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ID Date Author Type Category Subjectup
  347   Thu Sep 9 02:20:32 2010 taraNotes problem about PBS/QWP

We have used an instant PBS/QWP which is a PBS optically contacted to an aligned QWP in front of a reference cavity

(for PDH locking and optical isolation.) It cannot properly block the reflected beam, so certain amount of power got reflected back to

the PMC and back to the laser. This causes higher value of RIN. ()

  147   Fri Jun 4 22:10:24 2010 taracLaserLaserprogress on PSL setup

The maximum power after AOM double pass is 37%, worse than the expected 50% efficiency, but it should be enough.

The good news is, a new mode matching (RefCav and ACav) is calculated, and all positions for the lenses are clear.

I got all the lenses, and borrow one plcx-24.5-51.5-c-1064 from 58C

The problem about the position of the PBS is solved. It will be at the original place, since the clipped beam is the 0th order of the reflected beam which we do not use.

I'll put the lenses in their places and try to lock RefCav again.

  148   Fri Jun 4 22:48:24 2010 ranaLaserLaserprogress on PSL setup

Quote:

I'll put the lenses in their places and try to lock RefCav again.

 Groovy.                   

  131   Wed May 26 21:11:00 2010 taracLaserLaserprogress on PSL setup

 

I add the broad band EOM in the beam path. After adjusting the periscope, I can steer the beam into the RefCav and see the reflected light. It's not aligned yet.

The 35.5 MHz is set on the table with a lens to focus the beam on the PD.

I'm not sure if I have to use the laser controller for 126 model or I could use the 10W laser to scan the beam, I'll consult Peter tomorrow.

Right now we are using the 10W laser controller to power the 100mW laser. The connector had been unstable, but now it's working fine.

It will be better if I can use the 10W controller to dither the laser frequency because I won't have to switch the cable, and avoid the risk of having to deal with the cable again.

 

 

Forgot to log this yesterday:

The PMC servo in medm's command window is correct.

 

I need to make SMA cables (properly insulated kind) too.

From 21.5 MHz PD to servo, 25 feet,

from 35.5 MHz PD to servo,   25 feet,

from 35.5 MHz EOM to signal box, 5 feet,

from 35.5 MHz LO to signal box, 20 feet.

  828   Tue Feb 14 23:35:04 2012 FrankNotesBEATproposed (new) cable delay setup

cable-delay_v4.jpg

 

Mixer will be driven very hard to saturate it. To operate the mixer in the required saturated mode, the RF signal level should be at least:

  • +1 dBm for Standard Level (+7 dBm LO) mixers
  • +7 dBm for Standard Level (+13 dBm LO) mixers
  • +10 dBm for High Level (+17 dBm LO) mixers

so if we use the right (optimum) cable we would have ~8dBm, which should be perfect for a level 13 mixer.

Let's see if we can confirm the calculations...

  40   Thu Jan 28 16:07:29 2010 FrankComputingDAQpsl channels moved to C3 + new channels

here is a list of all channels of the psl subsystem. We changed the generic channel names to final names now.
Refcav channels are now C3:PSL-RCAV and analyzer cavity channels are C3:PSL-ACAV. Rest see below...

#####################
# 10W MOPA channels #
#####################
[C3:PSL-126MOPA_AMPMON]        # internal laser power monitor
[C3:PSL-126MOPA_126MON]        # internal NPRO power monitor
[C3:PSL-126MOPA_DS1]            # diode sensor 1
[C3:PSL-126MOPA_DS2]            # diode sensor 2
[C3:PSL-126MOPA_DS3]            # diode sensor 3
[C3:PSL-126MOPA_DS4]            # diode sensor 4
[C3:PSL-126MOPA_DS5]            # diode sensor 5
[C3:PSL-126MOPA_DS6]            # diode sensor 6
[C3:PSL-126MOPA_DS7]            # diode sensor 7
[C3:PSL-126MOPA_DS8]            # diode sensor 8
[C3:PSL-126MOPA_126PWR]        # NPRO power monitor
[C3:PSL-126MOPA_DTMP]        # diode temperature
[C3:PSL-126MOPA_LTMP]        # pump diode temperature
[C3:PSL-126MOPA_DMON]        # diode output monitor
[C3:PSL-126MOPA_LMON]        # pump diode output monitor
[C3:PSL-126MOPA_CURMON]        # pump diode current monitor
[C3:PSL-126MOPA_DTEC]        # diode heater voltage
[C3:PSL-126MOPA_LTEC]        # pump diode heater voltage
[C3:PSL-126MOPA_CURMON2]        # pump diode current monitor
[C3:PSL-126MOPA_HTEMP]        # head temperature
[C3:PSL-126MOPA_HTEMPSET]        # head temperature set point
[C3:PSL-126MOPA_FAULT]        # laser fault indicator
[C3:PSL-126MOPA_INTERLOCK]        # interlock control
[C3:PSL-126MOPA_SHUTTER]        # shutter control
[C3:PSL-126MOPA_126LASE]        # NPRO lase status
[C3:PSL-126MOPA_AMPON]        # power amplifier lase status
[C3:PSL-126MOPA_SHUTOPENEX]        #
[C3:PSL-126MOPA_STANDBY]        #
[C3:PSL-126MOPA_126NE]        # NPRO noise eater
[C3:PSL-126MOPA_126STANDBY]        # NPRO standby
[C3:PSL-126MOPA_DCAMP]        #
[C3:PSL-126MOPA_126CURADJ]        #
[C3:PSL-126MOPA_126SLOW]        #
[C3:PSL-126MOPA_BEAMON]        # beam on logical

#######################
# 80 MHz VCO channels #
#######################
[C3:PSL-FSS_VCODETPWR]        # 80 MHz VCO PWR
[C3:PSL-FSS_VCOTESTSW]        # enable/disable test input
[C3:PSL-FSS_VCOWIDESW]        # enable/disable wideband input

