| ID |
Date |
Author |
Type |
Category |
Subject |
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17795
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Fri Aug 18 15:40:23 2023 |
andrei | Update | PEM | Seismometer heater and temp sensors |
Dismantled the seismometer circuit
At Rana's request, Deven and I have pulled all the wires out of the seismometer at the X end that Adviat set up the heater and sensors for. Right now, the seismometer is uncovered (no can) and the can I had to move next to the server rack that is close to the X end. I am attaching pictures of both the seismometer and the can.
I now realize that I have not turned off the power supply for the heater. If someone can please turn off the power supply that is shown in Advait's elog, please turn it off and reply to this elog. If you are unsure which power supply to turn off, read the first line of the elog that I replied to. Thanks!
Advait's circuits have been removed from the seismometer and stored in a box underneath the desk at the end of the control room (see picture). There is even a label on the box which reads "ANDREI CIRCUITS". At the seismometer there are still a few BNC cables left there: these are the cables that were used to interact with Advait's circuits. They have labels on them so that I can put back the circuits when I come back/when the seismometer can is available again |
| Attachment 1: 20230818_114008.jpg
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| Attachment 2: 20230818_113959.jpg
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| Attachment 3: 20230818_114453.jpg
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17796
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Fri Aug 18 16:07:38 2023 |
deven | Update | PEM | Seismometer heater and temp sensors |
I've turned off the power supply. I've attached a picture of the rack with the switch that I flipped circled |
| Attachment 1: IMG_9136_(1).pdf
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-0.png "IMG_9136_(1).pdf")
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12
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Wed Oct 24 08:58:09 2007 |
steve | Other | PSL | laser headtemp is up |
C1:PSL-126MOPA_HTEMP is 19.3C
Half of the chiller's air intake was covered by loose paper |
| Attachment 1: htempup.jpg
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15
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Thu Oct 25 22:02:58 2007 |
rob | Routine | PSL | HEPAs maxed |
| In light of the SoCal fires, I turned the PSL HEPAs up to 100%. |
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81
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Wed Nov 7 16:07:03 2007 |
steve | Update | PSL | PSL & IOO trend |
1.5 days of happy psl-ioo with litle bumps in C1:PSL-126MOPA_HTEMP |
| Attachment 1: psl1.5dtrend.jpg
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84
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Thu Nov 8 15:57:53 2007 |
tobin | Configuration | PSL | shelf removed |
I removed the sheet metal shelf from the PSL enclosure, for easier access to the ISS.
ISS investigations ongoing. |
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85
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Thu Nov 8 18:44:01 2007 |
tobin | Configuration | PSL | ISS |
Tobin, Rob
With the Sense PD blocked, I adjusted the offset trim of the fourth stage in the ISS servo until the current shunt signal was zeroed. After this adjustment, we are able to crank the ISS gain all the way up to 30 dB without CS saturations (provided the HEPA is turned down to a very quiet level), getting about 35kHZ UGF at that gain setting. However, the current shunt mean value was still enormous.
Examining the current shunt signal on a fast scope, we saw an enormous (>2Vpp) 3.6 MHz sawtooth signal. Going up the chain of op-amps, we found that U1, as measured at the "Filter Out" testpoint, is oscillating wildly at 12 MHz (680 mVpp). |
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88
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Fri Nov 9 09:37:55 2007 |
steve | Update | PSL | head temp hiccup |
Just an other PSL-126MOPA_HTEMP hiccup.
The water chiller is at 20.00C |
| Attachment 1: headtempup.jpg
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89
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Fri Nov 9 17:33:33 2007 |
rob | Configuration | PSL | ISS |
The 3.7 MHz is actually on the light. It's the beat between the 29.5 MHz sidebands and the 33.2 MHz sidebands. There are pads in the ISS PCB for a filter to notch this frequency--John is working on it.
