EY:

• A clean cart was setup adjacent to the HEPA-enclosed mini cleanroom area (it cannot be inside the mini cleanroom, because of lack of space). 
• The FC tools (first contact, acetone, beakers, brushes, PEEK mesh, clean scissors, clean tweezers, Canon camera, green flashlight) were laid out on this cart for easy access.
• I inspected the optic - the barrel had a few specks of dust, and the outer 1.5" annular region of the HR face looked to have some streak marks
  • I was advised not to pre-wipe the HR side with any solvents
  • The FC was only applied to the centran ~1-1.5" of the optic
• After applying the FC, I spent a few minutes inspecting the status of the OSEMs 
  • Three out of the four face OSEMs, as well as the side OSEM, did not have a filter in
  • I inserted filters into them.
• Closed up the chamber with light door, left HEPA unit on and the mini cleanroom setup intact for now. We will dismantle everything after the pumpdown.

IY:

• Similar setup to EY was implemented
• Removed side OSEM from ITMY.
• Double-checked that EQ stops were engaged.
• Moved the OSEM cable tower to free up some space for accommodating ITMY.
• Undid the clamps of ITMY, moved it to the NE corner of the IY table.
• Inspected the optic - it was much cleaner than the 2016 inspection, although the barrel did have some specks of dust.
• Once again, I applied first contact to the central ~1.5" of the HR surface.
• Checked status of filters on OSEMs - this time, only the UL coil required a filter.
  • Attachment #3 shows the sensor voltage DC level before and after the insertion of the filter. There is ~0.1% change.
  • The filters were found in a box that suggests they were made in 2002 - but Steve tells me that it is just stored in a box with that label, and that since there are >100 filters inside that box, he thinks they are the new ones we procured in 2016. The coating specs and type of glass used are different between the two versions.

The attached photo shows the two optics with FC applied.

My original plan was to attempt to close up tomorrow. However, we are still struggling with Satellite box issues. So rather than rush it, we will attempt to recover the Y arm cavity alignment on Monday, satellite box permitting. The main motivation is to reduce the deadtime between peeling off the F.C and starting the pumpdown. We will start working on recovering the cavity alignment once the Sat box issues are solved.

In an earlier elog, I had claimed that the suspected clipping of the cavity axis in the Y arm was not solved even after shifting the heater. I now think that it is extremely unlikely that there is still clipping due to the heater. Nevertheless, the ASS system is not working well. Some notes:

1. The heater has been shifted nearly 1-inch relative to the cavity axis compared to its old position - see Attachment #1 which compares the overhead shot of the suspension cage before and after the Jan 2019 vent.
2. On Sunday, I was able to recover TRY ~ 1.0 (but not as high as I was able to get by intentionally setting a yaw offset to the ASS) by hand alignment with the spot on ETMY much closer to the center of the optic, judging by the camera. There are offsets on the dither alignment error signals which depend on the dither frequency, so the A2L signals are not good judges of how well centered we are on the optic.
3. By calculating the power lost by clipping a Gaussian beam cross-section with a rectangular block from one side (an admittedly naive model of clipping), I find that we'd have to be within 15 mm of the line connecting the centers of ITMY and ETMY to even see ~10 ppm loss, see Attachment #2. So it is hard to believe that this is still a problem. Also, see  Attachment #3 which compares side-by-side the view of ETMY as seen through the EY optical table viewport before and after the Jan 2019 vent.

We have to systematically re-commission the ASS system to get to the bottom of this.

Estimate loss along the Y arm beat path:

1. Measured the beam powers (before the beam combiner): 
Y Arm green = 35 uW
Y PSL green = 90 uW

==> P_beat ~ 2 * sqrt (35 uW * 90 uW) ~ 112 uW

2. Expected power of RF signal
Assuming the PD to have transimpedance ~ 2kV/A and responsivity ~ 0.3A/W, 
the expected power of the RF signal = (P_beat * Transimpledance* Responsivity)^2 / (2 * 50ohm) ~ 45uW = -13.5 dBm

3. Measured power of Y arm beat signal

Turned OFF the beat PDs and rerouted the RF cables such that the spectrum analyzer was reading the RF signal from the Y beat PD itself (without any amplifiers or the beat box itself in the path).  
Turned ON the beat PDs and the Y arm beat signal power on the spectrum analyzer measured -58dBm
Even if we consider for losses along the length of the cables, we are still at a very bad state. 

