Apparatus and method for optical stimulation of an optically activatable biological sample

an apparatus and a method for optical stimulation of an optically activatable biological sample with at least one light source, the light emitted will be described in at least one predeterminable wavelength, which strikes directly or indirectly on the sample. The invention is characterized in that the at least one light source couples thermally to a hollow channel portion so that the hollow channel portion is part of a fluid flowing through fluid circuit that a temperature control unit and a pump are arranged along the liquid circuit, and that the hollow channel section has a boundary wall at least to the directly or indirectly thermally couples the optically activated biological sample.