Abstract
We demonstrate mid-infrared (mid-IR) supercontinuum generation (SCG) with instantaneous bandwidth from 2.2 to 5 μm at 40 dB below the peak, covering the wavelength range desirable for molecular spectroscopy and numerous other applications. The SCG occurs in a tapered As(2)S(3) fiber prepared by in-situ tapering and is pumped by femtosecond pulses from the subharmonic of a mode-locked Er-doped fiber laser. Interference with a narrow linewidth c.w. laser verifies that the coherence properties of the near-IR frequency comb have been preserved through these cascaded nonlinear processes. With this approach stable broad mid-IR frequency combs can be derived from commercially available near-IR frequency combs without an extra stabilization mechanism.
Highlights
Broad mid-IR frequency combs [1] in the 2-20 μm wavelength range are desirable for many applications, such as molecular fingerprinting [2], trace gas detection [3], laser-driven particle acceleration [4], and x-ray production via high harmonic generation [5]; they are not as easy to produce as near-IR and visible frequency combs
As low loss optical fibers became prevalent, supercontinuum generation (SCG) sources quickly shifted to guided fibers [10], and as the wavelength increased, the glass host has migrated from silica to mid-IR glasses –mainly the chalcogenides, which include the sulfides, selenides, and tellurides [11]
A step index As2S3 fiber is chosen for supercontinuum generation in mid-IR because of its large nonlinear index ≃ 6 × 10−18 m2/W (220 times of that of silica in near-IR) [23], and low loss in mid-IR
Summary
Broad mid-IR frequency combs [1] in the 2-20 μm wavelength range are desirable for many applications, such as molecular fingerprinting [2], trace gas detection [3], laser-driven particle acceleration [4], and x-ray production via high harmonic generation [5]; they are not as easy to produce as near-IR and visible frequency combs. As low loss optical fibers became prevalent, SCG sources quickly shifted to guided fibers [10], and as the wavelength increased, the glass host has migrated from silica to mid-IR glasses –mainly the chalcogenides, which include the sulfides, selenides, and tellurides [11]. Due to their low loss in the mid-IR, as well as high nonlinearity, hundreds of times higher than silica, the chalcogenides have been an attractive option for an SCG host material [11]
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