40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 155 of 341  Not logged in ELOG logo
ID Date Author Type Categoryup Subject
  4593   Sat Apr 30 05:14:33 2011 KojiUpdateGreen LockingElectronics schematic for vertex beatbox

- AC coupling for the comparator circuit of the green locking

In order to relieve the power consumption of the RF buffer, ac coupling circuits have been added.

The ac coupling before the buffer amp helps to relieve the power consumption in the chip.
But because of the distortion of the signal (and the limitation of the bandwidth), the output still has some DC (~0.6V).
Therefore, the output is also AC coupled.

Note that the BW pin of BUF634P should be directly connected to -15V in order to keep the bandwidth of the buffer.

The drawings are also uploaded on the green electronics wiki

Attachment 1: freq_divider.png
freq_divider.png
  4846   Tue Jun 21 00:38:21 2011 SonaliUpdateGreen Lockingrepositioned "QPDY_PD"

1.The aim is the laser frequency stabilisation of PSL and AUX.

2.As a first step we want to couple some of the AUX laser beam into a single mode optical fibre and route the fibre to the PSL table.

3.The position of the optical fibre on the ETMY table is shown by the coupler in the attached picture. The yellow lines show the new scheme we want to implement.

4.WHAT WE DID TODAY.

  • The Y-arm was locked so that we could use the transmitted IR beam as the reference.
  • We shifted the position of the "QPDY_PD" .
  • We also shifted the "ETMYT" camera to make space for the "QPDY_PD".
  • The mirror  directing the beam into the "QPDY_PD" was rotated by 90 degrees to adhere to the new position of the "QPDY_PD".
  •  The attached photo shows the table as it is right now after the repositioning.
5.We continue with the positioning of the fibre-coupling tomorrow.
Attachment 1: ETMY_table_2011_June20.png
ETMY_table_2011_June20.png
Attachment 2: ETMY_table_change1.jpg
ETMY_table_change1.jpg
  4849   Tue Jun 21 19:54:33 2011 SureshUpdateGreen LockingLightWave NPRO power supply shifted to ETMY end table

The Lightwave NPRO power supply which is being shared between the AS table and the ETMY table has been shifted back to the ETMY table

The current to the laser is set at 1.5A.  The laser output is 200mW at this current level.

  4852   Wed Jun 22 01:59:43 2011 SonaliUpdateGreen Lockingfibre-coupling of the IR beam

 What I did today.

1. Collimation of a beam.

  • I then practiced collimation of a 700 nm laser (output) beam after being coupled through a fibre.
  • I put together the set-up as shown in the attached picture where I used ....... to couple 650nm light into the PM.... fiber.
  • I kept shifting the focus of the output beam to an appreciable distance till it was approximately collimated.

2. Coupling of the IR light at the ETMY table to a fibre.

  • The fibre coupler was put in place to couple light into the fiber.
  • I put in the mirrors as planned to direct the IR beam exiting the doubling crystal towards the fiber coupler (input).
  • The mirrors were aligned such that the beam falls on the input lens of the coupler.
  • The far-end of the fibre originally would have gone to to PSL table but it has been put on this table to study the power of the IR beam transmitted through this set-up.  The output end of the fiber has been connected to another fiber optic coupler to collimate the exiting beam.
  • The picture of the current status attached.
Attachment 1: ETMY_june_21.jpg
ETMY_june_21.jpg
Attachment 2: collimation_700nm_21_june.JPG
collimation_700nm_21_june.JPG
  4862   Thu Jun 23 02:12:12 2011 SonaliUpdateGreen Lockingwork schedule.

 June 22-June 24:

1.Coupling light into fibre at the ETMY.

2.Routing of the fibre to the PSL table.

June 27-June 30:

1.PSL optical table layout sketching.

2.Combining the PSL beam with fibre output onto a BS and then superpose them on a New Focus 1611 PD.

July 5-July 8:

1.Conversion of the PD output to voltage using MFD(Mixer Frequency Discriminator).

2. Report writing.

July 7: 5:00 pm: 1st Report Due.

July 11-July 22:

1.Locking Y-arm to PSL.

2.Setting up the feedback loop using the MFD output as the error signal and acting on the AUX laser frequency.

July 25-Aug 5:

1.Y-Arm cavity characterisation.

Measurement of the transmission of IR and green light through the cavity.

2.Analysis.

To obtain FSR, Finesse,Loss of the Cavity, Visibility, Transverse Modes(g-factor, astigmatism), Reflectivity, Q-factor.

3.Report and abstract writing.

Aug 1: 5:00 pm: 2nd Report and absract due.

Aug 8-11:

Preparation for talk and seminar.

  4882   Sat Jun 25 00:00:28 2011 SonaliUpdateGreen LockingFibre Coupling.

 What I did today.

