Coherent Radiation Filter Using Reticle Fourier Transforms
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Solution Overview
Problem
Detection systems in the electromagnetic spectrum are blinded or damaged by high-intensity coherent radiation, which is difficult to filter out efficiently due to the challenge of producing narrow-band stop-filters that are independent of the source size.
Innovation Solution
A filter system using a series of reticles and lenses to perform optical transforms, specifically Fourier, Abel, or Hankel transformations, which blocks coherent radiation while allowing polychromatic light to pass, independent of the source size, by selecting the spatial transmittance of the third reticle to block the diffracted image of the first reticle produced in the image plane of the second lens.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a narrow-band stop-filter is used to remove coherent radiation, then the filtering efficiency is improved, but the manufacturing difficulty increases significantly
Solution Approach 1:
The filter is divided into multiple reticles (first, second, and third reticles) positioned at different planes, each performing a specific function in the optical transformation chain. This segmentation allows the complex filtering task to be distributed across simpler components that are easier to manufacture and align than a single narrow-band stop-filter.
Solution Approach 2:
The patent replaces the conventional mechanical/narrow-band filtering approach with an optical transformation system using reticles and lenses. Instead of relying on difficult-to-manufacture narrow-band filters, the system uses Fourier or Hankel transformations to spatially separate and filter coherent radiation, substituting complex manufacturing requirements with optical design.
2Adaptability or versatility
If a stop-band filter is designed to be independent of source size, then the adaptability is improved, but the filtering efficiency deteriorates
Solution Approach 1:
The patent changes the spatial frequency parameters of the reticles to achieve source size independence. By carefully selecting the spatial frequencies of the first and third reticles and their relative orientations, the system creates a filtering mechanism that responds to the coherence properties of the radiation rather than the physical size of the source, maintaining effectiveness across different source configurations.
Solution Approach 2:
The patent moves the filtering operation from the spectral domain to the spatial frequency domain through optical transformations. By working in the Fourier or Hankel transform domain, the system can filter coherent radiation based on its spatial coherence properties rather than its spectral characteristics, achieving source size independence while maintaining filtering effectiveness.
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
Effectively removes coherent radiation from the field of view, allowing polychromatic light to transmit while protecting detection systems from blinding or damage, with the ability to operate over a wide field of view and adapt to various source sizes and spectral profiles.
Implementation Method 1
a first lens producing an optical transform of the first reticle at an image plane
Implementation Method 2
A monochromatic coherent source in the field of view produces a pattern of diffracted energy in the image plane of the second lens
Implementation Method 3
a second lens producing an optical transform of the second reticle in an image plane
Implementation Method 4
the spatial transmittance of the third reticle is selected to block at least part of the diffracted image of the first reticle
Data Source
AI summary
A filter for removing coherent radiation from a source in a field of view, substantially independent of the size of the source, comprises a first reticle 22 located in the path of received light 21, a first lens 23 producing an optical transform of the first reticle 22 at a second reticle 24 located in the image plane of the first lens 23, a second lens 25 producing an optical transform of the second reticle 24 and a third reticle 26 located in the image plane of the second lens 25. The arrangement is such that the spatial transmittance of the third reticle 26 is selected to block at least part of the diffracted image of the first reticle 22 produced in the image plane of the second lens 25 and characteristic of the coherent radiation. Preferably the optical transforms are Fourier Transforms. A monochromatic coherent source in the field of view produces a pattern of diffracted energy in the image plane of the second lens which is independent of the size of the source. Thus, by providing a suitable reticle 26 in the image plane of the second lens light from a coherent source in the field of view can be blocked while polychromatic light is transmitted. The first and second reticles may be periodic picket-fence reticles or different spatial frequencies may be used for the first and third reticles so as to vary the stop-band characteristics of the filter.