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4.1 Introduction
Second-harmonic generation (SHG) is a nonlinear eect that was discovered in 1961 by Franken, Hill,
and Weinreich [1] where frequency-doubled 347 nm light was generated when intense 694 nm light
from a ruby laser was focused on a quartz sample. Subsequently, with the development of short-pulse
lasers that produce much higher instantaneous light intensity and improved methods to grow uniaxial
birefringent crystals with large nonlinear susceptibility, SHG has been used as an eective approach for
new wavelength generation. is greatly extends scientic researchers’ capability as most primary laser
sources are in the visible/nea ...