Focusing light into scattering media with ultrasound-induced field perturbation

Author(s):

Cheng, Zhongtao & Wang, Lihong V.

Abstract:

“Focusing light into scattering media, although challenging, is highly desirable in many realms. With the invention of time-reversed ultrasonically encoded (TRUE) optical focusing, acousto-optic modulation was demonstrated as a promising guidestar mechanism for achieving noninvasive and addressable optical focusing into scattering media. Here, we report a new ultrasound-assisted technique, ultrasound-induced field perturbation optical focusing, abbreviated as UFP. Unlike in conventional TRUE optical focusing, where only the weak frequency-shifted first-order diffracted photons due to acousto-optic modulation are useful, here UFP leverages the brighter zeroth-order photons diffracted by an ultrasonic guidestar as information carriers to guide optical focusing. We find that the zeroth-order diffracted photons, although not frequency-shifted, do have a field perturbation caused by the existence of the ultrasonic guidestar. By detecting and time-reversing the differential field of the frequency-unshifted photons when the ultrasound is alternately ON and OFF, we can focus light to the position where the field perturbation occurs inside the scattering medium. We demonstrate here that UFP optical focusing has superior performance to conventional TRUE optical focusing, which benefits from the more intense zeroth-order photons. We further show that UFP optical focusing can be easily and flexibly developed into double-shot realization or even single-shot realization, which is desirable for high-speed wavefront shaping. This new method upsets conventional thinking on the utility of an ultrasonic guidestar and broadens the horizon of light control in scattering media. We hope that it provides a more efficient and flexible mechanism for implementing ultrasound-guided wavefront shaping.”

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Publication: Light: Science {&} Applications
Issue/Year: Light: Science {&} Applications, Volume 10; Number 1; 2021
DOI: 10.1038/s41377-021-00605-7

Singular Warped Beams Controlled by Tangent Phase Modulation

Author(s):

Funes, Gustavo; Peters, Eduardo & Anguita, Jaime

Abstract:

“We analyze the effect of spatial phase modulation using non-linear functions applied to singular warped beams to control their topological states and intensity distribution. Such beams are candidates for optical trapping and particle manipulation for their controllable pattern of intensities and singularities. We first simulate several kinds of warped beams to analyze their intensity profiles and propagation characteristics. Secondly, we experimentally validate the simulations and investigate the far-field profiles. By calculating the intensity gradients, we describe how these beams are qualified candidates for optical manipulation and trapping.”

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Publication: Photonics
Issue/Year: Photonics, Volume 8; Number 8; Pages 343; 2021
DOI: 10.3390/photonics8080343

All-optical image identification with programmable matrix transformation

Author(s):

Li, Shikang; Ni, Baohua; Feng, Xue; Cui, Kaiyu; Liu, Fang; Zhang, Wei & Huang, Yidong

Abstract:

“An optical neural network is proposed and demonstrated with programmable matrix transformation and nonlinear activation function of photodetection (square-law detection). Based on discrete phase-coherent spatial modes, the dimensionality of programmable optical matrix operations is 30∼37, which is implemented by spatial light modulators. With this architecture, all-optical classification tasks of handwritten digits, objects and depth images are performed. The accuracy values of 85.0% and 81.0% are experimentally evaluated for MNIST (Modified National Institute of Standards and Technology) digit and MNIST fashion tasks, respectively. Due to the parallel nature of matrix multiplication, the processing speed of our proposed architecture is potentially as high as 7.4∼74 T FLOPs per second (with 10∼100 GHz detector).”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 17; Pages 26474; 2021
DOI: 10.1364/oe.430281

25D microscopy with polarization independent SLM for enhanced detection efficiency and aberration correction

Author(s):

Ren, Jinhan & Han, Kyu Young

Abstract:

“Fast, volumetric imaging by fluorescence microscopy is essential in studying bi-ological phenomena and cellular functions. Recently, single-shot 2.5D microscopy showedpromising results for high-throughput quantitative subcellular analysis via extended depth offield imaging without sequentialz-scanning; however, the detection efficiency was limited and itlacked depth-induced aberration correction. Here we report that a spatial light modulator (SLM)in a polarization insensitive configuration can significantly improve the detection efficiency of2.5D microscopy, while also compensating for aberrations at large imaging depths caused bythe refractive index mismatch between the sample and the immersion medium. We highlightthe improved efficiency via quantitative single-molecule RNA imaging of mammalian cellswith a 2-fold improvement in the fluorescence intensity compared to a conventional SLM-basedmicroscopy. We demonstrate the aberration correction capabilities and extended depth of field byimaging thick specimens with fewerz-scanning steps.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 29; Number 17; Pages 27530; 2021
DOI: 10.1364/oe.434260

