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Coronavirus (CoVs) is a type of enveloped RNA virus that is found in animals and humans. There are near about six different species of CoVs are available and all of them can cause different health issue to human. In human this virus can effect respiratory, hepatic, enteric and neurological system. The past Middle East respiratory syndrome coronavirus and severe acute respiratory syndrome coronavirus has been transmitted from animal to human. Presently there is a new strain of corona virus, named SARS-CoV-2, causing serious health crises to human. This virus is highly contagious and has resulted in a rapid pandemic of COVID-19. The number of infected people and death caused by COVID-19 is increasing day by day. This review will provide a detailed overview of COVID-19 and its serious effect to the human health.

This work presents a theoretical approach to a highly multimode-guided wave-based fourth harmonic (FH) generation method by exploiting a zero-order Bessel-Gauss beam through the total internal reflection quasi phase-matching technique. An anisotropic crystal featuring a rectangular structure of beta barium borate has been used to carry out this analysis. In contrast to the conventional frequency conversion scheme using a Gaussian beam, the projected scheme yields a maximum six times superior efficiency of 6.9547% in a crystal length of nearly 6.3 mm, corresponding to a 266-nm FH wavelength. The analysis has also taken into account optical losses, such as absorption, Goos-Hänchen-shift, surface roughness, and the effect of the nonlinear law of reflection. Finally, a systematic study has been performed to describe the influence of parametric modification, such as variations in slab length and thickness, to provide a more comprehensive picture of the overall analysis.