Intensity fluctuations in closed and open systems

We consider the intensity pattern, generated by a monochromatic source, in a disordered cavity coupled to the environment. For weak coupling, and when the source frequency is tuned to a resonance, the intensity distribution $P\left(I\right)\mathrm{}$ is close to Porter-Thomas distribution. When the coupling increases, $P\left(I\right)\mathrm{}$ gradually crosses over to the Rayleigh distribution. The joint probability distribution for intensities at two different points is also discussed.