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ID Date Author Type Categoryup Subject
  16673   Tue Feb 15 19:40:02 2022 KojiUpdateGeneralIMC locking

IMC is locking now. There was nothing wrong: just a careful alignment + proper gain adj

=== Primary Alignment ===

- I used WFS error signals as the indicator of the PDH error signals. Checked C1:IOO-WFS1_(I/Q)n_ERR and ended up C1:IOO-WFS1_I4_ERR as it showed the largest PDH error PP.

- Then used MC2 and MC3 to align the IMC by maximizing the PDH error and the MC trans (C1:IOO-MC_TRANS_SUM_ERR)

=== Locking procedure ===

Note that the MC REFL path is still configured for the full power input

- (Only at the beginning) Run scripts/MC/mcdown for initialization / Run scripts/MC/MC2tickleOFF just in case

- Enable IOO-MC-SW1 (MC SERVO switch right after "IN1 Gain (dB)").
- Disable 40:4000 boost
- Increase VCO Gain from -15 to 0
- Jiggle IN1 Gain from low to +31 until the lock is achieved

- As soon as the lock is acquired, enable 40:4000
- Increase VCO Gain to +10
- Turn up "SUPER BOOST" from 0 to 3

=== Lock loss procedure ===

Note that the MC REFL path is still configured for the full power input

- Disable IOO-MC-SW1
- Disable 40:4000 boost
- Reduce VCO Gain 0
- Turn down "SUPER BOOST" to 0

- Then jiggle IN1 Gain again to lock the IMC

=== MC2 spot ===

- It was obvious that the MC2F spot was not on the center of the optic.
- I tried to move the spot on the camera as much as possible, but this did not make the trans beam to the center of the MC end QPD
- I had the impression that the trans beam started to be clipped when the beam was moved towards the end QPD,

We need to reestablish the reasonable/consistent MC2 spot on the mirror, the MC end optics, and the QPD.
We will need to use MC2 dithering and A2L coupling to determine the center of the mirror

But as long as the transmission is maximized, the transmitted beam thru MC1 and MC3 follows the input beam. So we can continue the vent work

The current maximized transmission was ~1300. MC1 refl CCD view was largely off -> The camera path was adjusted.

=== MC2 alignment note ===

During the alignment, I noticed a sudden change of the MC2 alignment. There might be some hysteresis in the MC2 suspension. If you are locking the IMC and noticed significant misalignment, the first thing to try is to touch MC2 alignment.

  16674   Wed Feb 16 15:19:41 2022 AnchalUpdateGeneralReconfigured MC reflection path for low power

I reconfigured the MC reflection path for low power. This meant the following changes:

  • Replaced the 10% reflection BS by 98% reflection beam splitter
  • Realigned the BS angle to get maximum on C1:IOO-MC_RFPD_DCMON when cavity is unlocked.
  • Then realigned the steering mirrors for WFS1 and WFS2.
  • I tried to align the light for MC reflection CCD but then I realized that the pickoff for the camera is too low for it to be able to see anything.

Note, even the pick-off for WFS1 and WFS2 is too low I think. The IOO WFS alignment does not work properly for such low levels of light. I tried running the WFS loop for IMC and it just took the cavity out of the lock. So for low power scenario, we would keep the WFS loops OFF.

 

  16676   Wed Feb 23 15:08:57 2022 AnchalUpdateGeneralRemoved extra beamsplitter in MC WFS path

As discussed in the meeting, I removed the extra beam splitter that dumps most of the beam going towards WFS photodiodes. This beam splitter needs to be placed back in position before increasing the input power to IMC at nominal level. This is to get sufficient light on the WFS photodiodes so that we can keep IMC locked for more than 3 days. Currently IMC is unlocked and misaligned. I have marked the position of this beam splitter on the table, so putting it back in should be easy. Right now, I'm trying to align the mode cleaner back and start the WFS loops once we get it locked.

  16677   Thu Feb 24 14:32:57 2022 AnchalUpdateGeneralMC RFPD DCMON channel got stuck to 0

I found a peculiar issue today. The C1:IOO-MC_RFPD_DCMON remains constantly 0. I wonder if the RFPF output is being read properly. I opened the table and used an oscilloscope to confirm that the DC output from the MC REFL photodiode is coming consistently but our EPICs channel is not reading it. I tried restarting the modbusIOC service but that did not affect anything. I power cycled the acromag chassis while keeping the modbusIOC service off, and then restarted teh modbusIOC service. After this, I saw more channels got stuck and became unresponsive, including the PMC channels. So then I rebooted c1psl without doing anything to the acromaf chasis, and finally things came back online. Everything looks normal to me now but I'm not sure if one of the many channels is not in the right state. Anyways, problem is solved now.

 

  16679   Thu Feb 24 19:26:32 2022 AnchalUpdateGeneralIMC Locking

I think I have aligned the cavity, including MC1 such that we are seeing flashing of fundamental mode and significant transmission sum value as well.However, I'm unable to catch lock following Koji's method in 40m/16673. Autolocker could not catch lock either. Maybe I am doing something wrong, I'll pickup again tomorrow, hopefully the cavity won't drift too much in this time.

  16685   Sun Feb 27 00:37:00 2022 KojiUpdateGeneralIMC Locking Recovery

Summary:

- IMC was locked.
- Some alignment change in the output optics.
- The WFS servos working fine now.
- You need to follow the proper alignment procedure to recover the good alignment condition.

