scholarly journals Iterative method for determination of the laser beam profile and τV-T

2008 ◽  
Vol 6 (1) ◽  
pp. 71-76
Author(s):  
Mihailo Rabasovic ◽  
Dragan Markushev
Keyword(s):  
Relaxation Time ◽  
Laser Beam ◽  
Photoacoustic Signal ◽  
Linear Process ◽  
Beam Profile ◽  
Photoacoustic Tomography ◽  
Spatial Profile ◽  
Photoacoustic Effect ◽  
Laser Beam Profile

Measuring the vibrational-to-translational relaxation time ?V-T in gases is one of the first applications of the photoacoustic effect. The spatial profile of the laser beam is crucial in these measurements because the multiphoton excitation is investigated. The multiphoton absorption is a non-linear process. Because of this, the top hat profile is preferable. It allows one to deal with nonlinearity in a simple manner. In order to reveal the real laser beam profile, we have slightly changed the theoretical profiles in such a manner that the best matching is obtained between theoretical and experimental photoacoustic signals. Still, there was a question: Is it possible to deduce the laser beam profile directly from the photoacoustic signal, thus avoiding manual changing of the laser beam profile? According to this paper, it is possible. The appropriate method has been found in another photoacoustics application: photoacoustic tomography. Thus, the method for the simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time is presented in this paper. It employs pulsed photoacoustics and an algorithm developed for photoacoustic tomography.

scholarly journals Computational intelligence based simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time by pulsed photoacoustics

2012 ◽  
Vol 10 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Mladena Lukic ◽  
Zarko Cojbasic ◽  
Mihailo Rabasovic ◽  
Dragan Markushev ◽  
Dragan Todorovic
Keyword(s):  
Genetic Algorithms ◽  
Relaxation Time ◽  
Laser Beam ◽  
Simultaneous Determination ◽  
Computational Intelligence ◽  
Spatial Profile ◽  
Multilayer Perception ◽  
Real Coded Genetic Algorithms ◽  
Pulsed Photoacoustics

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.

Study of optimal laser beam profile for laser induced thermal printing of organic film

2009 ◽  
Author(s):  
Jonghoon Yi ◽  
Kangin Lee ◽  
Kwangwon Lee ◽  
Lee Soon Park ◽  
Jin Hyuk Kwon
Keyword(s):  
Laser Beam ◽  
Beam Profile ◽  
Organic Film ◽  
Laser Beam Profile

scholarly journals INFLUENCE OF LASER BEAM PROFILE ON LIGHT SCATTERING BY HUMAN SKIN DURING PHOTOMETRY BY ELLIPSOIDAL REFLECTORS

2018 ◽  
Vol 9 (1) ◽  
pp. 56-65 ◽  
Author(s):  
M. A. Bezuglyi ◽  
N. V. Bezuglaya ◽  
S. Kostuk
Keyword(s):  
Monte Carlo Simulation ◽  
Adipose Tissue ◽  
Laser Beam ◽  
Human Skin ◽  
Cross Section ◽  
Beam Profile ◽  
Laser Beam Profile ◽  
Reflected Light ◽  
Section Profile ◽  
Cross Section Profile

The correct accounting of laser emitter parameters for improvement of diagnostic authenticity of methods of optical biomedical diagnostic is important problem for applied biophotonic tasks. The purpose of the current research is estimation of influence of energy distribution profile in transversal section of laser beam on light scattering by human skin layers at photometry by ellipsoidal reflectors.Biomedical photometer with ellipsoidal reflectors for investigation of biological tissue specimens in transmitted and reflected light uses laser probing radiation with infinitely thin, Gauss-type and uniform cross-section profile. Distribution of beams with denoted profiles, which consist of 20 million photons with wavelength 632.8 nm, was modeled by using of Monte-Carlo simulation in human skin layers (corneous layer, epidermis, derma and adipose tissue) of various anatomic thickness and with ellipsoidal reflectors with focal parameter equal to 16.875 mm and eccentricity of 0.66.The modeling results represent that illuminance distribution in zones of photometric imaging is significantly influenced by the laser beam cross-section profile for various thickness of corneous layer and epidermis in transmitted and reflected light, and also derma in reflected light. Illuminance distribution for adipose tissue in reflected and transmitted light, and also derma in transmitted light, practically do not depend of laser beam profile for anatomic thicknesses, which are appropriate for human skin on various sections of body.There are represented results of modified Monte-Carlo simulation method for biomedical photometer with ellipsoidal reflectors during biometry of human skin layers. For highly scattered corneous layer and epidermis the illumination of middle and external rings of photometric images changes depending from the laser beam profile for more than 50 % in transmitted and 30 % in reflected light. For weakly scattering skin layers (derma and adipose layer) the influence of profile can be observed only for derma in reflected layer and is equal not more than 15 %. 

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