Renishaw Plc

Chunwei Cheng

David N Batchelder

Brian J Smith

Raymond J Chaney

Ian P Hayward

Kurt J Baldwin

A sample placed under a microscope is illuminated by light from a laser beam. Raman scattered light is passed back via a dichroic filter to various optical components which analyse the Raman spectrum, and thence to a CCD detector. The optical components for analysing the Raman spectrum include tunable dielectric filters in a filter wheel; a Fabry-Perot etalon; and a diffraction grating. These various components may be swapped into the optical path as desired, for example using movable mirrors, enabling the apparatus to be used very flexibly for a variety of different analysis procedures. Various novel analysis methods are also described.

Spectroscopic apparatus and methods

In a Raman microscope, Raman scattered light from an illuminated area on a sample 10 is collected by an objective 12 and imaged by a lens 18 onto a detector in an image plane 20. A filter 16 selects only light of a desired Raman wavenumber shift. Since the tuning of this filter is sensitive to the angle of incidence, it is placed after the lens 18 instead of before it, and the distance from the objective 12 to the lens 18 is made substantially equal to the focal length of the lens 18. This ensures that chief rays 14A',14B' from different points on the sample 10 pass through the filter 16 at the same angle of incidence. The wavenumber selected by the filter is therefore the same for light from all points on the sample, which it would not be if the filter were placed before the lens 18.

Raman microscope

Raman analysis apparatus

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Yorkshire, United Kingdom

Chunwei Cheng