Three photon absorption in silicon for 2300–3300nm

We measure the spectral dependence of the degenerate three photon absorption coefficient, γ, for a Si [100] wafer using 200fs pulses in the range 2300–3300nm, i.e., photon energy between half and one-third the indirect band gap. For pulses linearly polarized along the [001] crystal axis γ increases from a value of near 0cm3∕GW2 at 3300nm to a peak value of 0.035cm3∕GW2 at 2700nm before decreasing with shorter wavelength; this is consistent with the dispersion expected from allowed-allowed-allowed transitions. At 2600nm the γ value is ∼30% larger for light polarized along [011] than along [001].

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