Beam Focus Detection Using Contrast-Modulated Sample Beams
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Solution Overview
Problem
Existing methods for determining the axial position of a laser beam focus in laser material processing are inaccurate due to thermal focal shifts and contamination effects, which affect the refractive index of optical elements and alter the beam focal position, making precise control of the beam focus challenging.
Innovation Solution
A beam analysis device that modulates the intensity distribution of the laser beam using a two-dimensional transmission function with contrast steps, allowing for precise determination of the axial position of the beam focus through a detector and evaluation device, enabling accurate measurement without relying on radiation emitted or reflected by the workpiece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-power lasers are used for material processing, then processing power and efficiency are improved, but thermal focal shift and contamination effects occur that alter the beam focal position
Solution Approach 1:
A beam analysis device is introduced as an intermediary component between the high-power laser and the workpiece. This device includes a beam sampler that extracts a portion of the laser beam and directs it through a lens system to a detector, allowing focal position measurement without the measurement system itself being affected by the high-power beam's thermal and contamination issues.
Solution Approach 2:
The patent replaces direct mechanical/optical measurement methods that would be affected by thermal focal shift with a detection system that uses a separate optical path. The beam analysis device substitutes the problematic direct measurement approach with an indirect detection method that samples the beam and measures its properties without being subject to the same thermal and contamination effects.
2Adaptability or versatility
If optical elements are used to focus the laser beam, then beam focusing capability is improved, but thermal focal shift occurs due to temperature-dependent refractive index changes
Solution Approach 1:
The beam analysis device provides real-time feedback on the actual focal position by detecting the beam's intensity distribution and calculating the second moment. This feedback information can be used to monitor and compensate for thermal focal shift, allowing the system to maintain accurate focal positioning despite temperature-dependent refractive index changes in the optical elements.
3Device complexity
If existing focal position determination methods are used, then device simplicity is maintained, but measurement accuracy is insufficient due to thermal and contamination effects
Solution Approach 1:
The patent replaces simple but inaccurate direct measurement methods with a more sophisticated beam analysis device that uses optical sampling and computational analysis. The system substitutes straightforward optical measurement with a method that captures the beam's intensity distribution and calculates focal position using the second moment, providing superior accuracy while maintaining reasonable device complexity.
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 robust, accurate, and versatile method for determining the axial position of the laser beam focus, improving precision and reducing uncertainties associated with thermal shifts and contamination effects, thus enhancing the control of laser processing operations.
Implementation Method 1
a beam-shaping device (12), in particular a modulation device (20), which is set up to modulate an intensity distribution (81) of the energy beam (77), or of the sample beam (70) decoupled from the energy beam (77), in a modulation plane (19) with a two-dimensional transmission function
Implementation Method 2
a detector (40), in particular a light radiation-sensitive sensor, resolving spatially in two dimensions, which is set up to convert the intensity distribution impinging onto the detector (40) into electrical signals
Data Source
AI summary
The invention relates to a beam analysis device (10) for determining the axial position of the focal point (71) of an energy beam or a sample beam (70) decoupled from an energy beam, comprising a beam-shaping device (12), a detector (40), and an analysis device (45). The beam-shaping device (12) is designed to modulate an intensity distribution (81) of the energy beam (77) or the decoupled sample beam (70) on a modulation plane (19) using a two-dimensional transmission function in order to form a modulated sample beam (79). The transmission function has at least two contrast stages (32, 33) with a distance a to each other in the form of transitions between at least one blocking region (25) and at least one passage region (21). The beam-shaping device (12) is designed to guide the modulated sample beam (79) onto the detector (40) along a propagation path in order to form the intensity distribution (83) on the detector (40) with at least two contrast features (92, 93) along the first lateral direction (31). The analysis device (45) is designed to determine the distance a along the first lateral direction (31) between positions of the contrast features (92, 93) on the detector (40) and to determine the axial position of the beam focus (71) on the basis of the distance a and/or to determine a change in the axial position of the beam focus (71) on the basis of a change in the distance a. The invention also relates to a corresponding method for determining the axial position of a beam focus (71).