Based on yesterdays post, we can fit a lorentzian to the tranmission peaks and find the FWHM. Using parameters of the laser we can find cavity BW in frequency for each wavelength of light. We can also calculate the expected finesse based on the quoted reflectivities of the superoptics. These values are as follows.
| 775 BW (measured) | 102 kHz |
| 1550 BW (measured) | 24.4 kHz |
| 775 finesse (measured) | ~600 |
| 1550 finesse (measured) | ~5000 |
| 775 finesse (expected) | 313 |
| 1550 finesse (expected) | 3556 |
The ratio between the measured finesses, ~8.35, is very acurate as this doesn't depend on the calibration of the actual value. I think Lee previously mentioned he expected the ratio to be about 10. The accuracy of the actual value depends on the accuracy of laser parameters which we know could be like +/-20%.
[Daniel, Torrey]
We can calculate this in an alternate way avoiding using any kind of calibration on the laser. The FSR, measured in time on a cavity scan, is 31 ms and 15.5 ms for the 1550 and 775 light, respectively. The FWHM or bandwidth in time is 1.86e-5 s and 7.8 e-05 s for 1550 and 775 respectively. This means we have a measured Finesse of 1660 and 221 for 1550 and 775 light, respectively. These agreed much closer with the expected values above.