Tunable phase-mismatched mid-infrared difference-frequency generation between 6 and 17 µm in CdTe

Area of Science:

• Nonlinear optics
• Quantum optics
• Materials science

Background:

• Parametric conversion typically relies on phase-matching (PM) techniques like birefringence or quasi-PM to conserve momentum.
• Phase-mismatched interactions in nonlinear media with high quadratic nonlinear coefficients have been largely unexplored.

Purpose of the Study:

• To investigate phase-mismatched difference-frequency generation (DFG) in isotropic cadmium telluride (CdTe) crystals.
• To compare this novel method with established DFG processes (birefringence-PM, quasi-PM, random-quasi-PM).
• To demonstrate the potential of phase-mismatched DFG for generating long-wavelength mid-infrared (LWMIR) radiation.

Main Methods:

• Utilized cadmium telluride (CdTe), an isotropic crystal with a large quadratic nonlinear coefficient (∼109 pm/V).
• Performed phase-mismatched DFG to generate LWMIR radiation.
• Compared the performance with birefringence-PM, quasi-PM, and random-quasi-PM DFG processes.

Main Results:

• Achieved an ultra-broadband spectral tuning range of 6-17 µm for LWMIR phase-mismatched DFG in CdTe.
• Obtained output power up to 100 µW, comparable to or exceeding random-quasi-PM DFG in ZnSe.
• Successfully demonstrated a proof-of-concept gas sensing application for CH₄ and SF₆.

Conclusions:

• Phase-mismatched parametric conversion in CdTe offers a simple and convenient method for generating useful LWMIR power and ultra-broadband tunability.
• This approach eliminates the need for precise control over polarization, phase-matching angle, or poling periods.
• Potential applications in spectroscopy and metrology are highlighted.