Invited paper. The interaction of mode-locked laser pulses with intrinsic silicon

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Abstract
Mode-locked Nd : YAG or Nd : glass laser pulses have picosecond durations and GW peak powers. The interaction of such light pulses, at 1[sdot]06 µm and 0[sdot]53 µm, with intrinsic silicon gives rise to photoconductivities which have been used in designing electronic switches and gates possessing picosecond precision. The physics of this interaction has been investigated in detail. An accurate account of the photoconductivity is obtained by means of a numerical solution of the continuity equation. This partial differential equation is extremely non-linear, because important parameters such as absorption coefficient and mobility are functions of temperature, free-carrier density, applied electric field, etc. These parameters are not only interrelated but they are also dependent on time and position within the semiconductor. The generation of free carriers is incorporated in a term which includes the temporal pulse shape and width. All kinds of relevant recombination mechanisms, including the dominant Auger recombination, are considered. It is shown that surface recombination, drift and diffusion of carriers play insignificant roles in this interaction. Tho rise of temperature within tho semiconductor as n result of the intense pulse is calculated by a numerical solution of tho heat conduction equation. This accounts for the variation of important parameters as a function of temperature. It is also demonstrated that, while absorption saturation does not occur, free-carrier absorption is of primary importance. It has been attempted to present a thorough theoretical model and a numerical analysis based on it which satisfactorily account for the experimental results obtained previously. A discussion of the design requirements (for picosecond electronic switching and gating systems) based on the results from the computer program, is provided at the end of the paper.