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Entry  Mon Dec 3 17:04:12 2012, Ayaka, Update, PSL, PMC calibration for MC_F calibration DSC_4955.JPGsweep_PZTdriver.pngPMC_PZT_FSR.pdftrans_fit.pngPMC-PZTcal_121203.zip
    Reply  Tue Dec 4 01:43:37 2012, rana, Update, PSL, PMC calibration for MC_F calibration 
    Reply  Tue Dec 4 11:30:36 2012, Zach, Update, PSL, PMC calibration for MC_F calibration 
       Reply  Thu Dec 13 17:24:53 2012, Ayaka, Update, PSL, PMC calibration for MC_F calibration 6x
Message ID: 7778     Entry time: Mon Dec 3 17:04:12 2012     Reply to this: 7779   7782
Author: Ayaka 
Type: Update 
Category: PSL 
Subject: PMC calibration for MC_F calibration 

In order to calibrate MC_F signal, I need to know the calibration value from thorlab's PZT driver to laser frequency.
The calibration value should be ~ 15MHz/V (the PZT driver has 15 gain, and the laser has the calibration value of ~ 1MHz/V according to the laser spec sheet), but I want to confirm it.
This can be measured by sweeping the input voltage of the PZT driver and see the transmission signal from unlocked PMC.
 

1. Response of PMC transmission when the signal is inputted to laser PZT

I inputted 0.2 Hz triangular wave with 5Vamp and 2.5V offset into the PZT driver and see the transmission signal from PMC. After the PZT driver and before the laser, there is an analog low pass filter but its cut off frequency is 1 Hz so I did not take it into consideration. 
DSC_4955.JPGsweep_PZTdriver.png(TEK00000.CSV, TEK00001.CSV in the zip file)

I could not the side-band resonances. I guess it was because the generated signal is not big enough (but still the maximum range of the signal generator.)
Therefore, in order to calibrate the input voltage to the frequency, I need to know finesse or FWHM frequency.
 

2. Responce of PMC transmission when the voltage of PZT on the PMC is swept

In order to measure the finesse and FWHM frequency, I also swept the PMC PZT voltage with the DC offset slider at the FSS.adl and tried to measure the finesse of PMC. (reference: elog #904)
PMC_PZT_FSR.pdftrans_fit.png(PMC-PZTcal_121203.xml in the zip file)

The result of fitting:

V_FSR (the PZT voltage difference between the 2 resonances) ~ 63 +/- 7 V (= 731MHz (given))
V_FWHM (the PZT voltage to sweep FWHM) ~  0.32 +/- 0.04 V (~ 3.7 MHz)
Finesse ~ 200 +/- 30

However, this finesse value is much smaller than the value on the Wiki, 800. (Manasa showed me.)
V_FSR is comparable to the result Rana got at the referenced elog. But I am not sure about the V_FWHM because it is hard to figure out how large the PZT voltage changed from the template file (PMC-PZTcal.xml).
Are those mode wrong? But if so, where is the correct mode resonances? I think they should be visible...
 

3. Calibration value 

When I know the FWHM frequency, I can calibrate the input on the PZT driver into laser frequency.

The results are:

if I take the finesse of 800 and FSR of 731 MHz (the values on the Wiki): ~5.0 MHz/V
if I take the finesse of 200 and FSR of 731 MHz (the measured value): ~20.0 MHz/V

Actually, the measured value is closer to the value calculated from the spec sheet.

Hmm... Does anyone find falses in my measurement?
If not, the finesse can be 4 times smaller than the value which was 5 years ago?

Attachment 5: PMC-PZTcal_121203.zip  66 kB
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