Laser interferometer probe

• US 4,171,915 A
• Filed: 10/07/1977
• Issued: 10/23/1979
• Est. Priority Date: 10/07/1977
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Hesselink, Lambertus
• Primary Examiner(s): Clark, Conrad J.
• Application Number:
  US05/840,331
• Time in Patent Office: 746 Days
• Field of Search: 356/106 R, 356/107, 356/113, 356/361
• US Class Current: 356/517
• CPC Class Codes: G01N 21/45 using interferometric methods; using Schlieren methods

Abstract

Index of refraction measurements are made by means of an optical device in which a coherent light beam is divided into an object beam and a reference beam, each of which is directed through a separate path in a common light transmitting medium. The object beam is also transmitted en route through a test volume that accommodates a substance to be tested. It is subsequently recombined with the reference beam to form a single output beam. The output beam is received by a photo detector and its intensity is measured. The intensity of the detected output beam is related to any phase shift between the object and reference beams. The phase shift in turn is a measure of the index of refraction of the test substance. Information relating to density, temperature and pressure of the test substance can be derived from measured index of refraction values by using conventional conversion formulas. An operating range control is provided by introducing a volume of pressurized gas into the paths of the object and reference beams. The operating range of the instrument is set by adjusting the pressure of the gas in the absence of a test substance.

Claims

1. An inteferometer probe comprising means for generating a beam of coherent light,

beam splitting means for dividing said beam of coherent light into an object beam and a reference beam,

a probe structure in the form of a transluscent axisymmetric member having a prismatic end that in part defines a test volume for the accommodation of a test substance, and a beam input/output end,

a beam splitter plate,

light beam combining means for recombining said object and reference beams to form an output beam, said beam splitting means and said light beam combining means being integral portions of said beam splitter plate, said beam splitter plate being in spaced proximity to the beam input/output end of said transluscent axisymmetric member,

a sleeve member encompassing said beam splitter plate and the outer end surface of said probe structure effecting a hermetically sealed volume therebetween,

pressurized gas in said hermetically sealed volume, the pressure of said gas being a function of the operating range of the interferometer probe,

means for directing said reference beam through said probe structure to terminate at said light beam combining means,

means for directing said object beam through said probe structure and said test volume to terminate at said light beam combining means, and

detector means for detecting and measuring the intensity of the combined output beam from said light beam combining means.

2. An interferometer probe as defined in claim 1 wherein said probe structure is configured to provide equal optical path lengths for said object and reference beams.

3. An interferometer probe as defined in claim 1 wherein said probe structure is configured to provide a longer optical path length for said object beam than for said reference beam.

4. An interferometer probe as defined in claim 1 wherein said beam splitter plate has a thickness and angle of incidence relative to said beam of coherent light that provides a high intensity reference beam and a low intensity object beam.