Locking:
- Basically followed the previous procedure 40m/16673.
- The autolocker was turned off. Used MC2 and MC3 for the alignment.
- Once I hit the low order modes, increased the IN1 gain to acquire the lock. This helped me to bring the alignment to TEM00
- Found the MC2 spot was way too off in pitch and yaw.
- Moved MC1/2/3 to bring the MC2 spot around the center of the mirror.
- Found a reasonably good visibility (<90%) at a MC2 spot. Decided this to be the reference (at least for now)

SP Table Alignment Work
- Went to the SP table and aligned the WFS1/2 spots.
- I saw no spot on the camera. Found that the beam for the camera was way too weak and a PO mirror was useless to bring the spot on the CCD.
- So, instead, I decided to catch an AR reflection of the 90% mirror. (See Attachment 1)
- This made the CCD vulnerable to the stronger incident beam to the IMC. Work on the CCD path before increasing the incident power.

MC2 end table alignment work
- I knew that the focusing lens there and the end QPD had inconsistent alignment.
- The true MC2 spot needs to be optimized with A2L (and noise analysis / transmitted beam power analysis / etc)
- So, just aligned the QPD spot using today's beam as the temporary target of the MC alignment. (See Attachment 2)

Resulting CCD image on the quad display (Attachment 3)

WFS Servo
- To activate the WFS with the low transmitted power, the trigger threshold was reduced from 5000 to 500. (See Attachment 4)
- WFS offset was reset with /opt/rtcds/caltech/c1/scripts/MC/WFS/WFS_RF_offsets
- Resulting working state looks like Attachment 5

Attachment 1: PXL_20220226_093809056.jpg
PXL_20220226_093809056.jpg
Attachment 2: PXL_20220226_093854857.jpg
PXL_20220226_093854857.jpg
Attachment 3: PXL_20220226_100859871.jpg
PXL_20220226_100859871.jpg
Attachment 4: Screenshot_2022-02-26_01-56-31.png
Screenshot_2022-02-26_01-56-31.png
Attachment 5: Screenshot_2022-02-26_01-56-47.png
Screenshot_2022-02-26_01-56-47.png
  16686   Sun Feb 27 01:12:46 2022 KojiUpdateGeneralIMC manual alignment procedure

We expect that the MC sus are susceptible to the temperature change and the alignment drifts away with time.

Here is the proper alignment procedure.

0) Assume there is no TEM00 flash or locking, but the IMC is still flashing with higher-order modes.

1) Use the CCD camera and WFS DC spots to bring the beam to the nominal position.

2) Use only MC2 and MC3 to align the cavity to have low-order modes (TEM00,01,02 etc)

3) You should be able to lock the cavity on one of these modes. Minimize the reflection (maximize the transmission) for that mode.

4) This should allow you to jump to a better lower-order mode. Continue alignment optimization only with MC2/3 until you get TEM00.

5) Optimize the TEM00 alignment only with MC2/3

6) Look at the MC end QPD. use one of the scripts in scripts/MC/moveMC2 . Note that the spot moves opposite to the name of the scripts. i.e. MC2_spot_down moves the spot up, MC2_spot_right moved the spot left, etc...
These scripts move MC1/2/3 and try to keep the good MC transmission.

7) moveMC2 scripts are not perfect. As you use them, it makes the MC alignment gradually degraded. Use MC2 and MC3 to recover good transmission.

8) If MC2 spot is satisfactory, you are done.

-------------

Step 6-8 can be done with the WFS on. This way, you can skip step 7 as the WFS servo takes care of it. But if the spot move is too fast, the servo can't keep up with the change. If so, you have to wait for the settling of the servo. Once the spot position is satisfactory, MC servo relief should be run so that the servo offset (in actuation) can be offloaded to the bias slider.

 

Attachment 1: PXL_20220226_100859871.jpg
PXL_20220226_100859871.jpg
  16725   Tue Mar 15 10:45:31 2022 PacoUpdateGeneralAssembled small in-vac optics

[Paco]

This morning I assembled LO3, LO4 and AS3 (all mirrors) onto polaris K1 mounts. The mounts stand as per this elog, on 4.5" posts with 0.5" Al spacers to match the beam heigth of 5.5". I also assembled ASL by adding a 0.14" Al spacer, and finally, recycled two DLC mounts (from the XEND flowbench) and posts to mount the 2 inch diameter beamsplitters BHDBS and AS2 (T=10%). I stored the previous 2" optics in the CVI and lambda optic cases and labeled appropriately.

  16775   Wed Apr 13 16:23:54 2022 Ian MacMillanUpdateGeneralSmell in 40m

[Ian, Paco, JC]

There is a strange smell in the 40m. It smells like a chemically burning smell maybe like a shorted component. I went around with the IR camera to see if anything was unusually hot but I didn't see anything. The smell seems to be concentrated at the vertex and down the y-arm

  16784   Mon Apr 18 15:17:31 2022 JancarloUpdateGeneralTool box and Work Station Organization

I cleaned up around the 40 m lab. All the Laser Safety Glasses have been picked up and placed on the rack at the entrance.

Some miscellaneous BNC Connector cables have been arranged and organized along the wall parallel to the Y-Tunnel.

Nitrogen tanks have been swapped out. Current tank is at 1200 psi and the other is at 1850 psi.

The tool box has been organized with each tool in its specified area.

  16787   Mon Apr 18 23:22:39 2022 KojiUpdateGeneralTool box and Work Station Organization

Whoa! Thanks!

Attachment 1: PXL_20220419_062101907.jpg
PXL_20220419_062101907.jpg
  16808   Mon Apr 25 14:19:51 2022 JCUpdateGeneralNitrogen Tank

Coming in this morning, I checked on the Nitrogen tanks to check the level. One of the tanks were empty, so I went ahead and swapped it out. One tank is at 946 PSI, the other is at 2573 PSI. I checked for leaks and found none.