4. Bad mode matching??
I don't think mode matching is our main problem here.
Toggling the shutter several times, even with the non-00 modes, the maximum beat power we can see is -50dBm which is still very far from the actual expected value.

The Y arm green transmission had come down to 0.3 and the green steering mirrors on the Y end table required some minor alignment adjustments to bring back transmission to around 0.75 counts.

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.

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.

I closed all 8 dither loops for the Y arm initial alignment: 2x2 centering servo (this worked before) and 2x2 input beam servo for both pitch and yaw.

So far it looks pretty good - the error points go to zero and the arm power goes up to 1.

The offloading to the alignment biases and the PZTs is not yet automated.

Today the PMC, MC, and Y arm were very cooperative and a pleasure to work with.

 Just a quick update... the Lightwave laser has now been moved up to the end of the Y arm. It's also been mounted on the new mounting block and heatsinks attached with indium as the heat transfer medium.

A couple of nice piccies...

Calibrating error signal to beat frequency;
  I injected 0 dBm RF sine wave into the beatbox and sweeped the frequency(just like we did in elog #6815).
  This time, we have different whitening filters. I sweeped the frequency from 0 to 100 MHz in 200 sec.
  The length of the delay line is ~1.5 m for COARSE.


Y arm length;
  Here, I think we need some assumption. Let's assume wavelength of IR lamb_IR = 1064 nm and Y end green frequency is nu_g = 2*nu_IR.
  There is a relation
    dnu_g / nu_g = dL / L
  So,
    dnu_g / (dL/lamb_IR) = 2*nu_IR * lamb_IR / L = 2c/L
  We know that dL/lamb_IR = 1/2 for difference in beat frequency between TEM00s. Therefore, slope of the dnu_g vs dL/lamb_IR plot gives us the arm length L(figure below, middle plot).

  Error estimation is not done yet, but I think the COARSE_I_IN1 error signal to the beat frequency calibration has the largest error because it seems like the amplitude of sine wave changes ~10% day by day.

Calibrating beat frequency to Y arm length change;
  I used L = 32.36 m (figure above, bottom plot).
    dnu_g / dL = c / lamb_g / L = 1.74 MHz/m

Wow. This is way too short.

You don't need to use Albertoo's arm length as his measurement was done before the upgrade.

I know!
But I think there's some error (~ 10% ?) in calibrating the beatbox. In elog #6815, slope near zero crossing point is about 68 counts/MHz, but now, its 60 counts/MHz. Also, zero crossing point in elog #6815 was 47 MHz, but now, its 45 MHz. 5FSR scan was done between these two calibration measurement.

The Y arm has been locked with the IR beam. The purpose is to use the arm as an alignment reference for the input PZTs.

Detail will be posted later. Here is a picture of ITMY suspension. You can see there is a beam spot in the middle of the test mass.

First of all, the conclusions / results from the exercise of the Y arm locking yesterday are:

   The position of the beam spots on both ETMY and ITMY are now not so bad ( ~ 5 mm off from the center).

   The input PZTs are coarsely aligned to the Y arm.

   Nevertheless IP_ANG is still too high to come out from the view port at the Y end station.

  After the alignments of PRM, SRM and Michelson, POP is still largely clipped.

(what I did)

  - Alignments of the Input PZTs

  - Adjustment of the demodulation phase  for the Y arm PDH.

  - Activation of oplev on ITMY

  - PDH locking

(Broken or likely broken stuff)

 * IP_ANG doesn't give a signal to the digital side.

 * ETMY coils look weak and 2 - 3 times weaker than the other test masses. (or OSEM readout gain maybe lower)

 * reload button on sitemap.adl doesn't work.

 * Farfalla, a lab laptop, seems out of network.

As far as I know, this button works only once after the launch of MEDM...

 If you look at the real host table instead of the misleading host table in the wiki, you will see that someone has deleted Farfalla from there. She needs to be re-added.

