STAR STATES

It is shown that the classical and quantum mechanical description of f irst and second order nonlinear optical processes (including squeezing ) are equivalent to the effect that in both cases an initial phase spa ce distribution is transformed in the same manner. Three-photon states - star states - are generated in third order nonlinear processes, whe re the classical and quantum descriptions give essentially different r esults. It is pointed out that the efficiency of the star state in a t hree photon process is superior to that of a coherent state with two o rder of magnitude.