Dual-comb absorption spectroscopy of molecular CeO in a laser-produced plasma.

Broadband and high-resolution absorption spectra of molecular cerium oxide (CeO) are obtained in a laser-produced plasma using dual-comb spectroscopy. Simultaneous measurements of Ce and CeO are used to probe time-resolved dynamics of the system. A spectral resolution of 1.24 GHz (2.4 pm) over a bandwidth of 378.7-383.7 THz (781.1-791.5 nm) allows simultaneous detection of hundreds of closely spaced rotational transitions in complex CeO bands.

Time-resolved dual-comb measurement of number density and temperature in a laser-induced plasma.

We utilize time-resolved dual-comb spectroscopy to measure the temporal evolution of the population number densities and absorption excitation temperature of Fe in a laser-induced plasma. The spectra of three excited-state transitions of Fe around 533 nm are simultaneously measured at different time delays following laser ablation of a stainless steel sample. This Letter probes late-time behaviors of laser-induced ablation plumes during plasma cooling. The high spectral resolution and broad spectral coverage of the dual-comb technique, combined with the time-resolved measurement capability shown here, will aid in the characterization of laser induced plasmas, including species identification and molecule and particle formation that can occur at later times in the plasma evolution.

Offset-free mid-infrared frequency comb based on a mode-locked semiconductor laser.

We demonstrate a carrier-envelope offset-free frequency comb in the mid-wavelength infrared (MWIR) based on a passively mode-locked vertical external cavity surface emitting laser (VECSEL) operating at a 1.6 GHz repetition rate. The 290 mW output spanning 3.0-3.5 µm is generated through difference frequency generation (DFG) in periodically poled lithium niobate. The VECSEL pulse train is centered at 1030 nm and amplified up to 11 W in a Yb fiber amplifier system. The output is split to generate a second pulse train at 1560 nm through nonlinear broadening in a Si3N4 waveguide followed by amplification in an Er gain fiber. DFG between the 1030 and 1560 nm pulse trains results in a coherent and offset-free MWIR frequency comb, verified with optical heterodyne beat note measurements. Active stabilization of the VECSEL repetition rate provides a fully stabilized high repetition rate frequency comb in the MWIR, uniquely suited for applications in molecular spectroscopy.