Supercontinuum generation in mixed thallous halides KRS-5 and KRS-6

We experimentally study supercontinuum generation in mixed thallous halides: thallium bromoiodide (KRS-5) and thallium chlorobromide (KRS-6), as pumped with mid-infrared femtosecond pulses. Almost 2 octave-wide supercontinuum spectra spanning wavelengths from ∼1.5μm to more than 5.5μm were produced by self-focusing of 60 fs pulses with central wavelengths of 3.1μm and 3.6μm in KRS-5 and KRS-6 samples of 6 mm thickness, in the single and multiple filamentation regimes. Our measurements revealed remarkably low energy thresholds (few hundreds of nanojoules) for supercontinuum generation in these materials due to very large values of nonlinear indexes of refraction (n2=10.5×10−15 cm2/W for KRS-5 and n2=5.4×10−15 cm2/W for KRS-6), which were experimentally evaluated from the nonlinear propagation dynamics. A combination of high nonlinearity and wide infrared transparency range make KRS-5 and KRS-6 very attractive bulk materials for SC generation in the mid-infrared spectral range.