.8 kHz respectively when the gain values are 3 dB, 7 dB and 10 dB
Attachment # 6 : Closed loop transfer function at different actuation slope value set in Marconi when the gain is 7 dB. The unity gain band width are 3 kHz, 9 kHz and 30 kHz respectively when the actuation slope values are 10 kHz/V, 30 kHz/V, and 100 kHz/V.
We also tried to estimate the open loop transfer function from the closed loop transfer function using the equation
Attachment # 7 : Comparison of Open loop transfer function that is measured from SR 785 and that is estimated from the closed loop transfer function using the above expression. These two values are significantly different. Kindly correct me.
I think you have made some coding error in your attachment 7 plot. Just pick a point in your plot and calculate by hand if your estimate is correct. Otherwise, we need to see your code to pinpoint the error. You can attach your code in a .zip file here.
The new photo detector has arrived (https://www.newport.com/p/818-BB-51F) . We did the DC and AC characterization of the same.
In this case, the input power was measured after the isolator.The power to voltage conversion is linear. The voltage levels are very low because this is a non-amplified detector. Also, the detector is coupled to a FC/UPC patch cord and we have all FC/APC fiber connectors. So, there could be some coupling loss from FC/APC to FC/UPC. FC/APC to FC/UPC conversion patch cord is ordered. We can check the performance again after it is arrived.
We then assembled the Mach-Zehnder interferometer (MZI) for the 2-micron laser source. Attachment #1 shows the schematic of the same. We measured a power level of 0.37 mW when the AOM was not turned on (RF power to AOM off). When AOM is turned ON, the power level measured at the output of MZI is 0.5 mW. Power meter was then replaced with the new photodetector and the beat note was observed on spectrum analyser.
After the discussion with Prof.Rana, we realised the mistake in our analysis. It was also suggested to make the measurement at the output of SR560. Attachment #1 shows the schematic of the setup for the measurement of closed loop transfer function. The RF power from AFG is 0 dBm and that from Marconi is 7 dBm.
The open loop transfer function is calculated from closed loop transfer function using the expression , where is the gain value set in SR560.
Attachment #2 : Closed loop and open loop transfer functions at different values of gain in SR 560 when the actuation slope in Marconi is 10 kHz/V. The unity gain frequencies are respectively 1kHz, 3 kHz and 5 kHz when the gain values are 3 dB, 7 dB and 10 dB.
Attachment #3 : Closed loop and open loop transfer function at different values of actuation slope in Marconi when the gain in SR 560 is 10 dB.The unity gain frequencies are respectively 5kHz, 16 kHz and 43 kHz when the actuation slope values are 10 kHz/V, 30 kHz/V and 100 kHz/V. It can be seen that the characteristics are significantly different for a larger value for the product of gain and actuation slope (G=10, S=100 kHz/V).
The probing signal from SR 785 was then disconnected. In this case, the oscilloscope measure the error signal in time domain and the measurement from SR 785 essentially gives the frequency noise of AFG. The measurement from SR 785 has the unit of V/rt Hz, which is then multiplied with actuation slope to get the frequency noise in Hz/rt Hz. During our measurements, the oscilloscope signal was showing a low level ( mV) DC line , confirming that the PLL is locked.
Attachment # 4 : Frequency noise of AFG at different gain value in SR 560 when the actuation slope in Marconi is 30 kHz/V. In the full span mode, the line width (resolution) is 128 Hz where as the line width is 2 Hz in short span mode. The peak at 60 Hz visible in short span plot corresponds to AC mains.
Attachment # 5 : Frequency noise of AFG at different actuation slope in Marconi when the gain in SR 560 is 10 dB. I was thinking, we should measure the same frequency noise irrespective of the setting in the PLL. It can be seen from attachment # 5 that the frequency noise measurement is affected by the value of actuation slope in Marconi. It was earlier observed that the phase noise of Marconi increases with increase in the actuation slope and , from these measurment shown in attachment #5, we are seeing increase in frequency noise value at larger values of actuation slope in Marconi.
