Third-Harmonic Generation in Absorbing Media of Cubic or Isotropic Symmetry

Abstract

Third-harmonic generation in strongly absorbing media has been measured in reflection, by means of a picosecond pulse train from a mode-locked Nd-glass laser. The nonlinear susceptibility ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}\left(3\mathrm{}\omega \right)$ has been measured in the semiconductors diamond, Si, Ge, and GaAs, and the metals Be, Mg, Al, Cu, Ag, and Au relative to LiF. The data are compared with data for ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ obtained in the infrared from frequency mixing with C${\mathrm{O}}_2$ lasers. The different dispersion characteristics for valence- and conduction-band contributions are pointed out. The cubic anisotropy of ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}\left(3\mathrm{}\omega \right)$ in silicon and several alkali halide crystals is determined by means of circularly polarized laser pulses. The selection rules for the generation of circularly polarized third harmonics have been confirmed both in transparent and in absorbing media.