A sample substrate adapted for use with fluorescence excitation light with a first wavelength. A reflector is disposed on a base. The reflector includes a reflecting multilayer interference coating with at least two layers. Not all of the layers L fulfill a quarterwave condition: dLnL=(2N+1)1/4 wherein dL is a physical thickness of layer L, nL is an index of refraction of layer L at the first wavelength, N is an integer equal to or greater than zero and 1 is the first wavelength. Thicknesses of the layers ensure that any fluorescent sample material disposed on top of said multilayer interference coating would be located near an antinode of a standing wave formed by the excitation light with the first wavelength incident on said substrate.