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Mid- and Far-Infrared Supercontinuum Generation in Bulk Tellurium Spanning from 5.3 $μ$m to 32 $μ$m

Supercontinuum generation is performed in the bulk semiconductor tellurium (Te) with a high-power picosecond CO$_2$ laser at peak intensities up to 20 GW/cm$^2$. The spectrum spans from the second harmonic of the pump at 5.3 $μ$m to 32 $μ$m. Stimulated Raman scattering along with self-phase modulation and four wave mixing are found to be the main nonlinear optical processes leading to the spectral broadening. Numerical simulations using the experimental conditions indicate that the nonlinear refractive index of Te, $n_{2,\textrm{eff}}$(Te) is about (40 $\pm$ 10) $n_{2,\textrm{eff}}$(GaAs), making this a very promising material for nonlinear optical devices.