The nonclassical light

Properties of the nonclassical light (NCL) have been considered with an emphasis on experimentally-observed features, which are underlain by the well-known Mandel's formula connecting the statistics of photocounts with that of light falling on the detector. A systematic operational approach is presented to study the NCL using two parallel sets of numbers measured: probabilities of photocounts {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 the week nonclassicality using 'generalised' moments {a_k(s)}. The effect of the linear absorption (amplification) and of the beam-splitting of the NCL, and the relation between the NCL and the absolute calibration of photodetectors are considered. The conditions are elucidated whereat the beam-splitter realises a mathematical operation of superposition of two one-mode fields useful in studying the NCL.