Hollow-core fiber enhanced CW CARS of gases

CW (continuous wave) coherent anti-Stoke Raman spectroscopy (CARS) of gases using a hollow-core photonic crystal fiber (HC-PCF) is demonstrated with gaseous CO2 as an example. Raman transition is pumped by a tunable dye laser. The seeding stokes light is provided by a home-made ECDL. Both lasers operate in single longitudinal mode. The output radiation from the fiber is filtered and coupled into an imaging spectrometer. Anti-stokes signal is observed with 10 mW pump power and 1 mW stokes power. The peak anti-Stokes signal of ν1 band of 6 atm CO2 is 59000 CCD counts with the exposure time set to 5 ms. The v1 and 2v2 components of the fermi dyad of CO2 is resolved.