Stefan, Kiwamu

As a part of the beat noise study, we locked the main infrared laser to the X arm cavity by feeding the reflection signal back to the MC length.

Although we succeeded in locking the IR,  the beatnote tonight was not great at all. It was roughly 500 Hz / sqrtHz in a band from 1 to 900 Hz when the infrared was locked. Plus, the mode hopping was so frequent that I was not able to integrate the spectrum lower than 1 Hz.

IR locking to the X arm:

Because the green light tonight was not stable enough for us to do the CARM hand off, we instead started locking the IR to the X arm. This is the first time for us to directly lock the infrared main laser to an arm cavity without an aid of the ALS technique. We started this from estimating the PDH optical gain of REFLAIR_RF9 by simply looking at the free swinging wave form. According to Alxea's math (alog 7054), we got ~ 1.21 counts/Hz for the optical gain. Also the MC2 M3 stage was approximated to be 18.2 / f^2  Hz / counts. Using these two information, we set the LSC gain to be 0.46 as an initial guess. Note that we cranked up the whitening gain of REFLAIR9 to its maximum. The demod phase was also adjusted to maximized the PDH signal in in-phase. We then fed it back to MC2.

A good servo gain was then empirically found to be about -0.2. Even though we didn't have a transmitted DC or reflected DC signal, we could tell if we grabbed a sideband resonance or carrier resonance by looking at the size of the Q-signal. This allowed us to detemie the right control sign.

The locking procedure is as follows:

1. Lock IMC
2. Remove all the notches and aggressive filters in MC2 M3 ISCINF_L.
3. Turn on only FM3 and FM6 in MC2 M3 LOCK_L to have a large phase margin from 40  to 500 Hz.
4. Run the beatnote tracking servo using ezcaservo (see Daniel's instruction in alog 9559).
5. Decouple the MCL at DC by enabling FM1 of LSC_MC
6. Make sure that the input matrix is set right so that REFLAIR_RF9_I will be used.
7. Engage the reflection PDH servo which is currently in LSC-SRCL filter. Use  FM2 FM3 and FM4 with a gain of -0.2.
8. Once the PDH signal becomes quitter, stop the ecaservo and also cut the LSC-MC path by enabling FM7.

One major difficulty we had during the IR lock was that a mechanical resonant mode at 41 Hz (bounce? roll? of MC2) rang up so much that we could not keep locking the IR. We often let the IMC alone to allow it to settle down for a while and this helped a lot. Also Stefan could introduce the additive offset path on top of the MC length control. He had to crank up the input gain of both common mode board and IMC board to the maximum of 31 dB. It seems that we could still go higher although we didn't quantitatively evaluate it yet. This additive offset technique should serve as a good mitigation for this 41 Hz mode issue while maintaining a high control bandwidth.

The attached is a screen shot of the IR locking configuration.

Noise of the green beatnote was far from good:

The noise performance of the green beatnote was not great. Something must be wrong. The smallest noise floor I could get was approximately 500 Hz/sqrtHz in a band from 1 Hz to 900 Hz.  I tried not include a mode hop during the spectrum integration. Even so, as you can see in the attached spectrum, it was suspiciously  flat. I used H1:ALS-C_COMM_PLL_CTRL for measuring the beat noise. The calibration was done by injecting a known RF frequency into the PLL and measuring the ADC counts. It was measured to be 7.916 Hz/counts. Also I added a z40/p1.6 filter to cancel the VCO response.

I noticed that IM4trans S1 and S2 channels were saturated, probably after the power increase (similar to the case for IMC WFS noted in entry 9094).

I adjusted the whitening gain down from 45dB to 36dB, which brought segments S1 and S2 down from the rails. IM4trans signal looks better now.

following the failure of one of the three cooling units in the MSR, as a precaution against a second failure we are keeping the hallway doors open and a fan running overnight.

Stefan, Kiwamu

We found that the ISS diffracted light had been high at 24%. According to the trend, it looks that both PD_A and PD_B suddenly got an offset of about 0.5-ish volt and it pushed the diffraction ratio to the high value. The jump happened at around 9:41 local in this morning. Neither Keita nor Yuta was at around the ISC/PSL rack at this specific time. At this point it is unclear what happened or what might have triggered it. The attached is the trend showing the funny jump which also decreased the carrier power everywhere.

For now, we changed the reference offset to bring it to approximately 9%. The new reference offset is:

H1:PSL-ISS_REFSIGNAL           -2.31548

A further investigation is needed.

