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Supercontinuum light (SC) is a broadband source with unique properties as the result of cascaded nonlinear dynamics when intense light propagates in a nonlinear material [1]. Recently, the generation of broadband SC sources operating in the mid-infrared (MIR) has attracted significant interest due to a wide range of potential applications in spectroscopy [2], microscopy, molecular fingerprinting [3], environmental monitoring and LIDAR [4], just to name a few. Fibers made of non-silica soft glasses such as fluoride, tellurite and chalcogenide are good candidates for SC generation in the MIR due to their high intrinsic nonlinearity and wide transparency window in this wavelength range. Supercontinuum generation in the MIR is typically achieved by propagating femtosecond pulses into the anomalous dispersion regime of a single-mode soft glass fibers. This typically leads to SC sources which are limited in terms of average power due to the low damage threshold associated with soft glasses and susceptible to noise due to the anomalous pump regime. These inherent limitations can be detrimental for many applications such as e.g. optical coherence tomography (OCT), photoacoustic imaging [5], or spectroscopy where the performance critically depends on the power and noise properties of the light source. In this work, we demonstrate for the first time the generation of a low noise high power SC in the MIR by injecting 350 fs pulses from an optical parametric amplifier into the normal dispersion regime of a one meter-long multimode step-index chalcogenide fiber with 100 µm core diameter. We show the generation of SC spanning from 1700 nm to 4800 nm for a pump wavelength at 3500 nm (located in normal dispersion regime of the used fiber) and an input peak power of 570 kW. A systematic study of the SC intensity noise is performed as a function of different pump parameters and for different output wavelengths show that the initial fluctuations on the pump laser are at most amplified by a factor of 2 at the spectral edge of the SC. Although the output beam in this case is multimoded, it can still be used for many practical applications such as long-distance remote sensing for which high power and low noise are more essential than the actual beam profile quality. Our results open novel perspective for the generation of high power low-noise broadband light sources in the MIR.
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