I found the VCO driver, that Rana asked me to locate, inside the 40m. I already have one VCO from PSL lab. Now, I have kept both of them inside the 40m lab(one on the cart in the side of the Y-arm and the other near the X-arm electronics table).
We have checked the transfer function of a bandpass filter using AG4395A network analyzer and retrieved the data through GPIB. The RF out signal of AG4395A had been divided by splitter with two outputs of the splitter going to through R and the filter which was connected to the A channel of the network analyzer. The GPIB data came in complex data format, from which the absolute value and phase had to be retrieved.
The plot for the TF is as following
I ve tested another bandpass filter today with similar set-up. This time I took the data with corrected reference level. To set this reference-level the filter was disconnected and the cable was connected "thru" according to the instructions provided in the manual of AG4395A at http://cp.literature.agilent.com/litweb/pdf/04395-90040.pdf, page 3-10. The transfer functions are as follows
I have started making the circuit to measure the transimpedance for the photodiode PDA10CF using Jenne's laser. I will continue it tomorrow.
I repeated my experiment to get noise level. To get that I disconnected the bandpass filter SBP-10.7 from channel A of network analyzer AG4395A and terminated both the open ends (open end of filter and open end of channel A) with 50ohm terminator.
Reference level had been corrected, signal and noise data had been collected separately w.r.t that level.
Command for GPIB: ./netgpibdata.py -i 192.168.113.105 -d AG4395A -a 10 -f filename
The result is as follows
Photodiode PDA10CF was under test. The RF out signal of AG4395A had been divided by splitter with one output of the splitter going to R channel of the network analyzer and the other to the laser. The splitted laser beams - splitted with beam splitter - fall on two photodiodes - one reference and the other on PDA10CF. The outputs of these two photodiodes go to channel B and A respectively of the network analyzer. The measured transimpedance data had been collected using the GPIB connection.
The result is as follows:
I have repeated the transimpedance measurement of PDA10CF. Also made the dark current noise measurement by connecting the PDA10CF output to the A channel of network analyzer. The results are as follows. I I started to take the reading for shot noise intercept current using a light bulb in front of the PD, changing the current through the bulb, but at higher current the bulb filament got broken, so the experiment is incomplete.
Today I have measured the transimpedance and dark-noise of the MC-REFL PD.
For transimpedance measurement I first collected the data of the reference Newfocus PD connecting it at channel B of Network-analyzer using the set-up of Jenne's laser. The data for the MC-REFL PD had been collected by connecting it to the A channel of Network Analyzer. To do that I shifted the Jenne's Laser to the table of MC-REFL PD, I moved the laser output on the table and fixed a lens and a mirror on the table. Taking the ratio of the two sets of datas I got the required trans-impedance.
Dark-noise readings were taken keeping the laser off.
I will upload the corresponding plots tomorrow.
Here I upload the plots corresponding to my last day's measurements.
You have to correct this transimpedance ratio by correcting for the different levels of DC photocurrent in the two devices.
For the dark noise, you must always include a trace showing the noise of the measurements device (i.e. the analyzer noise must be less than the dark PD noise) with the same input attenuation setting.
The correction for different levels of DC photocurrent in the two devices had been taken care by one MATLAB code, the code that originally was made by Koji.
The analyzer noise I had not recorded; today I am going to record it.
Here is the data for AG4395A network/spectrum analyzer noise data. I collected the data by putting 50ohm terminator on channel A with same input attenuation setting (0dB attenuation).
Today I have tested the MC transmission-end RF photodiode PDA255 for transimpedance and dark noise using Jenne's Laser and AG4395A network/spectrum analyzer. The dark noise voltage distribution for the transmission and reflection PDs of MC and the analyzer has been compared.
I am to do the input mode cleaner cavity mode scan. The electronic and shot noise of the components used , particularly photodiode noise, will affect the peak position of the modes, indicating the uncertainty in the measured frequencies of the modes. That will in turn give the uncertainty in the measured change of radius of curvature of the mirrors in presence of the laser beam, from which we will be able to calculate the uncertainty in the mirror-absorption value.
