Laser Ablation Sweep Synchronization to Reduce Surface Diffraction
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Solution Overview
Problem
Conventional laser ablation processes often result in surface damage and diffraction patterns on substrates, such as glass, due to regular periodicity, which are objectionable and undesirable, especially when removing coatings like chromium with picosecond green pulsed lasers.
Innovation Solution
The method involves varying the spacing and pitch of artifacts on the substrate surface and adjusting the laser's focal length and pulse frequency to reduce surface damage and diffraction severity, using out-of-focus laser ablation and beam shaping optics to minimize diffraction patterns, and employing actuated mirrors or variable lenses to create irregular surface structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional focused laser ablation is performed at the focal height to achieve highest energy density, then material removal efficiency is improved, but surface damage with regular periodicity occurs that forms diffraction gratings
Solution Approach 1:
The patent applies asymmetry by deliberately defocusing the laser beam to create an asymmetric intensity distribution across the beam profile. This defocusing transforms the symmetric focused spot into an asymmetric pattern with reduced peak intensity, which disrupts the formation of regular periodic surface damage and eliminates diffraction grating formation while maintaining effective material removal
Solution Approach 2:
The patent changes the focal position parameter from the focal plane to a defocused position above or below the focal plane. This parameter change modifies the beam intensity distribution and reduces the peak energy density that causes regular periodic surface damage, thereby eliminating diffraction patterns while maintaining material removal capability
2Productivity
If laser pulse frequency and scan speed are increased to improve processing speed, then productivity is improved, but the regular spacing between pulses creates more pronounced diffraction gratings
Solution Approach 1:
By defocusing the laser beam, the patent creates an asymmetric intensity profile that reduces the regularity of surface damage patterns. This asymmetric beam shape disrupts the formation of uniform diffraction gratings even at high pulse frequencies and scan speeds, allowing productivity improvement without proportional increase in diffraction effects
Solution Approach 2:
The patent changes the focal position parameter to reduce peak intensity, which allows higher pulse frequencies to be used without creating pronounced diffraction gratings. The defocused beam distributes energy more evenly, preventing the formation of regular periodic structures even at increased processing speeds
3Manufacturing precision
If the laser is focused to achieve smallest spot size change with height variations, then manufacturing precision is improved, but surface damage and diffraction artifacts are generated
Solution Approach 1:
The patent uses asymmetric defocusing to create a beam intensity distribution that is less sensitive to height variations. The defocused beam profile changes more gradually with height compared to a focused beam, reducing peak intensity fluctuations and minimizing surface damage while maintaining acceptable spot size stability
Solution Approach 2:
The patent changes the focal position from the focal plane to a defocused position, which modifies the depth of field and reduces sensitivity to height variations. This parameter change decreases peak intensity fluctuations caused by height variations, reducing surface damage while maintaining manufacturing 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 approach reduces the intensity and visibility of diffraction patterns, making the laser-ablated surfaces less objectionable by minimizing surface damage and diffraction effects, while maintaining effective material removal without modifying the ablation system's hardware.
Implementation Method 1
A laser ablation process generally includes selective removal of material at a surface of a workpiece by directing a laser beam at the workpiece. The laser beam is configured to deliver a controlled amount of energy at a laser spot defined where the beam impinges the desired surface. This controlled amount of energy is selected to liquefy, vaporize, or otherwise rapidly expand the surface material at the laser spot to cause it to separate from the workpiece for removal.
Implementation Method 2
the glass sustains surface damage to such an extent and with a regular periodicity that a diffraction grating is formed. Diffraction patterns that are produced by the diffraction grating can be an unwanted or unintended artifact of the ablation process.
Data Source
AI summary
A method for removing a material from a surface of a substrate includes impinging a laser beam on the material during a first sweep to remove the material from the surface along a first line and impinging the laser beam on the material during a second sweep to remove the material from the surface along a second line adjacent to the first line. The first line includes first artifacts that form a first portion of an array of artifacts on the surface. The second line includes second artifacts that form a second portion of the array of artifacts on the surface. A first laser pulse of the laser beam corresponding with the second sweep is synchronized with a start of the second sweep when transitioning between the first line and the second line such that the start of the second sweep coincides with the first laser pulse.