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ID Date Author Type Categoryup Subject
  1885   Sun Aug 17 15:49:22 2014 EvanThings to BuyPMC1064 nm PMC

Status of hardware:

  1. Optics: ordered. Delivery expected week 45 of 2014.
  2. Spacer, endcap, clamps: am waiting for one more quote early next week, then will put in the order. Lead time of quotes I've gotten so far is 4 weeks ARO, so the metal bits will probably arrive before the optics.
  3. PZTs: already here.

Left to do:

  1. PZT driver circuit [see D060283 for OMC HV D1300024 for OMC LV]
  2. How to glue PZT + mirror? [see omc:88, perhaps others]
  3. Heater circuit
  4. Mount
  5. Sapphire seats (may delay this until after we have a few PMCs built)
  6. O-rings
  7. Strain relief for PZT wire
  8. Design guide/manual/test procedure
  5   Fri Oct 26 15:38:43 2007 Tobin FrickeLaserPSLPolarizer
On Tuesday we installed a λ/2 plate and a polarized beamsplitter after the laser aperture; attached to this entry is a measurement of transmitted power versus polarizer angle.
Attachment 1: polarizer.pdf
polarizer.pdf
Attachment 2: polarizer.m
% Polarizer calibration / Rana's lab
% Tobin Fricke 2007-10-26

% Experimental setup:
%                                [Dump]   
%                                  |
%  +-------+                       |
%  | Laser |-------|lambda/2|----|PBS|----[Power Meter]
%  +-------+ 
%  
... 53 more lines ...
  6   Sun Nov 4 23:44:36 2007 ranaLaserPSLMore Laser setup info
Brought over a PMC mount from the 40m which Nergis is letting us borrow. Steve has made up a plate to
adapt that up to a 4" height from 3".

Still to do to get the optics of it set up:

  • RF Amp to boost the 35.5 MHz Wenzel
  • Attenuators to get the splitter output to not destroy the LO
  • Bandpass filters for 35.5 MHz
  • RFPD to take the PMC reflection and do locking
  • 2 steering mirrors
  • Mode matching lenses
  8   Thu Nov 8 18:54:41 2007 StefanLaserPSL35W laser ISS loop closed with LIGO ISS electronics
I closed the ISS loop using a iLIGO type ISS board, with an additional 2kHz pole at the last stage.

I haven't carefully measured noise or OLG yet, but it is not famous yet:
Looking at the in-loop diode I get a RIN of ~3e-7/rtHz at 100Hz, and ~1e-8 at 10kHz.

The gain is limited by two sharp resonances that rise at ~40kHz when the gain is increased.

TBD:
- Fix the ISS test point wiring - these cables have 800Ohm resistance!
(No not impedance... shield to core measures 800Ohms at DC...)
This brought back painful mamories from ~3years ago when we installed
the H1 ISS... apparently the known problem wasn't fixed on all versions.
- Measure OLG, in particular check whether weird AOM transfer function still
exists - it could be killing our gain.
- Measure sensing noise in-situ
- Install sensitive OL PD
  9   Mon Nov 12 21:33:41 2007 StefanLaserPSLISS servo work
I fixed a few things on the ISS board:
- Fixed the input THS4131 on the ISS board
- Fixed all monitoring point cables for the inner loop part.

With that I was able to lock the ISS with up to 400kHz UGF (limited by variable gain at max).

The sensing noise is about 60nV/rtHz at 100Hz without light, but there is some additional noise pick-up when the VCO driver is connected.

The In-loop noise, with 6V DC (~8mWatt on the diode) and a UGF of 400kHz is
100Hz: 170nV/rtHz (2.8e-8/rtHz)
200Hz: 60nV/rtHz (1.0e-8/rtHz)
500Hz: 50nV/rtHz (8.3e-9/rtHz)

The out-of loop noise is still a lot worse ( a few e-7/rtHz at 100Hz), but that's not surprising:
The table is quite noisy and not much care went into choosing good mounts.
  10   Tue Nov 13 19:06:18 2007 ranaLaserPSLISS servo work
400 kHz !? Wow.

We should lower the resistors in the PD head so that we can put ~20-30 mA per diode
and use the ISS style diodes for both the in-the-loop as well as out-of-loop diodes.


Then we have to dump the beams reflecting off the diodes onto razor dumps and also
put in a lens so that the beam has a 0.3 mm dia. on the diodes.


