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ID Date Author Typedown Category Subject
  103   Mon Apr 12 11:04:15 2010 Tara ChalermsongsakLaserLaserPSL layout for new setup

The layout for the new PSL setup ( lenses, and their positions are to be calculated.)

A Lightwave 100mW NPRO laser will be the source. AOM will be in the ACav path.

Two cavities will be covered by a box of insulation/ heater.

 

1) From the laser to the PMC,

    1/4 waveplate, to linearly polarize the elliptical polarized beam from NPRO

    1/2 wave plates and PBS, to adj the power of the beam

    lens, to focus the beam to the EOM

   two lens, two mirrors, to mode match the beam to the PMC

   a photodiode, a lens, two mirrors, (one for steering the beam, another one for attenuating the beam), for PDH locking

 a photodiode and a ccd camera, for the beam behind the PMC

* there will be a Faraday Isolator somewhere here. I forgot to add it.

 

2) From PMC to PBS

  a lens to focus the beam to 35.5 Mhz EOM

  1/2 wave plate, to adjust the power between two beams for  ACav and RefCav

 PBS, to split the beam into two paths

 

3) AOM path

 1 PBS, for reflected beam from the AOM

 a lens, an AOM, 1/4 waveplate, two irises, 1 curve mirror; to double pass the beam and shift the frequency

another iris and a mirror, to select only the 1st order beam and send it to  ACav.

 

4) RefCav/ACav path

 1/2 wave plate, to correct the polatization

two lens and a set of periscope, to mode match the beam to the cavity

 a pbs with 1/4 wave plate, a lens, a mirror, a photodiode, to PDH lock the beam

 

5) Transmitted beam

1/4 waveplate, to linearly polarize the transmitted beam

a photodiode/ a ccd camera to monitor the transmitted beam with necessary mirrors

lenses, to focus the beam to the PD that measures the beat signal

 a beam splitter, to mix two beams together

 

Attachment 1: psl_layout_04_11_10.png
psl_layout_04_11_10.png
  106   Tue Apr 13 15:06:35 2010 Tara ChalermsongsakLaserRefCavHOM, from carrier and both sidebands

HOM frequency shift for RefCav is plotted below. The second one has clearer dots.

Y axis is the frequency shift in MHz

X axis is the (n+m)th order of the Hermite Gauss mode

The waist of the beam inside the cavity is 261 um* (symmetric cavity, R =0.5m, L = 0.2032 m.) 
Thus, the frequency shift between n+m+1 and n+m mode is 219.763 MHz. (see Lasers, p 762 for details)

Blue line represents the 0th order of the carrier's frequency (thus =0) The purple and the brown lines, at y= 35.5 and -35.5 MHz, are the 0th of + and - sidebands respectively.

The color dots represent the frequency shift from Higher order mode which is specified on x-axis, blue for HOM from the carrier's frequency, purple and brown for HOM from +/- sidebands.

 Choosing 35.5 sideband seems to be ok, the 27th order should be small and negligible. 

 

*The number 237 um for waist size is the effective beam waist size of the "emerging beam," not the real waist size in the cavity. The beam passes through the mirror which acts as a negative thin lens and changes the

beam parameter. 

Attachment 1: HOM_df_219.32MHz_02.png
HOM_df_219.32MHz_02.png
Attachment 2: HOM_df_219.32MHz_03.png
HOM_df_219.32MHz_03.png
  114   Tue May 4 03:40:00 2010 ranaLaserRC noiseupdated noise budget

 code is in SVN

Attachment 1: rc_sio2_300.pdf
rc_sio2_300.pdf
  119   Tue May 11 22:26:34 2010 Tara ChalermsongsakLaserLaserBeam waist measurement

 

I measured the beam waist of Lightwave NPRO 1064nm 100mW with WinCamD.

The nominal beam waist are 380 um and 500 um, 5cm from the center. the number I got from the measurement are 237 um (major) and 187.3 um (minor) which are quite different from the nominal values.

I'll check it again tomorrow to see if the data are still the same.

 

 

Attachment 1: beamwaist.png
beamwaist.png
  120   Wed May 12 22:10:13 2010 Tara ChalermsongsakLaserLaserBeam waist measurement

I measured the beam waist again. The laser was operated at full power ~100mW. A mirror attenuated the beam to 60 uW and ND  4.0 was on the CCD.

The fits give

 Wx = 155 um, 3.45 cm in front of the opening.

Wy = 201 um, 2.8 cm in front of the opening.

 

Attachment 1: fit.png
fit.png
  121   Thu May 13 13:41:32 2010 Tara ChalermsongsakLaserLasermode matching from laser to PMC

Details for Mode Matching

 

1)   Laser to PMC

 

The laser has

              Wx = 155 um, 3.45 cm in front of the opening.

