Compact Freeform Echelle Spectrometer Design
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Solution Overview
Problem
Existing echelle spectrometers used with solid-state detectors often sacrifice one or more performance aspects such as spectral resolution, optical throughput, or flexibility in choosing emission lines, due to constraints in optical design and mechanical interferences, particularly when trying to cover a broad spectral range like UV light from 160 to 400 nm.
Innovation Solution
A compact echelle spectrometer design featuring a reflective echelle grating, cross-disperser, and a freeform imaging system with tilted mirrors having rotationally non-symmetric surfaces, optimized for area array detectors like CMOS sensors, which provides high resolution, optical throughput, and low stray light, while maintaining a compact and stable optical system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional high ruling density gratings are used with first order diffraction, then optical throughput is improved, but spectral resolution and angular dispersion are limited
Solution Approach 1:
The patent changes the diffraction order parameter from first order to higher orders (second order and above) to achieve both high optical throughput and high spectral resolution. The echelle grating is specifically designed to efficiently diffract light into higher orders while maintaining high throughput, resolving the traditional trade-off between these two parameters.
2Measurement precision
If higher diffraction orders are used to improve spectral resolution, then angular dispersion is improved, but wavelength overlap between orders occurs
Solution Approach 1:
The patent introduces a cross-dispersing element that adds a second dimension of dispersion orthogonal to the primary grating dispersion. This creates a two-dimensional spectral field-of-view where wavelengths from different orders are separated in the orthogonal direction, eliminating the overlap problem while maintaining high resolution.
3Measurement precision
If echelle grating with cross-dispersion is used to achieve high resolution, then spectral coverage is improved, but mechanical interferences constrain the selection of emission lines
Solution Approach 1:
The patent employs a movable or adjustable cross-dispersing element that can be dynamically positioned to accommodate different spectral ranges and emission line selections. This dynamic adjustment capability allows the system to maintain high resolution while providing flexibility in choosing which emission lines to detect, overcoming the mechanical constraints of fixed designs.
4Manufacturing precision
If spherical mirrors with long focal lengths are used in PMT-based systems, then imaging quality is improved, but system size and complexity increase
Solution Approach 1:
The patent changes the mirror geometry from conventional spherical mirrors with long focal lengths to freeform mirrors with optimized surface profiles. This parameter change allows the system to achieve high imaging quality with shorter focal lengths, significantly reducing the overall system size and complexity while maintaining or improving performance.
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 enables high-resolution imaging of UV spectra from 160 to 400 nm with improved spectral resolution and optical throughput, addressing the trade-offs in existing systems and enhancing the performance of echelle spectrometers for atomic spectroscopy applications.
Implementation Method 1
a collimator which collimates a diverging beam of light generated through the slit
Implementation Method 2
a reflective echelle grating which disperses the collimated light along a first dimension
Implementation Method 3
a cross-disperser which disperses at least a portion of the collimated light in a second dimension orthogonal to the first dimension
Implementation Method 4
an imaging system which images the two-dimensional spectral field-of-view onto a detector; wherein the imaging system comprises primary, secondary, and tertiary tilted mirrors
Data Source
AI summary
An echelle spectrometer includes a slit opening for incoming light, a collimator which collimates a diverging beam of light generated through the slit, a reflective echelle grating which disperses the collimated light along a first dimension; a cross-disperser which disperses at least a portion of the collimated light in a second dimension orthogonal to the first dimension to create a two-dimensional spectral field-of-view; and an imaging system which images the two-dimensional spectral field-of-view onto a detector; wherein the imaging system comprises primary, secondary, and tertiary tilted mirrors, where each of the tilted mirrors comprises a freeform, rotationally non-symmetric surface shape.