Silicon optoelectronics devices have been well explored in the near-IR regime with emphasis on telecom applications. In the mid-IR regime, group IV optoelectronic devices (silicon and/or germanium based) could one day serve as waveguides, nonlinear media for χ(2) and χ(3) wave mixing, and highly adaptable platforms for low cost, lab-on-chip chemical and biological sensors. However, nonlinear optical absorption in these materials limit potential applications. In this report, we observe dramatic decreases in transmission in silicon and germanium at middle-infrared wavelengths when utilizing intense (~ 10 GW/cm2) 100 fs pulses. We suggest potential mechanisms to explain the observed nonlinear effects and describe future experiments to decouple high order multiphoton absorption, electron-hole pair generation and light-dopant interactions which might contribute to observed effects.
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