Then we make an acrylic box with an entrance hole for the beam and put it over both
diodes.
  17   Wed Dec 26 21:30:05 2007 ranaLaserPSLlaser power
I have rewired the laser power so now the Diode Box goes directly to one of the
overhead umbilicals (circuit #29) which is energized by the wall switch which
is marked as "Master Laser". Cutting off that switch is NOT the desired way to
power down the laser; use the Beckoff touchpad instead. The wall switch is the
emergency cutoff.

The HEPA fans on the laser table are both routed to power strips on the table now.

With the laser on, the beam looks well clipped. As far as I can tell this comes
from inside the box so the next thing is to do a little more re-alignment inside
the box.

Also need some more lenses for cameras and more IR cards.

And we should slice the tires of anyone who borrows equipment without leaving a note!
  20   Mon Jan 28 16:51:06 2008 Stefan BallmerLaserPSLPDH locked pre-mode cleaner
Since we suspect that the ISS might be jitter-noise limited I started looking at the Pre-Mode Cleaner (PMC).

- Did a rough mode-matching with one lense into the PMC
- Aligned the PMC. Note that the camera is now in transmission of the PMC.
- Used 3MHz drive to the laser's EOM and a photo diode in reflection of the PMC for
PDH locking. Successfully closed the loop using a mixer and SR560, driving
the laser's piezo - however only on a 2-0 mode.
- The 30V power supply I currenctly use to pre-set the PMC PZT does not have
enough range to scan a full FSR, and I can't get the 00 mode into range.

David - feel free to dismantle the path into the PMC and properly measure the beam parameters.
  24   Wed Jan 30 12:57:53 2008 DmassLaserPSLCharacterizing Beam
1/28/08 - Took a series of beam waist measurements on the YAG.


-The polarizations (as measured by the photon beamscanner) had very different profiles. One polarization has a dual peak (probably a reflection from some optic). This shows up after the beam has passed through the polarizer, the PBS, and one mirror.

-Initial beam characterization yielded a waist inside the Laser Box by ~3", at a width of 200 microns. Will be rechecking this. (Impossible if there is a lens at the opening, which I'm not sure is the case).
  28   Tue Feb 12 16:54:13 2008 DmassLaserPSL35W profile/waist
The beam output by the 35W in 058 was significantly elliptical (up to a 10% difference in the waist measurements). I used the profile given by the "more gaussian" axis, and found a waist 9.7 cm inside the front of the enclosure, 250 microns in radius. We ended up using this axis to mode match to, but this ellipticity will probably need to be addressed as we try to maximize the power output through the PMC.

[plots to be added]
  29   Tue Feb 12 17:00:35 2008 DmassLaserPSLMode Matching/Lock
I got a solution for mode matching the 35W to the PMC with 2 100mm (focal length) lenses. I abandoned this since they were deemed too fast by Stefan, and were seperated by ~1 focal length. We ended up using a 1m and .5m lens (all lenses from the newport kit in 058). My code choked on this solution and needs some bugs ironed out (will attach afterwards), so we used Stefan's.

We then managed to get a 00 lock, at a somewhat meager power throughput. Pictures of the layout below:
Attachment 1: PMC_MM.JPG
PMC_MM.JPG
Attachment 2: lenses_mmJPG.JPG
lenses_mmJPG.JPG
  30   Sat Feb 16 13:46:19 2008 DmassLaserPSLLaser Aperture closed.
Laser was powered up with the aperture closed. It was fairly warm to the touch. I opened the aperture. I don't know if it is a "bad thing" to be dumping all 35W on the stop for large times. Sat @ 1:40.
  31   Sat Feb 16 15:33:25 2008 DmassLaserPSLRadial Beam Profile
The following were taken with the beam scanner (having gone through a number of optical elements).

After leaving the main laser housing, the beam hits:
polarizer -> PBS -> low reflectivity pickoff mirror -> 1m lens -> 0.5m lens -> 45-P HR mirror -> 45 P HR mirror -> beamscan.

In taking my initial waist measurements, I had the beamscan after the LR pickoff, and the beam looked similar.
Attachment 1: 2_16_0835w.bmp
  37   Tue Mar 4 16:00:28 2008 DmassLaserPSLISS
I moved the (non logging) ISS PD after the PMC, and changed the mirror/camera setup some.

