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ID Date Authorup Type Category Subject
  5070   Sat Jul 30 10:03:32 2011 JennyUpdateComputer Scripts / ProgramsMode matching

I ended up having to switch to a different mode-matching solution, because I was unable to find the f = 572.7 mm lens. See my next elog entry (5069).

  5096   Tue Aug 2 17:40:04 2011 JennyUpdatePSLReducing beam intensity incident on photodiode

I am using a PDA255 photodiode to measure the power outputted by the NPRO beam on the PSL table. (I'm going to then use a network analyzer to measure the amplitude response of the PZT to being driven at a range of frequencies. I'll detect the variation in in response to changing the driving frequency using this PDA255.)

The PDA255 has an active area of 0.8mm^2 and a maximum intensity for which the response is linear of 10mW/cm^2. This means that a beam I focus on the PD must have a power less than 0.08 mW (and even less if the spot size is smaller than the window size).

I used a power meter to measure the beam power and found it was 0.381 mW.

The second polarizing beam splitter in the setup transmits most of the beam power, but reflects 0.04 mW (according to the power meter). I'm going to place the photodiode there in the path of the reflected beam.

  5114   Thu Aug 4 00:04:52 2011 JennyUpdatePSLNetwork analyzer and PD set up to measure amplitude response of PZT

Today I placed the PDA255 photodiode on the PSL table to catch the small amount of beam power reflected by the second polarizing beam splitter in my setup. I plugged the PD output to the oscilloscope to measure the voltage output and positioned the PD such that the voltage output was maximized. At best I was able to achieve a 300 mV DC output voltage from the PD, (which seems a bit low, as the PD is specified to go from 0 to 5 V and the specifications say that the response becomes nonlinear after 10 mW/cm^2 and my beam has an intensity of approximately 5 mw/cm^2. I would therefore expect to get more beam power but after over an hour of maneuvering, 300 mV was the highest voltage output I could get).

I am planning, tomorrow afternoon, to take a measurement of the amplitude response of the PZT driving the NPRO laser. I moved the 4395 spectrum/network analyzer to near the PSL table and connected the RF output to an RF splitter. I fed one output of that into the PZT and the other output into the R port on the network analyzer. I fed the PD output into the A port. I plan to measure A/R as a function of driving frequency, sweeping from 10 Hz to 30 mHz.

I also worked to improve the mode matching of the NPRO beam coming from the AP table to the reference cavity. I drove the temperature of the NPRO at 0.100 Hz with an amplitude of 0.300 V, which Koji told me corresponds to a 1GHz change in the laser frequency. The transmission from the cavity is being monitored by a camera connected to a TV monitor, and also by a PD connected to an oscilloscope. I then repositioned the second lens in my mode matching setup in an attempt to increase the transmission peaks from the zeroth order spacial mode and decrease the transmission peaks from higher order modes. I may have improved the mode matching slightly but I was unable to improve it significantly.

  5126   Fri Aug 5 18:29:35 2011 JennyUpdatePSLNetwork analyzer and PD set up to measure amplitude response of PZT

Quote:

Today I placed the PDA255 photodiode on the PSL table to catch the small amount of beam power reflected by the second polarizing beam splitter in my setup. I plugged the PD output to the oscilloscope to measure the voltage output and positioned the PD such that the voltage output was maximized. At best I was able to achieve a 300 mV DC output voltage from the PD, (which seems a bit low, as the PD is specified to go from 0 to 5 V and the specifications say that the response becomes nonlinear after 10 mW/cm^2 and my beam has an intensity of approximately 5 mw/cm^2. I would therefore expect to get more beam power but after over an hour of maneuvering, 300 mV was the highest voltage output I could get).

I am planning, tomorrow afternoon, to take a measurement of the amplitude response of the PZT driving the NPRO laser. I moved the 4395 spectrum/network analyzer to near the PSL table and connected the RF output to an RF splitter. I fed one output of that into the PZT and the other output into the R port on the network analyzer. I fed the PD output into the A port. I plan to measure A/R as a function of driving frequency, sweeping from 10 Hz to 30 mHz.

I also worked to improve the mode matching of the NPRO beam coming from the AP table to the reference cavity. I drove the temperature of the NPRO at 0.100 Hz with an amplitude of 0.300 V, which Koji told me corresponds to a 1GHz change in the laser frequency. The transmission from the cavity is being monitored by a camera connected to a TV monitor, and also by a PD connected to an oscilloscope. I then repositioned the second lens in my mode matching setup in an attempt to increase the transmission peaks from the zeroth order spacial mode and decrease the transmission peaks from higher order modes. I may have improved the mode matching slightly but I was unable to improve it significantly.

The ABSL beam had been blocked so that it wouldn't enter the interferometer. I moved the block so that the beam I've been using is unblocked by the beam going to the interferometer is still blocked.

I positioned a fast lens (f=28.7mm) a little over an inch in front of the PDA255 in order to decrease the spot size incident on the PD. I adjusted the rotation angle of the half wave plate to maximize the transmitted power through the PBS to the cavity and minimize the power reflected to my PD. I then adjusted the lens potion to fix the beam on the PD. The voltage output of the PD is now 150mW, but I have the ability to increase the incident power by rotating the wave plate slightly.

Now all I need is to set up the network analyzer again to record the amplitude response to modulating the PZT from 10 Hz to 30 MHz, reduce the input voltage into the analyzer using a DC block.

  5144   Mon Aug 8 20:23:14 2011 JennyUpdatePSLNetwork analyzer and PD set up to measure amplitude response of PZT

Quote:

Quote:

Today I placed the PDA255 photodiode on the PSL table to catch the small amount of beam power reflected by the second polarizing beam splitter in my setup. I plugged the PD output to the oscilloscope to measure the voltage output and positioned the PD such that the voltage output was maximized. At best I was able to achieve a 300 mV DC output voltage from the PD, (which seems a bit low, as the PD is specified to go from 0 to 5 V and the specifications say that the response becomes nonlinear after 10 mW/cm^2 and my beam has an intensity of approximately 5 mw/cm^2. I would therefore expect to get more beam power but after over an hour of maneuvering, 300 mV was the highest voltage output I could get).

I am planning, tomorrow afternoon, to take a measurement of the amplitude response of the PZT driving the NPRO laser. I moved the 4395 spectrum/network analyzer to near the PSL table and connected the RF output to an RF splitter. I fed one output of that into the PZT and the other output into the R port on the network analyzer. I fed the PD output into the A port. I plan to measure A/R as a function of driving frequency, sweeping from 10 Hz to 30 mHz.

I also worked to improve the mode matching of the NPRO beam coming from the AP table to the reference cavity. I drove the temperature of the NPRO at 0.100 Hz with an amplitude of 0.300 V, which Koji told me corresponds to a 1GHz change in the laser frequency. The transmission from the cavity is being monitored by a camera connected to a TV monitor, and also by a PD connected to an oscilloscope. I then repositioned the second lens in my mode matching setup in an attempt to increase the transmission peaks from the zeroth order spacial mode and decrease the transmission peaks from higher order modes. I may have improved the mode matching slightly but I was unable to improve it significantly.

The ABSL beam had been blocked so that it wouldn't enter the interferometer. I moved the block so that the beam I've been using is unblocked by the beam going to the interferometer is still blocked.

I positioned a fast lens (f=28.7mm) a little over an inch in front of the PDA255 in order to decrease the spot size incident on the PD. I adjusted the rotation angle of the half wave plate to maximize the transmitted power through the PBS to the cavity and minimize the power reflected to my PD. I then adjusted the lens potion to fix the beam on the PD. The voltage output of the PD is now 150mW, but I have the ability to increase the incident power by rotating the wave plate slightly.

Now all I need is to set up the network analyzer again to record the amplitude response to modulating the PZT from 10 Hz to 30 MHz, reduce the input voltage into the analyzer using a DC block.

 I rolled the network analyzer over to the PSL table (on the south side). I'm borrowing the DC block from Kiwamu's green locking setup. I'm going to first measure the amplitude response of a low pass filter to made sure that the analyzer is outputting what I expect. Then I will measure the laser PZT amplitude response. I plan to finish the measurement and return the network analyzer to it's usual location tonight.