1. I tried to align the IR input beam by aligning the two mirrors, to couple input light into the fibre.

2.I was unsuccessful for a long time even though I tried a lot of tricks.

3. I also tried to use the optical fault locator to superpose the IR beam spot onto the beam spot of the other laser to facilitate effective coupling.

4.But the crucial point was to superpose the input beam path in the perfect direction of the output beam path and not just the beam spot.(the input cone and the output cone are perfectly aligned).

5.After one whole day of trial and thought, I managed to couple light into the fibre, and saw the output beam spot on the screen-camera-monitor set-up which we had arranged. Eurekka !!;)

6.I then used a power meter to measure the input beam power and the output beam power.

7.It was a disappointing 2% . I had read in project reports of many students of a 20% success.

8.After a lot of subtle tweaking of the mirrors using the knobs, I managed to increase the percentage of output beam to 12%.

9. This is a workable level.

10.A day of lot of new learning! Pictures of the setup are attached.:)

 

Attachment 1: Fibre_coupling_successful_24_june.jpg
Fibre_coupling_successful_24_june.jpg
Attachment 2: Beam_output_on_screen.jpg
Beam_output_on_screen.jpg
  4901   Tue Jun 28 16:52:37 2011 SonaliUpdateGreen LockingRouting of fibre to PSL complete.

1. Suresh and I completed the alignment of the fibre and the three mirrors on the ETMY table.

2. We managed to get an output beam power of around 60% using the Ophir(Orion/PD) power meter to finetune the alignment. The power of the input beam is 74.4 mW and of the output beam is 38.5 mW.

3. The coupler on the output side of the fibre which had been put there to help in the alignment has been removed.

4. The picture of the ETMY layout as of now has been attached.

5. The labels A stands for the mirror used to turn the beam direction and B and C stand for the three mirrors used in the alignment of the beam into the coupler,D.(attachment 3).

6. The fibre we used is 50m in length which was barely sufficient to reach the PSL table.

7. So, the fibre has been routed to the PSL table using the fibre tray running below the Y-arm tube as this was the shortest route possible(even though it is a rather acccident prone zone).

8. The fibre has been tied down at regular intervals so that it does not get snagged and pulled up inadvertently.

9. We will start with the preparation of the layout of the PSL table to superpose the two beams on Monday.

Attachment 1: coupled_fibre.jpg
coupled_fibre.jpg
Attachment 2: the_fibre_route.jpg
the_fibre_route.jpg
Attachment 3: ETMY_aftr_fibre_coupling2.png
ETMY_aftr_fibre_coupling2.png
  4958   Fri Jul 8 20:50:49 2011 sonaliUpdateGreen LockingPower of the AUX laser increased.

The ETMY laser was operating at 1.5 A current and 197 mW power.

For the efficient frequency doubling of the AUX  laser beam at the ETMY table, a higher power is required.

Steve and I changed the current level of the laser from 1.5 A to 2.1 A in steps of 0.1 A and noted the corresponding power output . The graph is attached here.

The laser has been set to current 1.8 Amperes. At this current, the power of the output beam just near the laser output is measured to be 390 mW.

The power of the beam which is being coupled into the optical fibre is measured to be between 159 mW to 164 mW (The power meter was showing fluctuating readings).

The power out of the beam coming out of the fibre far-end at the PSL table is measured to be 72 mW. Here, I have attached a picture of the beam paths of the ETMY table with the beams labelled with their respective powers.

Next we are going to adjust the green alignment on the ETMY and then measure the power of the beam.

At the output end of the fibre on the PSL, a power meter has been put to dump the beam for now as well as to help with the alignment at the ETMY table.

Attachment 1: Graph3.png
Graph3.png
Attachment 2: ETMY_beam_powers.png
ETMY_beam_powers.png
  4965   Thu Jul 14 02:32:11 2011 sonaliUpdateGreen LockingPower of the AUX laser increased.

Quote:

The power of the beam which is being coupled into the optical fibre is measured to be between 159 mW to 164 mW (The power meter was showing fluctuating readings).

The power out of the beam coming out of the fibre far-end at the PSL table is measured to be 72 mW. Here, I have attached a picture of the beam paths of the ETMY table with the beams labelled with their respective powers.

 For the phase locking or beat note measuring we only need ~1 mW. Its a bad idea to send so much power into the fiber because of SBS and safety. The power should be lowered until the output at the PSL is < 2 mW. In terms of SNR, there's no advantage to use such high powers.

  4973   Fri Jul 15 13:48:56 2011 sonaliUpdateGreen LockingPower of the AUX laser increased.

Quote:

Quote:

The power of the beam which is being coupled into the optical fibre is measured to be between 159 mW to 164 mW (The power meter was showing fluctuating readings).

The power out of the beam coming out of the fibre far-end at the PSL table is measured to be 72 mW. Here, I have attached a picture of the beam paths of the ETMY table with the beams labelled with their respective powers.

