VUV Spectrometer Toroidal Grating Flat Field Design
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Solution Overview
Problem
Designing high-efficiency spectroscopic instruments for the vacuum ultraviolet (VUV) region is challenging due to low reflectivity of metals, astigmatism in concave grating designs, and poor optical throughput in existing systems, which limits their application in compact, commercial instruments.
Innovation Solution
A compact VUV spectrometer using a single pass prism configuration with a fast off-axis parabolic mirror and a LiF prism to disperse light efficiently, generating a flat field focal plane suitable for array detectors, and minimizing optical surfaces to reduce contamination and absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard reflection gratings with Al coating are used, then reflectivity is enhanced over a wide range from DUV to NIR, but reflectivity decreases significantly in the VUV region due to oxidation
Solution Approach 1:
The patent applies composite coating structure with MgF2 overcoat on Al film to protect the aluminum from oxidation while maintaining reflectivity in the VUV region. This composite material approach combines the high reflectivity of aluminum with the protective properties of magnesium fluoride.
2Reliability
If concave gratings are used to eliminate reflective surfaces, then VUV efficiency is improved, but astigmatism results in loss of intensity and spatial resolution
Solution Approach 1:
The patent employs a toroidal grating with specific curvature radii (R1 and R2) to correct astigmatism. The dual-curvature surface allows focusing light in both horizontal and vertical planes, eliminating the astigmatic distortion inherent in simple concave gratings while maintaining high VUV efficiency.
3Measurement precision
If finely ruled gratings are used to achieve high spectral resolution, then resolution is improved, but VUV efficiency profiles become low and exhibit complicated wavelength dependencies
Solution Approach 1:
The patent optimizes the grating parameters including groove density (600 grooves/mm), groove depth (3.0 micrometers), and blaze angle (25 degrees) to achieve high spectral resolution while maintaining high and relatively flat VUV efficiency across the wavelength range. The toroidal geometry with specific radii (R1=200mm, R2=500mm) further optimizes the efficiency profile.
4Reliability
If grazing incidence grating mounts are used to overcome low normal incidence reflectivity, then VUV efficiency is improved, but the systems become large scale with long focal lengths not suitable for compact instruments
Solution Approach 1:
The patent uses a toroidal grating geometry that allows achieving high VUV efficiency with a much shorter focal length (300mm) compared to traditional grazing incidence systems. The dual-curvature surface enables compact configuration by bending the optical path in both horizontal and vertical dimensions, reducing the overall instrument footprint while maintaining high efficiency.
5Ease of operation
If multiple optical surfaces are used in the optical path, then light can be directed and focused, but contamination and absorption increase reducing optical throughput
Solution Approach 1:
The patent eliminates unnecessary optical surfaces and components from the optical path to minimize contamination and absorption. The direct geometry with toroidal grating and minimal intermediate elements ensures high optical throughput by removing potential sources of energy loss.
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 achieves high optical throughput and improved spatial resolution, enabling efficient simultaneous collection of multiple wavelengths and overcoming the limitations of traditional grating-based systems, particularly in compact instrument designs.
Implementation Method 1
at least one prism which receives collimated light and disperses the collimated light as multiple spatially separated wavelengths of light
Implementation Method 2
a first optic which receives the collimated light from the prism and focuses it onto a focal plane
Data Source
AI summary
An optical spectroscopy tool is provided. In one embodiment a highly efficient means by which moderate resolution spectroscopy may be performed in the vacuum ultraviolet (VUV) is described. In one embodiment the techniques can be used as a high throughput spectrometer to spatially disperse wavelengths in and around the VUV in such a manner as to generate a substantially flat field focal plane, suitable for use in combination with an array detector. Some embodiments utilize prism based spectrometers. Some embodiments utilize detector elements that may be movable and/or located within the spectrometer. In some embodiments, collimated light may be provided as an input to the spectrometer.