######################
# other FSS channels #
######################
[C3:PSL-FSS_SW1]            # frequency servo front panel switch
[C3:PSL-FSS_SW2]            # frequency servo front panel switch
[C3:PSL-FSS_INOFFSET]        # 21.5 MHz mixer input offset adjust
[C3:PSL-FSS_MGAIN]            # frequency servo common gain
[C3:PSL-FSS_FASTGAIN]        # phase correcting EOM gain
[C3:PSL-FSS_PHCON]            # 21.5 MHz phase control
[C3:PSL-FSS_RFADJ]            # 21.5 MHz oscillator output
[C3:PSL-FSS_SLOWDC]            # slow actuator voltage
[C3:PSL-FSS_MODET]            #
[C3:PSL-FSS_PHFLIP]            # 21.5 MHz 180 degree phase flip
[C3:PSL-FSS_MIXERM]            # 21.5 MHz mixer monitor
[C3:PSL-FSS_SLOWM]            # slow actuator voltage monitor
[C3:PSL-FSS_TIDALINPUT]        #
[C3:PSL-FSS_RFPDDC]            # 21.5 MHz photodetector DC output
[C3:PSL-FSS_LODET]            # detected 21.5 MHz output
[C3:PSL-FSS_PCDET]            #
[C3:PSL-FSS_FAST]            # fast actuator voltage
[C3:PSL-FSS_PCDRIVE]            # drive to the phase correcting EOM
[C3:PSL-FSS_RCTRANSPD]        # reference cavity transmission
[C3:PSL-FSS_RMTEMP]            # room temperature
[C3:PSL-FSS_RCTEMP]            # reference cavity temperature
[C3:PSL-FSS_HEATER]            # reference cavity heater power
[C3:PSL-FSS_TIDALOUT]        #
[C3:PSL-FSS_RCTLL]            # reference cavity transmitted light level
[C3:PSL-FSS_RAMP]            # slow actuator ramp, used in lock acquisition

################
# PMC channels #
################
[C3:PSL-PMC_SW1]            # PMC servo front panel switch
[C3:PSL-PMC_SW2]            # PMC servo front panel switch
[C3:PSL-PMC_MODET]
[C3:PSL-PMC_PHFLIP]            # 35.5 MHz 180 degree phase flip
[C3:PSL-PMC_PHCON]            # 35.5 MHz phase control
[C3:PSL-PMC_RFADJ]            # 35.5 MHz oscillator output
[C3:PSL-PMC_PMCERR]            # PMC error point
[C3:PSL-PMC_RFPDDC]            # 35.5 MHz photodetector DC output
[C3:PSL-PMC_LODET]            # detected 35.5 MHz output
[C3:PSL-PMC_PMCTRANSPD]        # PMC transmission
[C3:PSL-PMC_PCDRIVE]            #
[C3:PSL-PMC_PZT]            # PMC PZT voltage
[C3:PSL-PMC_INOFFSET]            # 35.5 MHz mixer input offset adjust
[C3:PSL-PMC_GAIN]            # PMC loop gain
[C3:PSL-PMC_RAMP]            # PMC PZT ramp, used in lock acquisition
[C3:PSL-PMC_BLANK]            # blanking input to the PMC PZT
[C3:PSL-PMC_PMCTLL]            # PMC transmitted light level

################
# ISS channels #
################
[C3:PSL-ISS_SW1]            # intensity servo front panel switch
[C3:PSL-ISS_SW2]            # intensity servo front panel switch
[C3:PSL-ISS_AOMRF]            # rf drive for intensity stabilization
[C3:PSL-ISS_ISERR]            # intensity servo error point
[C3:PSL-ISS_GAIN]            # intensity servo gain
[C3:PSL-ISS_ISET]            # intensity servo set point

#############################
# 16bit D/A channels - ACAV #
# 4116-card               #
#############################
[C3:PSL-ACAV_HEATER]            # analyzer cavity heater power
[C3:PSL-ACAV_SLOWDC]            # feedback to tidal input of other cavity

#############################
# 16bit A/D channels - ACAV #
# 3123-card                    #
#############################
[C3:PSL-ACAV_RCTEMP]            # reference cavity temperature
[C3:PSL-ACAV_RMTEMP]            # room temperature
[C3:PSL-ACAV_RCTRANSPD]         # analyzer cavity transmission
[C3:PSL-ACAV_RFPDDC]            # RF photodetector DC output
[C3:PSL-ACAV_PDHOUT]            # PDH servo output signal

#############################
# software channels - ACAV  #
#############################
[C3:PSL-ACAV_KP]                # pid loop p-gain
[C3:PSL-ACAV_KI]                # pid loop i-gain
[C3:PSL-ACAV_KD]                # pid loop d-gain
[C3:PSL-ACAV_LOCKEDLEVEL]       # threshold level below which pid does nothing
[C3:PSL-ACAV_TIMEOUT]           # pid loop sample time
[C3:PSL-ACAV_VERSION]           # pid loop software version
[C3:PSL-ACAV_DEBUG]             # pid loop debug messages on/off
[C3:PSL-ACAV_ENABLE]            # pid loop on/off
[C3:PSL-ACAV_SETPT]             # temperature setpoint
[C3:PSL-ACAV_SCALE]             # scaling factor

##############################
# software channels - REFCAV #
##############################
[C3:PSL-RCAV_KP]                # pid loop p-gain
[C3:PSL-RCAV_KI]                # pid loop i-gain
[C3:PSL-RCAV_KD]                # pid loop d-gain
[C3:PSL-RCAV_LOCKEDLEVEL]       # threshold level below which pid does nothing
[C3:PSL-RCAV_TIMEOUT]           # pid loop sample time
[C3:PSL-RCAV_VERSION]           # pid loop software version
[C3:PSL-RCAV_DEBUG]             # pid loop debug messages on/off
[C3:PSL-RCAV_ENABLE]            # pid loop on/off
[C3:PSL-RCAV_SETPT]             # temperature setpoint
[C3:PSL-RCAV_SCALE]             # scaling factor

