TUNABLE, SUBNANOSECOND KRF-RAMAN LASER IN THE ULTRAVIOLET

A 0.5 cm(-1) bandwidth injection-locked KrF laser pumps a rare-gas Bri llouin 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 o f laser amplifiers, subsequent excimer amplification of this pulse pro duces an intense 500 ps spike on the pulse leading edge. Stimulated Ra man scattering then separates the spike from the parent pulse, yieldin g a tunable short pulse at the first Stokes (S-1) wavelength. Varying the Raman cell length results in a variable Raman threshold and an adj ustable short pulse duration: 250 ps pulses at energies of 3-4 mJ at 2 68 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 reflec ted S-1 pulse, yields simultaneous S-1 pulses of 20-25 mJ in the 800 p s range and S-2 pulses of 550 ps at 5-6 mJ near 290 nm. This laser wil l avoid collision effects during laser excitation and enable quantitat ive, single pulse imaging of OH radicals in turbulent combustion becau se of its high pulse energy.