I also found a 1.2 ND filter on the lens which focuses the beam on the ISS diodes. I replaced it with a 0.6 ND filter, which brought the ISS DC level (on the screen) up to ~4.2 (it saturates at 5). Once John finishes the filter we should be able to crank up the gain. |
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90
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Fri Nov 9 21:36:14 2007 |
rob | Configuration | PSL | FSS |
rob, rana
We looked at the FSS a bit today. The most we could get out of it with the gain sliders was a UGF of around 95kHz. After a bit of tweaking the waveplate after the AOM, this got up to ~115kHz. We should be able to get at least 500kHz. This system needs a fair amount of work. |
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95
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Mon Nov 12 15:05:49 2007 |
rob | Configuration | PSL | FSS |
Spent a bit of time fiddling with the FSS again today. In a not-particularly-systematic manner, I raised the input-side of the 21.5MHz PC, adjusted the half-wave plate in front of it, touched up the RC alignment and the alignment onto the transmitted and reflected diodes. This got us a ~15% increase in
transmitted light, and I was able to push the UGF to 140kHz with the common gain slider at 30dB and the FAST gain slider at 22dB. The next options include adjusting the AOM setup, mode matching into the RC, and just increasing the pickoff fraction right from the getgo. |
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96
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Mon Nov 12 15:18:34 2007 |
rob | Update | PSL | ISS |
After John soldered a 3.7 MHz notch filter onto the ISS board, I took a quick TF and RIN measurement. The out-of-loop RIN is attached, including a dark noise trace, and with the gain slider at 10dB. The UGF is 35kHz with a phase margin of 30deg. John is currently doing a more thorough inspection, and will detail his findings in a subentry. |
| Attachment 1: ISS.png
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97
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Mon Nov 12 23:44:19 2007 |
John | Update | PSL | ISS |
| Quote: |
After John soldered a 3.7 MHz notch filter onto the ISS board, I took a quick TF and RIN measurement. The out-of-loop RIN is attached, including a dark noise trace, and with the gain slider at 10dB. The UGF is 35kHz with a phase margin of 30deg. John is currently doing a more thorough inspection, and will detail his findings in a subentry. |
No progress on the ISS tonight. I tried to implement a new filter (attached)to try and gain some phase before the notch. If anything this made things worse. More work is needed.
The ISS loop is off and the power is off at the chassis. |
| Attachment 1: ISSfilter.jpg
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98
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Tue Nov 13 14:33:40 2007 |
John | Update | PSL | ISS filter |
The transfer function from 'In Loop Error Point Monitor' to TP3 the filter out test point on the ISS board.
-33dB at 3.715MHz. |
| Attachment 1: PB130035.JPG
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| Attachment 2: DSC_0165.JPG
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101
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Wed Nov 14 12:47:19 2007 |
tobin | Update | PSL | ISS |
John, Tobin
With John's notch filter installed and the increased light on the ISS sensing diode, we were able to get a UGF of about 60 kHz with the gain slider set to about 20 dB. This morning we met with Stefan to learn his ISS-fu.
His recommendations for the ISS include:
- Replace the cables from the board to the front panel connectors if this hasn't already been done.
- Replace the input opamps with 4131's. Be sure to test both positive and negative input signals.
- Check that all the compensation capacitors are in place and are 68 pF
- Make sure all the feedback loops have high frequency rolloff
- The ISS board reads the PDs differentially; make sure the PD sends differentially.
- Add a big (ie 10uF tantalum) capacitor to the PD to suppress power supply noise
- Add bigger power supply bypass caps to the ISS
I just took sensing noise spectra (from the PD DC bnc ports) and then took the photodiodes off the table to check that they have the negative end of the differential line connected to ground. (I placed black metal beam blocks on the table in place of the ISS PD's. Also, from the ISS schematic, it looks like it sends a differential output to the PD DC bnc ports, but we have been plugging them directly into the SR785 (grounding the shield). We should make a little BNC-doodle that separates the signal+shield to go into the A and B inputs on the spectrum analyzer.) Opening up one of the photodiodes, it appears that the negative line of the differential output is not connected. Will continue later this afternoon. |
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103
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Wed Nov 14 17:50:00 2007 |
tobin | Update | PSL | ISS |
Here's the current wiring between the ISS and its PDs:
|
pin | cable | PD | ISS | |
1 | blue | +5 | +5 | |
2 | red | +15 | +15 | |
3 | white | -15 | -15 | |
4 | brown | OUT | IN PD + | |
5,6,7,8 | no connection | no connection | GND | |
9 | black | GND | IN PD -
|
The schematics for the ISS and the PDs are linked from our wiki.
We'll connect the ISS GND to the PD GND. |
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104
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Thu Nov 15 04:18:11 2007 |
John | Summary | PSL | PMC cavity pole measurements |
In connection with our work on the ISS I attempted to measure the PMC cavity pole.
I swept the PMC PZT and looked at the transmission through the cavity on the ISS Monitor diode (which is now back on the table, feel free to remove it again tomorrow).
