INVESTIGATION OF PECULIARITIES OF LIGHT SCATTERING BY NANOSTRUCTURAL CHANGES IN THE CRYSTAL LATTICE OF FERROELECTRIC BARIUM SODIUM NIOBATE CRYSTAL

2004 ◽  
Vol 03 (06) ◽  
pp. 815-818 ◽  
Author(s):  
S. V. IVANOVA
Keyword(s):  
Light Scattering ◽  
Laser Beam ◽  
Beam Width ◽  
Far Field ◽  
Sodium Niobate ◽  
Incident Laser Beam ◽  
Incident Laser ◽  
Elastic Light Scattering ◽  
Temperature Range ◽  
Thermal Changes

Thermal changes of light scattering images in the far-field were observed under steady illumination by an incident laser beam of finite beam width on barium sodium niobate crystals in the temperature range of 20–500°C. Different patterns of light scattering in far-field were observed — from striped to round-like form with dependence on temperature, conditions of grown, direction of beam and polarization. The round-like form was observed on cooling from 450°C to 240°C. Striped forms of light scattering were observed below 200°C. Correlation of the behavior of elastic light scattering was observed in this temperature range.

A high-speed-modulated retro-reflector for lasers using an acousto-optic modulator

2003 ◽  
Vol 81 (4) ◽  
pp. 625-638 ◽  
Author(s):  
G Spirou ◽  
I Yavin ◽  
M Weel ◽  
A Vorozcovs ◽  
A Kumarakrishnan ◽  
...  
Keyword(s):  
Laser Beam ◽  
Acoustic Waves ◽  
High Speed ◽  
Incident Beam ◽  
Bragg Diffraction ◽  
Heterodyne Detection ◽  
Incident Laser Beam ◽  
Signal To Noise ◽  
Incident Laser ◽  
Acousto Optic Modulator

We have used an acousto-optic modulator (AOM) to impose a frequency-modulated signal on an incident laser beam. The incident laser beam is focussed into the AOM where it undergoes Bragg diffraction and is then retro-reflected. The diffracted beam is also retro-reflected so that it is diffracted again by the AOM and overlaps the incident beam. The overlapped beams are frequency shifted with respect to each other. These features allow us to detect the frequency-modulated signal with high signal-to-noise ratio using heterodyne detection. Since the optical setup is simple and can be made very compact, this device may be ideal for certain forms of high-speed, free-space optical communication. We demonstrate a 1 MHz data transmission rate in the Bragg regime. We measured the acceptance angle of the device and find that it is limited only by the divergence of the focussed laser beam and the divergence of the acoustic waves in the AOM crystal. We have also studied the range of acoustic frequencies and drive power of the AOM, for which the retro-reflected beam can be detected with adequate signal to noise. PACS Nos.: 42.60.–V, 42.62.Cf, 42.62.Fi, 42.79.Sz, 42.79.Hp

scholarly journals Electric, magnetic Wakefields, and electron acceleration in quantum plasma

2012 ◽  
Vol 30 (2) ◽  
pp. 267-273 ◽  
Author(s):  
P. Kumar ◽  
C. Tewari
Keyword(s):  
Laser Pulse ◽  
Laser Beam ◽  
Quantum Effects ◽  
Electron Acceleration ◽  
Quantum Plasma ◽  
Incident Laser Beam ◽  
Incident Laser ◽  
High Energies ◽  
Test Electron ◽  
Radial Forces

AbstractA detailed study of Wakefield excitation in very dense quantum plasma is presented. Electric and magnetic Wakefields have been obtained for a particular profile of the laser pulse, using perturbative technique involving orders of the incident laser beam. The Wakefields can trap electrons and accelerate them to extremely high energies. It is observed that the quantum effects significantly change the classical nature of the Wakefield. The axial and radial forces acting on a test electron due to the Wakefields have been evaluated.

scholarly journals Higher harmonic generation by self-focused q-Gaussian laser beam in preformed collisionless plasma channel

2014 ◽  
Vol 32 (4) ◽  
pp. 621-629 ◽  
Author(s):  
Arvinder Singh ◽  
Naveen Gupta
Keyword(s):  
Differential Equation ◽  
Laser Beam ◽  
Plasma Wave ◽  
Harmonic Generation ◽  
Plasma Channel ◽  
Field Region ◽  
Incident Laser Beam ◽  
Gaussian Laser Beam ◽  
Incident Laser ◽  
Higher Harmonic

AbstractThis paper presents an investigation of self-focusing of a q-Gaussian laser beam and its effect on harmonic generation in a preformed collisionless parabolic plasma channel. In the presence of a q-Gaussian laser beam, the carriers get redistributed from high field region to low field region on account of ponderomotive force as a result of which a transverse density gradient is produced in the channel which in turn generates plasma wave at pump frequency. Generated plasma wave interacts with the incident laser beam and generate higher harmonics of the incident laser beam. Moment theory has been used to derive differential equation for the spot size of laser beam propagating through the channel. The differential equation so obtained has been solved numerically. The effect of the intensity of laser beam, deviation of intensity distribution of laser beam along its wave front from Gaussian distribution, plasma density and depth of channel on beam width of laser beam and harmonic yield has been investigated. The effect of order of higher harmonic on harmonic yield has been also investigated.

Multi-Time Step Modeling of Plume Dynamics in Nanosecond-Scale Carbon Ablation

2008 ◽  
Vol 8 (11) ◽  
pp. 6075-6081
Author(s):  
Kedar Pathak ◽  
Alex Povitsky
Keyword(s):  
Laser Ablation ◽  
Laser Beam ◽  
Computer Time ◽  
Time Span ◽  
Shielding Effect ◽  
Incident Laser Beam ◽  
Incident Laser ◽  
Time Step ◽  
Degree Of Ionization ◽  
Plume Dynamics

The time span of plume dynamics in laser ablation of carbon ranges from nanoseconds to milliseconds. Multi-time step approach is developed to study the plume dynamics over this entire range with minimum requirements of numerical computational resources. This approach is applied to study one of the important aspects of nanosecond-scale laser ablation, namely the shielding of incident laser beam with previously ejected plumes. Capturing the shielding effect requires smaller than nanosecond-scale time step because of large velocity and pressure gradients in plume. Use of this time step over the entire domain needs enormous amount of computer time to cover the whole time span of plume dynamics. Multi-time step modeling for such an application is therefore useful. In general, for nanosecond-scale laser ablation this shielding is caused by ionized particles and by gas molecules. It is shown for carbon plume resulting from the nanosecond-scale lasers that the degree of ionization is small. Ionization of ablated carbon is estimated by Saha equation for the given initial plume conditions. The shielding of incident laser beam is therefore calculated by normal molecular absorption. The laser-light intensity that reaches the target for subsequent pulses is evaluated.

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