[johannes, lydia, gautam]

• The Y arm has been locked to IR in air using POY11 as an error signal 
• We had been seeing flashes in the arm since yesterday, but were unable to lock
• Today we re-did the alignment procedure much the same way as yesterday
  • It is useful to put in the slide-on irides onto the suspension tower for this sort of alignment
  • We were a bit more systematic in aligning back-reflections to overlap each other today
  • It is useful to stick the IR card just in front of the iris, and align the tip tilts by looking at the scatter on the camera. At least for Yaw, this works pretty well, probably a more reliable reference than contorting oneself inside the vacuum chamber to see if we are well aligned or not.
• Two fixes that made locking possible today:
  • The POY error signal had a large DC offset. I zeroed the offset and adjusted the demod phase to make the error signal 0 when the IMC was unlocked
  • I replaced the 50-50 beam splitter that was dividing the transmitted light between the QPD and Thorlabs PDs with a 2" Y1 CVI mirror - this meant that the flashes we had with the arm roughly aligned went from < 0.1 to a healthier 0.25, which allowed easier locking
• The POY whitening gain was unchanged from when we locked the Y arm in air just after venting and before taking the doors off
• The mode is barely visible on ITMY face, although I guess this is to be expected given we are at low power
• Lydia then tuned the arm alignment more finely such that the transmission is now ~0.65 (See Attachemnt 2 for slider values)
• From values from normal (pre-vent) IFO operation, I would have expected us to get a transmission of about 1 assuming 100mW going into the IFO from the IMC - and so with the BS switched out for an HR mirror, a transmission of ~2. What we get is about 1/3 of this value. Perhaps the IMC isn't so well aligned, but it is hard to imagine we have only 30mW going into the IFO. Or perhaps the input pointing is sub optimal (I did not run ASS, perhaps I should have)

GV EDIT Sep 5: These numbers do make sense if the ND filter that was on the Transmon QPD had ND = 0.6 (there are two at the end, one labelled ND 0.6 and the other labelled ND10 though the latter label looks like some custom label so I don't really trust that value), even though only one was on, unfortunately I don't remember which. So, for 10% of input power with a factor of 8 increase because the ND filter is removed and also that the 50% BS has been replaced with a HR mirror, we expect a transmission level of ~0.6 (compared to the normalized value under normal IFO operation) which is close to what we see...

• The UL coil problems continue to plague us but we were able to lock the arm regardless

In any case, I think we can work on putting in the X arm now and work on recovering that. 

To do for the Y-arm (now that the F.C. is off, we should try and do this in as few chamber openings as possible):

• Fix problematic ITMY UL coil
• Rotation of all 5 ITMY OSEM coils for B-R peak reduction in sensor outputs
• Adjustment of axial position of all OSEM coils on ITMY and ETMY to better center the PD outputs to half their saturation value, given that the pitch and yaw biases to the optics have changed since this was last done
• Insertion of new baffles - try and center the IR and green beams as best as possible on these so that they serve as an alignment reference in the future

Then we need to do all of this for the X arm as well. The PRM LR coil is still giving no output - I will try moving the bias sliders around to see if this is a stuck magnet situation, but perhaps it is not. Since Eric's 3-satellite-box-monte did not yield any positive results, we have to consider the possibility that the LED or PD themselves are damaged. If so, I don't see any workaround without opening up the BS-PRM chamber, but if we can avoid this, we should. Perhaps when ITMX is open we can use the camera with the IR filter removed to see if all the OSEM LEDs are functional through the beam tube.

We are also piping POY11 error to the DAFI model and can hear it in the control room.

Rana suggested reviving the MC autolocker - I've made some changes to the low power MC autolocker scripts and they've been working the few times I tried today evening, but let's see how it does over the weekend. I've also changed the Y axis of the StripTool on the wall to better reflect the low-power range..

Y arm locked on green carrier in 00 mode!

It locked at almost 280 cts, and the transmitted power on the PSL table is  about 40 uW.

To make it lock on the carrier I had to flip the sign of the error signal in the PDH loop, so I put a phase shifter (a Pomona box with a 23 uF capacitor) right before the LO input of the PDH box (on the model of the X arm).

Tomorrow I will put more details about the power budget and the phase shifter transfer function.

Koji tweaked the alignment sliders till we were able to get the Y arm locked to green in a 00 mode, GTRY ~ 0.5 which is the prevent number I have in my head. The green input pointing looks slightly off in yaw, as the spot on the ITM looks a little misaligned - I will fix this tomorrow. But it is encouraging that we can lock to the green, suggests we are not crazily off in alignment.

