Detectable Information in a Photon Beam*
Ellen Hisdal · Journal of the Optical Society of America · 1967
The information content in a thermal photon beam and in a single-mode maser beam is computed, taking account of the limited quantum efficiency of the detector, and extending the results to polychromatic radiation in the thermal case. Formulas for fluctuations of the measured quantity in a polychromatic thermal beam are found, both for a photoelectric and for a thermal type of detector. Numerical examples of the information content are given for three common thermal light sources, using the eye as detector. For all three sources the information is found to be of the order of 104–105 bits/sec for a sample of 1 cm2 at 1 m distance from the the eye.