Shaped Aperture for Grating Spectrometer Resolution
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Solution Overview
Problem
Grating spectrometers face issues with stray light and aberrations due to overfilling and off-axis optical configurations, leading to reduced image quality and throughput, which are typically addressed by minimizing aperture size and fold angles, but this compromises sensitivity.
Innovation Solution
A shaped aperture with a narrow beam in the horizontal plane and a wider beam in the vertical plane is used, allowing for improved image quality without significant throughput loss, utilizing an elliptical aperture with a fixed height and variable width, and patterned on a transparent input block for ease of manufacture and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reduced diameter round aperture is used to minimize aberrations, then image quality improves, but throughput decreases significantly
Solution Approach 1:
The aperture is designed with different dimensions in different directions (narrow in horizontal, wide in vertical) to provide different beam constraints for different spatial orientations. This allows the system to maintain narrow beam width where needed for resolution while preserving throughput in directions where it matters less, thereby resolving the contradiction between image quality and throughput
Solution Approach 2:
The invention transitions from a symmetric round aperture to an asymmetric shaped aperture with elliptical cross-section. The asymmetric shape provides narrow horizontal beam width to reduce aberrations while maintaining larger vertical dimension to preserve throughput, thus resolving the trade-off between image quality and light transmission
2Measurement precision
If aperture size is minimized to reduce aberrations, then resolution improves, but sensitivity deteriorates
Solution Approach 1:
The shaped aperture applies different aperture dimensions in different spatial directions, providing narrow beam width horizontally to improve resolution while maintaining larger vertical dimension to preserve sensitivity. This directional differentiation resolves the contradiction by optimizing each dimension for its primary function
Solution Approach 2:
The invention moves from a single-dimensional aperture size parameter to a two-dimensional aperture shape parameter. By independently controlling horizontal and vertical dimensions, the system can optimize resolution in the horizontal direction while maintaining sensitivity through the vertical dimension, thus resolving the contradiction
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 solution maintains high sensitivity while reducing aberrations and peak intensity smearing, with overall throughput decreasing by a factor of 2 but peak intensity loss limited to 15-25%, primarily eliminating light from the 'tails', thus enhancing image quality.
Implementation Method 1
an aperture (2) is used after the slit (1) to limit the acceptance cone of the spectrometer to only light that will strike the input minor (3)
Implementation Method 2
M1 (3) is used as an off-axis collimating element. This introduces a variety of aberrations into the collimated beam, primarily astigmatism and coma
Implementation Method 3
The diffraction angle from the grating (5) depends non-linearly on the angle of incidence
Implementation Method 4
The diffraction angle from the grating (5) depends non-linearly on the angle of incidence, so the angular distribution present in the incident beam is broadened in the diffracted beam
Implementation Method 5
M2 (4) is also used as an off-axis element, and therefore contributes its own aberrations into the image formed at the detector (6)
Data Source
AI summary
An aperture shaped to provide a narrow beam in the horizontal plane but a wider beam in the vertical plane that will provide improved image quality in spectrometers without sacrificing as much throughput as typically experienced using a reduced diameter round aperture along with a method of mounting the entrance slit and the limiting aperture on a transparent block for optical stability and ease of alignment is disclosed.