            Wy = 201 um, 2.8 cm in front of the opening.

 

The average number for calculation is w = 180 um, 3cm  in front of the opening.

First, we focus the beam to the EOM, w can be  250 – 500 um.

We pick 350 um.

F= 200 mm,

W1= 180 um

W2=350 um

Distance from w1 to the lens, d1, = 9.36”.

Distance from w1 to w2, L, = 22.8 “.

 

 

Then we mode match this beam to PMC

F1= 50.2mm

F2= 63mm

W1=350 um

W2= 370um

Distance from w1 to first lens, d1,         =157mm =6.2”

Distance from first lens to 2nd lens, d2 =120mm = 4.7”

Distance from 2nd lens to PMC, d3         = 358mm

Distance from w1 to w2, L,                      =  63.5 cm = 25”

 

I'll check if I can find f =200mm, 63mm, 50mm in the lab or not.

  122   Thu May 13 20:56:57 2010 FrankLaserLaser100mW NPRO problems

we still have serious problems with the 100mW laser head. I traced it down to the connection between the PCB and the hermetically sealed optical part. There is a really loose connection somewhere. The connector seems to be OK, the PCB and all solder points are OK too (visually). But if you slightly touch the PCB you can see the yellow LED flickering, if you touch it a bit more the laser goes off and on. This happens too if you touch the D-SUB cable on the back. I added some little stress to the PCB when putting the thing back together, now the situation seems to be better, but is far away from being gone. In order to get started we are using it now as long as we can and think about a solution in the meantime. One option would be to fix the busted NPRO Peter has. This would probably take about a week or so. We have to align the laser diode and focusing lens and solder (!)  the focusing lens in place. The problem is that you can't align in vertical direction, so you have to remove the laser diode, put some more or less indium foil below and start again from zero. But it's an option. Peter had it already back to 550mW (out of 700mW) or so (for a couple of minutes, simply holding all parts in place. So the difficult part is to keep it permanent in the right place...

  123   Mon May 17 21:32:35 2010 Tara ChalermsongsakLaserLaserPMC alignment

I'm trying to align the PMC.  The transducer is connected to the PMC servo card's HV out.

HV in is driven by a function generator with triangular function. The output signal looks weird. It is not a nice triangular form, it's more like a u shape waveform connecting to each others with a plateau on top.

 

I'll check if the transducer on the PMC and the HV out from the card are working correctly or not. Right now, there is not a glimpse of signal coming out of the PMC on CCD.

  124   Tue May 18 15:21:12 2010 Tara ChalermsongsakLaserLaserPMC alignment

Quote:

I'm trying to align the PMC.  The transducer is connected to the PMC servo card's HV out.

HV in is driven by a function generator with triangular function. The output signal looks weird. It is not a nice triangular form, it's more like a u shape waveform connecting to each others with a plateau on top.

I'll check if the transducer on the PMC and the HV out from the card are working correctly or not. Right now, there is not a glimpse of signal coming out of the PMC on CCD.

don't the words HV IN ring a bell? look into the schematic. there are only a couple of inputs at the front so it's not too hard to figure out why there was already a BNC cable connected to that input. Did you check the monitor signal? If you would you would have seen that your HV supply is missing now

 

  125   Wed May 19 00:18:45 2010 Tara ChalermsongsakLaserLaserPMC alignment

After checking the PMC servo card,

ramp signal goes to ext DC 

HV in is applied properly,

HV out is fixed.

Now the PMC is scanning and working fine.

The alignment is done. Although optimization is still needed,  I can work on the rest of the setup.

 

*note on PMC servo card

Ratio between Voltage input (Vin), V monitor (Vmon), and High Voltage output (HVout),

HVout = 24 Vin

Vmon = 1/50 HVout

Vmon = 24/50 Vin

 see the attachment

Attachment 1: D980352-B.pdf
D980352-B.pdf
  126   Thu May 20 21:50:35 2010 taracLaserLaserPMC is almost ready to be locked

 We still need two SMA cables. One connects between 21.5Mhz EOM and PMC servo card, another one connects between PMC PD and the servo card.

The 21.5 and 35.5 local oscillator were in the wrong slots, we fixed them.

The 21.5 MHz  photo diode that detects the reflected beam from PMC saturates at 15 mW.

Now I'm trying to optimize the PMC setup so that we have maximum transmittedd power.

  127   Mon May 24 09:56:19 2010 ranaLaserPMCPMC is almost ready to be locked

You should make sure not to blow up the PMC PD: i.e. the total power on the PD out of lock should be less than 100 mW. The beam size on the PD should also be ~0.5 mm diameter with the actual beam waist being more like 0.3 mm dia.

