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We review neural and computational measurement of optical flow. Insects are sensitive to visual motion which has been established by elecrophysiological and behavioural studies over more than half a century. We discuss the elementary motion detector theory of how optical flow is detected in the nervous system and the limitations of this theory in predicting some insect visual behaviour that is apparently driven by a measurement of optical flow. The use of optical flow techniques in aerial robotics applications that mimic the challenges faced by flying insects are compared. The limitations of optical flow measurements in computing distance to targets or speed of travel is observed and the merits of proposed solutions discussed. Finally we examine a range of optical devices that were designed to overcome the limitations of monocular optical flow and consider the new limitations that they create which have prevented their wide acceptance in robotics. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the focusing properties and focal shift of a partially coherent vortex cosine-hyperbolic-Gaussian beam (PCvChGB) passing through a lens system. Based on the extended Collins formula, the analytical expression for a PCvChGB propagating through a thin lens is derived in detail. By using the obtained formula, the influences of the spatial coherence length, the Fresnel number, and the initial beam parameters on the focusing properties and the focal shift of a PCvChGB are discussed numerically. It is shown that the average intensity distribution in the focal region and the focal shift of the focused PCvChGB are strongly affected by the above factors. The obtained results could be beneficial for applications of vortex cosine-hyperbolic-Gaussian beam (vChGB) beams in beam shaping and atom optics. [ABSTRACT FROM AUTHOR]

We present simulations of stimulated X-ray Raman (SXRS) signals from covalent porphyrin heterodimers with different linkers, chemical bonding structures and geometries. The signals are interpreted in terms of valence electron wavepacket motion. One- and two-color SXRS signals can jointly indicate excitation energy transfer (EET) between the porphyrin monomers. It is shown that the SXRS signals provide a novel window into EET dynamics in multiporphyrin systems, and can be used as a powerful tool to monitor the subtle chemical environment which affects EET.

Light-induced states in He atoms were characterized using attosecond transient absorption spectroscopy. A 400 as pulse covering the 20-24 eV spectral range serves as the probe pulse, and the effect of a few-cycle near infrared pulse (12 fs, 780 nm) on the absorption spectrum is measured as a function of time delay and near-infrared intensities varying from (5.0 ± 2) × 1010 to (1 ± 0.4) × 1013 W/cm2. Light-induced states resulting from near-infrared coupling of 1s2p to 1s2s, 1s3d, and 1s3s states are observed. Absorption features that likely result from coupling of 1s3p to 1s4s, 1s4d, 1s5s, and 1s5d states are also observed. The light-induced states with the smallest detunings (1s3d and 1s3s) from the dressing frequency may shift to higher frequencies as the dressing intensity is increased. © 2013, Taylor & Francis.

Light-induced states in He atoms were characterized using attosecond transient absorption spectroscopy. A 400 as pulse covering the 20-24 eV spectral range serves as the probe pulse, and the effect of a few-cycle near infrared pulse (12 fs, 780 nm) on the absorption spectrum is measured as a function of time delay and near-infrared intensities varying from (5.0 ± 2) × 1010 to (1 ± 0.4) × 1013 W/cm2. Light-induced states resulting from near-infrared coupling of 1s2p to 1s2s, 1s3d, and 1s3s states are observed. Absorption features that likely result from coupling of 1s3p to 1s4s, 1s4d, 1s5s, and 1s5d states are also observed. The light-induced states with the smallest detunings (1s3d and 1s3s) from the dressing frequency may shift to higher frequencies as the dressing intensity is increased. © 2013, Taylor & Francis.

