Achromatic Retarder Using Total Internal Reflection

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Solution Overview

Problem

Existing compensator systems in ellipsometers and polarimeters face challenges in maintaining consistent retardance over a wide spectral range and are affected by changes in beam angle, leading to suboptimal performance.

Innovation Solution

A multiple sequential element system using total internal reflections in at least two elements, such as triangular prisms or parallelogram rhombs, with specific angles and orientations to minimize changes in retardance and beam deviation due to translation and rotation, ensuring the output beam remains undeviated from the input beam.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If traditional birefringent waveplates are used as compensator elements, then the device structure is simple, but the retardance varies significantly with wavelength over a wide spectral range

Engineering Contradiction:

Improvecompensator structureVSAvoidretardance consistency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The compensator is divided into multiple sequential waveplate elements (at least two) with different birefringent materials and orientations. Each waveplate contributes to the total retardance, and by carefully selecting the number, thickness, and orientation of each element, the system achieves substantially achromatic performance across a wide spectral range (190-1700 nm) while maintaining structural simplicity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses composite birefringent materials with different dispersion characteristics (e.g., quartz and MgF2) in sequential waveplate elements. These composite material arrangements are designed to minimize the (1/wavelength) dependence of retardance, providing consistent compensator performance across UV, visible, and near-infrared regions

Inventive Principle:

Principle #40Composite materials

2Device complexity

If a single waveplate is used as compensator, then the device complexity is low, but the performance degrades when beam angle changes occur

Engineering Contradiction:

Improvecompensator configurationVSAvoidellipsometer and polarimeter performance

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The compensator system is segmented into multiple waveplate elements that work together to maintain stable polarization transformation. This segmentation allows the system to compensate for beam angle variations more effectively than a single waveplate, improving measurement precision in ellipsometers and polarimeters without significantly increasing device complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The multi-element waveplate compensator serves multiple functions: it provides wavelength-independent retardance compensation and simultaneously maintains stable performance under varying beam angles. This multi-functionality makes the compensator robust for various measurement conditions in ellipsometry and polarimetry applications

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If dual/multiple waveplate design is used to minimize (1/wavelength) dependence, then the spectral range coverage is improved, but the device complexity increases

Engineering Contradiction:

Improvespectral range coverageVSAvoidcompensator element configuration

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The compensator is segmented into a specific number of waveplate elements (at least two) with optimized thicknesses and orientations. This segmentation strategy achieves substantially achromatic performance across 190-1700 nm while controlling device complexity through systematic design rules for element configuration

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent systematically adjusts key parameters of the waveplate elements including thickness, birefringence, and orientation angles to minimize (1/wavelength) dependence. By optimizing these parameters, the system achieves wide spectral range coverage with a manageable number of elements, balancing adaptability and complexity

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 design provides improved stability and accuracy by maintaining consistent retardance and minimizing polarization changes across a wide spectral range and varying beam angles, enhancing the performance of ellipsometers and polarimeters.

Implementation Method 1

said beam undergoes total internal reflection at least once in each of said elements

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

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

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS7460230B2Deviation angle self compensating substantially achromatic retarder

Publication Date: 2008.12.02 J A WOOLLAM CO

AI summary

A substantially achromatic multiple element compensator system for use in wide spectral range (for example, 190-1700 nm) rotating compensator spectroscopic ellipsometer and/or polarimeter systems. Multiple total internal reflections enter retardance into an entered beam of electromagnetic radiation, and the elements are oriented to minimize changes in the net retardance vs. the input beam angle resulting from changes in the position and/or rotation of the system of elements.