PD should also be tilted by ~30 deg from normal incidence and the reflection dumped. Its OK if the RF output saturates somewhat at the peak of the PDH signal, but the in-lock RF level should be below ~50 mVrms into 50 Ohms.

  128   Mon May 24 19:30:15 2010 ranaLaserPMCPMC is almost ready to be locked

Quote:

You should make sure not to blow up the PMC PD: i.e. the total power on the PD out of lock should be less than 100 mW. The beam size on the PD should also be ~0.5 mm diameter with the actual beam waist being more like 0.3 mm dia.

PD should also be tilted by ~30 deg from normal incidence and the reflection dumped. Its OK if the RF output saturates somewhat at the peak of the PDH signal, but the in-lock RF level should be below ~50 mVrms into 50 Ohms.

 The power is small, our laser is 100 mW. The power on the PD is not saturated. Right now it's receiving ~10mW. It's tilted a bit and the reflected beam is blocked appropriately.

  129   Mon May 24 19:40:12 2010 taracLaserLaserRef Cav prealignment

 

Dear elog

  I don't know why I can't lock the PMC. After changing the 21.5 MHz card because of the loosen SMA connector, the 21.5 MHz EOM is working.

The error signal looks good. I adjusted the gain, flipped the phase by 180 degree, and still cannot lock the cavity. 

(The medm was frozen this morning, Peter helped reset it back to work this after noon.) It might be insufficient amount of power coupling into the cavity.

The minimum reflected beam I could get is only ~1/2 of the total DC power, I'll try to align the beam and move the lens a little bit more to see if I can optimize it better.

So I skip this PMC part for now, and pre align the path to mode cleaner. The mode matching is ok. Two lens, f1=114.5 and f2=286.3 mm are good. A CCD behind the cavity is set in place.

 

  130   Tue May 25 17:01:57 2010 taracLaserLaserPMC cavity is locked

      After adding another 1/2 plate to have P wave into the cavity, I can lock the PMC cavity. It's been 30 minutes so far.

There is only one transmitted beam now (there were two when I used S wave.) 

 

     When I work or knock on the table, sometime the beam switches to another mode (might be it's side band.)

It's very close to the main TEM00 mode. I need to adjust the DC offset a little bit to get back.

 The incoming power is 9 mW, and the Transmitted beam has ~ 6 mW.

Current setting:

RF Amp: 7V

Phase shift: 2.87 + 180

Gain: 27.91 dB

DC offset: -2.3 V

   

  

     I tried to pre align the ref cavity. It's harder than I thought, can't see the beam that well. I'll have to check the manual for the laser controller, so that I can

scan the RefCav when I align the beam into the cavity.

  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.

  132   Thu May 27 11:18:51 2010 taracLaserLaserSchematic for FSS servo and Lightwave 126 1064 100mW

This is the schematic of PSL fss servo.

I have to make sure that the modulation voltage will not exceed the controller's limit (0-100V.)

 

Attachment 1: D980536-D.pdf
D980536-D.pdf
Attachment 2: npro125126_ds_cl_ae_020606-1.pdf
npro125126_ds_cl_ae_020606-1.pdf npro125126_ds_cl_ae_020606-1.pdf npro125126_ds_cl_ae_020606-1.pdf npro125126_ds_cl_ae_020606-1.pdf npro125126_ds_cl_ae_020606-1.pdf
  133   Thu May 27 18:20:42 2010 taracLaserLaserAligning RefCav

I switched the cable from the 10W controller to the original controller for 100 mW laser. It is working well now, the cables are tied properly.

For now, I don't need to use the FSS servo card to scan the laser frequency.

I'm using a function generator for fast channel (PZT), and a voltage calibrator for slow channel (thermal control.)

The alignment is in progress. With the aid of a CCD camera and a macroscopic lens, looking for the beam position on the mirror is getting easier.

Currently I see some light at the back of the cavity.

  134   Fri May 28 20:46:14 2010 taracLaserLaserProgress on PSL: Aligning RefCav

 Since the frequency of the laser going into RefCav is determined by PMC ,I decided to temporarily remove the PMC for now, so I can scan the laser frequency while aligning RefCav.

It might not be a good idea since the PMC might alter the beam path a little bit, but I just want to align the cavity first.

The plan is after  RefCav is aligned, I'll bring back the PMC and fine tune the beam going to RefCav again.

I still got many higher order modes coming out of the cavity.

 

  135   Sat May 29 12:01:17 2010 FrankLaserLaserProgress on PSL: Aligning RefCav

Quote:

 Since the frequency of the laser going into RefCav is determined by PMC ,I decided to temporarily remove the PMC for now, so I can scan the laser frequency while aligning RefCav.