  5149   Tue Aug 9 02:34:26 2011 JennyUpdatePSLPZT transfer function measurement

Using a PDA255 on the PSL table, I measured the amplitude response of the NPRO PZT, sweeping from 10kHz to 5 MHz.

I took a run with the laser beam blocked. I then took three runs with the beam unblocked, changing the temperature of the laser by 10 mK between the first two runs and by 100mK between the second and third runs.

At the end of the night I turned off the network analyzer and unplugged the inputs. I'm leaving it near the PSL table, because I'd like to take more measurements tomorrow, probing a narrow bandwidth where the amplitude response is low.

On the PSL table, I'm still monitoring the reflected light from the cavity and the transmitted light through the cavity on the oscilloscope. I'm no longer driving the NPRO temperature with the lock-in.

I closed the shutter on the NPRO laser at the end of the night.

I'll log more details on the data tomorrow morning.

  5156   Tue Aug 9 16:00:58 2011 JennyUpdatePSLAmplitude response of PZT

AMresponsePZT.png

The top plot shows a sweep from 10 kHz to 5 MHz of the ratio of the voltage output of the PD detecting power from the NPRO laser beam and the RF source voltage (the magnitude of the complex transfer function). The black trace was taken with the laser beam blocked. For runs 2 and 3 I changed the laser temperature set point by 10 mK and 100 mK respectively to see if there was a significant change in the AM response. The bottom plots shows runs 2 and 3 compared to run 1 plotted in dB (to be explicit, i'm plotting 10 times the base 10 log of the magnitude of the ratio of two complex transfer functions). Changing the temperature seems to have only a minor effect on the output except at around 450kHz, where the response has a large peak in run 1 and much smaller peaks in runs 2 and 3. 

The traces in the top plot consist of 16 averages taken with a 300Hz IF bandwidth, 15 dBm source power (attenuated with a 6 dB attenuator) and with 20dB attenuation of the input power from the PD.

Next I'm going to probe a narrow band region where the response is low (2.0MHz or 2.4MHz perhaps) and choose a bandwidth for the dither frequency for the PDH locking.

Attachment 1: AMresponsePZT.png
AMresponsePZT.png
  5165   Wed Aug 10 02:40:40 2011 JennyUpdatePSLDither freq for PZT chosen: 2.418 MHz

I've finished using the network analyzer to characterize find a dither frequency for driving the PZT to use in my PDH locking. I found a region in which the amplitude response of the PZT is low: The dip is centered at 2.418 MHz. Changing the NPRO laser temperature by 100mK has no significant effect on the transfer function in that region. I will post plots tomorrow.

I'm finished with the network analyzer. It is unplugged, and the cart is still near the PSL table. (I'll roll it back tomorrow when it won't disturb interferometer locking).

I closed the shutter on the NPRO at the end of the night.

Tomorrow I plan to put together the fast locking setup. I'll drive the PZT at 2.418 MHz. More details to come tomorrow.

  5179   Wed Aug 10 20:40:17 2011 JennyUpdatePSLPDH locking: got an error signal

I ended up choosing a different dither frequency for driving the NPRO PZT: 230 kHz, because the phase modulation response in that region is higher according to other data taken on an NPRO laser (see this entry). At 230 there is a dip in the AM response of the PZT.

I am driving the PZT at 230 kHz and 13 dBm using a function generator. I am then monitoring the RF output of a PD that is detecting light reflected off the cavity. (The dither frequency was below the RF cutoff frequency of the PD, but it was appearing in the "DC output", so I am actually taking the "DC output" of the PD, which has my RF signal in it, blocking the real DC part of it with a DC block, and then mixing the signal with the 230kHz sine wave being sent to the PZT.

I am monitoring the mixer output on an oscilloscope, as well as the transmission through the cavity. I am sweeping the laser temperature using a lock in as a function generator sending out a sine wave at 0.2 V and 5 mHz. When there is a peak in the transmission, the error signal coming from the mixer passes through zero.

My next step is to find or build a low pass filter with a pole somewhere less than 100 kHz to cut out the unwanted higher frequency signal so that I have a demodulated error signal that I can use to lock the laser to the cavity.

 

  5202   Fri Aug 12 03:49:45 2011 JennySummaryPSLNPRO PDH-Locked to Ref Cav

DMass and I locked the NPRO laser (Model M126-1064-700, S/N 238) on the AP table to the reference cavity on the PSL table using the PDH locking setup shown in the block diagram below (the part with the blue background):

 

LIGO_block_diagram_2.png

 

A Marconi IFR 2023A signal generator outputs a sine wave at 230 kHz and 13 dBm, which is split. One output of the splitter drives the laser PZT while the other is sent to a 7dBm mixer. Also sent to the mixer is the output of a photodiode that is detecting the reflected power from off the cavity. (A DC block is used so that only RF signal from the PD is sent to the mixer). The output of the mixer goes through an SR560 low-noise preamp, which is set to act as a low pass filter with a gain of 5 and a pole at 30 kHz. That error signal is then sent to the –B port of the LB1005 PDH servo, which has the following settings: PI corner at 10kHz, LF gain limit of 50 dB, and gain of 2.7 (1.74 corresponds to a decade, so the signal is multiplied by 35). The output signal from the LB1005 is added to the 230 kHz dither using another SR560 preamp, and the sum of the signals drive the PZT.

 

I am monitoring the transmission through the cavity on a digital oscilloscope (not shown in the diagram) and with a camera connected to a TV monitor. I sweep the NPRO laser temperature set point manually until the 0,0 mode of the carrier frequency resonates in the cavity and is visible on the monitor. Then I close the loop and turn on the integrator on the LB1005.

 

The laser locks to the cavity both when the error signal is sent into the A port and when it is sent into the –B port of the PDH servo. I determined that –B is the right sign by comparing the transmission through the cavity on the oscilloscope for both ways.

 

When using the A port, the transmission when it was locked swept from ~50 to ~200 mV (over ~10 second intervals) but had large high frequency fluctuations of around +/- 50 mV. Looking at the error signal on the oscilloscope as well, the RMS fluctuations of the error signal were at best ~40 mV peak to peak, which was at a gain of 2.9 on the LB1005.

 

Using the –B port yielded a transmission that swept from 50 to 250 mV but had smaller high frequency fluctuations of around +/- 20 mV. The error signal RMS was at best 10mV peak to peak, which was at a gain of 2.7. (Although over the course of 10 minutes the gain for which the error signal RMS was smallest would drift up or down by ~0.1).

 

 

The open loop error signal peak-to-peak voltage was 180 mV, which is more than an order of magnitude larger than the RMS error signal fluctuations when the loop is closed, indicating that it is staying in the range in which the response is linear.

openlooperror.jpg

 

In the above plot the transmission signal is offset by 0.1 V for clarity.

Below is the closed loop error signal. The inset plot shows the signal viewed over a 1.6 ms time period. You can see ~60 microsecond fluctuations in the signal (~17 kHz)

closedlooperror.jpg

The system remained locked for ~45 minutes, and may have stayed locked for much longer, but I stopped it by opening the loop and turning off the function generator. Below is a picture of the transmitted light showing up on a monitor, the electronics I'm using, and a semi-ridiculous mess of wires.

 

IMG_3034.JPG

 

I determined that it’s not dangerous to leave the system locked and leave for a while. The maximum voltage that the SR560 will output to the PZT is 10Vpp. This means that it will not drive the PZT at more than +/-5 V DC. At low modulation rates, the PZT can take a voltage on the order of 30 Vpp, according to the Lightwave Series 125-126 user’s manual, so the control signal will not push the PZT too hard such that it’s harmful to the laser.

 

 

  5228   Sun Aug 14 04:12:37 2011 JennyUpdatePSLTemperature steps and slow actuator railing

Below are some plots from dataviewer of temperature-step data taken over the past 32 hours. (They show minute trends). I am looking at the thermal coupling from the can surrounding the reference cavity on the PSL table to the cavity itself, and trying to measure the cavity temperature response via the control signal sent to heat the NPRO laser, which is locked to the cavity.