  16809   Mon Apr 25 14:49:02 2022 KojiUpdateGeneralNitrogen Tank

For your (and mine) info:

N2 pressure can be monitored on the 40m summary page: https://nodus.ligo.caltech.edu:30889/detcharsummary/day/20220425/vacuum/
(you need to hit "today" to go to the current status)

 

  2601   Fri Feb 12 18:58:46 2010 kiwamuUpdateGreen Lockingtake some optics away from the ETM end table

In the last two days Steve and I took some optics away from the both ETM end table.

This is because we need an enough space to set up the green locking stuff into the end table, and also need to know how much space is available.

Optics we took away are : Alberto's RF stuff, fiber stuff and some optics obviously not in used.

The picture taken after the removing is attached. Attachment1:ETMX, Attachment2:ETMY

And the pictures taken before the removing are on the wiki, so you can check how they are changed.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

Attachment 1: DSC_1164.JPG
DSC_1164.JPG
Attachment 2: DSC_1172.JPG
DSC_1172.JPG
  2604   Tue Feb 16 09:51:22 2010 AlbertoUpdateGreen Lockingtake some optics away from the ETM end table

Quote:

In the last two days Steve and I took some optics away from the both ETM end table.

This is because we need an enough space to set up the green locking stuff into the end table, and also need to know how much space is available.

Optics we took away are : Alberto's RF stuff, fiber stuff and some optics obviously not in used.

The picture taken after the removing is attached. Attachment1:ETMX, Attachment2:ETMY

And the pictures taken before the removing are on the wiki, so you can check how they are changed.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

The PD Kiwamu removed from the Y table was TRY, which we still need.

My bad if he took that. By mistake I told him that was the one I installed on the table for the length measurement and we didn't need it anymore.

I'm going to ask Kiwamu if he can kindly put it back.

  2606   Tue Feb 16 11:12:51 2010 kiwamuUpdateGreen LockingRe:take some optics away from the ETM end table

Quote:

Quote:

In the last two days Steve and I took some optics away from the both ETM end table.

This is because we need an enough space to set up the green locking stuff into the end table, and also need to know how much space is available.

Optics we took away are : Alberto's RF stuff, fiber stuff and some optics obviously not in used.

The picture taken after the removing is attached. Attachment1:ETMX, Attachment2:ETMY

And the pictures taken before the removing are on the wiki, so you can check how they are changed.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

The PD Kiwamu removed from the Y table was TRY, which we still need.

My bad if he took that. By mistake I told him that was the one I installed on the table for the length measurement and we didn't need it anymore.

I'm going to ask Kiwamu if he can kindly put it back.

 I am going to put the PD back to the Y end table in this afternoon.

  2609   Tue Feb 16 16:24:30 2010 kiwamuUpdateGreen LockingRe:Re:take some optics away from the ETM end table

I put the TRY_PD back to the end table and aligned it. Now it seems to be working well.

Quote:

The PD Kiwamu removed from the Y table was TRY, which we still need.

My bad if he took that. By mistake I told him that was the one I installed on the table for the length measurement and we didn't need it anymore.

I'm going to ask Kiwamu if he can kindly put it back.

 I am going to put the PD back to the Y end table in this afternoon.

 

  2619   Fri Feb 19 16:40:43 2010 kiwamuUpdateGreen Lockingrearrange the optics on the end table

Koji and kiwamu

The existing optics on the ETMX/ETMY end table were rearranged in this morning.

 


The main things we have done are -

1. relocation of the optical levers for ETMs ( as mentioned in koji's entry )

This relocation can make a space so that we can setup the green locking stuffs.

The optical path of the green locking is planed to start from the right top corner on the table, therefore we had to relocate the oplevs toward the center of the table.

2. relocation of the lens just before the tube

Because we are going to shoot the green beam into the arm cavity, we don't want to have any undesired lenses before the cavity.

For this reason we changed the position of the lens, it was standing just in front of the tube, now it's standing on the left side of the big mirror standing center top.

Since we did not find a significant change in its the spot size of the transmitted light, we did not change the position of all the TRANS_MON_PDs and its mirrors. And they are now well aligned.

Attachment1: ETMX end table

Attachment2: ETMY end table

Attachment 1: DSC_1202.JPG
DSC_1202.JPG
Attachment 2: DSC_1207.JPG
DSC_1207.JPG
  2706   Wed Mar 24 03:58:18 2010 kiwamu, matt, kojiUpdateGreen Lockingleave PLL locked

We are leaving the PLL as it is locked in order to see the long term stability. And we will check the results in early morning of tomorrow.

DO NOT disturb our PLL !!

  


(what we did)

After Mott left, Matt and I started to put feedback signals to the temperature control of NPRO.

During doing some trials Matt found that NPRO temperature control input has an input resistance of 10kOhm.

Then we put a flat filter ( just a voltage divider made by a resistor of ~300kOhm and the input impedance ) with a gain of 0.03 for the temperature control to inject a relatively small signal, and we could get the lock with the pzt feedback and it.

In addition, to obtain more stable lock we then also tried to put an integration filter which can have more gain below 0.5Hz.

After some iterations we finally made a right filter which is shown in the attached picture and succeeded in obtaining stable lock.

 

 

 

Attachment 1: DSC_1402.JPG
DSC_1402.JPG
  2707   Wed Mar 24 04:22:51 2010 kiwamu, mattUpdateGreen Lockingtwo NPRO PLL

Now some pedestals, mirrors and lenses are left on the PSL table, since we are on the middle way to construct a PLL setup which employs two NPROs instead of use of PSL laser.

So Please Don't steal any of them.

  2708   Wed Mar 24 12:38:17 2010 HartmutConfigurationGreen LockingBroadband PD for green PLL

Modified one of the PD assemblies carrying a large SI-Diode (~10mm diameter).

