Abstract

Broadband mid-infrared (mid-IR) sources with high radiance are in demand for spectroscopy applications in the molecular fingerprint region [1]. This type of radiation can be conveniently generated via intra-pulse difference frequency generation (IDFG) in nonlinear crystals. GaSe is a crystal with high nonlinearity capable of generating long wavelengths due to its transparency up to ca. 20 µm. However, it is usually favorable to pump these crystals at longer wavelengths (> 2 µm) to avoid damage induced by multi-photon absorption. Shorter wavelengths can be covered by LiGaS₂ (LGS), which shows a much larger bandgap. This makes it a suitable material for pumping with few-cycle pulses produced by temporal compression of broadly available laser systems operating at the 1 µm wavelength region [2]. Few-cycle pulses are here of special interest, as the bandwidth of the pumping pulses principally limits the lowest attainable wavelength from IDFG.

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