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ID Date Author Type Category Subject
  175   Wed Jun 1 23:19:45 2011 DmassDailyProgressLab WorkError signal smaller?

I swept the PZT directly to get the V/V calibration from the PMC to the error signal.

  • In another measurement yesterday, I measured the error signal to be 200mV/2ms.
  • While sweeping with a 10 Hz signal, it is now 60 mV over 2 ms. This is a factor of ~3 smaller than what I found yesterday.
  • The only thing I did differently is sweep the PZT directly with a normal function generator, and use the laser current to change the frequency so that I can get in range of the resonance.
  • I checked my drive signal (still 23 dBm into a splitter), the magnitude of the resonance dip (to check alignment), and the total power in (via 1st waveplate)
  • My 1st guess is that I have found a region where the diode is not very "single mode".
    • This appears to not be the case - I changed back to yesterday's measurement setup and swept through a decent current range (5 mA) around yesterdays nominal values (185 mA), and the error signal did not magically grow large
    • I FOUND A 1.3 ND FILTER IN THE BEAM PATH FROM AN EARLIER MEASUREMENT I MADE TODAY WHERE I NEEDED TO LOWER THE OPTICAL GAIN. This level of awesome should not go undocumented.

Moving on...I swept the PZT directly to get the V/V calibration from the PMC to the error signal.

  • I put the drive signal of the PMC and the error signal onto a scope to get the V/V calibration (a.k.a. DC transfer function values)...
    • [ Error Signal ] = 100mV/4ms
    • [ PMC Voltage ] = 780mV/4ms
    • Verr / Vpmc = 0.128
  • I measured the PZT capacitance: C_pzt = 246.6 nF with a BK Precision LCR Meter (Model 878A)
  • I borrowed the New Focus LB1005 Servo Controller from the 40m
    • The output impedance of the unit is nominally 50 Ohms
    • The pole of the Driver/PZT is 1 / (2 x pi x C_pzt x Z_output) = 12.9 kHz
    • The LB1005 servo has a PI crossover on the front - this should be set to as close to the 12.9 kHz pole as possible
      • 10 kHz seems to be the obvious choice here, since the next highest the LB1005 has is 30 kHz
    • The unit has a switchable integrator which is specified in "low frequency gain, in dB"
      • Koji says this is the gain between high frequency and low frequency, rather than the total servo box gain
  • I think my open loop transfer function is as follows:
    • Verr / Vpmc x HFGAIN x [ pole at 12.9k ] x [ zero at 10k ] x [ pole at low frequency ] - Integrator switched off
    • Verr / Vpmc x HFGAIN x [ pole at 12.9k ] x [ zero at 10k ] x [ pole at 0Hz ]- Integrator switched on
  • The gain knob of the unit controls the high frequency gain,
    • so for a UGF of ~1k we would want a gain setting of 1 and a PI crossover of 10 kHz
    • for a UGF of ~100k we want a gain of ~100 and a crossover of 10kHz

Marginally Better Lock

  • I tuned the LB1005 (via knobs on the back) so it could only output -40 mV to +10V (this is as close to 0-10V as it got)
  • I was able to get an OK lock of the PMC to the laser (it survived me leaving the room and tapping gently on the table with the back of a ball driver - too hard and it broke)
    • Settings: Gain = 345 // LF Gain Limit = 50 dB // Integrator On // PI crossover = 10 kHz
  • I am HIGHLY SUSPICIOUS of the LB1005's linearity - I put a 1Vpp sine wave into the input at a few different high frequencies, and was unable to recover it without pretty significant disortion. I believe this should not be the case if it works as described by the manual, and if I put the P-I frequency somewhere below the frequency I am putting into the thing, I should be able to recover it rather simply. Test this more later
  • I suspect I need more DC gain (among other things) - locking an in air PMC to a noise laser without anything more than 1/f at low frequencies seems sad.
  • The UGF seems to be around 100 Hz - The loop begins to oscillate like mad at higher frequencies (12 kHz) when I push it past this. This seems not great.

Summary

The short term goal (days) is currently diode characterization. I want to take the following measurements:

  • RIN
  • Frequency Noise
  • (maybe) Driver to Frequency Transfer Function
  • (maybe) Driver to Intensity Transfer Function

I was initially going to use the laser current modulation input on the ITC510 driver to get some reasonable bandwidth (the specs say it "works" up to 50 kHz, whatever that means to them) lock of the laser to the cavity, then look at the laser control signal (and figure out how to calibrate it) to get the laser frequency noise. Frank pointed out this might not be straightforward since the transfer function of current to frequency of the diode is not entirely simple (its sort of 1/f on a log linear scale with an unknown phase response).

The alternative to the above is locking the PMC to the laser(s), then measuring the calibrated control signal going to the PZT. Where the laser is noisier than the PMC, and within the bandwidth of the loop, this is a direct measurement of laser frequency noise. This turned out to be harder than expected, and I am not sure what exactly the culprit is...some ideas:

  • LB1005 showed some nonlinear behavior, this makes the dynamics too tricky to bother thinking about
    • I could put a 20k resistor in series with the PZT to make a ~35 Hz pole and use that to lock with something like an SR560 just as an amplifier
  • The PZT is glued onto the endcap which is glued onto back of the PMC with a few dallops of glue - this could be fairly non-rigid and have some serious resonances below the PZT body modes
  • The PZT is angled w.r.t. the cavity axis (because the back mirror is wedged), so we get axial shifting as we change the length

I will take spectra of the control (and error) signals below 100Hz or so (current bandwidth with the Newport servo)

  174   Wed Jun 1 00:50:08 2011 DmassDailyProgressLab WorkLaser Locked to PMC!!

Quote:

Making an Error Signal (try #2):

  • Currently found error signal with 30 MHz sidebands!!
    • Sidebands: generated with a SR DS345: 23 dBm at 30 MHz into a broadband EOM
    • PDs:
      • PDA50B (Slow Switchable gain Ge PD) in transmission
      • Ligo resonant PD (picture included) - D980454-D
        • Frank got his hands on a few of these for the PSL lab, and we decided to test them for our error signal. Out of three PDs, each was broken in some way.
          • The first we tried oscillated like madness
          • The second's transfer function was....odd (no obvious resonant peak).
          • The third had a burn spot on the PD itself
        • We decided to see if we could use the second one in the short term, and just suffer some loss of gain
        • The PD has a DC channel and AC channel
    • Swept the PMC PZT:
      • Drove the PZT with a Thorlabs MDT693A high voltage driver
        • 0-10V input -> 0-150V output
      • Used a SR DS335 to sweep a 5V + 8*triangle(w*t) into the MDT input
  • Measured the error signal to be 18.6 V/GHz
    • Error Signal ~ 200mV/2ms
    • Reflection Dip ~ 2xCavity Bandwidth/520us
    • Cavity Bandwidth ~ 1.4 MHz
    • [200mV / 2ms] x [520us/ 2*BW] x [BW / 1.4MHz] = 1.86 x 10^-8 V/Hz = 18.6 V/GHz
    • Picture of sweep included:
      • Purple: PZT driver input
      • Yellow: Error signal
      • Green: Transmitted power
      • Blue: Reflected power
  • Choose a reasonable loop for actuating on current!
    • 0.11V at ITC510 input gives ~1GHz shift => 9GHz/V at laser diode controller
    • 18V/GHz x SR560GAIN x 9 GHz/V = G*167
    • Start with a pole at 1 Hz and a gain of 10, see what happens!

