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Message ID: 6874     Entry time: Tue Jun 26 01:30:13 2012
Author: yuta 
Type: Summary 
Category: Green Locking 
Subject: simultaneous hold and release of the arm (aka two arm ALS) 

To get the feeling of the master of IFO, I;

1. Stabilized both arm length using ALS.

2. Ran findIRresonance.py for both arms and find what offset gives me IR resonances.

3. Holded X arm to IR resonance, holded Y arm to IR resonance, and released both arms.

Below is the time series data of what I did.
ALSboth20120625_2withAS.png


Issues:
 - Currently ALS is not stable enough. It only stays for about few minutes. I think it is because of the bad alignment of green from each end.
 - We can't tell end green frequency is higher or PSL green frequency is higher. So, the sign of the servo filter sometimes flips.
 - Wobbliness of X end green transmission beam spot was from the ETMX oplev. When the oplev servo is on, it got more wobbly when X end table is opened. But when the oplev servo was off, wobbliness was same even if the presence of air flow.
 - MICH contrast in plot above seems like it somehow got better when two arms are at resonance by ALS. I think this is not real because reflection from both arms at AS port was not well aligned and beam was clipped. Koji and I measured contrast of FPMI and MI(ETMs misalined), and they were 99.6 % and 99.9 % respectively. Beam clipping seems like it comes from some where between BS to AS port. We need to figure out where and fix this.

Things need to be done to make ALS more concrete:
 - Align Y end green beam!
 - Look into Y end green frequency servo
 - How do we hand-off servo using ALS to IR lock?
 - Noise budgeting for new phase tracker scheme
 - Linearity check of the beat box and phase tracker

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