Picture_6.png

Picture_7.png

  • Top left: out-of-loop temperature sensor on can surrounding ref cav (RCTEMP)
  • Top right: control signal sent to slow drive of laser (laser heater), which is supposed to follow the cavity temperature (TMP_OUTPUT)
  • Bottom left: in-loop can temperature sensors (MINCOMEAS)
  • Bottom right: room temperature reading (RMTEMP)

 

I stepped the temperature set point from 35 to 36 deg. C for the can at 12:30am last night. Then I waited to see the cavity temperature change and the slow actuator (laser heater: TMP_OUTPUT) follow that change.

I was a bit worried about the oscillations that were occuring in the TMP_OUTPUT signal even long after this temperature step was made, but I figured that they were simply room-temperature changes propagating into the cavity, since they seemed to have a similar pattern to the room-temperature variations, and since it is clear that the out-of-loop temperature sensor on the can (RCTEMP) experiences variations, even when the in-loop sensors are recording no variation.

At 8:46pm tonight I stepped the temperature down 2 degrees to 34 deg. C. The step had a clear effect on TMP_OUTPUT. The voltage to the heater dropped and eventually railed at its lowest output. I'm worried that the loop is unstable, although I haven't ruled out other possibilities, such as that a 2 deg. C temperature step is too large for the loop. I will investigate further in the morning.

  5230   Sun Aug 14 15:37:39 2011 JennyUpdatePSLTemperature steps and slow actuator railing

Quote:

Below are some plots from dataviewer of temperature-step data taken over the past 32 hours. (They show minute trends). I am looking at the thermal coupling from the can surrounding the reference cavity on the PSL table to the cavity itself, and trying to measure the cavity temperature response via the control signal sent to heat the NPRO laser, which is locked to the cavity.

Picture_6.png

Picture_7.png

  • Top left: out-of-loop temperature sensor on can surrounding ref cav (RCTEMP)
  • Top right: control signal sent to slow drive of laser (laser heater), which is supposed to follow the cavity temperature (TMP_OUTPUT)
  • Bottom left: in-loop can temperature sensors (MINCOMEAS)
  • Bottom right: room temperature reading (RMTEMP)

 

I stepped the temperature set point from 35 to 36 deg. C for the can at 12:30am last night. Then I waited to see the cavity temperature change and the slow actuator (laser heater: TMP_OUTPUT) follow that change.

I was a bit worried about the oscillations that were occuring in the TMP_OUTPUT signal even long after this temperature step was made, but I figured that they were simply room-temperature changes propagating into the cavity, since they seemed to have a similar pattern to the room-temperature variations, and since it is clear that the out-of-loop temperature sensor on the can (RCTEMP) experiences variations, even when the in-loop sensors are recording no variation.

At 8:46pm tonight I stepped the temperature down 2 degrees to 34 deg. C. The step had a clear effect on TMP_OUTPUT. The voltage to the heater dropped and eventually railed at its lowest output. I'm worried that the loop is unstable, although I haven't ruled out other possibilities, such as that a 2 deg. C temperature step is too large for the loop. I will investigate further in the morning.

 The lock was lost when I came in around noon today to check on it. The slow actuator was still railing.

1) I got lock back for a few minutes, by varying the laser temperature set point manually. TMP_OUTPUT was still reading -30000 cts (minimum allowed) and the transmission was not as high as it had been.

2) I toggled the second filter button off. The TMP_OUTPUT started rising up to ~2000 cts. I then toggled the second filter back on, and TMP_OUTPUT jumped the positive maximum number of counts allowed.

3) I lost the lock again. I turned off the digital output to the slow actuator.

4) I have so far failed at getting the lock back. My main problem is that when the BNC cable to the slow port is plugged in, even when I'm not sending anything to that port, it makes it so that changing the temperature set point manually has almost no effect on the transmission (it looks as though changing the setpoint is not actually changing the temperature, because the monitor shows the same higher order mode even when with +-degree temperature setpoint changes).

  5271   Fri Aug 19 19:08:40 2011 JennyUpdatePSLRelocking NPRO to reference cavity.

I am trying again to measure a temperature step response on the reference cavity on the PSL table.

I have been working to relock the NPRO to the cavity. I unblocked the laser beam, reassembled the setup described in my previous elog entry: 5202. I then did the following:

1) Monitored error signal (from LB1005 PDH servo), transmitted signal, and control signal sent to drive PZT on oscilloscope.

2) With loop open, swept through 0,0-mode resonance, saw a peak in the transmission, saw an accompanying error signal similar to the signal shown in 5202.

3) Tried to lock. Swept the gain on the LB1005 and could not find a gain that would make it lock. Tried changing the PI-corner freq. from 10 kHz to 30 kHz and back and still could not lock.

4) Noticed that the open loop error signal displayed on the scope was DC-offset from zero. Changed the offset to zero the error signal.

5) Tried to lock again and succeeded.

6) Noticed that upon closing the loop, the error signal became offset from zero again. Turning on the integrator on the LB1005 increased DC-offset.

7) Reduced the gain on the SR560 being used as a low pass filter from 5 to 1. Readjusted the open loop error signal offset on the LB1005.

8) Closed the loop and locked. Closing the loop then caused a much smaller DC change in the signal than I had seen with the larger gain (now around 3mV). RMS fluctuations in error signal are now 1 mV (well within the linear region of the error signal).

9) Noticed transmission has a strange distorted harmonic oscillation in it a 1MHz. (Modulation freq is 230kHz, so it's not that). Checked reflected signal and also saw a strange oscillation--in a sawtooth-like pattern.

 

I intend to

1) Post oscilloscope traces here showing transmitted and reflected signal when locked.

2) Look upstream to see if the sawtooth-like oscillation is in the laser beam before it enters the cavity:

  • Sweep the temperature of the laser so that the beam is no longer resonating in the cavity.
  • Compare the reflected signal off the cavity to the signal detected before being directed into the cavity (using the PDA255 that I used for measuring the AM response of the PZT) both with and and without the frequency modulation.

3) At some point, try to close the slow digital loop, perhaps readjusting the gain.

4) Try to measure a temperature step response.

  5272   Fri Aug 19 23:41:20 2011 JennyUpdatePSLRelocking NPRO to reference cavity.

Quote:

I am trying again to measure a temperature step response on the reference cavity on the PSL table.

I have been working to relock the NPRO to the cavity. I unblocked the laser beam, reassembled the setup described in my previous elog entry: 5202. I then did the following:

1) Monitored error signal (from LB1005 PDH servo), transmitted signal, and control signal sent to drive PZT on oscilloscope.

2) With loop open, swept through 0,0-mode resonance, saw a peak in the transmission, saw an accompanying error signal similar to the signal shown in 5202.

3) Tried to lock. Swept the gain on the LB1005 and could not find a gain that would make it lock. Tried changing the PI-corner freq. from 10 kHz to 30 kHz and back and still could not lock.

4) Noticed that the open loop error signal displayed on the scope was DC-offset from zero. Changed the offset to zero the error signal.

5) Tried to lock again and succeeded.

6) Noticed that upon closing the loop, the error signal became offset from zero again. Turning on the integrator on the LB1005 increased DC-offset.

7) Reduced the gain on the SR560 being used as a low pass filter from 5 to 1. Readjusted the open loop error signal offset on the LB1005.

8) Closed the loop and locked. Closing the loop then caused a much smaller DC change in the signal than I had seen with the larger gain (now around 3mV). RMS fluctuations in error signal are now 1 mV (well within the linear region of the error signal).

9) Noticed transmission has a strange distorted harmonic oscillation in it a 1MHz. (Modulation freq is 230kHz, so it's not that). Checked reflected signal and also saw a strange oscillation--in a sawtooth-like pattern.

 

I intend to

1) Post oscilloscope traces here showing transmitted and reflected signal when locked.

2) Look upstream to see if the sawtooth-like oscillation is in the laser beam before it enters the cavity:

  • Sweep the temperature of the laser so that the beam is no longer resonating in the cavity.
  • Compare the reflected signal off the cavity to the signal detected before being directed into the cavity (using the PDA255 that I used for measuring the AM response of the PZT) both with and and without the frequency modulation.

3) At some point, try to close the slow digital loop, perhaps readjusting the gain.

4) Try to measure a temperature step response.

I decided to go forward and try to close the digital loop in spite of the unexplained oscillations in the transmission.

1) Plugged the 20dB attenuator into the slow port on the laser drive. This pushed the laser out of lock and, for some reason, made the laser temperature stop responding to sweeping the set point manually with the knob.

