Adiabatic second-harmonic generation.

Area of Science:

• Nonlinear optics
• Quantum optics
• Photonics

Background:

• Adiabatic three-wave mixing offers broadband, efficient, and robust frequency conversion.
• Previous applications primarily assumed undepleted pump waves, limiting scope.
• Fully nonlinear adiabatic processes, where pump depletion occurs, remained less explored experimentally.

Purpose of the Study:

• To experimentally investigate fully nonlinear adiabatic processes in second-harmonic generation.
• To explore type I and type II second-harmonic generation under depleted pump conditions.
• To validate theoretical models for adiabatic processes with arbitrary initial conditions.

Main Methods:

• Implementation of quasi-phase-matched interactions in chirped gratings.
• Experimental study of type I and type II second-harmonic generation.
• Variation of input polarization angle to transition between depleted and undepleted pump regimes.

Main Results:

• Achieved conversion efficiencies approaching 60% (type I) and 80% (type II).
• Observed wide thermal acceptance bandwidths: >100°C (type I) and 30°C (type II).
• Experimental data showed excellent agreement with analytic predictions for fully nonlinear adiabatic processes.

Conclusions:

• Fully nonlinear adiabatic processes are experimentally viable and achieve high efficiencies.
• Chirped gratings enable robust frequency conversion with broad thermal tolerance.
• The study validates theoretical models for adiabatic processes under depleted pump conditions.