##############################
# software channels - TIDAL  #
##############################
[C3:PSL-TIDAL_KP]               # pid loop p-gain
[C3:PSL-TIDAL_KI]               # pid loop i-gain
[C3:PSL-TIDAL_KD]               # pid loop d-gain
[C3:PSL-TIDAL_LOCKEDLEVEL]      # threshold level below which pid does nothing
[C3:PSL-TIDAL_TIMEOUT]          # pid loop sample time
[C3:PSL-TIDAL_VERSION]          # pid loop software version
[C3:PSL-TIDAL_DEBUG]            # pid loop debug messages on/off
[C3:PSL-TIDAL_ENABLE]           # pid loop on/off
[C3:PSL-TIDAL_SETPT]            # temperature setpoint
[C3:PSL-TIDAL_SCALE]            # scaling factor

  1313   Sat Aug 24 15:42:54 2013 taraDailyProgressVacuumpumping down the chamber

I closed the chamber. The turbo pump is on and pumping down.

 I realigned the beams so the visibilities for both cavities were 80% or more. This made sure that the beams' path would be close to the optimized path.

Now, the window reflection won't overlap with the cavity reflection, and can be dumped properly.

Note about a few things to do:

  • The beam holes on the foam might have to be fixed, the beams slightly clip at the openings. I have to check if the beams are clipped at the periscope or not.
  • modification of the seismic stack as suggested by Koji. The teflon pieces at the bottom plate are not screwed down to the stack making it hard to put the stack in the chamber. I think this should be fixed after the SiO2/Ta2O5 measurement is done and we have to reopen/ installed AlGaAs cavities.
  • There is some strayed beam from the PBS in RCAV path. This is from left over beam in S-light that reflected off, and bounced back at the PBS surface before going to the PD. This might have to be fixed too.

FYI for torque wrench setting for CTN cavity:

Quote:

cf_torque2.pdf

 The CTN cavity is 10" OD,  the Torque required is 190 InchPound.

  1319   Thu Aug 29 13:25:49 2013 taraDailyProgressVacuumpumping down the chamber

The turbo pump is removed, and the ion pump is on. The initial value is ~7mA.

I removed the turbo pump and turn on the ion pump, see the procedure on wiki page. The initial value on the ion pump is ~ 7mA, similar to the last time we opened the chamber although this time I left the turbo pump on 4 days instead of 2 days. So I think this is the limit of this turbo pump.

 

  605   Wed May 25 18:29:09 2011 taraNotesopticpurchases

I ordered a few opto mechanical components to replace the current shaky periscopes.

The new  periscope is shown here, elog:574. Currently we have only one set, so I ordered a post clamp to complete another set. 

I also ordered 4 mirror mounts that can be mounted on 45 degree mounting adapters. The thickness of these mounts are thinner than a regular mirror mount, so it can be fit on the adapter. I plan to use these in Crackle experiment as well. 

 

 

  606   Mon May 30 15:23:53 2011 ranaNotesopticpurchases

The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.

 

  607   Tue May 31 11:31:18 2011 taraNotesopticpurchases

I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .

Quote:

The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.

 

 

  609   Wed Jun 1 01:50:35 2011 KojiNotesopticpurchases

They are found in DCC. Some comments

- You can not steer the beam. The beam should be steered before or after the periscope.

- The side plates were too thick. It can be 1/2" thickness to reduce the total weight.

D1001446-v1 40m Vertex Green Locking Periscope A Base Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001447-v1 40m Vertex Green Locking Periscope A Sidebar Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001448-v1 40m Vertex Green Locking Periscope A Mirror Holder Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001613-v1 40m Vertex Green Locking Periscope A PTFE Post Koji Arai Auxiliary Optics
Basic R&D
15 Jul 2010

Quote:

I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .

Quote:

The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.

 

 

 

  610   Wed Jun 1 21:00:05 2011 FrankNotesopticpurchases

we have to design our own. The 40m one has 2" mirrors (too large, we don't have the space), wrong height for incoming/outgoing beam and is clamped to the table, which i think is bad in terms of stability.
The design principle does not look much different compared to the original refcav periscope design, except for the mirror holder itself. That was bad designed for the old one.

 

Quote:

They are found in DCC. Some comments

- You can not steer the beam. The beam should be steered before or after the periscope.

- The side plates were too thick. It can be 1/2" thickness to reduce the total weight.

D1001446-v1 40m Vertex Green Locking Periscope A Base Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001447-v1 40m Vertex Green Locking Periscope A Sidebar Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001448-v1 40m Vertex Green Locking Periscope A Mirror Holder Daisuke Tatsumi et al. Auxiliary Optics
Basic R&D
15 Jul 2010
D1001613-v1 40m Vertex Green Locking Periscope A PTFE Post Koji Arai Auxiliary Optics
Basic R&D
15 Jul 2010

Quote:

I looked up 40m elog and found Daisuke's design for periscope. I'll make a sketch FSS' periscopes.

The design for 40m pericopes by Daisuke can be found here .

Quote:

The periscopes for the refcav ought to be made custom. None of the store bought type are stiff enough. Koji has a design from the 40m green that Daisuke made.

 

 

 

 

  361   Tue Sep 14 20:18:35 2010 taraDailyProgressComputerspwr monitor for NPRO is added

C3:PSL-NPRO_PWRMON channel, and npro.db file are added

for monitoring power output of the NPRO (reflected beam from Faraday Isolator)

I haven't reset the crate yet, so the channel may not appear in DAQ yet.

It's connected to VMIVME-3113 at #C0 S60.

