Anastigmatic Imaging Spectrograph With Aspheric Aberration Correction
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Solution Overview
Problem
Czerny-Turner spectrographs suffer from uncorrected spherical, coma, and astigmatism aberrations, particularly at low f/#, which degrade spatial and dispersive resolution, leading to image distortion and reduced performance in multi-channel spectroscopy and hyper-spectral imaging.
Innovation Solution
The spectrograph employs aspheric corrector plates and concave focusing elements to balance and correct residual spherical, coma, and astigmatism aberrations, ensuring anastigmatic imaging over the entire focal plane array detector, even at wavelengths away from the design wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Czerny-Turner spectrograph design is used with spherical mirrors, then the optical path is simplified and manufacturing is easier, but spherical, coma, and astigmatism aberrations are introduced that degrade imaging performance
Solution Approach 1:
The patent applies aspheric surfaces to the mirrors, changing the geometric parameters from spherical to aspheric. This allows the optical system to correct aberrations while maintaining manufacturability through precise surface figure control, resolving the contradiction between ease of manufacture and imaging performance.
Solution Approach 2:
The patent introduces a corrector plate as an intermediary optical element between the spherical mirrors and the focal plane. This corrector plate compensates for the aberrations introduced by the spherical mirrors, allowing the system to maintain both manufacturing simplicity and high imaging performance.
2Use of energy by moving object
If low f/# mirrors are used to increase light gathering capability, then sensitivity is improved, but spherical aberration increases as 1/(f/#)^3
Solution Approach 1:
The patent uses aspheric mirror surfaces that are specifically designed to correct spherical aberration at low f/# values. By changing the surface geometry from spherical to aspheric, the system maintains high light gathering capability while eliminating the 1/(f/#)^3 spherical aberration penalty.
Solution Approach 2:
The patent takes the harmful spherical aberration that naturally occurs at low f/# and converts it into a design feature by using aspheric surfaces. The aspheric shape is specifically optimized to produce the opposite aberration that cancels the spherical aberration, effectively converting the harmful effect into a beneficial correction.
3Volume of moving object
If off-axis chief rays are used in Czerny-Turner design, then compact configuration is achieved, but coma and astigmatism asymmetrically distort spectral features
Solution Approach 1:
The patent modifies the off-axis ray parameters by using aspheric mirror surfaces that are optimized for the specific off-axis geometry. This allows the compact Czerny-Turner configuration to be maintained while the aspheric surfaces correct the coma and astigmatism that would otherwise asymmetrically distort spectral features.
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
Achieves high-resolution, anastigmatic imaging across the focal plane array detector, minimizing image aberrations and enhancing the spectrograph's ability to resolve dispersed spectral features and spatial information.
Implementation Method 1
The spectrograph employs aspheric corrector plates and concave focusing elements to balance and correct residual spherical, coma, and astigmatism aberrations
Implementation Method 2
A dispersive element, usually a diffraction grating, is arranged to receive collimated light from the first mirror and disperse collimated light towards the second mirror
Data Source
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AI summary
An apparatus and method are disclosed for producing spectrographic images free of SI, SII, and SIII field aberrations. The apparatus includes a focusing element placed at a distance from a dispersing element equal to the radius of curvature of the focusing element. The apparatus further includes at least one correcting plate for adding or subtracting aberrations.