 For the phase locking or beat note measuring we only need ~1 mW. Its a bad idea to send so much power into the fiber because of SBS and safety. The power should be lowered until the output at the PSL is < 2 mW. In terms of SNR, there's no advantage to use such high powers.

 

Well,the plan is to put in  a neutral density filter in the beam path before it enters the fibre. But before I could do that, I set up the camera on the PSL table to look at the fiber output . I will need it while I realign the  beam after putting in the Neutral Density Filter. I have attached the ETMY layout with the Neutral Density filter in place herewith.

Attachment 1: ETMY_after_fibre_coupling_labelled.pdf
ETMY_after_fibre_coupling_labelled.pdf
  4977   Fri Jul 15 17:42:21 2011 SonaliUpdateGreen LockingPSL layout for superposition of the PSL,ETMX and ETMY beams.

The fibres carrying the beams from the ETMX as well as the ETMY have been routed to the PSL table now.

A part of the PSL beam has to be superposed on the fibre-outputs to obtain a beat signal. We have located a stray beam on the PSL(which is currently being dumped) which we plan to redirect for the same. The layout of the plan is attached herewith.

Attachment 1: PSL_change1.pdf
PSL_change1.pdf
Attachment 2: PSLnewspace1.pdf
PSLnewspace1.pdf
  4994   Wed Jul 20 06:17:04 2011 SureshUpdateGreen LockingY-end green laser power issues

The Y-end green beam power is 0.47 mW.

While aligning the Y-end aux laser light into the fiber we noticed that the green power out of the doubling crystal was in microwatts.  I checked to see what was the trouble and found that the oven was cold as the temperature controller had been disabled.  I enabled it and scanned the temperature to maximise the green output.  Yet the power is less than 10% of that at the X end (7mW).

To verify I checked the power of various beams on the Y-end table.  They are listed below in the picture

Y-end_table_powers.pdf

The green beam power is proportional to the square of the IR incident power and this explains the drop in green power by a factor of (210/730)^2  thus making 7 mW -->  0.5 mW.  However we may be able to double the power at the Y-arm oven if the uncoated lenses in the IR path are exchaned for coated ones. 

 

The green beam injection into the Y-arm cavity also needs to be cleaned up as noted here.  As seen in the picture below two of the mirrors which launch the beam into the arm cavity need to be fixed as well.

 Y-end_table.png




  4997   Wed Jul 20 10:10:19 2011 SonaliUpdateGreen LockingWeekly summary

 I finished wih the set-up at the ETMY table. Instead of the neutral Density Filter , I put in a mirror(Y1-1037-45S)  which is reflective for IR , so that only 1% of the light is incident on the fibre  as per Rana's suggestion.

Now, the power incident on the fibre is measured to be 6 mW and the power measured out of the fibre is 2.76 mW after the necessary alignments.

On the PSL able, I have routed the beam that is coming out of the back of the PMC(instead of the dumped light from the oven to prevent any light from reflecting back into the laser), to the area where I am putting the set-up for the superposition of the PSL and the ETMX and ETMY beams.

Today I will proceed with the layout.

  5039   Wed Jul 27 01:57:28 2011 SonaliUpdateGreen LockingWeekly Summary

1. I have used the PMC  trans beam in my set-up as the required PSL beam.

2. I have superposed the ETMX-Fibre output with the PSL beam on the PSL table.

3. I have used suitable beam splitters and lens to match the power and the  sizes of the overlapping beams and have aligned them to the optimum.

4. A lens having f=7.6 cms is used to focus the beam into the PD.

5. Initially, I used the broadband 1611 NewFocus PD to find the IR beat signal by scanning the oven temperature. (using the digital sitemap controls.)

6. I checked the previous elog entries by Suresh and Koji on the green beat signal they had worked on and used their data to get an idea of the temperature range of the oven where I could obtain a beat.

7. I obtained peaks at three different temperatures as had been noted previously and set the temperature so that I am now sitting in the middle stable regime.

8. Then I switched to the 1811 100 MHz PD as it has a larger gain. It has a saturation power of 100 microWatts. The input power at the PD is measured to be 80 microWatts.

9. I was having trouble getting a clean peak due to presence of many harmonics as seen on the spectrum analyser. This happened because there was too much power incident on the PD which led to arising of non-linearity giving rise to harmonics.

10.To reduce the power entering the PD, I put in a ND 1.0 Filter just before the beam enters the PD and obtained a clean signal.

11. I will use  the frequency counter tomorrow to check the resonant frequency and try to connect the output to acquire a digital signal.

12. Otherwise I will proceed to build a Mixer Frequency Discriminator.

13. After the feed-back loop is completed, I will proceed to compare the frequency-noises of the green-beat lock and the IR-beat lock.

  5052   Thu Jul 28 13:51:00 2011 SonaliUpdateGreen LockingZHL-32A-S.

Initially I was using RFPD-1611to get the IR beat frequency. Its gain was not very high, so I was getting a very low signal of power -37 dBm.

