Aerosol-induced laser breakdown thresholds: wavelength dependence.

Area of Science:

• Laser-induced breakdown phenomena
• Aerosol physics
• Nonlinear optics

Background:

• Laser-induced breakdown (LIB) in gases is well-studied, but LIB in liquid aerosols is less understood.
• Aerosols significantly alter laser propagation and interaction dynamics.
• Understanding breakdown thresholds is crucial for applications involving lasers and atmospheric aerosols.

Purpose of the Study:

• To experimentally determine the laser-induced breakdown thresholds for liquid droplets.
• To investigate the influence of laser wavelength and droplet properties on breakdown thresholds.
• To elucidate the physical mechanisms governing aerosol breakdown.

Main Methods:

• Utilizing a Q-switched Nd:YAG laser with pulse durations of 5-10 ns.
• Measuring breakdown thresholds for liquid droplets (e.g., water) at various wavelengths (1.064, 0.532, 0.355, 0.266 µm).
• Analyzing the effect of droplet composition (refractive index) and laser wavelength on breakdown intensity.

Main Results:

• Breakdown thresholds for droplets are 2-3 orders of magnitude lower than for clean air.
• Thresholds range from 4 x 10^7 to 3 x 10^9 W cm^-2 for 50-µm droplets.
• Thresholds decrease with decreasing laser wavelength and increasing real refractive index.
• For water, breakdown intensity scales approximately as λ^0.5.
• Laser transmission losses and suppression of stimulated Raman scattering were observed.

Conclusions:

• Aerosol composition and laser wavelength critically influence breakdown thresholds.
• Enhanced internal fields and multiphoton absorption contribute to lower breakdown thresholds at shorter wavelengths.
• Findings are relevant for understanding laser propagation in aerosolized environments and potential applications.