To avoid thermal effects I reduced the laser power using the half wave plate at the laser ouput (rotated from 6 deg to 340deg).
I swept the PZT using the triangle wave command "trianglewave C1: PSL-PMC_RAMP -3.5 3.3 20 200". I noticed that the functional form of the resonances deteriorated over the duration of the excitation. Each sweep was able to capture just over one FSR. The resonances were a little close to the 'points' of the triangle wave for my liking although I don't think PZT hysteresis was a big factor.
Looking at the data the peaks are not of uniform width across a sweep or between consecutive sweeps. Hence any results from this mesurement are not particularly useful. I can't be sure if this was due to misalignments, thermal effects, higher order mode content or some other affect.
Rob suggests sweeping the laser frequency using the NPRO PZT instead. |
| Attachment 1: Peaks.jpg
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116
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Tue Nov 20 10:11:33 2007 |
John | Summary | PSL | PMC pole measurements |
We measured the PMC pole in the following way.
1. Reduced laser power by rotating lambda/2 plate at laser output. Thermal effects in the PZT distort resonance peaks. Reducing power too much leads to problems with digitisation error.
2. Sweep NPRO PZT (C1: PSL-FSS_INOFFSET) using trianglewave. Record ramp, PMC transmission and reference cavity transmission ('C1: PSL-FSS_FAST','C1: PSL-ISS_INMONPD_F','C1: PSL-FSS_RCTRANSPD_F).
3. Since the PZT cannot sweep a full FSR in the PMC we looked at the sideband resonances within the reference cavity to calibrate the actuator.
Result: 7.35 +/- 0.22 MHz/V
4. Use #3 to calibrate the x axis of the PMC transmission.
5. Fit PMC resoances to an Airy function to get finesse. Take an average, weighted according to the resnorm. Calculate cavity pole frequency.
Result: 380kHz +/- 59kHz. This corresponds to a finesse of ~936. According to this plot the nominal pole is at 488kHz and the finesse is 732.
This is by no means a definitive measurement due to the misshapen resonance peaks recorded. |
| Attachment 1: FittedPMCPeak.jpg
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121
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Wed Nov 21 14:31:41 2007 |
rob | Update | PSL | FSS twiddle |
I `tweaked' the FSS path today. Here's what I did:
1) Shut down the FSS autolocker
2) Turn off FSS servo
3) Assume the beam coming back from the AOM is double-first-order, and don't make any changes large enough to lose it.
4) Tweak the alignment of these components to maximize the incident power on the RC reflected diode:
a) PBS before AOM
b) AOM
c) curved mirror after the AOM
5) Translate the AOM such that the beam moves away from the PZT, then when it levels off (no more power gains with movement),
move it back just a little bit so there's a teensy drop in power. This should but the beam as close to the edge as possible,
but whether or not it's the best place is still to be determined.
6) Lock the FSS, and align the mirrors into the frequency reference cavity.
After all this, the RC transmitted power went from .57 to .73 -- probably not a big enough change to account for the missing loop
gain, but we'll know more once the loop gets measured (after Alberto stops hogging the Agilent network analyzer).
Other possible routes include a systematic check of the upstream path (e.g., the Pockels cell) and just increasing the pickoff fraction for the FSS. |
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124
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Tue Nov 27 15:45:08 2007 |
rob | Configuration | PSL | FSS loop |
It's unclear (to me, at least) what was the end result of the FSS path tweaking before Thanksgiving. Today I measured the open loop gain, and it was still around 100kHz, even with the gain sliders maxed out, but it looked really crappy with a sharp cutoff around the UGF. Then, on a lark, I pushed around the "Input Offset Adjust" slider, which sums an offset into the signal coming out of the mixer. By moving this slider to 7V, I got the UGF to 500kHz with 45 deg of phase. That would be fine, and we could go offset hunting, but the same thing happens if one puts in a large negative value! I don't really understand what's going on, but it seems like weirdness in the electronics. Unfortunately the web interface to the conlog is not running (presumably because the `new' linux1 doesn't have its apache server running) and my command line conlog efforts have been stymied. So, I don't know what the historical settings of this offset are, but zero is definitely not a good setting right now. Here's a snapshot:
FSS
UGF: 500kHz
CG : 24dB
FG : 19dB
input offset: 7V
Phase Adjust: 1.09V
Phase Button: 0
RF Amp Adjust: 7.38V
margins:
phase: 45 deg
gain: 8dB |
| Attachment 1: FSSsmall.jpg
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127
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Tue Nov 27 20:47:00 2007 |
tobin | Update | PSL | FSS |
Rana, Tobin
We looked at the RF PD signal to the FSS (siphoning off a signal via a minicircuits directional coupler) and also took an open loop transfer function of the FSS. In the transfer function we saw the step at 100 kHz (mentioned by Rob) as well as some peculiar behavior at high frequency. The high frequency behavior (with a coupling of ~ -20 dB) turns out to be bogus, as it is still present even with the beam blocked. Rearranging the cabling had no effect; the cause is apparently inside the FSS. The step at 100 kHz turns out to be a saturation effect, as it moved as we lowered the signal amplitude, disappearing as we approached -60 dBm. (Above the step, the measurement data is valid; below, bogus.)
