Interferometer with Conjugate Area Light Source for Scattering Surfaces

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Solution Overview

Problem

Conventional interferometers are limited in measuring surface shapes with large differences between the examined and reference surfaces, and struggle to measure scattering surfaces due to non-conjugate relations between light sources and objects, leading to inadequate fringe contrast and measurement accuracy.

Innovation Solution

An interferometer with an area light source of low spatial coherence, arranged in an optically conjugate relation with the examined object, using a rotating diffuser plate and micro lens arrays to form interference fringes between measurement and reference light, allowing for accurate determination of surface shape differences across micro regions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a point light source is used in conventional interferometers, then the interferometer structure is simple, but the examined surface and light source are not optically conjugate, limiting the measurement range for surfaces with large curvature differences

Engineering Contradiction:

Improveinterferometer structureVSAvoidmeasurement range for surface curvature

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The invention divides the point light source into multiple discrete point sources arranged in a specific pattern. This segmentation allows each point source to independently illuminate corresponding regions on the examined surface, establishing optical conjugacy while maintaining the ability to measure surfaces with large curvature differences across the entire field of view.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention transitions from a single-point light source to a multi-point light source arrangement, adding a spatial dimension to the illumination system. This dimensional change enables simultaneous conjugate illumination of multiple regions on the examined surface, expanding the measurement range without significantly increasing system complexity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of stationary object

If an area light source is used in conventional interferometers, then the illumination coverage is improved, but the light sources and examined object are not conjugate, resulting in poor fringe contrast for scattering surfaces

Engineering Contradiction:

Improveillumination coverageVSAvoidfringe contrast

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

The invention segments the area light source into multiple discrete, spatially separated point sources. This segmentation maintains the extended illumination coverage of an area source while ensuring that each point source is optically conjugate to its corresponding region on the examined surface, thereby improving fringe contrast for scattering surfaces.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention applies local quality by ensuring that each point source in the array is conjugate to its corresponding local region on the examined surface. This local conjugacy relationship improves the fringe contrast and measurement precision for scattering surfaces while maintaining overall illumination coverage through the multi-point arrangement.

Inventive Principle:

Principle #3Local quality

3Measurement precision

If the aperture of light receiving elements is reduced to improve fringe contrast detection, then the fringe contrast is improved, but the quantity of light received becomes insufficient

Engineering Contradiction:

Improvefringe contrast detectionVSAvoidlight quantity received

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The invention segments the illumination into multiple discrete point sources, each contributing to the fringe pattern. This segmentation allows the use of smaller aperture light receiving elements for each individual point source while maintaining sufficient total light quantity through the combined contribution of multiple point sources, thereby improving fringe contrast detection without sacrificing light quantity.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables precise measurement of surface shapes with large curvature differences and scattering surfaces by improving fringe contrast and accuracy, allowing for effective surface shape determination across required regions.

Implementation Method 1

interference fringes are formed by interference between measurement light emitted from each small illuminant and reflected on each micro region of the examined surface and reference light emitted from the same small illuminant and reflected on a corresponding micro region of a reference surface

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 2

a light-guiding optical system configured to arrange the area light source and the examined object in an optically conjugate relation with each other

Methodology Applied

Scientific EffectOptical conjugacy: Lens

Data Source

PatentUS8339612B2Shape-measuring interferometer having low-coherence source conjugate to the examined object

Publication Date: 2012.12.25 NIKON CORP

AI summary

Interferometers are provided for measuring the surface shape of an examined object or a transmitted wavefront through the examined object. An exemplary interferometer includes an area light source having a low spatial coherence property, and a light-guiding optical system configured to arrange the area light source and the examined object in an optically conjugate relation with each other.