I used ZHL-32A-S with a gain of 25 dBm to amplify it before feeding it into the spectrum analyser.

I connected the ground of the amplifier circuit to the red of the power supply, which blew the amplifier.

I learnt that there is a small tab indicating the ground side of the BNC to banana connectors which I should have noticed.

I learnt to plug in the side with th little tab on it into the ground of the power supply. (Learnt it the hard way I guess!!)

 

 

  5066   Sat Jul 30 05:11:45 2011 SureshUpdateGreen LockingY- end table clean-up

The optics on the Y-end table which required to be moved have been repositioned.  Please see the attached pic for details.

The green beam is not yet aligned to the cavity. That is my next task.

Y-end_table_work.png

  5084   Mon Aug 1 20:21:05 2011 kiwamuUpdateGreen LockingY arm green beam axis : aligned

The beam axis of the Y green light has been aligned.

Now I can see TEM00 mode is flashing on the ETMY camera.

 

-- (What I will do tonight)

The next step is to refine some electronics in the PDH loops to get the green light locked to the Y arm cavity.

If the beam isn't locked, I guess the in-vac-work will be so difficult because of the low intensity of the green light.

According to a brief check on the circuits, a low pass filter after the demodulation mixer is in a sad situation.

It doesn't pass any signals and in fact it behaves more like an absorber.

On the other hand, the modulation system looks fine to me because I was able to see the 270 kHz sideband converted into AM due to the fringing.

Quote from #5078

  (not yet) Alignment of the Y green beam (#5066)

  5088   Tue Aug 2 02:20:09 2011 kiwamuUpdateGreen LockingY arm green beam axis : done

I succeeded in locking the green light to the Y arm cavity, but it wasn't so robust. Something is unhealthy in the electronics.

I am leaving the Y green system as it is because I already can see a plenty of the green light flashing in the BS chamber.

So just a flashing of the green light is good enough for the in-vac-work.

DONE.

Quote from #5084

The next step is to refine some electronics in the PDH loops to get the green light locked to the Y arm cavity. 

 

  5133   Sun Aug 7 14:01:58 2011 kiwamuUpdateGreen LockingX green beam re-aligned

[Jenne / Kiwamu]

 The X green beam has been realigned to compensate the effect of the ETMX repositioning.

After the alignment we became able to lock the 00 mode with the X green beam.

 

For the alignment:

  spot position on the ETMX mirror = within ~ 1 cm. This number is strictly constrained by a homemade aluminum iris that Jamie put last Friday.

  spot position on the ITMX mirror = unknown, but looks pretty good on the CCD camera.

  spot position on the PSL table = ~ 1 mm downward from what it used to be. The horizontal alignment is perfect.

Conclusions :

  The X green beam again became a reference of the beam axis.

  The ETMX suspension tower is in a good place.

Quote from #5127

Kiwamu will work on the green alignment over the weekend.  Assuming everything works out, we'll try the same procedure on ETMY on Monday.

 

  5135   Sun Aug 7 18:41:12 2011 JenneUpdateGreen LockingX green beam re-aligned

Quote:

The ETMY suspension tower is in a good place.

Quote from #5127

Kiwamu will work on the green alignment over the weekend.  Assuming everything works out, we'll try the same procedure on ETMY on Monday.

 

 You meant ETMX, right?  ETMY still hasn't been touched.

KI : sorry, I meant ETMX. I fixed the entry.

  5181   Thu Aug 11 02:16:57 2011 JenneUpdateGreen LockingY-green aligned and flashing

[Jenne, with ample supervision by Kiwamu and Suresh]

Y-green was aligned, and is now flashing.  The ETMY trans camera was very helpful for this alignment.  I didn't end up needing to use a foil aperture. 

Kiwamu and Suresh had just closed up the IOO doors, so we don't know yet where it's hitting on the PSL table (if the beam is making it that far).  Tomorrow we'll look at ITMY to see if the green beam is centered there, and if it's coming out to the PSL table.

  5328   Wed Aug 31 11:37:56 2011 steveUpdateGreen Lockingshutter in place at east end

Uniblitz mechanical shutter installed in the green beam path at ETMY-ISCT  The remote control cable has not been connected.

  5470   Mon Sep 19 21:19:25 2011 KatrinUpdateGreen LockingBroadband photodiode characterization

Another Hamasutu S3399 photodiode was tested with the electronic circuit as described in LIGO-D-1002969-v.

RF transimpedance is 1k although the DC transimpedance is 2k.

The noise level is 25pA/sqrt(Hz) which corresponds to a dark current of 1.9mA or 1.7mA in the independent measurement.

At all frequencies the noise is larger compared to Koji's measurement (see labbook page 4778).