The photo diode is Thorlab PDA55 with RG1000 filter.

Calibration for power is 1.81 mW/V, now it reads 5.56V.

  80   Fri Feb 26 15:15:56 2010 Tara ChalermsongsakLaserRC noisequarter wave plate added/power from Ref and A Cavs measured

I borrowed one of the quarter wave plate and added it after the beam from the Ref Cav. One more QWP is needed for the ACav.

The power after the Ref cav is measured:

1) just after the cavity : 5.4 mW

2)First BS: Reflected beam (to the PD): 3.8 mW, Transmitted beam: 1.4 mW

3) 2nd BS: Reflected beam (for beat measurement): 0.56 mW,  Transmitted beam(to the camera): 0.62 mW

The waveplate is set at 32 degree, for max transmitted beam from a PBS( horizontal polarization in this setup)

 

Power after the A cav:

1) just after the cavity: 19.3 mW

2) First BS: Reflected beam(to PD):19 mW, Transmitted beam: 0.21 mW

3) 2nd BS: Reflected beam(for beat msmt): 0.255 mW

  965   Thu May 17 17:35:17 2012 taraNotesPurchasesquote from ATF for substrate and spacer

I got the quote for substrates from ATF (AR coated on flat-wedge, blank on concave, R=0.5m side) quantity of 10 and 20. They also offer the cavity assembly as well, so I sent them the drawing of our cavity to ask for the quote.

For the spacer, I asked two other companies,cidra, and tecoptics, for the quote, but they have not replied back yet. So, I just asked another company,aiceramics.com, in hope of getting it done soon.

  974   Thu May 31 15:10:57 2012 taraNotesPurchasesquote from Coastline

I called Coastline about the lead time for the substrates and asked if we could speed up the process by changing the specs to be less demanding (coarser roughness/ sphericity). The answer is no, all the main features of the substrate (curve surface with polished annulus, wedge surface) are the main driving factors, not the roughness or how flat it is. Additionally, they told me that, from their experience, the width of the annulus of 2-3 mm is enough for optical contact. 5mm width would be too large and it causes the surface near the annulus to deform, and it takes longer time (he could not tell exactly how longer). I put the quotes on CTN wiki.

  666   Fri Sep 2 21:29:27 2011 FrankNotesRefCavradiation shields & heater

the shields/heaters for the two cavities will be delayed by an unknown amount at this point. I'm still waiting for the two polished copper tubes and mounting parts to be finished. Also the Kapton heaters still didn't arrive.Even if we would get everything beginning next week at will take at least a week to get it cleaned, heaters wired, glued, cleaned and baked. Same for temp sensors etc. So we will try to use the cavities without it for a first shot. We might be lucky and the difference in frequency is not that big. (370MHz max possible). If we are lucky it's small (and we can slightly tune it by choosing the absolute temperature if they are not equal in length)). We can still work on the alignment and locking and upgrade next week or so. But even if we have a beat at 300MHz we can check the performance of seismic isolation and scattered light and see if we made a big mistake...

  768   Fri Dec 23 18:39:10 2011 FrankNotesRefCavradiative heater

Situation: The heater wire should not go all the way to the vacuum feedthrough connector. Instead the connection from the heater to the connector should be made with some low conductivity material to only add heat where we want it.

So i tried to solder copper wires to the end of the Nichrome wire and failed. Whatever people suggest on the web does not work properly. i tried 6 different kind of tin with different fluxes, 3 separate fluxes incl rosin and acid flux for brazing steel. Oxidized, scratched, etched the surface - nothing worked. you can get a blob of tin at the end but not a clean solder joint.

will go for crimped connections unless someone has an idea....

  775   Thu Dec 29 17:56:39 2011 FrankDailyProgressRefCavradiative heater

went to Downs to get the right crimp tool for the d-sub connectors. It's a DMC crimper for D-sub contacts for UHV connectors (crimp tool). Turns out that the DMC tool does not properly fit the contacts we have, (female pins).. The contacts we have are NASA approved, space qualified, low outgassing crimp contacts (link) and are the same as delivered with the aLIGO, in-vacuum PEEK D-sub connectors. The crimp location seems to be too high for those contacts, but is still working. The insert is the correct one (description), (pdf).

562.jpg

Interesting is that the pins which come with the UHV connector have little colored markings on them as can be seen on the picture (see above link to female pins). Marking can not be removed with methanol, acetone etc.. My guess is that it's OK and actually might be not simply paint.

Will use d-sub contacts to crimp on the nicrome wire and run kapton insulated copper wire to the main vacuum feedthrough. Having the contacts right next to the copper tube makes it a lot easier to work on the whole cavity assembly.

  • wire can be stripped using an old rotary sanding tool where only the matrix is left (no abrasive stuff left).
  • Crimp tool has to be set to setting 1(!) to crimp correctly, default is 5.
  • clamped the wire using #2-56 screws and washers facing round side down to not have sharp edges which could cut the insulation of the wire.
  • added tiny amounts of the super thin kapton tape to further protect the wire
  • total amount of turns is 21
  • total resistance is 154ohms - calculated value was 147ohms
  • crimped femaile contacts to both ends
  776   Thu Dec 29 23:57:28 2011 FrankPhotosRefCavradiative heater prototype

564.jpg

569.jpg

572.jpg

574.jpg

  691   Mon Oct 3 23:54:19 2011 frank, taraDailyProgress re mode matching

As the cavities' height changed, I adjusted the lenses to fine tune the mode matching for RCAV, the visibility is ~85%

We might want to use a bigger beam splitter (the current one is 10mm cube) where the beam split to ACAV and RCAV paths, the spot radius is ~ 3mm. It might cause some diffraction problem.

The next step is to check the beat signal with the previous FSS. We suspect that something might be wrong with the TTFSS. If the old FSS can give us with better signal,

we will use the old one.