 

 Laser Locked to PMC!

  • Using an SR560, and hand tuning the PZT offset, I was able to lock the laser to the PMC for ~30 seconds at a time.
    • First I used a 10 Hz pole (checked the offset - small w.r.t. the error signal so don't care much) and slowly increased the SR560 gain to see what happened.
      • I was able to lock with a gain of 10, but the loop seemed to go unstable at higher gains
      • If my DC gain math is right, and there are no poles except the one I put there, then this should correspond to a 1Hz pole, with a UGF of ~1.7 kHz or so
    • Then I tried turning off the pole to see if there was a pole in the system I could use.
      • I could STILL lock with a gain of ~10 DC coupled through the SR560 with no filtering
      • I am suspicious, and Frank said previously that he was able to lock the (linear) cavity for short stretches just from absorption
    • The above was something silly. I had the control signal plugged into the wrong input on the ITC510. I do not know what the heck the dynamics were.
    • I plugged the right things into the right places, and was more successful.
      • With a 1 Hz pole and a gain of 20, I was able to get a definite lock.
      • I looked at the error signal and the transmission on a scope while playing with the loop and did a few sanity checks for myself
        • When I changed the sign of the feedback (using the INV button on the 560), I was not able to get transmission through the PMC when when I swept the PMC's PZT
        • I started (slowly, manually) sweeping the laser current, and when the PMC started to resonate / transmit, slow changes to the "current' knob would no longer change the current, until (what I think is) lock broke and then it would jump by ~10 mA. This is consistent with what I would expect from "closed loop" behavior if I started trying to add in an offset after the control point

I think the lock isn't tight enough to take transfer functions directly without some truly terrible happening to myself...so:

NEXT UP: Transfer function characterization of individual parts!

  173   Tue May 31 22:47:57 2011 DmassDailyProgressLab WorkError signal found!

Making an Error Signal (try #2):

  • Currently found error signal with 30 MHz sidebands!!
    • Sidebands: generated with a SR DS345: 23 dBm at 30 MHz into a broadband EOM
    • PDs:
      • PDA50B (Slow Switchable gain Ge PD) in transmission
      • Ligo resonant PD (picture included) - D980454-D
        • Frank got his hands on a few of these for the PSL lab, and we decided to test them for our error signal. Out of three PDs, each was broken in some way.
          • The first we tried oscillated like madness
          • The second's transfer function was....odd (no obvious resonant peak).
          • The third had a burn spot on the PD itself
        • We decided to see if we could use the second one in the short term, and just suffer some loss of gain
        • The PD has a DC channel and AC channel
    • Swept the PMC PZT:
      • Drove the PZT with a Thorlabs MDT693A high voltage driver
        • 0-10V input -> 0-150V output
      • Used a SR DS335 to sweep a 5V + 8*triangle(w*t) into the MDT input
  • Measured the error signal to be 18.6 V/GHz
    • Error Signal ~ 200mV/2ms
    • Reflection Dip ~ 2xCavity Bandwidth/520us
    • Cavity Bandwidth ~ 1.4 MHz
    • [200mV / 2ms] x [520us/ 2*BW] x [BW / 1.4MHz] = 1.86 x 10^-8 V/Hz = 18.6 V/GHz
    • Picture of sweep included:
      • Purple: PZT driver input
      • Yellow: Error signal
      • Green: Transmitted power
      • Blue: Reflected power
  • Choose a reasonable loop for actuating on current!
    • 0.11V at ITC510 input gives ~1GHz shift => 9GHz/V at laser diode controller
    • 18V/GHz x SR560GAIN x 9 GHz/V = G*167
    • Start with a pole at 1 Hz and a gain of 10, see what happens!

 

Attachment 1: IMG_0479.JPG
IMG_0479.JPG
Attachment 2: IMG_0480.JPG
IMG_0480.JPG
Attachment 3: LockingSetup.png
LockingSetup.png
  172   Mon May 30 16:50:24 2011 DmassDailyProgressLab WorkOops!

I misread the Covega datasheet (elog:67) and accidentally set the Thermistor resistance to 10K for ~5 minutes. The diode was not very stable at this temperature, which is around 297K = 24 C. I think this was OK since the datasheet gives 10 C as its absolute minimum rating, and 25C is still in its "operating range".

Preferred value is 7.16k ~ 30 C

 

  171   Sat May 28 17:16:42 2011 DmassDailyProgressLab WorkPMC Aligned

ALIGNMENT

I got an email with rough guidelines of "what is sort of ok" and "what is totally stupid" in terms of taking the back mirror off the PMC, so I did the following:

Changing the PMC Endcap:

  • Tapped the endcap of the PMC with a rubber mallet until the epoxy holding it on snapped
    • The glue could still hold the endcap in place via friction after I snapped it off the endcap, so I could wiggle the endcap around in place
  • I aligned a 532 nm beam to be coaxial with the 1550 nm input beam with 2 green steering mirrors ("borrowed" from doubling noise setup) using an iris in the near field, and a card in the far field
  • I pushed the endcap back on to be ~ flat
  • Aligned 532nm input beam height to 4" (+/- 0.03") and pitch to 0 deg (+/- 0.1 deg)
  • Aligned input beam yaw to ~0.5 deg of the (desired) cavity axis, and displacement to who knows what (I tried to make sure the spot hit somewhere close to the center of the back mirror)
  • I let the (lower power green) spots hit the wall in transmission and reflection (~factor of 3 different distances, so can get pitch and yaw misalignment from this)
  • I tapped gently on the (now semi free) endcap to tilt the back mirror, trying to make the 1st round trip spots overlap with the direct transmission and reflection, it was fairly easy to get the first 2-3 round trip spots to overlap at ~4" (in reflection on a black card) and ~4' (the wall) simultaneously
  • I dug around in the PSL lab for a bit (and recruited Tara) looking for the glue Frank used initially, in case there was some special epoxy, I convinced myself that there was no mysterious hidden special glue and grabbed some 30 minute epoxy
  • I used the epoxy to glue the endcap of the PMC in its new happier location

 Aligning to the PMC

  • Assuming that the alignment didn't change much in the gluing, or in the setting of the glue, I put the direct reflection on a (400 kHz) PD and looked at its output with a black N white 40 MHz scope
  • I used a 0.11Vpp 0.3 Hz (sine or triangle, unsure which) wave from a function generator to sweep the laser current about 180 mA
    • This corresponds to about 11 mA of current modulation, which is slightly more than 1 FSR of the PMC
  • I saw dips in the PD power time series while sweeping laser current, but saw nothing on a card in transmission so I was suspicious
    • I checked the Covega Datasheets (elog:67) to see that the laser was supposedly single mode over this whole range (by examining the side band suppression ratio)
    • I tweaked the laser current DC value about 10 mA to 170 mA to see if this made a difference
    • I still saw the power dips on the PD (great!)
  • I marked the current position of the input beam steering mirrors with a red sharpie
  • I slowly changed the pitch and yaw of the individual mirrors, and was able to get a dip of ~ 50% in reflected power
    • The dip was a single clean dip, but rather a small inverted forest: I think the laser noise was so high that even with such a low finesse cavity the laser frequency was shifting more than the cavity linewidth in the time it took to sweep across the resonance
    • Assuming I can lock the laser to the cavity, I am going to wait to try to do the common/differential alignment until I have a lock
  • I saw flashes of what looked like a 00 mode in transmission on a viewer card

ERROR SIGNAL

Testing the EOM:

