Laser Wavefront Correction for Deep Focusing in Transparent Media
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Solution Overview
Problem
Existing laser processing devices face challenges in maintaining precise focusing and efficient processing when irradiating deep inside a medium due to aberrations, which exceed the capabilities of current wavefront correction methods, particularly with spatial light modulators.
Innovation Solution
The method involves correcting laser beam aberrations by positioning the focal point within the range of longitudinal aberration occurring inside the medium, using phase wrapping techniques to reduce the peak-to-valley value of wavefront modulation, and employing spatial light modulators with limited phase modulation ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a laser beam is focused deep inside a transparent medium, then the processing position is achieved, but the focal region is expanded by aberration and the concentration of the focused laser beam is reduced
Solution Approach 1:
The invention changes the parameter of wavefront phase distribution to compensate for aberrations. By calculating and applying a correction wavefront that opposes the aberration wavefront, the system maintains focal point concentration at deep irradiation positions. The phase modulation amount and wavefront shape are adjusted as parameters to counteract the expanding focal region caused by medium-induced aberrations.
2Manufacturing precision
If the PV value of wavefront for correcting laser beam is increased to correct deep position aberration, then the correction capability is improved, but it exceeds the performance of spatial light modulator and becomes impossible to sufficiently correct aberration
Solution Approach 1:
The invention introduces phase wrapping to wrap the phase distribution around the limited modulation range of the spatial light modulator. By mapping the large PV value wavefront correction requirement onto the cyclic phase space of the SLM (where phase 0 equals phase 2π), the system achieves deep position aberration correction without exceeding the device's physical phase modulation range.
3Device complexity
If conventional aberration correction method is used, then the optical system can be simplified, but the focal point position cannot be accurately controlled and processing precision is reduced
Solution Approach 1:
The invention uses the spatial light modulator to generate and apply its own correction wavefront based on calculated aberration characteristics. The system self-corrects by computing the required phase compensation and implementing it through the SLM, eliminating the need for external wavefront sensing hardware while maintaining accurate focal point position control through computational methods.
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 allows for precise wavefront control and maintains excellent processing even when irradiating deep inside the medium, reducing the load on spatial light modulators and enhancing the concentration of the focused laser beam.
Implementation Method 1
a light modulator (hereinafter, referred to as an SLM) 40... a phase modulation-type spatial light modulator which applies a voltage to an independent pixel
Implementation Method 2
an objective lens (focusing means, condenser lens) 50... Focusing of a laser beam on a transparent medium
Data Source
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AI summary
In an aberration-correcting method according to an embodiment of the present invention, in an aberration-correcting method for a laser irradiation device 1 which focuses a laser beam on the inside of a transparent medium 60, aberration of a laser beam is corrected so that a focal point of the laser beam is positioned within a range of aberration occurring inside the medium. This aberration range is not less than n×d and not more than n×d+Δs from an incidence plane of the medium 60, provided that the refractive index of the medium 60 is defined as n, a depth from an incidence plane of the medium 60 to the focus of the lens 50 is defined as d, and aberration caused by the medium 60 is defined as Δs.