Interferometer

• US 4,830,496 A
• Filed: 01/22/1988
• Issued: 05/16/1989
• Est. Priority Date: 01/22/1988
• Status: Expired due to Fees

• Current Assignee: General Scanning, Inc. (KOCH Industries Incorporated)
• Original Assignee: General Scanning, Inc. (KOCH Industries Incorporated)
• Inventors: Young, Niels O.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US07/146,851
• Time in Patent Office: 480 Days
• Field of Search: 356/357, 356/363
• US Class Current: 356/508
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01B 2290/25 Fabry-Perot in interferometer, e.g. etalon, cavity
• CPC Class Codes: G01B 9/02019 contacting different points on same face of object

Abstract

A reference mirror (50) in an interferometer is fixed in position with respect to a laser (34). A refractive block (40) having parallel upper and lower surfaces is mounted for pivoting about a pivot axis (60) parallel to the reference mirror (40). The refractive block (40) is disposed in the path of the light beam (36) produced by the laser (34), and it includes a partially reflective surface (42) on its lower face that divides the incident beam (36) into two components (44 and 46), which travel along different paths, in which they are reflected from different portions (48 and 54) of the surface of the reference mirror (50) and from different portions (52 and 56) of a reflective surface on the upper face of the refractive block (40). A second partially reflective coating (58) rejoins portions of the two components to form an exit beam (32) in which the radiation from the two beams interferes in accordance with the angle of the refractive block (40). The angle that the exit beam (32) makes with the surface of the reference mirror (50) is independent of the angle of the refractive block (40).

Claims

1. An interferometer comprising:

A. a reference reflective element comprising first and second coplanar reference reflective surfaces;

B. a reference light source, fixed in position with respect to the reference reflective element, for emitting a narrow light beam;

C. a pivot element including a block of refractive material having first and second parallel faces, first and second coplanar pivot-element reflective surfaces on the first face, and first and second coplanar transmissive/reflective surfaces on the second face, the pivot element being positioned for reception and division of the light beam by the first transmissive/reflective surface into first and second components directed to the first pivot-element and reference reflective surfaces, respectively, and therefrom to the second reference and pivot-element reflective surfaces, respectively, and therefrom to the second transmissive/reflective surface to direct portions of first and second components along a common exit path, the paths of incidence and reflection from the reference reflective surface thereby defining a plane of incidence and reflection, the pivot element being pivotably mounted for pivoting about a pivot axis normal to the plane of incidence and reflection

wherein the angles a₀ formed with the normals to the first and second coplanar reference reflective surfaces by the light-beam components incident thereon are substantially equal to the value given by the equation

space="preserve" listing-type="equation">a.sub.0 =arcsin[N.sup.2 -N(N.sup.2 -1).sup.1/2 ].sup.1/2,

where N is the index of refraction of the block of refractive material.

2. An interferometer as defined in claim 1 wherein the angles a₀ formed with the normals to the first and second coplanar reference reflective surfaces by the light-beam components incident thereon are substantially equal to the value given by the equation

3. An interferometer comprising:

A. a reference reflective element comprising first and second coplanar reference reflective surfaces;

B. a reference light source, fixed in position with respect to the reference reflective element, for emitting a narrow light beam;

C. a pivot element including a block of refractive material having first and second parallel faces, first and second coplanar pivot-element reflective surfaces on the first face, and first and second coplanar transmissive/reflective surfaces on the second face, the pivot element being positioned for reception and division of the light beam by the first transmissive/reflective surface into first and second components directed to the first pivot-element and reference reflective surfaces, respectively, and therefrom to the second reference and pivot-element reflective surfaces, respectively, and therefrom to the second transmissive/reflective surface to direct portions of first and second components along a common exit path, the paths of incidence and reflection from the reference reflective surface thereby defining a plane of incidence and reflection, the pivot element being pivotably mounted for pivoting about a pivot axis normal to the plane of incidence and reflection

wherein the angles a₀ formed with the normals to the first and second coplanar reference reflective surfaces by the light-beam components incident thereon are substantially equal to the value given by the equation

space="preserve" listing-type="equation">a.sub.0 =arcsin [(4-N.sup.2)/3].sup.1/2,

where N is the index of refraction of the block of refractive material.