The Fresnel–Arago laws of interference are five laws describing the interference of polarized light and published in 1819. The fifth law has been systematically forgotten in almost all available references published during the last century, leading to the common, but incorrect, belief that Arago and Fresnel gave only four laws of interference. The fifth law describes the existence of an additional phase of 180 ∘ , not due to path or speed differences, in linearly polarized beams that undergo certain polarization transformations in double refracting crystals. Two years later, Fresnel provided a complete explanation for this unexpected phase, showing that he had a good understanding of what can unequivocally be pointed out as the first description of a geometric phase in optics. [ABSTRACT FROM AUTHOR]

Exposure to bright light appears to be protective against myopia in both animals (chicks, monkeys) and children, but quantitative data on human light exposure are limited. In this study, we report on a technique for quantifying light exposure using wearable sensors. Twenty-seven young adult subjects wore a light sensor continuously for two weeks during one of three seasons, and also completed questionnaires about their visual activities. Light data were analyzed with respect to refractive error and season, and the objective sensor data were compared with subjects' estimates of time spent indoors and outdoors. Subjects' estimates of time spent indoors and outdoors were in poor agreement with durations reported by the sensor data. The results of questionnaire-based studies of light exposure should thus be interpreted with caution. The role of light in refractive error development should be investigated using multiple methods such as sensors to complement questionnaires.

In neutron optics, we analyse the propagation of slow (thermal) neutrons along a semi-infinite waveguide limited by a large repulsive potential (reminding the propagation of light along an optical fibre). We set an ideal case of a straight empty two-dimensional semi-infinite waveguide limited by an infinitely repulsive potential (Dirichlet conditions on its boundaries). The neutron wave function is given through an integral representation involving the incoming wave with energy E, Green's function and certain functions defined on the boundaries. The latter functions follow from the Dirichlet conditions, thereby proposing a new formalism in neutron optics. We develop various approximations (through Fourier and Hilbert transforms) and numerical computations. We get: (a) the expected extinction of the incoming wave for very large penetration into the waveguide, (b) the generation of propagation modes and their number for suitably large penetration, as E increases, (c) an estimate of the critical angle. [ABSTRACT FROM AUTHOR]

Based on monolayer MoTe2 film, we have proposed a mode-locked fibre laser delivering single-wavelength and dual-wavelength solitons at the telecommunication band. The saturable absorber (SA) is synthesized by coating monolayer MoTe2 film on the pinhole of fibre pigtail. The experimental results show that our soliton lasers can work at the single- and dual-wavelength states, respectively, by appropriately adjusting the polarization controller. The proposed laser can work stably at the mode-locking state for several hours, indicating that monolayer MoTe2 film is an excellent SA material for ultrafast optics. [ABSTRACT FROM AUTHOR]

Fluorescent molecular tomography (FMT) is emerging as a reliable optics-based molecular imaging technique. The diffusion approximation is commonly employed as a forward model for reconstruction. However, the diffusion equation is not valid in regions where the medium is low scattering or nonscattering. In addition, reconstruction based on the coarse grid will result in the low reconstruction accuracy although the computational requirements can be reduced. This paper is concerned with a new method of image reconstruction for FMT. In this method, the tomographic image of FMT is reconstructed in combination with the modelling error. Furthermore, an iterative strategy of grouped light sources is incorporated into the reconstruction process. The results attest that the proposed algorithm can speed up the reconstruction process and improve the quality of image reconstruction. [ABSTRACT FROM AUTHOR]

We investigate the effect of the unavoidable optical loss on the recently reported optical analogue of the relativistic Thomas Effect which uses a photonic chip-based lossless All-Pass Filter (APF) circuit [J. of Mod. Optics 65.19 (2018): 2171-2178]. When the APF has loss, both its phase and amplitude responses are altered. This impacts the accuracy and operating range of the APF-based Thomas Effect analogue. To evaluate its impact on the phase output, we carry out a systematic evaluation of the phase response of the APF to explore when this Thomas Effect analogue breaks down. A lossy APF produces three dissimilar phase responses and varying dip in the amplitude response depending on the relative values of the coupling coefficient and the loss parameter. Numerical and analytical results show that APF must (i) be operated at an Over-Coupling (OC) condition (ii) with a loss parameter α ≥ 0.95 in order to have less than 1% phase error with the widest possible band coverage. [ABSTRACT FROM AUTHOR]

Nonclassical properties exhibited by a chain of cavity modes second harmonic generation in coupled oscillators system, designed by using multichannel optical waveguides, is explored. The solution for the Hamiltonian of the coupled-modes driven by coherent excitation is obtained via an exact formulation of the normal-ordered Fokker-Planck equation. Nonclassical effects, namely the sub-Poissonian photons, squeezing and entanglement are noticed. Multichannel coupling of the coupled oscillators induces new possibilities for correlation between the modes in different channels, henceforth, provides an effective way towards manipulation of quantum light. [ABSTRACT FROM AUTHOR]

