Nondegenerate two-photon absorption in zinc blende semiconductors

Abstract

An algorithm is presented for the calculation of the nondegenerate two-photon absorption coefficient by using second-order perturbation theory and a Kane band-structure model, including the effects of nonparabolicity and nonzone-center wave functions. The polarization dependence is included by correctly accounting for the symmetry of the electronic wave functions. A comparison is made with degenerate two-photon absorption data in various zinc blende semiconductors, and excellent agreement is found without the use of fitting parameters. Comparisons are also made with nondegenerate two-photon absorption spectra measured in ZnSe and ZnS by using a picosecond continuum and with some polarization-dependent measurements obtained by a two-color Z-scan measurement.

Ultrafast x-ray measurement of laser heating in semiconductors: Parameters determining the melting threshold

“…This is in excellent agreement, after extrapolation to 800 nm, with literature values. 14,15 The heating dynamics concluded from the x-ray measurements readily explain the pulse-width dependence of the thermal melting and ablation thresholds. In Ge the energy is rapidly redistributed by hot-carrier diffusion, with melting and ablation being determined, at least in this range of pulsewidths, only by the total absorbed energy and independent on the duration of the laser pulse.…”

“…By modeling the measured thermal/elastic response of the solids, a precise estimate of the laser-heated depth and of the critical parameters determining the characteristic scales of energy thermalization is achieved. Delayed Auger heating, 13 two-photon absorption, 14,15 and high-density carrier diffusion 16 are found to be key processes regulating the heating dynamics. The different pulse-width dependence observed in the thermal melting threshold for Ge and GaAs are in this way understood.…”

“…In Ge, then, the combination of efficient high-density carrier diffusion 6 (DϾ100 cm 2 /s) and slower Auger heating 14,15 (␥ Auger ϭ1.1ϫ10 Ϫ31 cm 6 /s) allows redistribution of the absorbed energy deep into the bulk of the solid. 28 Slow Auger recombination rates and significant heated volumes cause the observed long strain formation time, approxi- mately determined by Ge /c LGe (Ͼ100 ps͒, with c LGe being the longitudinal speed of sound in Ge.…”

“…Nonlinear absorption, neglibible in the case of Ge, is expected to contribute significantly to absorption in GaAs, 14,15 while delayed Auger heating 13 (␥ Auger ϭ7ϫ10 Ϫ30 cm 6 /s) will rapidly transfer the hot-carrier energy to the GaAs lattice before significant ambipolar diffusion. Inclusion of both these effects in our model accurately accounts for the decrease in the heating depth to about 275 nm.…”

Three-Level Description of Optical Nonlinearities in Semiconductors

“…IAb,l, IAcbl > y and Ab, --Acb then we find a transition rate: (a) proportional to the product of the irradiances at each frequency, (b) proportional to the product of the square of the matrix elements 1~, b / 2~~6 c 1 2 and (c) inversely proportional to the square of the detnning of the intermediate level. These dependencies can also be deduced from considering Fermi's Golden Rule [12].…”