 

  693   Tue Oct 4 23:20:57 2011 frank, taraDailyProgress re mode matching

 

  I readjusted the lenses for mode matching a bit more and the visibility for both cavities are now ~93%. We will check beat measurement with floated table tomorrow.

  714   Tue Oct 25 23:13:57 2011 Tara, FrankDailyProgressSeismicre-measured the spring constant for the RTV springs

as we only did a quick-and-dirty measurement of the spring constant last time we re-measured it a couple of times. The resonance frequency varies by a few Hz from measurement to measurement and it also depends on over how many periods (and where, beginning or more to the end) of the ring down we measure. So we will analyze some ring down measurements using the same setup (Al-block with accelerometer resting on one RTV spring sitting on the optical table) and take the average for a new calculation.

  764   Thu Dec 22 16:28:10 2011 FrankDailyProgressSeismicre-measuring seismic coupling to cavities

trying to verify our FE model for both cavities. In order to measure the coupling i tried different versions of attaching a "shaker" or PZT  to the table to excite the table in vertical direction. As i'm worried about attaching something to the floating table as it could easily destroy the attached PZT or shaker i try to excite the non-floating table. The best solution i found is to put a PZT right below the vacuum chamber underneath the optical table. It does not look very sturdy but the performance is very good. Driving the PZT with only a few volts using our HV piezo amplifier (old, modified PMC servo) i can easily get an SNR of 100 above the seismic noise. And it's making a lot of noise if you drive it even harder. Turns out that the optical table is a good loudspeaker. Also driving it a low frequencies one can feel the whole lab vibrating!

P1810521.JPG

Measurements of the coupling are currently performed. Check back later...

  821   Sun Feb 12 19:40:50 2012 FrankDailyProgressSeismicre-measuring seismic coupling to cavities

trying again to measure the coupling from seismic to cavity length for the individual cavities. Measuring the coupling to differential length (beat signal) is not a problem at all, but to the individual length.

The problem arises from the small coupling coefficient from vertical acceleration to changes in length. to not measure any effect from the filtering from the stack we have to measure at low frequencies. The first mechanical resonances occur at around 6Hz, the stack itself has it's first resonance at 16Hz. So we have to measure below 5Hz. The coupling to changes in length is small, about 1e-9 * Length of the cavity  [units: m/(m/s2)], so about 2e-10 m/(m/s2). The signal from shaking the table around 1Hz is estimated to be a few hundreds of Hz/rtHz with maximum modulation. However the laser frequency noise is 10kHz/rtHz @1Hz, so we have to integrate very long to get a reasonable SNR. We cant use anything on the table to pre-stabilize the laser to reduce it's noise as this would be shaked as well and we don't really know which one we actually measure.

For the first cavity we have to look at the feedback to the laser pzt as this tells us how much the laser frequency has to be corrected. We assume that shaking the table at 1Hz does not mechanically modulate the laser frequency in any other way. For the second cavity we can't simply lock it the usual way as we would have two coupled cavities (that's what we measure using the beat signal already). So we have to lock the laser to the second cavity instead without using the FSS path by feeding back to the laser (fast actuator) instead of the VCO.

A first measurement showed that we have an additional mechanical resonance around 6Hz which we currently don't have in our current stack model (and actually don't know exactly where it's coming from).
We measured the Eigenmodes of the stack some time ago and have two candidates for it (see here)

  1. beam line, translational motion, f = 6.96 Hz, Q = 21.5 
  2. horizontal transverse motion, f = 6.35Hz, Q = 25.9.

So i will re-measure the TF below 10Hz to clearly identify which one it is.

table2beat_TF.pngtable2f_TF.pngfnoise_RCAV.png

resonance frequencies of the stack : 16.1Hz and 55.6Hz
other resonance frequency: 6.5Hz

coupling to cavity length: COMSOL model: 53 kHz / (m/s2)
                                               measured:
~100 kHz / (m/s2)

All data and plots on the svn in /measurements/2012_02_12.

 


Notes for calibration:

TF to beat signal:

  • accelerometer sensitivity: 1023mV/g
  • range of PLL VCO: 10kHz -> 7kHz/V

TF to fast actuator:

  • accelerometer sensitivity: 1023mV/g
  • FAST MON output:  3.07 MHz/V

 

  753   Thu Dec 8 15:59:21 2011 FrankSummaryPMCrealignment

started realigning everything from scratch and calibrate all channels right. PMC optical power channels need re-calibration.

input beam to PMC: 28.9mW
PMC transmitted beam: 23.4mw
transmission trough curved mirror: 1.63mW

--> only 81% visibility (87% including back mirror leakage), but should be enough for what we want to do. Don't know the loss mechanism (didn't investigate)

  754   Thu Dec 8 20:28:06 2011 taraSummaryPMCrealignment

A reminder for Frank about the setup, 

  • The AOM's case on RCAV beam path is not screwed down to the body, so it will be blocking the beam.
  • The height for Faraday isolator behind the PMC is not correct, i think only ~80% of the power is transmitted. I haven't had it fixed yet
  • When I measured the visibility of RCAV, I scanned the cavity and minimize the dip as seen on the REFL RFPD. I got sth ~90% transmission, but when I measured the actual tranmitted power, the visibility is lower than that, maybe only~ 75%.
  • There is some weird reflection on ACAV RFPD, I'm not sure if it comes from the window or not.
  755   Thu Dec 8 21:06:10 2011 FrankSummaryPMCrealignment

thanks, for the info.

I only did the PMC so far as i has to fix the daq and add the new channels. What's the problem with beam height of the isolator? Is the beam too low or the mount too high? Do you know?