Attachment # 1 shows the schematic of the experimental setup for the frequency noise measurement of 2-micron laser source using PLL. Instead of Brimrose driver, another Marconi is used to provide the RF power to the AOM. We know from the characterisation of AOM that we need to give RF power of 28 dBm at 78.8 MHz to achieve maximum diffraction efficiency to the first order port of AOM. The maximum output power from Marconi is 13 dBm. Hence, we used another RF amplifier (ZHL-3-A+) to amplify the RF power from Marconi. We initially tested the RF output from RF amplifier on spectrum analyser (RF power fed into spectrum analyser with proper attenuation in the path) and adjusted the RF frequency and power in Marconi such that we get 28 dBm output power from the RF amplifier at 78.8 MHz. The two marconis are set such that they are share the same time standard.
Now, the output power from the photodetector in MZI (Laser diode operated at input current of 90 mA) is fed into the RF input port of the mixer, instead of AFG. The 600 Ohm output of SR 560 is observed on oscilloscope and SR 785 simultaneously.
We observed dc line in the oscilloscope when the gain in SR 560 is set to 13 dB (20 times). Gain value below this ( 10 dB) or above this (17 dB) was showing oscillations in the oscilloscope with frequency varying with the actuation slope in Marconi. Attachment #2 shows the frequency noise measurement from SR 785 (V/rt Hz value from SR 785 multiplied with the actuation slope).
It is observed that, the time domain trace on the oscilloscope was not very stable. In between, we could see the oscillation was popping up. Also, the trace on SR 785 was swinging a lot (attached the video). As we observed in the case of AFG, the FM noise measured increses with the value of actuation slope in Marconi.
In this case, the RF power that is fed into the RF port of the mixer is very small (~ -40 dBm) compared to our previous experiment with AFG. So, I would like to repeat the sample experiment (locking AFG to Marconi) with AFG set to RF power comparable with that from the actual experiment.I should then find out the unity gain frequency of that particular combination of gain and actuation slope,which would help us to find the frequency range upto which the PLL measurment is valid.
I also need to measure the actual delay line length. I will also clean up the fiber connectors again and we can also use the FC/UPC to FC/APC patch cord for the detector after it is arrived. I still must understand the results better.Since we are using Non-PM fibers, the polarisation fluctuation might have also affected the measurement .Kindly give me further suggestions.
FC/UPC to FC/APC patch cord has arrived. I repeated the DC characterisation of the photodetector with this patchcord. The couping is improving by about 2 dB (Table below shws the result)
I added one more amplifier stage (ZFL-500 LN) after the detector. Since noise figure of ZFL-500LN (2.9 dB) is lower than that of ZHL-3A (5 dB), ZFL-500LN is the first amplifier stage after the photo detector and it is followed by ZHL-3A.
Attachment # 1 shows the beat note spectrum measured from the spectrum analyser. There was a 30 dB attenuator in the path during the measurement. So, the output RF power from the MZI (with two stages of amplification) is now about 3 dBm and the SNR of 37 dB is preserved even after two stages of amplification.
So, now the RF power to the RF port of the mixer is 3 dBm. I have attached the video of signal from the PLL loop at different gain (G=1, G=2,G=5) values in SR 560. The time domain trace seems to very noise. I suspect this is because of the inherent large noise in 2-micron laser diode with a broad line width of 2 MHz.
I then attempted to do the closed loop transfer function in the present PLL configuration by injecting the signal from SR 785. Attachment 2 shows the closed and open loop transfer functions at different gain values in SR 560 when the actuation slope is 10 kHz/V. Attachment 3 shows the closed and open loop transfer functions at different values of actuation slope when the gain is 5. The magnitude and phase traces are not very smooth as we observed when we did the similar measurement with an arbitrary function generator (AFG) as the RF source. In this case, when MZI output is fed in as the RF source, the RF power is fluctuating.
I also tried to do the frequency noise measurement. Attchement # 4 is the FM noise at different gain values when the actuation slope is 10 kHz/V. Attachement 5 is the FM noise at different actuation slope values when the gain is 5. This time, depending on the gain value and the actuation slope value, a short frequency span was considered in SR 785 for the frequency noise measurement. The frequency span is considered based on the value of unity gain frequencies that are approximated from the open loop transfer functions measured from attachment # 2 and #3
Attachment #1 shows the oscilloscope traces at different gain values when the actuation slope is 100 kHz/V. It also shows the base line when there is no input to the oscilloscope. Even in the absence of any signal to the oscilloscope, there is an offset with mean value, RMS value and peak to peak value respectively of 35 mV, 42 mV and 200 mV.
