An electronic device is described. The electronic device includes a housing, a set of one or more SMI sensors attached to the housing, and a processor. The set of one or more SMI sensors includes a set of one or more electromagnetic radiation emitters having a set of one or more resonant cavities and configured to emit a set of one or more beams of electromagnetic radiation. The set of one or more SMI sensors also includes a set of one or more detectors configured to generate indications of self-mixing within the set of one or more resonant cavities. The processor is configured to characterize, using the indications of self-mixing, an optical field speckle of a target. The processor is also configured to characterize, using the characterization of the optical field speckle, a surface quality of the target.