Setup post PMC should now have ~5% of the power going to the camera, with the rest going to a BS for the ISS photodiodes.
  42   Mon Apr 7 16:43:15 2008 DmassLaserPSLProfile of 35W PSL
I scanned the beam on the 35W laser again (for the first time since it was fixed by our German friends during the LSC meeting).

A picture of the setup is below.

Images of the profile, 2d and 3d are below as .bmp, and the generating data for these is in Apr7_08scan.asc (zipped text)

This profile is significantly cleaner than the one measured in entry 31 of the elog.
Attachment 1: scancap.png
scancap.png
Attachment 2: 3dbeamprof.bmp
Attachment 3: flatprof.bmp
Attachment 4: Apr7_08scan.asc.zip
  45   Tue Apr 22 16:25:24 2008 robLaserPSLProfile of 35W PSL

Quote:
I scanned the beam on the 35W laser again (for the first time since it was fixed by our German friends during the LSC meeting).



What did they fix? And how?
  46   Tue Apr 22 20:07:50 2008 DmassLaserPSLProfile of 35W PSL
The total power seemed to be down about 10%, and that lower number was divided between two beams at the output. They opened up the amplifier and realigned things within it, which seems to have fixed the multibeam/lower power we were encountering before.


Quote:

Quote:
I scanned the beam on the 35W laser again (for the first time since it was fixed by our German friends during the LSC meeting).



What did they fix? And how?
  47   Fri Apr 25 13:33:35 2008 DmassLaserPSLpower drift
Here is a trend of the power drift taken over 10 days. The units are in counts produced by a photodiode stationed at a lower power pickoff of the beam.

The first plot is a full 10 days - you can see the times during which the laser was off where the counts go to zero.

The second plot is the full data over 10 hours, which seems to imply that the sharp increases in power are real.

Negative values correspond to an increase in power.
Attachment 1: trend2.png
trend2.png
Attachment 2: trend3.png
trend3.png
  49   Fri May 2 21:39:13 2008 DmassLaserPSLLaser power on table lowered
I have changed the polarizer before the polarizing beam splitter to minimize output power.

I did this to measure the PMC pole at as low a power as possible.

This will make power trends (which are picked off after the PBS) look VERY low for a bit.
  63   Thu Jul 17 16:44:27 2008 DmassLaserPSLLaser is off
Leaving laser off while I hack at screens downstairs. Feel free to turn on for anything.

I also turned the ISS drive box off.
  68   Fri Jul 25 15:23:14 2008 DmassLaserPSLNew Vertical PSL
With the installation of the new "clear top" on the PSL (see picture), an interesting design feature has come to light.

There are a few noteworthy things about this feature:

-We have a vertically oriented window after the NPRO.
-The vertically oriented window shoots some beam up.
-The new clear top appears to be transparent to IR.
-The HEPA filter is right above the window.

Possible worries:

-Light leaking back into the NPRO.
-Dumping beam onto the HEPA filter might not be the best thing.

It might be a good idea to do a proper dumping of that beam. I am unsure as to whether it would be better to do so inside or outside the enclosure.
Attachment 1: NPRO.png
NPRO.png
Attachment 2: HEPA.png
HEPA.png
  84   Tue Sep 2 22:48:47 2008 DmassLaserPSLConnectors needed
I am trying to chase down the source of the long time scale sharp fluctiations in intensity. I need to start reading out the diagnostic PD from inside the MOPA head unit to see if the power fluctuations are coming before or after the amplification (e.g. NPRO or MOPA problems).

I need the following connectors from Wilson house:
Attachment 1: connectors.png
connectors.png
  89   Fri Sep 5 03:24:37 2008 DmassLaserPSLConnectors needed

Quote:
I am trying to chase down the source of the long time scale sharp fluctiations in intensity. I need to start reading out the diagnostic PD from inside the MOPA head unit to see if the power fluctuations are coming before or after the amplification (e.g. NPRO or MOPA problems).

I need the following connectors from Wilson house:



Update: I talked to Peter King about swapping the chiller which appears to be the cause of the fluctuations in the power. Our current model, as the prototype, is an earlier generation from what he has, which is current with what is on site. He needs to talk to LZH to figure out if there is any additional hardware we need for the swap.

