METHOD FOR OPTICAL DETECTION AND/OR MEASUREMENT OF MOVEMENT OF A DIFFRACTION GRATING

• US 3,726,595 A
• Filed: 01/05/1971
• Issued: 04/10/1973
• Est. Priority Date: 01/07/1970
• Status: Expired due to Term

• Current Assignee: Kazuya Matsumoto
• Original Assignee: Kazuya Matsumoto
• Inventors: Matsumoto, Kazuya
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/104,006
• Time in Patent Office: 826 Days
• Field of Search: 356/106-113
• US Class Current: 356/499
• CPC Class Codes: G02B 27/42 Diffraction optics , i.e. systems including a diffractive element being designed for providing a diffractive effectG02B27/60 takes precedence
• CPC Class Codes: G02B 27/4255 for alignment or positioning purposes optical displacement encoding scales G01D5/347

Abstract

A method for optical detection and/or measurement of movement of a diffraction grating which is characterized in that the vertical movement of the diffraction grating in respect to a standard parallel beam is detected based on variation in interference fringes produced by diffracted waves from the grating moving in the standard parallel beams.

Claims

1. The method of optically detecting movement of a diffaction grating, which comprises orienting a light beam toward an optical apparatus which includes the grating, within the optical apparatus forming interference fringes with light waves from the beam by two steps, said two steps including the step of causing light waves from the beam to diverge from each other and the step of superposing the diverging light waves on each other so as to produce interference between the light waves, one of said steps including diffracting the light waves with said grating, and sensing the change in intensity of the interference fringes.

2. The method as in claim 1, wherein the step of causing the light waves in the beam to diverge includes the diffracting of the light waves with said grating.

3. The method as in claim 1, wherein the step of superposing includes directing the diverging light waves into the diffraction grating from different directions and diffracting these light waves.

4. The method as in claim 1, wherein the other of said steps includes the step of reflecting the waves and passing them through a half-mirror.

5. The method as in claim 1, wherein the interference fringes are formed by the additional step of focusing the superposed light waves onto a point and, wherein the step of sensing the change in intensity includes measuring the change in intensity of the fringes.

6. The method as in claim 1, wherein the step of superposing the pair of waves superposes waves of different diffraction orders whose difference in order is not equal to 1.

7. The method as in claim 1, wherein the waves forming the interference fringes have a symmetrical relationship with each other.

8. The method of determining the straightness of a surface on an object, which comprises holding a diffraction grating transverse to the surface and moving the grating along the surface, orienting a light beam at an optical apparatus which includes the grating, within the optical apparatus forming interference fringes with light waves from the beam by two steps, said two steps including the step of causing light waves from the beam to diverge from each other and the step of superposing the diverging light waves on each other so as to produce interference between the light waves, one of said steps including diffracting the light waves with said grating, and sensing the change in intensity of the interference fringes.

9. A method as in claim 8, wherein the step of causing the light waves in the beam to diverge includes the diffracting of the light waves with said grating.

10. The method as in claim 8, wherein the step of superposing includes directing the diverging light waves into the diffraction grating from different directions and diffracting these light waves.

11. The method as in claim 8, wherein the other of said steps includes the step of reflecting the waves and passing them through a half-mirror.

12. The method as in claim 8, wherein the interference fringes are formed by the additional step of focusing the superposed light waves onto a point and, wherein the step of sensing the change in intensity includes measuring the change in intensity of the fringes.

13. An apparatus for determining the movement of a grating, comprising orienting means for orienting a light beam toward the grating, interference fringe forming means for interacting with the grating and producing interference fringes, said fringe forming means including first light controlling means for causing light waves from the beam to diverge from each other and second light controlling means for superposing the diverging light waves on each other so as to produce interference between the light waves, one of said light controlling means including the diffraction grating, and means for sensing the change in intensity of the interference fringes.

14. An apparatus as in claim 13, wherein said fringe forming means includes focusing means and forms a focusing plane, said focusing means focusing the fringes on the plane.

15. An apparatus as in claim 13, wherein said sensing means includes means for measuring the intensity of the interference fringes.

16. An apparatus for determining the straightness of a surface, comprising a diffraction grating, orienting means for orienting a light beam toward the grating, interference fringe forming means for interacting with the grating and producing interference fringes, said fringe forming means including first light controlling means for causing light waves from the beam to diverge from each other and second light controlling means for superposing the diverging light waves on each other so as to produce interference between the light waves, one of said light controlling means including the diffraction grating, and means for sensing the change in intensity of the interference fringes.

17. An apparatus as in claim 16, wherein said fringe forming means includes focusing means and forms a focusing plane, said focusing means focusing the fringes on the plane.

18. An apparatus as in claim 16, wherein said sensing means includes means for measuring the intensity of the interference fringes.