  We report the experimental observation of photon bunching noise through shot
noise measurements made on a pseudo-thermal state of light using balanced
detection. A full theory describing the measurement is developed, and in
agreement with theory it is found that the shot noise variance in the balanced
signal reproduces the time series of the flux of the primary incoherent beam.
Moreover, when the average power of the pseudo-thermal light is varied, the
balanced detection is seen to track this change. A comparison of direct
detection and balanced detection of the thermal field, shows that the balanced
detection performs at least as well the direct detection and under some
conditions appears to outperform the direct detection. There is not necessarily
a contradiction with quantum field theory which predicts that at best the
performance of the balanced detection should be equal to the direct detection,
because the direct detection process is subject to nonlinearity that has not
been excluded by measurements (even though any tests we performed suggest such
effects are small). This is the first time that the bunching noise effect of
high occupation number chaotic light via the shot noise of the field has
successfully been measured, to the point of using it to infer the flux of the
field. The findings may be relevant to radio receiver design, specifically from
the viewpoint of sensitivity improvement.
