Propagation Of High-power Laser Beams Research Articles

The Effects of Step Bulk Arrangement in Propagation of High-power Laser Beam in Atmosphere

The Effects of Step Bulk Arrangement in Propagation of High-power Laser Beam in Atmosphere

Wave-optics investigation of turbulence thermal blooming interaction: II. Using time-dependent simulations

Part II of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number, the number of wind-clearing periods, and the distortion number to gauge the strength of the simulated turbulence and TDTB. These parameters simply greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and TDTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation.

Wave-optics investigation of turbulence thermal blooming interaction: I. Using steady-state simulations

Part I of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and steady-state thermal blooming (SSTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number and the distortion number to gauge the strength of the simulated turbulence and SSTB. These parameters simplify greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and SSTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation.

Megafilament in air formed by self-guided terawatt long-wavelength infrared laser

The diffraction-compensated propagation of high-power laser beams in air could open up new opportunities for atmospheric applications such as remote stand-off detection, long-range projection of high-energy laser pulses and free-space communications. Here, we experimentally demonstrate that a self-guided terawatt picosecond CO2 laser beam forms in air a single centimetre-scale-diameter megafilament that, in comparison with a short-wavelength laser filament, has four orders of magnitude larger cross-section and guides many joules of pulse energy over multiple Rayleigh distances at a clamped intensity of ~1012 W cm–2. We discover that this megafilament arises from the balance between self-focusing, diffraction and defocusing caused by free carriers generated via many-body Coulomb-induced ionization that effectively decrease the molecular polarizability during the long-wavelength laser pulse. Modelling reveals that this guiding scheme may enable transport of high-power picosecond infrared pulses over many kilometres in the 8–14 μm atmospheric transmission window. A terawatt picosecond CO2 laser beam is shown to form a centimetre-scale-diameter filament in air that is capable of carrying several joules of energy.

Investigation on the properties of the formation and coherence of intense fringe near nonlinear medium slab

Abstract Near medium intense (NMI) fringe is a kind of intense fringe which can be formed near Kerr medium in high-power laser beam propagation. The formation properties of NMI fringe and the relations between NMI fringe and related important parameters are systematically investigated. It is found that it is the co-existence of two wirelike phase-typed scatterers in the incident beam spot which is mainly responsible for the high intensity of NMI fringe. From the viewpoint of coherent superposition, the formation process of NMI fringe is analyzed, and the mechanism that NMI fringe is formed by the coherent superposition of the localized bright fringes in the exit field of Kerr medium slab is demonstrated. The fluctuations of NMI fringe properties with beam wavelength, scatterer spacing and object distance are studied, the coherence of NMI fringe are revealed, and the approximate periodicity of the appearance of remarkable NMI fringe for these parameters are obtained. Especially, it is found that the intensity of NMI fringe is very sensitive to scatterer spacing. Besides, the laws about how NMI fringe properties will be changed by the modulation properties of scatterers and the medium thickness are demonstrated.

Stimulated Raman and Brillouin scattering, nonlinear focusing, thermal blooming, and optical breakdown of a laser beam propagating in water

The physical processes associated with propagation of a high-power laser beam in a dielectric include self-focusing, stimulated Raman scattering, stimulated Brillouin scattering, thermal blooming, and multiphoton and collisional ionization. The interplay between these processes is analyzed using a reduced model consisting of a few differential equations that can be readily solved, enabling rapid variation of parameters and the development of theoretical results for guiding new experiments. The presentation in this paper is limited to propagation of the pump, the Stokes Raman, and the Brillouin pulses, ignoring the anti-Stokes Raman. Consistent with experimental results in the literature, it is found that self-focusing has a dramatic effect on the propagation of high-power laser beams in water. A significant portion of the pump laser energy is transferred to Stokes Raman forward scatter along with a smaller portion to Brillouin backscatter.

High-power laser-plasma interaction in nanosecond regimes ‘at a glance’ using proton deflectometry

Recent experiments indicate that controlling the propagation of high-power laser beams through millimeter long and low-density plasmas still remains challenging. In such plasma conditions, it is equally important to consider the impact of the plasma on laser propagation and laser properties, and the impact of the laser on plasma conditions. These complex phenomena are still difficult to implement in fluid models owing to the highly non-linear physics at play. Yet, electromagnetic fields prove to be good signatures of most of these low frequency phenomena. In particular, local pressure gradients and electron transport can be inferred from the electric fields. Such in-depth plasma characterization can be achieved through proton deflectometry. For that purpose, we have developed a three-dimensional simulation capability in order to compute protons’ trajectories modified by the local electric fields.

High-power laser interaction with low-density C–Cu foams

We study the propagation of high-power laser beams in micro-structured carbon foams by monitoring the x-ray output from deliberately introduced Cu content. In particular, we characterize this phenomenon measuring absolute time-resolved x-ray yields, time-resolved x-ray imaging, and x-ray spectroscopy. New experimental results for C–Cu foams show a faster heat front velocity than simulation that assumed homogeneous plasma. We suggest the foam micro-structure may explain this trend.

