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

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Our nonlinear optical spectra and ultrafast nonlinear optical spectroscopy theory
of GaN form the core of this thesis. The nonlinear optical spectroscopy theory required
the solution to the nonlinear wave equation for a thin film geometry. \Ve then
incorporated ultrafast effects into the theory, which explicitly accounted for group velocity
mismatch. We performed second-harmonic generation spectroscopy of Ga:\ in
the s-in/p-out and p-in/p-out polarizations over a two photon energy of 2.6 to 3.-1 e V.
\Ve observed a slight enhancement in x~7jx at a two photon energy of 2.80 e\". By contrast.
X~~x is spectrally flat. \Ve attributed the sub-band gap resonant enhancement
to an intrinsic bulk defect state. This conclusion is derived from the magnitude of
the effect and its presence in all of our GaN samples. \Ve further investigated the role
of our sample miscut on the nonlinear optical properties of GaN. \Ve used rotational
SHG to determine the sample miscut to be 0.8 0 • In addition, we were unable to
observe any strain induced nonlinearity of GaN by rotational SHC; this effect could
be produced by the sample miscut.
\Vhile further investigations of the nonlinear optical properties of Ca.\" are certainly
of interest, our future investigations lie in nonlinear optical microscopy. \Ye
have studied the spectra of CaN, and now must move on to other investigations. :\onlinear
optical microscopy combines the strengths of nonlinear optical spectroscopy,
e.g. sensitivity to symmetry, with the spatial sensitivity of optical microscopy. We
suggest that this technique is well suited for the investigation the nonlinear optical
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