TUNABLE, SUBNANOSECOND KRF-RAMAN LASER IN THE ULTRAVIOLET

A 0.5 cm(-1) bandwidth injection-locked KrF laser pumps a rare-gas Brillouin cell to produce a reflected pulse with a leading edge risetime of 1 ns, tunable from 248.1 to 248.7 nm. Consistent with Lamb theory of laser amplifiers, subsequent excimer amplification of this pulse produces an intense 500 ps spike on the pulse leading edge. Stimulated Raman scattering then separates the spike from the parent pulse, yielding a tunable short pulse at the first Stokes (S-1) wavelength. Varying the Raman cell length results in a variable Raman threshold and an adjustable short pulse duration: 250 ps pulses at energies of 3-4 mJ at 268 nm with a 50 cm methane cell and 350 ps, 5 mJ pulses from a 100 cm cell are measured with a streak camera. First pass Raman conversion of the spike to S-1 followed by second pass backward Raman amplification, where the parent 248 nm pulse serves as the pump beam for the reflected S-1 pulse, yields simultaneous S-1 pulses of 20-25 mJ in the 800 ps range and S-2 pulses of 550 ps at 5-6 mJ near 290 nm. This laser will avoid collision effects during laser excitation and enable quantitative, single pulse imaging of OH radicals in turbulent combustion because of its high pulse energy.