Plasma-free water droplet shattering by long-wave infrared ultrashort pulses for efficient fog clearing

Abstract

Plasma-free water droplet shattering by long-wave infrared ultrashort pulses for efficient fog clearing," Optica 7, 115-122 (2020)

Highly efficient difference-frequency generation for mid-infrared pulses by passively synchronous seeding

“…Therefore, the demonstrated system here would provide a practical picosecond MIR light source for potential applications such as laser selective cutting of biological tissues [30] and plasma-free water droplet shattering for efficient fog clearing [31] . Moreover, the presented configuration might be engineered to access MIR pulses from femtosecond to nanosecond with the help of proper fiber-laser design and intra-cavity dispersion management.…”

Tunable Near‐ to Far‐Infrared Optical Breakdown in Nonlinear Interactions of Ultrashort Laser Pulses with Water Microdroplets in Ambient Air

“…Laser excitation of single 3D spherical water droplets of different sizes irradiated by near-to far-IR pulses of 150 fs duration (full width at half maximum) is studied, showing the averaged intensity and electron density distributions in the propagation plane x0z, as shown in Figure 1. We focus on particular laser wavelengths of 800 nm, 1.5 μm, 3.9 μm, and 10 μm, which have found applications in filamentation and self-trapped beam propagation, [22,23] fog clearing, [10][11][12] laser ablation, [17,18] and so on. Plane wave excitation is considered, imitating the cases where the laser beam waist is much larger than the typical dimensions of aerosols or water droplets.…”

“…Another important transient optical characteristic is the attenuation length or optical skin depth L abs , given by the ratio between laser wavelength λ and the extinction coefficient 2πK plotted as a function of free carrier density in Figure 2d on a logarithmic scale. The nonzero linear extinction coefficient, pronounced for longer wavelengths, [12,16] is taken into account. Consequently, for weak excitation conditions, the attenuation length for near-IR appears to be greater than for mid-IR/ long-wave IR.…”

“…In most considered cases, the ultrashort pulsed laser irradiation of water droplets results in the transient creation of nanoscale absorbed energy and electron plasma confinement inside the rear-side of the droplet. Further hydrodynamic evolution on a slower scale beyond this point might be complex, including pressure wave-driven cavitation (in case of temperature confinement, it occurs T i % 450 K and negative pressures of %À150 MPa [12,35] ), droplet expansion and deformation by surface tension forces, jet production, partial evaporation, and for higher intensities, fragmentation and phase explosion. [29] For some practical applications, the resulting hydrodynamic processes may play a defining role and specific laser systems should be chosen to benefit from laser interaction with droplets.…”

“…Water droplets are omnipresent in biophysical environments and ecosystems, playing an important role in communication through the atmosphere (i.e., aerosols and contaminants, fog, mist, haze, drizzle, clouds) and being involved in a variety of physicochemical reactions and biological processes (respiratory droplets due to breathing, talking, coughing, etc., biological cells, bioaerosols, water clusters, surface adhesion, and wettability). Broad opportunities in analysis, detection, and control over droplet distributions are enabled by the application of powerful lasers used for laser breakdown, [ 1–3 ] electron photoemission [ 4–7 ] and cavity‐enhanced droplet spectroscopy, [ 8,9 ] long‐distance optical communications, [ 10–12 ] and high harmonic generation from water microdroplets. [ 13–15 ] The processes of ultrashort laser excitation and ionization of water droplets and aerosols remain poorly explored for a wide range of photon energies and wavelengths from visible to long‐wave infrared (IR) range.…”