We calculate the nonlinear free-carrier absorption coefficient of an intense terahertz (THz) electromagnetic wave propagating in a bulk semiconductor and the absorption percentage when an intense THz radiation passes through a quasi-two-dimensional (2D) sheet, with the help of the balance-equation approach to hot-electron transport in semiconductors subject to an intense high-frequency field. We find that at frequency around 1 THz, the absorption coefficient in a bulk GaAs system increases with increasing amplitude of the radiation field from zero and reaches a maximum at around 8 kV cm-1 before decreasing quickly with further increase of the field strength. The absorption percentage of a quasi-2D system exhibits an even stronger nonlinearity than that of a three-dimensional bulk. It is shown that high-order multiphoton processes play a major role in determining the absorption of an intense THz field.
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Lei et al. (2000) studied this question.
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