Narrowband mid-infrared optical parametric generator based on a type-II BaGa₄Se₇ crystal.

Area of Science:

• Nonlinear optics
• Laser physics

Background:

• Optical parametric generators (OPGs) are crucial for tunable laser light generation.
• Mid-infrared (MIR) light sources are valuable for spectroscopy and sensing applications.
• Improving the efficiency and spectral quality of OPGs is an ongoing research area.

Purpose of the Study:

• To report a novel mid-infrared OPG using a BaGa4Se7 (BGSe) crystal.
• To enhance the performance of MIR OPGs through a cascaded crystal scheme.
• To achieve high pulse energy and narrow spectral bandwidths in the mid-infrared region.

Main Methods:

• A double-pass optical parametric generator (OPG) was designed using a type-II phase-matching BGSe crystal.
• A cascaded OPG scheme employing type-I ZnGeP2 (ZGP) and type-II BGSe crystals was investigated.
• Pumped at 2.1 µm, the OPG systems were characterized for pulse energy, wavelength, and spectral bandwidth.

Main Results:

• The single BGSe OPG generated narrowband MIR laser pulses with a maximum energy of 55 µJ.
• The cascaded OPG scheme significantly improved spectral bandwidths, achieving narrower outputs (<170 nm) compared to a ZGP OPG.
• The cascaded OPG demonstrated a high optical-to-optical conversion efficiency (OOCE) of 14.9% and a maximum pulse energy of 0.329 mJ.

Conclusions:

• The single BGSe crystal OPG is effective for generating narrowband MIR pulses.
• The cascaded ZGP and BGSe OPG design offers superior spectral quality and significantly enhanced output performance.
• This work presents a promising approach for efficient, high-energy, narrowband MIR laser generation.