Transfer functions will be attached to this entry.
Some things to check tomorrow: the RF signal to the PC, RF AM generation by the PC, LO drive level into the FSS, RF reflection from the PC, efficiency of FSS optical path, quality of RF cabling. |
| Attachment 1: fss-tf0001.pdf
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128
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Wed Nov 28 04:21:46 2007 |
rana | Update | PSL | FSS |
| Quote: | Rana, Tobin
We looked at the RF PD signal to the FSS (siphoning off a signal via a minicircuits directional coupler) and also took an open loop transfer function of the FSS. In the transfer function we saw the step at 100 kHz (mentioned by Rob) as well as some peculiar behavior at high frequency. The high frequency behavior (with a coupling of ~ -20 dB) turns out to be bogus, as it is still present even with the beam blocked. Rearranging the cabling had no effect; the cause is apparently inside the FSS. The step at 100 kHz turns out to be a saturation effect, as it moved as we lowered the signal amplitude, disappearing as we approached -60 dBm. (Above the step, the measurement data is valid; below, bogus.)
Transfer functions will be attached to this entry.
Some things to check tomorrow: the RF signal to the PC, RF AM generation by the PC, LO drive level into the FSS, RF reflection from the PC, efficiency of FSS optical path, quality of RF cabling. |
I would also add to Tobin's entry that we believe what Rob was seeing was saturation.
With the bi-directional coupler in there, the RF signal into the FSS board clearly went UP if moved the offset slider away from zero.
With a scope looking at the IN2 testpoint, we can see that there's less than 2 mV offset at zero slider offset.
One tangential thing we noticed with the coupler is that, in lock, the amount of reflected RF is around the same as that going in to the mixer.
I have always wanted to look at this but have only had uni-directional couplers in the past. I think that the double balanced mixer is inherently
not a 50 Ohm device during the times where the diodes are being switched. IF that's the case we might do better in the future by having an RF
buffer on board just before the mixer to isolate the PD head from these reflections. |
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134
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Wed Nov 28 17:41:34 2007 |
rob | Update | PSL | FSS again |
| I investigated the FSS a bit more today. I looked at the signals coming out of the FSS frequency reference, and saw that both the LO and PC drive were distorted, non-symmetric waveforms. In addition, the LO path had a 3dB attenuator, meaning the mixer was starved. I placed mini-circuits SLP-30 filters in both paths, and now both are nice sine waves. I also took out the 3dB att. With this work, and the CG slider maxed out at 30, the FSS open loop gain (for real this time) goes up to ~250kHz. Still needs more investigation. |
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136
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Wed Nov 28 19:44:18 2007 |
tobin | Update | PSL | HEPA |
| I found the HEPA turned off completely. I turned it on. |
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137
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Wed Nov 28 21:51:52 2007 |
tobin | Configuration | PSL | ISS |
I replaced the front-end differential receivers for the ISS's "inner-loop" sensor and monitor diode inputs with lower-noise THS4131's (formerly THS4151's). I verified operation by taking the transfer function from the "PD+" and "PD-" inputs (separately) to the testpoint following the differential receiver; the surgery appears successful.
I measured the dark spectra at the ISS's DC PD BNC ports and found a noise floor of ~ 16 nV/rtHz, compared with a floor of ~ 22 nV/rtHz last week. This seems to add up, assuming the DC PD port has 0dB gain: the 4131 has a rated noise of 1.3 nV/rtHz and the 4151 a noise floor of 7.6 nV/rtHz, a difference of 6 nV/rtHz. The other change made in that time was to add a larger power supply bypass capacitor in the PD.