He also said that the sites used Deionized water for cooling, but said that filtered water would probably be fine. I did not get a good definition on what "filtered" consisted of. If we did move to DeI, then we might need some new plumbing. I told Peter that if things needed to be purchased we would find the money if it meant pulling copper piping from homes in Inglewood.

As we think this is the problem, I may wait on setting up data logging from the diagnostic (pre-mopa) photodiode in the head unit.
  91   Tue Sep 9 16:36:01 2008 DmassLaserPSLConnectors needed
I got the replacement chiller (a Neslab Thermoflex1400) from 046 W. Bridge. I unpacked it and moved it by the PSL optics table in 058 W. Bridge. Peter King called LZH and is going to make the connector adaptation we need for the new Chiller unit.

I also siphoned the water out of the old chiller to see what plumbing fittings we may need in moving to the new unit. It was delicious.

I will not be firing the 35W laser back up until I have had the all clear from Rana after I make the chiller swap.

Update: The plastic pipe fittings from the old unit are 3/8" BSPT tapered threads. The new chiller takes 1/2" normal threads. The 1/2" male to 3/8" female adapter I got from Home Depot are relatively useless as a long term solution and would probably damage the BSPT tapered threading. We can either get some cheap barbed style T-splitter and make stuff with hoses or order some BSPT adapters. I am inclined to order both and sort it out later as they are relatively cheap. This appears to be the only remaining hitch in the chiller swap.

Update2: I have ordered more new fittings from McMastercarr. I will make a summary post of all the wonderful things learned in this process.



Quote:

Quote:
I am trying to chase down the source of the long time scale sharp fluctiations in intensity. I need to start reading out the diagnostic PD from inside the MOPA head unit to see if the power fluctuations are coming before or after the amplification (e.g. NPRO or MOPA problems).

I need the following connectors from Wilson house:



Update: I talked to Peter King about swapping the chiller which appears to be the cause of the fluctuations in the power. Our current model, as the prototype, is an earlier generation from what he has, which is current with what is on site. He needs to talk to LZH to figure out if there is any additional hardware we need for the swap.

He also said that the sites used Deionized water for cooling, but said that filtered water would probably be fine. I did not get a good definition on what "filtered" consisted of. If we did move to DeI, then we might need some new plumbing. I told Peter that if things needed to be purchased we would find the money if it meant pulling copper piping from homes in Inglewood.

As we think this is the problem, I may wait on setting up data logging from the diagnostic (pre-mopa) photodiode in the head unit.
  92   Tue Sep 16 22:55:30 2008 DmassLaserPSLConnectors needed
Peter King and I hooked up the chiller to itself and ran it looking for "gunk" in the system. We satisfied ourselves that there was none, and I connected it to the laser and control box after a minor undertaking to get the adapters we need to hook the new chiller up to the old hardware. I ended up only adding one 3 inch piece of tubing with barbed 3/8 inch connections + wire clamps to hold it on.

We turned on the system and there are no obvious leaks. I replaced the DI water with distilled, since there are loads of brass fittings in the new chiller (PK agreed with this logic). There was a small light on the back which goes red if the conductivity of your water is too high. It did.

There is also a DI filter to reduce the conductivity of your water. It seems to work, as our warning light turned to green after about 10 minutes of running.

Peter gave me a dongle (15 pin dsub to 15 pin dsub) to adapt the the new chiller to the old control box. He made this via Christian's instructions. We were unable to get the diode box to turn the diodes on, and were presented with the following errors:
Flow control error - system off (when nothing was connected) and:
Chiller overtemp error - system off (when we had the adapter connected),

We tried using the old breakout "cheater" board to short the various pins to each other, and were unable to bypass the diode control box's unhappiness. PK is contacting Christian about this.

The chiller seems ok - but it will not play nice with the control box, so the 35W is still off at this point


Quote:
I got the replacement chiller (a Neslab Thermoflex1400) from 046 W. Bridge. I unpacked it and moved it by the PSL optics table in 058 W. Bridge. Peter King called LZH and is going to make the connector adaptation we need for the new Chiller unit.

I also siphoned the water out of the old chiller to see what plumbing fittings we may need in moving to the new unit. It was delicious.

I will not be firing the 35W laser back up until I have had the all clear from Rana after I make the chiller swap.

