6.7-8.1 µm tunable single-frequency difference frequency generation in ZGP for high-resolution spectroscopy.

Area of Science:

• Optics and Photonics
• Spectroscopy
• Nonlinear Optics

Background:

• Tunable single-frequency mid-infrared (MIR) light sources are crucial for high-resolution spectroscopy, sensing, and imaging.
• Difference frequency generation (DFG) is a key technique for generating MIR light.
• Existing DFG sources often face limitations in tunability and integration.

Purpose of the Study:

• To demonstrate a novel continuous-wave (CW) single-frequency DFG source in a ZnGeP2 (ZGP) crystal.
• To utilize all-fiber near-infrared (NIR) fiber lasers as pump sources for DFG.
• To explore the potential of this DFG source for high-resolution optical spectroscopy.

Main Methods:

• Employed all-fiber CW tunable single-frequency erbium-doped (1.5 µm) and thulium-doped (1.9 µm) fiber lasers.
• Utilized a ZnGeP2 (ZGP) crystal, known for its high nonlinear coefficient and birefringence, for DFG.
• Achieved DFG by mixing the two NIR laser outputs within the ZGP crystal.

Main Results:

• Demonstrated, for the first time, CW single-frequency DFG in a ZGP crystal pumped by all-fiber NIR lasers.
• Achieved a broad spectral tuning range from 6.7 to 8.1 µm with output power at the 10 µW level.
• Successfully performed precise detection of C2H2 gas by scanning the DFG source over 1.1 THz (34 cm-1).

Conclusions:

• The developed all-fiber DFG source offers a new platform for spectroscopy in the molecular fingerprint region.
• The broad tuning range and precise spectral scanning capabilities highlight its potential for high-resolution applications.
• This work paves the way for advanced spectroscopic techniques using compact and tunable MIR light sources.