  • Aligned the (adjustable) EOM mount to the beam with a card
  • Use SR DS345 (function generator - borrowed from ATF lab, formerly in green setup) to generate 15 MHz sidebands at +13 dBm (2.83 Vpp) - this is comparable to what I used for the broadband EOM in the PSL laser, and the spec sheet seems to allow for high voltage input (Half wave voltage = 350V @ 1550nm), so this level should be fine
    • EOM is broadband (Thorlabs EO-PM-NR-C3)
    • I used to impedance matching network on the input
  • I used the HP4395 RF spectrum analyzer to measure the beat between the carrier and its sidebands with a pickoff downstream of the EOM
    • DC Level: 5.24 V (Couldn't see it on the crummy 40 MHz scope AC coupled at 100 ns time res/div)
    • I was slightly confused about what the 4395 measurement units were...at 1Hz RBW:
      • 15 MHz peak:
        • Noise Mode:(-87.3 dBm/Hz) = (17.5 uV/Hz)
        • Spectrum Mode: (-81.5 dBm)
      • White noise level:
        • Noise Mode: (-137 dBm/Hz) = ~(26nV/Hz - didn't record)
        • Spectrum Mode: (-132 dBm)
      • I don't really understand where to file "amplitude/Hz" with regards to everything else I know about PSDs, is this just RF people talk about everything in power, so implicit in the measurement is that Voltage goes as power, so they use V/Hz as a PSD?
  • The sidebands are clearly visible without a resonant circuit! Huzzah!

Making an Error Signal:

  • To figure out where to actually put the sidebands, we should think about:
    • PDs we have on hand for photodetections:
      • Thorlabs PDA10CS (17 MHz at lowest gain setting)
      • Newport 818-BB-30 (1 GHz but annoying to align to - would be ick for optimizing alignment)
    • Cavity Bandwidth (elog:150)
      • FSR = c/2L = c/(2*210mm) = 714 MHz
      • In s-pol (currently easier because of EOM placement and waveplate number)
        • Finesse = 522
        • BW = FSR/Finesse = 1.37 MHz
      • In p-pol (requires one more waveplate)
        • Finesse = 71
        • BW = FSR/Finesse = 10 MHz
  • It seems that 15 MHz is fine in the current configuration, with the PDA10CS, assuming we don't get too much phase delay that close to its maximum specified bandwidth
    • This is probably a bad assumption in reality, but we can always start here and swap out the PD later when we want to actually push the bandwidth of the loop up
  •  The PDA10CS was "totally broken"
    • Some amplifier inside is likely borked, as it gave us silly results when we swept the PMC through resonance with

 

  170   Thu May 26 14:13:28 2011 DmassDailyProgressLab WorkDaily To Do

I'm not sure if there is anything special I need to do regarding the cleanliness of the PMC spacer itself. I know that it is not hermetic by inspection, but recall *certain people* saying that the inside should be kept clean. If I can't really mess anything too important up I'll just tweak it in some way (find an appropriate thickness shim) and reglue it.

  169   Thu May 26 06:58:52 2011 FrankDailyProgressLab WorkDaily To Do

i've checked the specs for the mirror, my fault:
Laser Mirror: FS, pl-concave, Ø=12.7-0.1mm, te=6.35±0.1mm, wedge=30min, S1: L/10, AR(0°, 1480-1630nm)<0.25%, S2(^): L/4, r=1000mm, HR(0°,1480-1630nm)>99.98% (Low Loss), T(1510nm)~0.005%

I didn't pay attention to that as so far i always glued the concave side to the pzt, not the rear side.
So we have two options:

  1. if we exchange it by the 0.5m mirror it should be fine as it has no wedge specified: (Laser Mirror: FS, pl-concave, Ø=12.7-0.1mm, te=6.35±0.1mm, S1:L/10, S2:L/4, r2=500mm, HR(0°,1450-1600nm)>99.975% (Low Loss),T at 1530nm~0,012%)
  2. we tilt the end cap a little bit

Do ypu want to try the second one? simply remove the end cap, there are only a few little spots of epoxy. You can use a 2" mirror mount, hold the aluminum cap with it (try to push it against the back of the spacer to have as little space between the cap and the sapcer as possible) and align it properly and if everything looks good add a little bit of glue and fix it to the spacer. It's not super rigid anymore but shouldn't matter as we will replace everything in 4 weeks or so anyway.

Quote:

Quote:

Figure out alignment problem to PMC

Get online document describing of all subparts of project

Come up with schedule for action based on the (est) arrival of the bigger ticket items

 

 After several futile attempts to align the PMC (as built by Frank, see elog:155), I had Koji come in to confirm that there was something wrong with the PMC alignment and not my alignment to the PMC and tried to align a green laser pointer to the PMC. This failed and looked like a back mirror pitch misalignment (yaw looked fine). A quick estimate of misalignment, probably good to 10%

Procedure for measurement of misalignment:

  • Align input beam to 4" height in near and far field
  • Align yaw into PMC so that we hit the back mirror without clipping
  • Measure the vertical displacement between direct reflection (off inside surface of 1st optic) and the transmission of the 1st round trip beam (15" from end mirror)
    • displacement was 10/32"
    • angle = ((10/32")/15") rad = 21 mrad
    • Back mirror angle is 21 mrad/2 = 10.5 mrad = 0.6 degrees
    • axial displacement is thus 1m * 10.5 mrad = 1.05 cm
    • The substrate diameter is 1.27 cm, so the axial displacement puts the beam axis OFF THE BACK MIRROR
    • THE PMC AS BUILT (GLUED) CAN'T BE ALIGNED
    • THE BACK MIRROR OF THE PMC IS MISALIGNED BY 10 mrad = 0.6 deg

Looks like we need to pull the endcap and redo the mirror placement, possibly with some beam to help align the back mirror

N.B. Frank has told me that the inside of the PMC is still clean, so I will wait for him to get back before pulling the thing apart since I don't know what I'm doing on that front.

We also may want to consider using the faster (smaller r_curve) mirror, since this is more forgiving in terms of cavity axis displacement as a function of back mirror angular misalignment. Frank had wanted to save it for use with a (possible) AOM, but I think we should just toss it in.

If we put the 0.5m mirror (which we have on hand) into the PMC:

  • For 10.5 mrad misallignment we get .525 cm displacement, which leaves us (barely) on the substrate
  • I am assuming we can do slightly better than the pitch misalignment we already have, so I believe that we can get this the cavity axis on the coating with a little care

 

  168   Wed May 25 17:41:13 2011 DmassDailyProgressLab WorkRIO Lasers

I made an entry in the CryoWiki detailing the RIO's responses to our inquiries. It is well worth checking out.

  167   Wed May 25 15:13:16 2011 DmassDailyProgressLab WorkDaily To Do

Quote:

Figure out alignment problem to PMC

Get online document describing of all subparts of project

Come up with schedule for action based on the (est) arrival of the bigger ticket items

 

 After several futile attempts to align the PMC (as built by Frank, see elog:155), I had Koji come in to confirm that there was something wrong with the PMC alignment and not my alignment to the PMC and tried to align a green laser pointer to the PMC. This failed and looked like a back mirror pitch misalignment (yaw looked fine). A quick estimate of misalignment, probably good to 10%.