Removed elements used for resonant operation and changed PD readout to transimpedance

configuration. The opamp is a CLC409 with 240 Ohm feedback (i.e. transimpedance) resistor.

To prevent noise peaking at very high frequencies and get some decoupling of the PD,

I added a small series resistor in line with the PD and the inverting opamp input.

It was chosen as 13 Ohm, and still allows for operation up to ~100MHz.

Perhaps it could be smaller, but much more bandwith seems not possible with this opamp anyway.

Changes are marked in the schematic, and I list affected components here.

(Numbers refer to version 'PD327.SCH' from 30-April-1997):

-removed L4

-connected L3 (now open pad) via 100 Ohm to RF opamp output. This restores the DC sognal output.

-removed c17

-connected pin 3 of opamp via 25 Ohm to GND

-connected kathode of PD via 13 Ohm to pin 2 of opamp

-removed L6, C26, L5, C18, and C27

-shorted C27 pad to get signal to the RF output

 

Measured the optical TF with the test laser setup.

(Note that this is at 1064nm, although the PD is meant to work with green light at 532nm!)

Essentially it looks usable out to 100MHz, where the gain dropped only by about

6dB compared to 10MHz.

Beyond 100MHz the TF falls pretty steeply then, probably dominated by the opamp.

 

The maximal bias used is -150V.

If the bias is 'reduced' from -150V to -50V, the response goes down by 4dB at 10MHz and

by 9dB at 100MHz.

 The average output was 30mV at the RF output, corresponding to 60mV at the opamp output (50Ohm divider chain).

With 240 Ohm transimpedance this yields 250µA photo-current used for these transfer functions.

SiAmpl.png

 

SiPhase.png

 

 

  2710   Wed Mar 24 14:52:02 2010 AlbertoUpdateGreen Lockingtwo NPRO PLL

Quote:

Now some pedestals, mirrors and lenses are left on the PSL table, since we are on the middle way to construct a PLL setup which employs two NPROs instead of use of PSL laser.

So Please Don't steal any of them.

 Can I please get the network analyzer back?

  2712   Wed Mar 24 15:59:59 2010 kiwamu, mattUpdateGreen Lockingleave PLL locked

Matt checked it in this morning and he found it's been locked during the night.

 

 

  2714   Thu Mar 25 17:29:48 2010 kiwamu, mottUpdateGreen LockingPLL two NPROs

In this afternoon, Mott and I tried to find a beat note between two NPROs which are going to be set onto each end table for green locking.

At first time we could not find any beats. However Koji found that the current of innolight NPRO was set to half of the nominal.

Then we increased the current to the nominal of 2A, finally we succeeded in finding a beat note.

Now we are trying to lock the PLL.

P.S. we also succeeded in acquiring the lock

 

nominal setup
  innolight  lightwave
T [deg] 39.75 37.27
current [A] 2 2
laser power [mW] 950 700


  2718   Sun Mar 28 17:28:26 2010 matt, kiwamuUpdateGreen Lockingfrequency discriminator for green PLL

Last Friday, Matt made a frequency discriminator circuit on a bread board in order to test the idea and study the noise level. I think it will work for phase lock acquisition of Green locking.

As a result a response of 100kHz/V and a noise level of 2uV/rtHz @ 10Hz are yielded. This corresponds to 0.2Hz/rtHz @ 10Hz.

The motivation of using frequency discriminators is that  it makes a frequency range wider and easier for lock acquisition of PLLs in green locking experiment.

For the other possibility to help phase lock acquisition, Rana suggested to use a commercial discriminator from Miteq.


(principle idea)

The diagram below shows a schematic of the circuit which Matt has built.

FD.png

Basically an input signal is split into two signals right after the input, then one signal goes through directly to a NAND comparator.

On the other hand another split signal goes through a delay line which composed by some RC filters, then arrive at the NAND comparator with a certain amount of delay.

After going through the NAND comparator, the signal looks like a periodic pulses (see below).

If we put a signal of higher frequency we get more number of pulses after passing through the NAND.

pulses.png

Finally the pulse-signal will be integrated at the low pass filter and converted to a DC signal.

Thus the amplitude of DC signal depends on the number of the pulses per unit time, so that the output DC signal is proportional to the frequency of an input signal.

 

 

(result)

By putting a TTL high-low signal, an output of the circuit shows 100kHz/V linear response.

It means we can get DC voltage of 1 V if a signal of 100kHz is injected into the input.

And the noise measurement has been done while injecting a input signal. The noise level of 0.2Hz/rtHz @ 10 Hz was yielded.

Therefore we can lock the green PLL by using an ordinary VCO loop after we roughly guide a beat note by using this kind of discriminator.

 FDnoise.png

Attachment 1: DSC_1407.JPG
DSC_1407.JPG
Attachment 2: FD.png
FD.png
Attachment 3: FDnoise.png
FDnoise.png
  2728   Mon Mar 29 15:19:33 2010 mevansUpdateGreen Lockingfrequency discriminator for green PLL

Thanks for the great entry!

In order to make this work for higher frequencies, I would add Hartmut's suggestion of a frequency dividing input stage.  If we divide the input down by 100, the overall range will be about 200MHz, and the noise will be about 20Hz/rtHz.  That might be good enough... but we can hope that the commercial device is lower noise!

Quote:

Last Friday, Matt made a frequency discriminator circuit on a bread board in order to test the idea and study the noise level. I think it will work for phase lock acquisition of Green locking.

As a result a response of 100kHz/V and a noise level of 2uV/rtHz @ 10Hz are yielded. This corresponds to 0.2Hz/rtHz @ 10Hz.

