Generation of near-diffraction-limited, high-power supercontinuum from 1.57 μm to 12 μm with cascaded fluoride and chalcogenide fibers.

We generate a supercontinuum (SC) spectrum ranging from 1.57 μm to 12 μm (20 dB bandwidth) with a soft glass fiber cascade consisting of ---- fiber, fiber, and fiber pumped by a nanosecond thulium master oscillator power amplifier system. The highest on-time average power generated is 417 mW at 33% duty cycle. We observe a near-diffraction-limit beam quality across the wavelength range from 3 μm to 12 μm, even though the fiber is multimode below 12 μm. Our study also shows that parameters of the fiber, such as numerical aperture, core size, and core/cladding composition, have significant effects on the long wavelength edge of the generated SC spectrum. Our results suggest that the high numerical aperture of 0.76 and low-loss / core/cladding material all contribute to broad SC generation in the long-wave infrared spectral region. Also, among our results, 10 μm core diameter selenide fiber yields the best spectral expansion, while the 12 μm core diameter selenide fiber yields the highest output power.