It might not be a good idea since the PMC might alter the beam path a little bit, but I just want to align the cavity first.

The plan is after  RefCav is aligned, I'll bring back the PMC and fine tune the beam going to RefCav again.

I still got many higher order modes coming out of the cavity.

 

 the PMC is locked to the laser, so it follows the NPRO frequency when you scan the frequency

  136   Sun May 30 22:49:28 2010 taracLaserLaserRefCav is locked

I see TEM00 transmitted beam out of RefCav. I think I have to fine tune the FSS gain a bit more becasue the spot still oscillates a bit.

The left monitor shows the spot from  PMC. The right monitor shows the spot from RefCav. it looks distorted becasue of the filter.

 

The common gain is 16.1 dB

slow actuator is 9 V

Fast Gain 15dB

Optimization is yet to be done. There is still plenty of reflected power.

 

Attachment 1: Photo_36.jpg
Photo_36.jpg
  137   Tue Jun 1 07:39:47 2010 FrankLaserLaserRefCav is locked

Quote:

I see TEM00 transmitted beam out of RefCav. I think I have to fine tune the FSS gain a bit more becasue the spot still oscillates a bit.

The left monitor shows the spot from  PMC. The right monitor shows the spot from RefCav. it looks distorted becasue of the filter.

 

The common gain is 16.1 dB

slow actuator is 9 V

Fast Gain 15dB

Optimization is yet to be done. There is still plenty of reflected power.

 

 nice

  138   Tue Jun 1 14:16:00 2010 taracLaserLaserPSL setup: next step

This is the schematic for PSL setup.

http://131.215.115.52:8080/PSL_Lab/117

At this point, Pre Mode Cleaner (PMC) and Reference Cavity (RefCav) are locked. The rest will be locking Analyzer Cavity (ACav) and setting up for beat noise measurement.

ACav's beam path will have double pass AOM [Crystaltech 3080 194]. We'll use +1st order beam. When hook up the VCO, make sure that the power is on only when the VCO and the AOM are connected, otherwise the VCO dies.

Next is aligning the AOM. A good alignment will maximize the power of the +1st order beam. The beam should get close to the AOM's transducer as much as possible to minimize time delay.

The beam at the AOM will be focused to 75 um.

The mirror that reflects the beam back to the AOM is a 0.3m concave mirror, which will be placed 0.3 m away from the AOM. The reflected beam should completely overlap on itself. This will neutralize

the pointing instability when the modulating frequency shifts.

 

Then we can align ACav, this time I'll try not to remove the PMC when I scan the beam frequency (at~3-10Hz.) If the PMC cannot catch up with the laser, increase the gain of the PMC, sideband power. 

 ACav should be locked before Monday June 8.

 

  139   Tue Jun 1 19:26:41 2010 taracLaserLaserA mirror gets into the insulation's border

I'm aligning the AOM. The R=0.5m mirror's position crosses the insulation border by 1.5" (see attached picture.) The black line on the table shows the border of the insulator. The mirror is on a translational stage.

I'm thinking of 2 choices to solve this,

 1)using a mirror to turn the beam to the side of the table. The mirror will be placed after the AOM, around the edge the border.

2) using 2 mirrors (after the beam is split to RefCav and ACav's paths) to shift the beam path to the side of the table.

The first choice will be better, since I won't have to recalculate the mode matching, but there might be unexpected problems.

The VCO is working fine, I can see +/- 1st order beams coming out.

Attachment 1: Photo_37.jpg
Photo_37.jpg
  140   Thu Jun 3 00:52:37 2010 taracLaserLaserAligning AOM

 I'm aligning the AOM and maximizing the diffracted beam's power by positioning the AOM and adjusting the beam size by moving the lens.

For single pass, the maximum efficiency I could get is only ~60%, so for double pass, the power will be down to 36%, but for now I'll settle with this number.

I could not find the manual for Crystal technology AOM 3080-194. The closest one is model 3080-197 which is attached below.

I'm not sure what is the difference between the two model, but 3080-197 has 70% diffraction efficiency.

Because of adjusting the lens, the RefCav's beam path also changes, now I have to realign RefCav again.

 

  Another step for AOM alignment is adjusting the mirror that reflects the transmitted beam back to the AOM again.

The distance between the mirror and the center of the AOM should be the same as ROC of the mirror.

After this I should be able to start locking ACav.

Attachment 1: 97-02848-01r0.pdf
97-02848-01r0.pdf
  141   Thu Jun 3 08:42:44 2010 FrankLaserLaserAligning AOM

Quote:

 I'm aligning the AOM and maximizing the diffracted beam's power by positioning the AOM and adjusting the beam size by moving the lens.