Update: The plastic pipe fittings from the old unit are 3/8" BSPT tapered threads. The new chiller takes 1/2" normal threads. The 1/2" male to 3/8" female adapter I got from Home Depot are relatively useless as a long term solution and would probably damage the BSPT tapered threading. We can either get some cheap barbed style T-splitter and make stuff with hoses or order some BSPT adapters. I am inclined to order both and sort it out later as they are relatively cheap. This appears to be the only remaining hitch in the chiller swap.

Update2: I have ordered more new fittings from McMastercarr. I will make a summary post of all the wonderful things learned in this process.



Quote:

Quote:
I am trying to chase down the source of the long time scale sharp fluctiations in intensity. I need to start reading out the diagnostic PD from inside the MOPA head unit to see if the power fluctuations are coming before or after the amplification (e.g. NPRO or MOPA problems).

I need the following connectors from Wilson house:



Update: I talked to Peter King about swapping the chiller which appears to be the cause of the fluctuations in the power. Our current model, as the prototype, is an earlier generation from what he has, which is current with what is on site. He needs to talk to LZH to figure out if there is any additional hardware we need for the swap.

He also said that the sites used Deionized water for cooling, but said that filtered water would probably be fine. I did not get a good definition on what "filtered" consisted of. If we did move to DeI, then we might need some new plumbing. I told Peter that if things needed to be purchased we would find the money if it meant pulling copper piping from homes in Inglewood.

As we think this is the problem, I may wait on setting up data logging from the diagnostic (pre-mopa) photodiode in the head unit.
  93   Fri Sep 19 13:18:00 2008 DmassLaserPSLChiller on. 35W on.
Peter got word back from Christian and told me how to modify the adapter he made (schematic to be posted later when he emails it to me). The errors disappeared and then we modified the chiller settings to LZH specifications except for

r.start (we had to set it to off rather than on to get the chiller to turn on).

The chiller has shown no signs of leaking and it has been on for ~24 hours now.
The 35W is back on. There is something wrong with the DAQ again, and I can not get it to write. I do not think anyone has modified anything at our end since we last had it working.

I am turning the laser off over the weekend since we are not trending. I am leaving the chiller on with a bucket underneath the new fittings incase it develops a drip.
  94   Sun Sep 21 15:45:21 2008 DmassLaserPSLChiller on. 35W on.

Quote:
Peter got word back from Christian and told me how to modify the adapter he made (schematic to be posted later when he emails it to me). The errors disappeared and then we modified the chiller settings to LZH specifications except for

r.start (we had to set it to off rather than on to get the chiller to turn on).

The chiller has shown no signs of leaking and it has been on for ~24 hours now.
The 35W is back on. There is something wrong with the DAQ again, and I can not get it to write. I do not think anyone has modified anything at our end since we last had it working.

I am turning the laser off over the weekend since we are not trending. I am leaving the chiller on with a bucket underneath the new fittings incase it develops a drip.


There appears to have been a small (a few cc's over a couple days) leak coming from the circled fitting. I tightened the offending wireclamp significantly (~3.5 turns) without worrying about damaging the hose as we are using the incredibly thick walled clear plastic hose. I also noticed some wetness coming from the joint indicated in the picture by the green arrow. I removed it, replaced the teflon tape, and re-tightened it.

I also used some cable ties to support the plumbing so it wouldn't put all the weight on my plumbing joint.

I left the bucket underneath, and will be checking the chiller daily to see if the leak is still there.

There was no apparent wetness after several hours.
Attachment 1: Chiller_Back.png
Chiller_Back.png
  99   Wed Oct 8 13:40:02 2008 DmassLaserPSLChiller Noise
The new chiller was making a noise (as reported to me by John).

It was emitting a continuous high pitched tone, and the display alternated between the set point temp, and "d1" or "di".
I hit enter twice, and it stopped. To be safe, I have turned the 35W off until I spend some time down here and make sure
that the chiller is ok. I have left the chiller on.
  101   Sat Nov 8 21:38:17 2008 DmassLaserPSLChiller Noise

Quote:
The new chiller was making a noise (as reported to me by John).

It was emitting a continuous high pitched tone, and the display alternated between the set point temp, and "d1" or "di".
I hit enter twice, and it stopped. To be safe, I have turned the 35W off until I spend some time down here and make sure
that the chiller is ok. I have left the chiller on.


