Laser Beam Focal Position Detection Using Offset Back-Reflection Sensing
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Solution Overview
Problem
Current methods for detecting the focus position of a laser beam during laser material processing face challenges in achieving precise and real-time control due to thermal lens effects, which cause focus shifts and deteriorate beam quality, often requiring complex structural integration and reference measurements that are not highly accurate.
Innovation Solution
A device with an optical element for decoupling back reflections and a sensor arrangement to measure beam properties along the beam propagation direction, allowing for precise determination of the focus position using the entire beam cross-section, enabling real-time focus position control and beam diagnosis without additional laboratory devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors and motors are used to detect and compensate thermal lens effects, then focus position control is improved, but device complexity increases
Solution Approach 1:
The patent extracts the back reflection of the laser beam from the main beam path and directs it to a separate sensor arrangement. This allows focus position measurement without the sensor being exposed to the full laser power, eliminating the need for temperature sensors and motors while maintaining measurement precision
Solution Approach 2:
The patent uses an optical element as an intermediary to couple out the back reflection from the laser beam. This intermediary allows the measurement function to be performed separately from the main beam path, reducing device complexity while maintaining focus control precision
2Ease of operation
If focus position is determined using back reflection through focusing lenses, then measurement is enabled, but measurement accuracy deteriorates due to aberrations
Solution Approach 1:
The patent extracts the back reflection from the main beam path before it passes through the focusing lenses multiple times. By measuring the back reflection at an intermediate point, the system avoids the cumulative aberrations that would otherwise degrade measurement accuracy
Solution Approach 2:
Instead of sending the back reflection through the focusing lenses to the focus point and back (which causes aberrations), the patent inverts the approach by capturing the back reflection at an intermediate point before it re-enters the focusing optics, thereby avoiding the aberration-prone path
3Measurement precision
If beam diameter is measured at multiple points to determine focus position, then accurate focus detection is achieved, but real-time control during processing is compromised
Solution Approach 1:
The patent performs preliminary measurement of the back reflection properties during the laser processing operation itself. By continuously monitoring the back reflection at the intermediate point, the system maintains real-time focus position data without requiring separate measurement steps, thus preserving productivity while ensuring measurement precision
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 provides precise and real-time focus position control, improving processing quality by accurately compensating for thermal lens effects and maintaining high beam quality, while being structurally compact and minimizing structural complexity.
Implementation Method 1
an optical element arranged in the laser beam converging towards the focus for coupling out at least one back reflection from the laser beam path
Implementation Method 2
coupling out at least one back reflection from the laser beam path
Implementation Method 3
a sensor arrangement for detecting beam properties of the laser beam in the region of the focus along its propagation direction
Data Source
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AI summary
The invention relates to a method and a device for detecting a focal position of a laser beam, particularly a machining laser beam in a laser machining head (10), comprising an optical element (26) which is arranged in the laser beam (12) converging toward the focal point (20) and which is designed to outcouple a reflection (30) from the laser beam path, and a sensor arrangement (36) which is designed to detect beam characteristics of said laser beam (12) in the region of the focal point (20) in the laser extension direction, and which measures the outcoupled reflection (30) of the laser beam (12) at at least two locations that are offset to one another in the extension direction, in order to determine the current focal position.