Generation of second harmonics of self-focused quadruple-Gaussian laser beams in collisional plasmas with density ramp
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RESEARCH ARTICLE
Generation of second harmonics of self-focused quadrupleGaussian laser beams in collisional plasmas with density ramp Naveen Gupta1 • Sandeep Kumar1
Received: 27 February 2020 / Accepted: 31 July 2020 Ó The Optical Society of India 2020
Abstract This paper presents a scheme for generation of second harmonics of intense laser beams propagating through collisional plasmas. In order to see the effect of uniformity as well as nonuniformity of the irradiance over the cross section of the laser beam on yield of generated harmonics, the field distribution in the medium has been expressed in terms of quadruple Gaussian (Q.G) profile instead of Gaussian profile. Moment theory has been adopted to find semi-analytical solution of the wave equation for the slowly varying envelope of the laser beam. When laser beam with frequency x0 propagates through plasma it makes the plasma electrons to oscillate at pump frequency x0 . These oscillations of the plasma electrons in the presence of thermal velocity generate an electron plasma wave (EPW) at frequency x0 . The generated EPW beats with the pump beam to produce its second harmonics. By using hydrodynamic fluid model of plasma, nonlinear current density for the SHG has been obtained. Emphasis are put on investigation of the effect of various laser and plasma parameters on propagation dynamics of pump beam and conversion efficiency of second harmonics. Keywords Self focusing Quadruple Gaussian Density ramp Collisional plasma
& Naveen Gupta [email protected] Sandeep Kumar [email protected] 1
Lovely Professional University, Phagwara, India
Introduction The quest for short wavelength coherent radiation sources for medical treatment and diagnostics [1], homeland security [2], plasma diagnostics [3], etc has a long history. For past few decades, only two main facilities, namely free electron lasers [4] and synchrotrons [5] are being considered for this purpose. Such large facilities have provided scientists with the tools to probe and image matter on very small length scales and over very short periods of time, enabling ground breaking work in the fields as diverse as biology and archaeology. A large infrastructure involving accelerators, beam lines and massive gantries of more than 1000 tons are required for these facilities. Hence, significant capital investment is required for the construction and maintenance of these so-called third (synchrotrons) and fourth (FELs) generation radiation sources. As a result, these facilities are not affordable for less affluent institutes like universities and hospitals. Therefore, research related to them is not growing at a faster pace. By producing similar extreme ultraviolet (XUV) and soft X-ray (SXR) radiations on bench top scale, the phenomenon of HHG can serve as a cost effective means of extending access and application of light in this part of spectrum. The reduction in cost is not only due to the replacement of accelerator but also due to the fact that there will be no requirement of large building f
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