F-theta Lens Diffractive Element Femtosecond Laser Chromatic Aberration
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Solution Overview
Problem
Current optical systems using F-theta lenses struggle to effectively focus ultrashort pulse lasers like femtosecond lasers due to chromatic aberrations and increased spectral bandwidth, leading to inefficient processing and potential substrate damage.
Innovation Solution
Incorporating a diffractive optical element with a multi-level diffractive structure and a series of spherical lenses, specifically designed to correct chromatic aberrations, where the diffractive optical element is made of fused silica and has a focal length ratio greater than 1.5 to the F-theta lens, and the spherical lenses are sequentially arranged to achieve precise focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional F-theta lenses are used for ultrashort pulse laser processing, then the optical system structure remains simple, but the laser beam cannot be effectively focused at the target spot due to chromatic aberrations and increased spectral bandwidth
Solution Approach 1:
The patent combines a diffractive optical element with multiple spherical lenses into a single integrated F-theta lens assembly. The diffractive optical element is positioned within the lens system, merging chromatic aberration correction functionality with the existing focusing optics, thereby achieving diffraction-limited spot focusing without significantly increasing overall system complexity
Solution Approach 2:
The diffractive optical element acts as an intermediary component that corrects chromatic aberrations introduced by the spherical lenses. It mediates between the broadband ultrashort pulse laser input and the focal plane, compensating for wavelength-dependent focal shifts and enabling accurate focusing across the spectral bandwidth
2Measurement precision
If multiple optical elements are arranged or combined to accurately focus the laser beam, then the focusing accuracy improves, but the structure of the optical system becomes complicated
Solution Approach 1:
The patent merges the diffractive optical element with the spherical lenses into a compact integrated assembly. Rather than using separate correction optics and focusing lenses, the design combines these functions into a single modular unit that maintains diffraction-limited performance while simplifying system integration and alignment
3Reliability
If the pulse duration of the laser beam becomes shorter, then the substrate can be processed before heat conversion, but the spectral bandwidth increases causing ineffective focusing
Solution Approach 1:
The patent converts the harmful effect of increased spectral bandwidth into a beneficial outcome by using the diffractive optical element to exploit the broadband nature of ultrashort pulses. The diffractive structure is designed to compensate for chromatic dispersion, transforming what would be a focusing error into an opportunity for enhanced depth of focus and diffraction-limited spot size across the entire spectral bandwidth
Solution Approach 2:
The patent changes the optical parameters of the system by introducing a diffractive optical element with specific focal length ratios (greater than 1.5 relative to the F-theta lens). This parameter change enables the system to maintain diffraction-limited focusing for ultrashort pulse durations by compensating for the wavelength-dependent phase delays introduced by the broadband spectrum
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 solution enables high-accuracy focusing of femtosecond laser beams into a diffraction-limited spot, reducing chromatic aberrations and improving processing efficiency while maintaining a relatively simple optical system structure.
Implementation Method 1
the diffractive optical element includes a multi-level diffractive structure having three or more levels and defined on a surface thereof
Implementation Method 2
a plurality of spherical lenses sequentially arranged after the scanner on a path of the laser beam
Data Source
AI summary
An F-theta lens includes a diffractive optical element and a plurality of spherical lenses. The diffractive optical element includes multi-level diffractive structure having three or more levels and defined on a surface thereof, and the diffractive optical element is arranged before the spherical lenses on a path of a laser beam.