In the case of a rigid cavity, we can estimate internal losses without locking. We just need to scan cavity and look for the reflection signal as shows in Fig.1.

1. We scan cavity and know that about gamma = 5% power is not coupled to cavity for TEM00 resonance.

2. We take the reflected power when cavity is on resonance for TEM00 (33.2mV) and off resonance (36.6mV)

3. We get Rcav = ((33.2/36.6)-gamma)/(1-gamma)

4. RTL = T1*(1-Rcav)/2/(1+Rcav) = 0.206%, here T1 = 0.08. Note: the polishing/coating company (LASEROPTIK) specifies AR coating reflectivity is less than 0.1%.

5. escape efficiency is T1/(T1+L)

In this way, we get escape efficiency of 97.5% for the new OPO.