Laser beam spatial profile determination by pulsed photoacoustics: exact solution

2010 ◽  
Vol 21 (6) ◽  
pp. 065603 ◽  
Author(s):  
Mihailo D Rabasović ◽  
Dragan D Markushev
2012 ◽  
Vol 10 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Mladena Lukic ◽  
Zarko Cojbasic ◽  
Mihailo Rabasovic ◽  
Dragan Markushev ◽  
Dragan Todorovic

This paper is concerned with the possibilities of computational intelligence application for simultaneous determination of the laser beam spatial profile and vibrational-to-translational relaxation time of the polyatomic molecules in gases by pulsed photoacoustics. Results regarding the application of neural computing and genetic optimization are presented through the use of feed forward multilayer perception networks and real-coded genetic algorithms. Feed forward multilayer perception networks are trained in an offline batch training regime to estimate simultaneously, and in real-time, laser beam spatial profile R(r) (profile shape class) and vibrational-to-translational relaxation time ?V?T from a given (theoretical) photoacoustic signals ?p(r,t). The proposed method significantly shortens the time required for the simultaneous determination of the laser beam spatial profile and relaxation time and has the advantage of accurately calculating the aforementioned quantities. Real coded genetic algorithms are used to calculate ?V?T by fitting the ?p(r,t) with the theoretical one. The previously developed methods determine the laser beam profile and relaxation time with sufficient precision, but the methods based on the application of artificial intelligence are more suitable for practical applications, such as the real-time in-situ measurements of atmospheric pollutants.


2015 ◽  
Vol 33 (4) ◽  
pp. 741-747 ◽  
Author(s):  
Ram Kishor Singh ◽  
R. P. Sharma

AbstractThis paper presents a theoretical model for efficient terahertz (THz) radiation by self-focused amplitude-modulated laser beam in preformed ripple density plasma. The density of plasma is modified due to ponderomotive nonlinearity which arises because of the nonuniform spatial profile of the laser beam in magnetized plasma and leads to the self-focusing of the laser beam. The rate of self-focusing depends on the intensity of the amplitude-modulated beam as well as on the externally applied magnetic field strength. The electron also experiences time-dependent ponderomotive force by the laser beam at modulated frequency. A nonlinear current at THz frequency arises on account of the coupling between the ripple density plasma and nonlinear oscillatory velocity of the electrons. The yield of the generated THz radiation enhances with enhancement in self-focusing of the laser beam and applied magnetic field.


2010 ◽  
Vol 97 (23) ◽  
pp. 231106 ◽  
Author(s):  
F. Tissandier ◽  
S. Sebban ◽  
M. Ribière ◽  
J. Gautier ◽  
Ph. Zeitoun ◽  
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1994 ◽  
Vol 60 (5) ◽  
pp. 657-661
Author(s):  
Osami ICHIKO ◽  
Naoya HAMADA ◽  
Katsuhiro MINAMIDA

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