Among the quantum systems capable of emitting single photons, the class of recently discovered defects in hexagonal boron nitride (hBN) is especially interesting, as these defects offer much desired characteristics such as narrow emission lines and photostability [1]. Like for any new class of quantum emitters, the first challenges to solve are the understanding of their photophysics as well as to find ways to facilitate integration in photonics structures. Here, we will show our investigation of the optical transition in hBN with different methods: Employing excitation with a short laser pulse the emission properties in case of linear and non-linear excitation can be compared [2]. We find clear antibunching signals that prove the single emitter character in both excitation cases. To gain further knowledge, we also obtain saturation curves. From a comparison of one- and two-photon case insights about the level structure of the defects can be obtained. The possibility to perform two-photon excitation makes this single photon emitter an interesting candidate as a biosensor.