Absorptive Neutral Density Filter for Laser Ghost Image Reduction
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Solution Overview
Problem
Laser imaging systems face the issue of ghost images due to Fresnel reflections at optical media interfaces, which are not effectively mitigated by existing anti-reflection coatings, especially in systems with sensitive pixelated detectors and broader wavelength bands.
Innovation Solution
An absorptive neutral density filter with an optical density of at least −1 is positioned between the laser source and the pixelated detector, featuring a highly reflective surface facing the laser and an anti-reflective surface facing the detector, absorbing reflected light to reduce ghost images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If anti-reflection coatings are applied to optical media, then ghost images are reduced, but the effectiveness is insufficient for extremely sensitive pixelated detectors and broad wavelength bands
Solution Approach 1:
The patent introduces an absorptive neutral density filter as an intermediary component positioned between the optical media and the pixelated detector. This filter serves as a mediator that absorbs reflected light before it reaches the detector, thereby eliminating ghost images. The filter has an optical density of at least -1 and features an anti-reflective surface facing the detector to minimize additional reflections. This intermediary solution addresses the insufficiency of conventional anti-reflection coatings for extremely sensitive detectors and broad wavelength bands.
2Object-affected harmful factors
If absorptive neutral density filter with OD of at least -1 is used, then ghost images are significantly reduced, but light transmission to the detector is reduced
Solution Approach 1:
The absorptive neutral density filter is designed with non-uniform optical properties: one surface features high absorption (OD of at least -1) to eliminate ghost images, while the other surface features an anti-reflective coating to minimize reflections. This local differentiation of optical properties allows the filter to perform multiple functions - absorbing reflected light to reduce ghost images while maintaining optimal light transmission characteristics at each interface.
Solution Approach 2:
The patent specifies that the absorptive neutral density filter should have an optical density of at least -1, which represents a specific parameter threshold for effective ghost image reduction. The filter material and thickness are selected to achieve this optical density while maintaining adequate light transmission for the application. This parameter-based approach allows optimization of the trade-off between ghost image reduction and light transmission.
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 solution significantly reduces ghost images, improving the accuracy of laser beam measurement by minimizing interference fringes and enhancing the signal-to-noise ratio, even in systems sensitive to ghost reflections and broad wavelength bands.
Implementation Method 1
absorbing the reflected portion of light, by the absorptive neutral density filter, to reduce ghost images at the pixelated detector
Implementation Method 2
the second surface is an anti-reflective surface
Implementation Method 3
The non-zero reflection and transmission of light is a result of the difference in the refractive index on either side of the interface
Implementation Method 4
another portion of the incident light is reflected. The reflected light then propagates back to another optical media surface, which is reflected again
Data Source
AI summary
A method and apparatus for reducing ghost images in a laser imaging system. The method includes, positioning an absorptive neutral density filter, having an optical density (OD) of at least −1, between a pixelated detector and a laser source. The method further includes, emitting a laser beam, from the laser source onto the absorptive neutral density filter, transmitting a portion of the light incident upon a first surface of the absorptive neutral density filter to a second surface of the absorptive neutral density filter, reflecting a portion of light incident upon the second surface of the absorptive neutral density filter and absorbing the reflected portion of light, by the absorptive neutral density filter, to reduce ghost images at the pixelated detector.