2) Plugged the output from the digital system into the slow port (with the attenuator still in place).

3) Displayed the beam seen by the camera on a monitor in the control room

4) Stepped the laser temperature using MEDM until finding the 0,1 mode. Locked to that mode.

5) Closed the digital loop (input to slow laser drive attenuated 20dB attenuator). Gain 0.010

6) Loop appeared stable for 30 minutes, then temperature began shooting off. I opened the loop, cleared history, reduced the gain to 0.008, and started it again. Loop appears stable after 15 minutes of watching. I'm going to leave it for a few hours, then come back to check on it and, if it's stable, step the can temperature.

  5274   Sat Aug 20 23:01:39 2011 JennyUpdatePSLTaking temperature step-response data: successes and tribulations

After finishing my last elog entry, I monitored the digital loop's error signal (the control signal for the fast loop) and the output to the laser heater remotely, (from West Bridge), using dataviewer. The ref cav surrounding can temperature was set to 36 degrees C.

With the loop closed and a gain of 0.008, after seeing the output voltage to the laser heater (TMP_OUTPUT) remain fairly constant and the error signal (TMP_INMON) stay close to zero for ~3 hours, I tried to step the temperature. (This was at 2am last night). I was working remotely from West Bridge. To step the temperature I used the following command:

ezcawrite C1:PSL-FSS_RCPID_SETPOINT 35.5

 

Rather than change the can temperature to 35.5 C, it outputted:

C1:PSL-FSS_RCPID_SETPOINT=0.

 

It had set the setpoint to 0 degrees C, which was essentially turning the heater off. I tried resetting it back to 36 and had no luck. I tried changing the syntax slightly.: ezcawrite C1:PSL-FSS_RCPID_SETPOINT=36 and ezcawrite C1:PSL-FSS_RCPID_SETPOINT (36). No success.

I ran over to the 40m and changed the temperature back to 36 manually. The in-loop temp sensor had decreased to 31.5 degrees C before I was able to step the setpoint back up. The system seems to have recovered from this large impulse though, and the laser has remained locked.

5hourwbigimpulse.jpg

 5hourwbigimpulse2.jpg

(5 hours of minute-trend data)

From left to right: 

Top: Out-of-loop can temp sensor; Voltage sent to heat can

Middle: signal sent to heat the laser (TMP_OUTPUT); room temp

Bottom: Error signal for slow loop (sampled control signal from fast loop); In-loop can temp sensor

 

At 9:30 this morning (7 and a half hours after accidentally setting the setpoint to zero), I came in to the 40m. TMP_OUTPUT was still decreasing but was slowing somewhat, so I decided to step the can temperature up half a decree to 36.5 C.

TMP_OUTPUT responded to the step, but it is also oscillating slowly with room-temperature changes, and these oscillations are on the same order as the step response. The oscillations look like the room-temp oscilations, but inverted. (TMP_OUTPUT reaches maxima when RMTEMP reaches minima). Oddly, there does not appear to be much of a time delay between the room temperature and TMP_OUTPUT signals. I would expect a time delay since there's a time constant for a room-temperature change to propagate into the cavity. Perhaps the laser itself is susceptible to room-temperature changes and those propagate into the laser cavity on a much faster time scale. I don't know the thermal coupling of ambient temperature changes into the laser.

23hoursbefore920pm.jpg

23hoursbefore920pm2.jpg

(24-hours of second-trend data)

 

Options are:

--If the system can handle it, do a larger temperature step (3 degrees, say), so that I can more clearly distinguish the oscillations with room temp from the step response.

--Insulate the cavity with foam (will in principle make the temperature over the can surrounding the ref cav more uniform and less affected by room temperature changes).

--Insulate the laser? Is this possible?

--Leave the system as is and, as a first approximation, fit the room-temp data to a sine wave and subtract it off somehow from my data to just see the step response.

--Don't bother with steps and just try to get the transfer function from out-of-loop temperature (RCTEMP, which is affected by temperature noise from the room) to TMP_OUTPUT via taking the Fourier transforms of both signals.

 

I'm flying out tomorrow morning, so I'll either need to figure out how to step the temperature set point of the can remotely, successfully, or I'll need someone to manually enter in the temperature steps for me in the control room.

  11392   Tue Jul 7 17:22:16 2015 JessicaSummary Time Delay in ALS Cables

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. 

Attachment 1: cableA_fit.jpg
cableA_fit.jpg
Attachment 2: cableA_resid.jpg
cableA_resid.jpg
Attachment 3: cableB_fit.jpg
cableB_fit.jpg
Attachment 4: cableB_resid.jpg
cableB_resid.jpg
  11395   Wed Jul 8 17:46:20 2015 JessicaSummaryGeneralUpdated Time Delay Plots

I re-measured the transfer function for Cable B, because the residuals in my previous post for cable B indicated a bad fit. 

I also realized I had made a mistake in calculating the time delay, and calculated more reasonable time delays today. 

Cable A had a delay of 202.43 +- 0.01 ns.

Cable B had a delay of 202.44 +- 0.01 ns. 

Attachment 1: resid_CableA.png
resid_CableA.png
Attachment 2: resid_CableB.png
resid_CableB.png
  11416   Wed Jul 15 17:05:06 2015 JessicaUpdateGeneralBandpass Pre-Filter created

I applied a bandpass filter to the accelerometer huddle data as a pre-filter. The passband was from 5 Hz to 20 Hz. I found that applying this pre-filter did very little when comparing the PSD after pre-filtering to the PSD with no pre-filtering. There was some improvement though, just not a significant amount. For some reason, it also seemed as though the second accelerometer improved the most from pre-filtering the data, while the first and third remained closer to the unfiltered noise. Also, I have not yet figured out a consistent method for choosing passband ripple and stopband attentuation, both of which determine how good the filter is. 

My next step in pre-filtering will be determining a good method for choosing passband ripple and stopband attenuation, along with implementing other pre-filtering methods to combine with the bandpass filter. 

Attachment 1: acc1.png
acc1.png
Attachment 2: acc2.png
acc2.png
Attachment 3: acc3.png
acc3.png
  11421   Thu Jul 16 16:33:56 2015 JessicaUpdateGeneralAdded Bode Plots of Bandpass Filter

I updated the bandpass filter I was using, finding that having different stopband attenuations before and after the passband better emphasized the area from 3 Hz to 20 Hz. I chose a low passband ripple but high stopband attenuation to do this. My passband ripple was 2 dB, the first stopband was 25 dB, and the second stopband attenuation was 40 dB. As can be seen in the filter Magnitude plot, this resulted in a fairly smooth passband and a fairly step dropoff to the stopband, which will better emphasize the region I am trying to isolate. My goal was to emphasize the 3-20 Hz region 10-30 times more than the outside regions. I think I accomplished this by looking at the Bode plot, but I may have chosen the second stopband attenuation to be slightly too high for this. 

Attachment 1: acc1_update.png
acc1_update.png
Attachment 2: acc2_update.png
acc2_update.png
Attachment 3: acc3_update.png
acc3_update.png
Attachment 4: bp_BodeMag.png
bp_BodeMag.png
Attachment 5: bp_BodePhase.png
bp_BodePhase.png
  11440   Thu Jul 23 20:54:42 2015 JessicaUpdateGeneralALS Delay Line Box

The front panels for the ALS delay line box came in last week. Some of the holes for the screws were slightly misaligned, so I filed those and everything is now put together. I just need to test both front panels to determine if the SMAs should be isolated or not.

 

Koji had also suggested making the holes in the front and back panel conical recesses so that flat head screws could be used and would counteract the anodization of the panel and avoid the SMAs being isolated. I think if we did that then conductivity would be ensured throughout the panel and also through the rest of the box. I also think one way we could test this before drilling conical recesses would be to test both front panels now, as one has isolated SMAs and one has conductive SMAs. If the anodization of the panel isolated the SMA regardless, we could potentially figure this out by testing both panels. But, would it also be that it is possible that the isolation of the SMA itself does not matter and so this test would tell us nothing? Is there a better way to test if the SMAs are being isolated or not? Or would this be more time consuming than just drilling conical recesses as a preventative measure?

