Longwave infrared (6.6-11.4 µm) dual-comb spectroscopy with 240,000 comb-mode-resolved data points at video rate

Area of Science:

• Spectroscopy
• Laser Physics
• Infrared Technology

Background:

• Mode-locked Cr:ZnS lasers provide a driving source for advanced spectroscopic techniques.
• Frequency comb generation in the longwave infrared (LWIR) is crucial for molecular analysis.

Purpose of the Study:

• To develop and demonstrate high-resolution dual-frequency-comb spectroscopy in the LWIR range.
• To achieve fast acquisition of massive spectral data for molecular identification.

Main Methods:

• Utilized sub-3-cycle pulses from mode-locked Cr:ZnS lasers (λ ≈ 2.4 µm).
• Generated broadband LWIR frequency combs (6.6–11.4 µm) via intrapulse difference frequency generation in zinc germanium phosphide (ZGP) crystals.
• Achieved fast spectral acquisition (0.1 s/spectrum) with 240,000 comb-mode-resolved data points (80 MHz spacing), referenced to a Rb clock.

Main Results:

• Demonstrated metrology-grade molecular spectra of nitrous oxide (N₂O) and methane (CH₃OH).
• Achieved low intensity and phase noise in the LWIR combs.
• Obtained high downconversion efficiency (7.5%) resulting in 300 mW LWIR power per comb.

Conclusions:

• The developed technique enables rapid, high-resolution spectroscopic analysis in the LWIR.
• Low noise and high efficiency are key for high-speed, massive spectral data acquisition.
• This advancement has implications for molecular spectroscopy and metrology.