For single pass, the maximum efficiency I could get is only ~60%, so for double pass, the power will be down to 36%, but for now I'll settle with this number.

I could not find the manual for Crystal technology AOM 3080-194. The closest one is model 3080-197 which is attached below.

I'm not sure what is the difference between the two model, but 3080-197 has 70% diffraction efficiency.

Because of adjusting the lens, the RefCav's beam path also changes, now I have to realign RefCav again.

 

  Another step for AOM alignment is adjusting the mirror that reflects the transmitted beam back to the AOM again.

The distance between the mirror and the center of the AOM should be the same as ROC of the mirror.

After this I should be able to start locking ACav.

 did you measure the power of the vco? How much is it if you tune it to maximum?

Here a copy of a general datasheet for the 3080-194. maximum efficiency is ~80% @2W RF power. You should ask peter about the detailed datasheet which comes with each AOM and contains measured values for the one you are using. Measured values depend on the beam size and RF power. Typical values are 87% in reality.

AOM3080-194.JPG

  142   Thu Jun 3 14:47:58 2010 FrankLaserLaserAligning AOM

Quote:

Quote:

 I'm aligning the AOM and maximizing the diffracted beam's power by positioning the AOM and adjusting the beam size by moving the lens.

For single pass, the maximum efficiency I could get is only ~60%, so for double pass, the power will be down to 36%, but for now I'll settle with this number.

I could not find the manual for Crystal technology AOM 3080-194. The closest one is model 3080-197 which is attached below.

I'm not sure what is the difference between the two model, but 3080-197 has 70% diffraction efficiency.

Because of adjusting the lens, the RefCav's beam path also changes, now I have to realign RefCav again.

 

  Another step for AOM alignment is adjusting the mirror that reflects the transmitted beam back to the AOM again.

The distance between the mirror and the center of the AOM should be the same as ROC of the mirror.

After this I should be able to start locking ACav.

 did you measure the power of the vco? How much is it if you tune it to maximum?

Here a copy of a general datasheet for the 3080-194. maximum efficiency is ~80% @2W RF power. You should ask peter about the detailed datasheet which comes with each AOM and contains measured values for the one you are using. Measured values depend on the beam size and RF power. Typical values are 87% in reality.

AOM3080-194.JPG

 Oh, I see, the beam diameter is 1100 um, I use 150um. I'll try changing the beam size and see what happens. Thanks Frank. I'll measure the power of the VCO too.

  143   Thu Jun 3 15:45:39 2010 FrankLaserLaserAligning AOM

Quote:

Quote:

Quote:

 I'm aligning the AOM and maximizing the diffracted beam's power by positioning the AOM and adjusting the beam size by moving the lens.

For single pass, the maximum efficiency I could get is only ~60%, so for double pass, the power will be down to 36%, but for now I'll settle with this number.

I could not find the manual for Crystal technology AOM 3080-194. The closest one is model 3080-197 which is attached below.

I'm not sure what is the difference between the two model, but 3080-197 has 70% diffraction efficiency.

Because of adjusting the lens, the RefCav's beam path also changes, now I have to realign RefCav again.

 

  Another step for AOM alignment is adjusting the mirror that reflects the transmitted beam back to the AOM again.

The distance between the mirror and the center of the AOM should be the same as ROC of the mirror.

After this I should be able to start locking ACav.

 did you measure the power of the vco? How much is it if you tune it to maximum?

Here a copy of a general datasheet for the 3080-194. maximum efficiency is ~80% @2W RF power. You should ask peter about the detailed datasheet which comes with each AOM and contains measured values for the one you are using. Measured values depend on the beam size and RF power. Typical values are 87% in reality.

AOM3080-194.JPG

 Oh, I see, the beam diameter is 1100 um, I use 150um. I'll try changing the beam size and see what happens. Thanks Frank. I'll measure the power of the VCO too.

 have a look into the datasheet which came with the AOM. Don't make it too large. Clear aperture is about 1.7mm max. You can also have a look into the manual of the 35W laser (ATF lab). It contains a copy of one of these datasheets as well (with the graph of efficiency vs beam size). You don't need more than 60%, but you should try to get around 50% for the double-passed beam as we don't have so much laser power in total available. Assuming the original 15mW on the RF detector you need about 45mW for the acav now and 15mW for the refcav, so 60mW total after the PMC. With the current 95mW out of the laser it should be no problem( in principle). After the isolator and EOM you might have something about 85mW upstream of the PMC which means you need 70% transmission through the PMC. Anyway, a larger beam size gives you better eff.  If you make it 500um or so you should get 50% in the double-passed configuration.