There are two of the old 4151 chips still on the ISS board on the two "outer-loop" channels that we don't use. If I dig up any more 5131's I will replace these too for completeness.
There is currently no light on the ISS diodes; I'm not sure where it's intended to come from. |
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141
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Thu Nov 29 15:17:53 2007 |
rob | Configuration | PSL | ISS |
I put some ISS beam on the diode on the PSL table. In the previous layout, this was the monitor diode (and it's labeled monitor) but I plugged it into the sensor jack anyways so we can run with the loop closed for now; we can just switch the cables later. The reason the beam was unclear is because someone popped up a flipper mirror which redirects the beam from the ISS into an OSA.
With the ISS gain slider at 15 dB the UGF is around 40kHz.
Why do we have such short cables for the ISS diodes? |
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162
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Mon Dec 3 22:20:09 2007 |
tobin | Configuration | PSL | ISS |
| I replaced the painfully short 1' cables on the ISS photodiodes with luxurious five foot cables, made by chopping a ten foot Amphenol cable (P/N:CS-DSPMDB09MM-010) in half and using each half for one of the diodes. All of the ISS GND connections are wired to the PD GND, as is the PD- differential signal. The diodes are installed on the PSL table, but I have not tested them beyond looking at the DC values as I blocked/unblocked the beam. |
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163
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Tue Dec 4 23:16:35 2007 |
tobin | Update | PSL | ISS |
I was confused to find that I could increase the ISS gain slider all the way from 15dB to 30dB without seeing much of any increase in gain in the measured open-loop transfer function. While making these swept-sine measurements, the saturation indicator almost never tripped, indicating it was seemingly happy. But then I noticed an odd thing: if I disable the test ("analog excitation") input, the saturation indicator trips immediately. I hooked up a scope to the current shunt test point (TP12). With the test input enabled, the loop closed, and the analog excitation port connected to the SR785, I see a a 5 Vpkpk, 2.55 MHz triangle wave there. It is there even if I set the SR785 excitation amplitude to zero, but it disappears if I disconnect the cable from the SR785.
I found oscillations at TP20, TP30, TP36, TP41, and TP42. Many of these are in the (unused) "outer loop" circuitry and currently lack compensation capacitors. |
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167
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Wed Dec 5 17:49:57 2007 |
tobin | Update | PSL | ISS |
Attached is a plot of the ISS RIN with a variety of gain settings.
Unfortunately the dark noise is huge now--a result of the new cables & wiring? |
| Attachment 1: rin.pdf
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169
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Wed Dec 5 18:22:03 2007 |
tobin | Update | PSL | ISS dark noise |
| Attached is a plot of the dark noise spectrum of the ISS photodiodes (1) before fooling with them, (2) after replacing the 4151's with 4131's (improvement!), and (3) after replacing the cables and changing the wiring (disaster!). |
| Attachment 1: sense_noise.pdf
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171
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Wed Dec 5 20:32:51 2007 |
tobin | Update | PSL | ISS dark noise |
The ISS dark noise is not coming from the PD heads; the spectrum is essentially unchanged when the PD is unplugged from the ISS. Did the input opamps both get semi-fried in the same way? (They worked so well when they were first installed.) What else changed? I'm baffled.  |
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177
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Thu Dec 6 19:30:43 2007 |
tobin | Update | PSL | ISS dark noise - 60 Hz! |
A higher resolution spectrum [attached] shows that nearly all of the excess dark noise on the ISS is in 60 Hz harmonics (with some 256 Hz harmonics too--are these from the DAQ?).
With the loop closed and the slider at 5dB, the laser light coming out has a noise floor of 10^-7 RIN or better from 40 Hz to 8 kHz.
Now to figure out why all this 60 Hz is getting in... (I tried turning off all the lights and the HEPA, and moving the SR785 further away, none of which did anything.) |
| Attachment 1: iss.pdf
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183
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Fri Dec 7 19:14:30 2007 |
tobin | Update | PSL | ISS dark noise - ground loop enlightenment |
My alleged 60 Hz harmonics were all from a ground loop created by connecting the SR785 ground to the ISS circuit ground; they disappeared when I set the SR785 input to "floating ground." doh!
