Optical system for a scanning fluorometer

A method and apparatus for determining the fluorescence, luminescence, or absorption of a sample is provided. The sample may either be contained within a cuvette or within one or more sample wells within a multi-assay plate. A combination of a broadband source, a monochromator, and a series of optical filters are used to tune the excitation wavelength to a predetermined value within a relatively wide wavelength band. A similar optical configuration is used to tune the detection wavelength. An optical scanning head assembly is used that includes mirrored optics for coupling the excitation source to the sample and the emitted light to the detector. An elliptical focussing mirror is used to magnify and focus the light projected from an optical fiber coupled to the source subassembly onto the sample. A portion of the source light is reflected by a beamsplitter onto a reference detector used to monitor the output of the source. The light from the elliptical mirror passes through an aperture in a second elliptical mirror prior to impinging upon the sample. The light emitted by the sample within the sample well is reflected by the second elliptical mirror and imaged onto the entrance aperture of an optical fiber coupled to the detector subassembly. The optical axes of both mirrors are slightly offset from the sample well normal. The mirror offset minimizes the amount of light reflected from the meniscus of the sample or the bottom surface of the sample well that enters the detection subassembly.