Deformable Dispersive Mirror for Ultra-Short Pulse Dispersion Compensation
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Solution Overview
Problem
Ultra-short pulse light beams experience significant distortion due to material dispersion when propagating through optical materials, particularly in the two-digit femtosecond range, leading to propagation time differences and group velocity dispersion, which vary with scan angle and radial position, causing temporal broadening and other distortions.
Innovation Solution
A scanning optical system incorporating a deformable, dispersive mirror with an actuator device that adjusts its shape based on the scan angle to compensate for spatial variations in group delay and dispersion, using a multilayer structure to introduce non-uniform dispersion characteristics across the mirror surface, and a bulk compensator for uniform dispersion correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ultra-short pulse light propagates through optical materials in a scanning system, then the beam can be scanned across different angles, but material dispersion causes temporal broadening and group delay variations that distort the pulses
Solution Approach 1:
The patent applies local quality by creating a dispersive mirror with spatially varying dispersion characteristics. The mirror surface is designed with different local properties: the path length through the mirror varies with radial position and incident angle, introducing position-dependent group delay compensation. This local variation in dispersion properties allows the system to correct pulse distortion at different scan angles simultaneously, resolving the contradiction between scan adaptability and pulse temporal precision
Solution Approach 2:
The patent changes physical parameters of the dispersive mirror to achieve angle-dependent dispersion compensation. By varying the mirror curvature radius, thickness, and material composition as functions of radial position, the system creates a mirror whose dispersion parameters change across its surface. This parameter variation enables the mirror to compensate for group delay variations caused by different scan angles, maintaining pulse precision across the full scan range
2Adaptability or versatility
If the beam is focused through a lens system during scanning, then the beam can be delivered to different positions, but the path length through the lens varies with radial distance causing additional dispersion
Solution Approach 1:
The dispersive mirror incorporates local quality by designing its structure to compensate for lens-induced dispersion variations. The mirror's path length and curvature are specifically engineered to vary with radial position, creating local dispersion compensation that counteracts the position-dependent dispersion introduced by the focusing lens. This allows the system to maintain pulse temporal consistency while delivering the beam to different positions through scanning
3Device complexity
If a static dispersive mirror is used to compensate dispersion, then the system structure is simple, but it cannot compensate for angle-dependent group delay variations
Solution Approach 1:
The patent resolves this contradiction by implementing a static mirror with spatially varying local properties. Rather than using a complex dynamic system, the mirror is designed with fixed but position-dependent characteristics: different radial zones have different path lengths, curvatures, and material compositions. This static structure with local quality variations provides angle-dependent dispersion compensation without requiring complex active control mechanisms, achieving both structural simplicity and compensation accuracy
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 system effectively minimizes dispersion-related distortion by adjusting the relative delay between wave packets and spatial distribution of group delay, ensuring reduced pulse broadening and improved focus accuracy across different scan angles, particularly beneficial in femtosecond laser systems for ophthalmic surgery.
Implementation Method 1
material dispersion may cause unwanted distortion of the pulses when they propagate through glass or other optical materials
Implementation Method 2
the dispersive mirror may be designed to introduce a negative chirp, which compensates at least partially a positive chirp
Implementation Method 3
Changing the shape of the deformable, dispersive mirror can be effective to introduce, or alter, a relative delay between wave packets incident at different positions of the mirror
Implementation Method 4
a lens system including a focusing objective for focusing the deflected beam
Implementation Method 5
an optical source providing a beam of pulsed light of ultra-short pulse duration
Data Source
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AI summary
An embodiment of a scanning optical system (10) comprises: an optical source (22) providing a beam (38) of pulsed light of ultra-short pulse duration; a deflector (26) for deflecting the beam through a scan angle; a lens system including a focusing objective (30) for focusing the deflected beam; a dispersion compensating device (25) for reducing dispersion-related distortion of a pulse of the beam by the lens system, the dispersion compensating device including a deformable, dispersive mirror (42) and an actuator device (44) for the mirror; and a controller (18) for controlling the actuator device to change a shape of the mirror in accordance with the scan angle.