Surface sensing in automated sample analysis

A system, comprising:

• an illumination source;
• an objective lens;
• a light modulator;
• a detector;
• a stage;
• and
• a controller connected to the illumination source, the detector, and the stage,
• wherein the objective lens defines an object plane of the system;
• and
• wherein the controller is configured to:
• activate the illumination source to generate illumination light and direct the illumination light to the light modulator to generate a modulated light pattern;
• activate the stage to position a surface of a substrate on the stage at a plurality of different distances relative to the objective lens;
• activate the detector to obtain images of the modulated light pattern at the detector corresponding to each of the plurality of different distances;
• analyze the images to determine a reference location of the substrate surface relative to the objective lens that corresponds to positioning of an image of the modulated light pattern formed by the objective lens at the object plane;
• and
• activate the stage to adjust a position of the substrate relative to the objective lens based on the reference location.