Spatial Low-Pass Filter for Optical Measurement Instruments
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Solution Overview
Problem
Conventional optical measurement instruments are sensitive to misalignment of components, leading to deterioration of spatial coherence in the light beam, and require precise manufacturing of small pinholes, which complicates manufacturing and reduces light throughput.
Innovation Solution
Incorporating a spatial low-pass filter with a relay lens arrangement functioning as a Fourier transform lens and an aperture plate, which reduces sensitivity to misalignment and allows for larger pinhole diameters, improving beam quality and light throughput while maintaining compactness and temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pinhole-based spatial filter is used, then spatial coherence of the light beam is improved, but the apparatus becomes highly sensitive to misalignment and manufacturing precision requirements increase
Solution Approach 1:
The spatial filtering function is segmented into two stages: first a pinhole-based filter, then a relay lens arrangement with aperture plate. This segmentation allows each stage to handle different aspects of spatial filtering, reducing the burden on individual components and lowering alignment precision requirements.
Solution Approach 2:
The relay lens arrangement acts as an intermediary between the pinhole filter and the final beam output. It performs Fourier transformation of the spatial frequencies, allowing the aperture plate to selectively pass desired spatial frequency components while rejecting others, thereby maintaining spatial coherence with relaxed alignment tolerances.
2Reliability
If a small pinhole is used to achieve good spatial frequency separation, then spatial coherence is improved, but light throughput is reduced and manufacturing becomes more difficult
Solution Approach 1:
The system changes the spatial frequency parameters through the relay lens arrangement, transforming the spatial domain into the frequency domain. This allows effective spatial filtering with a larger pinhole aperture, thereby increasing light throughput while maintaining spatial coherence through the aperture plate's frequency selection.
3Reliability
If multiple optical components are added to improve beam quality, then spatial coherence is improved, but device complexity increases
Solution Approach 1:
The relay lens arrangement serves multiple functions simultaneously: it acts as a Fourier transform lens for spatial frequency analysis, as an imaging lens for the aperture plate, and as a beam conditioning element. This multi-functionality justifies the addition of components by consolidating several optical functions into a single optical subsystem.
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 provides a well-collimated light beam with high spatial coherence, improved manufacturing ease, and increased light throughput, reducing the impact of misalignment and environmental degradation on measurement repeatability.
Implementation Method 1
a relay lens arrangement functioning as a Fourier transform lens
Implementation Method 2
spatial low-pass filter arranged to filter a beam provided by the beam shaping means
Data Source
AI summary
An apparatus for providing a light beam for use in a diffraction instrument (1) includes a device (10; 17; 28) for generating a light beam; and means (12, 21; 24) for shaping the light beam generated by the device (10; 17; 28), dimensioned, in use, to determine the beam shape, and including: an aperture (21; 25) and means (13; 24) for rejecting spatial frequency components above a certain range in the light beam. The apparatus further includes a spatial low-pass filter (14; 15; 26; 27) arranged to filter a beam provided by the beam shaping means.