Abstract : This thesis describes several experiments, in which the quantization of the electromagnetic fiels plays a crucial role to describe theoretically and to understand physically the observed phenomena. In particular, the need for a quantum approach appears by evidencing a quantum state of the field where a single quantum is excited (single photon Fock state). A single photon state can be characterized by using two photomultipliers on both sides of a beamsplitter : the probability for two photodetections within a time w has to be much smaller than the product of probabilities for single detections during the same time. This "non-classical" property, that we call "anticorrelation", is demonstrated by using a radiative cascade in Calcium, and fast photon counting techniques. Then we present an interference experiment, using the same light as the one exhibiting the anticorrelation effect. With a Mach-Zehnder interferometer adjusted close to zero path difference, the visibility of the interference fringes has been measured to be larger than 98%, in excellent agreement with the value expected from the interferometer design. Finally we present two other experiments, also illustrating the general idea of single photon interferences : a quantum beat experiment in a continuously excited radiative cascade, and an interference effect in the fluorescence of two atoms, obtained by photodissociating a Ca2 molecule with a short laser pulse.