Continuous-wave difference-frequency generation based on BaGa₄Se₇ crystal

Area of Science:

• Nonlinear Optics
• Laser Physics
• Materials Science

Background:

• Continuous-wave (CW) mid-infrared (MIR) radiation is crucial for various spectroscopic applications.
• Efficient generation of tunable MIR radiation remains a significant challenge in laser technology.

Purpose of the Study:

• To demonstrate CW mid-infrared radiation generation via difference frequency generation (DFG) for the first time.
• To investigate the tunable range and efficiency of DFG using a BaGa4Se7 crystal.

Main Methods:

• Mixing of CW Ti:sapphire and CW YAG laser outputs.
• Utilizing a 15 mm long BaGa4Se7 crystal for nonlinear frequency conversion.
• Employing type I phase-matching by rotating the crystal to achieve tunability.

Main Results:

• Achieved a tunable DFG output range from 3.15 to 7.92 μm.
• Obtained a maximum DFG power of 1.41 μW at 5 μm.
• Measured a DFG power conversion efficiency of 20.2 μW/W², with a length-normalized slope efficiency of 15.5 μW/cmW².

Conclusions:

• BaGa4Se7 is a viable nonlinear crystal for generating tunable CW mid-infrared radiation via DFG.
• The demonstrated DFG system offers a promising approach for MIR spectroscopy and other applications.
• Further optimization could enhance conversion efficiency across the entire tuning range.