Second-harmonic generation based on quasi-phase matching: a novel configuration.

Area of Science:

• Nonlinear optics
• Waveguide optics
• Second-harmonic generation

Background:

• Second-harmonic generation (SHG) is a key process in nonlinear optics.
• Quasi-phase-matching (QPM) in second-order nonlinear media enables efficient SHG.
• Waveguide structures confine light for enhanced nonlinear interactions.

Purpose of the Study:

• To investigate the generation of second-harmonic radiation via counterpropagating fundamental waves in a QPM waveguide.
• To compare the conversion efficiency of counterpropagating versus copropagating fundamental waves.
• To determine the optimal pump intensity for maximum conversion efficiency.

Main Methods:

• Theoretical analysis of nonlinear wave interaction in a waveguide.
• Modeling of second-order nonlinear polarization.
• Calculation of conversion efficiency based on pump intensity and material properties.

Main Results:

• The conversion efficiency for counterpropagating waves reaches a maximum at an optimum pump intensity.
• For a significant range of pump intensities, counterpropagating waves yield higher efficiency than copropagating waves.
• Saturation intensities for 72% efficiency in KTiOPO(4) and LiNbO(3) are achievable with current laser technology.

Conclusions:

• Counterpropagating fundamental waves in QPM nonlinear waveguides provide an efficient route for second-harmonic generation.
• The optimal pump intensity is crucial for maximizing SHG efficiency.
• This approach offers advantages over copropagating configurations and is feasible with available laser systems.