Supercontinuum generation and absorption spectroscopy from 3 to 20 μm using a highly nonlinear telluride glass rod

Abstract Broadband light sources extending deep into the long-wavelength mid-infrared are of strong interest for molecular spectroscopy, sensing, and nonlinear photonics, but their generation remains challenging because of the limited availability of suitable materials and efficient nonlinear conversion schemes. Here, we demonstrate broadband supercontinuum generation in a bulk GeTe₄–AgI chalcohalide glass using intense femtosecond pulses centered at approximately 8.5 μm. The generated supercontinuum extends from 3 to 20 μm, corresponding to a spectral coverage of approximately 2.7 octaves, and reaches an output average power of 2.1 mW at a 1-kHz repetition rate. The high peak power relative to the estimated self-focusing critical power leads to strong nonlinear spectral broadening in the bulk glass, consistent with the regime of filamentation-assisted supercontinuum generation. The generated broadband source is further evaluated for long-wavelength mid-IR spectroscopy through absorption measurements of a 100-µm-thick polytetrafluoroethylene film. The main absorption features measured using the supercontinuum source agree well with those obtained using a conventional Fourier-transform infrared spectrometer, including characteristic bands around 16 and 18 μm. These results demonstrate the potential of telluride glasses for broadband nonlinear light generation and spectroscopy extending into the long-wavelength mid-IR.