Abstract
Abstract We report on the generation of a mid-infrared (mid-IR) frequency comb with a maximum average output power of 250 mW and tunability in the 2.7–4.0 μm region. The approach is based on a single-stage difference frequency generation (DFG) starting from a compact Yb-doped fiber laser system. The repetition rate of the near-infrared (NIR) comb is locked at 75 MHz. The phase noise of the repetition rate in the offset-free mid-IR comb system is measured and analyzed. Except for the intrinsic of NIR comb, environmental noise at low frequency and quantum noise at high frequency from the amplifier chain and nonlinear spectral broadening are the main noise sources of broadening the linewidth of comb teeth, which limits the precision of mid-IR dual-comb spectroscopy.
Highlights
Mid-infrared laser sources are becoming enabling tools for cutting-edge applications, including greenhouse gas sensing[1, 2], medical diagnosis[3], and security and defense[4]
The power amplifier relies on chirped pulse amplification consisting of a 100 m fiber stretcher and two-stage amplifiers, which operate in gain-saturation state to reduce the amplified spontaneous emission (ASE), and delivers 89 nJ energy pulses centered at 1038 nm
The laser emits 3 mW pulses with 30 nm full width at half maximum (FWHM) and 75 MHz repetition rate. As this pulse energy is insufficient for broad signal laser generation, chirped pulse amplifier (CPA) is employed to scale pulse energy
Summary
Mid-infrared (mid-IR) laser sources are becoming enabling tools for cutting-edge applications, including greenhouse gas sensing[1, 2], medical diagnosis[3], and security and defense[4]. There is a wide array of innovative solutions to generate coherent mid-IR laser sources, with novel gain media[11], quantum cascade lasers[12] and micro-resonators[13], and supercontinuum generation in waveguides and fibers[14, 15]. Compared with these approaches, detecting and controlling the offset frequency of the mid-IR sources is a challenge, which is the prerequisite for frequency comb spectroscopy. A more direct approach is to employ nonlinear frequency conversion of ultrashort pulses in the visible or near-infrared (NIR) regime to generate coherent mid-IR sources.
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