Quote:

A reminder for Frank about the setup, 

  • The AOM's case on RCAV beam path is not screwed down to the body, so it will be blocking the beam.
  • The height for Faraday isolator behind the PMC is not correct, i think only ~80% of the power is transmitted. I haven't had it fixed yet
  • When I measured the visibility of RCAV, I scanned the cavity and minimize the dip as seen on the REFL RFPD. I got sth ~90% transmission, but when I measured the actual tranmitted power, the visibility is lower than that, maybe only~ 75%.
  • There is some weird reflection on ACAV RFPD, I'm not sure if it comes from the window or not.

 

  759   Fri Dec 9 06:32:24 2011 TaraSummaryPMCrealignment

The V-block's height is a bit too high. The beam height is very close to 3".

Quote:

thanks for the info.

I only did the PMC so far as i had to fix the daq and add the new channels. What's the problem with beam height of the isolator? Is the beam too low or the mount too high? Do you know?

 

 

 

  437   Mon Dec 20 19:55:11 2010 taraDailyProgressopticrearraging optics for beat measurement

I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.

  440   Thu Dec 23 22:41:28 2010 taraDailyProgressopticrearraging optics for beat measurement

Beat measurement optics' height is changed to 3". I cleaned all optics already, but I couldn't really clean 1/2 and 1/4 wave plates, one of the f =200 mm lens is quite hard to clean.

I'll wait and ask someone before trying to clean again. I cannot lock both cavities at the same time, once I can, I'll align the beam on the PD.

Also ACAV's PD for ACAV_trans_PD is broken. It gives out 11 V regardless of the beam falling on the PD, so I replace it with a PD that is used for NPRO_PWRMON.

 

Quote:

I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.

 

  441   Sun Dec 26 02:42:47 2010 taraDailyProgressopticrearraging optics for beat measurement

Both cavities are locked at the same time. The temperature setting are, RCAV = 34.95, ACAV = 37.2.

I realigned the beam onto the PD to get maximum contrast. I'll readjust the setting back to the original value

and see if the beat noise is improved.

I just notice that one of the beam on the mirror on ACAV's path behind the cavity is almost clipped. I'll readjust it tomorrow.

Quote:

Beat measurement optics' height is changed to 3". I cleaned all optics already, but I couldn't really clean 1/2 and 1/4 wave plates, one of the f =200 mm lens is quite hard to clean.

I'll wait and ask someone before trying to clean again. I cannot lock both cavities at the same time, once I can, I'll align the beam on the PD.

Also ACAV's PD for ACAV_trans_PD is broken. It gives out 11 V regardless of the beam falling on the PD, so I replace it with a PD that is used for NPRO_PWRMON.

 

Quote:

I designed the layout for optics behind the cavities for beat measurement, and calculated the mode matching for the beam.

Since the current optics height for beat is quite high (7 inches), we want to lower it to 3 inches, make it more symmetric, and more compact.

The PD's diameter is 300 mm, so the beam spot on it will be ~50um.

All the lenses I need are prepared.

 

 

  442   Mon Dec 27 02:51:33 2010 taraDailyProgressopticrearraging optics for beat measurement

I measured the beat noise after I realigned all optics behind the cavities. The power has not been reduced to 1 mW yet.

This is just a quick measurement to see where we stand (red curve). The noise gets worse compared to the best measurement (green) before the optics behind the

cavities are rearranged, but the mechanical peaks around 1kHz are suppressed significantly.

Attachment 1: beat_2010_12_27.png
beat_2010_12_27.png
  1385   Fri Nov 8 03:36:44 2013 taraDailyProgressopticredo- PMC path

I'm re-arranging the optics in PMC path a bit. The work is in progress, so ACAV path is still down.

I'm investigating why ACAV TTFSS performance is worse than that of RCAV. One thing is that ACAV has the PMC. This area has not been optimized for awhile, so I'm checking everything.

  1386   Mon Nov 11 19:37:13 2013 taraDailyProgressopticredo- PMC path

PMC path is back, I aligned the polarization of the input beam to the BB EOM for TTFSS. The visibility of PMC is now ~ 80%.

  829   Wed Feb 15 14:09:34 2012 FrankDailyProgressBEATreduced RG58 cable length to optimum value

reduced our RG58C/U cable length to optimum value (134.2ft) and characterized it. Below the confirmation that it is what it should be.

loss is 8.6dB, delay 206.4ns

RG58_134ft.png

  351   Thu Sep 9 23:03:40 2010 taraSummaryRefCavreduced back reflection

    After PBS is rotated to the right position (yesterday I made a mistake by minimizing the split beam.

The split beam is minimized. This guarantees that the beam passing through is highly linearly polarized.

The reflection back to PMC is reduced from 1.9 mW to ~1.1 mW.

The cross correlation between the beat measurement and RIN is measured before and after the reduction of back reflection.

The plot shows certain correlation between RCAV's RIN and beat measurement when there is back reflection to PMC.

  1243   Wed Jul 17 18:29:37 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
Went on a tour to 40m lab led by Jenne. It's basically a prototype of the ones in Livingston and Hanford. It allows LIGO to test coatings, control systems, etc. before AdvLIGO is even built.

I tried making the drift go away, but it seems to me it got better, and then got worse.
I tried turning off just one HEPA filter, then two. I couldn't really find that much stuff to insulate the fiber, so I used the bubble wrap that the coil came with to wrap around the coiled fiber. However, that didn't seem to really help at all.

With only 1 HEPA filter off (the one closest to the input), I was able to get a rise time of about 35s, which is pretty similar to what there was yesterday. With the 2 HEPA filters off, I got a rise time of about 5s.

For some reason, at one point the signal just started oscillating like crazy. I lowered the power coming from the output fiber (from 0.5 to 0.4mW) so it would be closer to the original beam (0.3mW) and there wasn't noise any more, but I'm not sure if it was because of the power differential at all.


Questions:
How much drift is allowable? Does it have to be flat or is it okay if it is simply linear?

I can increase the output from the fiber to 1.3 mW.


