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Spectral broadening and dispersion compensation of mid-infrared femtosecond pulses

Efficient spectral broadening of mid-infrared pulses by use of a GaAs crystal has been demonstrated. The spectral bandwidths of the pulses at 5-μm wavelength increased from 540 nm to 2060 nm. The main advantages of this material are its large third-order nonlinearity and its transparency range (1 18 μm), which fully covers the molecular fingerprint region. We have also demonstrated that the second-order dispersion compensation with a CaF2 plate generated the compressed pulses with 3 optical cycles. The demonstrated scheme should work at any wavelength within the materials transparency range, and therefore be useful for spectral broadening of pulses generated from the well-established OPA-DFG system. Arbitrary shaping of the broadband mid-infrared pulses using 4f-pulse shaper would be beneficial for nonlinear vibrational spectroscopy and coherent control experiments.