Grazing Incidence Interferometer with Rotatable Half-Wave Plate

Solution Overview

Problem

Grazing incidence interferometers face challenges in accurately measuring surface profiles when machining marks or similar defects are present on the target surface, as they affect the reflection beam intensity, leading to difficulties in analyzing interference fringes during continuous rotation of the workpiece.

Innovation Solution

The interferometer incorporates a λ/2 plate rotatable around the main optical axis to adjust the light intensity ratio between the measurement and reference beams, along with detection units to maintain optimal light levels, ensuring accurate profile measurement by controlling the light source and beam splitter configurations to counteract changes in reflection due to surface defects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the workpiece is mounted on a rotary stage and continuously measured to measure a wider area profile, then the measurement area is expanded, but the reflection beam amount significantly changes due to machining marks causing difficulty in profile analysis

Engineering Contradiction:

Improvemeasurement areaVSAvoidprofile analysis accuracy

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent introduces a rotatable λ/2 plate that can dynamically adjust the light amount ratio between the measurement beam and reference beam during the measurement process. This dynamic adjustment compensates for variations in reflection beam intensity caused by machining marks on the target surface, maintaining reliable profile analysis across the expanded measurement area.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the light amount ratio parameter between the measurement beam and reference beam to adapt to varying reflection conditions. By adjusting this parameter through the rotatable λ/2 plate, the system maintains optimal interference fringe contrast even when the reflection beam amount changes due to surface features like machining marks.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the light amount ratio between measurement beam and reference beam is fixed, then the device structure is simple, but the interference fringe contrast decreases when reflected light amount is reduced due to machining marks

Engineering Contradiction:

Improvedevice structureVSAvoidinterference fringe contrast

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces a rotatable λ/2 plate that can dynamically adjust the light amount ratio between the measurement beam and reference beam during the measurement process. This dynamic adjustment compensates for variations in reflection beam intensity caused by machining marks on the target surface, maintaining reliable profile analysis across the expanded measurement area.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the light amount ratio parameter between the measurement beam and reference beam to adapt to varying reflection conditions. By adjusting this parameter through the rotatable λ/2 plate, the system maintains optimal interference fringe contrast even when the reflection beam amount changes due to surface features like machining marks.

Inventive Principle:

Principle #35Parameter changes

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

This solution enables highly accurate surface profile measurement even with machining marks, by dynamically adjusting the light intensity ratio and controlling the light source, thereby maintaining the contrast and precision of interference fringes.

Implementation Method 1

the beam splitter splits the light from the light source into the reference beam with a first linear polarization direction and the measurement beam with a second linear polarization direction orthogonal to the first linear polarization direction

Methodology Applied

Scientific EffectPolarization: Polarisation

Implementation Method 2

cause an interference with a reference beam, the grazing incidence interferometer including: a light source that emits light; a beam splitter that splits the light from the light source into the reference beam and the measurement beam

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 3

the ratio changer comprises a λ/2 plate rotatable around a main optical axis of the light from the light source

Methodology Applied

Scientific EffectPolarization rotation: Polarisation

Data Source

PatentUS9644941B2Grazing incidence interferometer

Publication Date: 2017.05.09 MITUTOYO CORP

AI summary

A grazing incidence interferometer is configured to measure a profile of a target surface using a measurement beam radiated on the target surface in a direction oblique to a normal line of the target surface and reflected on the target surface to cause an interference with a reference beam. The grazing incidence interferometer includes: a light source to emit light; a first polarization beam splitter that splits the light from the light source into the reference beam and the measurement beam; a ratio changer that changes a light amount ratio between the reference beam and the measurement beam; a second polarization beam splitter that synthesizes the measurement beam reflected on the target surface and the reference beam; and an image capturing camera that receives the synthesized beam of the reference beam and the measurement beam.