Shinobu OHARA, Shigeru YAMAGUCHI, Masamori ENDO, Kenzo NANRI and Tomoo FUJIOKA

Department of Physics, School of Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan

(Received April 24, 2003; Accepted July 24, 2003)

Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼ 10300 achieved a stable TEM₀₀ mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/-0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.

Key words: Raman spectroscopy, coupled cavity, gas sensing, spatial filtering, cavity mode