Procedure for measurement of misalignment:

  • Align input beam to 4" height in near and far field
  • Align yaw into PMC so that we hit the back mirror without clipping
  • Measure the vertical displacement between direct reflection (off inside surface of 1st optic) and the transmission of the 1st round trip beam (15" from end mirror)
    • displacement was 10/32"
    • angle = ((10/32")/15") rad = 21 mrad
    • Back mirror angle is 21 mrad/2 = 10.5 mrad = 0.6 degrees
    • axial displacement is thus 1m * 10.5 mrad = 1.05 cm
    • The substrate diameter is 1.27 cm, so the axial displacement puts the beam axis OFF THE BACK MIRROR
    • THE PMC AS BUILT (GLUED) CAN'T BE ALIGNED
    • THE BACK MIRROR OF THE PMC IS MISALIGNED BY 10 mrad = 0.6 deg

Looks like we need to pull the endcap and redo the mirror placement, possibly with some beam to help align the back mirror

N.B. Frank has told me that the inside of the PMC is still clean, so I will wait for him to get back before pulling the thing apart since I don't know what I'm doing on that front.

We also may want to consider using the faster (smaller r_curve) mirror, since this is more forgiving in terms of cavity axis displacement as a function of back mirror angular misalignment. Frank had wanted to save it for use with a (possible) AOM, but I think we should just toss it in.

If we put the 0.5m mirror (which we have on hand) into the PMC:

  • For 10.5 mrad misallignment we get .525 cm displacement, which leaves us (barely) on the substrate
  • I am assuming we can do slightly better than the pitch misalignment we already have, so I believe that we can get this the cavity axis on the coating with a little care

[edit: added a picture of the green laser pointer going into the setup]

Attachment 1: IMG_0470.JPG
IMG_0470.JPG
  166   Wed May 25 13:13:15 2011 DmassDailyProgressLab WorkDaily To Do

Figure out alignment problem to PMC

Get online document describing of all subparts of project

Come up with schedule for action based on the (est) arrival of the bigger ticket items

 

  165   Wed May 25 03:36:55 2011 DmassDailyProgressLab WorkEOM razor blade scans

Couldn't quite get aligned to the PMC. Progress:

  • I modified the mode matching lens position based on elog:164
  • I took razor blade scans of the input beam to the PMC to check the mode overlap
  • I couldn't align totally blind, so I grabbed a green laser pointer and used it as an "auxiliary beam"
  • I tried to use the overlapping visible beam to align the input optics to the axis of the PMC, but failed to find the "sweet spot" after a couple hours.
  • Since this PMC has never been locked to before, I am not positive if there us any way to tell if the alignment of the mirrors themselves are OK
  • I will consult the great benevolent Koji tomorrow, and see if he thinks I am being stupid, or if there is some more fundamental problem with the PMC itself
Attachment 1: PMCInputBeam.pdf
PMCInputBeam.pdf
  164   Tue May 24 02:27:00 2011 DmassDailyProgressLab WorkEOM razor blade scans

I made some measurements of the waist size as described in elog:162 and elog:163 using a razorblade and a photodetector.

I used a Thorlabs PDA50B (1/2 cm diameter photodiode), and put the razor blade as close to its face as I could ( < 1cm from PD case).

I did a couple things with the fit (because I was curious how the answers would differ):

  1. Used a linear approximation since I took points starting at 2-3 times the rayleigh range to get the beam waist (slope ~ lambda / (pi*w_0))
  2. Used this as my number for the waist, and found its location with fminsearch ("black" numbers on plot)
  3. Did a fminsearch over waist size and location for the four points I took ("yellow" numbers on plot)
  4. Yellow fit looks better (residuals are clearly smaller by crudely inspecting the plot)

MATLAB code used:

poss = [13 10 7 5]*0.0254;
waists = 2*[0.0505 0.043 0.0345 0.029]*1e-2;
outs = polyfit(poss,waists,1);

% linear approximation when we are out of the raleigh range is:
% w(z) ~ lambda/(pi*w0) * z

w0=1550e-9/(pi*outs(1))
zr=pi*w0^2/1550e-9;
wz = @(z,zoff) w0*sqrt(1+((z-zoff)./zr).^2);
outs1 = fminsearch(@(var) sum(abs(wz(poss,var)-waists).^2),-.3);

zr2 = @(w00) pi*w00.^2/1550e-9;
wz2 = @(w00,zoff2,z2) w00*sqrt(1+((z2-zoff2)./zr2(w00)).^2)
outs2 = fminsearch(@(var2) sum(abs(wz2(var2(1),var2(2),poss)-waists).^2),[300e-6 -.15])

posarr = linspace(-.2,.35,30);

figure(1)
clf
plot(posarr/.0254,1e6*outs(1)*posarr+outs(2),'b',...
    posarr/.0254,1e6*wz(posarr,outs1),'k',...
    posarr/.0254,1e6*wz2(outs2(1),outs2(2),posarr),'y',...
    poss/.0254,1e6*waists,'rx')
axis tight
grid

legend('Linear Fit to Data','fminsearch on xwaist',...
    'fminsearch on w0 and xwaist$\;\;\;\;$','Data from Razor Scans',...
    'Location','NorthWest')
xlabel('Position (in)')
ylabel('Waist Size (um)')
title('Razorblade Waist Measurements')
ylim([0 1050])

writ(1)={strcat('Black: w0=',num2str(floor(w0*1e6)),'$\,$um, xwaist=',num2str(floor(100*outs1/.0254)/100),'$\,$in')};
writ(2)={strcat('Yellow: w0=',num2str(floor(outs2(1)*1e6)),'$\,$um, xwaist=',num2str(floor(100*outs2(2)/.0254)/100),'$\,$in$\;\;\;\;\;\;\;\;$')};
text(4,100, writ,'HorizontalAlignment','left',...
    'BackgroundColor',[.7 .9 .7])
orient landscape

Attachment 1: RazorbladeModeScans.pdf
RazorbladeModeScans.pdf
  163   Mon May 23 13:17:44 2011 DmassDailyProgressLab WorkDaily To Do

NotLab

  • Review and compare existing quotes for the windows
    • Email American Photonics for revised quote
  • Get new quotes (send emails to coating companies)?
  • Purchase PMC from local company (~4 week delivery)
    • Update drawings to A3 from A4
    • Fill out bottom right part of drawings tolerances, units, finishing, etc
    • Add drawings to svn (some files were added as bin file type - not sure if this is a problem)
    • Email drawings (which reflect the current quote) to ASCO
    • Place requisition for PMC via techmart
  • Find list (from one of the main companies) listing focal length at 1550nm as a function of EFL for BK7 lenses
    • I have used this one from the CVI catalogue before (linked here), though it only has 1319 nm for BK7. The difference is small enough where I am going assume reasonable dispersion (and reasonable extrapolation from the chart) , and stop thinking about it.
  • Figure out what to do with the response about lasers from RIO
    • Email asking for more detailed info about PLANEX lasers

Lab

  • Razor blade measurements of waist size / at EOM (as described here - more info in elog:164)
  • " " measurements of waist size / loc at PMC
  • Align to PMC sans viewer (as described here)

 

  162   Sat May 21 18:45:03 2011 DmassNotesLab WorkAligning to the PMC

More work aligning and modematching to PMC.

  1. 300mm lens at 0.14m in front of coupler => 185um @ 0.431m
  2. 400mm lens @ 31 cm from EOM waist
  3. 500 lens @ 43 cm from EOM waist

I tried the wincamD to see if I could confirm spot size anywhere, but it wasn't sensitive at 1550nm, so I go to plan B: razor blades!

