Thesis Committee: Daniel Gauthier, Henry Everitt, Ronen Plesser,
Calvin Howell (exofficio non-voting member)
ABSTRACT: The main goal of this research is to examine instabilities
in laser beams counterpropagating through a highly nonlinear optical material.
In this case, rubidium vapor is used as the material and the laser beams
are tuned close to the frequency of the 5S1/2 <--> 5P3/2
atomic transition, which resonantly enhances the nonlinear optical
interaction strength.
I observe that the polarization of the laser beams
is unstable above a critical threshold. This finding is made by measuring
the power emitted from the vapor in the state of polarization orthogonal
to the linear polarization of the input beams. The light generated in the
orthogonal polarization is at the same frequency as the input beam and
is emitted at a small angle with respect to the input beam axis. The threshold
is observed to occur at 2.3 mW for one beam and 0.3 mW for the other beam
at a blue detuning of 20 MHz, and red detunings of 75 MHz and 150 MHz from
the F=1 <--> F=2 transition. The atomic number density is 2×1012
atoms/cm3.
The instability occurs at a power on the same order
as the powers observed in recent studies, but occurs at an atomic number
density that is 5.5 times lower. This study is important because it identifies
the physical mechanism responsible for laser beam instabilities, which
degrade nonlinear optical process that use counterpropagating laser beams.
Here is the thesis in PDF: sclark_thesis.pdf (about 1.6 MBytes)