Burst-Mode Laser Structuring of Transparent Substrates Without Cracks
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Solution Overview
Problem
Existing methods for structuring transparent materials with laser pulses often result in the formation of cracks, making it difficult to achieve controlled surface modification without inducing damage.
Innovation Solution
A method using a femtosecond laser in burst mode, emitting a train of pulses with a specific time interval and energy density, to structure the surface of transparent substrates without inducing cracks, allowing for smooth and edge-free structures by manipulating plasma dynamics and optimizing energy absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high energy density laser pulses are used to structure the material surface, then structuring capability is improved, but crack formation within the material increases
Solution Approach 1:
The laser pulse train is segmented into multiple individual pulses (typically 3-10 pulses per train) with specific time intervals between them. This segmentation allows the energy to be delivered in controlled increments, enabling surface modification while preventing the accumulation of excessive energy that would cause subsurface crack formation.
Solution Approach 2:
The laser operates in a periodic burst mode where pulse trains are delivered at controlled repetition rates. The periodic structure of the pulse trains, with specific intra-pulse intervals (e.g., 100-1000 ns between pulses in a train) and inter-train cooling periods, enables sufficient heat dissipation between pulses to prevent thermal runaway and crack formation while maintaining effective surface structuring.
2Manufacturing precision
If multiple laser pulses are applied to structure the surface, then structuring quality is improved, but processing time increases
Solution Approach 1:
The laser processing operates in a continuous burst mode where pulse trains are delivered without interruption across the workpiece. The high repetition rate within each pulse train (enabling processing at several Hz to kHz) maintains continuous useful action for surface modification, while the rapid pulse duration (nanosecond to picosecond scale) ensures each pulse contributes effectively to structuring without excessive delay.
Solution Approach 2:
The laser system dynamically adjusts the pulse train parameters including the number of pulses per train, the repetition rate, and the energy per pulse based on the specific material and desired structuring outcome. This dynamic control allows optimization of the balance between processing quality and speed for different application requirements.
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
The method effectively structures transparent substrates with minimal crack formation, achieving high energy delivery close to the ablation threshold without heating the substrate, enabling precise control and better resolution than single-pulse techniques, and allowing for the formation of features like domes and craters without edges.
Implementation Method 1
a laser source for irradiating said transparent substrate from its top surface with a laser beam according to said burst mode
Implementation Method 2
The structure obtained by the method of the invention is on the top surface, the laser processing is a three-dimensional process where the laser pulse can achieve a certain skin depth for where a portion of the energy will be absorbed
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
Method for structuring a top surface of a transparent substrate, said substrate being transparent to visible light with a laser source able to emit a laser beam in a burst mode, said burst mode being characterized by a train of pulses comprising sets of laser pulses repeated over time; wherein - each of said sets of laser pulses of said train of pulses comprises a first and second pulses with a time interval between them comprised between 5 ns to 50 ns, preferably between 10 ns to 40 ns, and more preferably about 25 ns; wherein - each of said first and second pulses has an energy density on said top surface comprised between 0.5 nJ/um2 and 50 nJ/um2; and wherein - said train of pulses is able to structure said top surface.