Artifact-free holographic light shaping through moving acousto-optic holograms

Abstract

Holographic light modulation is the most efficient method to shape laser light into well-defined patterns and is therefore the means of choice for many intensity demanding applications. During the last two decades, spatial light modulators based on liquid crystals prevailed among several technologies and became the standard tool to shape light holographically. But in the near future, this status might be challenged by acousto-optic deflectors. These devices are well known for their excelling modulation rates and high optical power resilience. But only few scattered precedents exist that demonstrate their holographic capabilities, despite the many interesting properties that they provide. We implemented a holographic acousto-optic light modulation (HALM) system, that is based on displaying holograms on acousto-optic deflectors. We found that this system can eliminate the ubiquitous coherent artifacts that arise in holography through the inherent motion of acousto-optic holograms. That distinguishes our approach from any other holographic modulation technique and allows to reconstruct intensity patterns of the highest fidelity. A mathematical description of this effect is presented and experimentally confirmed by reconstructing images holographically with unprecedented quality. Our results suggest that HALM promotes acousto-optic deflectors from highly specialized devices to full-fledged spatial light modulators, that can compete in a multitude of applications with LC-SLMs. Especially applications that require large optical output powers, high modulation speeds or accurate gray-scale intensity patterns will profit from this technology. We foresee that HALM may play a major role in future laser projectors and displays, structured illumination microscopy, laser material processing and optical trapping.

Vector Differential Interference Contrast Microscopy Based on a 3-in-1 Phase Mask through a Dynamic Diffractive Optical Element

“…The coherent length of LED (typically around 1 mm) satisfies the requirement of the interference between the differential waves. Although high coherent sources, such as lasers, have a high contrast of interference, their coherent nature inevitably results in coherent artifacts akin to speckles, which significantly degrades the imaging quality . However, the quantitative phase imaging feature of the v-DIC relies on the intensity variation of the phase-shifted interferograms rather than the contrast.…”

“…Although high coherent sources, such as lasers, have a high contrast of interference, their coherent nature inevitably results in coherent artifacts akin to speckles, which significantly degrades the imaging quality. 26 However, the quantitative phase imaging feature of the v-DIC relies on the intensity variation of the phase-shifted interferograms rather than the contrast. Therefore, a low coherent source is a guarantee of obtaining the high-quality imaging results.…”

Two-dimensional acousto-optic SLM

“…Acousto-optic (AO) spatial light modulators (SLMs) are widely used in advanced microscopy, Fourier optics, microwave spectral analysis, ultrafast laser pulse shaping, and digital holography. [1][2][3][4][5][6][7][8][9] A dynamic hologram can be created in the acousto-optic crystal by an arbitrary wave generator (AWG) to create complex field distributions in the far field.…”

Using an Acousto-Optic Modulator as a Fast Spatial Light Modulator

“…While these works have demonstrated high modulation and switching rates for the generated light patterns, they simply use AOMs to synthesize rapidly movable focal spots, which are then used to address different regions of a conventional SLM, rather than for directly generating arbitrary complex spatial light fields. In a recent result, Treptow et al implemented a holographic acousto-optic light modulation (HALM) system, which can reconstruct any two-dimensional intensity pattern by applying one acousto-optic deflector (AOD) as a holographic modulator to reconstruct image lines, and another AOD as a line deflector [26]. In [26], the AOD is assumed to be illuminated with a light pulse of duration much greater than the inverse acoustical frequency, resulting in an averaging out of any phase coherence between different diffracted components of the output light beam.…”

“…In a recent result, Treptow et al implemented a holographic acousto-optic light modulation (HALM) system, which can reconstruct any two-dimensional intensity pattern by applying one acousto-optic deflector (AOD) as a holographic modulator to reconstruct image lines, and another AOD as a line deflector [26]. In [26], the AOD is assumed to be illuminated with a light pulse of duration much greater than the inverse acoustical frequency, resulting in an averaging out of any phase coherence between different diffracted components of the output light beam. This results in the generation of a desired intensity distribution which is primarily suitable for imaging applications.…”