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KR-20260064719-A - Dynamic interferometer illuminator

KR20260064719AKR 20260064719 AKR20260064719 AKR 20260064719AKR-20260064719-A

Abstract

An illumination system for an interferometer is disclosed, and the illumination system for an interferometer comprises: a source of system light; a steering-mirror assembly for receiving and reflecting system light in at least two orthogonal directions; a tracking mechanism for tracking the angular orientation of the steering-mirror assembly in two orthogonal directions and providing electronic signals indicating the angular orientation; a focusing lens assembly for focusing the system light reflected from the steering-mirror assembly onto a focused spot on a two-dimensional plane corresponding to the source plane of the interferometer; and an electronic controller operably coupled to the steering-mirror assembly and configured to cause the focused spot on the source plane to follow a predetermined motion trajectory.

Inventors

  • 덱 레슬리 엘.
  • 수비츠키 제임스 에이.

Assignees

  • 지고 코포레이션

Dates

Publication Date
20260507
Application Date
20241007
Priority Date
20240830

Claims (20)

  1. As a lighting system for an interferometer, (a) Source of system light; (b) a steering-mirror assembly for receiving and reflecting the system light in at least two orthogonal directions; (c) A tracking mechanism for tracking the angular orientation of the steering-mirror assembly in the two orthogonal directions and providing electronic signals indicating the angular orientation; (d) a focusing lens assembly for focusing the system light reflected from the steering mirror assembly onto a focused spot on a two-dimensional plane corresponding to the source plane of the interferometer; and (e) A system comprising an electronic controller operably coupled to the steering-mirror assembly and configured to cause the focused spot on the source plane to follow a predetermined motion trajectory.
  2. In paragraph 1, A system in which the steering-mirror assembly comprises at least one mirror and transducer element, and the electronic controller is configured to operably control the orientation of the at least one mirror using the transducer elements.
  3. In paragraph 2, A system in which at least one mirror comprises a single two-dimensional steering mirror.
  4. In paragraph 2, A system comprising at least one mirror configured to steer a beam in two orthogonal directions.
  5. In paragraph 1, The above focusing lens assembly is a telecentric system.
  6. In paragraph 1, The tracking mechanism comprises electromechanical sensors or photoelectric sensors directly coupled to the steering-mirror assembly to provide the electronic signals indicating the angle orientation.
  7. In paragraph 1, The above tracking mechanism is a system comprising a position-sensing detector to provide the electronic signals indicating the angle orientation.
  8. In Paragraph 7, The tracking mechanism further comprises a control beam source for detecting the control beam with a position-sensing detector to illuminate at least one mirror in the steering-mirror assembly with a control beam and subsequently provide the electronic signals indicating the angle orientation.
  9. In Paragraph 7, The tracking mechanism comprises an optical device for directing a portion of the system light to the position-sensing detector to pick-off a portion of the system light reflected by the steering-mirror assembly in order to provide electronic signals indicating the angle orientation.
  10. In paragraph 1, A system in which the electronic controller is additionally operably coupled to the tracking mechanism, and during operation, the electronic controller corrects the angular orientation of the steering-mirror assembly based on the difference between the required mirror orientation and the measured electronic signals of the mirror orientation provided by the tracking mechanism.
  11. In paragraph 1, A system in which the electronic controller stores calibration information for mapping the angular orientation of the steering-mirror assembly to the position of a focal spot within the source plane of the interferometer.
  12. In paragraph 1, The electronic controller comprises a system including a user interface for receiving information defining the predetermined motion trajectory.
  13. In paragraph 1, The electronic controller comprises a system including a memory for storing information defining the predetermined motion trajectory.
  14. In paragraph 1, A system in which the above-determined motion trajectory comprises a plurality of arcs having different radii from the optical axis of the interferometer.
  15. In paragraph 1, A system in which the above-determined motion trajectory includes a plurality of circles of different radii centered on the optical axis of the interferometer.
  16. In paragraph 1, A system in which the above-determined motion trajectory comprises at least one spiral centered on the optical axis of the interferometer.
  17. In paragraph 1, The above system light source includes a laser.
  18. In paragraph 1, The above interferometer is a system that is a Michelson interferometer, a Twyman-Green interferometer, or a Fizeau interferometer.
  19. In Paragraph 18, A system configured such that the interferometer is configured to illuminate a sample across the interferometer aperture with a wavefront defined by the position of the focused spot within the source plane of the interferometer.
  20. In Paragraph 19, The above-described focusing lens assembly is a system that defines an numerical aperture (NA) that provides divergence of the focused spot sufficient to cover the aperture of the interferometer.

