Laser Beam Focus Detection Using Decoupled Back Reflection
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Solution Overview
Problem
Current methods for detecting the focal position of a laser beam in laser material machining are not precise enough for real-time control, especially due to thermal lens effects, leading to suboptimal machining quality.
Innovation Solution
A device with an optical element to decouple back reflections from the laser beam path and a sensor arrangement to measure beam properties along the beam propagation direction, allowing for precise determination of the focal position using the entire beam cross-section, enabling real-time control and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If temperature sensors are used to measure thermal lens extent and drive motors move lenses to compensate focal position, then focal position control is achieved, but measurement precision and machining quality are insufficient
Solution Approach 1:
The patent introduces a beam splitter as an intermediary component that separates a portion of the laser beam to create a reference beam path. This reference beam serves as a mediator between the thermal lens distortion in the main beam path and the measurement system, allowing precise measurement of focal position shifts without directly measuring the distorted main beam.
Solution Approach 2:
The patent creates an optical copy of the laser beam through the beam splitter, generating a reference beam that replicates the beam characteristics. This copied reference beam is then used for measurement purposes, enabling accurate focal position detection by comparing the reference beam path with the main beam path affected by thermal lens effects.
2Ease of manufacture
If focal position control is performed using characteristic diagrams describing focus shift as function of laser power, then construction effort is minimal, but high precision focal position control and machining quality are not achieved
Solution Approach 1:
The patent implements a real-time feedback measurement system using the beam splitter and reference beam. The system continuously monitors the actual focal position by comparing optical path differences between the reference beam and main beam, providing immediate feedback data that enables precise dynamic compensation of thermal lens effects during machining operations.
Solution Approach 2:
The patent replaces the mechanical/empirical approach of using pre-determined characteristic diagrams with an optical measurement system. By substituting the mechanical adjustment based on power-dependent diagrams with an optical feedback system using beam splitting and reference beam comparison, the system achieves higher precision while maintaining real-time control capability.
3Measurement precision
If back reflection of laser beam is imaged onto sensor through focusing lenses and objective, then focal position can be detected, but considerable aberrations affect measurement accuracy
Solution Approach 1:
The beam splitter acts as an intermediary that creates a separate reference beam path, eliminating the need to image back reflections through complex focusing lenses and objectives. By using the beam splitter to generate a reference beam that travels through a different optical path, the system avoids the aberrations introduced by the complex imaging optics required for back reflection measurement.
4Productivity
If focal position measurement is performed during laser material machining, then real-time control is enabled, but integration into laser machining head is challenging
Solution Approach 1:
The beam splitter is designed with multi-functionality, serving both as a reference beam generator for focal position measurement and as an integral component of the laser machining head's optical system. This universal component performs multiple functions: creating the reference beam path, enabling real-time measurement, and maintaining the structural integrity of the machining head, thereby simplifying integration while enabling real-time control.
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 provides precise and real-time focal position control, improving machining quality by accurately compensating for thermal lens effects without additional laboratory equipment.
Implementation Method 1
an optical element arranged in the laser beam converging towards the focus for decoupling at least one back reflection from the laser beam path
Implementation Method 2
decoupling 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 the direction of propagation thereof
Data Source
AI summary
A method and a device for detecting a focal position of a laser beam, particularly a machining laser beam in a laser machining head, includes an optical element which is arranged in the laser beam converging toward the focal point and which is designed to outcouple a reflection from the laser beam path, and a sensor arrangement which is designed to detect beam characteristics of said laser beam in the region of the focal point in the laser extension direction, and which measures the outcoupled reflection of the laser beam at at least two locations that are offset to one another in the extension direction, in order to determine the current focal position.