In a Raman spectroscopy apparatus, exciting light is focussed on a sample (26) as a line focus (38). Spectra from points in the line focus are dispersed in rows 46 on a CCD detector (34), having a two-dimensional array of pixels. The line focus moves longitudinally in a direction Y relative to the sample. Simultaneously and synchronously, charge is shifted in a parallel direction Y' within the CCD, so that data from a given point in the sample continues to accumulate, hi order to provide averaging in the X direction during fast, low resolution scanning, the line focus is swept across the sample in a zig-zag fashion, between boundary lines 60.