DENSITY-MATRIX FROM PHOTON NUMBER TOMOGRAPHY

We provide a simple analytic relation which connects the density opera tor of the radiation field with the number probabilities. The problem of experimentally ''sampling'' a general matrix element is studied, an d the deleterious effects of nonunit quantum efficiency in the detecti on process are analyzed showing how they can be reduced by using the s queezing technique. The obtained result is particularly useful for int racavity field reconstruction states.