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phase coherence

Srilatha Vantipalli, Jiasong Li, Manmohan Singh, Salavat R Aglyamov, Kirill V Larin, Michael D Twa
SIGNIFICANCE: Measured corneal biomechanical properties are driven by intraocular pressure, tissue thickness, and inherent material properties. We demonstrate tissue thickness as an important factor in the measurement of corneal biomechanics that can confound short-term effects due to UV riboflavin cross-linking (CXL) treatment. PURPOSE: We isolate the effects of tissue thickness on the measured corneal biomechanical properties using optical coherence elastography by experimentally altering the tissue hydration state and stiffness...
March 21, 2018: Optometry and Vision Science: Official Publication of the American Academy of Optometry
Margherita Maiuri, Johanna Brazard
During the last two decades, 2D optical techniques have been extended to the visible range, targeting electronic transitions. Since the report of the very first 2D electronic measurement (Hybl et al. in J Chem Phys 115:6606-6622, [2001]), two-dimensional electronic spectroscopy (2DES) has allowed fundamentally new insights into the structure and dynamics of condensed-phase systems (Ginsberg et al. in Acc Chem Res 42:1352-1363, 2009; Jonas in Annu Rev Phys Chem 54:425-463, 2003), producing experiments that measure correlations among electronic states of an absorbing species within complex systems...
March 20, 2018: Topics in Current Chemistry (Journal)
Kosmas L Tsakmakidis, Pankaj K Jha, Yuan Wang, Xiang Zhang
Self-organized criticality emerges in dynamical complex systems driven out of equilibrium and characterizes a wide range of classical phenomena in physics, geology, and biology. We report on a quantum coherence-controlled self-organized critical transition observed in the light localization behavior of a coherence-driven nanophotonic configuration. Our system is composed of a gain-enhanced plasmonic heterostructure controlled by a coherent drive, in which photons close to the stopped-light regime interact in the presence of the active nonlinearities, eventually synchronizing their dynamics...
March 2018: Science Advances
C Schnedermann, X Yang, M Liebel, K M Spillane, J Lugtenburg, I Fernández, A Valentini, I Schapiro, M Olivucci, P Kukura, R A Mathies
Vibronic coupling is key to efficient energy flow in molecular systems and a critical component of most mechanisms invoking quantum effects in biological processes. Despite increasing evidence for coherent coupling of electronic states being mediated by vibrational motion, it is not clear how and to what degree properties associated with vibrational coherence such as phase and coupling of atomic motion can impact the efficiency of light-induced processes under natural, incoherent illumination. Here, we show that deuteration of the H11 -C11 =C12 -H12 double-bond of the 11-cis retinal chromophore in the visual pigment rhodopsin significantly and unexpectedly alters the photoisomerization yield while inducing smaller changes in the ultrafast isomerization dynamics assignable to known isotope effects...
March 19, 2018: Nature Chemistry
Lyndon da Cruz, Kate Fynes, Odysseas Georgiadis, Julie Kerby, Yvonne H Luo, Ahmad Ahmado, Amanda Vernon, Julie T Daniels, Britta Nommiste, Shazeen M Hasan, Sakina B Gooljar, Amanda-Jayne F Carr, Anthony Vugler, Conor M Ramsden, Magda Bictash, Mike Fenster, Juliette Steer, Tricia Harbinson, Anna Wilbrey, Adnan Tufail, Gang Feng, Mark Whitlock, Anthony G Robson, Graham E Holder, Mandeep S Sagoo, Peter T Loudon, Paul Whiting, Peter J Coffey
Age-related macular degeneration (AMD) remains a major cause of blindness, with dysfunction and loss of retinal pigment epithelium (RPE) central to disease progression. We engineered an RPE patch comprising a fully differentiated, human embryonic stem cell (hESC)-derived RPE monolayer on a coated, synthetic basement membrane. We delivered the patch, using a purpose-designed microsurgical tool, into the subretinal space of one eye in each of two patients with severe exudative AMD. Primary endpoints were incidence and severity of adverse events and proportion of subjects with improved best-corrected visual acuity of 15 letters or more...
March 19, 2018: Nature Biotechnology
Mikhail E Kandel, Michael Fanous, Catherine Best-Popescu, Gabriel Popescu
As a label-free, nondestructive method, phase contrast is by far the most popular microscopy technique for routine inspection of cell cultures. However, features of interest such as extensions near cell bodies are often obscured by a glow, which came to be known as the halo . Advances in modeling image formation have shown that this artifact is due to the limited spatial coherence of the illumination. Nevertheless, the same incoherent illumination is responsible for superior sensitivity to fine details in the phase contrast geometry...
