Interferometric Laser Processing Thin Films
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Solution Overview
Problem
Current laser material processing techniques fail to generate a thin, isolated laser interaction zone within thin films, limiting the creation of new structures and functionalities in materials like CMOS, flexible electronics, and photovoltaic devices, where thin films are crucial.
Innovation Solution
The method involves confining laser-material interaction to an array of narrow zones within transparent films using Fresnel reflections to create a Fabry-Perot intensity modulation, allowing for strong ionization and quantized ejection of film segments or formation of nano-voids at specific fringe maxima, thereby controlling the laser modification process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If laser light is focused onto a thin transparent film, then the laser interaction volume extends through the full depth of focus and full film thickness, but this prevents generation of a thin, isolated laser interaction zone within the film
Solution Approach 1:
The patent segments the continuous laser interaction volume into discrete, thin interaction zones by introducing optical interference fringes within the film. The laser beam is divided into multiple interference patterns with spacing of λ/2n f, creating separate modification locations at each fringe maximum rather than a continuous modified region through the full film thickness.
Solution Approach 2:
The patent applies local quality by creating spatially varying interference patterns within the film that produce localized high-intensity regions at specific fringe maxima. Each fringe maximum creates a distinct zone of modified material properties, allowing precise control over where laser modification occurs within the film thickness while maintaining the original beam parameters.
2Manufacturing precision
If optical interference patterns are generated to create narrow processing zones, then thermal diffusion spreads energy beyond fringe-to-fringe separation, but this washes out process resolution
Solution Approach 1:
The patent employs periodic action by using ultrashort laser pulses with duration shorter than the thermal diffusion time scale (τ p < τ d =λ 2n f 2). This periodic pulsed delivery allows the laser to deposit energy faster than thermal diffusion can spread it, confining the modification to the fringe width scale (∼λ/4n f ) rather than allowing thermal blurring to expand the affected zone to the beam waist scale.
3Manufacturing precision
If the laser pulse duration is shortened to reduce thermal diffusion, then spectral bandwidth increases, but this broadens and merges interference fringes toward a uniform intensity profile
Solution Approach 1:
The patent applies parameter changes by carefully selecting the laser pulse duration to satisfy the inequality τ p < min(λ 2n f 2, z/c n f ), where z is film thickness and c is light speed. This parameter optimization ensures the pulse is short enough to prevent thermal diffusion but long enough to maintain sufficient spectral coherence for fringe visibility, balancing both requirements through precise temporal parameter control.
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 precise internal structuring and quantized ejection of thin film segments, extending control over laser modification and enabling the creation of novel structures and functionalities in thin films, such as nano-voids and blisters, with improved resolution and precision.
Implementation Method 1
A focused laser beam (12) on entering the film (14) from above undergoes Fresnel reflections at the first (air-film) (20) and second (film-substrate) (22) boundary interfaces
Implementation Method 2
to lead to the formation of a Fabry-Perot interference pattern (18) inside the film (14)
Implementation Method 3
nonlinear optical interactions by the ultrashort duration laser predicts a strong ionization with an electron density profile to follow the shape of the optical interference pattern
Implementation Method 4
At the threshold exposure for internal material structuring, the electron density reaches a critical threshold at the predicted fringe maxima positions to facilitate the quantized ejection of the film or the formation of thin nano-voids inside the film
Data Source
Figure 1(a)~1(k)
Figure 2(a)~2(c)
Figure 3(a)~3(b)
AI summary
The present disclosure relates to the field of laser induced modification and processing of materials. Modification is achieved by confining laser-material interaction within an array of narrow zones characterizing an optical interference profile. Disclosed is a method of laser induced modification of a material comprising applying at least one laser pulse to the material, the at least one laser pulse being incident on the first interface of the material, wherein the material is selected on the basis that it can support an optical interference pattern such that a thin volume at a site of at least one intensity maxima of the optical interference pattern is characterized by a laser intensity above a threshold value to responsively produce the laser induced modification of the material at a location relative to the first interface.