Imaging moving targets through scattering media

Author(s):

Michelle Cua and Edward (Haojiang) Zhou and Changhuei Yang

Abstract:

“Optical microscopy in complex, inhomogeneous media is challenging due to the presence of multiply scattered light that limits the depths at which diffraction-limited resolution can be achieved. One way to circumvent the degradation in resolution is to use speckle- correlation-based imaging (SCI) techniques, which permit imaging of objects inside scattering media at diffraction-limited resolution. However, SCI methods are currently limited to imaging sparsely tagged objects in a dark-field scenario. In this work, we demonstrate the ability to image hidden, moving objects in a bright-field scenario. By using a deterministic phase modulator to generate a spatially incoherent light source, the background contribution can be kept constant between acquisitions and subtracted out. In this way, the signal arising from the object can be isolated, and the object can be reconstructed with high fidelity. With the ability to effectively isolate the object signal, our work is not limited to imaging bright objects in the dark-field case, but also works in bright-field scenarios, with non-emitting objects.”

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Publication: Optics Express
Issue/Year: Optics Express Vol. 25, Issue 4, pp. 3935-3945  (2017)
DOI: 10.1364/OE.25.003935

Diffraction-free light droplets for axially-resolved volume imaging.

Author(s):

Antonacci, G. and Domenico, G. Di and Silvestri, S. and DelRe, E. and Ruocco, G.

Abstract:

“An ideal direct imaging system entails a method to illuminate on command a single diffraction-limited region in a generally thick and turbid volume. The best approximation to this is the use of large-aperture lenses that focus light into a spot. This strategy fails for regions that are embedded deep into the sample, where diffraction and scattering prevail. Airy beams and Bessel beams are solutions of the Helmholtz Equation that are both non-diffracting and self-healing, features that make them naturally able to outdo the effects of distance into the volume but intrinsically do not allow resolution along the propagation axis. Here, we demonstrate diffraction-free self-healing three-dimensional monochromatic light spots able to penetrate deep into the volume of a sample, resist against deflection in turbid environments, and offer axial resolution comparable to that of Gaussian beams. The fields, formed from coherent mixtures of Bessel beams, manifest a more than ten-fold increase in their undistorted penetration, even in turbid milk solutions, compared to diffraction-limited beams. In a fluorescence imaging scheme, we find a ten-fold increase in image contrast compared to diffraction-limited illuminations, and a constant axial resolution even after four Rayleigh lengths. Results pave the way to new opportunities in three-dimensional microscopy.”

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Publication: Scientific Reports
Issue/Year: Scientific Reports volume 7, Article number: 17 (2017)
DOI: 10.1038/s41598-017-00042-w

Characterization, design, and optimization of a two-pass twisted nematic liquid crystal spatial light modulator system for arbitrary complex modulation

Author(s):

A. J. Macfaden and T. D. Wilkinson

Abstract:

“Arbitrary two-dimensional complex modulation of an optical field is a powerful tool for coherent optical systems. No single spatial light modulator (SLM) offers true arbitrary complex modulation, but they can be combined in order to achieve this. In this work, two sides of a twisted nematic (TN) liquid crystal SLM are used sequentially to implement different arbitrary modulation schemes. In order to fully explore and exploit the rich modulation behavior offered by a TN device, a generalized Jones matrix approach is used. A method for in situ characterization of the SLM inside the two-pass system is demonstrated, where each side of the SLM is independently characterized. This characterization data is then used to design appropriate polarizer configurations to implement arbitrary complex modulation schemes (albeit without 100\% efficiency). Finally, an in situ optimization technique that corrects states by applying a translation in the complex plane is demonstrated. This technique can correct both for variations across the SLM and bulk changes in the SLM behavior due to the changing temperature.”

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Publication: Journal of the Optical Society of America A
Issue/Year: Journal of the Optical Society of America A Vol. 34, Issue 2, pp. 161-170 (2017)
DOI: 10.1364/JOSAA.34.000161

New opportunities for custom-shape patterning using polarization control in confocal laser beam interference setup

Author(s):

Indrišiūnas, Simonas; Voisiat, Bogdan; Gedvilas, Mindaugas; Račiukaitis, Gediminas

Abstract:

“Fabrication of photonic devices requires fast and reliable microstructuring approach. For example, efficient generation of fine 2D patterns in thin metal films is needed in plasmonic metamaterial devices. In this paper, the authors present an approach for the flexible generation of the periodic pattern using a laser beam interference patterning setup. So far, interference patterning was mostly limited to the periodic patterns of lines and dots. A variety of interference patterns can be significantly increased by controlling the polarization orientation of each interfering beam. The authors demonstrate the experimental setup for polarization control in the confocal six-beam interference configuration. Various periodic intensity patterns were generated and observed with a CCD camera using this setup. Additionally, the generated patterns were replicated in a thin metal film experimentally. Efficient and simple fabrication process and relatively high patterning flexibility suggest that interference patterning with polarization control may become an important tool in metamaterial fabrication.”

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Publication: Journal of Laser Applications
Issue/Year: Journal of Laser Applications, Volume 29; Number 1; Pages 011501; 2017
DOI: 10.2351/1.4976679