scholarly journals Relativistic Propagation of Linearly/Circularly Polarized Laser Radiation in Plasmas

ISRN Optics ◽  
2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Sonu Sen ◽  
Meenu Asthana Varshney ◽  
Dinesh Varshney
Keyword(s):  
Dielectric Constant ◽  
Critical Power ◽  
Laser Pulses ◽  
Interaction Process ◽  
Laser Beams ◽  
Laser Beam Propagation ◽  
Circularly Polarized ◽  
Nonlinear Dielectric ◽  
Laser Plasma Interaction ◽  
Self Focusing

Paraxial theory of relativistic self-focusing of Gaussian laser beams in plasmas for arbitrary magnitude of intensity of the beam has been presented in this paper. The nonlinearity in the dielectric constant arises on account of relativistic variation of mass. An appropriate expression for the nonlinear dielectric constant has been used to study laser beam propagation for linearly/circularly polarized wave. The variation of beamwidth parameter with distance of propagation, self-trapping condition, and critical power has been evaluated. The saturating nature of nonlinearity yields two values of critical power of the beam ( and ) for self-focusing. When the beam diverges. When the beam first converges then diverges and so on. When the beam first diverges and then converges and so on. Numerical estimates are made for linearly/circularly polarized wave applicable for typical values of relativistic laser-plasma interaction process in underdense and overdense plasmas. Since the relativistic mechanism is instantaneous, this theory is applicable to understanding of self-focusing of laser pulses.

scholarly journals Relativistic self-focusing of transmitted laser radiation in plasmas

2000 ◽  
Vol 18 (1) ◽  
pp. 101-107 ◽  
Author(s):  
MEENU V. ASTHANA ◽  
DINESH VARSHNEY ◽  
M.S. SODHA
Keyword(s):  
Dielectric Constant ◽  
Laser Radiation ◽  
Critical Power ◽  
Interaction Process ◽  
Gaussian Laser Beam ◽  
Laser Plasma Interaction ◽  
Paraxial Ray Approximation ◽  
Self Focusing ◽  
Beam Incident ◽  
Paraxial Ray

This paper presents an analysis of relativistic self-focusing of a Gaussian laser beam incident normally on a plane interface of a linear medium and a nonlinear, nonabsorbing plasma with an intensity dependent dielectric constant. Considering the nonlinearity to arise from the relativistic variation of mass and the Lorentz force on electrons. Following Wentzel–Kramers–Brillouin (WKB) and paraxial ray approximation the phenomenon of relativistic self-focusing of the transmitted laser radiation has been analyzed for the arbitrary magnitude of nonlinearity. Change in the intensity distribution along the wavefront of the Gaussian beam, due to refraction at the interface has also been taken into account. The variation of beamwidth parameter with distance of propagation, self trapping condition and critical power has been evaluated. Numerical estimates for typical parameters of laser plasma interaction process indicate the refraction at the interface to have a significant effect on self-focusing.

Steady-state self-focusing of rippled laser beams in plasmas: arbitrary nonlinearity

1992 ◽  
Vol 48 (1) ◽  
pp. 107-118 ◽  
Author(s):  
M. S. Sodha ◽  
S. Konar ◽  
K. P. Maheshwari
Keyword(s):  
Dielectric Constant ◽  
Thermal Conduction ◽  
Critical Power ◽  
Laser Beams ◽  
Main Beam ◽  
Effective Dielectric Constant ◽  
Beam Power ◽  
Nonlinear Part ◽  
Self Focusing ◽  
Paraxial Ray

This paper presents an analysis of the self-focusing of a rippled Gaussian laser beam in a plasma when the nonlinear part of the effective dielectric constant is arbitrarily large. Considering the nonlinearity to arise from ponderomotive, collisional or thermal-conduction phenomena and following the approach of Akhmanov, Sukhorukov and Khokhlov (which is based on the WKB and paraxial-ray approximation) the phenomenon of self-focusing of rippled laser beams is studied for arbitrary magnitude of nonlinearity. For ponderomotive and collisional nonlinearities, the present theory leads to two values of the critical power for self-focusing of the beam, Pcrl and Pcr2, which depend on the amplitudes and phase difference of the main beam and the ripple. When the beam power P lies between the two critical values (i.e. Pcr1 < P < Pcr2), the medium behaves as an oscillatory waveguide; the beam first converges and then diverges, again converges, and so on. For P < Pcr2, the beam first diverges, then converges, then diverges, and so on. When thermal conduction is the dominant mechanism of nonlinearity of the dielectric constant, only one value of the threshold critical power Pcr for self-focusing of the beam exists. When the beam power P < Pcr, the medium behaves as an oscillatory waveguide.

