Diffuse reflectance method and apparatus for determining thickness of an infrared translucent layer

• US 6,459,488 B1
• Filed: 02/10/2000
• Issued: 10/01/2002
• Est. Priority Date: 02/10/2000
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Heffner, Kenneth H.
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): CONNOLLY, PATRICK J
• Application Number:
  US09/502,059
• Time in Patent Office: 964 Days
• Field of Search: 356/504, 356/632, 250/339.06, 250/559.28
• US Class Current: 356/504
• CPC Class Codes: G01B 11/0675 using interferometry

Abstract

A method for producing an interferogram of an infrared translucent layer that is on a reflective substrate, comprising generating parallel infrared interferometer beams by means of an infrared interferometer, converging the parallel infrared interferometer beams into converging infrared interferometer beams, sending the converging infrared interferometer beams onto the infrared translucent layer to produce diffusely reflected infrared interferometer rays from above and below the infrared translucent layer, and making the diffusely reflected infrared interferometer rays into parallel reflected infrared interferometer rays.

Claims

1. A method for producing an interferogram of an infrared translucent layer that is on a reflective substrate, comprising:

(a) generating parallel infrared interferometer beams by means of an infrared interferometer;

(b) converging the parallel infrared interferometer beams into converging infrared interferometer beams;

(c) sending the converging infrared interferometer beams onto the infrared translucent layer to produce diffusely reflected infrared interferometer rays from above and below the infrared translucent layer; and

(d) making the diffusely reflected infrared interferometer rays into parallel reflected infrared interferometer rays.

2. A method for producing an interferogram of an infrared translucent layer on a reflective substrate, comprising:

(a) generating parallel infrared interferometer beams by means of an infrared interferometer;

(b) converging the parallel infrared interferometer beams into converging infrared interferometer beams;

(c) sending the converging infrared interferometer beams onto the infrared translucent layer to produce diffusely reflected infrared interferometer rays from above and below the infrared translucent layer;

(d) making the diffusely reflected infrared interferometer rays into parallel reflected infrared interferometer rays;

(e) detecting the strengths of the parallel reflected infrared interferometer rays; and

(f) scanning a movable mirror of the interferometer over a distance, in order to generate varying strengths of diffusely reflected infrared interferometer rays;

(g) displaying the detected strengths as a function of an incremental amount of a scanned distance of the movable mirror, to produce an interferogram of the infrared translucent layer.

3. A method for determining a thickness of an infrared translucent layer on a reflective substrate, comprising:

(a) generating parallel infrared interferometer beams by means of an infrared interferometer;

(b) converging the parallel infrared interferometer beams into converging infrared interferometer beams;

(c) sending converging infrared interferometer beams onto the infrared translucent layer to produce diffusely reflected infrared interferometer rays from above and below the infrared translucent layer;

(d) making the diffusely reflected infrared interferometer rays into parallel reflected infrared interferometer rays;

(e) detecting the strengths of the parallel reflected infrared interferometer rays;

(f) scanning a movable mirror of the interferometer over a distance, in order to generate varying strengths of the diffusely reflected infrared interferometer rays;

(g) displaying the strengths as a function of an incremental amount of a scanned distance of the movable mirror, to produce an interferogram of the infrared translucent layer;

(h) measuring the distance between a first side burst and a centerburst of the interferogram of the infrared translucent layer; and

(i) comparing the measured distance to a calibration standard to determine the thickness of the infrared translucent layer.

4. Apparatus for producing an interferogram of an infrared translucent layer on a reflective substrate, comprising:

(a) infrared interferometer means for generating parallel infrared interferometer beams;

(b) means for converging parallel infrared interferometer beams toward each other;

(c) means for holding the infrared translucent layer within a path of the converging infrared interferometer beams to produce diffuse reflected infrared interferometer rays from above and below the infrared translucent layer; and

(d) means for making the diffuse reflected infrared interferometer rays into parallel reflected infrared interferometer rays.

5. Apparatus for producing an interferogram of an infrared translucent layer on a reflective substrate, comprising:

(a) infrared interferometer means for generating parallel infrared interferometer beams;

(b) means for converging parallel infrared interferometer beams toward each other;

(c) means for holding the infrared translucent layer within a path of the converging infrared interferometer beams to produce diffuse reflected infrared interferometer rays from above and below the infrared translucent layer;

(d) means for making the diffuse reflected infrared interferometer rays into parallel reflected infrared interferometer rays;

(e) means for scanning a movable mirror of the infrared interferometer in order to generate varying strengths of the diffusely reflected infrared interferometer rays;

(f) means for detecting strengths of the varying strenghs of the parallel reflected rays; and

(g) displaying the strengths as a function of an incremental amount of a scanned distance of the movable mirror, to produce an interferogram of the infrared translucent layer.

6. Apparatus for producing an interferogram for an infrared translucent layer on a reflective substrate, comprising:

(a) interferometer means for producing a first parallel pair of infrared interferometer beams, the interferometer means having a movable mirror that causes the collimated pair of infrared interferometer beams to destructively or constructively interfere with each other as the movable mirror is scanned;

(b) first reflective means, having a concave reflective surface, for reflecting and converging the parallel pair of infrared interferometer beams toward the infrared translucent layer on the reflective substrate, diffuse reflected infrared rays being reflected from above and below the infrared translucent layer;

(c) second reflective means, having a concave reflective surface for collimating the diffuse reflected infrared rays into collimated infrared rays;

(d) means for sending the collimated infrared rays toward a detector means;

(e) means for detecting changing amounts of energy in the collimated infrared rays, as the movable mirror is being scanned, and for producing a signal proportional to the changing amounts of energy in the collimated infrared rays; and

(f) means for recording the signal as a function of distance that the movable mirror is scanned, to produce an interferogram for the infrared translucent layer.