Laser studies of internal conical diffraction. III. Second-harmonic conical refraction in α-iodic acid

The phenomenon of nonlinear conical refraction in a noncentrosymmetric biaxial crystal is investigated experimentally. Both free and forced second-harmonic cones are observed, depending on whether the incident laser pulse has wave normals encompassing the optic axis at the second-harmonic or the fundamental frequency, respectively. The photographically recorded second-harmonic intensity patterns at the wavelengths of 0.53 and 0.42 μm are in good agreement with theoretical predictions. © 1978 The American Physical Society.