  In this thesis we present a direct scheme for measuring quasidistribution
functions of light. This scheme, based on photon counting, is derived from a
simple relation linking the Wigner function with photon statistics. We develop
a full multimode theory of the scheme, and show that the principle of the
measurement can be straightforwardly generalized to the detection of the
multimode radiation. We also discuss practical aspects of the scheme, including
statistical error, non-unit detection efficiency, and imperfect interference
visibility. Next, we report experimental realization of the scheme, and present
measurements of the Wigner function for several quantum states of light.
Finally, we study the general problem of statistical uncertainty in
quantum-optical photodetection measurements.
