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
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)