Abstract: An optical system is disclosed which significantly enhances the throughput of a grating spectrometer intended to determine impurity concentrations on the surface of semiconductor materials (usually single crystal silicon) used for integrated circuits. The system, which uses a laser beam as the photo-excitation means impinging on a Dewar-contained sample, includes a pre-sample series of lenses which so shapes the laser beam that its shape at the point of impingement on the sample is proportionally similar to the shape of the monochromator slit in the spectrometer. The same lens which provides final focusing of the laser beam on the sample also collects the sample-emitted radiation, which is thereafter focused by suitable optics on the monochromator slit, where it preferably substantially matches the shape of the slit, but slightly overfills the slit.