Abstract
This thesis is a study of coherence theory in light in classical
electromagnetism and quantum optics. %The coherence is quantified
Specifically two quantities are studied: The degree of first-order
temporal coherence, which quantifies the field-field coherence, and
the degree of second-order coherence, quantifying the intensity-intensity
coherence. In the first part of the thesis these concepts are applied to classical
electric fields; to both the ideal plane wave and to chaotic light.
We then study how they can be measured using two interferometer
technologies from optical astronomy, specifically with the
Michelson stellar interferometer and the intensity interferometer.
In the second part we define the
quantum degrees of first- and second-order coherence. These are calculated
for light in a quantum coherent state, in a Fock state and for light
in a mixed thermal state. The results for the coherent state and
the thermal state are found to be analogous to
those obtained for the ideal plane wave and chaotic light, respectively,
from the classical coherence theory seen in the first part.
We proceed to investigate the properties of the three-level laser with
the aim of showing that far above threshold it develops similar photon
statistics and values for the degrees of first- and second-order coherence,
to light in a coherent state. The mechanism of phase-drift in the laser
is also looked into. Subsequently the Mølmer-model is discussed, where it is
demonstrated that the coherent state is not a necessary construct, but
merely a convenient one, in describing phenomena in quantum optics.