I modified the ISS PD's to have a 100 ohm resistor in series with the output (in place of 20 ohms). The diodes are again in place on the table, ready for action. |
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185
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Mon Dec 10 18:42:20 2007 |
tobin | Update | PSL | ISS RIN script |
I wrote a script to measure the ISS RIN. The script uses the "labca" interface (described in an earlier entry) to read and twiddle EPICS settings and mDV to get DAQ data. The script measures open loop RIN, closed loop RIN at each of several gain slider settings, and dark noise. The dark noise is obtained by misaligning (unlocking) the PMC. The script also compares the whitened and unwhitened spectra for an open loop measurement and performs a fit of a simple pole to find the dewhitening filter.
This is all very exciting, but I don't quite believe the results, since the closed loop RIN seems to bottom out at 2e-7/rtHz regardless of the gain slider setting.
Sample output attached. The script may be found at scripts/PSL/ISS/rin.m. |
| Attachment 1: rin-20071210-1831.pdf
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186
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Mon Dec 10 19:08:03 2007 |
tobin | Configuration | PSL | MZ |
The MZ seems finicky today--it keeps unlocking and relocking.
I've temporarily blocked one of the MZ arms while I work on the ISS. |
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197
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Tue Dec 18 21:31:31 2007 |
tobin | Update | PSL | ISS RIN |
| My measurements of the ISS RIN via the SR785 and via the DAQ disagree considerably. The spectral shapes are very similar, however, so I expect that a constant factor is creeping in somewhere. Measurements taken at the PD DC monitor points using the SR785 attached. There is a lot of excess noise in the 300 Hz - 1 kHz region. |
| Attachment 1: iss-rin.pdf
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211
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Sat Dec 22 00:52:57 2007 |
tobin | Configuration | PSL | ISS surgery |
| In an attempt to quell oscillations in the (unused) outer loop portion of the ISS, I shorted the "PD+" and "PD-" signals from the (nonexistent) outer-loop diodes, and soldered in 47pf compensation capacitors in C92 and C220. This seems to have eliminated oscillations seen at TP41 and TP42. There's still something amiss at TP30 and maybe TP20. Otherwise, the ISS seems happy. I can turn the gain slider to +15dB without saturation (with the HEPA off), though there seems to be less light on the diode (~3.9V) than a week or two ago. |
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221
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Thu Jan 3 09:12:59 2008 |
steve | Update | PSL | MZ servo |
Here is MZ trend for one year and 40 days.
Now days it runs out of range on the low side.
This is the weakest link in the psl today. |
| Attachment 1: mz1y.jpg
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| Attachment 2: mz40d.jpg
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293
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Fri Feb 1 17:17:05 2008 |
John | Summary | PSL | Mach-Zender tweaking |
I helped Rob adjust the alignment of the Mach-Zender to try and reduce any AM on the laser light. Our goal was to reduce the large offsets in the DD signals.
We reduced the MZ refl from 0.54 to 0.39. We were able to re-lock the mode cleaner without problems. We then centred the WFS heads.
No change in the DD signal offsets. |
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325
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Wed Feb 20 11:34:17 2008 |
steve | Update | PSL | laser head temp is up |
MOPA head temp is running at 20.3C now
Nomally it is at 18.5C |
| Attachment 1: htempup.jpg
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326
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Wed Feb 20 16:24:37 2008 |
steve | Update | PSL | the laser is recovering slowly |
Head temp is still 20.5C and decreasing slowly.
Power output 2.9W
NPRO power 22 mW is increasing as head is cooling down |
| Attachment 1: laserecoverring.jpg
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327
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Thu Feb 21 09:56:26 2008 |
steve | Update | PSL | the laser is back |
The laser and the psl recovered.
The water chiller temp is 19.98C and head temp 18.4C
Power 3.2W
PMC_T 3.1
c1iovme was restarted and the mc is locking now |
| Attachment 1: laserisback.jpg
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365
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Fri Mar 7 19:04:39 2008 |
steve | Omnistructure | PSL | laser pointer |
Green laser pointer was found in my desk.
I blamed Rana for not returning it to me after a conference talk.
It is surprisingly bright still.
I will bring sweets for Wednesday meeting. |
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450
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Fri Apr 25 15:44:21 2008 |
steve | Update | PSL | scattering measurments |
In pursuit of a low back scattering, high power beam dump we looked at materials such:
polished copper, polished aluminum, diamond cut aluminum, variety of polished & heat treated stainless steel and shades of black glasses.
