This morning, I decided to adjust RCAV's temperature setpoint (C3:PSL-RCAV_RCPID_SETPOINT) up by 1 Kelvin. As I saw not much change in the readout of the PT1000 sensor overnight, I'm afraid that the signal might be too small for a 0.1 k change.

We might be able compare the readout from C3:PSL-GEN_DAQ16 to C3:PSL-FSS_SLOWDC level. SLOWDC controls the temperature of the NPRO crystal for adjusting laser frequency.

The calibration for SLOWDC is 4700 MHz/V*. The resolution of SLOWDC is 0.0001 V => 0.47 MHz. 

Use df/f = dL/L to compute the equivalent cavity's length change, dL ~ 3 e-10 m.

Compare this dL to the effect of thermal expansion of the cavity.

dL = alpha x L x dT =>

3 e-10 [m]= 0.51 e-6 [1/K/m]  x 0.203 [M] * dT [ K]

dT [K] = 3 milliKelvin is the resolution of the temperature we can measure, so we should be able to measure 1 K change on the cavity easily, and we can compare with what we see on the sensor.

From above equations, the cavity's temperature is related to SLOWDC by

dT  = dV_slowdc x 32.91 [K/V].

 For 1 kelvin change on the cavity, SLOWDC should change by 0.0304 [V]

Cavity's parameters

cavity's length, L = 0.2032 [m]

SiO2 expansion coeff, alpha = 0.51 e-6 [1/K/T]

channel list:

C3:PSL-RCAV_RCPID_SETPOINT    set temperature for PID cavity's thermal control

C3:PSL-RCAV_TEMAVG                   average temperature on the outside surface of the can

C3:PSL-FSS_SLOWDC                     thermal control on laser's PZT for adjusting frequency

C3:PSL-GEN_DAQ16                         readout from the temperature sensor on the top seismic stack 

* About the calibration, I used sidebands (35.5MHz x2 =71 MHz) to calibrate SLOWDC to frequency. I also used the cavity's free spectral range (737 MHz) for comparison as well. The results agree well.