[Ed by KA: slider values: ETMY (P, Y) = (-3.5459,  0.7050), ITMY (P, Y) =  (0.3013, -0.2127)]

While we were locked to the green, ITMY UL coil acted up quite a bit - with a large number of clearly visible excursions. Since the damping was on, this translated to somewhat violent jerking of ITMY (though the green impressively remained locked). We need to fix this. In the interest of diagnosis, I have switched in the SRM satellite box for the ITM one, for overnight observation. It would be good to narrow this down to the electronics. Since SRM is EQ-stopped, I did not plug in any satellite box for SRM. The problem is a difficult one to diagnose, as we can't be sure if the problem is with the LED current driver stage or the PD amplifier stage (or for that matter, the LED/PD themselves), and because the glitches are so intermittent. I will see if any further information can be gleaned in this regard before embarking on some extreme measure like switching out all the 1125 OpAmps or something...

Does anyone know if we have a spare satellite box handy? 

[Annalisa, Nic]

After connecting the PD with the reflection from the arm  to the PDH box, theY  arm has been locked on the 01 mode.  Maximizing the alignment, we obtained a 00 mode locking, but we couldn't maximize the power.

The size of the reflected beam was different with respect to the size of the incoming beam, so probably a bad mode matching was one of the issues.

Moreover, the reflected beam is very low power. We need to figure out why it is so (bad alignment? related to mode matching?)

After measuring better all the distances, I did a new mode matching calculation. I put the lenses after measuring the beam waist, so the size of the beam on the lenses was the same as expected from the calculation. Nevertheless, the beam size on the beam splitter looks bigger than expected, and also in this case green flashes into the cavity at some HOM (again 01).

I also tried to lock again the cavity and maximize the alignment, but I didn't get any improvement with respect to the previous mode matching.

Still no good locking!

After making the reflected beam size closer to the injected one, I maximized alignment. I locked again in 00 mode, but I couldn't maximize the power. 

I just realized that maybe I'm not using the correct radius of curvature for the ETMY in the simulation. Tomorrow I will start checking from that.

 Also make sure you are taking into account the substrate of the ETM.

 For the mode matching calculation I was using the ETMY focal length that I found on Kiwamu's plot on the wiki page. 

Taking into account also the substrate, the focal length turns out to be

fl = ((n-1)*(1/R1 - 1/R2 + (n-1)d/(nR1R2)))^(-1) = -125.81 m

with n = 1.46071 (refraction index of fused silica at 532nm)

R1 = 5625 m (radius of curvature of the first surface)

R2 = 57.37 m (radius of curvature of the second surface)

d = 25mm (thickness)

The value of the focal length is sligthly different from the one I was using before in the calculation, but maybe it is enough to change the coupling.

The mode matching solution I found is very sensitive to the lenses position. 

The beam waist position can vary up to 20m varying by 1cm the first lens position, while it is slightly less sensitive to the second lens displacement.

As shown in the picture, along the green beam path there is also a 1m focal length lens. It's position is fixed, because it is along the IR transmetted beam path also. I tried to get a better solution without it, but I found that the waist position was still strongly dependent on one of the two lenses position, so it would not solve the problem to remove this lens.

I think that the main issue of this mode matching is related to the "space contraints", because the two lenses' positions can vary in a very small space, even though the green beam path on the table is quite long.

Eventually, I put the MM lenses found from this last simulation on the table, and it seems to work, since I've seen very strong 00 flashes. Unfortunately, while trying to maximize the alignment I broke it  and I have to do it again, but I feel confident! 

After restoring alignment I could see again strong 00 flashes (about 250-300 counts on ALS-TRY). So I locked the arm with IR and after enabling the PDH servo for the green locking, I also locked the green on the Y arm in 00 mode. Then I moved the two mode matching lenses to maximize the power into the 00 mode, but I didn't reach more than 30-35 counts.

Green power injected into the Y arm                    0.680mW

Green power reflected back                                  0.090mW

Green power transmitted on the PSL                  few uW

I would expect more power on the PSL table (maybe 10x more).

Hmmm.  You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement? 
We should look at it with fresh eyes in the morning. 

> Hmmm.  You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement? 
> We should look at it with fresh eyes in the morning. 

Also, if you have been measuring the power of green refl at the rejection port of the green faraday, the polarization of the light entering the green faraday should be checked once again to make sure that you are measuring 
only the reflected power from the arm cavity.

> > Hmmm.  You seem to be saying that more light is reflected than is injected. Is this a units problem? Or was some IR on the power meter during the 'reflected' measurement? 
> > We should look at it with fresh eyes in the morning. 
> 
> Also, if you have been measuring the power of green refl at the rejection port of the green faraday, the polarization of the light entering the green faraday should be checked once again to make sure that you are measuring 
> only the reflected power from the arm cavity.