Black glass is ideal at low power. Superpolished SS 304 #8 is the only material that measures close to bg
We are still looking for a conductive low back scattering material that would be ideal for a good high power beam trap.
Black glass-shade 12, ss304 superpolished #8 and white paper-B98-24lbs back scattering were compared at 1064 nm
Atm 1: data plot numbers from front panel of SR830 display,
sensitivity: 1x1 mV for bg and ss
1x1 V for wp
Atm 2: drawing of measurement set up
Atm 3: SR830 lock.amp settings
Atm 4: view from steering mirror
Atm 5: view from black glass trap
Atm 6: white paper |
| Attachment 1: scatmeas20080425.xls
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| Attachment 2: scattring_set_up_20080425.ppt
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| Attachment 3: sr830settings.pdf
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| Attachment 4: viewfmirror.pdf
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| Attachment 5: viewfbgtrap.pdf
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| Attachment 6: wpnmount.pdf
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479
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Thu May 15 12:05:49 2008 |
josephb | Configuration | PSL | Path to PSL Position QPD |
The 50/50 beamsplitter that was being used as the last turning mirror to the PSL Position QPD has been replaced with a Y1-1037-45-S plate. This turning mirror was also moved 4" farther along the beam path, so as to produce as small (few microwatts) transmission through the plate. The lensing optics were also shifted so as to maintain a focused beam on the photodiode. Lastly, the rotating ND filter was increased from 1.5 to 2.0 to reduce the incident power on the photodiode, since twice the power is now reaching it.
The small beam on transmission will be used by the digital cameras as a test beam. |
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Sun May 25 20:30:25 2008 |
rana | Summary | PSL | PMC Mode Matching |
I checked the PMC mode matching by ramping the gain down to -10 dB (from +20 dB) and
moving the DC offset around until it caught lock on the different HOMs. Then I recorded
the output power (PMCTRANSPD). The DC offset on this EPICS channel was -0.013 V, so I
used its AOFF field to zero this out. Here is a list of the power in the largest modes:
Mode Power (V)
---- ---------
00 2.7
10 0.2
04 0.04
02 0.02
BE 0.36 **Bull's Eye mode is TEM02 + TEM20. This can be fixed by lens adjustment.
N.B. To make a PNG file with DTT, just make an EPS file -- then use the eps2png perl script. |
| Attachment 1: pmc.png
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Wed May 28 14:19:47 2008 |
steve | Update | PSL | kaleidoscope of psl |
atm 1: scattering psl table optics from the top of the output periscope f4, 60s @MOPA 3 W
atm 2: scattering psl table optics from the top of the output periscope f4, 20s
atm 3: competing GigE cameras on the north end of psl table
atm 4: yellow "soft" washer to be replaced on psl output periscope
atm 5: ETMY-ISCT in disarray |
| Attachment 1: pslscat.png
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| Attachment 2: pslscat2.png
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| Attachment 3: 2GigEs.png
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| Attachment 4: perwash.png
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| Attachment 5: etmydisarray.png
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Wed Jun 4 10:18:52 2008 |
steve | Update | PSL | wedged SS beam trap |
I moved the SS trap over to the psl table.
Texas super # 8 was used from the large shipment.
TXs#8 scattering measured as before, meaning the polishing is good.
Go's squeezing power pick up 350 mW was used.
I made two ~30 degrees wedge traps using 6" x 4" and 12" x 4" SS 0.039" thick
with copper backing of similar size.
There was too much scattering and I could not minimize them all.
It is very helpful to have so much space on the psl table.
It shows more of the weakness of this kind of trap.
I did not dare to turn up the power. |
| Attachment 1: trap1.png
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| Attachment 2: trap2.png
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Fri Jun 6 16:10:51 2008 |
steve | Update | PSL | HEPA filters are running at 100% |
| The psl HEPA filters were turned up to run at 100% to accommodate beam trap work on Tuesday, June 3, 2008 |
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Mon Jun 9 17:32:14 2008 |
Yoichi | Configuration | PSL | PMC transmittance |
I checked the current PMC transmissivity at a low power.
The input laser power to the PMC was reduced to 75mW by rotating the HWP in front of the PBS.
In this configuration, the output power from the PMC was 50mW. So the transmittance is about 66%.
The reading of C1:PSL-PMC_PMCTRANSPD is now 0.1 whereas it was 2.7 before turning the power down.
I will check the transmittance at a higher power when I get the cable for the 35W calorie meter, which is missing now. |