Daniel L. Maser

Mid-infrared optical frequency combs based on difference frequency generation for molecular spectroscopy

Mid-infrared femtosecond optical frequency combs were produced by difference frequency generation of the spectral components of a near-infrared comb in a 3-mm-long MgO:PPLN crystal. We observe strong pump depletion and 9.3 dB parametric gain in the 1.5 μm signal, which yields powers above 500 mW (3 μW/mode) in the idler with spectra covering 2.8 μm to 3.5 μm. Potential for broadband, high-resolution molecular spectroscopy is demonstrated by absorption spectra and interferograms obtained by heterodyning two combs.

Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy

Infrared spectroscopy is a powerful tool for basic and applied science. The molecular spectral fingerprints in the 3 um to 20 um region provide a means to uniquely identify molecular structure for fundamental spectroscopy, atmospheric chemistry, trace and hazardous gas detection, and biological microscopy. Driven by such applications, the development of low-noise, coherent laser sources with broad, tunable coverage is a topic of great interest. Laser frequency combs possess a unique combination of precisely defined spectral lines and broad bandwidth that can enable the above-mentioned applications. Here, we leverage robust fabrication and geometrical dispersion engineering of silicon nanophotonic waveguides for coherent frequency comb generation spanning 70 THz in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides significant spectral broadening and engineered spectra targeted at specific mid-infrared bands. We use this coherent light source for dual-comb spectroscopy at 5 um.

Nonlinear Si-waveguides for mid-infrared comb generation and dual comb spectroscopy at 5 μm

Dispersive-waves in Si-waveguides extend mid-IR frequency combs to 3–5 µm with negligible added intensity noise through four-wave-mixing. A Si-chip-based dual-comb-spectroscopy system is demonstrated with 40 GHz spectral resolution at 5 µm.

Frequency stabilization of a mid-infrared optical frequency comb to single-frequency optical references

A mid-infrared (MIR) optical frequency comb produced by difference frequency generation is stabilized to cw optical references with residual linewidth <10 Hz. This stabilization will be important for dual-comb spectroscopy in the MIR.

Mid-infrared optical frequency combs based on difference frequency generation for dual-comb spectroscopy

Dual optical frequency combs at 2.8-3.4 μm with powers >210 mW were produced with femtosecond fiber-lasers and difference frequency generation. Interferograms between the combs have been demonstrated as a step towards mid-infrared dual-comb spectroscopy.

Tunable Broadband Source of Femtosecond Pulses in the 2 μm Region

A polarization maintaining Er:fiber-based source of femtosecond pulses was constructed using a 250 MHz mode-locked oscillator, fiber amplifier, and highly nonlinear fiber. The system generated 35 fs pulses with power variation of 1.3% on a timescale of days.

Frequency comb sources and techniques for mid-infrared spectroscopy and sensing

We review broad bandwidth mid-infrared frequency comb sources based on Yb, Er, and Tm fiber-laser technology and describe their use in spectroscopic approaches aimed at rapid, time-resolved detection of trace gases.