Sorry Sorrry Sorry!!
It was 0.090 mW, I just forgot a zero!!!
Sorry!

Is this reflection measured with the cavity locked or unlocked?

So what's the actual designed reflectivity of the ETM for green? No one seems to be able to give me a straight answer about this.

Looking at the reflected beam when the beam is misaligned makes it look like it's << 0.9. Is that expected given the coating spec?

You say the cavity scan goes as high as 300cts but you can only lock to 30cts, are you locked on the sideband?

-The reflection is measured when the cavity is unlocked. I measured it with the power meter in front of the PD, so I interrupted the PDH loop.

- From the specs of ETM we have:

T(S1,HR,532nm)=5.0%+/-3% (+/-1% target),  R(S2,AR,532nm)<1000ppm

It means that I should have about 600-550 uW in reflection, but I don't. I can say that there are many losses, and maybe some power is clipping inside the Faraday. Nonetheless, the reflected beam looks less strong than the injected one, so most of the losses should be on the ETM table.

(- The reflected power is 0.090 mW, I just wrote it wrong yesterday, sorry!)

- The last question is actually very interesting. Maybe I was locking on the sideband when I locked to 30 cts, but if it is the case I cannot really explain why today I locked on the carrier (I locked the cavity to about 200-250 cts), and everything I changed was the PD gain and the amplitude on signal generator connected to the PDH box. It seems like there should be some sign flip somewhere, but I need to think about.

[Koji, Yuta]

We aligned Y arm to Y green and tweaked TT1/TT2 to get IR locked in Y arm.

Alignment procedure:
  1. Align ETMY/ITMY to maximize TEM00 green transmission to PSL table. We reached ~240 uW.

  2. Aligned PRM and TT2 so that PRM reflected beam go through FI and get ITMY-PRM cavity flashing. This is to coarsely align input pointing to Y arm. After this alignment, we got tiny Y arm flash. Input pointing to IPANG QPD was lost.

  3. Aligned TT1/TT2 to maximize TRY in TEM00. We reached ~0.92.

Failed procedure:
  I was struggling with finding Y arm flash. I was using IPPOS/IPANG as input pointing reference, and slider values (C1:SUS-(ITMY|ETMY)_(PIT|YAW)_COMM) or OSEM values (C1:SUS-(ITMY|ETMY)_SUS(PIT|YAW)_IN1) before pumping for Y arm alignment reference. But it was a lot more easier if Y arm is aligned to green and having Yarm cavity axis assured.

Next:
  - X arm flash in IR
  - Steer X end green
  - If X arm or AS looks bad, adjust IR input pointing and Y arm alignment. We have to steer Y end green afterwards.

 That's good news. I was ready to give up and say we should vent and remove the baffles. It will be interesting if you can find out how much the sensors and OL and IPANG are off from their pre-pump values. We should think about how to have better references.

Also, what is the story with the large drift we are seeing in IPANG?

I implemented this today. For now, the LSC output matrix is set to actuate on MC2 for Y arm locking. As expected, the transmission was much more stable, and the PLL control signal RMS was also reduced by factor of ~3. MC2 control signal does pick up a large (~2000 cts) DC component over a few hours, so we need to relieve this periodically.

Now that we have a workable ASS for the Y arm as well, we should be able to have more confidence in returning to the same beam spot position on the ETM and staying there during a scan using this technique.

The main improvement to be trialled next in the scanning is to improve the speed of scanning. As things stand, my script takes ~2.5 seconds per datapoint. If we can cut this in half, that'd be huge. On Wednesday night, we were extraordinarily lucky to avoid MC3 glitching, EPICS/slow machine failures, and GPIB freezes. Today, the latter reared its head. Fortunately, since I'm dumping data to file for each datapoint, this means we at least have data till the GPIB freeze.

Not related to this work: Terra, Sandrine, Keerthana and I cleaned up the lab a bit today, and made better cable labels. Aaron and I have to clean up the OMC area a bit. Huge thanks to Steve for taking care of our mess elsewhere in the lab!

Ah. With MC2 feedback, we have about 3 times smaller "optical gain" for the ASS A2L. We have same dither, same actuator, but we need only 1/3 actuation of the MC2 compared to the ETMY case.
We had to reduce the ASS spot servo from 1 to 0.3 to make is stable, so this means that the ASS is really merginally stable.

