Pencil beam interferometer

• US 4,498,773 A
• Filed: 05/04/1983
• Issued: 02/12/1985
• Est. Priority Date: 05/04/1983
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: von Bieren, Karlheinz
• Primary Examiner(s): Willis, Davis L.
• Application Number:
  US06/491,496
• Time in Patent Office: 650 Days
• Field of Search: 356/357, 356/359, 356/360, 356/371, 356/376
• US Class Current: 356/516
• CPC Class Codes: G01B 11/306 for measuring evenness
• CPC Class Codes: G01B 9/02061 Reduction or prevention of effects of tilts or misalignment

Abstract

An interferometer which provides for the precise figure measure of optical surfaces through the interference of two pencil beams, reflected off the optical surface, comprises a laser for generating a laser beam which is split into two parallel beams by a beam splitter and a mirror, the two pencil beams are reflected off a second beam splitter, through an alignment invariant optical device and onto the optical surface to be measured. The two pencil beams are reflected and back-trace through the alignment invariant optical device, propagate through the second beam splitter and enter an optical lens which is capable of focusing two beams in its back focal plane where the interference of the two pencil beams takes place. This information is then relayed through optical spatial filter and optional micro objective into the readout section.

Claims

1. A pencil beam interferometer for measuring optical surfaces, comprises:

a light beam;

a first beam splitter optically oriented to receive and to split said incoming light beam into a first and a second pencil beam;

means for deflecting said second pencil beam, wherein said deflected second pencil beam is displaced from but parallel to said first pencil beam;

means for redirecting and transmitting said parallel pencil beams while concurrently maintaining them in parallel;

an alignment invariant optical device disposed to receive the output of said means for redirecting and transmitting said parallel pencil beams, and wherein said alignment invariant optical device directs said pencil beams to the optical surface to be measured;

an optical lens capable of focusing said two pencil beams in its back focal plane, and wherein said optical lens is disposed to receive the reflected pencil beams from said optical surface after they pass back through said alignment invariant optical device and said means for redirecting and transmitting said parallel pencil beams; and

a readout section optically positioned to detect the interference pattern generated by said focused beams.

2. The interferometer of claim 1 wherein said means for redirecting and transmitting said parallel pencil beams is a second beam splitter.

3. The interferometer of claim 1 wherein said alignment invarient device is a prism.

4. The interferometer of claim 3 wherein said prism is a penta prism.

5. The interferometer of claim 3 wherein said prism is a deflection prism.

6. The interferometer of claim 3 wherein said prism is a rhomb prism.

7. The interferometer of claim 1 further comprising a spatial filter and micro objective optically aligned between said optical lens and said readout to enhance the interference pattern inputted to said readout.