Laser Pulses In Atmosphere Research Articles

各阶克尔非线性折射率对强激光大气传输的影响

各阶克尔非线性折射率对强激光大气传输的影响

Influence of Higher-Order Kerr Effect on Femtosecond Laser Filamentation in Air at Different Pressures

Utilizing the pressure dependent high-order kerr indices, the propagation of intense ultrashort laser pulse in atmosphere at different pressures can be investigated. The results of spectroscopic investigation provide an effective way to generate supercontinuum as well as higher conversion efficiency high-order harmonic generation.

Comparison between geometrically focused pulses versus filaments in femtosecond laser ablation of steel and titanium alloys

Kerr self-focusing of high-power ultrashort laser pulses in atmosphere may result in a structure or structures of high intensity that can propagate over long distances with little divergence. Filamentation has garnered significant interest in the nonlinear optics community due to its unique properties. Salient features of filaments include a central region of intense laser power (greater than the ionization threshold of the propagation medium) and a low temperature plasma column that lasts up to nanoseconds in duration after the passage of the laser pulse. Steel and titanium samples are ablated by filaments and by sharply focused sub-picosecond laser pulses. We then performed metrology on the samples to compare the ablation features in addition to modeling of the plasma ablation process. Ablation with filaments leads to a wider range of material responses as compared to ablation with sharply focused pulse. This results in potential complications for applications of filament ablation that depends on the rate of material removal and spectroscopic analysis.

Multifilamentation of high-power femtosecond laser pulse in turbulent atmosphere with aerosol

The filamentation of a femtosecond laser pulse in atmosphere under the joint influence of turbulence and aerosol has been numerically studied for the first time. A result of these studies is that the presence of aerosol in a turbulent atmosphere increases the distance to the onset of multifilamentation. We have studied the competition between two factors of aerosol coherent scattering in the process of multiple filamentation of a femtosecond pulse in the atmosphere: generation of light field perturbations and energy losses. Similarity parameters have been determined for different conditions in the problem of multifilamentation in aerosol.

Generation of extended plasma channels in air using femtosecond Bessel beams

Extending the longitudinal range of plasma channels created by ultrashort laser pulses in atmosphere is important in practical applications of laser-induced plasma such as remote spectroscopy and lightning control. Weakly focused femtosecond Gaussian beams that are commonly used for generating plasma channels offer only a limited control of filamentation. Increasing the pulse energy in this case typically results in creation of multiple filaments and does not appreciably extend the longitudinal range of filamentation. Bessel beams with their extended linear foci intuitively appear to be better suited for generation of long plasma channels. We report experimental results on creating extended filaments in air using femtosecond Bessel beams. By probing the linear plasma density along the filament, we show that apertured Bessel beams produce stable single plasma channels that span the entire extent of the linear focus of the beam. We further show that by temporally chirping the pulse, the plasma channel can be longitudinally shifted beyond the linear-focus zone, an important effect that may potentially offer additional means of controlling filament formation.

Propagation of self-focusing laser pulses in atmosphere: experiment versus numerical simulation

Numerical simulations of self-focusing laser pulses obtained via a slowly evolving wave approach (modified nonlinear Schrodinger equation) are compared with published experimental results in fused silica as well as with experimental results in air and fused silica obtained in our laboratory. The mathematical model includes group-velocity dispersion and third-order dispersion, optical shock, and both instantaneous Kerr and delayed Raman nonlinearities as well as a perfectly matched layer absorbing boundary condition. Second-harmonic frequency-resolved optical gating data taken after 10.91 m of propagation allow a direct comparison between experimental and computational envelopes at a number of pulse energies. FWHM measurements of the spectral width, intensity autocorrelation duration, and pulse radius at distances of 4.35, 10.91, 17.47, and 22.73 m provide a view of model fidelity across both energy and propagation distance variables. The magnitude of the nonlinear refractive index, n2, is inferred.