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Abstract

A dispersive grating, preferably in the form of a volume-phase holographic optical element, or HOE, is used as a beam combiner in an optical measurement probe of the type used to analyze induced radiative effects such as Raman or fluorescence detection. Although a reflective grating may be used, a transmission grating of holographic derivation is used in the preferred embodiment. Although the grating may define an area substantially equivalent to the cross-section or aperture of the collection path, a grating which consumes a fraction of the collection aperture may instead be utilized, thereby allowing collected light to pass around the grating to further enhance the efficiency of detection. As a further advantageous option, the grating may be fabricated with `power,` that is, with the capability of collimating excitation energy that has been focused onto the grating surface. In this manner, a 'spot' grating may be positioned centrally along the axis of the collection path, thereby realizing the multiple advantages of relaxed alignment demand, reduced spurious scattering, and high efficiency and throughput.

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First Claim