February 1, 2018: Biomedical Optics Express
Boy Braaf, Sabine Donner, Ahhyun S Nam, Brett E Bouma, Benjamin J Vakoc
Complex differential variance (CDV) provides phase-sensitive angiographic imaging for optical coherence tomography (OCT) with immunity to phase-instabilities of the imaging system and small-scale axial bulk motion. However, like all angiographic methods, measurement noise can result in erroneous indications of blood flow that confuse the interpretation of angiographic images. In this paper, a modified CDV algorithm that corrects for this noise-bias is presented. This is achieved by normalizing the CDV signal by analytically derived upper and lower limits...
February 1, 2018: Biomedical Optics Express
Laurin Ginner, Tilman Schmoll, Abhishek Kumar, Matthias Salas, Nastassia Pricoupenko, Lara M Wurster, Rainer A Leitgeb
We demonstrate a high-resolution line field en-face time domain optical coherence tomography (OCT) system using an off-axis holography configuration. Line field en-face OCT produces high speed en-face images at rates of up to 100 Hz. The high frame rate favors good phase stability across the lateral field-of-view which is indispensable for digital adaptive optics (DAO). Human retinal structures are acquired in-vivo with a broadband light source at 840 nm, and line rates of 10 kHz to 100 kHz. Structures of different retinal layers, such as photoreceptors, capillaries, and nerve fibers are visualized with high resolution of 2...
February 1, 2018: Biomedical Optics Express
K R Prathyusha, Silke Henkes, Rastko Sknepnek
We use Langevin dynamics simulations to study dynamical behavior of a dense planar layer of active semiflexible filaments. Using the strength of active force and the thermal persistence length as parameters, we map a detailed phase diagram and identify several nonequilibrium phases in this system. In addition to a slowly flowing melt phase, we observe that, for sufficiently high activity, collective flow accompanied by signatures of local polar and nematic order appears in the system. This state is also characterized by strong density fluctuations...
February 2018: Physical Review. E
Lei Li, Jian Zou, Hai Li, Bao-Ming Xu, Yuan-Mei Wang, Bin Shao
We investigate the heat transport between two nonthermal reservoirs based on a microscopic collision model. We consider a bipartite system consisting of two identical subsystems, and each subsystem interacts with its own local reservoir, which consists of a large collection of initially uncorrelated ancillas. Then a heat transport is formed between two reservoirs by a sequence of pairwise collisions (intersubsystem and subsystem-local reservoir). In this paper we consider two kinds of the reservoir's initial states: the thermal state and the state with coherence whose diagonal elements are the same as that of the thermal state and the off-diagonal elements are nonzero...
February 2018: Physical Review. E
Jingshan Han, Thibault Vogt, Christian Gross, Dieter Jaksch, Martin Kiffner, Wenhui Li
We present an experimental demonstration of converting a microwave field to an optical field via frequency mixing in a cloud of cold ^{87}Rb atoms, where the microwave field strongly couples to an electric dipole transition between Rydberg states. We show that the conversion allows the phase information of the microwave field to be coherently transferred to the optical field. With the current energy level scheme and experimental geometry, we achieve a photon-conversion efficiency of ∼0.3% at low microwave intensities and a broad conversion bandwidth of more than 4 MHz...
March 2, 2018: Physical Review Letters
Ronald L Cappelletti, Terrence Jach, John Vinson
It has been shown that single-particle wave functions, of both photons and electrons, can be created with a phase vortex, i.e., an intrinsic orbital angular momentum (OAM). A recent experiment has claimed similar success using neutrons [C. W. Clark et al., Nature, 525, 504 (2015)NATUAS0028-083610.1038/nature15265]. We show that their results are insufficient to unambiguously demonstrate OAM, and they can be fully explained as phase contrast interference patterns. Furthermore, given the small transverse coherence length of the neutrons in the original experiment, the probability that any neutron was placed in an OAM state is vanishingly small...
March 2, 2018: Physical Review Letters
Jose M Sanchez Bornot, KongFatt Wong-Lin, Alwani Liyana Ahmad, Girijesh Prasad
The brain's functional connectivity (FC) estimated at sensor level from electromagnetic (EEG/MEG) signals can provide quick and useful information towards understanding cognition and brain disorders. Volume conduction (VC) is a fundamental issue in FC analysis due to the effects of instantaneous correlations. FC methods based on the imaginary part of the coherence (iCOH) of any two signals are readily robust to VC effects, but neglecting the real part of the coherence leads to negligible FC when the processes are truly connected but with zero or π-phase (modulus 2π) interaction...