 


In file idet_S3399.pdf the first point is not within its error bars on the fitted curved. This point corresponds to the dark noise measurement

I made this measurement again. Now it is on the fitted curve. In the previous measurement I pushed the save button a bit too early. The

averaging process has not been ready while I pushed the 'save'  button.

Dark current is 1.05mA and noise is lower than in the previous measurement.

New file are the XXX_v2.pdf files

current_noise_S3399_v2.pdf

 idet_S3399_v2.pdf

 


 idet_S3399.pdf

 current_noise_S3399.pdf

S3399_response.pdf

  5511   Thu Sep 22 01:05:28 2011 KatrinUpdateGreen LockingNew modulation frequency (Y arm)

[Kiwamu / Katrin]

 

On Wednesday, the green light was locked to the Y arm cavity.

Modulation frequency was changed from 279kHz to 178875Hz. The amplitude was changed from 10Vpp to 0.01Vpp to achieve a modulation index of 0.38. The modulation frequency was changed to minimize AM. With the new modulation frequency the laser light could still locked to the cavity.

The signal of the LO and the photodiode are multiplied by a ZAD-8 mini circuit mixer (Level 7). This mixer requires LO input is +7dBm = 1.4Vpp. Thus we put a 36dB attenuator between the LO and the PZT at the laser. PDH error signal shows lots of peaks that are most likely higher order sidebands. Thus, the next step is to work on the low-pass filter. However the SNR of the error signal has improved with the new modulation frequency. With the old mod. frequency the PDH signal was 4mVpp and the noise floor was 2mVpp.

Phase between the photodiode signal and LO is shifted by about 10 degrees. Step two is to work on a phase shifter.

 

 

  5531   Fri Sep 23 17:31:14 2011 KatrinUpdateGreen LockingStray light reduction (Y)

I inserted several beam blocks and iris on the Y arm Green table. There was/is lots of stray light because a lot of the mirrors are not under an angle of incident of 45°. Some stray light is left since couldn't find an appropriate beam block/dump due to lack of space on the table.

 

  5585   Fri Sep 30 15:22:17 2011 KatrinUpdateGreen LockingWhat happened on green YARM?

 

This is a kind of summary of what I have worked on this week.

After all the changes made last week, I could not manage to lock the green light to the cavity, but the PDH error signal looks nicer.....at least something.

 

Alignment of the light to the cavity:

  • DC level of green PD when light is non-resonating 100%
  • DC level of green PD when light resonates 75%
  • --> Not sure if this alignment is good enough
  • In comparision to last week the cavity mirrors seem to move more or my alignment is way worse than last week. The bright spot on ETMY could not be observed for more than let's say a second in the unlocked configuration.

 

Low-pass filter (LPF)

  • The PDH error signal was covered with oscillations of 3.3 kHz, 7.1 kHz and 35 kHz.
  • Measured cut-off frequency of the LPF used so far is 35 kHz
  • Designed and build a new LPF: second order, cut of frequency of 1.1 kHz (this is just the design value, haven't measured that so far)
  • With the new LPF the PDH error signal is free of the above mentioned oscillations.
  • Impedance should be checked

 

PDH error signal

  • Signal-to-noise ratio (SNR) could be improved to values between 7.8 and 11.1 (old SNR was 5 to 7)
  • Looks more like a PDH signal than with the old LPF (now just derivative of the carrier and the first order sidebands show up)
  • Amplitude of the first order sidebands are smaller than the zero order, but are still too high (about 80% of the first order), need to work on the proper value of the LO amplitude an the voltage averager

 

Phase shift between green PD signal and LO

  • Phase shift is about 1MHz
  • Tried to find a capacity that compensates the phase shift. This was not successful since the PD frequency changed every now and than by +/- 20 kHz
  5586   Fri Sep 30 16:17:10 2011 kiwamuUpdateGreen Lockingthings to be done for the Yarm green lock

Thank you for the summary.

I think now you are getting into a phase where you should start doing some quantitative and careful checks.

    1. Calculate how much light will be reflected from the cavity if the alignment is perfect.

    2. Investigate where those kHz oscillations are coming from.

    3. Estimate how much the 1.1 kHz corner frequency in LPF will reduce the phase margin around 10 kHz.

    4. Calculate the estimated amplitude of the PDH signal.

    5. Compute how big the gain of the PDH box should be.

Quote from #5585

 This is a kind of summary of what I have worked on this week. 

  • DC level of green PD when light resonates 75%
                    --> Not sure if this alignment is good enough
  • The PDH error signal was covered with oscillations of 3.3 kHz, 7.1 kHz and 35 kHz.
  • Designed and build a new LPF: second order, cut of frequency of 1.1 kHz (this is just the design value, haven't measured that so far)
  • Signal-to-noise ratio (SNR) could be improved to values between 7.8 and 11.1 (old SNR was 5 to 7)

  5619   Tue Oct 4 20:34:20 2011 KatrinUpdateGreen Locking7kHz Peak in servo input YARM

[Kiwamu, Katrin]

As reported earlier an oscillation around 7kHz is an the PDH error signal. The lower spectrum show that there is a peak from 6-7kHz.