I borrowed a translation stage from the gyro and mounted a razor blade onto it (picture below). For occluding a PD (from math):

  1. Measure offset of PD
  2. Measure "full power" level of PD with beam illuminating
  3. Occlude beam with razor blade so that half of beams power is blocked - call this 50%
  4. Move razor blade until power increases to 84% (1/2 + erf(1/sqrt(2))/2) [picture of derivation attached]
  5. Distance moved is half the waist size (if I go one waist in distance from the center I have to make a 2.5% measurement of power level change, this is harder with cheap scopes and
  6. Sanity check - looking at the plot from this elog from when I did the full blade scan and erf fitting, this seems consistent with the scale

 

 

Attachment 1: RazorBlade.png
RazorBlade.png
Attachment 2: ERFderiv.png
ERFderiv.png
  161   Fri May 20 15:28:55 2011 DmassNotesLab WorkAligning to the PMC

I have set out all the optics with a mode matching solution found using the javascript modematching tool from one of Franks buddies in Germany - I have previously done sanity checks so I trust it

 

Aligning to the PMC:

I am trying to align to the PMC using a PDA10CS in reflection with a pickoff mirror for attentuation. I am used to having a viewer to get the spot close enough, so will be doing this more blind than I am used to.

Technique:

  • Assume the front PMC mirror is mounted flat onto the PMC face and thus is roughly perpendicular to the table
  • Get differential height DOF by looking at the beam in front of the last steering mirror at 1/2", 3", and 11" (after reflection) - set this to parallel to table plane
  • Get common height DOF by dead reckoning the center of the PMC front mirrors, and hope that the back mirror was mounted on the same plane (it should be)
  • Guess "wildly" at the horizontal DOFs by eyeballing from the top
  • Look at reflection off the PMC on a PD
    •  Align with 10 mW
    • PDA10CS gives 10mW x (0.9 A/W) x (7.5 x 10^2 V/A w/ 50 ohm load) = 6.75V (with no optical attenuation)
  • Sweep diode current via slow DC input on the front of the Thorlabs driver
    • PMC FSR = c/2L = c/(420mm) = 713 MHz
    • Covega df/dI = 90 MHz/mA
    • 10 mA modulation gives us slightly more than 1 FSR in frequency shift
    •  0.11Vpp signal (at 0.1 Hz) gives us a ~10 mA sweep on current

I tried to use the WINCAMD from the ATF to see if it had any sensitivity to 1550, but it seems pretty clearly to have ~0 response there. I think we should getting something from dataray to solve this problem. In the meantime mode profiling is going to have to be done with razor blades.

  160   Thu May 19 12:39:17 2011 DmassNotesGeneralMeeting

Quote:

Me Rana and Frank's stand in had a meeting:

Dick gave us some drawings to review, I have distributed these via email, here are the questions

 

 

TO DO

  • Write Procedure for cycling dewar!
  • Ask Dick what the wall thicknesses are
  • Ask him how much clearance we have at windows and middle joint
  • Ask if the cold plate is where the holes are tapped or if there is an extra part as the drawings seem to indicate
  • Change the diameter of the bottom lip
  • Ask for the hole pattern on top with helicoil inserts to be called out
  • Ask if he thinks Aluminum is OK (since he has designed it as such)
  • Cymak - poke JR to do this / figure out what he's doing
  •  Make big ole chart with urrthang in it
  • Chat with Steve about life, the universe, and Dewars
  • Confirm that the Sapphire windows have similar thermal expansion to Aluminum
  • Make first version of suspension mechanical design
  • Get the windows coated - quicker over quality
  • Talk to G$ about laser quotes

Other TO DO

  • Mode match and align to PMC
  • Sweep laser current, look at trans / refl of beam through PMC
  • Lock laser to PMC
  • Find HV driver
  • Align / mode match PMC transmission to low quality REFCAV
  • Use PMC PZT to lock to REFCAV
  • ???
  • Profit

Dewar Notes:

Walls are: 1/8"

LN2 chamber is 1/" or 0.09"

G10 - 0.02"

  159   Thu May 19 00:26:29 2011 FrankThings to BuyCavityQuote from Coastline

we finally got a quote from coastline. Delivery time is ~12-14 weeks and the price is rather high see full quote posted on the wiki

  158   Wed May 18 18:18:06 2011 DmassNotesGeneralMeeting

Me Rana and Frank's stand in had a meeting:

Dick gave us some drawings to review, I have distributed these via email, here are the questions

 

 

TO DO

  • Write Procedure for cycling dewar!
  • Ask Dick what the wall thicknesses are
  • Ask him how much clearance we have at windows and middle joint
  • Ask if the cold plate is where the holes are tapped or if there is an extra part as the drawings seem to indicate
  • Change the diameter of the bottom lip
  • Ask for the hole pattern on top with helicoil inserts to be called out
  • Ask if he thinks Aluminum is OK (since he has designed it as such)
  • Cymak - poke JR to do this / figure out what he's doing
  •  Make big ole chart with urrthang in it
  • Chat with Steve about life, the universe, and Dewars
  • Confirm that the Sapphire windows have similar thermal expansion to Aluminum
  • Make first version of suspension mechanical design
  • Get the windows coated - quicker over quality
  • Talk to G$ about laser quotes

Other TO DO

  • Mode match and align to PMC
  • Sweep laser current, look at trans / refl of beam through PMC
  • Lock laser to PMC
  • Find HV driver
  • Align / mode match PMC transmission to low quality REFCAV
  • Use PMC PZT to lock to REFCAV
  • ???
  • Profit
  157   Tue May 17 10:42:52 2011 FrankThings to BuyCavityCoastline stock material properties

Optical Grade Silicon
Resistivity Ohm-cm: >20
Purity: >99.999%
Type: P
Orientation:  Monocrystalline <100>

This information is from the certificate of conformance for the 1"Ø blanks
of silicon that they currently have in house.

  156   Thu May 12 22:47:37 2011 DmassLab InfrastructurePlotsSteering Mirror Reflectivity Measurements

We bought twi]o different types of steering mirrors for the lab. I forgot that there was more than one type when unpacking and mounting the "new" ones and thus did not label them / note which is which. (OOPS!)

I can tell the difference between the two types based on the tint, but here are some measurements to make sure one of the two types of mirror doesn't suck so we can buy more (of both). One is more green if you look through the back one is more orange, and when I look at one of the room lights, there is a slightly different tint to each.

 

 

I have labeled the two with the beautifully descriptive "SM1" and "SM2" labels. Reflectivities are measured with the ultraprecise awesome Thorlabs power meter!

Attachment 1: MirrorRefls.pdf
MirrorRefls.pdf
  155   Wed May 11 23:06:16 2011 FrankDailyProgressPMCPMC prototype assembled

As getting a new spacer for the 1550nm PMC will take a couple of more weeks we decided build a temporary PMC to be able to perform our locking test.
We re-use an old glass PMC spacer and old end-cap with old pzt. The mirrors are glued to the spacer using only a minimum of epoxy at a few point, just enough to keep it in place.
That makes it easier to remove and re-use the mirrors later once we get the new parts, which also lowers the risk of damaging them while removing.

