Supercontinuum generation in chalcogenide: application to gas spectroscopy in atmospheric band III

This thesis work aims to contribute to the development of new fiber sources emitting over a wide range of wavelengths in the IR, in particular to detect greenhouse gases in the mid-infrared range. Our spectroscopy results with nitrous oxide N₂O and methane CH₄ are obtained in band III. To achieve this, the generation of supercontinuum (SC) covering band III was made possible by using chalcogenide optical fibers, purified and free of highly toxic elements according to REACH regulations, in particular arsenic and antimony. The fibre vitreous composition belonging to the Ge-Se-Te ternary system fits perfectly into the context of sustainable development, it is the one that has been identified and developed in the ICB laboratory. The setting up of experimental setups with different femtosecond sources was carried out in order to generate a supercontinuum covering the interval between 8 μm and 12 μm, belonging to the third band of atmospheric transparency. The optimization of many experimental parameters led to obtaining a wide supercontinuum from 1.7 μm to 18 μm with 40 dB of dynamic range, the fiber being pumped with a non-collinear optical parametric amplifier. Other non-fibered and fibered sources have made it possible to achieve original results concerning SCs with our step-index fibers and three-hole suspended core fibers. This led to the development of gas spectroscopy experiments. Several setups with different gas cells have been made with different sources, leading to important results. Nitrous oxide and methane have both been detected at wavelengths little explored so far, around 8 μm. The best experimental configuration led, with the supercontinuum emitted by a Ge-Se-Te fiber, to the detection of 14 ppm of methane when the fiber is pumped by an optical parametric oscillator. Detection goes down to 11 ppm of this gas if the Ge-Se-Te fiber is pumped by a fiber source. (author)