Continuum generation in Mid-IR from Tm-doped germanate fiber using femtosecond Cr:ZnS laser
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The mid-IR supercontinuum generation in fibers has received much attention due to its broad applicability to high-resolution spectroscopy and trace gas analysis, frequency metrology and optical coherence tomography (OCT). Supercontinua reaching out to 4.3 μm, 4.8 µm and 6 μm have been demonstrated in fluoride and telluride fibers, however, these experiments required complex multistage amplifier systems or microstructured fibers. In this work we focus on a simpler approach, where supercontinuum generation is produced directly from a femtosecond oscillator using a step-index single-mode chalcogenide or germinate-doped silica fiber. As a source of the femtosecond pulses in mid-IR spectral region we use the Kerr-lens mode-locked Cr:ZnS oscillator , pumped by the 5-W 1.61 µm Er-fiber laser. The laser produced about 72-fs pulses at the central wavelength of 2.38 µm, repetition rate of 150 MHz and output power up to 350 mW. The spectral bandwidth of output emission reached 81 nm.