  144   Thu Jun 3 22:00:21 2010 FrankLaserLaserAligning AOM

Quote:

Quote:

Quote:

Quote:

 I'm aligning the AOM and maximizing the diffracted beam's power by positioning the AOM and adjusting the beam size by moving the lens.

For single pass, the maximum efficiency I could get is only ~60%, so for double pass, the power will be down to 36%, but for now I'll settle with this number.

I could not find the manual for Crystal technology AOM 3080-194. The closest one is model 3080-197 which is attached below.

I'm not sure what is the difference between the two model, but 3080-197 has 70% diffraction efficiency.

Because of adjusting the lens, the RefCav's beam path also changes, now I have to realign RefCav again.

 

  Another step for AOM alignment is adjusting the mirror that reflects the transmitted beam back to the AOM again.

The distance between the mirror and the center of the AOM should be the same as ROC of the mirror.

After this I should be able to start locking ACav.

 did you measure the power of the vco? How much is it if you tune it to maximum?

Here a copy of a general datasheet for the 3080-194. maximum efficiency is ~80% @2W RF power. You should ask peter about the detailed datasheet which comes with each AOM and contains measured values for the one you are using. Measured values depend on the beam size and RF power. Typical values are 87% in reality.

AOM3080-194.JPG

 Oh, I see, the beam diameter is 1100 um, I use 150um. I'll try changing the beam size and see what happens. Thanks Frank. I'll measure the power of the VCO too.

 have a look into the datasheet which came with the AOM. Don't make it too large. Clear aperture is about 1.7mm max. You can also have a look into the manual of the 35W laser (ATF lab). It contains a copy of one of these datasheets as well (with the graph of efficiency vs beam size). You don't need more than 60%, but you should try to get around 50% for the double-passed beam as we don't have so much laser power in total available. Assuming the original 15mW on the RF detector you need about 45mW for the acav now and 15mW for the refcav, so 60mW total after the PMC. With the current 95mW out of the laser it should be no problem( in principle). After the isolator and EOM you might have something about 85mW upstream of the PMC which means you need 70% transmission through the PMC. Anyway, a larger beam size gives you better eff.  If you make it 500um or so you should get 50% in the double-passed configuration.

 I manage to get 70% efficiency from P wave. When I try S wave, I get 78% which is close to the specified value. So for double pass, the efficiency should be upto 50%. The beam size is ~550 um.  I redo the mode matching calculation for the AOM (and also RefCav and ACav) and move the beam a bit to the side of the table so that the insulation box won't get in the way.

  145   Thu Jun 3 23:55:38 2010 taracLaserLaserAligning AOM 2: the Return of the Beam

I'm aligning double pass AOM. After maximizing the power of the 1st order of the transmitted beam, I place the R=0.3m mirror to reflect the beam  back to the AOM.

The mirror is mounted on a translational stage for a fine adjustment.

At the right distance L away from the AOM(L = ROC), the size of the reflected beam at the AOM should be the same as the incoming beam.

Thus, there are 3 things to adjust.

First is the angle of the quarter wave plate that rotates the polarization of the beam after 2 passes by 90 degrees.

Second, the angle of the mirror, and

third, the distance of the mirror. At right position the power of the 1st order beam should be maximized.

 

I might have to change the position of the PBS that reflected the AOM double passed beam. Currently, the PBS is placed before 2 mirrors that move the

beam to the side of the table to avoid the insulation box. The problem is the double passed beam might clip on the mirror. So now I put the PBS after the steering mirrors, just in front of the AOM, but this limits the space for mode matching. I'll have to check which one will be better. From the attached picture,  two PBS's are placed on two possible locations. On the bottom right the, and down at the middle next to the AOM.

Attachment 1: Photo_38.jpg
Photo_38.jpg
  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.                   

  150   Sun Jun 6 23:01:58 2010 taracLaserLaserRefCav is almost locked

When I try to lock the cavity, it's not very stable yet. The transmitted power fluctuates alot.

I try changing the gains, but still could not stabilize the lock . The transmitted beam power is about 60% during the stable lock (I got it nicely locked for 5- 10 mins.)

After RefCav is locked, I'll try to optimize the transmitted power, by adjusting the lenses' positions before moving on to work on ACav

 

  151   Mon Jun 7 19:24:04 2010 taracLaserLaserRefCav is locked

RefCav is locked , the beam is more stable than yesterday setup. I'll write down the values of the setting for a quick reference.