  11441   Thu Jul 23 20:57:15 2015 JessicaSummaryGeneralApplying Pre-filter to data before IIR Wiener Filtering

I updated my bandpass filter and have included the bode plot below in Figure 1. It is a fourth order elliptic bandpass filter with a passband ripple of 1dB and a stopband attenuation of 30 dB. It emphasizes the area between 3 and 40 Hz.

Below, I applied this filter to the huddle test data. The results from this were only slightly better in the targeted region than when no pre-filter was applied. 

When I pre-filtered the mode cleaner data and then used an IIR wiener filter, I found that the results did not differ much from the data that was not pre-filtered. I'm not sure yet if I'm targeting the right region of this data with my bandpass filter, and will be looking more into choosing a better region. Also, I am only using certain regions of ff when calculating the transfer function, and need to optimize that region also. I uploaded the code I used to make these plots to github.

Attachment 1: BodePlot.png
BodePlot.png
Attachment 2: acc_bandpass.png
acc_bandpass.png
Attachment 3: mcl_seis.png
mcl_seis.png
  11456   Tue Jul 28 20:42:50 2015 JessicaSummaryGeneralNew Seismometer Data Coherence

I was looking at the new seismometer data and plotted the coherence between the different arms of C1:PEM_GUR1 and C1:PEM_GUR2. There was not much coherence in the X arms, Y arms, or Z arms of each seismometer, but there were within the x and y arms of the seismometer.

I think the area we should focus on with filtering is lower ranges, between 0.01 and 0.1, because that it where coherence is most clearly high. It is higher in high frequencies but also incredibly noisy, meaning it probably wouldn't be good to try to filter there. 

Attachment 1: Coherence1.png
Coherence1.png
Attachment 2: Coherence2.png
Coherence2.png
  11458   Wed Jul 29 11:15:21 2015 JessicaSummaryLSCPSDs of Arms with seismometer subtraction

Ignacio and I downloaded data from the STS, GUR1, and GUR2 seismometers and from the mode cleaner and the x and y arms. The PSDs along the arms have the most noise at frequencies greater than 1 Hz, so we should focus on filtering in that area. The noise levels start dropping at around 30 Hz, but are still much higher than is seen at frequencies below 1 Hz. However, because the spectra is so low at frequencies below that, Wiener filtering alone injected a significant amount of noise into those frequencies and did not do much to reduce the noise at higher frequencies. Pre-filtering will be required, and I have started implementing a pre-filter, but with no improvements yet. So far, I have tried making a bandpass filter, but a highpass filter may be ideal in this case because so much of the noise is above 1 Hz. 

Attachment 1: Arms_PSD.png
Arms_PSD.png
Attachment 2: XArm_PSD.png
XArm_PSD.png
Attachment 3: YArm_PSD.png
YArm_PSD.png
  11471   Thu Jul 30 18:58:36 2015 JessicaUpdateGeneralALS Delay Line Box Front Panel Testing

I tested both of the front panels (conductive and isolated SMAs) with the ALS Delay Line Box by driving extremely close frequencies through the cables. By doing this, we would expect that a spike would show up in the PSD if there was crosstalk between the cables. 

In the plots below, for the conductive panel, the frequencies used were

               X Arm:  22.329 MHz                        Y Arm: 22.3291 MHz        

For the isolated panel, the frequencies were

              X Arm: 22.294 MHz                         Y Arm: 22.2943 MHz    

This gives a difference of 100 Hz for the conductive panel and 300 Hz for the isolated panel. Focusing on these areas of the PSD, it can be seen that in the Y Arm cable there is a very clear spike within 30 Hz of these differences when frequencies are being driven through both cables as opposed to the signal being in only the Y Arm. In the X Arms, the noise in general is higher when both cables are on, but there is no distinct spike at the expected frequencies. This indicates that some sort of crosstalk is probably happening due to the strong spikes in the Y Arm cables.          

 

Attachment 1: Xarm_diff.png
Xarm_diff.png
Attachment 2: Yarm_diff.png
Yarm_diff.png
Attachment 3: Xarm_isolated.png
Xarm_isolated.png
Attachment 4: Yarm_isolated.png
Yarm_isolated.png
  11477   Mon Aug 3 18:19:09 2015 JessicaUpdateGeneralAnodization of front panels accounted for

Previously, I had gotten the same results for the conductive and the isolated front panels. Today, I sanded off the anodized part on the back of the conductive front panel. I checked afterwards with a mulitmeter to ensure that it was indeed conductive through all the SMA connectors. 

I drove a frequency of 29.359 Hz through the X Arm cable and 29.3592 Hz through the Y Arm cable, giving a difference of 200 Hz. Previously, there would only be a spike in the Y Arm at the difference, while the X Arm did not change if the Y arm was on or off. Now that the panel is fully conductive, a spike can also be seen in the X arm, indicating that crosstalk may possibly be happening with this panel, now that the spike corresponds to both the X arm and Y arm. These results are only after one set of data. Tomorrow I'll take two more sets of data with this panel and do a more in depth comparison of these results to what had been previously seen.  

Attachment 1: redo_conduct1X.png
redo_conduct1X.png
Attachment 2: redo_conduct1Y.png
redo_conduct1Y.png
  11484   Thu Aug 6 11:45:01 2015 JessicaUpdateGeneralALS Delay Line front panel testing

Koji had suggested that I sync up the two function generators to ensure that they have the same base frequency and so that crosstalk will actually appear at the expected frequency. After syncing up the two function generators, I drove the following frequencies through each cable:

Conductive SMAs:

     X: 29.537 MHz           Y: 29.5372 MHz

Isolated SMAs:

     X: 29.545 MHz           Y: 29.5452 MHz

Each time, the difference between the frequencies was 200 Hz, so if there was crosstalk, a spike should appear in the PSDs at 200 Hz when frequencies are being driven through both cables simulataneously, but not when just one is on. We very clearly see a spike at 200 Hz in both the X arm and the Y arm with the conductive SMAs, indicating crosstalk. For the front panel with isolated SMAs, we see a spike at 200 Hz when both frequencies are on, but it is much less pronounced than with the conductive SMAs. It seems as though there will be crosstalk using either panel, just less with the isolated SMAs. 

Attachment 1: conductive_X.png
conductive_X.png
Attachment 2: conductive_Y.png
conductive_Y.png
Attachment 3: isolated_X.png
isolated_X.png
Attachment 4: isolated_Y.png
isolated_Y.png
  11491   Tue Aug 11 10:13:32 2015 JessicaUpdateGeneralConductive SMAs seem to work best

After testing both the Conductive and Isolated front panels on the ALS delay line box using the actual beatbox and comparing this to the previous setup, I found that the conductive SMAs improved crosstalk the most. Also, as the old cables were 30m and the new ones are 50m, Eric gave me a conversion factor to apply to the new cables to normalize the comparison.

I used an amplitude of 1.41 Vpp and drove the following frequencies through each cable:
      X: 30.019 MHz          Y: 30.019203 MHz

which gave a difference of 203 Hz. 

In the first figure, it can be seen that, for the old setup with the 30m cables, in both cables there is a spike at 203 Hz with an amplitude of above 4 m/s^2/sqrt(Hz). When the 50m cables were measured in the box with the conductive front panel, the amplitude drops at 203 Hz by a factor of around 3. I also compared the isolated front panel with the old setup, and found that the isolated front panel worse by a factor of just over 2 than the old setup. Therefore, I think that using the conductive front panel for the ALS Delay Line box will reduce noise and crosstalk between the cables the most. 

Attachment 1: best4.png
best4.png
Attachment 2: isolated4.png
isolated4.png
  11495   Tue Aug 11 18:43:42 2015 JessicaUpdateIOOMCL Online Subtraction

Today I finished fitting the transfer function to a vectfit model for seismometers T240_X and T240_Y, and then used these to filter noise online from the mode cleaner. 

The Bode plot for T240_X is in figure 1, and T240_Y is in figure 2. I made sure to weight the edges of the fit so that no DC coupling or excessive injection of high frequency noise occurs at the edges of the fit.

I used C1:IOO-MC_L_DQ as the first channel I filtered, with C1:IOO-MC_L_DQ(RMS) for RMS data. I took reference data first, without my filter on. I then turned the filter on and took data from the same channel again. The filtered data, plotted in red, subtracted from the reference and did not inject noise anywhere in the mode cleaner. 

