Detection of Nonlinear Laser Absorption in Solids by Means of Photoacoustic Effect.
Abstract
A photoacoustic detection technique was developed to measure nonlinear optical absorptions in oriented single crystals ZnS, ZnO, SrTiO(,3) and TiO(,2) over a wide frequency range from 3.6 to 5.6 eV. Nonlinear two photon absorption processes were extensively investigated by measuring the dependence of two photon absorption coefficient (beta) on the frequency as well as the polarization of the laser beam. A 5ns pulsed dye laser operating at 15 pps was the excitation source. A PZT transducer was used as a detector of the acoustic wave. The resonant characteristics of the transducer were theoretically eludicated. The resonant behavior was fully utilized in this experiment and (beta) less than 10('-6) cm/MW could be detected. For the II-VI compounds, the dispersion of (beta) was compared with an existing theory. For ionic crystals, it was compared with the theory developed in this thesis. A good agreement was found toward the band edge of the crystals. A theoretical connection was also made between the imaginary parts of third-order susceptibilities and the polarization dependent-values of (beta). The result was used to deduce the relative magnitudes of several components of the nonlinear susceptibilities. It was also proved that the linear-circular dichroism (LCD) of (beta) is a sensitive measure of determining the nature of the two photon absorption processes. From our measurements of the LCD and the dispersion of (beta), we conclude that allowed-forbidden transitions are the dominant mechanism in the nonlinear optical absorption effects and that linear absorptions as well as two-stage absorptions did not make noticeable effect on the present two photon absorption data.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1981
- Bibcode:
- 1981PhDT.......118B
- Keywords:
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- Physics: Optics