Four-wave mixing of picosecond pulses in hollow fibers: expanding the possibilities of gas-phase analysis

Summary form only given. Our experiments have shown that the use of short light pulses allows the sensitivity of gas phase analysis based on (i) third-harmonic generation (ii) two-color difference frequency generation (DFG) /spl omega//sub DF/ = 2/spl omega//sub 1/ - /spl omega//sub 2/, and (iii) two-color sum-frequency generation /spl omega//sub SF/ = 2/spl omega//sub 1/ + /spl omega//sub 2/ in hollow fibers to be improved as compared with the nanosecond regime. The use of picosecond pulses allowed us to couple pump beams with a power density up to 10/sup 12/ W/cm/sup 2/ into a hollow fiber, thus considerably increasing the intensity of FWM signals generated through third harmonic, sum-frequency and difference-frequency generation processes in hollow fibers as compared with the nanosecond regime. It was shown that hollow fibers permit third-harmonic and sum-frequency generation, which give zero signals in the regime of tight focusing in a medium with normal dispersion, to be employed for gas-phase monitoring and analysis.