For PD transimpedance measurement I used Jenne's laser along with AG4395 network analyzer. The RF out signal of AG4395A had been divided by splitter with one output of the splitter going to R channel of the network analyzer and the other to the laser. The splitted laser beams - splitted with beam splitter - fall on two photodiodes - one reference(Newfocus1617? PD, the DC and RF transimpedance values were taken from its datasheet ) and the other on PDA255. The outputs of these two photodiodes go to channel B and A respectively of the network analyzer. The measured transimpedance data had been collected using the GPIB connection. It had been ensured that the PD under test is not going to saturation, for that the source power level was kept to -40dBm. transimpedance measurements were compensated by the ratio of DC photocurrent.
For dark noise measurement the output of the PD was connected to the A channel of the AG4395A, when there was no light falling on it. The response is collected using GPIB. The attenuation of channel A was made 0dB. ( AG4395A was kept in Spectrum analyzer mode in Noise Format).
The plots corresponding to the measurements are attached.
The comparison for the dark noise voltage levels of the MC transmission PD (PDA255) with MC REFL PD has been made with analyzer dark noise voltage. It is shown in the attachment (I will upload the dark noise current comparison too....since the output darknoise depends on the gain of the circuit, it is important to divide this voltage spectra by transimpedances.)
Today I have taken the reading for shot noise intercept current for the PDA255 - MC transmission RF PD. To do that I have put an incandescent bulb (JKL lamps, 222 bulbs, voltage and current rating 2.25V and 0.25A) in front of the PD and varied the current through it from 0A to 0.29A at 2.2V. I measured the corresponding DC voltage and took the noise data (4395A spectrum analyzer/ format noise, channel attenuation 0dB) through GPIB .
I will process the data and upload the result soon.
Summary: I am stuck with the measurement of shot-noise-intercept-current of PDA255. Seeking help.
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.
Method: It is as described in the elog 7907
Result: The plot is attached here.
Discussion: The result I got is really unexpected, the noise voltage should increase with the DC current level that corresponds to the increment of light level too. But actually it is decreasing. Three times I have repeated this experiment and got the same result. I want some suggestion on this regard.
- The data should be plotted in a log-log scale.
- The data points were only taken in the high current region.
- The plot may suggest that the amplifier saturate at the RF.
PDA255 has the nomial transimpedance gain of 10^4 Ohm.
The DC current of 10^-3 gives the output of 10V.
This plot may tell that the saturation starts even at the 1/10 of the full DC range.
The plot doesn't have many points below 0.1mA.
Consult with my plots for the similar measurements.
The measured points are logarithmically spaced. Use the same technique.
- It is also very unknown that how the noise level is calculated. No info is supplied in the plot or the elogs.
Here I am attaching the plot in loglog scale. I have taken the data-points from no light condition to the maximum light condition, the minimum variation possible in the current supply was 0.01A. The noise was visibly decreasing at higher light level.
For the noise level calculation I took the average of total noise in the range 7-60MHz. For each range the formula used was
noisevalue= sqrt(data(:,2)*100)/sqrt(2)/sqrt(channel BW); -- this conversion is needed since the data was collected in the 2 column format: frequency, spectrum(W).
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.
This work was done in-situ, so no optics on the AS table were moved. The PSL shutter was blocked since the IR beam was not necessary, and would scatter off the bulb Riju put in front of the PD.
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.
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?
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.
I think you have the splitter that splits the RF signal from the network analyzer in the wrong place.
Usually you split the signal immediately after the RF Out, so that half of the signal goes to the A-input of the Analyzer, and the other half goes to your controller (here, the laser diode controller). Then you would take the output of your controller and go straight to the actual laser diode, with no splitting in this path.
Here our device under test is the photodiode. So for the reference I wanted to retain the response of the laser diode controller. Otherwise I have to consider the transfer function of that LDC too. I may check both the options at the time of experiment.
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.
Ok, will do it on the coming week.