I also looked at C1:LSC-YARM_OUT_DQ and C1:LSC-YARM_OUT_DQ(RMS) for its RMS to see if noise was being injected into the Y-Arm when my filter was implemented. I took reference data here also, shown in blue, and compared it to data taken with the filter on. My filter, in pink, subtracted from the Y-Arm and injected no noise in the region up to 10 Hz, and only minimal noise at frequencies ~80 Hz. Frequencies this high are noisy and difficult to filter anyways, so the noise injection was minimal in the Y-Arm. 

Attachment 1: SeisX_bode.png
SeisX_bode.png
Attachment 2: SeisY_bode.png
SeisY_bode.png
Attachment 3: MCL_first.png
MCL_first.png
Attachment 4: Yarm_first.png
Yarm_first.png
  11502   Thu Aug 13 12:06:39 2015 Jessica SummaryIOOBetter predicted subtraction did not work as well Online

Yesterday I adjusted the preweighting of my IIR fit to the transfer function of MC2, and also managed to reduce the number of poles and zeros from 8 to 6, giving a smoother rolloff. The bode plots are pictured here:

The predicted IIR subtraction was very close to the predicted FIR subtraction, so I thought these coefficients would lead to a better online filter.

However, the actual subtraction of the MCL was not as good and noise was injected into the Y arm.

The final comparison of the subtraction factors between the online and offline data showed that the preweighting, while it improved the offline subtraction, needs more work to improve the online subtraction also.

Attachment 1: newBodeX.png
newBodeX.png
Attachment 2: newBodeY.png
newBodeY.png
Attachment 3: pred_Sub.png
pred_Sub.png
Attachment 4: MCLSub.png
MCLSub.png
Attachment 5: YarmSub.png
YarmSub.png
Attachment 6: comparison.png
comparison.png
  6372   Wed Mar 7 13:30:17 2012 JimUpdatePEMadded TPs and JIMS channels to PEM front-end model

[Jim Ryan]

The PEM model has been modified now to include a block called 'JIMS' for the JIMS(Joint Information Management System) channel processing. Additionally I added test points inside the BLRMS blocks that are there. These test points are connected to the output of the sqrt function for each band. I needed this for debugging purposes and it was something Jenny had requested.

The outputs are taken out of the RMS block and muxed, then demuxed just outside the JIMS block. I was unable to get the model to work properly with the muxed channel traveling up or down levels for this. Inside the JIMS block the information goes into blocks for the corresponding seismometer channel.

For each seismometer channel the five bands are processed by comparing to a threshold value to give a boolean with 1 being good (BLRMS below threshold) and 0 being bad (BLRMS above threshold). The boolean streams are then split into a persistent stream and a non-persistent stream. The persistent stream is processed by a new library block that I created (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 EPICS variables for the thresholds are of the form (in order of increasing frequency):

C1:PEM-JIMS_GUR1X_THRES1

C1:PEM-JIMS_GUR1X_THRES2

etc.

The EPICS variables for the persist step size are of the form:

C1:PEM-JIMS_GUR1X_PERSIST

C1:PEM-JIMS_GUR1Y_PERSIST

etc.

I have set all of the persist values to 2048 (1 sec.) for now. The threshold values are currently 200,140,300,485,340 for the GUR1X bands and 170,105,185,440,430 for the GUR1Y bands.

The values were set using ezcawrite. There is no MEDM screen for this yet.

PEM model was restarted at approx. 11:30 Mar. 7 2012 PST.

 

  6397   Fri Mar 9 20:44:24 2012 Jim LoughUpdateCDSDAQ restart with new ini file

DAQ reload/restart was performed at about 1315 PST today. The previous ini file was backed up as c1pem20120309.ini in the /chans/daq/working_backups/ directory.

I set the following to record:

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:
[C1:PEM-RMS_ACC1_F0p1_0p3_DQ]
[C1:PEM-RMS_ACC1_F0p3_1_DQ]

On monday I intend to look at the weekend seismic data to establish thresholds on the JIMS channels.

256 was the lowest rate possible according to the RCG manual. The JIMS channels are recorded at 2048 because I couldn't figure out how to disable the decimation filter. I will look into this further.

  12140   Mon May 30 18:19:50 2016 JohannesUpdateCDSASS medm screen update

I noticed that the TRY button in the ASS main screen was linking to LSC_TRX instead of LSC_TRY. Gautam fixed it.

  12175   Tue Jun 14 11:29:25 2016 JohannesSummaryASCYArm OpLev Calibration

In preparation for the armloss map I checked the calibration of the Y-Arm ITM and ETM OpLevs with the method originally described in https://nodus.ligo.caltech.edu:8081/40m/1247. I was getting a little confused about the math though, so I attached a document at the end of this post in which I work it out for myself and posteriority. Stepping through an introduced offset in the control filter for the corresponding degree of freedom, I recorded the change in transmitted power and the reading of the OpLev channel with the current calibration. One thing I noticed is that the calibration for ITM PIT is inverted with respect to the others. This can of course be compensated at any point in any readout/feedback chain, but it might be nice to establish some sort of convention where positive feedback to the mirror will increase the OpLev reading.

The calibration factors I get are within ~10% of the currently stored values. The table (still incomplete, need to relate to the current values) summarizes the results:

Mirror DoF Current Relative New
Y-Arm OpLev Calibration
ETM PIT   0.974 ± 0.029  
  YAW   1.077 ± 0.021  
ITM PIT   -0.972 ± 0.020  
  YAW   0.920 ± 0.048  

The individual graphs:

ETM PIT

ETM YAW

ITM PIT

ITM YAW

 

The math:

 

 

Attachment 1: CavityCoupling.pdf
CavityCoupling.pdf CavityCoupling.pdf
  12176   Tue Jun 14 11:52:08 2016 JohannesUpdateGeneralEPICS Installation | SURF 2016

We generally want to keep the configuration of the 40m close to that of the LIGO sites, which is why we chose BusWorks, and it is also being established as a standard in other labs on campus. Of course any suitable DAQ system can do the job, but to stay relevant we generally try to avoid patchwork solutions when possible. Did you follow Aidan's instructions to the book? I haven't set up a system myself, yet, so I cannot say how difficult this is. If it just won't work with the Raspberry Pi, you could still try using a traditional computer.

Alternatively, following Jamie's suggestions, I'm currently looking into using python for the modbus communications (there seem to be at least a few python packages that can do this), which would reportedly make the interfacing and integration a lot easier. I'll let you know when I make any progress on this.

Quote:

About acquiring data: Initially I couldn't start with proper Acromag setup as the Raspberry pi had a faulty SD card slot. Then Gautam gave me a working pi on which I tried to install EPICS. I spent quite a time today but couldn't setup acromag over ethernet.  But, it would be great if we have a USB DAQ card. I have found a good one here http://www.mccdaq.com/PDFs/specs/USB-200-Series-data.pdf It costs around 106$ including shipping (It comes with some free softwares for acquiring data) . Also, I know an another python based 12bit DAQ card (with an inbuilt constant current source) which is made by IUAC, Delhi and more information can be found here http://www.iuac.res.in/~elab/expeyes/Documents/eyesj-progman.pdf  It costs around 60$ including shipping.

About temperature sensing: The RTD which I found on Omega's list is having a temperature resolution of 0.1 deg C. I have also asked them for the one with good resolution. Also according to their reply, they have not performed any noise characteristics study for those RTDs.

 

 

  12188   Thu Jun 16 11:25:00 2016 JohannesUpdateLSCY-Arm round-trip loss measurement with ALS

Using the ALS green beat and armlength feedback I mapped an IR resonance of the Y-Arm by stepping through a ramp of offset values.

First I optimized the IR alignment with the dither scripts while LSC kept the arm on resonance, and then transitioned the length control to ALS. The beat frequency I obtained between the Y-arm green and the PSL was about 25 MHz. Then I applied a controlled ramp signal (stepping through small offset increments applied to LSC-ALSY_OFFSET, while logging the readback from channels LSC-TRY_OUT16 and ALS-Y_FC_SERVO_INMON with an averaging time of 1s.