scholarly journals Nonlinear relativistic self-focusing of laser radiation in plasmas: Arbitrary intensity

1994 ◽  
Vol 12 (4) ◽  
pp. 623-632 ◽  
Author(s):  
M. Asthana ◽  
K.P. Maheshwari ◽  
M.S. Sodha
Keyword(s):  
Dielectric Constant ◽  
Critical Power ◽  
Laser Pulses ◽  
Density Fluctuations ◽  
Effective Dielectric Constant ◽  
Gaussian Laser Beam ◽  
Nonlinear Part ◽  
Self Focusing ◽  
Paraxial Ray ◽  
Arbitrary Intensity

A paraxial theory of relativistic self-focusing of a Gaussian laser beam in plasmas, when the nonlinear part of the effective dielectric constant is arbitrarily large, is presented. The plasma is taken to be homogeneous without any density fluctuations being necessary. The approach of Akhmanov et al. based on the WKB and paraxial ray approximations has been followed. It is seen that the saturating nature of nonlinearity leads to two values of critical power of the beam (Pcrl and Pcr2) for self-focusing. When the power of the beam P lies between the two critical values (i.e., Pcr1 < P < Pcr2), the medium behaves as an oscillatory waveguide; the beam first converges and then diverges, converges again, and so on. For P > Pcr2 the beam first diverges, then converges, then diverges, and so on. Because the relativistic mechanism is instantaneous, the theory is applicable to the understanding of selffocusing of laser pulses also.

INTERACTION OF INTENSE SHORT LASER PULSES WITH AIR AND DIELECTRIC MATERIALS

2007 ◽  
Vol 21 (03n04) ◽  
pp. 615-625 ◽  
Author(s):  
S. EISENMANN ◽  
Y. KATZIR ◽  
A. ZIGLER ◽  
G. FIBICH ◽  
E. LOUZON ◽  
...  
Keyword(s):  
Critical Power ◽  
Laser Pulses ◽  
Dielectric Materials ◽  
Laser Beams ◽  
Threshold Fluence ◽  
Short Pulses ◽  
Self Focusing ◽  
Chirped Pulses ◽  
Short Laser Pulses ◽  
Wide Gap

A study of the propagation of intense short laser pulses in air and the interaction of these pulses with distant targets is described. It is shown that the beam filamentation pattern can be controlled by introducing beam astigmatism. In addition, it is demonstrated that the collapse distance of intense femtosecond laser beams scales as P -1/2 for input powers that are moderately above the critical power for self focusing, and that at higher powers the collapse distance scales as P -1. Related to the interaction of intense short pulses with distant targets, it is measured that the threshold fluence for optical damage in wide gap materials is lower by up to 20% for negatively chirped pulses than for positively chirped, at pulse durations ranging from 60 fs to 1 ps.

scholarly journals Self-focusing limits at the laser-plasma interaction for treatment of cataract with nanosecond and picosecond pulses

1992 ◽  
Vol 10 (1) ◽  
pp. 163-178 ◽  
Author(s):  
Rosemarie H. Hora ◽  
Hans G. L. Coster ◽  
Clement J. Walter ◽  
Heinrich Hora
Keyword(s):  
Optical Breakdown ◽  
Laser Pulses ◽  
The Self ◽  
Laser Beams ◽  
Temperature Plasma ◽  
Picosecond Pulses ◽  
Laser Plasma Interaction ◽  
Self Focusing ◽  
Nanosecond Range ◽  
Transparent Area

Laser pulses are focused in the interior of a human eye in areas of opacity to produce there an optical breakdown resulting in a high-temperature plasma, after which the filling up with liquid results in a transparent area. The empirically given limits for Q-switch laser pulses in the nanosecond range and for mode-locked pulses in the picosecond range are analyzed, and it is shown that these limits are below the self-focusing condition of laser beams in plasmas. A further analysis evaluates theoretically where the maximum limits are given in order to provide the parameters for the highest possible pulse energy that avoids damage in the eye by self-focusing.

