Download (4Mb) - Etheses - Saurashtra University

Chapter I Brief Introduction...
light, with a dark hole in the centre. This corkscrew of light with darkness at
the centre is called an optical vortex.
Non – imaging optics is the branch of optics deals with the optical
transfer of light radiation between a source and target. Unlike the traditional
imagining optics, the techniques involved do not attempt to form an image of
source, but an optimized optical system for optical radiative transfer from
source to target is achieved, for example in photomultiplier tubes.
Nonlinear Optics (NLO) is the branch of optics that describes the
behaviors of light in non-linear media, that is, the media in which the dielectric,
polarization P gives response to the electric field E of light non-linearly. This
non-linearity is only observed at very high intensity of light having values of
the electric field comparable to the inter-atomic electric fields 10 8 V/m, which
is provided by pulsed laser. In nonlinear optics, the superposition principle no
longer holds [3, 4]. After the discovery of lasers, the dimension of optics
changed completely. A review is written by Rao [5], on the completion of 50
years of discovery of lasers. There are also branches of optics like Statistical
Optics [6] and Fourier Optics [7] and many more.
The present author interested to give a brief introduction to NLO and
NLO crystals, which will be covered in the following section.
1.1 Origin of NLO
Before the advent of the lasers, it was assumed that the optical
parameters of the medium were independent of the intensity of the light
propagating in that medium. The electric field strength generated by the non-
laser light sources is of the order of 10 3
V/cm, which is very much smaller than
the inter-atomic fields. Whereas, the inter-atomic electric field strength of the
3