Time evolution of Wigner function in laser process derived by entangled state representation

Evaluating the Wigner function of quantum states in the entangled state representation is introduced, based on which we present a new approach for deriving time evolution formula of Wigner function in laser process. Application of this formula to photon number measurement in laser process is also presented, as an example, the case when the initial state is a photon-added coherent state is discussed.