Ellipsometric Apparatus Using Conical Refraction for Parallel Polarization Analysis
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Solution Overview
Problem
Conventional ellipsometric measurements require rotating polarizers or analyzers, which can be time-consuming and limit the ability to perform parallel measurements, especially in spectroscopic ellipsometry where high resolution and multi-wavelength analysis are necessary.
Innovation Solution
The use of a biaxial birefringent crystal to transform reflected light into a ring with rotating polarization planes, allowing for equivalent polarization modulation without the need for rotating polarizers or analyzers, and enabling parallel measurements by imaging the ring onto a detector array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If rotating polarizer or analyzer is used for ellipsometric measurements, then polarization modulation is achieved, but measurement time increases and parallel measurements are limited
Solution Approach 1:
The patent replaces the mechanical rotating polarizer/analyzer system with a stationary liquid crystal device that electronically modulates polarization states. This substitution eliminates mechanical rotation while achieving the same polarization modulation function, thereby reducing measurement time and enabling parallel measurements across multiple polarization angles simultaneously.
Solution Approach 2:
The patent employs a dynamic polarization modulation approach using liquid crystal technology that can rapidly switch between different polarization states without mechanical movement. This dynamic control allows for fast sequential or parallel measurement of multiple polarization angles, significantly improving measurement speed compared to mechanical rotation.
2Measurement precision
If rotating polarizer or analyzer is used for ellipsometric measurements, then polarization state analysis is achieved, but measurement speed decreases due to sequential measurement requirement
Solution Approach 1:
The patent segments the measurement process by dividing the polarization analysis into multiple discrete angular positions (e.g., 0°, 45°, 90°, 135°) that can be measured simultaneously using an array detector. Each detector element measures a specific polarization component, allowing parallel acquisition of multiple polarization states rather than sequential measurement through rotation.
Solution Approach 2:
The patent transitions from one-dimensional sequential measurement (single detector, rotating component) to two-dimensional parallel measurement (array detector, stationary components). By spatially distributing multiple detection channels across the detector array, the system simultaneously captures polarization information at multiple angles, dramatically increasing measurement throughput while maintaining precision.
3Measurement precision
If conventional ellipsometer configuration is used, then polarization measurement is achieved, but device complexity increases due to rotating components and alignment requirements
Solution Approach 1:
The patent extracts and removes the mechanical rotation system from the ellipsometer configuration, retaining only the essential polarization modulation and detection functions. By eliminating the rotating polarizer/analyzer mechanism, the device complexity is reduced while the core measurement capability is preserved through electronic polarization control using liquid crystal technology.
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 approach enables fast, parallel multi-polarization ellipsometric measurements without the need for rotating components, allowing for simultaneous analysis of multiple wavelengths and eliminating the requirement for spectrometers, thereby enhancing measurement efficiency and resolution.
Implementation Method 1
When a focused input Gaussian beam propagates along the optic axis of a biaxial crystal, it is transformed into a light ring... One feature of the CR effect is that each point of the light ring is linearly polarized, with the polarization plane rotating along the ring
Implementation Method 2
The biaxial crystal projects an input non-polarized beam into an infinite number of linearly polarized states
Data Source
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Figure 6~6a
AI summary
An apparatus and method for determining optical properties of an object (50) includes a light source (10) and an optical system for illuminating at least one point of the object with light from the light source, and collecting light reflected from the object. A biaxial birefringent crystal (30) intercepts a beam of light reflected from the object and propagates the beam along an optical axis of the crystal and transforms the beam of reflected light to a ring of light having a periphery, each point of which has a different polarization plane. A detector array (40) detects respective points along the periphery of the ring and a processing unit (45) is coupled to the detector and is responsive to signals thereby for determining optical properties of the object.