Note:
  • A message has popped up on the oscilloscope that I've been using saying it needs to be recalibrated.
  • The wire connecting the probe to the power meter (PM100D, the red one) is coming out of the insulator.
  • Rana had me bring the SR620 to 40m so that's where it is.
  1245   Sat Jul 20 23:39:09 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
July 18
Redid inventory of the lenses and printed out a new sheet because there are fused silica and BK7 lenses, which have different focal lengths for a given radius of curvature. It only has the lenses in the box. Tara had like 6 to 8 other ones but I don't know where they are.

Looked for papers that give numbers for noise added... Like before, I'm having trouble.

got login for SVN to work

Evan helped come up with other solutions to try to reduce the drift on signal from the recombined beam. We put UHV aluminum foil on the coil of fiber to reduce the acoustic noise but it didn't seem to have much effect on the drift. Acoustic sound affected the fiber because the drift seemed to speed up a little bit when we closed the cabinet door and jumped around. When the lab door was closed, there was a spike in the signal but thing settled down fairly quickly. We turned off both Hepa filters but like yesterday, it also didn't seem to do much. We elevated the coil off the table by using the black rectangular clamps to dampen possible transfer of movement from the table to the coil.
We locked the laser to the cavity to reduce the laser noise. The error and control signals were very steady compared to the drift in the beam signal.

We calculated the change in frequency over 1 period of drift is about 5 MHz, and for the fiber to change by 1 wavelength, it would take a temperature change of 16 mK. Looking at Rana's graph of for noise calculations (http://nodus.ligo.caltech.edu:8080/PSL_Lab/1205), we calculated the rms temperature noise due to ambient air at 100 mHz (because the period of the drift was on the order of 10s) was 100mK rms, which is an order of 10 larger than the calculated change in temperature.

The fiber passes by the laser, which is emitting a bit of heat, which may be a part of what is causing the drift.
  1251   Tue Jul 23 10:29:12 2013 EricaDailyProgressfiber opticreducing drift in the recombined beam
July 22, 2013

We placed a plastic container from the GYRO lab over the spool of fiber. We wiped everything down w/ isopropanol. The cap is placed top side up and then the bottom is placed upside down on to the top of the cap. This is because the inside of the cap has ridges. There are two holes that the fiber is threaded thru. We used bubble wrap to cover it. It's not the most airtight but it should be okay. We left the aluminum foil surrounding the spool, to restrict air flow into the fiber. Then we left it there for awhile but coming back to it, there wasn't much improvement.

Evan suggested using a AD 590 to measure the temperature fluctuations of the table. Rana suggested we use the substitute for AD 743 that Zach found, which I need to find. Went to 40m to get a nicer circuit board and find a FET OpAmp with low current noise. We got a Vector Circboard 8015 and two OPA604's. We'll be building two setups so we can cross-correlate them and make sure the measurements are accurate.


tomorrow we will be soldering stuff.


  1102   Sun Feb 24 01:16:26 2013 taraDailyProgressRefCavrefcav and mount assembly

Thermal shields and caps are ready. I cleaned them in ultra sonic bath with Isopropanol. They fit nicely to the mount.

The caps are teflon.

photo(9).JPG    photo(8).JPG

 

==Wire Heater==

I'm think about how to wire the heater around the cavity. I'm reading Frank's entries in PSL:765,768 ,776,786, . Seems like I might need to drill a few holes on the shields for the wires.  There are still more similar wire left. I'll calculate how long the wire has to be for heating the cavity up by 20 K.

 

  185   Tue Jun 29 15:13:26 2010 FrankNotesRefCavrefcav physical properties

refcav physical properties from CAD model for heat capacity calculation

volume (incl. mirrors, center bore, venting hole) : 23.47900 (in^3) = 0.000384751876 m^3

mass (incl. mirrors, center bore, venting hole) : 1.86900 pounds = 0.84776414 kilograms

 

  33   Fri Jan 15 11:35:17 2010 FrankLaserRefCavrefcav update

the last couple of days we fixed a couple of thinks:

We found a wrong calibration of the temp readout of the first refcav, which gave us a wrong residual noise level compared to the other one. The absolute value was almost correct so we didn't realize this before. Now we are limited by the DAQ noise so the next step will be improving the gain settings in the temp sensor readout-box.

A big problem is the changing room temperature as soon someone opens the door even for only a couple of seconds. The temp control of the lab goes crazy and changes a couple of degrees and is oscillating half a day after that. The delay to the cavities is about 30min and a couple of deg changes of the room temp also change the cavity temperature, only a couple of tens of mK but enough to shift both cavities away from each other as the room temp couples different into both due to the different thermal insulation (insulation and time constants are different). We opened the room temp sensor and adjusted the temperature to i higher level, removed surrounding parts to get a better air flow to the sensor. We don't understand why opening the door has such a large effect on the room temp as 10 seconds of open door don't change the room temp by 2 degC or so. So if anybody has an idea plz let us know even if it seems to be stupid.

In order to improve the temp stability of the analyzer cavity we added a second layer of insulation and wrapped the whole thing in aluminum foil, see picture below. The insulation is 2" thick, except a small part at the large flanges at the end where its only 1" thick. We also changed the gain of the temp sensor readout in order to reduce the influence of DAQ noise. If nobody is working in the lab we have a stability of about 6mKpp within hours. As soon someone is working in one of the labs this changes to tens of mK for working in other labs to about a hundred mK if working in the PSL lab. We are currently working on improved servo settings...

