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osamu.miyakawa - 19:24 Monday 15 December 2025 (35875) Print this report
PMC actuator efficiency

Abstract:

The actuator efficiency of PZT was measured as 167.1V/FSR, and it corresponds to 0.889MHz/V at K1:PSL-PMC_PZT_HV_MON_OUTPUT if we assume the FSR:148.35MHz.

 

Detail:

I used a similar way of klog:16311. While applying some large offset (-9V to 9V) on K1:PSL-PMC_PZT_SLOW with 60sec ramp time, carrier peaks are measured at the PMC transmitted light (Fig.1). The separation between the 2 carrier peaks corresponds to the FSR. I used the measured value of 148.35MHz for FSR in klog:5892 (klog says the value 147.35, but it does not correspond to the cavity length 2.0208m, so it was a typo, I guess.) to convert it to an actuator efficiency on the PMC feedback signal at K1:PSL-PMC_PZT_HV_MON_OUT, which is convenient to measure the frequency noise. 

Actually, I used diaggui instead of ndscope, since I could use the more accurate cursors. I measured 10 times for each forward (higher voltage on HV driver) and backward (lower voltage on HV driver) direction. The results showed some discrepancy btween the directions;

  • Forward (10 times average): 161.5V/FSR -> 0.9191MHz/V
  • Backward (10 times average): 172.8V/FSR -> 0.8586MHz/V

I am not sure the reason for this difference, but the response of PZT is obviously different for each direction shown in Fig.2. See the shape of the green line for each direction. Backward shapes always show steeper. We should accept this anti-symmetric response since we are using such a PZT, in fact.

So the accuator efficiency should be averaged between forward and backward; it will be 167.1V/FSR, and it corresponds to  0.889MHz/V.

 

The last measurement by Yamamoto-kun in klog:16311 shows ~169V/FSR. So, we can say that the PMC does not show any significant change.

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osamu.miyakawa - 17:00 Monday 05 January 2026 (36019) Print this report

I measured the PZT efficiency of PMC using the same method as klog:35875, but with lower laser power in order to avoid thermal expansion at the PMC body.

I set the neoLASE current to 3A, corresponding to 2.7W. Originally, it was 7.7A, for ~30W, so the power is roughly 1/10.

As Fig.1, the difference in the shape of the carrier transmission between forward and backward, which was seen with 30W, is perfectly gone. Note that the dotted line in the normalized transmitted light shows the height of the carrier, and it is much lower than 1 because the mode matching is bad since neoLASE is operated with lower power.

10 times measurements were done for each forward and backward with such low power. The results are;

  • Forward (10 times average): 162.01+/-1.01 V/FSR -> 0.9160+/-0.0056 MHz/V
  • Backward (10 times average): 162.09+/-0.73 V/FSR -> 0.9154+/-0.0042 MHz/V

Both results corresponded quite well, within the error bars. If we take the average of them;

  • PMC actuator efficiency: 162.05+/-0.87 V/FSR -> 0.9158+/-0.0048 MHz/V

 

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