Laser Wavefront Correction for Machining Through Tilted Surfaces

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Solution Overview

Problem

Laser machining within materials is hindered by the disruptive effects of the material itself on laser focusing, leading to aberrations that reduce the control and efficiency of the process, particularly when focusing through tilted or non-planar surfaces.

Innovation Solution

A method involving the measurement of the sample's tilt and surface position to apply corrections to the active optical elements of the laser system, counteracting coma and spherical aberrations, thereby improving the Strehl ratio and focusing efficiency by modifying the wavefront properties of the laser.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If laser focusing is performed through a tilted or non-planar sample surface, then the laser can access target locations inside the material, but aberration effects (coma and spherical aberration) increase, reducing the Strehl ratio and focusing precision

Engineering Contradiction:

Improveability to focus through tilted surfacesVSAvoidfocus precision and Strehl ratio

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The system performs preliminary measurement of the sample surface tilt and position before laser focusing. Based on these measurements, correction values are calculated and applied to the active optical element (deformable mirror or spatial light modulator) in advance, so that when the laser focuses through the tilted surface, the wavefront has already been pre-corrected to compensate for the expected coma and spherical aberration, maintaining high Strehl ratio and focus precision

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback loop where the sample surface tilt and position are continuously measured, the aberration correction is dynamically adjusted based on these measurements, and the corrected wavefront is applied in real-time. This closed-loop feedback ensures that even as the sample or focus position changes, the system maintains optimal focusing conditions by continuously compensating for tilt-induced aberrations

Inventive Principle:

Principle #23Feedback

2Productivity

If traditional laser focusing methods are used without correction, then the system is simpler to operate, but the Strehl ratio drops below 0.5 when focusing at depth through tilted surfaces, significantly reducing machining efficiency

Engineering Contradiction:

Improvelaser machining efficiencyVSAvoidoptical correction system complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The system introduces an active optical element (deformable mirror or spatial light modulator) as an intermediary component between the laser source and the sample. This intermediary dynamically modifies the wavefront to compensate for tilt-induced aberrations, enabling high Strehl ratio focusing through tilted surfaces. The intermediary adds complexity but is essential for achieving the productivity improvement through maintained focusing efficiency at depth

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system changes the wavefront parameters (phase and amplitude distribution) of the laser beam dynamically based on measured sample tilt and position. By adjusting the wavefront parameters through the active optical element, the system compensates for aberrations and maintains high Strehl ratio, thereby improving laser machining efficiency without requiring mechanical repositioning or manual intervention

Inventive Principle:

Principle #35Parameter changes

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 enables a laser focus with a Strehl ratio of greater than 0.5, significantly reducing aberration effects and enhancing the precision and efficiency of laser modification within the sample, allowing for the creation of precise features and structures, even at depths where traditional methods fail.

Implementation Method 1

applying the correction to the active optical element to modify wavefront properties of the laser to counteract an effect of coma on laser focus

Methodology Applied

Scientific EffectWavefront modification:

Implementation Method 2

focusing through high numerical aperture lenses. The combination of energy confinement in the time and spatial dimensions leads to high instantaneous focal intensities that create material modifications

Methodology Applied

Scientific EffectLaser focusing: Focusing

Implementation Method 3

Light focused from an objective lens into a sample will be aberrated from its ideal focus because of refraction at the sample's surface

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS11685003B2Method for laser machining inside materials

Publication Date: 2023.06.27 OXFORD UNIVERSITY INNOVATION LTD

AI summary

The invention provides a method for laser modification of a sample to form a modified region at a target location within the sample. The method comprises positioning a sample in a laser system for modification by a laser; measuring tilt of a surface of the sample through which the laser focusses; using at least the measured tilt to determine a correction to be applied to an active optical element of the laser system; applying the correction to the active optical element to modify wavefront properties of the laser to counteract an effect of coma on laser focus; and laser modifying the sample at the target location using the laser with the corrected wavefront properties to produce the modified region.