William Angerer - Department of Physics and Astronomy - University ...

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2.6 Conclusion
In this brief section we relate the theoretical results derived in this chapter to the
nonlinear optical properties of GaN, which are presented in the subsequent chapters.
In section 2.2, we discuss the properties of the second-order nonlinear susceptibility,
x;}L(w = 2wo). vVe suggest which states lead to a resonant enhancement of
x~~L(w
= 2wo) for both GaN bulk and defect states in sections 5.-1.1 and 6.5, respectively.
The determination of the states that contribute to the nonlinear optical
response follows directly from the application of group theory to equation 2.8.
In section 2.3 we discuss the relationship between material symmetry and secondorder
susceptibility elements. Using symmetry, we determined the unique nonzero
susceptibility elements for GaN. These elements, combined with experimental geometry.
influence nonlinear optical transmittance spectra of GaN (see chapter 6).
Finally, the majority of this introductory nonlinear optics chapter is concerned
with a detailed investigation of nonlinear optical interference, i.e. Maker fringes. vVe
contrast nonlinear optical interference for monochromatic and ultrafast laser sources.
\Ve demonstrated that nonlinear optical interference, which is due to wavevector
mismatch, is damped by group velocity mismatch. We apply this ultrafast analysis to
determine the second-order susceptibility elements from the nonlinear optical spectra
of GaN in sections 6.3 and 6.4.
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