Optical sum frequency mixing as a source of tunable coherent vacuum ultraviolet radiation

The production of intense, coherent, tunable, monochromatic radiation at wavelengths from 21 to 217 nm by three wave optical sum mixing in a crystalline solid is described. Two separate laser inputs are mixed in a crystal of potassium pentaborate tetrahydrate (KB5) to produce radiation at a frequency equal to the sum of the two input frequencies. The mixing of two dye lasers, one dye laser with a nitrogen laser and one frequency doubled dye laser with a ruby laser are investigated. Combinations of input wavelengths, propagation direction in the crystal and crystal temperature which yield efficient phasematched mixing are presented. Monochromatic outputs of 1^1 to 1^13 photons per second have been produced. Theoretical calculations are discussed which suggest that wavelengths as short as 18 nm may be conveniently generated using this technique