Verification of the Scaling Rule for Two-photon Absorption in Semiconductors

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Abstract
The simple parametric scaling rules for the two-photon absorption coefficients, g2, predicted by recent theory, have been experimentally confirmed by the measurement of g2 in ten different semiconductors using carefully characterized picosecond 1 and 0·5 wm pulses. We find g2 (cm/GW) = (3·1 - 0·5) 2 103 ¡ EpF2(2Ey/Eg)n m2E m3 g, where Ep ­ 21 eV for the semiconductors studied, Eg is the energy gap in eV, n the refractive index and F2(x) = (x m 1)3/2/x5 . This relation allows the prediction of g2 in other materials at other wavelengths, which is useful in the design of nonlinear optical elements. The strong self-defocusing observed is consistent with nonlinear refraction by the two-photon-generated free carriers.

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