I tried to lock the Y arm cavity length to the PSL frequency using POY11_I as an error signal. Even though I think the cavity alignment is good (I see TRY flashes ~0.8), I am unable to achieve a lock. I checked the signal conditioning, and as far as I can tell, all the settings are correct, but there may be some settings that have not been re-assigned correct values. The other possibility is that something is not quite right with the new c1iscaux. The PDH error signal and arm cavity flashes all seem good though (see Attachment #1), so I'm not sure what obvious thing I'm missing.

To be continued...

(Preparation of Y arm locking)

(A) The f2a filters were newly designed and applied to ETMY (see the attachment)

(B) Once the Y arm is aligned such that the TEM00 mode flashes, the transmitted light is visible on the ETMYT CCD camera.

(C) With the newly installed resonant EOM circuit the PDH signal from AS55 looks healthy.

(some notes)

(A) To design the f2a filters there is a handy python script called "F2A_LOCKIN.py" in /scripts/SUS.

The script measures the coil imbalance at high frequency and low frequency using a LOCKIN module and then gives us the information about the imbalance.

The script hasn't yet been completed, so it doesn't return the intuitive answers but returns something non-intuitive. I will modify it.

(B)  To see the transmitted light from the Y arm I was going to align the CCD camera on the Y end table.

However I found that once the green light is blocked, the transmitted light can be visible on the camera without any re-alignment.

Therefore I haven't rearranged anything on the Y end table, but I just blocked the green light.

Perhaps we still need to align the photo diodes for the transmitted light.

(C) While Suresh was working on MC, I looked at the signal from AS55 with all the optics misaligned except for ITMY, ETMY and BS.

The signal from the Y arm looked very PDH signal, and the demodulation phase seemed to be about 45 deg to maximize the I signal.

I tried locking it by feeding the signal back to ETMY but failed due to a too much POS to angle coupling in the ETMY actuators.

I was momentarily able to capture a higher order mode with a negative gain in LSC-YARM_GAIN, but it was quite difficult to keep it locked.

This was because once I increased the gain to make it stable, the angle instability became more significant and lost the lock immediately.

This was the reason why I had to do the f2a filter redesign. Tomorrow we can try locking the Y arm.

The Y arm has been locked with AS55.

A next thing is to check the spot positions on the ETMY and ITMY mirrors so that we can evaluate the recent beam pointing.

- - - parameter settings - - -

C1:LSC-YARM_GAIN = -0.03

AS55 demod phase = 0.2

WF gains = 21 dB

C1:LSC-TRY_OUT = 0.57 (maximized by steering PZT2)

Although we did some of the Input Matrix diagonalization, we have not yet actually used this knowledge. As a result all of the optics are shaking all over the place.

Sunshine Task: Set the input matrices to their calculated values and then adjust the OSEM damping gains for all optics so as to get a Q ~ 5.

Summary:

There are still several data quality issues that can be improved. I think there is little point in reading too much into this until some of the problems outlined below are fixed and we get a better measurement.

Details:

1. Mainly, we are plagued by the inability of the ASS system to get back to the good transmission levels - I haven't done a careful diagnosis of the servo, but the ITM PIT output always seems to run away. As a result, the later measurements are poor, as can be seen in Attachment #2.
2. For this reason, we can't easily sample different spot positions on the ETM.
3. Data processing:
   • Download AS reflection and MC transmission DQ channels
   • Take their ratio
   • Downsample to 4 Hz by repeated application of scipy.signal.decimate by a factor of 8 each time, thrice, with the filtfilt option enabled
4. Attachment #1 and #2 are basically showing the same data - the former collects all locked (top left) and misaligned (top right) data segments and plots them with the corresponding TRY values in the bottom row. The second plot shows a pseudo-continuous time series (pseudo because the segments transitioning from locked to misaligned states have been excised).

As an interim fix, I'm going to try and use the Oplevs as a DC reference, and run the dither alignment from zero each time, as this prevents the runaway problem at least. Data run started at 11:20 pm.

Attachment #1 shows estimated systematic uncertainty contributions due to 

1. ITM transmission by +/- 0.01 % about the nominal value of 1.384 %
2. ETM transmission of +/- 3 ppm about the nominal value of 13.7 ppm
3. Mode matching efficiency into the cavity by +/- 5% about the nominal value of 92%.

