Multi-Element Retarder for Wideband Ellipsometry

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Solution Overview

Problem

Existing ellipsometer and polarimeter systems face challenges in maintaining acceptable performance over a wide spectral range due to wavelength-dependent retardance issues, and require improved retarder systems that minimize beam deviation and contamination while securing and protecting the components effectively.

Innovation Solution

A multiple element retarder system comprising at least two sequential elements, such as triangular prisms or parallelogram shaped rhombs, that introduce relative phase retardation through internal reflection, with geometry and symmetry ensuring minimal angular and lateral deviation of the output beam, and an optional containment system for purging and alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a single waveplate is used as compensator element, then the device complexity is low, but the retardance exhibits strong (1/wavelength) dependence across the spectral range

Engineering Contradiction:

Improvecompensator element structureVSAvoidretardance uniformity across spectrum

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent divides a single waveplate into multiple sequential waveplates (typically three) with different retardances and orientations. This segmentation allows each waveplate to contribute differently to the total retardance, enabling the system to maintain more uniform retardance across a wide spectral range by compensating for the (1/wavelength) dependence of individual plates.

Inventive Principle:

Principle #1Segmentation

2Ease of manufacture

If traditional birefringent waveplates are used, then ease of manufacture is good, but beam deviation and lateral offset occur

Engineering Contradiction:

Improvewaveplate fabricationVSAvoidbeam locus accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent introduces wedge angles to the waveplates, creating asymmetric geometries that deliberately induce beam deviation in opposite directions for different wavelengths. This asymmetry, when combined with multiple plates of different orientations, allows the system to compensate for beam locus errors and achieve better overall beam alignment across the spectral range.

Inventive Principle:

Principle #4Asymmetry

3Adaptability or versatility

If the spectral range is extended, then the versatility of the system is improved, but the retardance uniformity deteriorates due to wavelength dependence

Engineering Contradiction:

Improvespectral range coverageVSAvoidretardance consistency

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent changes multiple parameters simultaneously: the number of waveplates, their individual retardances, their orientations, and their wedge angles. By optimizing these parameters together, the system achieves relatively uniform retardance across an extended spectral range (e.g., 190-1700 nm), enabling versatile spectroscopic ellipsometry and polarimetry measurements.

Inventive Principle:

Principle #35Parameter changes

4Manufacturing precision

If multiple waveplates are used to minimize wavelength dependence, then the retardance uniformity is improved, but the device complexity increases

Engineering Contradiction:

Improveretardance uniformity across spectrumVSAvoidcompensator element structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent designs the multi-waveplate system with universal applicability to both spectroscopic ellipsometry and polarimetry. The same compensator assembly serves multiple functions: providing uniform retardance across spectrum, minimizing beam deviation, and working with rotating element configurations. This multi-functionality justifies the increased complexity by delivering broad performance benefits.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

The system achieves stable and accurate phase retardation across a wide spectral range with minimal beam deviation and polarization change, even when the input beam angle changes, and effectively protects the components from contamination.

Implementation Method 1

at least one location selected from the group consisting of: between said source of electromagnetic radiation and said stage for supporting a sample; and between said stage for supporting a sample and said detector

Methodology Applied

Scientific EffectInternal reflection: Total Internal Reflection

Implementation Method 2

a system for introducing a relative phase retardation between orthogonal components of a polarized electromagnetic beam entered thereinto

Methodology Applied

Scientific EffectPhase retardation: Birefringence

Data Source

PatentUS8462341B2Mounting for deviation angle self compensating substantially achromatic retarder

Publication Date: 2013.06.11 J A WOOLLAM CO

AI summary

A system, method of configuring, and application a system for introducing a relative phase retardation into orthogonally polarized components of an electromagnetic beam entered thereinto, wherein the system involves a substantially achromatic multiple element retarder system for use in wide spectral range (for example, 190-1700 nm) rotating compensator spectroscopic ellipsometer and/or polarimeter systems.