Spiral-chirped nonlinear photonics enabling broadband orbital angular momentum second harmonic generation

Area of Science:

• Nonlinear Optics
• Quantum Optics
• Laser Physics

Background:

• Generating structured light with orbital angular momentum (OAM) is crucial for advanced optical applications.
• Conventional methods for generating second-harmonic (SH) vortex beams often have limited spectral bandwidths.

Purpose of the Study:

• To demonstrate a novel nonlinear frequency conversion strategy for generating SH vortex waves with engineered OAM.
• To achieve ultrabroad bandwidths in the generated OAM-entrained SH vortex beams.
• To explore applications in tunable structured light sources and high-capacity optical imaging.

Main Methods:

• Utilized spiral-chirped quasi-phase-matching (QPM) in a femtosecond-laser-poled Sr_0.61Ba_0.39Nb₂O₆ (SBN) crystal.
• Implemented simultaneous azimuthal phase modulation and longitudinal period chirp for dual modulation.
• Converted collimated Gaussian beams (1200-1300 nm) into SH vortex waves.

Main Results:

• Successfully generated second-harmonic (SH) vortex waves with engineered orbital angular momentum (OAM).
• Achieved ultrabroad spectral bandwidths, significantly surpassing conventional helical-phase-matched systems.
• Maintained stable efficiency in the nonlinear frequency conversion process.

Conclusions:

• The demonstrated dual modulation strategy enables controllable generation of SH OAM vortices.
• This method offers a wider spectral acceptance bandwidth compared to existing techniques.
• The findings pave the way for advanced applications in tunable structured light, optical imaging, and quantum light generation.