The pinhole acts as a spatial filter in front of the detector. Light originating away from the focal region is rejected, while signal from the focused location can pass through. This selective detection reduces background from out-of-focus regions, improving image contrast and depth resolution for quantitative examination of structures and surfaces.
Scanning a focused laser or other point source samples the specimen at defined locations rather than collecting an undifferentiated image from the entire field. Repeating this process across the specimen produces optical sections at different positions. These sections can be assembled into image stacks that support three-dimensional analysis of geometry and surface features.
The measurement can use emitted light from a specimen or reflected light from a surface, depending on the available signal. In either case, the detected light passes through the spatial-filtering path before reaching the detector. This allows the same measurement principle to examine internal structures or engineered surfaces without relying on physical sectioning.
Rejecting out-of-focus light separates signals from different optical depths more effectively than an image that combines them. The resulting sections provide clearer information about the location and shape of features. For engineering analysis, that improved separation supports measurements of surface form, microfabricated geometry, and dimensional relationships within a specimen.
A typical workflow positions the specimen for optical examination, focuses a point source, and scans it across the area of interest. Emitted or reflected light travels through the pinhole to the detector. Measurements collected at successive optical positions are then organized into image stacks for three-dimensional analysis, height mapping, or cross-sectional evaluation.
Image stacks can be processed to represent the measured specimen as a height map or cross-sectional view. A height map describes surface variation, whereas a cross-section reveals dimensional relationships through the measured region. These outputs convert optical sections into information that can support evaluation of structures, surfaces, and microscale features.
Engineers apply the method to surface topography measurement, dimensional inspection, material characterization, and analysis of microfabricated features. Because image stacks provide height and cross-sectional information without physically sectioning the sample, the technique can also support quality control, failure analysis, and microscale design evaluation.