A spectrometry system for spectroscopically analyzing a sample is provided. The system includes an excitation source for interacting with the sample; a detector for detecting at least a portion of light absorbed or emitted by the sample, the excitation source and detector being optically coupled via an optical pathway; and an aperture positioned in the optical pathway for limiting transmission of light from the excitation source to the detector; wherein the aperture is configured to have a spatially varying distribution of one or more geometric features that provide regions of variable transmission around an edge of the aperture. Also provided is a mask for use with a spectrometry system, the mask configured to be positioned in an optical pathway between an excitation source and a detector, wherein the mask has a spatially varying distribution of one or more geometric features that provide regions of variable transmission around an edge of the aperture. A method for limiting light throughput from an excitation source to a detector via an aperture in a spectrometry system is also provided.