In this paper, we consider a multi-hop teleportation protocol for transfer of certain five-qubit entangled states. The speciality of this protocol is that intermediate nodes between the sender and the receiver are introduced. Teleportation processes over long distances are problematic because of the existence of the environmental noise which is almost unavoidable and adversely affects the entangled quantum channel. With a view to the above, intermediate nodes are introduced which are connected in series by entanglement. These short range quantum channels minimize the risk of the protocol being affected by noise. The present protocol is performed in an integrated manner in which the parties in the intermediate nodes act independently. A remarkable feature of the protocol is that only 3.13% of the basis elements are involved in the measurements. We also calculate the efficiency and indicate the advantages of the present protocol. The work is in the direction of research for transferring entangled quantum states. [ABSTRACT FROM AUTHOR]

We have examined both single and entangled two-mode multiphoton coherent states and shown how the ‘Janus-faced’ properties between two partner states are mirrored in appropriate tomograms. Entropic squeezing, quadrature squeezing and higher-order squeezing properties for a wide range of nonclassical states are estimated directly from tomograms. We have demonstrated how squeezing properties of two-mode entangled states produced at the output port of a quantum beamsplitter are sensitive to the relative phase between the reflected and transmitted fields. This feature allows for the possibility of tuning the relative phase to enhance squeezing properties of the state. Finally, we have examined the manner in which decoherence affects squeezing and the changes in the optical tomogram of the state due to interaction with the environment. [ABSTRACT FROM AUTHOR]

In this paper, we present a rotational symmetry for an ultrashort throw (UST) lens with offset field. The UST lens has a throw ratio of 0.23 and a total track of 195 mm. The optical elements of the UST lens are comprised of two parts. First, a catadioptric projection lens where the catadioptric function permits reaching an ultrashort throw ratio, short total track, while at the same time requiring fewer lens elements. The second part is a collimating lens which takes advantage of the telecentric condition to generate uniform total internal reflection (TIR) in the TIR prism. With this design, an effective focal length of -1.96 mm and a f-number of 2.4 can be obtained. The root mean square spot size and lateral colour of all fields are smaller than one pixel in size. The maximum optical distortion of −0.97% and TV distortion of 0.2% are acceptable. In terms of image quality, the modulation transfer function (MTF) values for all fields are above 0.65 at 0.245 line pairs/mm. Even when the tolerance error is considered, the MTF values for all fields are still above 0.3. The suitability of the novel UST lens design for projection applications is discussed. [ABSTRACT FROM AUTHOR]

The Winter Colloquium on the Physics of Quantum Electronics (PQE) has been a seminal force in quantum optics and related areas since 1971. It is rather mind-boggling to recognize how the concepts presented at these conferences have transformed scientific understanding and human society. In January 2017, the participants of PQE were asked to consider the equally important prospects for the future, and to formulate a set of questions representing some of the greatest aspirations in this broad field. The result is this multi-authored paper, in which many of the world’s leading experts address the following fundamental questions: (1) What is the future of gravitational wave astronomy? (2) Are there new quantum phases of matter away from equilibrium that can be found and exploited - such as the time crystal? (3) Quantum theory in uncharted territory: What can we learn? (4) What are the ultimate limits for laser photon energies? (5) What are the ultimate limits to temporal, spatial and optical resolution? (6) What novel roles will atoms play in technology? (7) What applications lie ahead for nitrogen-vacancy centres in diamond? (8) What is the future of quantum coherence, squeezing and entanglement for enhanced super-resolution and sensing? (9) How can we solve (some of) humanity’s biggest problems through new quantum technologies? (10) What new understanding of materials and biological molecules will result from their dynamical characterization with free-electron lasers? (11) What new technologies and fundamental discoveries might quantum optics achieve by the end of this century? (12) What novel topological structures can be created and employed in quantum optics? [ABSTRACT FROM AUTHOR]