Ultrafast Laser Figuring for Mid-Spatial Frequency Error Correction
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Solution Overview
Problem
Existing sub-aperture manufacturing techniques for high-precision optical components leave residual mid-spatial-frequency (MSF) errors, such as spirals or raster patterns, which degrade imaging system resolution and cause optical damage due to diffraction patterns, and current mechanical and chemical polishing methods are insufficient for steep slope variations.
Innovation Solution
Utilizing ultrafast lasers for non-contact material removal, measuring and quantifying MSF errors, and removing material with nanometer precision to correct these errors by generating and overlapping grooves according to a predicted pattern, achieving single-digit-nanometer surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sub-aperture manufacturing techniques (diamond turning, grinding, magnetorheological finishing) are used to fabricate high-precision optical components, then manufacturing capability and precision are improved, but residual mid-spatial-frequency (MSF) surface errors remain that degrade imaging system resolution and cause optical damage
Solution Approach 1:
The patent replaces mechanical and chemical polishing tools with an ultrafast laser system to remove MSF errors. The laser ablates material through photothermal and photomechanical effects, eliminating the need for contact-based mechanical tools that cannot handle steep slope variations on freeform surfaces. This substitution enables effective MSF error removal while preserving the overall surface form.
Solution Approach 2:
The patent employs ultrafast laser parameters (pulse duration, repetition rate, fluence) to achieve precise material removal. By controlling the laser pulse width in the femtosecond range and adjusting the repetition rate and fluence, the process removes MSF errors down to single-digit-nanometer roughness without causing thermal damage or subsurface defects, resolving the contradiction between removing MSF errors and maintaining surface integrity.
2Manufacturing precision
If mechanical and chemical polishing tools are used to reduce MSF errors, then surface smoothness is improved, but the methods become insufficient for steep slope variations on freeform or aspheric surfaces
Solution Approach 1:
The patent replaces contact-based mechanical polishing tools with a non-contact ultrafast laser system. This substitution eliminates the limitation of mechanical tools that cannot adapt to steep slope variations on freeform surfaces. The laser beam can precisely follow complex surface geometries and remove MSF errors regardless of local slope angle, achieving single-digit-nanometer roughness while maintaining adaptability to any surface form.
3Productivity
If continuous-wave or longer pulse laser processing is used for polishing and form correction, then material removal efficiency is improved, but subsurface damage and heat-affected zones are created
Solution Approach 1:
The patent uses ultrafast laser pulses (femtosecond duration) with controlled repetition rates to process the surface. The periodic pulsed action allows each pulse to remove material through nonlinear absorption and photomechanical stress before heat can diffuse into the substrate. This results in clean ablation with minimal heat-affected zone and no subsurface damage, maintaining surface integrity while achieving efficient material removal for MSF error correction.
Solution Approach 2:
The patent changes the laser pulse duration parameter to the femtosecond range, which is orders of magnitude shorter than continuous-wave or nanosecond pulses. This parameter change enables precise control of energy deposition, confining the interaction to the surface layer and preventing thermal diffusion that causes subsurface damage. The ultrafast timescale allows efficient material removal while preserving surface integrity.
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 reduces MSF errors to single-digit nanometers, enhancing optical component performance by reducing scattering and preventing optical damage, while maintaining high precision and avoiding thermal damage.
Implementation Method 1
removing material from the 3D features to reduce the height down to the valley of the mid-spatial-frequency (MSF) errors with an ultrafast laser
Data Source
AI summary
Methods and systems for optical figuring to create a periodic pattern using an ultrafast laser and for removing material from peaks down to the valleys of mid-spatial-frequency (MSF) errors with an ultrafast laser resulting in the surface smoothness to single-digit-nanometer surface roughness are disclosed.