System and method for interferometric autofocusing

An apparatus suitable for interferometric autofocusing, comprising:

• a camera disposed along a primary optical axis, wherein the camera is configured to collect a portion of light reflected from a surface of one or more specimens disposed on a specimen stage;
• a two beam interference optical system including a shutter-less reference path, wherein the two beam interference optical system includes:
• an illumination source;
• a reference mirror;
• a first beam splitter configured to direct a first portion of light from the illumination source along an object path to the surface of one or more specimens disposed on the specimen stage and a second portion of light from the illumination source along the shutter-less reference path toward the reference mirror;
• and
• a ninety degree mirror positioned along the shutter-less reference path between the illumination source and the reference mirror, wherein the ninety degree mirror is configured to divert light impinging on the ninety degree mirror from the shutter-less reference path along a direction substantially perpendicular to the reference path such that substantially no light from the shutter-less reference path impinges a central region of the reference mirror;
• wherein the first beam splitter is configured to direct a portion of light reflected from the surface of the reference mirror along a primary optical axis,
• wherein the camera and reference mirror are arranged such that light reflected from peripheral regions of the reference mirror does not impinge on a field of view (FOV) of the camera;
• an autofocusing system disposed along a secondary optical axis, wherein the autofocusing system is configured to analyze one or more interference fringes created by a superposition of light reflected from the surface of the specimen and light reflected from a peripheral region of the surface of the reference mirror simultaneously with an imaging of the surface of the one or more specimens by the camera.