The chiller was making the noise again. Again it said di on the screen. The noise and warning went away when I pushed any button on the front panel. I think it's just a warning that the water no longer qualifies as DI, as the light on the back of the chiller was red (it's green when the resistance is high, red when low - either change the di cartridge or figure out how toe disable the noise. As we don't necessarily want to use DI water because of the metal plumbing, I am inclined to disable the warning noise if I can.
  107   Fri Jan 23 16:48:29 2009 DmassLaserPSLChiller noise and DeI water
John Miller emailed me about the chiller once again whining. The water level was almost at the "min" line, and he filled it. This appears to not have been the culprit for the alarm. The screen on the chiller read "filters" and the noise stopped when I touched a button. The light in back which turned red when the water started to fail the deionized test is still red.

To my knowledge the following is the story

The new chiller wants Deionized water. It has brass fittings in it's plumbing, and by 40m lore, we do not mix brass fittings and deionized water - also Peter King said that it would be ok to use distilled water - I filled it with distilled water, and after a few weeks of stable operation (no noise or leaks) the red light on the back of the chiller went off (which I believe is triggered by the resistance of the water dropping too low). The high pitched whine of an alarm noise would periodically come on, and I would periodically turn it off. After this last time which I was notified of ~1 week ago by John Miller, the readout on the chiller said "filters" instead of "dei". I do not know how much attention we should pay to the purity of the water, and we may want to look into disabling the alarm if we continue using distilled water with the deionized water system.
  108   Wed Mar 4 15:20:14 2009 pkingLaserPSLlaser re-aligned
I fired up the laser this afternoon because Ken Mailand wanted to
test the silicon beam dump. The output power of the laser was pretty low,
around 8W or so. I re-aligned things a bit and now the output power is
around 32W. Further improvement involves opening up the amplifier I think.
This was all without adjusting any diode currents and wotnot. Just the
alignment.
  115   Sun Apr 19 16:01:35 2009 dmassLaserPSLLaser On

I found the 35W on with the shutter closed @ 4pm Sunday. It was off as of 8pm friday, with the shutter closed. I checked the power out, and it was ~ 29W. The steering mirrors into the PMC are gone, and the DAQ system is down, so there will be no trending of power from the pickoff diode.

 

Since there seems to be nothing useful to do with the PSL without an unknown amount of troubleshooting, I am turning off the laser rather than leaving ir dumping onto the shutter, which is now nice and toasty.

I hope to have the DAQ and PMC Servo back soon.

 

  116   Sun Apr 19 16:08:03 2009 dmassLaserPSLThe chiller wants new filters

The chiller has been begging for new filters for a while. I don't know if we ever starting loggin the chiller data, but I expect the water to have the conductivity of lemon juice by now.

  126   Wed May 13 17:13:29 2009 DmassLaserPSLBeam Scans

In the course of troubleshooting the PMC locking I took some beam scans of the PSL output.

They can be compared to the old scans

The scan in the attachement was taken right after the polarizing beam splitter.

 

Do we now have two beams coming out of the PSL?

 

I will wait for Rana or Stefan to get back before I chase th at one, as it's inside the PSL

 

Attachment 1: afterPBS.bmp
  132   Fri May 15 17:53:25 2009 DmassLaserPSLChiller making funny noises

The chiller wants new filters really badly. It was also making funny noises (somewhere around 1 Hz) that didn't sound all that healthy. I have turned the PSL and chiller off.

  139   Mon Jun 1 15:59:42 2009 DmassLaserPSLChiller Almost Empty

The chiller was making funny noises (tens of seconds time scale brief grating type noises - like if you took a piece of paper and let it touch a high speed fan). It was also below the "min fill level" line for water. I watered the thirsty beast and it is now quiet.

We may have been running the PSL with the chiller underfilled. I have been keeping it off lately for other reasons (the filters), though no longer feel the need to do so after talking to some people (Anamaria) about what they do at LHO. We may want to eventually change them, but we don't need DI water for the chiller.

 

I think it is fine to turn the PSL back on.

  144   Sat Jun 27 22:09:36 2009 DmassLaserPSLI did some things in lab, some of which were bad.

I fired up the 35W, and everything was still working as per my last entry - we still could lock the PMC, and were generating small amounts of green.