The plots show the acquired data with fits to  T(x)=\frac{T_0}{1+\frac{(x-x_0)^2}{\mathrm{HWHM}^2}}+\mathrm{offset} and f(x)=mx+b, respectively.

 

The fits, weighted with inverse rms uncertainty of the data points as reported by the cds system, returned HWHM = 0.6663 ± 0.0013 [offset units] and m = -0.007666 ± 0.000023 [MHz/offset unit], which gives a combined FWHM = 10,215 ± 36 Hz. The error is based purely on the fit and does not reflect uncertainties in the calibration of the phase tracker.

This yields a finesse of 388.4 ± 1.4, corresponding to a total loss (including transmissivities) of 16178 ± 58 ppm. These uncertainties include the reported accuracies of FSR and phase tracker calibration from elog 9804 and elog 11761.

The resulting loss is a little lower than that of elog 11712, which was done before the phase tracker re-calibration. Need to check for consistency.

Attachment 1: T_vs_steps.pdf
T_vs_steps.pdf
Attachment 2: f_vs_steps.pdf
f_vs_steps.pdf
  12192   Thu Jun 16 18:08:57 2016 JohannesUpdatePSLBefore the AOM installation

There was only one razor blade beam dump labeled for atmospheric use left, but that's all we need. Steve is working on restocking. I placed the modified AOM mount on the PSL table near its intended location (near the AOM where it doesn't block any beams).

Things to keep in mind:

  • The laser power needs to be turned down for the installation of the AOM. Current laser settings are: Crystal Temperature: 29.41 C, Diode Current: 2.1 A.
  • The AOM driver must not be left unterminated when turned on (which it currently is and will be).
  • The HEPA filters are currently running at ~50%. While the PSL enclosure is open for the work we'll set them to 100% and lower them after a job well done.

The setup:

The AOM has a deflection angle of about 20 mrad, which requires about 10cm of path for a separation of 2mm of the two beams. I need to survey closer and confirm, but I hope I can fit the beam dump in before the PMC (this of course also depends on the spot size). Alternatively, the PMC hopefully isn't resonant for anything remotely relevant at 80MHz offset, in which case we can also place the beam dump in its reflection path.

So this is the plan:

  • Determine coupling efficiency into PMC for reference
  • Turn down laser power
  • No signal on AOM driver modulation input
  • Mount AOM, place in beam path, and align
  • Correct alignment into PMC?
  • Secondary beam detectable? Adjust modulation input and laser power until detectable.
  • Find a place for beam dump
  • Confirm that primary beam is not clipping with PMC
  • Turn up laser power
  • Determine coupling efficiency with restored power to compare

Any thoughts? Based on the AOMs resting place I assumed that it is supposed to be installed before the PMC, but I'm actually not entirely sure where it was sitting before.

  12196   Fri Jun 17 22:36:11 2016 JohannesUpdatePSLAOM installation

Subham and I have placed the AOM back into the setup right in front of the PMC.

Steps undertaken:

  1. The HEPA filters were turned off for some reason. They were turned back on, running at 100% while the enclosure was open.
  2. Before the installation, after initial realignment, the PMC TRANSPD read out 748 mV.
  3. The laser injection current was dialed down to 0.8 A (just above the threshold, judging by PMC cameras.
  4. AOM was attached to the new mount while staying connected to its driver. Put in place, a clamp prevents the cable from moving anywhere near the main beam.
  5. Aligned AOM to beam, centering the beam (by eye) on front and back apertures.
  6. We then applied an offset to the AOM driver input, eventually increasing it to 0.5 V. A secondary beam became clearly visible below the primary beam.
  7. In order to place the razor blade dump (stemming from a box, labeled "cleaned for atm use") before the PMC, where the beam separation was about 3 mm, to make sure we can hit the edged area, we had to place the dump at an angle, facing up.
  8. Keeping the 0.5V offset on the driver input, with the lights off, we increased the laser diode current in steps of ~200 mA to its original value of 2.1A, while checking for any IR light scattered from the beam dump. Not a trace.
  9. At original current setting, we realigned the beam into the PMC, and obtained 743 mV on the TRANSPD in the locked state.
  10. Closed off PSL table, dialed HEPAs down to 50%

              

 

Attachment 1: aom_new_mount.jpg
aom_new_mount.jpg
  12270   Thu Jul 7 17:12:50 2016 JohannesUpdateGeneralVent progress

I performed a visual inspection of ITMY in its natural habitat today. I did not get any great pictures from the HR side because it's located very towards the edge of the table towards the arm. Before that I checked the levelness of the table. East-west direction was fine, north-south was slightly off but still within the marks for 'level'.

The AR side had several speckles, a few of them located somewhat near the geometrical center of ITMY. The top of the barrel was worse of, as expected. The HR side was a little better, but there were a few pieces of dust? near near the center. Sample pictures are attached, I uploaded all the good ones to Picasa.

Clamps that mark the position of ITMY were already in place. I did not move the optic just yet, and we will have to move a cable block out of the way to bring ITMY near the opening for us to work on it. We will markt the position of that to preserve the weight distribution. Then we can probably take some better before/after pictures. Tomorrow I will be looking at ETMY.

  12291   Tue Jul 12 09:35:51 2016 JohannesUpdateGeneralSlippery substance mystery

I've noticed the spot that Rich means before, too. I think you only notice this when you're wearing the shoe covers, not sneakers or crocs. I didn't see any 'substance', it seems more like the floor finish (wax?) seems to be more slippery in that area than others.

Quote:

I found a note on Steve's desk that R. Abbott left yesterday afternoon about an unidentified slippery substance being present on the floor by cabinet S12, along the X arm. (Steve is away this week)

Just now, I found no trace of the substance in the vicinity of that cabinent (which is one of the cabinets for clean objects). Maybe the janitor cleaned it already?

 

  12295   Tue Jul 12 23:51:16 2016 JohannesUpdateGeneralVent progress - ETMY inspection

On Monday I inspected ETMY, and found nothing really remarkable. There was only little dust on the HR side, and nothing visible in the center. The AR side has some visible dust, nothing too crazy, but some of it near the center.

  12296   Wed Jul 13 00:01:38 2016 JohannesUpdateGeneralITMX dust

We ran out of illuminator juice, and short-term charging couldn't restore enough battery life to continue the work. We should be able to get some better pictures tomorrow.

Quote:

Looked at ITMX. Johannes and I both saw a fairly large speck of dust near the center of the HR side. We tried to take some photos but couldn't get any with good focus

 

  12297   Wed Jul 13 00:38:25 2016 JohannesUpdateGeneralVent progress - ETMY attempted repositioning

[Lydia, Johannes]

We attempted to move the ETMY suspension near the access port in preparation for the cleaning process. The plan was to move in the face restraints first to the point of almost making contact, then the ones underneath so the optic is sitting on them, followed by the top one facing down, and then bringing in the stops on the faces.

While moving in the stoppers I noticed that the far lower stopper on the HR side was barely touching the face of the optic in its resting position and was basically pushing it sideways when moved forward. It was just on the edge, so I tried to compensate minimally by moving the underneath stops a little further on the near side, trying to let it 'slide' over a little so the screw would have better contact. I must have been too generous with the adjustment, because while proceeding I noticed at some point that the stick magnets on one side of the optic were not attached anymore but laying inside the OSEMs. The side magnet was also missing, it is now sitting on the suspension jig base plate. The dumbbells all seem intact, but we'll test them before we reglue the magnets to the optic. This is extremely unfortunate, but hopefully won't take too long to fix. At the very least, as Koji put it, the cleaning will be easier with the optic out of the suspension. Still, what a bummer.

  12310   Tue Jul 19 13:21:42 2016 JohannesUpdateGeneralVent progress - ETMY attempted repositioning

[Lydia, Johannes]

We moved ITMY from its original position to a place near the access point. We took the OSEMs off first, and noticed that the short flat head screw driver was still a little too long to properly reach the set screws for the lower OSEMs. We were able to gradually loosen them, though and thus remove the lower OSEMs as well. We had to move a cable tower out of the way, but used clamps to mark its position. After making sure the optic is held by its earthquake stops, we moved it to its cleaning location. All magnets are still attached.