Relativistic cross-focusing of two coaxial Gaussian laser beams in a plasma

1998 ◽  
Vol 60 (4) ◽  
pp. 811-818 ◽  
Author(s):  
RAJ KUMAR ◽  
H. D. PANDEY ◽  
R. P. SHARMA ◽  
M. KUMAR
Keyword(s):  
Laser Beam ◽  
Relativistic Effect ◽  
Laser Pulses ◽  
The Self ◽  
Laser Beams ◽  
Particle Accelerators ◽  
Wave Excitation ◽  
Homogeneous Plasma ◽  
Self Focusing ◽  
Ponderomotive Nonlinearity

The paper presents a paraxial theory of the relativistic cross-focusing of two coaxial Gaussian laser beams of different frequencies in a homogeneous plasma. We discuss the self-focusing of a weaker laser beam in the plasma due to the optical inhomogeneities introduced by another stronger copropagating laser beam. In the presence of the second stronger beam (Pcr21<P2<Pcr22), the plasma behaves as an oscillatory waveguide for the first, weaker, beam (P1<Pcr11) as it propagates in the plasma. When both the beams are strong (Pcr11,21<P1,2<Pcr12,22), the nonlinearities introduced by the relativistic effect are additive in nature, such that one beam can undergo oscillatory self-focusing and the other simultaneously defocusing, and vice versa. A comparison reveals that cross-focusing due to relativistic nonlinearity is possible for a wider range of powers of the laser pulses than is cross-focusing due to ponderomotive nonlinearity. Relativistic cross-focusing is important in plasma beat-wave excitation and collective laser particle accelerators.

scholarly journals The effects of circularly polarized laser pulse on generated electron nano-bunches in oscillating mirror model

2014 ◽  
Vol 32 (2) ◽  
pp. 285-293 ◽  
Author(s):  
M. Shirozhan ◽  
M. Moshkelgosha ◽  
R. Sadighi-Bonabi
Keyword(s):  
Laser Pulse ◽  
Laser Plasma ◽  
Dense Plasma ◽  
Ponderomotive Force ◽  
Laser Pulses ◽  
Incident Laser ◽  
Circularly Polarized ◽  
Plasma Surface ◽  
Laser Plasma Interaction ◽  
Incident Laser Pulse

AbstractThe effects of the polarized incident laser pulse on the electrons of the plasma surface and on the reflected pulse in the relativistic laser-plasma interaction is investigated. Based on the relativistic oscillating mirror and totally reflecting oscillating mirror (TROM) regimes, the interaction of the intense polarized laser pulses with over-dense plasma is considered. Based on the effect of ponderomotive force on the characteristic of generated electron nano-bunches, considerable increasing in the localization and charges of nano-bunches are realized. It is found that the circularly polarized laser pulse have Ne/Ncr of 1500 which is almost two and seven times more than the amounts for P-polarized and S-polarized, respectively.

scholarly journals Numerical programming of self-focusing at laser–plasma interaction

2000 ◽  
Vol 18 (1) ◽  
pp. 59-72 ◽  
Author(s):  
F. OSMAN ◽  
R. CASTILLO ◽  
H. HORA
Keyword(s):  
Collisionless Plasma ◽  
Relativistic Effects ◽  
Laser Beams ◽  
Moderate Intensity ◽  
Lateral Direction ◽  
Laser Plasma Interaction ◽  
Relativistic Mass ◽  
Self Focusing ◽  
Wide Range ◽  
Nonlinear Force

This paper presents an investigation into the behavior of a laser beam of finite diameter in plasma with respect to forces and optical properties, which lead to self-focusing of the beam. The transient setting of ponderomotive nonlinearity in a collisionless plasma has been studied, and consequently the self-focusing of the pulse, and the focusing of the plasma wave occurs. The description of a self-focusing mechanism of laser radiation in the plasma due to nonlinear forces acting on the plasma in the lateral direction, relative to the laser has been investigated in the nonrelativistic regime. The behavior of the laser beams in plasma, which is the domain of self-focusing at high or moderate intensity, is dominated by the nonlinear force. The investigation of self-focusing processes of laser beams in plasma results from the relativistic mass and energy dependency of the refractive index at high laser intensities. Here, the relativistic effects are considered to evaluate the relativistic self-focusing lengths for the Nd glass radiation, at different plasma densities of various laser intensities. A numerical program in c++ that incorporates both the ponderomotive force in self-focusing mechanism and relativistic effects has been developed to explore in depth self-focusing over a wide range of parameters.

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