The motivation of using frequency discriminators is that  it makes a frequency range wider and easier for lock acquisition of PLLs in green locking experiment.

FD.png

  2735   Tue Mar 30 21:11:42 2010 kiwamuSummaryGreen Lockingconversion efficiency of PPKTP

With a 30mm PPKTP crystal the conversion efficiency from 1064nm to 532nm is expected to 3.7 %/W.

Therefore we will have a green beam of more than 20mW by putting 700mW NPRO.

Last a couple of weeks I performed a numerical simulation for calculating the conversion efficiency of PPKTP crystal which we will have.

Here I try to mention about just the result. The detail will be followed later as another entry.


The attached figure is a result of the calculation.

The horizontal axis is the waist of an input Gaussian beam, and the vertical axis is the conversion efficiency.

You can see three curves in the figure, this is because I want to double check my calculation by comparing  analytical solutions.

The curve named (A) is one of the simplest solution, which assumes that the incident beam is a cylindrical plane wave.

The other curve (B) is also analytic solution, but it assumes different condition; the power profile of incident beam is a Gaussian beam but propagates as a plane wave.

The last curve (C) is the result of my numerical simulation. In this calculation a focused Gaussian beam is injected into the crystal.

The numerical result seems to be reasonable because the shape and the number doesn't much differ from those analytical solutions.

Attachment 1: efficiency_waist_edit.png
efficiency_waist_edit.png
  2736   Tue Mar 30 22:13:49 2010 KojiSummaryGreen Lockingconversion efficiency of PPKTP

Question:

Why does the small spot size for the case (A) have small efficiency as the others? I thought the efficiency goes diverged to infinity as the radius of the cylinder gets smaller.

Quote:

With a 30mm PPKTP crystal the conversion efficiency from 1064nm to 532nm is expected to 3.7 %/W.

Therefore we will have a green beam of more than 2mW by putting 700mW NPRO.

Last a couple of weeks I performed a numerical simulation for calculating the conversion efficiency of PPKTP crystal which we will have.

Here I try to mention about just the result. The detail will be followed later as another entry.


The attached figure is a result of the calculation.

The horizontal axis is the waist of an input Gaussian beam, and the vertical axis is the conversion efficiency.

You can see three curves in the figure, this is because I want to double check my calculation by comparing  analytical solutions.

The curve named (A) is one of the simplest solution, which assumes that the incident beam is a cylindrical plane wave.

The other curve (B) is also analytic solution, but it assumes different condition; the power profile of incident beam is a Gaussian beam but propagates as a plane wave.

The last curve (C) is the result of my numerical simulation. In this calculation a focused Gaussian beam is injected into the crystal.

The numerical result seems to be reasonable because the shape and the number doesn't much differ from those analytical solutions.

 

  2737   Wed Mar 31 02:57:48 2010 kiwamuUpdateGreen Lockingfrequency counter for green PLL

Rana found that we had a frequency counter SR620 which might be helpful for lock acquisition of the green phase lock.

It has a response of 100MHz/V up to 350MHz which is wide range and good for our purpose. And it has a noise level of 200Hz/rtHz @ 10Hz which is 1000 times worse than that Matt made (see the entry).

The attached figure is the noise curve measured while I injected a signal of several 100kHz. In fact I made sure that the noise level doesn't depends on the frequency of an input signal.

The black curve represents the noise of the circuit Matt has made, the red curve represents that of SR620.

Attachment 1: FCnoise.png
FCnoise.png
  2740   Wed Mar 31 11:52:32 2010 kiwamuSummaryGreen LockingRe:conversion efficiency of PPKTP

Good point. There is a trick  to avoid a divergence.

Actually the radius of the cylindrical wave is set to the spot size at the surface of the crystal instead of an actual beam waist. This is the idea Dmass told me before.

So that the radius is expressed by w=w0(1+(L/2ZR)2)1/2, where w0 is beam waist, L is the length of the crystal and ZR is the rayleigh range.

In this case the radius can't go smaller than w0/2 and the solution can not diverge to infinity.

Quote:

Question:

Why does the small spot size for the case (A) have small efficiency as the others? I thought the efficiency goes diverged to infinity as the radius of the cylinder gets smaller.

 

 

 

  2741   Wed Mar 31 12:30:31 2010 ranaUpdateGreen Lockingfrequency counter for green PLL

Its a good measurement - you should adjust the input range of the 620 using the front panel 'scale' buttons to see how the noise compares to Matt's circuit when the range is reduced to 1 MHz. In any case, we would use it in the 350 MHz range mode. What about the noise of the frequency discriminator from MITEQ?

  2751   Thu Apr 1 15:21:12 2010 ranaUpdateGreen Lockingfrequency counter for green PLL

 

  2752   Thu Apr 1 16:34:29 2010 HartmutUpdateGreen LockingSilicon PDs

just a few infos on Silicon PDs I looked up.

If you want to go beyond the 100MHz achievable with the device I worked on,

the one thing to improve is the opamp, where Steve is trying to find OPA657.

This is a FET with 1.6GHz BWP, minimum stable gain of 7, and 4.8nV/rt(Hz) noise.

Should be ok with 750-1000 Ohm transimpedance.

The other thing you might want to change is the PD

(although it might be the 1cm PD with high bias is as fast as smaller ones with lower bias).

There are two types of other Si diodes at the 40m right now (~3mm):

-Rana and I found a Centronic OSD 15-5T in the old equipment

-Frank gave me a Hamamatsu S1223-01 on a Thorlabs pre-amp device (could be taken out).

 

The Centronic OSD 15-5T has up to 80pF with 12 V bias according to the datasheet.

The Hamamatsu S1223-01 is stated with 20pF only, but stated to have a max. frequency resp. of 20MHz ('-3db point').

