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Holographic light shaping through acousto-optic deflectors
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[eng] The invention of the laser in the 1960s triggered a new era of optical technologies which revolutionized many fields of industry and research. At the same time, a new demand for technologies emerged that allow to dynamically control the optical properties of a laser beam and to shape laser light into arbitrary patterns.
This need led to the development of spatial light modulators, which are programmable diffractive elements that shape laser light into well-defined intensity distributions through optical phase or amplitude modulation. Their capability to display computer generated holograms made them an indispensable tool in a broad range of optics and photonics applications, because it allows to reconstruct optical wavefronts from digital models without the need of physical counterparts. This most versatile control over an optical wavefront enables complex functionalities such as holographic beam shaping, aberration correction, adaptive optics applications and optical micro-manipulation, to name only a few.
Various spatial light modulator technologies exist with inherent capabilities that define their possible applications. The high light efficiency and outstanding modulation capabilities of spatial light modulators based on liquid crystals (LC-SLMs) found a myriad of applications and represent the current standard for dynamic light modulation based on digital holograms. There are, however, several applications that require other capabilities than those offered by LC-SLMs. Ultra-fast light modulation, high laser power applications and high-quality pattern formation are difficult to achieve with liquid crystal devices, so that alternatives to this prevailing technology are needed.
An interesting candidate for high performance spatial light modulation are acousto-optic deflectors (AODs). These devices are commonly used for high-speed beam deflection, but it has also been demonstrated in few scattered precedents that they are capable of holographic light modulation. Acousto-optic deflectors are based on a considerably different technology than LC-SLMs, which complicates their use as full-fledged spatial light modulators. But at the same time, they provide promising light modulation capabilities, such as very high optical power thresholds, modulation rates of several kilohertz and a continuous (non-pixelated) wavefront modulation, which potentially make them a complement or even competitor to existing spatial light modulator technologies.
The scope of this thesis is the investigation and application of the holographic modulation capabilities of a spatial light modulator system based on acousto-optic deflectors. Such a system is realized in the frame of this work as a common optical Fourier transform setup with off the shelf hardware. The principal effort in the implementation is the development of calculation methods for acousto-optic holograms and the corresponding electronic driving signals, which on the one hand need to consider the specific capabilities and constraints of AODs, and on the other hand have to provide high light efficiencies of the displayed holograms and a high reconstruction quality of the formed patterns. Thus, the one-dimensionality of the acousto-optic modulation and the resulting separability restrictions for two-dimensional AOD modulation are discussed, and different reconstruction strategies for arbitrary two-dimensional patterns are investigated. Furthermore, various image degrading effects are analyzed, and corresponding correction methods are proposed. Especially the inherent reduction of coherent artifacts through the motion of acousto-optic holograms is analyzed in detail.
The capabilities of such implemented acousto-optic SLM are demonstrated by reconstructing arbitrary laser patterns with very high perceived image fidelity. Through the combination of different correction methods, also high-speed reconstructions of separable patterns at rates of several kilohertz are achieved, which eventually come into play in a structured illumination microscope.
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TREPTOW, Dorian. Holographic light shaping through acousto-optic deflectors. [consulta: 13 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/178000]