Enhancing second harmonic generation by Q-boosting lossless cavities beyond the time bandwidth limit

Area of Science:

• Optics and Photonics
• Nanotechnology
• Nonlinear Optics

Background:

• Nanostructures offer precise control over electromagnetic fields at the subwavelength scale.
• High-quality-factor nanocavities enhance light-matter interactions for nonlinear frequency generation.
• Conventional nanocavities struggle to fully utilize the bandwidth of ultrashort laser pulses due to intensity requirements.

Purpose of the Study:

• To present a general theoretical treatment for second harmonic generation in time-modulated nanocavities.
• To investigate the impact of time-varying quality factors on nonlinear optical processes.
• To identify optimal conditions for maximizing nonlinear conversion efficiency.

Main Methods:

• Coupled mode theory was employed to model the system.
• Analysis focused on a doubly resonant cavity with a time-modulated quality factor at the fundamental frequency.
• Simulations explored the relationship between initial quality factor and second harmonic generation efficiency.

Main Results:

• A theoretical framework was established for time-varying optical systems.
• The initial quality factor that maximizes second harmonic generation efficiency during Q-boosting was identified.
• A theoretical energy conversion efficiency approaching unity was predicted.

Conclusions:

• Time-varying optical systems, specifically modulated nanocavities, can overcome the time-bandwidth limit.
• This approach significantly enhances nonlinear frequency conversion efficiency.
• The findings pave the way for next-generation time-dependent metasurfaces for ultrashort pulse applications.