Manipulating aqueous droplets by light-induced virtual electrodes

Author(s):

Zamboni, Riccardo; Imbrock, Jörg & Denz, Cornelia

Abstract:

“The precise spatio-temporal manipulation of droplets is fundamental for many lab-on-a-chip systems with applications in biology, healthcare and chemistry. Different approaches have been investigated, including thermal, chemical and electrical methodologies. Among this latter, electrophoresis (EP) and dielectrophoresis (DEP) play a key role, since they are highly compatible with microfluidic systems and provide sufficiently strong forces to control up to microliter volume aqueous droplets. However, EP and DEP techniques typically require the presence of metallic electrodes to create the desired electric fields, making these approaches less flexible and efficient than those exploiting pure optical techniques. Iron-doped lithium niobate (LiNbO3:Fe) allows for the generation of strong electric field modulation due to an inhomogenous illumination, thanks to its photovoltaic properties. These photoinduced fields interact as EP and DEP forces with microdroplets, while guaranteeing the flexibility provided by optical field-based modulation. Indeed, the combination with well-known techniques to control and modulate light fields can be exploited to generate virtual electrodes on the material, achieving reliable as well as flexible devices for water droplets control. In our approach, the photoinduced fields generated by the complex illumination of LiNbO3:Fe are exploited to control motion and trajectory of water droplets inside microfluidic channel. Moreover, the crystal is integrated in standard droplet microfluidic polymeric device, substituting the usual glass substrate and, thus without hindering the portability. This feature combined with the control of positions of aqueous droplets represents a key tool for several applications of customized lab-on-a-chip systems, highlighting the capabilities of LinbO3:Fe-based virtual electrodes.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE 11798, Optical Trapping and Optical Micromanipulation XVIII, 1179824, 2021
DOI: 10.1117/12.2594165

Optically Manipulated Microtools to Measure Adhesion of the Nanoparticle-Targeting Ligand Glutathione to Brain Endothelial Cells

Author(s):

Tamás Fekete, Mária Mészáros, Zsolt Szegletes, Gaszton Vizsnyiczai, László Zimányi, Mária A. Deli, Szilvia Veszelka*, and Lóránd Kelemen

Abstract:

“Targeting nanoparticles as drug delivery platforms is crucial to facilitate their cellular entry. Docking of nanoparticles by targeting ligands on cell membranes is the first step for the initiation of cellular uptake. As a model system, we studied brain microvascular endothelial cells, which form the anatomical basis of the blood–brain barrier, and the tripeptide glutathione, one of the most effective targeting ligands of nanoparticles to cross the blood–brain barrier. To investigate this initial docking step between glutathione and the membrane of living brain endothelial cells, we applied our recently developed innovative optical method. We present a microtool, with a task-specific geometry used as a probe, actuated by multifocus optical tweezers to characterize the adhesion probability and strength of glutathione-coated surfaces to the cell membrane of endothelial cells. The binding probability of the glutathione-coated surface and the adhesion force between the microtool and cell membrane was measured in a novel arrangement: cells were cultured on a vertical polymer wall and the mechanical forces were generated laterally and at the same time, perpendicularly to the plasma membrane. The adhesion force values were also determined with more conventional atomic force microscopy (AFM) measurements using functionalized colloidal probes. The optical trapping-based method was found to be suitable to measure very low adhesion forces (≤ 20 pN) without a high level of noise, which is characteristic for AFM measurements in this range. The holographic optical tweezers-directed functionalized microtools may help characterize the adhesion step of nanoparticles initiating transcytosis and select ligands to target nanoparticles.”

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Publication: ACS Applied Materials & Interfaces
Issue/Year: ACS Applied Materials & Interfaces, Volume 13; Number 33; Pages 39018–39029; 2021
DOI: 10.1021/acsami.1c08454