Interferometric device for measurement of variations in length of a sample under the influence of temperature

• US 3,930,730 A
• Filed: 09/06/1973
• Issued: 01/06/1976
• Est. Priority Date: 09/06/1972
• Status: Expired due to Term

• Current Assignee: Republic of France
• Original Assignee: Republic of France
• Inventors: Durand, Jean-Pierre, Christy, Jean-Paul, Laurens, Albert Adelin Suffrein
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/394,552
• Time in Patent Office: 852 Days
• Field of Search: 356/106 R, 356/108, 356/109, 356/110, 356/112, 356/113
• US Class Current: 356/498
• CPC Class Codes: G01B 9/02 Interferometers
• CPC Class Codes: G01N 25/16 by investigating thermal coefficient of expansion

Abstract

An interferometric device is provided for measurement of the variations in length of a sample under the influence of temperature, the length of the sample being within a plane of reference and a plane of measurement defined by two plane terminal faces of the sample. The device comprises a source of monochromatic light, means to form parallel beams from the light source, a controllable temperature thermostatic enclosure containing a sample holder, a reflecting measurement surface joined to the plane of measurement for receiving one of the beams, a reflecting reference surface for receiving the other beam, a bearing face presented by the sample holder for the terminal reference face of the sample which is elastically applied against the bearing face, and support means for supporting the reflecting reference surface inside the enclosure and ensuring that the variation of distance between the two reflecting surfaces will always be equal to the variation in length of the sample when the temperature of the thermostatic enclosure is varied. The two beams reflected respectively by the two reflecting surfaces are caused to interfere, and a sensor observes and measures interference fringes.

Claims

1. In an interferometric device for measurement of the variations in length of a sample under the influence of temperature, the length of the sample being within a plane of reference and a plane of measurement defined by two plane terminal faces of the sample, the device comprising a source of monochromatic light, means to form parallel beams from said source, a controllable temperature thermostatic enclosure, a sample holder placed in the enclosure, a reflecting reference surface for receiving one of said beams, a reflecting measurement surface joined to the plane of measurement for receiving the other of said beams, means to cause interferences of the two beams reflected respectively by the two reflecting surfaces, and a sensor to observe and measure interference fringes, the improvement comprising a bearing face presented by said sample holder for the terminal reference face of the sample, elastic means for applying the sample against said bearing face, and support means for supporting said reflecting reference surface inside said enclosure and ensuring that the variation of distance between the two reflecting surfaces will be equal to the variation in length of the sample when the temperature of the thermostatic enclosure is varied, said sample holder comprising a support for the reflecting measurement surface, of thickness a₁ and with coefficient of thermal dilatation λ

₁, applied against the terminal measurement face of the sample, the support means for the reflecting reference surface having a thickness a₂, measured from the plane of reference, and a coefficient of dilatation λ

₂, and these thicknesses and these coefficients of dilatation satisfying the equation a₁ λ

₁ equals a₂ λ

₂.

2. Device as in claim 1, wherein the support means for the reflecting reference surface is an integral part of the sample holder.

3. Device as in claim 1 wherein the support of the reflecting measurement surface presents straps that bear elastically against the rear part of the sample holder to apply the support of the reflecting measurement surface against the measurement face of the sample.

4. In an interferometric device for measurement of the variations in length of a sample under the influence of temperature, the length of the sample being within a plane of reference and a plane of measurement defined by two plane terminal faces of the sample, the device comprising a source of monochromatic light, means to form parallel beams from said source, a controllable temperature thermostatic enclosure, a sample holder placed in the enclosure, a reflecting reference surface for receiving one of said beams, a reflecting measurement surface joined to the plane of measurement for receiving the other of said beams, means to cause interferences of the two beams reflected respectively by the two reflecting surfaces, and a sensor to observe and measure interference fringes, the improvement comprising a bearing face presented by said sample holder for the terminal reference face of the sample, elastic means for applying the sample against said bearing face, said sample holder presenting a straight concave seat for the sample of substantially trapezoidal section as viewed parallel to said other of said beams such that said sample lies within the concave seat and is supported by the diverging walls of the trapezoidal section to facilitate maintenance of alignment of the axis of the sample and prevent pinching, swinging or compression of the sample, and support means for supporting said reflecting reference surface inside said enclosure and ensuring that the variation of distance between the two reflecting surfaces will be equal to the variation in length of the sample when the temperature of the thermostatic enclosure is varied.

5. Device as in claim 4, wherein the reflecting measurement surface coincides with the measurement plane of the sample, the reflecting reference surface is in the plane of reference, and said support means is an integral part of the sample holder.

6. In an interferometric device for measurement of the variations in length of a sample under the influence of temperature, the length of the sample being within a plane of reference and a plane of measurement defined by two plane terminal faces of the sample, the device comprising a source of monochromatic light, means to form parallel beams from said source, a controllable temperature thermostatic enclosure, a sample holder placed in the enclosure, a reflecting reference surface for receiving one of said beams, a reflecting measurement surface joined to the plane of measurement for receiving the other of said beams, means to cause interferences of the two beams reflected respectively by the two reflecting surfaces, and a sensor to observe and measure interference fringes, the improvement comprising a bearing face presented by said sample holder for the terminal reference face of the sample, elastic means for applying the sample against said bearing face, support means for supporting said reflecting reference surface inside said enclosure and ensuring that the variation of distance between the two reflecting surfaces will be equal to the variation in length of the sample when the temperature of the thermostatic enclosure is varied, at least two centering feet and corresponding mating formations carried by respective ones of said sample holder and said enclosure for releasably positioning the sample holder in the enclosure, the axes of said centering feet and said mating formations lying substantially in said plane of reference.

7. Device as in claim 6 further comprising a base bearing the enclosure and the means to cause interference of the beams, and at least two centering feet and cooperating mating formations carried by respective ones of said enclosure and said base for positioning the enclosure on the base, the axes of these second-mentioned centering feet and mating formations lying substantially in said plane of reference.

8. Device as in claim 7 further comprising at least two further centering feet, whose axes are in a plane parallel to the plane of reference, for cooperation with mating formations to position on the base supports for said means to cause interference of the beams.