  • I replaced the old home made mode matching lens slider mounts with real slider mounts
  • I then realized that I had no transverse adjustment with these sliders, which ended up being a royal PITA for alignment
  • I went back to the old mounts and tried to restore their position very faithfully, but had not documented their placement
  • I am now not aligned well into the PMC, and can't find the 00 - some combination of lens position adjustment and angular alignment should fix this.

 

I took a series of beam scans to find the waist size/position of the beam coming into the PMC and noticed a few things:

  • The beam scan IS UNHAPPY <edit with specific error> when it boots up the software
  • This *seems* to be making a number of features unavailable (i.e. the position dot, the contour plots, dual axis display...)
  • All of the things that I was unable to get to work involved needing both axes of the beamscan to work.
  • It seems like there is at least one ghost beam which is ~ on axis. I am unsure as to whether this is modal content of the PSL or a ghost from some optic.
  • The horizontal axis was FUGLY in modal content; the near vertical was pretty, and resembled a guassian. <Pics to be attached>

NEXT:

  • Troubleshoot: Look at the beamscan documentation regarding its startup errors/running the features that were "greyed out"
  • Enter data into mode matching program - get desired adjustments to lens positions
  • Verify orientation of lenses (both are plano convex, and I currently have the curved surfaces pointed towards each other)
  • Once I get a lock to the 00 mode, do fine tune of mode matching and angular alignment by hand
  • Move on to making my SHG more efficient, and maybe move up to tens of uW

 

  163   Wed Jul 8 19:05:49 2009 DmassLaserPSLMode Matching and the PMC

I measured the waist of the input beam to the PMC after putting the mode matching lenses back. In the process of this, I noticed some problems with the beamscan.

I played with the beamscan axis until I found something that looked gaussian to the eye, and took a series of measurements, and fit the data (see attached).

 

 

I calculated the expected power loss from mode mismatch a la Dana Anderson's paper on cavity (mis)alignment and got some results:

I get estimates for power losses of:

6% due to waist position mismatch

12% due to waist size mismatch

NOTA BENE: The formulas in the Anderson paper start to break down as the linear approximations break down, which is happening for us...

 

If b is my mismatch parameter in waist position, my condition for the linear approximation is:

lambda*b/(pi*waist^2) <<1          but the LHS quantity is .492

and if w0' and w0 are my input beam and cavity waists, respectively, my condition is:

w0'/w0 - 1 <<1                            but the LHS is .34 here

Summary: I don't know how bad the Anderson formulas are in this regime of mismatch, but I can clearly do better in my mode matching. Next step: mode match/fix lens positions

 

Attached Image:

RED is roughly the PMC waist and position (based on the 40m PMC's waist - we have no measurement of this PMC's waist size yet afaik: put this on to do list)

GREEN is weighted least squares fit

BLUE is the data

 

Attachment 1: PMCbeamwaist.pdf
PMCbeamwaist.pdf
  164   Thu Jul 9 02:24:07 2009 ranaLaserPSLMode Matching and the PMC
The Anderson formulas are sort of OK in this regime but should only be used to estimate the mismatch.
Of course, its easy just to do the overlap integral and get the exact number. Its of limited use, since
the cavity will often not lock at the right point of the mismatch is so big.

Another possible method is to turn the power way down (less than 1 mW) and then scan it and fit
for the modes in transmission. The low power is to avoid thermal self-locking distortion of the fringe.

One can use knowledge of the PZT coefficient and the wavelength of the laser and modulation frequencies
to determine the cavity's g-factors and therefore the waist sizes. The cavity g-factor is defined as
g = 1 - L/R.
  171   Tue Jul 14 15:08:07 2009 Connor MooneyLaserPSLBeam Divergence of PSL

A while ago, Dmass made some beamscans of the PSL beam after it passed through two lenses. Here is a link to the Dmass Modematching elog.

We wanted to make sure that these measurements are consistent with what we think the incoming beam parameter is.  I wrote a matlab file which works backwards from his data to find the incoming beam parameter using ABCD matrices.  I used the focal lengths indicated on the lenses.

I found a disagreement of 20cm in the PSL waist location with a yesteryear elog entry  Dmass checked to see if my computation matched with his, and got the same result.

The first thing that we thought might have been wrong is that the focal lengths need to be switched, but switching them didn't significantly our change our results (in fact, it made them worse).

