Mixing of X-Ray and Optical Photons

Nonlinear effects involving x-ray and optical photons are described with particular emphasis on the generation of sum and difference frequencies. Efficiencies for sum and difference frequency generation are calculated and found to be large enough to be observable. The expected advent of x-ray lasers should enhance the usefulness of such mixing techniques in the measurement of excited-state wave functions. Under favorable circumstances, the mixing technique may provide a means of efficiently tuning x-ray laser outputs.