In all the measurements so far, the ratio seems to be < 1, so this would seem to set a lower bound on the loss of ~35 ppm. The dominant source of systematic uncertainty is the 5% assumed fudge in the mode-matching

To do: 

1. Account for uncertainties on modulation depths
2. To estimate if the amount of fluctuation we are seeing in the reflected signal even after normalizing by the MC transmission, get an estimate of statistical uncertainty in the reflected power due to 
   • Pointing jitter - is there some spec for the damped angular displacement of the TT1/TT2?
   • Cavity length in-loop residual

Bottom line: I think we need to have other measurements and simultaenously analyse the data to get a more precise estimate of the loss.

As shown in the noise budget below, the 60 Hz line noise currently dominates the arm displacement.

       About Noise Budget       

I was working around the PSL table and Y endtable today.

I modified the Y arm optical layout that couples the 1064nm light leaking from the SHG crystal into the fiber for frequency offset locking.

The ND filter that was used to attenuate the power coupled into the fiber has been replaced with a beam sampler (Thor labs BSF-10C). The reflected power after this optic is ~1.3mW and the trasmitted power has been dumped to a razor blade beam dump (~210mW).

Since we have a spare fiber running from the Y end  to the PSL table, I installed an FC/APC fiber connector on the PSL table to connect them and monitored the output power at the Y end itself. After setting up, I have ~620uW of Y arm light on the PSL table (~48% coupling).

During the course of the alignment, I lowered the power of the Y end NPRO and disengaged the ETMY oplev. These were reset after I closed the end table.

Attached is the out of loop noise measurement of the Y arm ALS error signal before (ref plots) and after.

 Prior to the works on the Y end setup I propose to perform the temperature scan business like Koji and Suresh did before (see this entry).

This business will allow us to easily find a beatnote at 532nm after the installation on the Y end.

 I guess the right persons for this work are Bryan and Suresh.

Bryan will have a safety guidance from Steve in this after noon. So after that they can start working on it.

/* - - - coarse plan - - - */

* remove Alberto's laser from the AS table

* setup Alberto's laser on the PSL table

* put some stuff such as lenses, mirrors and etc. (Use the IR beam picked off after the doubling crystal for the main laser source)

* mode matching

* measurement

Which laser are we going to use,  Alberto's laser or MOPA laser ?

I found the beat note for the Y arm. Nothing was changed with respect to yesterday night, but the beat is back!

As I didn't have the green laser PZT feedback for the laser temp control, I went to the yend to check out what's the situation.

I found horrible and disgusting "remnants".

WHAT ARE THESE BSs AT THE Y END?

- The table enclosure was left open

- A (hacky) DB25 cable with clips was blocking the corridor and I was about to trip with the cable.

- This DB25 cable went to the table without going through the air tight feedthrough that is designed for this purpose.

- An SR560 (presumably for the openloop TF measurement) was left inserted in the loop with entangled cables connected to the servo box.

- Of course the laser PZT out mon was left unplugged.

Even after cleaning these cables (a bit), the end setups (including the X end too) are too amature.
Everything is so hacky. We should not allow ourselves to construct this level of setup everytime
we work on any system. This just adds more and more mysteries and eventually we can't handle
the complexity.

Beam colors: 1064 nm red, 514 nm green and 633 nm yellow.

There should be room for lens in front of the pd at red3 and a mirror for alignment in the new layout.

This picture may help you how to improve the new ETMX 4' x 3' optical layout.

[Tomotada / Kiwamu]

  The open loop transfer function of the Y end PDH loop was remeasured : the UGF was found to be at 17 kHz.

The phase margin at the UGF was about 27 deg.

While the measurement we noticed that the modulation onto the laser PZT was too big

and it was creating a big AM on the reflected light with an amplitude of a few mV.

So we put a 20 dB attenuator to decrease the modulations and the reflected light became much quitter.

Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).

 As promised, I will get on this this week.

The doubling oven is now ready to go for the Y arm. The PPKTP crystal is mounted in the oven:

Note - the crystal isn't as badly misaligned as it looks in this photo. It's just an odd perspective shot. I then closed it up and checked to make sure the IR beam on the Y bench passes through the crystal. It does. Just need to tweak the waist size/position a bit and then we can actually double some frequencies!

The Y arm green PDH servo is working fine with a sufficient amount of suppression.

(Servo filters)

  

And the servo configuration looks like this :

(the Error signal)

I took a spectrum of the error signal when the laser was locked to the Y arm and found that it meets the requirement.