Here's a sort of rough analysis of the aligned PRM-PR2 cavity mode scan.
On Friday we took some mode scan measurements of the PRM-PR2 cavity by pushing PRM (C1:SUS-PRM_LSC_EXT) with a 0.01 Hz, 300 count sine wave. We looked at the transmitted power on the POP DC PD and the error signal on REFL11_I.
Below is a detail of the scan, chosen because the actuation was in its linear region and there were three relatively ok looking transmission peaks with nice PDH response curves:
The vertical green lines on the bottom plot indicate the rough averaged separation of the 11 MHz side-band resonances from the carrier, at +- 0.0275 s. If we take this for our calibration, we get roughly 400 MHz / second.
The three peaks in top plot have an average FWHM of 0.00381 s. Given the calibration above, the average FWHM = ~1.52 MHz.
If we assume a cavity length of 1.91 m, FSR = 78.5 MHz.
Putting this together we get a finesse = ~51.6.
Analysis of misaligned mode scans to follow. |