Here are some pictures:

 P1020489.JPG

P1020465.JPG

P1020469.JPG

 P1020432.JPG

  154   Wed May 11 01:30:03 2011 FrankDailyProgressDrawingstable layout draft

draft sketch of the table layout to see how we can fit everything on the table and to count parts which are still missing.
Free space  (upper half) can be either a second, independent laser source or we use the AOM in the beginning.
Long term plan is to have two independent lasers so we try to come up with a table layout which does not require rearranging everything if we change plans.
The layout below has some parts (like EOMs) as placeholders, but the plan is to still use the diode for modulation or the pzt of the PMC for locking the PMC.
Would be nice to have a layout where we can try different options without having to change the layout. Beat part is a bit squeezed but should fit. Other options are possible but not shown. Tried to make optical pathes as short and equal as possible. Cryostat can be replaced by our single ULE cavity for testing, or we put it next to it where we still have space and use it as a third cavity with a flipper mirror somewhere.

Footprints of parts are close to actual size.
Grid is 1". Table is 6ft x 4ft. Hole in center 10" diameter. Cryostat about 18" diameter.

cryolayout_v1.png

 

cryotable.vsd

  153   Tue May 10 23:52:23 2011 DmassLaserSchematicsMode Matching in new setup

I need to do the mode matching for the new layout.

 

Fiber Coupler ---> Lens1 ----> EOM ---> MMLens2 ---> MMLens 3 -----> PMC ----> MMLens 4 ------> MMLens 5 ------> Fused Silica Cavity

What are the relevant waists?

Fiber Couple Output - from the F240APC-1550 datasheet

  • They give angle of divergence: 0.075 deg ( = 2*theta: defined later)
    • This can give us the waist size since w(z) = w_0 * sqrt(1+(z/zr)^2) ==> w(z) = w_0 * z/zr    for z>>zr
    • zr = pi * w_0^2 / lambda ===> w(z) = lambda * z / (pi * w_0)
    • dw(z) / dz = lambda / (pi * w_0) = tan(theta)50
    • w_0 = lambda / (pi * tan(theta)) = 1.55 um / (pi * tan(0.075 deg / 2)) = 753 um
  • and 1/e^2 diameter at 1 focal length from lens: 1.5 mm
    • zr = pi * w_0^2 / lambda = pi * (743 um)^2 / 1.55 um = 1.12 m
    • Since they say the spot size is 2 x the waist size 8mm in front of the collimator, I'll start by assuming the waist is 1/3 inches in front of the collimator, and seeing if the mode matching is affected by this assumption (I check with a card and couldn't really tell where the waist was since the divergence was so small. I will use 8mm for now).

EOM - Thorlabs EO-PM-NR-C3

  • L/2 = zr at EOM = 1 inch
  • w0 = sqrt(zr * lambda / pi ) = 110 um

PMC - 370 um (double check)

Fused Silica Cavity - 348 um

 Available Lenses: (there is no V-coating available from our normal vendors at 1550, so we intend to take the broadband AR [1-1.55 um] coated lenses from the ATF and replace them with 1064 V-coating lenses off the Cryo Lab budget). The BBAR coating is AR.18 from Newport.

Plano Convex:

  • 50 mm  (2)
  • 75 mm
  • 88 mm
  • 100
  • 150
  • 300
  • 400
  • 500 (2)
  • 750
  • 1000 (2)

Bi Convex:

  • 38.1
  • 50.2 (2)
  • 500

 

Mode Matching:

300 mm lens 7" in front of fiber output coupler => 195 um waist @ EOM

Try 2 lenses after EOM

PMC 39 - 51 inches from EOM

  • Not sure which mirror is in PMC...
  • PMC length is 210mm (according to 40m elog)
  • R = 0.5m => 450 um waist
  • R = 1m    => 350 um

If the waist is 450 um, we can try

  • f = 150mm @ 0.16m
  • f = 500mm @ 0.744m
  • gives 435um waist @ 1.10m

If the waist is 350 um, we can use:

  • f = 150mm @ 0.168m
  • f = 400mm @ 0.72m
  • gives 360um waist @ 0.993m

 

  152   Tue May 10 23:50:02 2011 DmassDailyProgressGeneral 

Today Frank and I stripped the table, wiped it down with Acetone, then took the old (ghetto) optics setup apart.

We thought a little bit about intermediate layouts, and have layed out a preliminary (pictures to follow) setup with the Laser Diodes and the PMC.

  151   Tue May 10 11:37:26 2011 DmassDailyProgressPMCmirror transmission measured

The values were too small so I fixed a typo and made them less wrong.

  150   Tue May 10 04:00:02 2011 DmassDailyProgressPMCmirror transmission measured

 The angle is right.

From Siegmann:

  • Finesse = pi*sqrt(Grt)/(1-Grt) 
  • Grt = r1*r2*r3*sqrt(1-Loss) is roundtrip gain

For p-polarization

  • Grt_p = ( 1 - 0.0433)^.5 * (1 - 0.0433)^.5 * (1) * (ignore extra loss from end mirror) = 0.957
  • Fin_p = 71

For s-polarization

  • Grt_s = (1 - 0.0057)^.5^2 = 0.994
  • Fin_s = 522

Either should be easy enough to work with, and not so low that they are stupid. GREAT!

I will be frolicking in lab tomorrow on and around the laser table

  149   Mon May 9 22:40:06 2011 FrankDailyProgressPMCmirror transmission measured

As the flat mirrors i bought are specified for 0 deg i measured the transmission vs angle of one of them (assuming they are both "identical" as they are from the same coating run) as we want to use them at ~42deg as input/output coupler.
Here the simple setup using a large rotational stage, half wave plate to adjust the polarization and the power meter to measure the incident and transmitted power.

setup.jpg

 

Here the results. Error bars for absolute values are probably large as even 1deg was hard to reproduce and read as the scale on the stage had 2deg steps. But better than nothing. It's enough for an order-of-magnitude calculation.

transmission.jpg

and here the data files

angular_reflectivity_104070_ppol.dat

angular_reflectivity_104070_spol.dat

 

@DMASS: can you please check if my assumption for the angle is correct and make an estimation for the finesse for s and p-pol using the above numbers

  148   Mon May 9 22:28:16 2011 FrankUpdatePMCPMC mirrors arrived

they arrived today

I scanned all the measured spec sheets and put it on the wiki

  147   Mon May 9 15:00:37 2011 DmassUpdateSchematicsTriangular PMC

I have updated the Wiki (here) with the information about quotes from the two machine shops.

  146   Fri May 6 03:23:14 2011 DmassUpdateSchematicsTriangular PMC Schematics

Here are the drawings I submitted to the local machine shops for our 1550 nm triangular metal PMC.

 

The round trip path length is 2 x 6.3 inches. We want to use either 1m or 0.5m curved mirrors in the back, which give a waist size of:

1m => 425 um waist

0.5m => 340 um waist

 Cavity FSR is***:

936 MHz

 The PZT we have ordered and plan to use, the PI P-016.10H, has a 15 um range with a 1000V max voltage. Assuming linearity gives us 15 nm / V.

The voltage required to move 1.5 FSR is:

1.5 * (dL = L x FSR / f) * V / 15 nm = (6.3" x 0.0254 m/") x 936 MHz / (1.93x10^14 Hz) * V / (10^-8 m) = 77 V

Frank wanted to get some (specific) 60V power supplies, if we use these we only get a 1.17 FSR full range. Is this "good enough?" It means that we might not be able to sweep out two TEM00 modes in the full range unless we tune its length with a heater.

 

 

 

 

*** I am guessing a tiny bit. Since the FSR of a Fabry Perot of length L is c/2L, and the triangular cavity is like a flat/curved Fabry Perot with 2L = roundtrip length of triangular cavity, I think the FSR of a triangular cavity is c/(roundtrip length)

Attachment 1: pmc_drawings.pdf
pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf pmc_drawings.pdf
Attachment 2: pmc_endcap.PDF
pmc_endcap.PDF
  145   Thu May 5 12:24:11 2011 FrankUpdatePurchasesPMC mirrors shipped
Monday, 05/09/2011, by 10:30 A.M.

