scholarly journals Modulation instability of two laser beams in plasma

2013 ◽  
Vol 31 (4) ◽  
pp. 753-758 ◽  
Author(s):  
Vijay Singh
Keyword(s):  
Growth Rate ◽  
Phase Modulation ◽  
Wave Equations ◽  
Modulation Instability ◽  
Group Velocity Dispersion ◽  
Laser Beams ◽  
Homogeneous Plasma ◽  
Single Beam ◽  
Linearly Polarized ◽  
Set Up

AbstractIn the present paper, spatial amplitude modulation instability arising due to relativistic self-phase modulation and relativistic cross phase modulation of two co-propagating, linearly polarized laser beams (with arbitrary relative polarization) interacting with homogeneous plasma, has been studied. Wave equations including finite perturbation length effects, group velocity dispersion, and coupled nonlinear source term have been set up. Coupled dispersion relation for the two laser beams has been derived and solved numerically. The growth rate of modulation instability has been obtained and compared with the growth rate of a single beam propagating in homogeneous plasma. It has been shown that modulation instability of a single beam may either be enhanced or suppressed by co-propagation of another laser beam having appropriate polarization.

Harmonic generation by the propagation of two-colour laser beams in an underdense plasma

2013 ◽  
Vol 79 (5) ◽  
pp. 933-938 ◽  
Author(s):  
PALLAVI JHA ◽  
NIRMAL KUMAR VERMA ◽  
AKANKSHA SAROCH
Keyword(s):  
Laser Beams ◽  
Harmonic Amplitude ◽  
Arbitrary Integer ◽  
Third Harmonic ◽  
The Third ◽  
Fundamental Frequencies ◽  
Linearly Polarized ◽  
Colour System ◽  
Set Up ◽  
Underdense Plasma

AbstractAn analytical theory is developed for studying the phenomenon of generation of efficient odd and even high harmonics by the propagation of two-colour linearly polarized laser beams in a homogeneous underdense plasma. The wave equation governing the evolution of the amplitude of various harmonics driven by the current density at corresponding frequencies is set up. The ratio of the fundamental frequencies of the two laser beams is considered to be an arbitrary integer. A numerical evaluation of amplitudes of the third, fourth and fifth harmonics has been presented. It is seen that the third harmonic amplitude generated by the two-colour system is enhanced in comparison to that obtained by a single laser beam. The detuning distance for the former is also increased in comparison to the latter case.

scholarly journals Nonlinear backward Raman scattering in the short laser pulse interaction with a cold underdense transversely magnetized plasma

2011 ◽  
Vol 29 (3) ◽  
pp. 373-380 ◽  
Author(s):  
Alireza Paknezhad ◽  
Davoud Dorranian
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Laser Pulse ◽  
Raman Scattering ◽  
Initial Conditions ◽  
Nonlinear Effects ◽  
Magnetized Plasma ◽  
Short Laser Pulse ◽  
Linearly Polarized ◽  
Set Up

AbstractRaman backward scattering is investigated in the interaction of linearly polarized ultra short laser pulse with a homogenous cold underdense magnetized plasma by taking into account the relativistic effect and the effect of nonlinearity up to third order. The plasma is embedded in a uniform magnetic field perpendicular to both of propagation direction and electric vector of the radiation field. Nonlinear wave equation is set up and differential equations, which model the instability, are derived. Using of the Fourier transformation, analytical solutions are obtained for a set of physically relevant initial conditions and the temporal growth rate of instability is calculated. Results are significantly different in comparison with lower order computations. The growth rate of backward Raman scattering shows an increase due to the presence of external magnetic field as well as nonlinear effects.

scholarly journals Formation of half-period surface relief gratings in azobenzene containing polymer films

2020 ◽  
Vol 126 (9) ◽  
Author(s):  
Joachim Jelken ◽  
Carsten Henkel ◽  
Svetlana Santer
Keyword(s):  
Polymer Film ◽  
Polymer Films ◽  
Surface Relief ◽  
Incident Light ◽  
Glassy State ◽  
Polarized Light ◽  
Half Period ◽  
Polarization Distribution ◽  
Linearly Polarized ◽  
Set Up

Abstract We study the peculiar response of photo-sensitive polymer films irradiated with a certain type of interference pattern where one interfering beam is S-polarized, while the second one is P-polarized. The polymer film, although in a glassy state, deforms following the local polarization distribution of the incident light, and a surface relief grating (SRG) appears whose period is half the optical one. All other types of interference patterns result in the matching of both periods. The topographical response is triggered by the alignment of photo-responsive azobenzene containing polymer side chains orthogonal to the local electrical field, resulting in a bulk birefringence grating (BBG). We investigate the process of dual grating formation (SRG and BBG) in a polymer film utilizing a dedicated set-up that combines probe beam diffraction and atomic force microscopy (AFM) measurements, and permits acquiring in situ and in real-time information about changes in local topography and birefringence. We find that the SRG maxima appear at the positions of linearly polarized light (tilted by 45° relative to the grating vector), causing the formation of the half-period topography. This permits to inscribe symmetric and asymmetric topography gratings with sub-wavelength period, while changing only slightly the polarization of one of the interfering beams. We demonstrate an easy generation of sawtooth profiles (blazed gratings) with adjustable shape. With these results, we have taken a significant step in understanding the photo-induced deformation of azo-polymer films.

scholarly journals Self-compression of two co-propagating laser pulse having relativistic nonlinearity in plasma

2017 ◽  
Vol 35 (4) ◽  
pp. 722-729
Author(s):  
S. Kumar ◽  
P. K. Gupta ◽  
R. K. Singh ◽  
R. Uma ◽  
R. P. Sharma
Keyword(s):  
Laser Beam ◽  
Pulse Width ◽  
Pulse Compression ◽  
Group Velocity Dispersion ◽  
Refractive Index Profile ◽  
Intense Laser ◽  
Laser Beams ◽  
Critical Parameters ◽  
Beam Power ◽  
Laser Beam Intensity

AbstractThe study proposes a semi-analytical model for the pulse compression of two co-propagating intense laser beams having Gaussian intensity profile in the temporal domain. The high power laser beams create the relativistic nonlinearity during propagation in plasma, which leads to the modification of the refractive index profile. The co-propagating laser beams get self- compressed by virtue of group velocity dispersion and induced nonlinearity. The induced nonlinearity in the plasma broadens the frequency spectrum of the pulse via self-phase modulation, turn to shorter the pulse duration and enhancement of laser beam intensity. The nonlinear Schrodinger equations were set up for co-propagating laser beams in plasmas and have been solved in Matlab by considering paraxial approximation. The propagation characteristics of both laser beams inside plasma are divided into three regions through the critical divider curve, which has been plotted between pulse width τ01 and laser beam power P01. Based on the preferred value of critical parameters, these regions are oscillatory compression, oscillatory broadening, and steady broadening. In findings, it is observed that the compression of the laser beam depends on the combined intensity of both beams, plasma density, and initial pulse width.

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