Today I have rerouted the fibers on AP table to remove the fiber rolls out of the AP table. I removed the fibers one by one from both ends - from the 1x16 splitter and from the AP table - keeping the fiber roll intact, and then connected it in reverse way, i.e. the fiber end which was on AP table now is connected to the splitter (since length of the outside the roll is shorter that side) and the fiber end connected to splitter is now rerouted on AP table.
We need to keep the fibers in such a fashion so that no sharp bending occurs anywhere, and also it does not get strained due to its weight, particularly near the 1x16 splitter. Jenne suggested to use a plastic box over the splitter rack to keep the fiber rolls for time-being. We discussed a lot how this can be done nicely; in future we may use array of hooks, Koji suggested to use cable hangers and to tie the rolls using more than one hanging point, Jenne suggested to use the bottom shelf of the rack or to use one plastic box with holes. We tried to make holes on the plastic box using drill, but it developed crack on the box. So ultimately I used the opened box only and put it over the rack.
The corresponding photographs are attached herewith.
Tomorrow we will reroute the fibers for POX table.
Today I have rerouted the fibers on POX table. The aim was to lay it overhead through the plastic pipe. A pipe ~50ft (~15.5m) long was taken for this purpose. I disconnected the two 25m long fibers for POP55 and POX11 PD (those had been already routed) from both of their ends - i.e. from the POX table and also from 1x16 splitter. Jenne and Koji suggested that we may have another two PDs ( POP22 and POP110) on POX table in future. So we used another 25m long fiber for these two (POP22/POP110). We could not use two fibers for these two since we have only four 25m long fibers and one of them we need for POY11 PD on POY table. Jenne and me put the three fibers inside the pipe using a copper tube. The tube then was put on the overhead rack, Manasa helped me to do it. The fiber ends were finally laid on the POX table at one end and connected to the 1x16 splitter at the other end.
The corresponding photos are attached herewith.
Today I routed fiber from 1x16 splitter to POY table. Manasa helped me doing that. The fiber(25m) was laid on overhead rack through plastic pipe of length ~76ft. We put the fiber inside the pipe using one copper tube, and then tied the plastic pipe on the overhead rack. Finally one end of the fiber was laid on POY table and the other end was connected to the 1x16 splitter. The photographs corresponding are attached. There is no picture of splitter end, cause it was dark that time.
[Eric, Riju, Annalisa]
Today we have cleared up the fiber spool near AP table. We have put the 1x16 fiber splitter and a box (we made two openings on it) for fiber spool on a different part of the rack. Also put a plastic tubing or the fibers coming out of AP table. Now the fibers coming out from AP table and also from POX table first enter the box through one opening and the end of the fibers come out of the other opening to get connected to to splitter. Photographs of the work are attached. I don't think enough fiber is there to make a similar loop for fiber coming from POY table.
Here I am attaching the schematic diagram of the experimental set-up for IMC cavitymode scanning. A 30- 45MHz scanning signal generated by Agilent 4395A network analyzer enters EOM, which in turn modulates the laser beam entering IMC. The cavity response can be verified from reflected/transmitted beam.
I worked with the reflected beam last days. But I got no clue about the percentage of reflected light reaching the photodiode and also the photodiode response. I would like to measure the power reaching photodiode and also would like to perform the test with transmitted beam - on wednesday if possible.
Today I checked the optical lay-out in MC REFL board of the MC REFL path on the AS table (I will put the updated diagram in a few hours), and took a record of the reflected power of unlocked MC and power entering MC REFL PD. The power coming out of MC cavity when unlocked is 1.25W and power entering REFL PD 112mW (Jenne measured these powers for me).
I also got a description of the MC demodulation board from Jenne.
(Edits by Jenne)
Today I have checked the optical layout of the MC transmission RFPD table and measured the laser powers at different points. Manasa helped me for that. I found the power entering the RF photodiode is 0.394mW while the transmitted power of the cavity is 2.46mW. (I will give the diagram later).
Aim: to scan the cavitymodes of IMC
The circuit used:
IMC transmission photodiode has been aligned.