I'm not sure what universal names for all these channels are. I just explain them in more details for my future reference and next generation archeologists.

fss controller:

Common Gain(  for both fast and PC paths): 23.6 dB (fast path controls the PZT which changes the length of the NPRO, PC path controls the phase

shift of the beam)

Fast Gain ( for PC path only): 12.5 dB

Phase shift: 0 + 180 degree. ("+180 degree" means phase flip)

RF Amplifier Adj (power for 35.5 MHz sidebands): 6.28 V.

Thermal control ADj (a voltage calibrator connected to slow channel of the laser controller): -0.010V

PMC controller

Servo gain Adj (over all gain of the demodulated signal): 27.75 dB

Output DC offset (offset voltage that governs the length of the PMC): -3.12 V

Phase shift: 2.87 V + 180 degree

RF Amp Adj (power for 21.5 MHz sidebands): 5.36V.

 

Now I'm working on ACav path. I made a cable for a photo diode.

I'm not sure if the last PD is a working 35.5 MHz PD, I'll see if it works or not.

Now I'm using two 2-channel monitors to simultaneously see the  beams after PMC and RefCav. It will be more convenient if I use a 4 channel monitor, I'll  clear some space for it.

 

  152   Tue Jun 8 03:16:21 2010 FrankLaserLaserRefCav is locked

nice good job!

you can get the names for the channels if you click on the corresponding object (slider, button, textbox, ...) using the center mouse button. You will get a green on black box containing the full channel name...

both 35.5MHz photodetectors should be ok as we used them in the previous setup already...

  153   Tue Jun 8 20:16:21 2010 taracLaserLaserscanning ACav

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

Attachment 1: aom_eff.png
aom_eff.png
  154   Wed Jun 9 03:55:40 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  156   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  155   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  157   Thu Jun 10 00:21:15 2010 taracLaserLaserscanning ACav

I'm scanning the laser to align ACav. It's a long day of adjusting 4 knobs and 1 lens (and one periscope for a while.) 

I see higher order TEM modes at the back of the cavity, but still cannot see TEM 00 yet.

Thu Jun 10 00:20:39 2010

 

I saw TEM 00 and trying to minimize the reflected power on the PD.

I just realize that the beam path is very close to the edge of the hole (see attached.) Part of the beam might be clipped.

I'll check that with IR viewer tomorrow.

The value for Voltage Calibrator is 6.17 V.

Thu Jun 10 00:58:56 2010

 

Attachment 1: Photo_42.jpg
Photo_42.jpg
  158   Fri Jun 11 01:04:42 2010 taracLaserLaserscanning Acav2

From yesterday, after getting TEM 00 out of the cavity, I checked the beam if it's clipped on the edge of the hole or not. There is small light on as seen by an IR viewer. Since it seems to be very small, I'll leave it as it is for now.

There was one problem. The beam was almost on the edge of the periscope's top mirror, I decided to change the height and move the periscope , and other optics in the row, side way, since the beam was really close to the edge of the opening ( I set the beam path to the center of the hole before, so it's bit off ( 5mm, 0.2") from the cavity's natural axis), and made sure that the beam is on the center of every mirror. Then, it's 4 knob adjustment which takes me a whole day again

As of now, I got TEM00, out of the cavity. I still have to adjust the lens' position to minimize the reflected beam. Before doing so, I'll prepare a mixer, a power splitter for locking the cavity.

 

One thing about the AOM, the beam after double pass is quite elliptic. I'm not sure how to correct it, and whether it's going to be a problem or not. I'll find something to read about this.

Fri Jun 11 01:00:17 2010

  168   Wed Jun 16 19:43:00 2010 taracLaserPMCPMC and EOM alignment

We try optimizing the PMC transmission in P wave. The maximum we can get for now is ~82%.

The 21.5 EOM is prealigned. We will do fine adjustment again when insulating cables are made.

EOM alignment means to align the polarization of the beam to match the applied electric field in the EOM. This will minimize the amplitude modulating effect.

There are 3 degrees of freedom, 2 for EOM positions, another one is the polarization of the beam.

The 35.5 EOM is also pre aligned, the signal is very small, probably because of its broadband type. I use 4395A spectrum analyzer to see the peak at 35.5 MHz, but it's really hard to tell if I minimize it or not.

I see the thermal effect on EOM crystal clearly when I adjust the EOM. After I minimize the Amplitude Modulation (AM) and left the EOM for awhile, the misalignment gradually increase.

Frank suggests that the calibration of the error signal should be done, so that we can approximate how well the temperature must be controlled to reach our noise budget. I'll think about that measurement.

As I finished my elog, the peak at 35.5 just went up. Case in point.

  170   Mon Jun 21 19:19:12 2010 taracLaserPMCProgress on PSL setup: Tuning phase shift/RF power for PMC

All SMA cables for locking RefCav are made and wired up in their places.

