Three Mirror Anastigmat Spectrograph Low F-Value Design
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Solution Overview
Problem
Echelle spectrographs face challenges with high effective f-values, limiting light throughput and image quality, and are not suitable for applications like Raman spectroscopy due to low f-value requirements.
Innovation Solution
A three-mirror anastigmat (TMA) design with a common vertex axis, incorporating a collimating mirror, diffraction grating, dispersive prism, primary, secondary, and tertiary mirrors, allows for adjustable f-value and increased light throughput by optimizing the focal length and aperture stop, effectively reducing the f-value to f/3 or faster.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a typical echelle spectrograph design is used, then spectral resolution and order separation are achieved, but light throughput is limited due to high effective f-value
Solution Approach 1:
The patent changes the optical parameters of the spectrograph by implementing a TMA design with specific mirror curvatures and positions, reducing the effective f-value from f/7 or greater to f/3 or faster. This parameter change increases light throughput by approximately 10 times while maintaining spectral resolution through optimized optical path design.
2Measurement precision
If a high effective f-value design is used, then spectral order separation is maintained, but the spectrograph cannot be used for applications like Raman spectroscopy requiring low f-value
Solution Approach 1:
The TMA design with adjustable focal length and aperture stop allows the effective f-value to be reduced to f/3 or faster, expanding the spectrograph's applicability to Raman spectroscopy and other low-light applications while maintaining spectral order separation through the three-mirror anastigmat configuration.
3Loss of energy
If the focal length is reduced to lower f-value, then light throughput increases, but optical aberrations may increase
Solution Approach 1:
The patent segments the optical system into three separate mirrors (primary, secondary, and tertiary) with specific curvature and positioning. This segmentation allows each mirror to correct specific aberrations while collectively achieving anastigmatism, enabling low f-value design without sacrificing optical quality.
Solution Approach 2:
The TMA design introduces a complex three-dimensional optical path with multiple reflections and specific mirror orientations. This dimensional complexity allows the system to achieve both low f-value and aberration correction by distributing optical functions across multiple surfaces in three-dimensional space.
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 enhances light throughput by approximately 10 times compared to prior art, enabling better image quality and spectral resolution while maintaining spectral order separation, making it suitable for applications like Raman spectroscopy and LIBS.
Implementation Method 1
An echelle grating to diffract light at high resolutions and high diffraction orders
Implementation Method 2
A second cross-dispersing element is used to spatially separate the orders
Data Source
AI summary
A spectrograph including a primary mirror, a secondary mirror, and a tertiary mirror forming a TMA having a common vertex axis. The spectrograph also may include a collimating mirror, a diffraction grating, and a dispersive prism. The collimating mirror and an entrance aperture form an interchangeable module. Radiation received through the entrance aperture is reflected in a collimated pattern towards an aperture stop. The diffraction grating, located between the collimating mirror and prism, diffracts radiation passed through the aperture stop into multiple beams directed onto the prism. A flat mirror, located to one side of the vertex axis. receives and reflects the multiple beams exiting the prism onto the primary mirror, where they are reflected onto the secondary mirror. The secondary mirror reflects the beams to the tertiary mirror where they are reflected onto an image plane located on the other side of the vertex axis.