(Kiwamu, Yuta)
We succeeded in coarse locking the green beat frequency, using a frequency counter and feeding back the signal to the X-end laser temperature.
Setup:
beat note -> RF PD -> SHP-25 -> SLP-100 -> ZFL-1000LN -> ZFL-1000LN -> ZFL-500LN -> ZFRSC-42 -> SBP-70 -> ZFRSC-42 -> SR620 -> c1psl(C1:PSL-126MOPA_126MON)
c1auxey(C1:LSC-EX_GREENLASER_TEMP) -> X-end laser temp
The frequency counter SR620 converts the beat frequency to voltage.
We added some filters (SHP-25, SLP-100, SBP-70). Otherwise, SR620 doesn't count the frequency correctly.
What we did:
1. Getting green beat note again
Set PSL laser temp to 31.81 °C and X-end laser temp to 37.89 °C.
Set PPKTP crystal temp to 37.6 °C, which maximizes output green beam power.
2. ADC channel and DAC channel
Disconnected one channel going into VME-3123 (at 1X1) and used c1psl's C1:PSL-126MOPA_126MON as ADC channel for the output from SR-620
Made a new DAC channel on c1auxey named C1:LSC-EX_GREENLASER_TEMP, and disconnected one channel from VME-4116 (at 1X9) to use it as DAC channel for X-end laser temperature control.
3. Coarse lock by ezcaservo
Ran;
ezcaservo C1:PSL-126MOPA_126MON -s 150 -g -0.0001 C1:LSC-EX_GREENLASER_TEMP
"-s" option is a set value. The command locks C1:PSL-126MOPA_126MON to 150 (in counts), using 0Hz pole integrator.
Result:
The beat frequency locked on to ~77MHz. The frequency fluctuation of the beat note during the servo is ~3MHz with ~10sec timescale.
VCO has ~+/-5MHz range, so this coarse locking meets the requirement.
Here's a plot of the error signal and feed back signal;
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