Continuous-wave 4.3-mum intracavity difference frequency generation in an optical parametric oscillator

Area of Science:

• Nonlinear optics
• Laser physics
• Mid-infrared photonics

Background:

• Periodically poled lithium niobate (PPLN) optical parametric oscillators (OPOs) face challenges with mid-infrared (mid-IR) absorption and high thresholds, limiting continuous-wave (cw) performance beyond 4 µm.
• Existing methods for mid-IR generation often require complex, multi-crystal configurations.

Purpose of the Study:

• To demonstrate a simple and effective method for achieving high cw output power in the mid-IR using PPLN OPOs.
• To overcome the absorption-loss limitations in PPLN OPOs for wavelengths greater than 4 µm.

Main Methods:

• Utilized difference frequency mixing (DFM) within a singly resonant OPO cavity.
• Pumped the PPLN OPO with a 14-W, 1.06-µm Nd:YAG laser to generate signal (1.7 µm) and idler (2.8 µm) waves.
• Mixed the generated signal and idler waves within the same crystal at a fixed temperature and grating period.

Main Results:

• Achieved 150 mW of cw output power at 4.3 µm.
• Successfully generated mid-IR emission via DFM, circumventing the typical mid-IR absorption issues.
• Demonstrated a viable alternative to more complex multi-crystal setups for fixed-wavelength mid-IR generation.

Conclusions:

• Difference frequency mixing in a PPLN OPO offers a straightforward approach to achieving significant cw mid-IR output.
• This technique effectively bypasses the absorption-loss limitations that hinder conventional PPLN OPO performance at longer mid-IR wavelengths.
• The method provides a simple, single-crystal alternative for generating specific mid-IR wavelengths when tunability is not a primary requirement.