Distance measuring system

Abstract

A distance measuring device capable of being used in microscopes or other optical systems. Embodiments of the invention employ one or more scanning mirrors to scan a reference beam over a target to be inspected. The reference beam is returned and detected by a photodetector. The reference beam may be created by using a knife-edge element which allows the outgoing reference beam and incoming reference beam to follow the same path so that the apparent motion of the spot on the target surface is not detected by the photodetector. The photodetector generates an electronic signal corresponding to the displacement of the target away from the ideal focal point. The electronic signal may be used to drive a servomechanism to displace either the target or the microscope objective lens to bring the target in focus.

1 . A distance measuring system for use in an optical system that is capable of examining a target surface and that has an objective lens defining a system in-focus region, comprising: 
 a light source emitting an outgoing reference beam of light, wherein a portion of the outgoing reference beam is reflected from the target surface as an incoming reference beam;    a photodetector positioned in the path of the incoming reference beam and adapted to generate an electronic signal according to the position of the incoming reference beam on the surface of the photodetector; and    a reflecting knife-edge element defining a plane, the knife-edge element positioned to obstruct any portion of the outgoing reference beam on a first side of the plane and to subtend the incoming reference beam on the first side of the plane.    
   
   
       2 . The distance measuring system of  claim 1 , further comprising: 
 a collimating lens in the path of the outgoing reference beam.    
   
   
       3 . The distance measuring system of  claim 1 , further comprising: 
 a beamsplitter positioned to reflect the outgoing reference beam, to reflect the incoming reference beam, and to transmit an image beam that passes through the objective lens;    whereby the beamsplitter separates the outgoing reference beam from the image beam.    
   
   
       4 . The distance measuring system of  claim 1 , further comprising: 
 an afocal relay positioned to transmit the outgoing reference beam and the incoming reference beam;    whereby the afocal relay allows the knife-edge element to be spaced a distance away from the beamsplitter without substantially impairing the focus sensing capability of the system.    
   
   
       5 . The distance measuring system of  claim 1 , wherein the light source is a laser diode.  
   
   
       6 . An automatic focusing microscope for examining a target surface, comprising: 
 an objective lens conducting an image beam of light reflected from the target surface and defining an optical axis;    a light source emitting an outgoing reference beam of light, wherein a portion of the outgoing reference beam is reflected from the target surface as an incoming reference beam;    a photodetector positioned in the path of the incoming reference beam and adapted to generate an electronic signal according to the position of the incoming reference beam on the surface of the photodetector;    a knife-edge element positioned to obstruct a portion of the outgoing reference beam on a first side of the optical axis and to reflect a portion of the incoming reference beam on the first side of the optical axis to the photodetector; and    a beamsplitter positioned to reflect the outgoing reference beam, to reflect the incoming reference beam, and to transmit the image beam.    
   
   
       7 . The distance measuring system of  claim 6 , wherein the light source is a laser diode.  
   
   
       8 . The distance measuring system of  claim 6 , further comprising: 
 a collimating lens in the path of the outgoing reference beam.    
   
   
       9 . The microscope of  claim 6 , further comprising: 
 an afocal relay positioned to transmit the outgoing reference beam and the incoming reference beam;    whereby the afocal relay allows the knife-edge element to be spaced a distance away from the beamsplitter without substantially impairing the focus sensing capability of the system.    
   
   
       10 . An optical reference beam generator for use in measuring the distance to a target surface, comprising: 
 a light source emitting a beam of light; and    a rectangular prism having a blocking surface and a reflective surface, wherein the blocking surface is positioned to block a portion of the beam of light, an unblocked portion of the beam of light defines a reference beam, the reflective surface is positioned to reflect a portion of the reference beam that is reflected from the target surface, and the rectangular prism does not conduct any portion of the reference beam.    
   
   
       11 . A method of creating an in-focus image, comprising: 
 emitting an outgoing reference beam through a microscope objective lens;    blocking a portion of the outgoing reference beam with a knife-edge element;    directing the outgoing reference beam onto a target surface, wherein the outgoing reference beam is reflected as an incoming reference beam;    reflecting the incoming reference beam from a surface of the knife-edge element to a detector;    detecting the relative displacement of an in-focus region from the target surface; and    adjusting the displacement of the in-focus region.    
   
   
       12 . A device for focusing a microscope, comprising: 
 beamsplitter means for emitting an outgoing reference beam through a microscope objective lens;    detector means for detecting the relative displacement of an in-focus region from the target surface;    edge means for blocking a portion of the outgoing reference beam, the edge means operative to reflect an incoming reference beam to the detector means;    relay means for spacing the beamsplitter means away from the edge means; and    means for adjusting the displacement of the in-focus region.