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

Abstract

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 ZrF₄-BaF₂-LaF₃-AlF₃-NaF fiber, As₂S₃ fiber, and As₂Se₃ 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 As₂Se₃ fiber is multimode below 12 μm. Our study also shows that parameters of the As₂Se₃ 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 As₂Se₃/GeAs₂Se₅ 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.