I dont know what this means, as the corner freq. of 10pF into 50Ohm is still 160MHz.

In any case there are faster 3mm types to start with, as for example Hamamatsu S3399 (~ 90$),

which is stated to have the corner at 100MHz with 50 Ohm load.

For this type the stated capacity (20pF) looks consistent with ~100MHz corner into 50 Ohm.

So probably you can get higher BW with this one using much smaller load, as in transimpedance stage.

 

 

  2757   Thu Apr 1 20:29:02 2010 HartmutUpdateGreen Lockingsimple PD test circuit

I made a simple PD test circuit which may allow to test PD response up to few 100MHz.

Its not for low noise, only for characterising PD response.

Here is the circuit:

The 2 capacitor values (for bypassing) are kind of arbitrary, just what I found around

(one medium, one small capacity). Could be improved by better RF types (e.g. Mica).

The PD type has no meaning. I put in the Centronic 15-T5 for a start.

The bias can be up to 20V for this diode.

The signal appears across R1. It is small, to make a large bandwidth.

R2 is just for slightly decoupling the signal from the following RF amplifier.

The wire into the RF amplifier is short (~cm). And the amplifier is supposed to have 50 Ohm

input impedance.

I use a mini circuits ZFL 500 here.

power supply for this is 15V.

pdtest.png

  2788   Mon Apr 12 14:20:10 2010 kiwamuUpdateGreen LockingPZT response for the innolight

I measured a jitter modulation caused by injection of a signal into laser PZTs.

The measurement has been done by putting a razor blade in the middle way of the beam path to cut the half of the beam spot, so that a change of intensity at a photodetector represents the spatial jitter of the beam.

However the transfer function looked almost the same as that of amplitude modulation which had been taken by Mott (see the entry).

This means the data is dominated by the amplitude modulation instead of the jitter. So I gave up evaluating the data of the jitter measurement.

  2793   Mon Apr 12 19:50:30 2010 AidanSummaryGreen LockingTemperature sweep of the Lightwave: df/dT = 2.8GHz/K

The beams from the Innolight and Lightwave NPROs were both incident on a 1GHZ New Focus PD. Mott and I swept the temperature of the Lightwave and tracked the change in frequency of the beatnote between the two. The Innolight temperature was set to 39.61C although the actual temperature was reported to be 39.62C.

Freq. vs temperature is plotted below in the attached PDF. The slope is 2.8GHz/K.

The data is in the attached MATLAB file.

Attachment 1: LightWave_temp_sweep.pdf
LightWave_temp_sweep.pdf
Attachment 2: LightWave_Temp.m
% plot the data from the Lightwave Temperature sweep

% Lightwave temperature

LWTemp = [0.2744
    0.2753
    .2767
    .2780
    .2794
    .2808
... 67 more lines ...
  2794   Mon Apr 12 20:48:51 2010 Aidan, MottSummaryGreen LockingTemperature sweep of the Innolight: df/dT ~ 3.3GHz/K

Quote:

The beams from the Innolight and Lightwave NPROs were both incident on a 1GHZ New Focus PD. Mott and I swept the temperature of the Lightwave and tracked the change in frequency of the beatnote between the two. The Innolight temperature was set to 39.61C although the actual temperature was reported to be 39.62C.

Freq. vs temperature is plotted below in the attached PDF. The slope is 2.8GHz/K.

The data is in the attached MATLAB file.

 Same thing for the Innolight Mephisto.

Not unexpected values with dn/dT around 11E-6 K^-1 and coefficient of thermal expansion = 8E-6 K^-1 and a laser resonator length of order 10cm.

Attachment 1: Innolight_temp_sweep.pdf
Innolight_temp_sweep.pdf
Attachment 2: Innolight_Temp.m
% plot the data from the Innolight Temperature sweep

% Innolight temperature

InnTemp = [0.60
    .59
    .56
    .52
    .65] + 39;

... 25 more lines ...
  2797   Tue Apr 13 12:39:51 2010 Aidan, MottSummaryGreen LockingTemperature sweep of the Innolight: df/dT ~ 3.3GHz/K

Please put those numbers onto wiki somewhere at the green page or laser characterization page.

Quote:

Quote:

The beams from the Innolight and Lightwave NPROs were both incident on a 1GHZ New Focus PD. Mott and I swept the temperature of the Lightwave and tracked the change in frequency of the beatnote between the two. The Innolight temperature was set to 39.61C although the actual temperature was reported to be 39.62C.

Freq. vs temperature is plotted below in the attached PDF. The slope is 2.8GHz/K.

The data is in the attached MATLAB file.

 Same thing for the Innolight Mephisto.

Not unexpected values with dn/dT around 11E-6 K^-1 and coefficient of thermal expansion = 8E-6 K^-1 and a laser resonator length of order 10cm.

 

  2799   Tue Apr 13 19:53:06 2010 MottUpdateGreen LockingPZT response for the innolight and lightwave

 

 I redid the PZT Phase Modulation measurement out to 5 MHz for both the Innolight and the Lightwave.  The previous measurement stopped at 2MHz, and we wanted to see if there were any sweet spots above 2MHz.  I also reduced the sweep bandwidth and increased the source amplitude at high frequency to reduce the noise (the Lighwave measurement, especially, was noise dominated above 1MHz).  I also plotted the ratio of PM/AM in rad/RIN, since this is the ultimate criterion on which we want to make a determination.

It looks like there is nothing extremely useful above 2MHz for either laser.  There are several candidates for the lightwave at about 140 kHz and again at about 1.4 MHz.  The most compelling peak, however, is in the innolight at 216 kHz, where the peak is about 2.3e5 rad/RIN.