Table below summarises the mean value, RMS value and peak to peak value for different combinations of actuation slope and gain.
The RMS value and the peak to peak value is increasing with increase in gain and the mean value is not showing any trend. I was pressing the Run/stop button before saving the data. I press the same to make the trace alive after saving the data as well. But the mean value read out from the oscilloscope shows different /random values in either case. If I don’t save the data, but only increases the gain, the mean value readout from oscilloscope shows almost the same.
I saw the beat note on the oscilloscope and I was trying to find the change in frequency. The frequency readout from oscilloscope was showing very large fluctuation (60-100 MHz). I feel its not a reliable measurement, but I don’t know whether we have an option to measure the frequency jitter in this oscilloscope (TDS 3032).
RXA: we have a few options for measuring large frequency fluctuations:
We tried the Lock in amplifier in Moku lab for the frequency noise measurement. In this case, the output of the photo detector , after dc block and one stage of amplification, is fed into input 1 of Moku. It gives out the inphase and quadrature component. We have saved the data. I will process the data offline and update later.
[Aidan, Chris, Koji]
We went down to the lab to check the situation of the setups for 2um laser measurement and stabilization and the new cryostat.
[2um laser frequency noise measurement]
Attachment # 1 show the schematic of the lock in amplifier configuration used in Moku lab. We saved the in phase and quadrature components.
In phase =
where corresponds to 2 -micron , is the delay time in the delay fiber and .
is the phase noise of the laser.
From the inphase and quadrature component value is extracted. So, we are actually extrating the combined effect of phase noise of laser as well the phase noise due to fiber length fluctuations due to environmental fluctuations. ASD of this is converted to frequency noise in Hz/rt Hz. Attachment # 2 shows the frequency noise estimated from two sets of measurements. This curve exhibit a 1/f characteristics from about 240 Hz upto 30 kHz
There was a correction in the script I used to estimate the frequency noise from the inphase and quadrature component. Attachment #1 shows the frequency noise estimated after the correction.
I have also attached the Matlab script ( I am not able to attach the zip file with data files). I remember, while saving the data, we gave the time duration as 70 s. But while processing the data only I realised that the time domain data is captured only upto 2 s. Even in this case, I would expect the frequency axis to start from 0.5 Hz, but I don't see that in the FM noise plot. Kinldy let me know whther I am doing anything wrong in data proocessing.
c=3e8;%velocity of light
n=1.5;%refractive index of fiber
len=15;%length of delay fiber
omeg=2*pi*(c/lam);%optical frequency corresponds to 2-micron
tau=(len*n)/c;%time delay due to delay fier
Fiber Collimator (Thorlabs F028APC-2000+AD11F+LMR1) and MIR sensor cards (Thorlabs VRC6S Qty2) were delivered.
The sensor card is liquid crystal and seems temperature sensitive. It's slow and diffused. But at least we can now see 2um beams in a certain condition.
The fiber collimator seems working fine, but this gave me another issue. Now because the beam is small (w<500um) everywhere, I can't focus it very well. To make a focused beam, one needs a large beam, of course. Previously, the beam was not well focused. Therefore the final focused beam with f=150mm was sufficiently small like w=50um.
It looks like some kind of telescope is necessary.
Attached is a drawing of the first phase (minimal vibration isolation) cryocooler attachment, where the main tank connects via the blue rimmed feedthrough. Boxed/circled components are those that will require custom fabrication:
Currently there are only two connections that require viton o-ring rather than conflat connections (cooler to piece 1, piece 3 to HV feedthrough).
The PD mounts were delivered from ProtoLabs. The order was sent on Tue last week and it's here on Monday. Excellent!
And the quality looks pretty good.
The surfaces are sandblasted. Do we want to do any process on the bottom surface to reduce the thermal resistance?
An indium solder string also came in.
Normal solder (Sn63 Pb37): with flux, wetting o
Pure Indium - In 99.995: no flux, wetting x, low melting temp, like paste
Pb93.5 Sn5 Ag1.5: with flux, wetting o, high melting temp (soldering iron setting 380~430F)
Cryo solder In97 Ag3: no flux, wetting x, low melting temp, like paste