This peak is somehow dependent on the modulation frequency. This means the peak can be shifted to a higher frequency when the modulation frequency is increased (see for comparsion f_mod=279kHz).

If the power supply for the green PD is switched of the peak vanishes. The same happens if the LO is switched of.

servoinput.png servoinput2.png

  5623   Wed Oct 5 18:31:02 2011 KatrinUpdateGreen LockingExchanged mirror on YARM table

On the Green YARM end table the second mirror behind the laser has been exchanged.

Reason: The light is impinging on the mirror under an angle of  about 10 degrees, but the old mirror was coated for angle of incidence (aoi) of 45°.

Thus it was more like a beam splitter. The new mirror is a 1" Goock & Housego mirror which has a better performance for an aoi of 10 degree.

Realignment through Faraday Isolator and SHG cristall as well as 532nm isolator is almost finished.

  5625   Thu Oct 6 15:37:26 2011 JenneUpdateGreen LockingY-green Mech Shutter Button

[Katrin, Jenne]

We were poking around and tried to make a button for the Y-green shutter, just like the X-green already has.  I don't know where the X-green shutter button goes to in model-land, so I can't figure out if there is already a channel set up for the Y end.  Just switching the X for a Y didn't work.  Someone (maybe me) should fix this in the next soon.

  5631   Fri Oct 7 17:35:26 2011 KatrinUpdateGreen LockingPower on green YARM table

After all realignment is finished, here are the powers at several positions:

 

DSC_3496_power.JPG

  5646   Mon Oct 10 18:53:04 2011 KatrinUpdateGreen LockingMirrors whose angle of incidence is not 45

The angle of incidence of light is for some mirrors on the YARM end table different from 45° even though the mirrors are coated for 45°.

The mirrors below are useful if there are plans to replace these mirrors by properly coated ones.

 

Mirror
Angle of incidence (degree)
1st 1" mirror right after laser* 10
2nd 1" mirror right after laser 35
1st 2" steering mirror to vacuum system 15
2nd 2" steering mirror to vacuum system 28

 

* This is the new mirror as decribed on http://nodus.ligo.caltech.edu:8080/40m/5623

 

  5657   Wed Oct 12 18:54:02 2011 KatrinUpdateGreen Locking60 Hz oscillation due to broken BNC cable

There was a 60 Hz and 120 Hz oscillation on the green PDH photo diode output. After a long search, I could identify that

the source was a broken BNC cable which was connected to the photo diode. I exchanged that BNC cable and the 60 Hz

and 120 Hz are gone :-)

With the new cable the PD output was less noisy so that it was easier to achieve a better alignment of the light to the cavity.

The reflected power could be reduced from 40% to 30%. For perfect alignment the reflected power would be 20%.

  5658   Wed Oct 12 19:58:32 2011 KatrinUpdateGreen LockingPower splitter is unbalanced

The mini circuit power splitter ZFRSC-42S+ used at the YARM has no balanced output as it should have according to the data sheet.

@ 0.05MHz  the amplitude unbalance should be 0.03 dB

A quick measurement shows that there is a LO amplitude dependent unbalance:

LO amplitude input (Vpp)  unbalanced output (dB)
1.3 3.66
1.4 4.08
1.5 4.28
1.6 4.36

So my question is, shall I replace the power splitter just in case it is further degrading?

  5661   Thu Oct 13 20:25:32 2011 KatrinUpdateGreen LockingLPF transfer function YARM

It is a 4th order filter with cut of frequency of 120 kHz.

 

Design

designLPF.png

 

Measurement

 LC_LPF.TIF

  5701   Wed Oct 19 16:28:35 2011 steveUpdateGreen LockingETMY mechanical shutter is working

Quote:

Uniblitz mechanical shutter installed in the green beam path at ETMY-ISCT  The remote control cable has not been connected.

The ETMY  shutter can be remotely switched from medm screen POY of mechanical shutters.

The new cable from ETMY controller goes to east vertex EV-ISCT where it is connected to POY shutter hook up BNC cable.

  5704   Wed Oct 19 17:33:07 2011 kiwamuUpdateGreen LockingETMY mechanical shutter : fully functional

The mechanical shutter on the Y end is now fully functional.

 

 It is newly named to 'C1AUX_GREEN_Y_Shutter' in the EPICS world.

It uses the same binary output channel which had been served for the POY shutter.

To change the EPICS name I edited a db file called ShutterInterLock.db, which resides in /cvs/cds/caltech/target/c1aux.

After editing the file I rebooted the c1aux machine, by telnet and the reboot command in order to make the change effective.