UPS tracking number: 1ZER25556663912015

  144   Thu May 5 11:33:15 2011 ranaUpdatePurchasesPMC mirrors

 I agree - wedge probably doesn't matter with a T=50 ppm

  143   Wed May 4 13:06:04 2011 FrankUpdatePurchasesPMC mirrors

Unfortunately the concave mirror i've ordered and which was in stock according to their online shop turned out to be out of stock 

So i've changed the order to a similar one. The only difference is that the new one doesn't have a wedge which shouldn't matter for our prototype as the transmission is only 50ppm (and it's still AR-coated on the back)

  142   Sun May 1 15:06:25 2011 DmassNotesCavityCavity Dimensions

We have been tasked to think about in what ways the two cavity measurement is sensitive to the machining of the Silicon, so that we know if we need to ask for anything special in the machining of t.

  1. Absolute Length
  2. Relative Length
  3. Absolute Diameter
  4. Relative Diameter
  5. Parallelism of Faces
  6. Concentricity of Bore Hole
  7. Flatness of Surface

 

1. Absolute Length

  1. Sets cavity FSR determines how much frequency shifting we might need.
  2. Magnitude of cavity length noise goes up linearly with length (as described by the half infinite mirror treatment of the problem)
  3. Coating thermal noise coupling (uncorrelated between cavities so no reason to care about this even if we only match the cavity lengths to 10^-1)
  4. Seismic coupling

2.Relative Length

  1. Difference in cavity FSRs (if we could choose this, what would we want it to be)
  2. We get common mode rejection of the laser noise from matching the length of the two cavities (unimportant and at uninteresting frequencies)
  3. Room temperature common mode rejection of thermoelastic changes (also applicable if we are not operating at the zero CTE point at various cryogenic temperatures)

3.Absolute Diameter

  1. Magnitude of cavity length noise goes down as the inverse square of its diameter (as described by the half infinite mirror treatment of the problem)
  2. Seismic coupling

4.Relative Diameter

  1. ?

5.Parallelism of Faces

  1. Cavity Mode axis gets shifted, and is no longer such a clean 00 (depending on how far the g-factor is away from 1)

 

 SOME CRUDE CALCULATIONS/DISCUSSION OF THESE EFFECTS

1-1: If we use 100mm for the cavity length (~4 inches), the FSR is c/2L = 1.5 GHz (too much for an AOM)

2-1: If we have a length mismatch of dL, so that the lengths are L and L+dL, the FSR of the cavities will be slightly different (which seems unimportant). The cavities will differ by some number of lambda, (probably ~20 lambda). Worst case scenario here is they differ by (n+1/2) lambda, so if we made one cavity resonant for a laser, the other cavity would be anti resonant. In the picture where we use a single laser and frequency shift it, this would require us to do ~750 MHz of shifting. CAN WE DO THIS WITH AN AOM? If not, then we will either have to individually tune the temperature of the cavities (the absolute temperature of each cavity at room temperature doesn't matter much).

       Further down the road when we are trying to operate at 120K, we could possibly detune the temperature of one cavity away from the zero CTE point (at the cost of higher temperature noise coupling) and still do useful work like that. If the cavities happen to have a worst case type condition, and we can't get our hands on a frequency shifter which can do the job, we can always move to a 2 laser setup (duplicating other components like a PMC, etc).

2-2: The only common mode rejection of laser frequency noise issue I can think of is the following: if the cavity lengths differ, then the cavity poles differ, and above the cavity pole, we will lose some common mode rejection of the high frequency noise based on this pole shift. Since the cavity pole for a 100 mm Finesse of 10k cavity is FSR/10k = 150 kHz. The difference in rejection between 0.005" and 0.001" seems like it probably doesn't matter for us, since we still have ~60 dB if we match the lengths to 10^-3.

         We should also note that most of the loops we are thinking of using to lock the laser to the cavity have a UGF above the cavity pole, so the frequency noise will already be suppressed down at 150 kHz, thought not by all that much (a factor of 3-6 for a 500kHz - 1MHz UGF with 1/f at high frequency).

         Since it wasn't clear before: In terms of laser frequency noise, I see no sort length mismatch dependent coupling of laser frequency noise to the beat signal which we should concern ourselves with. In the band of interest for us (1 mHz to 100 Hz), we expect 1/f laser noise, and f^2 or f^3 loop shape, with a ~500kHz UGF. This means we should be shot noise limited in our lock to the cavity, so there is no more classical laser noise.

1-4 and 3-2: The seismic coupling (in m/m of seismic displacement noise to cavity length noise) is dependent on the cavity geometry. If we can match the geometries very well, and they are suspended identically, we can have some rejection of the seismic coupling, since the seismic noise at the cold plate should be somewhat coherent over its length scale at those low frequencies (below 1Hz).

       The way to figure out how cavity geometric tolerances couple into the seismic coupling (and therefore the common mode rejection of the seismic noise from the beat signal) seems to be COMSOL.

 

  140   Wed Apr 27 13:43:21 2011 FrankUpdatePurchasesNIR CCD camera

bought one of the NIR intensified CCDs which have the phosphor coating on the chip as we need at least one good one for mode identification. My home-made ones need still too much power, so you can't identify higher order modes
Edmund has one with 15% discount at the moment, so it's "only"  $1700. Also bought two turning mirrors to see how they are. Specs are not bad, but so far i couldn't find any turning mirror not being frosted on the back.
A full beam analyzer for 1550nm is about $6k, which me might wanna buy in the future if we do more 1550nm stuff. For now i think we don't need one.

UPDATED THE SPREADSHEET

  139   Tue Apr 26 16:51:18 2011 DmassDailyProgressPurchasesSubmitted some POs

I did some purchase legwork today:

  • Asked Light Machinery to verify that they can take the stock Si from Virginia Semiconductors and turn it into spacers we can use
  • Submitted PO for the PZT from PI (P-016.10H - they told Frank via email that they have it in stock in Germany, so ~2 weeks)
  • Updated the metal PMC drawings and sent the updated drawings to the two local machine shops (wiki page on the PMC incoming)

Still to be done - sketch up an endcap in solidworks and amend it to the drawings sent sent

  138   Tue Apr 26 16:25:23 2011 FrankUpdatePurchasesPMC mirrors ordered

submitted the order, my credit card has been charged already so they might actually ship them this time

  137   Mon Apr 25 18:08:17 2011 FrankLaserLaserquote for RIO’s PLANEX lasers

pricing quotation for RIO’s PLANEX lasers: see wiki

  135   Mon Apr 25 14:06:44 2011 FrankLab InfrastructureDrawingsrack drawing

made the first draft rack drawing as requested. Can be found on the Wiki in /Documents/Mechanical Drawings/

  134   Mon Apr 25 11:09:38 2011 FrankLaserLaseralternative laser source

here are the detailed datasheets i got from them:

PLANEX_Laser_RIO009x_Datasheet_Rev.0.1_(5).pdf

ORION_Module__Datasheet_Rev_0.1.1_(2).pdf

 

Quote:

found this one, which is much better than the ones we have. It's the first company i've found which shows a frequency noise plot .

http://www.rio-inc.com/pdf/PLANEXLatestProductBrief.pdf

they also have a turnkey system, see here

Requested a quote, just in case...

