High-power broadband source tunable from 2.8 to 4 μm based on difference frequency generation

Abstract

Mid-infrared (MIR) frequency comb sources enable high-speed and accurate detection of various species, since many molecules possess their fingerprints in this wavelength range. Usually, broadband radiation in this spectral region is obtained from optical parametric oscillators (OPOs), which provide high output power and broad tuning capabilities [1]. However, OpO sources require locking of the cavity to the pumping oscillator, which increases the complexity. MIR sources based on difference frequency generation (DFG) are interesting alternatives to OPOs, due to their simplicity, single-pass configuration, broad tunability, and fully passive cancellation of the carrier-envelope offset in the generated idler pulses. However, the conversion efficiency of the DFG process is usually insufficient to reach the output power levels easily achieved in OPO systems. Here, we demonstrate a widely tunable DFG source based on a mode-locked Yb-doped fiber laser, with average MIR output power reaching 165 mW, which is more than in previous reports on similar DFG systems [2, 3].