Also I added this new shutter on the ALS overview screen (see the attachment below)

MechShutter.png

Quote from #5701

The ETMY  shutter can be remotely switched from medm screen POY of mechanical shutters.

The new cable from ETMY controller goes to east vertex EV-ISCT where it is connected to POY shutter hook up BNC cable.

  5713   Thu Oct 20 16:33:24 2011 KatrinUpdateGreen LockingTransfer function YARM PDH box

Yesterday, I measured the transfer function of the YARM PDH box.

SCRN0000.pdf

 

I tested the electronic board and couldn't find a frequency dependent behaviour. So I measured the TF again and it looked nice.

PDH_box.png

Today's nice measurement could is/was reproducible. I suppose yesterday's measurement is just an artefact.

The electronic board is modified according to Kiwamu's wiki entry http://blue.ligo-wa.caltech.edu:8000/40m/Electronics/PDH_Universal_Box

 

Btw. The light could be locked to the cavity for ~3min.

  5726   Fri Oct 21 16:59:14 2011 KatrinUpdateGreen LockingYARM PDH box broken

I could not improve the locking. So, I checked the transfer function of the PDH box again. The transfer function looks okay if the gain knob is <=2.0.

If the gain knob is >2.0 the 20dB step appears in the transfer function (see elog page 5713). This step is shifted to higher frequencies if the gain is

increased. The PZT drive out was not saturated at any time. Yesterday, I checked the electronic circuit with a gain of 2.0. Thus,  I couldn't find the broken

gain amplifier (AD8336). The amplifier is ordered in will arrive on Monday.

  5742   Wed Oct 26 11:35:08 2011 KatrinUpdateGreen LockingYARM PDH box

PDH_w_wo_jump.png

From time to time the 20 dB jump in the transfer function still occurs. The new AD8336 op amp did not change that issue. I am sure that the op amp was broken,

because the amplitude of the sine did not change when I turned the gain knob.

The above two curves were measured with different input amplitude of the sine from the spectrum analyzer. Nothing changed in between except that there was no

jump when Kiwamu was around. Very strange. Testing the electronic board led to no clue what is happening.

For now, I will just use the PDH box as it is, but one should keep this odd behaviour in mind.

  5769   Mon Oct 31 14:01:56 2011 KatrinUpdateGreen LockingYARM locks for 2h

Today, I could lock the YARM laser for 2h to the YARM cavity. After to hours the output of the servo is saturated. I need to work on thermal feedback to the laser.

It is a nice TEM00 mode and the green light enters PSL table.

20111031_OLTF.png

Measured with pin-ball machine spectrum analyzer (I forgot the real name, but it is the one that makes sounds like a pin-ball machine), source power10mVp, Lb1005 gain 2.05.

 

Setup

YARM_setup.png

Input offset of LB1005 is zero

 

Locking history

On Thursday, Oct 27, lock for 3 min

On Friday, Oct 28, lock up to 18 min, improvements done by

  • finding the right adjustment of PI Corner frequency and gain
  • better alignment of the light to the cavity
  • I used a high-pass filter between LO and LB1005, but no improvement of lock. In contrast, it got worse.

On Monday,Oct 31, careful adjustment of summing box (rear of of LB1005), lock up to 2h, limited by saturated feedback signal --> work on slow control

 

Some more plots

feedback.png

 PD_DC1.png

PDH_error1.png

Attachment 1: 20111031_OLTF.png
20111031_OLTF.png
Attachment 2: YARM_setup.png
YARM_setup.png
  5787   Wed Nov 2 17:33:28 2011 KatrinUpdateGreen LockingADC channels for slow control

connector J9B of hardware ADC --> ch1 in software ADC --> GCY_ERR

connector J14 of hardware ADC --> ch11 in software ADC --> GCY_PZT

connector J15 of hardware ADC --> ch13 in software ADC --> GCY_REFL_DC

 

 

  5797   Thu Nov 3 16:43:44 2011 KatrinUpdateGreen LockingSHG temperature (YARM)

Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.

The power emitted by the laser was the same as in the case without that cable. Note LT, i.e. measured crystal temperature, of the laser show a

different value when the BNC is connected, but the manual clearly states that this display does not work properly if a cable is connected to the

slow BNC plug, an offset is added.

The power of the 532nm light behind the SHG oven has been reduced from 1mW to 0.4mW. I changed the crystal temperature such that the power

of the green light is 1mW. With this new temperature setting the laser can be locked again.

 

  w/o BNC cable at slow plug w/ BNC cable at slow plug
T (°C) 29.776 29.776
LT (°C) 39.2 48.4
1064nm power (mW) 440 448
Temp. at TC200 (°C) 35.7 36.4
532nm power in front of Isolator (mW) 1.0 1.0

 

 

 

  5798   Thu Nov 3 17:04:23 2011 KojiUpdateGreen LockingSHG temperature (YARM)

Changing the crystal temperature changes the laser frequency. This will causes the beat note missing at the vertex.

