Summary

The JAC cavity was locked in vacuum for the first time. Alignment was performed using the JM1 suspension and PSL PZT scan. After lock acquisition, the demodulation phase was optimized and a new Guardian state (NORMALIZE_SIGNALS) was implemented to automatically normalize several signals based on a slow PZT sweep.

Details

First in-vacuum lock

• The JAC cavity was successfully locked in vacuum.
• Prior to lock acquisition, the cavity alignment was adjusted using JM1 suspension and PSL PZT scanning.
• The PSL PZT was scanned with a 10 s period, and the alignment was tuned so that the TEM00 peak became dominant.
• After locking, the alignment was fine-tuned by maximizing the transmitted power.

Demodulation phase optimization

• A 300 Hz excitation was injected into L_SERVO.
• The demodulation phase was adjusted to minimize the signal appearing in the Q phase.
• The optimized demodulation phase is 63.37° (MEDM value)

Guardian update: NORMALIZE_SIGNALS state

• A new Guardian state NORMALIZE_SIGNALS was added.
• In this state, a 100 s PZT sweep is performed and used to normalize several signals automatically.

Normalization steps

1. JAC_REFL_A_RF43 input offset
The median value of JAC_REFL_A_RF43_I/Q_IN1 during the scan is taken as the offset
The negative value is applied as the input offset.

2. PDH error signal normalization
The peak-to-peak value of JAC-L_SERVO_IN1 during the scan is measured.
The signal is normalized so that the peak-to-peak becomes 1, by setting
REFL_A_RF43 filter gain = 1 / (max − min). The normalized signal is shown in the attached plot.

3. PZT scan trigger normalization
The peak photocurrent during the scan is measured.
This value is written to the Beckhoff channel JAC-TRANS_A_DC_NOMINAL to normalize the current signal.

4. Normalization report
A summary plot is automatically generated and saved as
/opt/rtcds/userapps/release/ioo/h1/medm/plots/normalize_report.png
You can open the plot from the button in the bottom-right of the MEDM screen