Relativistic-ponderomotive effects on cross-focusing of hollow Gaussian laser beams in plasma

AbstractThe present work aims to study the influence of relativistic–ponderomotive effects on cross-focusing of two co-propagating high-power hollow Gaussian laser beams [high-power laser beams (HGLBs)] in collisionless plasma. The effective dielectric constant has been derived on account of relativistic–ponderomotive nonlinearity. The phenomenon of cross-focusing for higher-order modes of HGLB is compared for the case when only relativistic nonlinearity is operative in the system and it is seen that the relativistic–ponderomotive effects make the focusing much stronger and relatively faster. The critical curves for various order of HGLB is discussed and compared with the case when only ponderomotive nonlinearity is present and it reveals that in the case of relativistic–ponderomotive case the spot size reduces effectively. The higher-order modes of propagation of HGLB are also found to be governed by the parameter of another propagating HGLB. The present study is useful in determining the propagation dynamics of HGLB.

Nonlinear formation of hot image and double intense image for gain-typed wirelike scatterers

The propagation of high-power laser beams modulated by gain-typed small-scale wirelike scatterer through a Kerr medium slab and free spaces is investigated. The formation of intense hot image is proved by analytical study and computer simulation. Moreover, the formation of double intense images is revealed by computer simulation. It is found that the double intense images are in a plane dozens of centimeters ahead the hot image plane and that the intensities of them are almost directly proportional to the intensity gain of the scatterer. The double intense image intensity and the hot image intensity have the similar variation tendency as the scatterer size increases, but the scatterer size difference between the maximums of them is dozens of micrometers. Moreover, interestingly, the distance between the two fringes for the double intense images has a relation with wavelength, similar to that for the distance between the fringes in single slot diffraction. Besides, the effect of object distance on the formation of double intense images is discussed. • The formations of hot image and double intense image are presented. • The double intense image plane is about 40 cm ahead the hot image plane. • The distance between the double intense image fringes increases as the wavelength increases. • The hot image and the double intense image peak at different scatterer size.

Propagation of LIL/LMJ beams under the interaction with contamination particles and component surface defects

This paper presents recent studies of the propagation of high-power laser beams like Laser Integration Line (LIL) and Laser MegaJoule (LMJ) beams, when interactions occur with environmental pollution particles and component defects. The studies are mainly achieved with the CEA-DAM MIRO beam propagation code. The highest intensifications in the downstream propagation are obtained for phase objects like dielectric particles, scratches or laser damage rather than for amplitude objects like metallic particles. Dramatic amplification of Kerr nonlinear effect leading to beam self-focusing inside the component is predicted depending on the particle size. The effect of statistical distributions of end-of-line phase defects on the LIL/LMJ 0.351-μm-wavelength focal spot intensity and size is quantified.

Stimulated Raman scattering of intense laser pulses in air.

Stimulated rotational Raman scattering (SRRS) is known to be one of the processes limiting the propagation of high-power laser beams in the atmosphere. In this paper, SRRS, Kerr nonlinearity effects, and group velocity dispersion of short laser pulses and pulse trains are analyzed and simulated. Fully time-dependent, three-dimensional, nonlinear propagation equations describing the Raman interaction, optical Kerr nonlinearity due to bound electrons, and group velocity dispersion are presented and discussed. The effective time-dependent nonlinear refractive index containing both Kerr and Raman processes is derived. Linear stability analysis is used to obtain growth rates and phase matching conditions for the SRRS, modulational, and filamentation instabilities. Numerical solutions of the propagation equations in three dimensions show the detailed evolution of the Raman scattering instability for various pulse formats. The dependence of the growth rate of SRRS on pulse duration is examined and under certain conditions it is shown that short (approximately psec) laser pulses are stable to the SRRS instability. The interaction of pulses in a train through the Raman polarization field is also illustrated.

Theory of the propagation of high-power laser radiation in a nonlinear medium

The propagation of high-power laser beams in media with the Kerr nonlinearity is discussed allowing for various types of nonlinear absorption. A parabolic equation for the complex amplitude of the electric field is derived from the Maxwell equations under conditions of greatest practical interest. This equation is analyzed under steady-state conditions and for laser pulses of 10-8 sec or shorter duration. A numerical solution of the steady-state problem shows that a multifocus structure appears in a beam of supercritical power. It is shown that this multifocus structure is universal, i.e., it appears irrespective of the nature of the nonlinear absorption in the medium and of other factors allowed for in the theory. The structure of the foci is studied in detail. Within light beams such foci usually move at velocities close to that of light. A theory of moving foci is presented. The trajectories of the motion of the foci and their parameters are calculated and the broadening of the laser pulse spectra due to the motion of the foci is evaluated. Explanations are given of various experimental data on the stimulated scattering, optical breakdown, and broadening of the laser radiation spectra.