Nonlinear absorption and parametric gain interaction in green-pumped subnanosecond MgO:PPLN OPG

Area of Science:

• Nonlinear Optics
• Laser Physics
• Materials Science

Background:

• Periodically poled MgO-doped LiNbO3 (MgO:PPLN) is a key material for nonlinear optical devices.
• Subnanosecond optical parametric generation (OPG) requires high peak intensities and efficient nonlinear processes.
• Nonlinear absorption can limit performance in high-intensity OPG systems.

Purpose of the Study:

• To investigate optical parametric generation in a 532 nm-pumped MgO:PPLN crystal under high peak pump intensities.
• To analyze the effects of nonlinear absorption and explore methods to mitigate performance losses.
• To optimize the OPG output characteristics for use as a seed source in the visible spectral range.

Main Methods:

• Utilized a 532 nm-pumped Nd:YAG microlaser-based optical parametric generator (OPG) with MgO:PPLN.
• Operated the OPG in the subnanosecond regime at GW/cm^2 peak pump intensities.
• Employed an off-axis pumping geometry to exploit the QPM grating edge effect and developed a comprehensive numerical model.

Main Results:

• Observed significant nonlinear absorption at 532 nm, despite which achieved μJ-level output energies and up to 62% conversion efficiency.
• Demonstrated that off-axis pumping reduces non-collinear QPM interaction and decreases far-field divergence of signal and idler waves by twofold.
• Developed a numerical model that qualitatively explains the observed OPG behavior.

Conclusions:

• The 532 nm-pumped MgO:PPLN OPG system exhibits high conversion efficiency despite nonlinear absorption losses.
• Off-axis pumping effectively controls spatial and spectral properties, reducing divergence and enhancing suitability as a seed source.
• The developed OPG is a promising seed source for subnanosecond optical parametric amplification in the visible spectral range.