Below about 30kHz, the loop suppresses the measurement, so one should focus on the region above there.

Attachment 1: Innolight_PM.png
Innolight_PM.png
Attachment 2: Innolight_AM_PM.png
Innolight_AM_PM.png
Attachment 3: Innolight_PM_AM_Ratio.png
Innolight_PM_AM_Ratio.png
Attachment 4: Lightwave_PM.png
Lightwave_PM.png
Attachment 5: Lightwave_AM_PM.png
Lightwave_AM_PM.png
Attachment 6: Lightwave_PM_AM_Ratio.png
Lightwave_PM_AM_Ratio.png
  2804   Sat Apr 17 18:30:12 2010 ZachUpdateGreen Locking1W NPRO output profile

NOTE: This measurement is wrong and only remains for documentation purposes.

Koji asked me to take a profile of the output of the 1W NPRO that will be used for green locking. I used the razor-scan method, plotting the voltage output of a PD vs the position of the razor across the beam, both vertically and horizontally. This was done at 6 points along the beam path out of the laser box.

I determined the beam spot size at each point by doing a least-squares fit on the plots above in Matlab (using w as one of the fitting parameters) to the cumulative distribution functions (error functions) they should approximate.

I then did another least-squares fit, fitting the above "measured" beam profiles to the gaussian form for w vs z. Below is a summary.

It seems reasonable, though I know that M2 < 1 is fishy, as it implies less divergence than ideal for that waist size. Also, like Koji feared, the waist is inside the box and thus the scan is almost entirely in the linear regime.

profile_fit_4_17_10.png

  2807   Mon Apr 19 11:31:04 2010 AidanUpdateGreen Locking1W NPRO output profile

Quote:

 Koji asked me to take a profile of the output of the 1W NPRO that will be used for green locking. I used the razor-scan method, plotting the voltage output of a PD vs the position of the razor across the beam, both vertically and horizontally. This was done at 6 points along the beam path out of the laser box.

I determined the beam spot size at each point by doing a least-squares fit on the plots above in Matlab (using w as one of the fitting parameters) to the cumulative distribution functions (error functions) they should approximate.

I then did another least-squares fit, fitting the above "measured" beam profiles to the gaussian form for w vs z. Below is a summary.

It seems reasonable, though I know that M2 < 1 is fishy, as it implies less divergence than ideal for that waist size. Also, like Koji feared, the waist is inside the box and thus the scan is almost entirely in the linear regime.

profile_fit_4_17_10.png

There is a clearly a difference in the divergence angle of the x and y beams - maybe 10-20%. Since the measurements are outside the Rayleigh range and approximately in the linear regime, the slope of the divergence in this plot should be inversely proportional to the waists - meaning the x- and y- waist sizes should differ by about 10-20%. You should check your fitting program for the waist.

 

  2809   Mon Apr 19 16:27:13 2010 AidanUpdateGreen LockingRaicol crystals arrived and we investigated them

Jenne, Koji and I opened up the package from Raicol and examined the crystals under the microscope. The results were mixed and are summarized below. There are quite a few scratches and there is residue on some of the polished sides. There is a large chip in one and there appear to be gaps or bands in the AR coatings on the sides.

There are two albums on Picassa

1. The package is opened ...

2. The crystals under the microscope.

 

Crystal Summary
724 Chip in the corner of one end face, Otherwise end faces look clean. Large scratch on one polished side.
725 End faces look good. Moderate scratch on one polished face. Residue on one polished face.
726 Tiny dot on one end face, otherwise look okay. Large bands in one polished face. Moderate scratch on polished face
727 Large, but shallow chip on one polished face. End faces look clean. Bands in one of the polished faces.

 

  2816   Tue Apr 20 11:14:31 2010 AidanUpdateGreen LockingRaicol crystals arrived and we investigated them

 

 Here is Crystal 724 polished side 2 with all photos along the length stitched together

  2818   Tue Apr 20 13:02:14 2010 ZachUpdateGreen Locking1W NPRO output profile

EDIT: I used an IFIT (inverse fast idiot transform) to change the x-axis of the plot from Hz to m. I think xlabel('Frequency [Hz]') is in my muscle memory now..

I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.

 
profile_fit_4_19_10.png
  2819   Tue Apr 20 13:37:36 2010 JenneUpdateGreen Locking1W NPRO output profile

Quote:

I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.

 
profile_fit_4_19_10.png

 Are you sure about your x-axis label? 

  2821   Tue Apr 20 19:37:02 2010 KojiUpdateGreen Locking1W NPRO output profile

Beautiful fitting.

Quote:

EDIT: I used an IFIT (inverse fast idiot transform) to change the x-axis of the plot from Hz to m. I think xlabel('Frequency [Hz]') is in my muscle memory now..

I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.

 
profile_fit_4_19_10.png

 

  2823   Wed Apr 21 10:09:23 2010 kiwamuUpdateGreen Lockingwaist positon of Gaussian beam in PPKTP crystals

Theoretically the waist position of a Gaussian beam (1064) in our PPKTP crystal differs by ~6.7 mm from that of the incident Gaussian beam.

So far I have neglected such position change of the beam waist in optical layouts because it is tiny compared with the entire optical path.

But from the point of view of practical experiments, it is better to think about it.

In fact the result suggests the rough positioning of our PPKTP crystals;

we should put our PPKTP crystal so that the center of the crystal is 6.7 mm far from the waist of a Gaussian beam in free space.


(How to)

The calculation is very very simple.

The waist position of a Gaussian beam propagating in a dielectric material should change by a factor of n, where n is the refractive index of the material.

In our case, PPKTP has  n=1.8, so that the waist position from the surface of the crystal becomes longer by n.

