Eighth wave corner cube retarder for laser radar

Patent metadata

Field	Value
Publication number	US-2016209496-A1
Application number	US-201414914616-A
Country	US
Kind code	A1
Filing date	Aug 29, 2014
Priority date	Aug 30, 2013
Publication date	Jul 21, 2016
Grant date	—

Abstract

Laser radar systems include focusing optical systems having a retroreflector such as a corner cube that is translatable with respect to an objective lens. The retroreflector provides a selected retardance to an interrogation optical beam that is directed to a target as well as to a returned portion of the interrogation optical beam that is directed to a detection system. Typically, an input linearly polarized interrogation beam is returned by the retroreflector as a circularly polarized beam that is directed to the target. Returned beam portions from the target are coupled by the retroreflector to a detection system in a linear polarization that is orthogonal to that of the input linearly polarized optical beam. The retroreflector produces state of polarization changes based on retardance associated with total internal reflection from coated or uncoated optical surfaces. Retroreflector surfaces that are not to introduce retardance are coated with suitable zero or low retardance coatings.

First claim

I claim:

1 . A focus system for a laser radar, comprising:
a prism that includes a plurality of reflective surfaces, wherein at least one surface is situated to receive an interrogation optical beam in a first state of polarization and reflect the interrogation optical beam in a second state of polarization; and a return reflector situated to receive the interrogation optical and reflect the interrogation optical beam back to the prism, wherein the prism is translatable with respect to the return reflector so as to establish a focus distance for the interrogation optical beam at a target.

2 . The focus system of claim 1 , wherein the return reflector is situated to direct the interrogation optical beam received in the second state of polarization to the prism.

3 . The focus system of claim 2 , wherein the return reflector is situated to direct the interrogation optical beam received in the second state of polarization to the to the prism in a third state of polarization, and the prism is situated so the plurality of reflective surfaces produce an output interrogation optical beam in a fourth state of polarization.

4 . The focus system of claim 1 , wherein the plurality of reflective surfaces provides a one-eighth wave linear retardation to the interrogation optical beam in the first state of polarization to produce the interrogation optical beam in the second state of polarization.

5 . The focus system of claim 1 , wherein the prism is a corner cube, and the at least one surface provides a one-eighth wave retardation.

6 . The focus system of claim 5 , wherein the prism includes a first surface that receives the interrogation beam from a beam source, wherein the first surface provides a retardance of about one-eighth wave.

7 . The focus system of claim 6 , wherein the first surface has a surface coating that provides the one-eighth wave retardance.

8 . The focus system of claim 6 , wherein the one-eighth wave retardance is produced based on an angle of incidence to the first surface and a prism refractive index.

9 . The focus system of claim 6 , wherein the prism includes a second surface that receives the interrogation beam from the first surface, wherein the second surface has a coating that provides a retardance of less than λ/50, λ/100, or λ/200.

10 . The focus system of claim 9 , wherein the prism is a solid corner cube.

11 . The focus system of claim 9 , wherein the prism is an air spaced corner cube.

12 . A laser radar, comprising:
a laser that produces an interrogation optical beam in a first state of polarization; an objective lens situated to direct the interrogation optical beam to a target in a second state of polarization and receive a portion of the interrogation optical beam returned from the target; and a focus optical system that includes a retroreflector and a return reflector, wherein at least one of the retroreflector and the return reflector is translatable with respect to the objective lens so as to shape the interrogation beam at the target, and further wherein the retroreflector provides a retardance that converts the first state of polarization to the second state of polarization.

13 . The laser radar of claim 12 , wherein the first state of polarization is a linear state of polarization and the second state of polarization is a circular state of polarization.

14 . The laser radar of claim 13 , wherein the retroreflector is situated to provide a one-eighth wave retardance for input beam propagation from an input surface of the retroreflector to the return reflector.

15 . The laser radar of claim 14 , wherein the retroreflector provides the one-eighth wave retardance based on reflection at a selected reflective surface of the retroreflector.

16 . The laser radar of claim 15 , wherein the selected reflective surface of the retroreflector is oriented with respect to the interrogation beam to provide one-eighth wave retardance by total internal reflection.

17 . The laser radar of claim 16 , further comprising a multilayer coating situated at the selected reflective surface of the retroreflector, wherein the one-eighth wave retardance is provided by the multilayer coating.

18 . The laser radar of claim 15 , further comprising a low retardance coating situated at a least one reflective surface of the retroreflector that is different than the selected reflective surface.

19 . The laser radar of claim 15 , wherein the retroreflector is a corner cube prism, an air corner cube, or a roof prism.

20 . The laser radar of claim 19 , wherein the retroreflector is a crown glass corner cube prism situated so that an angle of incidence of the interrogation optical beam to the selected surface is between 47 and 53 degrees.

21 . A method of interrogating a target, comprising:
directing an input interrogation optical beam in a first state of polarization to a retroreflector that produces an output interrogation optical beam in a second state of polarization; adjusting a focus of the output interrogation optical beam at the target by translation of the retroreflector; detecting a portion of the output interrogation optical beam received from the target; and based on the detected portion, estimating at least one of a target dimension or position.

22 . The method of claim 21 , wherein the first state of polarization is a linear state of polarization and the second state of polarization is a circular state of polarization.

23 . The method of claim 22 , further comprising producing the output interrogation optical beam in the second state of polarization by total internal reflection at a selected surface of the retroreflector.

24 . The method of claim 22 , further comprising producing the output interrogation optical beam in the second state of polarization by total internal reflection at a multilayer coated surface of the retroreflector.

25 . An apparatus for measuring a distance to a target, comprising:
a laser source that produces a measurement beam in a first state of polarization; a focus optical system that includes a retroreflector, the focus optical system situated to direct the measurement beam in a second state of polarization to the target; a stage coupled to the focus optical system and movable along a first axis so as to select a propagation distance to the target of the measurement beam in the second state of polarization; and a detector that detects a reflected portion of the measurement beam from the target, wherein reflected portions in the first state of polarization are converted into the second state of polarization by the focus optical system reflector.

26 . The apparatus of claim 25 , wherein the first state of polarization is a linear state of polarization and the second state of polarization is a circular state of polarization.

27 . The apparatus of claim 26 , wherein the retroreflector provides a one-eighth wave retardance based on reflection at a selected reflective surface of the retroreflector.

28 . The apparatus of claim 27 , further comprising a low retardance coating situated on at a least one reflective surface of the retroreflector other than the selected reflective surface.

29 . The apparatus of claim 26 , wherein a portion of the measurement beam returned from the target in a third state of polarization is converted to a fourth state of polar

Assignees

• Nikon Corp

Inventors

• Smith Daniel Gene

Classifications

• G01S7/4812 Primary

  transmitted and received beams following a coaxial path · CPC title

• G01S17/08

  for measuring distance only (indirect measurement G01S17/46; active triangulation systems G01S17/48) · CPC title

• G01S7/4818

  using optical fibres · CPC title

• G02B5/122

  cube corner, trihedral or triple reflector type · CPC title

• G01S17/42

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title