Which PD? The 'regular' DC one, or the newer one? Why did it need realigning? What mirrors did you touch to do the alignment?
Did you do anything else in the last 3 days? I want to see ALL the gory details, because it can help people doing future measurements, or help us debug if something is wrong with the interferometer later.
MORE WORDS! Thanks.
No, not the "regular DC one", the "newer one" along with the controls of the corresponding mirror only i touched.
It needed to be realigned cause last week when we fitted a longer cable there, which may reach the network analyzer, it got misaligned since it got touched.
No other component in that box except that PD and the corresponding mirror controls I touched.
For my last 2 days work, I feel my last elog is reliable.
Today other than doing this, I checked for the higher order modes of the cavity, misaligning one of the MC mirror though the software only. I didn't mention it in my elog cause although I saw the presence of the higher order modes I didn't record it, so I can not upload any picture in support of such a statement.
Summary: Recorded the presence of higher order modes in IMC
What I did: Misaligned the flat mirror MC1 by small amount in both pitch and yaw (it was needed to be done cause at the beginning of the experiment no higher order modes were present) and scanned the cavity for frequency-range 32MHz to 45MHz.
I found the presence of higher order modes around 36.7MHz (1st order) and 40.6MHz (2nd order) along with two other strong modes near 35MHz and 42.5MHz.
example of plots illustrating DAC range / saturation
The PEM model has been modified now to include the JIMS(Joint Information Management System) channel processing. Additionally Jim added test points at the outputs of the BLRMS.
For each seismometer channel, five bands are compared to threshold values to produce boolean results. Bands with RMS below threshold produce bits with value 1, above threshold results in 0. These bits are combined to produce one output channel that contains all of the results.
A persistent version of the channel is generated by a new library block that called persist which holds the value at 0 for a number of time steps equal to an EPICS variable setting from the time the boolean first drops to zero. The persist allows excursions shorter than the timestep of a downsampled timeseries to be seen reliably.
The JIMS Channels are being recorded and written to frames:
The two JIMS channels at 2048:
[C1:PEM-JIMS_CH1_DQ] Persistent version of JIMS channel. When bit drops to zero indicating something bad (BLRMS threshold exceeded) happens the bit stays at zero for >= the value of the persist EPICS variable.
[C1:PEM-JIMS_CH2_DQ] Non-persistent version of JIMS channel.
And all of the BLRMS channels at 256:
Names are of the form:
For additional details about the JIMS Channels and the implementation, please see the previous elog entries by Jim.
I have a working aLIGO Conlog/EPICS Log installed and running on megatron.
Please see this wiki page for the details of use:
I also edited this page with restart instructions for megatron:
Please see Ryan's previous elog entries for installation details.
Over the next few days, I will be working on upgrading the aLIGO Conlog install to include new bugfixes distributed by Patrick T. The currently running conlog *should* not be affected, but please let me know if it is (email@example.com).
The upgrade to the aLIGO Conlog is completed. The conlog is once again running on megatron in a screen session. (see http://nodus.ligo.caltech.edu:8080/40m/6396)
In order to install the necessary extensions to epics to make the aLIGO conlog work, I have edited one file in the base epics install that affects makefiles:
Jamie said he prefers diffs, so I regenerated the original file and did a diff against the current file:
megatron:configure>diff CONFIG_COMMON.orig.reconstructedMar72012 CONFIG_COMMON.bck.Mar72012
< USR_CPPFLAGS =
< USR_DBDFLAGS =
> USR_CPPFLAGS = -I $(EPICS_BASE)/include
> USR_CPPFLAGS += -I $(EPICS_BASE)/include/os/Linux/
> USR_CPPFLAGS += -I $(EPICS_BASE)/../modules/archive/lib/linux-x86_64/
> USR_DBDFLAGS = -I $(EPICS_BASE)/dbd
> USR_DBDFLAGS += -I $(EPICS_BASE)/../modules/archive/dbd
This is saved in CONFIG_COMMON.diff.Mar72012_1