We decide to turn the power up to 50mW before it enters PMC. With ~80% efficiency, we get 40 mW out.

I adjusted RF power and phase shift for PMC and saved it in the init file so that next time we reboot the crate, the values will be set.

Next: I'll lock the RefCav and optimize the alignment.

  174   Wed Jun 23 23:52:48 2010 taracLaserRefCavRefCav is locked and optimized

I adjust the mode matching lenses and align the beam so that the transmitted power is ~97% of the input power. Actually I scan the beam and look at the reflected power. The reflected beam has power ~3%. The knobs on one of the periscope mirror acting weird. There's still thread (~ 4 or 5 turns, I guess) left but it seems to be very sensitive to my hand pressure when I rotate the knob, making fine adjustment rather hard .

Phase shift is adjusted by looking at the error signal. The laser is scan while the error signal from the fss servo mixer out is monitored. Feedback signals from the servo to EOM and laser must be removed.

RF power for RefCav is tuned. I assume that all sidebands' power will be reflected, and only power in the carrier will be transmitted, and to maximize the error signal's slope, we need Pcarrier/ Psideband ~ 2 [Black] .

So I measure the power of the incoming beam and adjust the RF power so that the transmitted beam's power is 1/2 of the input power. Another 1/2 of the input power will be the power of 2 sidebands that reflect back. 

 I use a photo diode to see the transmitted power and adjust the gain. The goal is to maximize the gain and have a stable transmitted power. However, the power still oscillates even when I decrease the gain, more than that and it loses lock. So I can only minimum the osicllation (You can see the beam spot pulsating on the monitor.)

All values are saved in the "startup.cmd" file.

a

  175   Thu Jun 24 09:37:16 2010 ranaLaserRefCavRefCav is locked and optimized

For the sideband power, you don't really want to make it so large. All that you really want is to make sure that the shot-noise signal is bigger than the electronics noise.

Once you guys start working on the noise budget, you will see that the input referred noise of the RFPD is equivalent to roughly 2 mA of photocurrent. So, for a reasonable

signal you should set the modulation depth (Gamma) equal to ~0.3-0.5.

Remember that we are also going to be fighting against the residual RFAM from the EOM, so its important to maximize the signal amplitude relative to the RFAM. The RFAM

signal will increase with increasing modulation depth...

  176   Fri Jun 25 18:27:59 2010 taracLaserLasermode matching to ACav

  The new driver for AOM is working, the maximum power is ~1.3w. There's a switch for int/ext signal.

We use internal signal to drive the AOM for alignment purpose.

The mode matching for ACav is on hold. Because the1st order beam coming out of the AOM looks very elliptic.

I'm not sure if it's the result of the large beam size in the AOM or the alignment problem.

the beam might clip on the edge of AOM, the beamsize is quite large, the data sheet give 80% 1st order efficiency for 1100 um diameter spot [AOM] and I adjusted the beam size to maximize the power before. I'll try decrease the beam size and see if this reduce the elliptical shape of the beam. Once the beam size on the AOM is determined, the rest of the mode matching can be calculated.

 

  171   Tue Jun 22 17:52:32 2010 FrankLab InfrastructureEnvironmenttemperature time series for the last week

temperature time series for the last couple of days measured right above the table between both cavities.

AmbMon_061710-062210.png

  179   Tue Jun 29 11:45:47 2010 FrankHowToNoiseBudgetunit converter

http://www.matweb.com/tools/unitconverter.aspx

  188   Wed Jun 30 00:37:49 2010 ranaHowToComputersPMC servo debugging

Quote:

 I was going to check the TF on each stage of PMC's servo.

Unfortunately, I couldn't find the floppy disc drive, so I slide the sliders (gain, RF power) around. When I add more RF power (from 1V to 7V) to 21.5 MHz EOM, the oscilaltion subsides*.

 How sad. Stop using the floppies and get one of the GPIB-Ethernet converters from Dmass. You can download the python scripts from the 40m wiki.

  189   Wed Jun 30 00:59:13 2010 FrankHowToComputersPMC servo debugging

Quote:

Quote:

 I was going to check the TF on each stage of PMC's servo.

Unfortunately, I couldn't find the floppy disc drive, so I slide the sliders (gain, RF power) around. When I add more RF power (from 1V to 7V) to 21.5 MHz EOM, the oscilaltion subsides*.

 How sad. Stop using the floppies and get one of the GPIB-Ethernet converters from Dmass. You can download the python scripts from the 40m wiki.

 we already have one but i was waiting for one the wireless bridge devices someone wanted to buy to make it wireless.

But why do you need a floppy to measure a TF?

ELOG V3.1.3-