Non-classical light

Properties of the non-classical light (NCL) are considered with the emphasis on experimentally observed signatures, which are underlied by the well-known Mandel's formula relating the statistics of photon counts to that of the light incident on the detector. A systematic operational approach is presented to study the NCL using two parallel sets of numbers measured: probabilities of photon counts {p(m)} and normalised factorial moments of counts {g(k)}. Two particular examples are examined in detail: a 'heated' squeezed vacuum and a 'heated' one-photon state. An alternative method is proposed to discover weak non-classicality using 'generalised' moments {a(k)(s)}. The influence the linear absorption (amplification) and the beam-splitting exert on the NCL, and the relation between the NCL and the absolute calibration of photodetectors are considered. The conditions are round under which the beam-splitter realises a mathematical operation of superposition of two one-mode fields, which is useful in studying the NCL.