We have used the second harmonic of a Nd: glass laser and a continuously tunable dye laser to measure the variation of the third-order nonlinear susceptibility ${\left|{\chi }^{\mathrm{}\left(3\right)\mathrm{}}\right(-2\mathrm{}{\omega }_1+{\omega }_2, {\omega }_1, {\omega }_1, -{\omega }_2\left)\right|}^2$ when ${\omega }_1-{\omega }_2$ passes through the optical-phonon resonance in diamond. The frequency difference between the observed maximum and minimum determines the nonlinear electronic susceptibility ${\chi }^{\mathrm{}\left(3\right)E}$ both in sign and magnitude with respect to the Raman susceptibility. A theoretical discussion of this interference is presented.

• Received 12 June 1972

DOI:https://doi.org/10.1103/PhysRevB.6.3962