Graduated Neutral-Density Filter Beam Analysis for Precise Position Sensing
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Solution Overview
Problem
Existing systems for analyzing light beams in EUV light sources or laser plasma sources face challenges in accurately measuring light beam position and focusing properties due to strong variations in light beam divergence and direction, particularly when the beam defocuses or laterally displaces relative to the target droplet, leading to weak reflected infrared radiation intensity.
Innovation Solution
A system utilizing a gray gradient filter arrangement in the far-field plane of beam guidance optics, combined with a light intensity sensor in the near-field plane, which measures intensity through the filter to minimize the impact of parasitic beam variations, ensuring precise light beam analysis by translating position information into pure intensity data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light intensity sensor is used to measure the reflected infrared radiation from target droplets, then the beam position can be determined, but the measurement precision deteriorates due to strong variations in beam divergence and direction
Solution Approach 1:
The patent transforms the measurement from direct spatial position detection to intensity detection by mapping beam position information to the intensity distribution in the far-field plane. The gray graduated filter converts position variations into intensity variations that can be measured by a simple intensity sensor, effectively changing the measurement dimension from spatial to intensity domain.
Solution Approach 2:
The gray graduated filter acts as an intermediary element between the beam guidance optics and the intensity sensor. It translates beam position and divergence information into intensity modulations that the sensor can detect, mediating the measurement process to make it insensitive to direct beam parameter variations.
2Device complexity
If direct intensity measurement is used in the near-field plane, then the measurement system is simple, but the sensitivity to parasitic beam variations increases
Solution Approach 1:
The patent moves the measurement plane from near-field to far-field, where beam position information is transformed into intensity distribution patterns. This dimensional change in the optical path allows simple intensity measurement to yield precise beam position information while being immune to near-field beam variations.
Solution Approach 2:
The system changes the measurement parameter from direct spatial coordinates to intensity values after optical transformation. By measuring intensity in the far-field plane rather than position in the near-field plane, the system achieves precision without complexity.
3Illumination intensity
If the light beam intensity is weak (as with reflected infrared radiation), then the measurement signal is insufficient, but adding amplification or other sensors increases system complexity
Solution Approach 1:
The gray graduated filter serves as an intermediary that amplifies the measurement signal optically by converting small beam position deviations into large intensity modulations. This optical signal enhancement eliminates the need for electronic amplification or complex sensor arrays, maintaining system simplicity while handling weak signals.
Solution Approach 2:
The system changes the measurement approach from direct weak signal detection to transformed strong signal detection. By optically transforming the weak beam position information into stronger intensity variations through the gray filter, the system achieves adequate signal levels without active amplification.
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 approach enables highly precise light beam analysis with reduced sensitivity to parasitic beam variations, effectively overcoming the limitations of existing technologies by diluting the light intensity and suppressing interference effects, allowing for accurate measurement even in the long-wave infrared range.
Implementation Method 1
A gray graduated filter arrangement, which is arranged in a far field plane of the beam guidance optics and has at least one gray graduated filter with locally varying transmission
Implementation Method 2
A light intensity sensor arrangement with at least one light intensity sensor, which is arranged in a near-field plane of the beam guidance optics and measures the light intensity transmitted through the gray graduated filter
Data Source
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AI summary
The invention relates to a system and to a method for analyzing a light beam conducted by a beam-conducting optical unit. A system according to the invention comprises a graduated neutral-density filter assembly (120, 520), which is arranged in a far-field plane of the beam-conducting optical unit and has at least one graduated neutral-density filter (121, 521, 522, 523) having spatially varying transmittance, and a light intensity sensor assembly having at least one light intensity sensor (140, 540), which light intensity sensor assembly is arranged in a near-field plane of the beam-conducting optical unit and measures (141, 541, 542, 543), for each graduated neutral-density filter (121, 521, 522, 523) of the graduated neutral-density filter assembly (120, 520), the light intensity transmitted by the graduated neutral-density filter.