March 15, 2018: Brain Topography
S Hemmer, H Almansour, W Pepke, M M Innmann, M Akbar
BACKGROUND: In the light of the increasingly aging population and the widespread understanding of the sagittal profile of symptomatic patients with adult spinal deformity (ASD), pervasive utilization of osteotomies on the vertebral column should be expected. These surgeries are accompanied with relatively high complication rates. However, there is no uniform definition or classification in terms of grading the severity or chronological incidence of complications after ASD surgery. OBJECTIVES: The aim of this work is to give an overview of the different classifications described in the literature hitherto and to propose a standardized, clinically utile classification of complications after ASD surgery...
March 15, 2018: Der Orthopäde
Michael J Willatt, Michele Ceriotti, Stuart C Althorpe
Matsubara dynamics is the quantum-Boltzmann-conserving classical dynamics which remains when real-time coherences are taken out of the exact quantum Liouvillian [T. J. H. Hele et al., J. Chem. Phys. 142, 134103 (2015)]; because of a phase-term, it cannot be used as a practical method without further approximation. Recently, Smith et al. [J. Chem. Phys. 142, 244112 (2015)] developed a "planetary" model dynamics which conserves the Feynman-Kleinert (FK) approximation to the quantum-Boltzmann distribution...
March 14, 2018: Journal of Chemical Physics
H Le Jeannic, A Cavaillès, K Huang, R Filip, J Laurat
Non-Gaussian states, and specifically the paradigmatic cat state, are well known to be very sensitive to losses. When propagating through damping channels, these states quickly lose their nonclassical features and the associated negative oscillations of their Wigner function. However, by squeezing the superposition states, the decoherence process can be qualitatively changed and substantially slowed down. Here, as a first example, we experimentally observe the reduced decoherence of squeezed optical coherent-state superpositions through a lossy channel...
February 16, 2018: Physical Review Letters
Zaineb Al-Qazwini, Zhen Yu Gordon Ko, Kalpesh Mehta, Nanguang Chen
We report an ultrahigh-speed and high-resolution line-scan spectral-domain optical coherence tomography (SD-OCT) system that integrates a number of mechanisms for improving image quality. The illumination uniformity is significantly improved by the use of a Powell lens; Phase stepping and differential reconstruction are combined to suppress autocorrelation artifacts; Nonlocal means (NLM) is employed to enhance the signal to noise ratio while minimizing motion artifacts. The system is capable of acquiring cross-sectional images at more than 3,500 B-scans per second with sensitivities between 70dB and 90dB...
March 1, 2018: Biomedical Optics Express
Serhat Tozburun, Cedric Blatter, Meena Siddiqui, Eelco F J Meijer, Benjamin J Vakoc
We present a swept-wavelength optical coherence tomography (OCT) system with a 19 MHz laser source and electronic phase-locking of the source, acquisition clock, and beam scanning mirrors. The laser is based on stretched-pulse active mode-locking using an electro-optic modulator. Beam scanning in the fast axis uses a resonant micro-electromechanical systems (MEMS) -based mirror at ~23.8 kHz. Acquisition is performed at 1.78 Gigasamples per second using an external fixed clock. Phase sensitive imaging without need for k-clocking, A-line triggers, or phase-calibration methods is demonstrated...
March 1, 2018: Biomedical Optics Express
Irina I Ignatova, Andrew S French, Roman V Frolov
Natural visual scenes are rarely random. Instead, intensity and wavelength change slowly in time and space over many regions of the scene, so that neighboring temporal and spatial visual inputs are more correlated, and contain less information than truly random signals. It has been suggested that sensory optimization to match these higher order correlations (HOC) occurs at the earliest visual stages, and that photoreceptors can process temporal natural signals more efficiently than random signals. We tested this early stage hypothesis by comparing the information content of Calliphora vicina photoreceptor responses to naturalistic inputs before and after removing HOC by randomizing phase...
March 14, 2018: Journal of Neurophysiology
Xiaoliang He, Hua Tao, Xingchen Pan, Cheng Liu, Jianqiang Zhu
Coherent modulation imaging (CMI) is a promising technique for online laser beam diagnostics; however, obvious speckle noise is always generated in the reconstruction, seriously degrading the spatial resolution and, accordingly, the accuracy. To solve this problem, both the optical setup of the common CMI and its reconstruction algorithm are slightly modified, and the performance of CMI in laser beam diagnostics can be obviously improved. By adding the second detector to record additional intensity distribution and using it to strengthen the intensity constraint of common CMI algorithm, the speckle noise in the reconstructed image can be distinctively reduced, and thus both the spatial resolution and the measurement accuracy are improved significantly...
March 5, 2018: Optics Express
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