Raman spectroscopy of gases using a low-power diode laser passively locked to an external Fabry-Perot cavity

Semiconductor lasers can be tuned over a wide range of frequencies, but are limited in power. Raman spectroscopy requires significant power to get a strong signal. By AR coating the emission facet of the diode laser, and focusing the beam into a confocal Fabry- Perot cavity, we can tune the laser to a resonant frequency of the cavity, while at the same time building up a circulating intensity within the cavity which greatly exceeds the laser's rated output. It was then possible to detect the Raman scattering of N₂ and O₂ in airAerospace Engineerin