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Optical parametric noise has been produced in a centrosymmetric medium, water, by a 9-MW ruby laser beam. The wavelengths, in the visible, and the angles of emission agree with the tuning curve calculated for a phase-matched four-photon process. A power of ≈½μW emitted into a 38-Å band is observed in the low-loss wavelength range, in approximate agreement with theory. Very strong idler absorption has little apparent effect on the signal power or bandwidth.
D. L. Weinberg (1969) studied this question.