In other words, you will find the beat note at the vertex when the actual temperature of the crystal is reproduced as before,
no matter how the dial setting/temp voltage input is.

  5800   Thu Nov 3 17:24:59 2011 ZachUpdateGreen LockingSHG temperature (YARM)

I must confess that I changed the temperature of the laser via the dial yesterday. I believe the initial (displayed) temperature was ~19o, whereas it is now probably in the high 20s. Sorry.

Quote:

Changing the crystal temperature changes the laser frequency. This will causes the beat note missing at the vertex.

In other words, you will find the beat note at the vertex when the actual temperature of the crystal is reproduced as before,
no matter how the dial setting/temp voltage input is.

 

  5807   Fri Nov 4 13:04:50 2011 ZachUpdateGreen LockingPassive summing box modifications

I spent some time the other day trying to diagnose the problem with the Y Arm universal PDH box (S/N 17), which Katrin has been unable to use for locking the green beam. As far as I can tell, there is nothing wrong with the box itself (though the weird TF behavior that Katrin noticed was not initially reproducible, so its cause may still be there).

I did notice that I was unable to generate a PDH error signal using the universal box. In this configuration, a summing circuit is needed to add the PZT modulation signal (fmod = 178875 Hz) in along with the feedback signal. To do this, Katrin was using a slightly different version of the passive summing box that Kiwamu built for the X Arm. I read this entry to understand how it is supposed to work and noticed that the "expected transfer functions" were not what the circuit actually does. I have talked to Kiwamu about it and he found that he posted the wrong TFs (he has the right ones on his computer). As you can see from the plot below, there is extra low passing that severely attenuates the modulation path to the PZT. In addition, there is a phase shift of ~-60 degrees, which is bad.

To combat this, I propose we simply change the resistor in the modulation path from 1M to 10k. This leaves the feedback path TF unchanged, and changes the mod path into a sort of bandpass filter for the modulation frequency. The fact that the phase is near zero at fmod means we don't have to come up with some way to phase shift the signal for demodulation. The attenuation level of ~-36 dB is also convenient: The ZAD-8 mixer wants 7 dBm, so, 10 dBm (FG) - 3 dB (splitter) - 36 dB (sumbox) = -25 dBm ~ 12 mV. This is roughly the desired PZT voltage level.

sum_circuit_new.png sumbox_TFs.png

  5808   Fri Nov 4 13:13:25 2011 ZachUpdateGreen LockingPDH box #17 modified, too

I also modified the Y-Arm PDH box itself slightly. Previously, there was a flying 10k resistor from the SWEEP input to TP2. I don't see the point of this, so I moved it from TP2 across R19 (to the same point where it is on the gyro PDH boxes) to allow for excitation signals to be injected with the loop closed (i.e., with the SWEEP switch off). This is useful for OLTF measurements.

  5809   Fri Nov 4 13:53:33 2011 KatrinUpdateGreen LockingSHG temperature (YARM)

Quote:

I must confess that I changed the temperature of the laser via the dial yesterday. I believe the initial (displayed) temperature was ~19o, whereas it is now probably in the high 20s. Sorry.

Quote:

Changing the crystal temperature changes the laser frequency. This will causes the beat note missing at the vertex.

In other words, you will find the beat note at the vertex when the actual temperature of the crystal is reproduced as before,
no matter how the dial setting/temp voltage input is.

 

Okay, my elog entry was not clear I changed the temperature of the SHG which only changes the conversion efficiency. 

 

 

Anyhow, since the laser set temperature and thus the laser frequency has been changed by Zach and I couldn't find a note

of the original laser crystal temperature, my plan is to reset the SHG temperature to the old value, set the laser crystal temperature

around 19°C and do fine adjustment of that temperature by optimising the doubling efficiency. Okay?

 

  5815   Fri Nov 4 21:15:38 2011 KatrinUpdateGreen LockingNew fiber coupler (YARM)

63% coupling efficiency into the new fiber collimator (Thorlabs XXXX) and the blue fiber.This should be sufficient for a beat measurement with the PSL laser.

I think the coupling efficiency is not too bad with having no mode matching lenses and no adjustable collimator lens.

 

252mW in front of the fiber

159 mW fiber output

  5820   Sat Nov 5 04:30:21 2011 kiwamuUpdateGreen LockingRe:Passive summing box modifications

I think you also should check the PZT's capacitance of the 700mW LightWave because 2.36 nF is the one for the 1W Innolight laser.

Quote from #5807

To combat this, I propose we simply change the resistor in the modulation path from 1M to 10k. This leaves the feedback path TF unchanged, and changes the mod path into a sort of bandpass filter for the modulation frequency. The fact that the phase is near zero at fmod means we don't have to come up with some way to phase shift the signal for demodulation.

ELOG V3.1.3-