Pulsed Bessel-Gauss beams: a depleted wave model for type II second-harmonic generation

Area of Science:

• Nonlinear Optics
• Crystallography
• Wave Physics

Background:

• Second-harmonic generation (SHG) is crucial for frequency conversion.
• Understanding fundamental wave depletion is key for accurate nonlinear optical modeling.
• Pulsed Bessel-Gauss beams offer unique propagation characteristics.

Purpose of the Study:

• To develop a 3D, time-dependent nonlinear wave model for pulsed Bessel-Gauss SHWs.
• To investigate the validity of the nondepleted wave approximation in KTiOPO4 (KTP) crystals.
• To determine the interaction length for type II SHG considering fundamental wave depletion.

Main Methods:

• Solving three coupled nonlinear wave equations for ordinary and extraordinary fundamental waves and extraordinary SHWs.
• Utilizing a 3D, time-dependent model.
• Analyzing the impact of pulse energy, beam spot size, and crystal length on SHG efficiency.

Main Results:

• The model accurately describes type II SHG in KTP crystals.
• Fundamental wave depletion significantly affects SHG.
• The nondepleted wave approximation is invalid for KTP crystals longer than approximately 5 mm for pulses with 80 μm spot size and 0.8 J energy.

Conclusions:

• The developed model provides insights into pulsed SHW generation.
• Accurate modeling requires considering fundamental wave depletion.
• Crystal length must be carefully chosen to ensure the validity of approximations in SHG processes.