Acousto-optic deflectors for laser beam steering
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Solution Overview
Problem
Conventional laser scanning confocal microscopy is limited in imaging biological activity deep within living tissue due to light penetration issues and scattering, and galvanometer-based systems are too slow for accurate imaging of neuronal signaling, which requires rapid three-dimensional scanning and high temporal resolution.
Innovation Solution
The use of acousto-optic deflectors (AODs) to steer and focus a laser beam in three dimensions, combined with chromatic aberration correction techniques, such as chirping acoustic waves and telecentric relay optics, to achieve faster scanning and improved spatial resolution, allowing for more efficient two-photon microscopy and photolysis applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If galvanometer mirrors are used to scan the laser beam, then the system structure is simple and reliable, but the scanning speed is limited due to mirror mass and inertia
Solution Approach 1:
The patent replaces the mechanical galvanometer mirror system with an acousto-optic deflector (AOD) system that uses acoustic waves to diffract and steer the laser beam. This substitution eliminates the inertia limitations of mechanical mirrors while achieving rapid beam steering speeds exceeding 1000 Hz, directly resolving the contradiction between scanning speed and system complexity.
2Measurement precision
If conventional confocal imaging is used, then the system can image at shallow depths, but it cannot penetrate deep (>100μm) into living tissue due to light scattering
Solution Approach 1:
The patent employs two-photon excitation microscopy which uses longer wavelength infrared light (700-1000 nm) instead of conventional visible light wavelengths. This parameter change in excitation wavelength reduces light scattering in biological tissue, enabling imaging depths greater than 100 μm while maintaining spatial resolution and overcoming the limitation of conventional confocal imaging.
3Measurement precision
If galvanometer-based systems are used for 3D imaging, then the system is relatively simple to implement, but the temporal resolution is too slow to accurately image neuronal signaling
Solution Approach 1:
The patent replaces the mechanical galvanometer scanning system with an acousto-optic deflector system that uses acoustic wave modulation to steer the laser beam. This enables rapid 3D scanning with temporal resolution sufficient to capture neuronal signaling events (millisecond scale) while reducing total image acquisition time from minutes to seconds, directly addressing the contradiction between temporal resolution and imaging speed.
4Speed
If acousto-optic deflectors are used to steer the laser beam, then the scanning speed increases significantly, but chromatic aberration occurs due to wavelength-dependent deflection angles
Solution Approach 1:
The patent introduces telecentric relay optics as an intermediary between the acousto-optic deflectors and the sample. This relay optical system corrects the chromatic aberration introduced by the AODs by ensuring that all wavelengths are focused to the same point despite different deflection angles, thereby maintaining spatial resolution while preserving the high scanning speed benefits of the AOD system.
Data Source
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AI summary
Methods, systems and apparatus for manipulating electromagnetic radiation such as laser beams. A method and apparatus for correcting magnification chromatic aberration utilises one or more dispersive lenses such that long wavelength components are magnified less than short wavelength components. A telecentric relay is preferred to achieve this aim. Further, the use of polarisers to block the undesired zeroth order components of diffraction emanating from acousto-optic deflectors (AODs) is disclosed. Furthermore, specific designs of AOD including narrow transducer AODs which produce a diverging acoustic wave and AODs having two transducers and a selection switch are disclosed. Further, the invention provides methods, systems and apparatus for allowing the wavelength of radiation to be changed, for providing a user selectable degree of compensation, for providing a scanning and/or a pointing system and for providing a compact system that does not require telecentric relays between adjacent acousto-optic deflectors.