Photoacoustic study of two‐photon absorption in hexagonal ZnS

Photoacoustic detection technique is employed to investigate two‐photon absorption (TPA) effects in ZnS over a wide frequency range with polarized 5 nsec dye laser pulses. By analyzing the dispersion and polarization dependence of TPA, we find that near the band gap, the TPA in ZnS occurs via allowed‐forbidden type one‐step, two‐photon transitions.