  12456   Wed Aug 31 18:07:43 2016 JohannesUpdateSUSITMY free swinging

[Lydia, Gautam, Koji, Johannes]

Summary of things done today:

  • Rebalanced ITMY table
    • After waiting until today to see if the table would relax into a level position, engaged the earthquake stops for SRM and moved the large counterweight by ~4 inches. The table is now level to within ~0.1 mrad in direction of the access port
    • Since the relaxing seems to take some time, we will open ITMX and ETMX chamber tomorrow and level the tables with additional weights, so the springs can get used to 'levelness' again
  • Cleaned ITMY, SRM and SR2 optics
    • Koji drag-wiped all three optics and cleaned the table in general where accessible. He was able to remove the sliver discussed in elog https://nodus.ligo.caltech.edu:8081/40m/12455
    • We measured the particle count in the chamber and found it to be 4000 for 0.3 microns and 660 for 0.5 microns.
  • We pulled out stops on ETMY ITMY and roughly centered the OSEMs half-way, using photos of the previous OSEM rotation as a reference point for their orientation. We foudn that the green beam is hitting ITMY almost centered and that the reflection doesn't seem to steer off too much, but were not yet able to see any returned light on the ETMY cameras.

Unless we get lucky and get the green light to flash in the cavity by playing with the mirror alignment, we will open the ETMY chamber tomorrow. On one hand we can look for the reflected green light in the chamber, or alternatively the IR beam transmitted by ITMY. This way we can obtain estimates for the OSEM biasing and perform the final centering of the OSEMs. We will then also address the bounce mode minimization in ITMY and check if the previous orientations still hold.

  12464   Thu Sep 1 19:18:14 2016 JohannesUpdateSUSITMX and ETMX preemptive table leveling

I balanced the ITMX and ETMX tables into level position today, for which I had to move quite a few of the on-table weights. I'm recording their original positions for future use here.

ETMX

This table was only off in 'pitch', I moved the middle weight to a new location as shown in the pictures. I added secondf disk weight on top of the one I moved, this one has to come out again when we install ETMX.

ETMX chamber original configuration
Reference for original position
Moved weight here

ITMX

I moved some weights around as shown in the image, but didn't have to add any. We simply have to move them back to their original location when the time comes.

ITMX chamber original configuration
Reference for square blocks: the lower one is a double stack
Reference for disk weights: These two are stacked.

 

While in the chambers, I also took some pictures of the ETMX window and PR2, motivated by the dirty state of SR2. We might want to consider cleaning both, specifically PR2 is relatively easily accessible and can be cleaned when we open the ITMX chamber to remove its FC and move it back into position.

 

  12465   Thu Sep 1 19:59:22 2016 JohannesUpdateSUSIR mode flashes in Y arm

[Gautam, Lydia, Johannes]

  • After placing the irises on the ETMY and ITMY cages we found that the green beam pointing was off in YAW and corrected it to hit the center of ITMY
  • The green beam was well centered on ETMY to begin with, so we used it as a reference for the alignment of ITMY, sending it back through the ETMY iris
  • We used the green transmission to tune the pitch and yaw of ETMY
  • Using TT1 and TT2 we steered the beam IR through both irises and were hoping to see mode flashes in the IR arm transmission, which we did

The next step is the tip tilt fine alignment of the IR into the arm, using TRY, from which we removed the ND filter for the time being.

  12482   Mon Sep 12 17:15:22 2016 JohannesUpdateGeneralPRM SRM alignment

[Gautam, Steve, Johannes]

We put on the remaining heavy doors on the chambers (ITMY, ITMX,ETMX, in this order) this morning. On the ITMY and ETMX tables we placed old OpLev steering mirrors that are clean and baked as witness plates such that may one day provide some insight into dust accumulation on optics.

With the heavy doors on we confirmed that we were still able to lock both IFO arms and used the dither scripts to optimize the alignment. Following that we centered all OpLevs and aligned the X and Y green beams.

ITMY table witness plate
ETMX table witness plate

 

  12493   Wed Sep 14 19:41:23 2016 JohannesUpdateGeneralPSL back to high power

Today's summary:

  • Replaced mirror in MC REFL path with R=10% BS and aligned beam on PD while still at low power
  • Replaced HR mirror in Transmon path at EY table with 50/50 BS. Alignment onto QPD not yet confirmed because we need IR from the YARM for it.
  • Put ND filters back on Transmon QPDs at both X and Y ends. For now I put all the filters on, for a combined OD of 1.6 at both ends (1.0 + 0.6 at YEND and 1.0 + 0.4 + 0.2 at XEND).
  • Put ND filter back on Transmon CCD on EY table.
  • Reverted MC autolocker to nominal, high power version.
  • Raised PSL output power back to nominal level by turning the waveplate. At the PSL shutter I measured a power of 1.03W. It occured to me too late that I realigned the PMC only afterwards and increased its transmission by a few percent, so I'll have to re-measure the actual PSL power.
  • MC is locked with its transmission back up to ~15,400 counts. The autolocker is not very good at obtaining the lock, as it seems to try to turn the VCO gain up too far and loses lock. The script probably needs a revision.
  • The YARM was pretty badly aligned. We used the green light to visually center the beam on the test masses AND had to go exploring with the TTs to see IR flashes in the first place. We got the YARM to lock to IR and were able to run the dither alignment. The maximum transmission we saw was on the order of 0.85. However, something strange is happening with the LSC control of the armlength. When the lock is engaged it drives PIT and YAW, which manifests itself in the OpLev signal and variable transmitted power on the TRY PDs. Osamu helped us diagnose this and was able to reduce the effect by tuning the POS gains to the individual ETMY OSEMS. The problem persisted even after using the new matrix diagonalization coefficients, we'll have to investigate this further and also take a look at the filters in the feedback path.
  • ITMX is still stuck and way out of alignment, so we couldn't even start with the green light in the XARM.
  12524   Thu Sep 29 20:21:29 2016 JohannesUpdateGeneralYARM loss measurement

[Gautam, Johannes]

I scripted a series of YARM DC reflectivity measurements last night alternating between locked state and unlocked state (with ETMY misaligned) for measuring the after-vent armloss. The general procedure is based on elog 11810, but I'll also give a brief summary here.

  • To measure the locked reflectivity the dither script is executed with a stop condition that depends on the rms values of its error signals.
  • The dithering is stopped, and while the arm is locked the reflected power is recorded from both POX/POY DC and ASDC, as well as the mode cleaner transmission for normalization.
  • The arm locking is switched off, and ETMY moved to is 'misaligned' position. This gets rid off unwanted mode flashes.
  • In the unlocked state the same quantities are recorded.
  • Rinse and repeat for a set number of times (for this run I set it to 100 and left the interferometer alone).

I did this back in June (but strangely never posted what I found, shame on me). What I found back then was a YARM loss of 237 ppm +/- 41 ppm and an XARM loss of 501 ppm +/- 105 ppm

Last night's data indicates a YARM loss of 143 ppm +/- 24 ppm after cleaning with first contact. yeslaugh

THIS IS STILL ASSUMING THAT THE MODE-MATCHING HASN'T CHANGED. We had however moved ETMY closer to ITMY during the vent by 19mm. Gautam and I had some trouble setting up the ALS to confirm the mode-matching, but we're in the process of recovering the XARM IR beat.

  12528   Mon Oct 3 21:24:02 2016 JohannesUpdateGeneralXARM loss measurement

[gautam, johannes]

I started a script on Friday night to collect some data for a reflection armloss measurement of the XARM. Unfortunately there seemed to have been a hickup in some data transfer and some errors were produced, so we couldn't really trust the numbers.

Instead, we took a series of manual measurements today and made sure the interferometer is well behaved during the averaging process. I wrote up the math behind the measurement in the attached pdf.

The numbers we used for the calculations are the following:

While we average about 50 ppm +/-15 ppm for the XARM loss with a handful of samples, in a few instances the calculations actually yielded negative numbers, so there's a flaw in the way I'm collecting the data. There seems to be a ~3% drift in the signal level on the PO port on the order of minutes that does not show in the modecleaner transmission. The signals are somewhat small so we're closing the shutter over night to see if it could be an offset and will investigate further tomorrow. I went back and checked my data for the YARM, but that doesn't seem to be affected by it.

Attachment 1: ReflectionLoss.pdf
ReflectionLoss.pdf ReflectionLoss.pdf
ELOG V3.1.3-