  Forces and torques exerted on dielectric disks trapped in a Gaussian standing
wave are analyzed theoretically for disks of radius $2~\mu\text{m}$ with index
of refraction $n=1.45$ and $n=2.0$ as well as disks of radius 200 nm with
$n=1.45$. Calculations of the forces and torques were conducted both
analytically and numerically using a discrete-dipole approximation method.
Besides harmonic terms, third order ro-translational coupling terms in the
potential energy can be significant and a necessary consideration when
describing the dynamics of disks outside of the Rayleigh limit. The coupling
terms are a result of the finite extension of the disk coupling to both the
Gaussian and standing wave geometry of the beam. The resulting dynamics of the
degrees of freedom most affected by the coupling terms exhibit several
sidebands as evidenced in the power spectral densities. Simulations show that
for Gaussian beam waists of $1-4~\mu\text{m}$ the disk remains stably trapped.