Now remember the fact that the maximum conversion efficiency can be achieved if the waist locates at exact center of a crystal.

Therefore the waist position in the crystal should be satisfied this relation; z*n=15 mm, where z is the waist position of the incident beam from the surface and 15 mm is half length of our crystal.

Then we can find z must be ~8.3 mm, which is 6.7 mm shorter than the position in crystal.

The attached figure shows the relation clearly. Note that the waist radius doesn't change.

Attachment 1: focal_positin_edit.png
focal_positin_edit.png
  2835   Fri Apr 23 18:30:49 2010 Aidan, Jenne, KojiSummaryGreen LockingGreen means GO!

Jenne, Koji and I assembled the Covesion Oven today, inserted a PPKTP crystal from Raicol, aligned the crystal to a 50mW focus and
got some green beam coming out.

Covesion Oven assembly

The oven contains a brass clip that can clamp a crystal up to 10mm wide x 0.5mm high x 40mm long (according to the instructions). According to the correspondence from Covesion the clip can accomodate a crystal up to 1.5mm high. Our crystal is 1mm x 1mm x 30mm.

  1. We removed the brass springs from the clip - see Koji's photos
  2. We placed the Raicol PPKTP crystal (#725) into the clamp with the long polished surfaces facing out to the sides and the roughened surfaces facing up and down.
  3. We balanced the 10mm x 40mm x 1mm glass plate on top of the crystal.
  4. We replaced the brass springs in the top of the clip but only tightened the screws a couple of turns so they wouldn't fall out.
  5. Very carefully and slowly, I tightened the screws a few turns in a star-shaped order to distribute the pressure evenly across the glass top
  6. Each time I tightened all eight screws, I jiggled each of the four springs to see if there was any compression in them
  7. Once the springs started to show signs of compression I stopped tightening them and tested the stability of the glass plate - a reasonable amount of pressure was required to move the plate - about the same amount required to push a SR560 across an optical table with your index finger.
  8. We loosely attached the lid and moved the oven to the table

Alignment of the crystal to the focus

The oven was mounted on a 4-axis Newport translation stage. We plonked the assembly onto the table, removed the lid and adjusted the rough position so that a focus of the 1064nm beam, from a 100mm lens, was positioned near the center of the crystal - then it was clamped down to the table. From here we adjusted the alignment of the stage, using an IR card and a viewer to guide us, until we eventually saw some green beam coming out. We were all very excited by this! We optimized the alignment as best we could using the IR card and then we replaced the lid on the oven. At this point the temperature of the PPKTP was around 26.5C and the green beam coming out look quite dim. We turned the oven up to around 36 degC and observed the beam getting much brighter and we approached the optimum phase-matching condition.

We haven't done anyway quantitative measurements yet but we were pleased with how easy this first stage was.

 

[Edit by Koji] More photos are on Picasa album

Attachment 1: IMG_2405.jpg
IMG_2405.jpg
Attachment 2: IMG_2417.jpg
IMG_2417.jpg
  2843   Mon Apr 26 11:14:04 2010 KojiUpdateGreen LockingTemperature scan for PPKTP

I scanned the temperature of the crystal oven on Friday night in order that we can find the optimal temperature of the crystal for SHG.

The optimal temperature for this crystal was found to be 36.2 deg.


The crystal is on the PSL table. The incident beam on the crystal is 27.0mW with the Newport power-meter configured for 1064nm.
The outgoing beam had 26.5mW.

The outgoing beam was filtered by Y1-45S to eliminate 1064nm. According to Mott's measurements, Y1-45S has 0.5% transmission for 1064nm, while 90% transmission for 532nm. This means I still had ~100uW after the Y1-45S. This is somewhat consistent with the offset seen in the power-meter reading.

First, I scanned the temperature from 28deg to 40deg with 1deg interval.The temperature was scaned by changing the set point on the temperature controller TC-200.The measurements were done with the temperature were running. So, the crystal may have been thermally non-equilibrium.

Later, I cut the heater output so that the temperature could be falling down slowly for the finer scan. The measurement was done from 38deg to 34deg with interval of 0.1deg with the temperature running.

I clearly see the brightness of the green increase at around 36 deg. The data also shows the peak centered at 36.2deg. We also find two lobes at 30deg and 42deg. I am not sure how significant they are.

Attachment 1: SHG_pow.png
SHG_pow.png
  2850   Tue Apr 27 14:18:53 2010 kiwamuUpdateGreen Lockingwaist positon of Gaussian beam in PPKTP crystals

The mode profile of Gaussian beams in our PPKTP crystals was calculated.

I confirmed that the Rayleigh range of the incoming beam (1064 nm) and that of the outgoing beam (532 nm) is the same.

And it turned out that the waist postion for the incoming beam and the outgoing beam should be different by 13.4 mm toward the direction of propagation.

These facts will help us making optical layouts precisely for our green locking.


(detail)

The result is shown in the attached figure, which is essentially the same as the previous one (see the entry).

The horizontal axis is the length of the propagation direction, the vertical axis is the waist size of Gaussian beams.

Here I put x=0 as the entering surface of the crystal, and x=30 mm as the other surface.

The red and green solid curve represent the incoming beam and the outgoing beam respectively. They are supposed to  propagate in free space.

And the dashed curve represents the beams inside the crystal.

A trick in this calculation is that: we can assume that  the waist size of 532 nm is equal to that of 1064 nm divided by sqrt(2) . 

If you want to know about this treatment in detail,  you can find some descriptions in this paper;

"Third-harmonic generation by use of focused Gaussian beams in an optical super lattice" J.Opt.Soc.Am.B 20,360 (2003)"

Attachment 1: mode_in_PPKTP.png
mode_in_PPKTP.png
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