We also suspected that the engineering tolerance of the lenses might allow for the difference. I tried changing the focal lengths of the lenses by 10% for both lens orientations, but the computations made only small changes to our original result, so this is probably not the culprit.

 

 

 

  175   Wed Jul 15 16:05:53 2009 DmassLaserPSLPSL Realigned, now better

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

  177   Thu Jul 16 04:59:38 2009 DmassLaserPSLRazor Blades!

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Attachment 1: Photo_1.jpg
Photo_1.jpg
Attachment 2: Photo_3.jpg
Photo_3.jpg
  178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

  179   Thu Jul 16 17:43:59 2009 DmassLaserPSLRazor Blades!

Quote:

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

 

I got about a .002" error using a micrometer with my other setup, I expect this will suffice. If the errors in position end up too large I will use the new setup.

  180   Thu Jul 16 17:46:41 2009 DmassLaserPSLPSL Realigned, now better

Quote:

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

 

I will add pictures of what knobs we touched and how much each was turned by here

  181   Thu Jul 16 23:21:40 2009 DmassLaserPSLPSL Diode Powers and temperatures

At Anamaria's request, I recorded the diode powers (and temperatures) of the PSL.

~5 min after power up they were:

temp/power

20C  / 29.8W

23.8C / 28.6W

24C / 25.2W

25C / 27.8W

6 hours later they were

20C / 29.0W

23.8C / 28.1W

24C / 24.8W

25C 27.3W

  182   Fri Jul 17 15:39:31 2009 DmassLaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 Using the setups in the quoted post, I took manual beamscans 23" in front of the PSL enclosure, before the first steering mirror, and fit P = A erf(B*x + C)

 I measured the relative position of my razorblade with a micrometer and calculated the error from an estimated uncertainty of it's angle. This seemed to agree with repeatability of measurements for a given experimental state. Uncertainty < .002"

I watched the Power meter for ~ 60 seconds for each measurement, it fluctuated around some point and seemed to not be drifting @ DC, so the upper and lower error bars of each point included are the bounds of the fluctuation of the power meter. These were less than +/- 5mW about my points, so a fractional uncertainty of about 2% at my maximum power.

 

I got waists of:

Vertical: 799 +/- 4.5 microns

Horizontol 827 +/- 1.2 microns

Attached plot includes data w/ error and functional form of fit

 

As expected, my Chi^2 is "bad" since I am fitting the input beam to the PMC with a 00 mode description of the waist, which ignores all higher order modal content.

Attachment 1: RazorScans.pdf
RazorScans.pdf
  184   Mon Jul 20 23:19:49 2009 ranaLaserPSLRazor Blades!
Yeah, real micrometer with a reading is > plain screw.
  185   Tue Jul 21 02:09:45 2009 DmassLaserPSLPSL Realigned, now better

Quote:

Koji came down to the dungeon to help me with the "what is the junk coming out of the PSL" problem.

We noticed that the beam right after the PBS looked funky, and the beam before the power amplifier stage inside the PSL looked fine.

We decided to realign the optics inside the PSL. We only touched the two steering mirrors immediately preceeding the power amplifier.

We got a 35% increase in power and the output mode looked cleaner to the eye. (No more solar flares)

We are now happy.

 

 The following image contains approximations of the changes we made to the PSL steering mirrors (~5 degree accuracy)

Attachment 1: PSLRealignment.png
PSLRealignment.png
  187   Tue Jul 21 20:39:18 2009 DmassLaserPSLPSL Beam Scans

I took a bunch of scans of the PSL with the Beamscan and compared them with some razorblade occlusion measurements

The first steering mirror after the beam exits the PSL was removed, and data was taken at this point in the beam path.

The numbers for the waist derived from my razorblade measurements are on the plot in green. The disagreement seems not horrible to me.

 

We should still fix the beamscan, and think about buying another (newer) one.

 

I am told that the beamscan axis drawn on the head (labeled "1" and "2"), not the slit axis is what sets the direction of the field you are sampling. Data for both vertical and horizontal spatial modes of the beam are included. There is some ellipticity to the beam that I will have to account for in choosing my (new?) mode matching solution.

 

Error bars are included on the green point, they are just small.

Attachment 1: VertPSLScan.pdf
VertPSLScan.pdf
Attachment 2: HorPSLScan.pdf
HorPSLScan.pdf
ELOG V3.1.3-