 

  133   Fri Apr 22 01:19:31 2011 FrankLaserLaseralternative laser source

found this one, which is much better than the ones we have. It's the first company i've found which shows a frequency noise plot .

http://www.rio-inc.com/pdf/PLANEXLatestProductBrief.pdf

they also have a turnkey system, see here

Requested a quote, just in case...

  132   Thu Apr 21 08:59:41 2011 FrankUpdateGeneralspacer/mirror quotes on wiki updated

i thought the company we are talking about is doing everything (drilling, polishing) except the polishing of the part which requires flatness for contacting. The second company is then doing the re-polishing of the end surfaces, right?

Quote:

Quote:

see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

 Checked the update - w.r.t. a certain company- they were nonresponsive (to use the nomenclature) when I asked them to quote on the spacer. As far as we are concerned, they are just another Si supplier. Your concern about that supplier sounds to me like we are asking them to give us certain surface quality / precise geometry, neither of which I think we need from the raw materials, but from what I understand, we have very limited requirements for the spacer BEFORE machining.

Or did you mean you were concerned that there weren't things like purity, doping, not being broken specifically in the quote. This all seems sort of moot, since it seems like a not-so-hot idea to use something with the fabrication/shipping process and lead times given in the elog.

 

  131   Fri Apr 15 15:54:00 2011 DmassCryostatCavityMirrors..

I asked a certain (unnamed) company whether or not they could do superpolishes, and they told me:

"We believe our silicon surfaces are as good as it gets.  We have compared them to 'super polished' sufaces using our white light zygo and do no see any difference but we could be missing something..."

I don't know enough to know whether this is the way you would do a non phase-mapping comparison and totally reasonable, or if this statement is so ridiculous we should consider completely ignoring this company when it comes to mirror polishes.

  130   Fri Apr 15 15:49:31 2011 DmassUpdateGeneralspacer/mirror quotes on wiki updated

Quote:

see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

 Checked the update - w.r.t. a certain company- they were nonresponsive (to use the nomenclature) when I asked them to quote on the spacer. As far as we are concerned, they are just another Si supplier. Your concern about that supplier sounds to me like we are asking them to give us certain surface quality / precise geometry, neither of which I think we need from the raw materials, but from what I understand, we have very limited requirements for the spacer BEFORE machining.

Or did you mean you were concerned that there weren't things like purity, doping, not being broken specifically in the quote. This all seems sort of moot, since it seems like a not-so-hot idea to use something with the fabrication/shipping process and lead times given in the elog.

  129   Fri Apr 15 14:00:26 2011 FrankUpdateGeneralspacer/mirror quotes on wiki updated

see https://nodus.ligo.caltech.edu:30889/CryoWiki/doku.php?id=equipment:spacer_quotes

  128   Tue Apr 12 22:06:04 2011 DmassCryostatCavityRadiative Thermal Time Costant

Some actual numbers for the pertinent "RC" time constants are discussed in the PSL elog. There has been debate about what the radiative pole from the can to the cavity will be for the cryo cavity, and what it is for the current room temperature cavity. See section titled:

WHY AM I DOING THIS?

  127   Mon Apr 11 15:47:37 2011 DmassCryostatCryoTrouble in Paradise (Windows)

Quote:

The cryostat window schedule is currently behind. Tommorrow's to do list to help remedy:

  • Get John from ISI/MDC on the phone to finally give us a firm quote for the brazing process (Meller has the windows we want to use)
  • Confirm the clear aperture with Dick from Precision Cryo (who is making the window flange) so we know if 1" windows are actually OK to use
  • Get quotes for an AR coating from American Photonics and VLOC for 8 windows (1 run) (waiting for reply)

 

 Dick seems to think he might have a problem welding Kovar to stainless (he's never done this before)....

The windows we want to get (and were planning on getting) from MDC/ISI are Kovar brazed to Sapphire. MDC seems to be able to weld/bond this to stainless with no problem as their window flanges are stainless. I don't yet know if there is anything tricky about welding stainless to Kovar, but I'll bug MDC about this. If there is some tricky process required to do the joint, it seems our least bad option might be to have Dick ship his custom fab'ed stainless parts to MDC and have them do the joint.

Old window plan:

Meller Sapphire Windows -> MDC for brazing -> coating company for AR coating -> Dick for welding to stainless flange

Possible new plan:

Meller Sapphire Windows -> MDC for brazing -> coating company for AR coating -> MDC for welding to Dicks flange which he also ships to MDC

One might ask why we have a custom flange at all...This is all born from Dick's idea of what is good / bad: He did not want to do a cold CF joint between stainless (the flange) and Cu (the 77K cold shield), his words were "you need one of the surfaces to be stainless in a CF flange". This left us with the choice of either doing a stainless 77K shield, or abandoning CF and having him do something custom. Since Rana and Warren seemed strongly opposed to stainless b/c or thermal gradients (low spatial correlation over the shields surface) I said F it and went for the custom flange.

At this point we will probably have the cryostat before we have windows for the cryostat, so I'm having Dick fab some (simple) covers for the window ports so we can get started on the temperature stabilization once the cryostat gets here.

 

  125   Wed Apr 6 23:19:02 2011 DmassCryostatCryoWindows for Cryostat

The cryostat window schedule is currently behind. Tommorrow's to do list to help remedy:

  • Get John from ISI/MDC on the phone to finally give us a firm quote for the brazing process (Meller has the windows we want to use)
  • Confirm the clear aperture with Dick from Precision Cryo (who is making the window flange) so we know if 1" windows are actually OK to use
  • Get quotes for an AR coating from American Photonics and VLOC for 8 windows (1 run) (waiting for reply)

 

  124   Wed Apr 6 21:14:47 2011 DmassCryostatCavityRadiative Thermal Time Costant

Quote:

I have been delinquent about elogging the calculation I did some time ago about what the radiative time constant between the cavity and its can would be.

I added what the numbers I get for the room temperature situation is as well.

 

[edit: I added the slew rate limit from cooling if we paint everything black]

We had some concerns about being able to get a high enough UGF for the heater around the cavity. The slew rate limit of cooling the heater via direct radiation to the 77K shield, using order of magnitude calculation, seems to be ~0.4 K/second. See section 3 of the attachement for details

 I thought I would post a helpful drawing to help anchor my/our (future) discussion of the temperature servo for the cavity heater.

Since we want to know about the closed loop dynamics of the system, I think it makes sense to talk about the whole thing in terms of "equivalent thermal circuits", where we have R's, C's and V's. And dQ/dt=DeltaT/R is our equivalent of Ohm's law.

Initially, I will do the first order thing and make the following assumptions:

  • Rcond1 is large
  • Rcond 3 is large
  • Rcond2 is small
  • Rcond4 is small
  • Heat Capacities of the heater and temperature sensor are small

 

Attachment 1: HeatPoleModel.png
HeatPoleModel.png
  123   Fri Apr 1 21:23:26 2011 DmassCryostatCavityRadiative Thermal Time Costant

I have been delinquent about elogging the calculation I did some time ago about what the radiative time constant between the cavity and its can would be.

I added what the numbers I get for the room temperature situation is as well.

 

[edit: I added the slew rate limit from cooling if we paint everything black]

We had some concerns about being able to get a high enough UGF for the heater around the cavity. The slew rate limit of cooling the heater via direct radiation to the 77K shield, using order of magnitude calculation, seems to be ~0.4 K/second. See section 3 of the attachement for details

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