Enhanced second harmonic generation in laser-induced air plasma.

Area of Science:

• Nonlinear Optics
• Laser-Induced Plasmas
• Quantum Electronics

Background:

• Second harmonic generation (SHG) is a key nonlinear optical process.
• Laser-induced air plasmas offer unique environments for studying light-matter interactions.
• Understanding temporal dynamics is crucial for optimizing nonlinear processes.

Purpose of the Study:

• To investigate the mechanisms behind significantly enhanced SHG in laser-induced air plasma.
• To analyze the temporal dynamics and polarization characteristics of the generated second harmonic wave.
• To explore the influence of fundamental pulse duration and polarization configurations on SHG efficiency.

Main Methods:

• Systematic investigation of temporal dynamics of frequency conversion.
• Analysis of the polarization of the emitted second harmonic beam.
• Utilizing an orthogonal pump-probe configuration with varying fundamental pulse durations (0.1 ps to >2 ps).

Main Results:

• Observed a near hundred-fold enhancement in SHG efficiency.
• Enhanced SHG efficiency was confined to a sub-picosecond temporal window.
• Efficiency remained constant across a broad range of fundamental pulse durations.
• Demonstrated a complex polarization dependence of the second harmonic field on both input beams.

Conclusions:

• The enhanced SHG in laser-induced air plasma exhibits unique temporal characteristics distinct from typical nonlinear optical processes.
• The observed phenomenon is highly sensitive to the temporal dynamics within the plasma.
• The orthogonal pump-probe configuration reveals intricate polarization dynamics crucial for understanding the underlying physics.