Interferometric Gas Sensor Retarder Design
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Solution Overview
Problem
Existing gas detection systems using optical interferometry suffer from significant radiation loss due to polarizers, which is problematic for space applications where detection of small amounts of radiation is critical.
Innovation Solution
A detector system with a retarder comprising multiple birefringent media, arranged to create polarized beam components with a mutual path difference, minimizing focal shift and angular dependency of the Optical Path Difference (OPD) value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a polarizer is used in the interferometer system, then the radiation from one polarisation state can be detected, but a significant amount of radiation is lost
Solution Approach 1:
The invention removes the polarizer from the optical path entirely. Instead of using a polarizer to select one polarisation state, the system uses a beam splitter to divide the incoming radiation into two separate detection paths, each equipped with its own detector. This extraction of the polarizer eliminates the inherent radiation loss while preserving the ability to detect polarisation-dependent absorption features
Solution Approach 2:
The invention segments the single detection path into two separate paths. Each path has its own detector that measures radiation from a specific polarisation state. By segmenting the detection system, both polarisation states can be detected simultaneously without one blocking the other, thus eliminating the radiation loss associated with using a single polarizer
2Measurement precision
If a retarder is used to create optical path difference, then phase difference between polarisation components is achieved, but a focus error is induced between the two interferometer branches
Solution Approach 1:
The invention addresses the focus error by introducing an additional optical element (a compensating plate or lens) in one of the interferometer branches. This compensating element is positioned at a different location in the optical path, effectively using another dimension (position in optical path) to counteract the focus error without altering the retarder's primary function of creating optical path difference
Solution Approach 2:
The invention compensates for focus error by adjusting parameters of optical elements in the system. Specifically, the thickness or refractive index of compensating plates is tuned to match the focal shift introduced by the retarder, thereby restoring focal plane alignment while maintaining the required optical path difference
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 minimizes radiation loss by optimizing the optical path difference and reducing focal shift, enabling more efficient detection of gases in space applications while maintaining flexibility in optical path difference settings.
Implementation Method 1
The retarder comprises multiple birefringent media having mutually different materials and each having optical axes that are not aligned with the polarized beam in order to create polarized beam components traveling along the respective optical axes of the birefringent media having a mutual path difference
Implementation Method 2
at least one interferometric stage is arranged to receiving one of said polarized beams to produce an interferometric image on said at least one detector
Implementation Method 3
a band filter arranged in the optical beam path before the detector; for transferring a beam with a wavelength spectrum including an absorption wavelength corresponding to said gas substance
Data Source
AI summary
A detector system for spatially resolved detection of a gas substance in an area is described. The detector system includes a detector comprising an image sensor; a band filter arranged in an optical beam path before the detector for transferring a beam with a wavelength spectrum including an absorption wavelength corresponding to the gas substance, a telescope, a polarizing beam splitter, and an interferometric stage including a retarder for creating an optical path difference for measuring absorption dips due to the presence of the gas substance. The retarder includes multiple birefringent media arranged with the optical axes relative to each other so that at least one increases an optical path difference and at least one decreases an optical path difference between the polarized beam components, and the thicknesses of the birefringent media are tuned to minimize a focal shift between the polarized beam components.