Patent ID: 7109459

Claim:
An auto-focusing method for determining an in-focus position of a sample supported on one surface of a substrate plate made of a material transparent with respect to incident electromagnetic radiation, the method utilizing an optical system capable of directing incident electromagnetic radiation towards the sample and collecting reflections of the incident electromagnetic radiation which are to be detected, and comprising: (i) locating a focal plane of an objective lens arrangement at a predetermined distance from a surface of the substrate, which is opposite to said surface supporting the sample; (ii) providing continuous displacement of the focal plane relative to the substrate along the optical axis of the objective lens arrangement, while concurrently directing the incident radiation towards the sample through the objective lens arrangement to thereby focus the incident radiation to a location at the focal plane of the objective lens arrangement; and (iii) continuously detecting reflected components of the electromagnetic radiation collected through said objective lens arrangement, said detected reflected components being characterized by a first intensity peak corresponding to an in-focus position of said opposite surface of the substrate, and a second intensity peak spaced in time from the first intensity peak and corresponding to an in-focus position of said sample-supporting surface of the substrate, thereby enabling imaging of the sample when in the in-focus nposition of the sample-supporting surface of the substrate.