100_0542.JPG

  791   Sat Jan 21 01:20:28 2012 FrankDailyProgressRefCavrefcav work

re-did the RF wiring for both cavities:

  • Power splitters are now located on the table below the TTFSS box. This keeps all cables from/to the PDs and EOMs very short
  • Power level at res. EOM is ~20dBm, LO is ~7dBm (TTFSS has an internal amplifier) - Master LO is still a SR345 with 23dBm.
  • Removed all old cables which we don't need anymore and moved the ones used from the table to the framing structure to get less seismic coupling to the floating table from them.
  • Finished phase adjustment for the TTFSS and locked the cavity using all three actuators.
  • Temp feedback to the laser is now done by the TTFSS unit. There is NO computer control for any of the FSS stuff anymore - only for the PMC. cable to laser unit is temporary as we don't have the right cable length available.
  • Power is adjusted to 1mW (total)
  • We still don't have enough gain. Common gain is at max, fast at 782, (offset 500).
  • Measured in-loop ep noise floor - will add plot later. Noise floor measured at OUT1 of TTFSS box (common path, mixer output) is ~10nV/rtHz
  • Error signals are still pretty tiny (230 mVpp)
  • re-wired beat setup. Need to add a coupler to hook up the frequency counter in parallel. Will use that for characterization of radiative heater and temp feedback to it for beat note stabilization.

Next steps:

  • Full characterization of 14.75MHz res. PD from TNI
  • build a second PD for 14.75MHz.
  • add some channels to DAQ - there are currently no FSS channels at all
  • measure beat note by Tue
  • finish in-vac wiring
  • open vacuum can and install rad shields+heater
  • while in air measure TF from table to top stack with small accelerometer and compare with model
  793   Mon Jan 23 09:16:43 2012 ranaDailyProgressRefCavrefcav work

 

 The PD seems certainly good enough - no need for new pre-amp. With such a high Q resonance, you might be limited by the 1 pA/rHz of the preamp, but if so that's OK.

Error signal size seems too small: for 1 mW and 6 kOhm from the RFPD...

  794   Mon Jan 23 11:36:18 2012 FrankDailyProgressRefCavrefcav work

Right, it's certainly good enough for now and the next months. However there are better opamps available which might give us a better SNR at lower power levels which i would like to try (and replacing opamps is only a few minutes). This would give us the chance to operate at lower power levels with better SNR, which might be useful later.

The error signal size mentioned has been measured with an un-characterized PD from the TNI, where i already mentioned that they are too small but i don't know what's inside the PD. We will check today what we get from the new PD and then either fix/modify the TNI PD or a second PD from LLO (where i have to replace the diode which has a big burn spot)

Quote:

 

 The PD seems certainly good enough - no need for new pre-amp. With such a high Q resonance, you might be limited by the 1 pA/rHz of the preamp, but if so that's OK.

Error signal size seems too small: for 1 mW and 6 kOhm from the RFPD...

 

  112   Sun May 2 19:18:36 2010 FrankMiscRefCavreference cavity moved to new chamber

i finally moved the reference cavity to the new chamber and pump it since Friday. The legs are now insulated and it comes with a removable, thick insulation using the good CertiFoam25 insulation.The sensors for stabilization are now glued to small pieces of Kapton tap which is sticks directly to the chamber surface. I'm still using the four AD590 sensors as we have all the electronics available and ready to use. I modified the temperature sensor readout box a little bit to gain a little more SNR. The gain in the first stage (TIA) is now 29.4k (~9.2V output). The individual outputs are now connected to the DAQ. In addition the sum of all four is subtracted from a reference voltage (AD586 reference) so that the output is 0 at 35C with a range of +-5K (we need at least 4.5K for tuning one FSR, so to not be stuck at either ends i made it a bit larger ). This signal is also connected to the DAQ. An additional sensor (PT1000)  is now connected to the top plate of the stack, right below the reference cavity. Readout electronics is in preparation, as well as for the other platinum sensors we can put on the outside of the chamber (not done yet). I'm also planning on replacing the noisy power supplies by low-noise current sources to drive the heaters. The required heating power could be reduced a lot to ~10W total now, measured with a not fully sealed insulation and missing parts. So i expect even less when we are done with that.

  298   Thu Aug 19 19:17:44 2010 FrankSummaryDAQremoved connecting blocks J21 & J22

removed both 9-pin D-SUB blocks (blocks J21 & J22) which were used for the RF photodiodes (PMC, RCAV) before (only to power them).
As we hooked them up to individual power supplies a long time ago they are free to use for the temp readout of the cavities.

  420   Mon Dec 6 22:09:59 2010 frank, taraDailyProgressBEATreplacing PMC, adding EAOM

Today we 1)replaced out PMC with DMASS' PMC and get better transmission efficiency, 2) added EAOM to modulate the laser intensity

3) measured TF to see how RIN couples into laser frequency shift, it is small and not the current limiting source for now.

 

Our PMC is not very clean and get the transmission only ~60-70%. The PMC we got from DMASS is much better, now the transmission is up to ~80-90%, we have not

align it carefully yet.  After replacing the PMC, the beat noise did not change.

 

The Faraday isolator was re-installed and optimized, I used the wrong side before and dumped the beam inside the isolator, instead of outside.

A PBS and a 1/2 wave plate were installed after the PMC to adjust the power without changing the power input of the PMC, the beat noise gets higher

a bit.  I mounted the beam splitter for beat signal on a more rigid post, and aligned the two beams, then measure the beat noise.

See plot.

 Intensity modulation set was installed. The set consists of a 1/2 WP, an EAOM, a PBS. Then we amplitude modulated by sending a sine wave to

the EAOM, and measured the TF between (The excitation is sent to the EAOM)

 

1) intensity modulation and ACAV_trans_PD

2)intenisity and RCAV_trans_PD

3) intensity and beat noise

4) ACAV_trans_PD and VCO feed back to AOM

extra: we measure the TF between PMC_trans_PD and ACAV/RCAV_trans_PD, since the line width of PMC is much larger than that of RCAV/ACAV,

we can measure the TF of their poles.

 [The plot will be posted soon]

Attachment 1: beat_2010_12_07.png
beat_2010_12_07.png
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