After confirming that the readout path output of COMM PLL (for CM board) has a large offset (about 4.8V) regardless of the PLL board setting while the output for VCO path was seemingly OK, we pulled out the chassis.

It was U37 (AD829 for z1.6Hz:p40Hz) that was busted. 

Jax tested the board, replaced the broken chip and tested again. She also found that the VCO path output was only routed to the external connector on the back panel, so she connected the internal VCO path SMA cable.

The fixed unit was put in place, the offset was not crazy (about 430mV when input was off, 13dB gain, two common filters on, went down to 13mV when both of the common filters were turned off), we cabled it up. 

8:30–9:00 Going into the LVEA to work on dust monitor – Patrick
9:01      PSL Check List done (noticed the ISS Diffracted Power was                     
          Close to 24% - It should be 5-15%)
9:00–10:30 Water Ground staff on site for water sampling – Hanford
9:27–10:03 Back in the LVEA to swap dust monitor power supply–Patrick                      
9:36-      Starting Initial Alignment of Ham 4 optical table- Hugh
9:41       PSL Check List done (noticed the ISS Diffracted Power was                       
           close to 24% - It should be 5-15%)
9:49–12:06  Working on ACB in LVEA West Bay – Mitchell/Scott
13:05-13:59 Back to work on ACB in LVEA West Bay – Mitchell/Scott
13:10-15:14 Periscope assembly on H2 PSL – Joe
13:46-14:48 Installing Tablecloth bracket on SR2 (LVEA) – Jeff B.
13:50-15:14 Joining Joe for periscope assembly on H2 PSL – Craig/Sam
15:00       Safety Meeting 

This afternoon I went to ISCT1 to begin setting up for the beam size measurements that we hope to use to diagnose the PRC mode matching situation (see LIGO-T1400013).

I took the beam analyzer cart from the optics lab out to ISCT1 and left it set up there. I measured beam powers in two locations just after the REFL periscope: one in reflection of the pick off window directly after the lower periscope mirror, and one after. Since we aim to measure two beams in the REFL path with powers differing by a factor ~4000 it's useful to have low and high attenuation locations. The window is not AR coated so there are two beams visible in reflection. I measured the power of one to be 890uW, and the other to be 800uW, with the low-power head on the VEGA power meter. The beam in transmission of the window was measured to be 123mW. I left the table with the window reflected beam dumped, and the photon inc. beam analyzer behind the dump.The window transmitted beam is still dumped on the shutter.

I took a new safe snapshot of ETMX after correcting the gain of 10 spotted yesterday in the L1 sensalign matrix, and engaging the "norm" R0 damping filters.

We are trying to record the frequency of the ifr, but there is a 4Hz offset between the EPICS readback and the value reported by dataviewer and/or saved by the DAQ.

(Alexa Daniel)

We went to EX to try to make a more precise measurement of the cavity length. For this measurement we use the fact that in reflection of a locked cavity a phase-modulated RF sideband will not convert into AM, if it is exactly on a free-spectral-range even in the presence of length locking offset. The setup is as follows:

• We split the RF signal coming from the PDH locking diode into the second demodulator channel. (The first channel is used for the PDH locking as usual.)
• We used the ifr to generate a second RF modulation. Its output was split between an LO and a modulator path.
• The LO path was connected to a spare line on the RF patch panel and was hooked up to the LO input of the second demodulator channel on the other side.
• The modulator path was combined with the main modulator signal using a splitter in reverse.
• The SR785 was set up to excite the error point of the PDH servo using the first excitation input of the CM servo board. The B channel was hooked up to the I-phase monitor of the second demodulator channel, whereas the A channel was the readback of the excitation.
• The ifr was set to 13 dBm at a frequency near 666 times the free-spectral-range.
• The ifr frequency was then scanned around this FSR to find the minimum in the response using a 1-2 kHz dither through the SR785.
• After, the measurement we connected the ifr to a spare frequency input of the comparator to measure the exact frequency.

At first glance the accuracy of this method seems to be about 5 Hz, maybe even 2 Hz. We will repeat the measurement in the afternoon to see how repeatable it is.

This is the Comtrol Ethernet to serial converter in the H1 PSL electronics racks being used for testing the Lighthouse dust monitors in the enclosure. The connection between the power supply and the box was flaky and had failed. I swapped power supply S/N 00089 for S/N 01411. It appears that it is just a bad sizing tolerance mismatch between the two.

From the alarm log, the power appears to have failed at 10:19 on January 24, 2014. The last data point before today was recorded around 15:56 on January 24, 2014.