Fig. 1
From: Cavity-enhanced continuous-wave microscopy with potentially unstable cavity length
Cavity setup and characterization. (a) Ray tracing picture showing the self-imaging properties of the 4f cavity. The sample is illuminated with a collimated beam (red); the diffracted light (green) is imaged onto the sample after one full roundtrip. (b) Cavity length scan monitored by the output voltage (normalized) of a photodiode placed at the output of the cavity. The separation between the two resonance peaks yields a free spectral range (FSR) of \(488\, \text {MHz}\) and a FWHM of \(35.1\, \text {MHz}\) in that specific realisation (accordingly the finesse is 13.9; see Methods for Details). (c) We test the degeneracy of transversal modes by projecting the image of a US Air Force (USAF) Target onto the cavity image plane. The recorded light intensity in a conjugate plane after the cavity, and a cross-section thereof, demonstrate its image transmission capabilities.
