Laser Focal Position Control via Partial Beam Segmentation
Solution Overview
Problem
Existing focal position sensors for laser beams in laser material processing face challenges such as thermal focus shift, parasitic reflections, and reduced accuracy due to multiple back reflections, which complicate precise focal position control and monitoring.
Innovation Solution
A beam analysis device with a partial beam imaging system that selects a small off-center partial aperture region from the measurement beam, imaging it onto a spatially-resolving detector to generate a beam spot, allowing for accurate determination of lateral position changes, which correlates with focal position shifts, even in the presence of multiple reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a back reflection from one of the surfaces of one of the last optical elements is used for focal position detection, then the focal position can be determined, but multiple parasitic back reflections from other surfaces create disturbing signals that reduce detection accuracy
Solution Approach 1:
The patent segments the beam detection process by using multiple detectors positioned at different locations to detect different back reflections separately. Each detector is assigned to monitor a specific reflection from a specific optical surface, allowing the system to process multiple reflections without them interfering with each other. This segmentation eliminates the parasitic signal problem while maintaining detection accuracy.
Solution Approach 2:
The patent introduces an intermediary processing step where the evaluation unit analyzes signals from multiple detectors and identifies which detector received the desired back reflection. By using this intermediary evaluation process, the system can distinguish the useful signal from parasitic reflections and determine the focal position accurately despite the presence of multiple reflections.
2Productivity
If high laser power is used for material processing, then processing efficiency increases, but thermal focus shift occurs due to heating of optical elements
Solution Approach 1:
The patent implements a feedback mechanism where the focal position is continuously monitored using back reflection detection, and the positioning of the laser beam focus is adjusted based on the detected position. This closed-loop feedback system compensates for thermal focus shift in real-time, maintaining focal position stability even during high-power processing operations.
Solution Approach 2:
The patent performs preliminary detection of the back reflection signal characteristics before the thermal focus shift becomes significant. By monitoring the focal position continuously and making adjustments proactively, the system prevents focal position drift rather than correcting it after it occurs, maintaining processing precision throughout high-power operation.
3Measurement precision
If a complex optical device with moving components and beam splitting is used for focal detection, then focal position can be tracked, but the device complexity increases
Solution Approach 1:
The patent uses the optical system's own back reflections as the measurement signal, eliminating the need for separate beam splitting devices or external reference beams. The system serves itself by utilizing the natural back reflections from its optical elements for focal position detection, thereby avoiding additional complex components while maintaining tracking capability.
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 a robust, sensitive, and real-time focal position control system that is insensitive to beam quality variations and multiple back reflections, enabling precise tracking of the laser beam focus during processing.
Implementation Method 1
a detector unit with at least one, at least one-dimensionally spatially-resolving, light-sensitive detector arranged at a distance from the partial beam imaging device
Implementation Method 2
imaging device with at least one imaging optical element. The beam analysis device is configured to receive at least a first measurement beam
Data Source
AI summary
The present disclosure relates to a beam analysis device for determining a light beam state, e.g., determining the focal position of a light beam, where the device has a partial beam imaging device having at least one first selection device for forming a first partial beam from a first partial aperture region of the first measurement beam, and an imaging device for imaging the first partial beam for generating a first beam spot onto a detector unit having a spatially-resolving detector. The beam analysis device also can have an evaluation unit for processing the signals of the detector unit, for determining a lateral position (a1) of the first beam spot, and for determining changes in the lateral position (a1, a1′) of the first beam spot over time. An optical system for focal position control with a laser optics and with a beam analysis device. Additionally, the disclosure relates to a corresponding beam analysis method and methods for focal position control of a laser optics and for focal position tracking of a laser optics.