Description

Dynamic interferometer illuminator This application claims priority to U.S. application No. 18/820,383 filed on August 30, 2024, which in whole is incorporated herein by reference to provisional application No. 63/544,007 filed on October 13, 2023. The present disclosure relates to an optical interferometer. Interferometers are widely used tools for the high-precision characterization of engineering surfaces. Surface profiling is one such application, where interferometers are applied to analyze surface topography across a wide range of spatial scales and resolutions. Interferometers designed for the topographical analysis of optically smooth surfaces of medium size (~10 mm to > 1 m) are employed due to their ease of use, speed, high (nm-level) precision, and non-contact nature of measurement. Often, phase-shifting interferometry (PSI) techniques are integrated to enable rapid and convenient surface measurement down to nanometer fractions without the risk of damage to high-value surfaces. These interferometers are available in various optical geometries that optimize different measurement characteristics. For example, Michelson interferometers are light source-friendly and accommodate a wide range of source sizes and/or bandwidths, whereas Twyman-Green geometry allows for convenient access to reference paths. Lasers have made Fizeau geometry particularly popular due to its ease of installation and common path architecture, which minimizes sensitivity to manufacturing errors in the tool's optics. Fizeau combined with a laser is ideally suited for the long optical paths often encountered when characterizing large or complex optical assemblies. Regardless of the architecture used, these tools often have similar lighting configurations; the light source is focused on a point (or spot) located on the back focal plane (BFP) of the lens (collimator). The source spot located on the BFP and on the optical axis defined by the collimator covers the entire aperture and generates a flat wavefront that propagates parallel to the optical axis. Changes in the wavefront after reflection from the surface(s) of interest are captured by a camera and often analyzed using PSI techniques to reconstruct the surface topography. Additional refractive/diffractive elements after the collimator provide alternative wavefronts for matching to different test surfaces; there are lenses for testing convex or concave spherical surfaces or computer-generated holograms (CGH) for non-spherical surfaces. In all cases, the lighting source point must be stable to minimize errors in the measurement process and generally spatially constrained to maximize wavefront quality and interference contrast, which directly affects the measurement signal-to-noise ratio (SNR). It is known that static lighting source shapes other than a single point offer different advantages. For example, when using coherent lighting, static and spatially extended disks with a diameter larger than the spatial resolution limit of the interferometer have been used to reduce coherent noise; however, this technique is limited to a disk size and a cavity optical thickness smaller than the longitudinal coherence limit defined by the optical system. Another prior art method discloses a source shape different from a single point or disk that provides advantages. One prior art shape, a thin fixed-radius ring centered on an optical axis and diffraction-limited along the radial dimension (see US Patents 5,643,024 and 6,804,011), provides coherent noise reduction without the cavity thickness limitation of a disk. Such a source shape can be created by either static or dynamic means. For example, a static ring shape can be created as a holographic optical element or an axicon. Static shapes have the advantage of being physically stable and all points within the shape contribute to interference simultaneously, but they have the disadvantage when used with coherent light due to mutual interference between different points of the source shape. Therefore, in coherent illumination, static shapes often require additional optical elements to eliminate the extra interference generated by mutual coherence, such as a rotating diffuser, which is itself a dynamic element. It may be more efficient and common to dynamically generate source shapes using moving point sources that track the desired shape. In this way, any shape can be generated with the same device, and each interferogram includes contributions from all points of the shape without mutual interference effects. The conventional method used with ring shapes is referred to as a coherent artifact reduction system (CARS), which consists of averaging phase maps sequentially acquired from many locations distributed around the ring. Although effective, this stop-and-stare technique is slow. Furthermore, an alternative described in the prior art is to dynamically track the entire ring shape within the camera's frame integration time. In this way, each