A particularly interesting though not yet practical approach takes this notion to its fullest conceptual extent (Oron et al., 2005). In this method, the laser simultaneously illuminates the entire field of view continuously. In a sense this is like “bathing” the sample in epifluorescent excitation but relies on two-photon excitation and on focusing the excitation pulse in time, therefore providing excellent Z-resolution. As might be imagined, the limitation of this method is average laser power – despite the high power of currently available lasers, this method demands so many photons per unit time that fluorescence intensities are very low and imaging is necessarily slow to allow sufficient integration. However in the future, with more powerful lasers this may be a promising approach.