Light-sensitive Elements Research Articles

Carl Bergmann (1814–1865) and the discovery of the anatomical site in the retina where vision is initiated

ABSTRACT A preeminent quest of nineteenth-century visual neuroscience was to identify the anatomical elements of the retina that respond to light. A major breakthrough came in 1854, when Carl Bergmann discovered through direct observation that the human fovea contains only rods and cones. On this basis, he argued that these must necessarily be the light-sensitive elements (i.e., photoreceptors) that initiate vision. Bergmann also argued that Henle’s fibers form part of the necessary anatomical link between these distal elements and the proximal ganglion cells, which transmit visual signals to the brain via the optic nerve. However, despite his achievement, Heinrich Müller, not Bergmann, is remembered as the discoverer of human photoreceptors in the literature. This article seeks to correct the record. It situates Bergmann’s work alongside that of his contemporaries, sets out his arguments and the critique he received using archival documents, and makes this history more accessible for current readers by comparing what was said to what we know now. We argue that Bergmann’s arguments are at least as compelling as those of Müller, and that he should be recognized as a codiscoverer of the anatomic site in the retina where vision is initiated.

Review of Random Fiber Lasers for Optical Fiber Sensors.

A random fiber laser does not need a traditional resonant cavity and only uses the multiple scattering of disordered media to provide feedback to achieve laser output. Therefore, it has the advantages of a simple structure, narrow linewidth, and low noise and is particularly suitable for fiber optic sensors. This paper provides an introduction to the categories and corresponding principles of random fiber lasers. The research progress of random fiber lasers in the sensing field in recent years, including various aspects of random fiber lasers as low-noise light sources or sensitive elements for fiber sensing systems, is the main focus. Finally, the future development trend of random fiber lasers for optical fiber sensors is explored.

An Electronic Microsaccade Circuit with Charge-Balanced Stimulation and Flicker Vision Prevention for an Artificial Eyeball System

This paper presents the first circuit that enables microsaccade function in an artificial eyeball system. Currently, the artificial eyeball is receiving increasing development in vision restoration. The main challenge is that the human eye is born with microsaccade that helps refresh vision, avoiding perception fading while the gaze is fixed for a long period, and without microsaccade, high-quality vision restoration is difficult. The proposed electronic microsaccade (E-μSaccade) circuit addresses the issue, and it is intrinsically safe because only charge-balanced stimulus pulses are allowed for stimulation. The E-μSaccade circuit adopts light-to-frequency modulation; due to the circuit’s leakage and dark current of light-sensitive elements, stimulus pulses of a frequency lower than tens of Hz occur, which is the cause of flickering vision. A flicker vision prevention (FVP) circuit is proposed to mitigate the issue. The proposed circuits are designed in a 0.18 μm standard CMOS process. The simulation and measurement results show that the E-μSaccade circuit helps refresh the stimulation pattern and blocks the low-frequency output.

Nonlinear optical properties of single-walled carbon nanotubes/water dispersed media exposed to laser radiation with nano- and femtosecond pulse durations

The constant increase in the power of laser systems and the growth of potential fields for the application of lasers make the problem of protecting sensitive elements of electro-optical systems and visual organs from high-intensity radiation an urgent issue. Modern systems are capable of generating laser radiation in a wide range of wavelengths, durations, and pulse repetition rates. High-quality protection requires the use of a universal limiter capable of attenuating laser radiation, not causing colour distortion, and having a high transmission value when exposed to low-power radiation. For this, dispersed media based on carbon nanotubes with unique physicochemical properties can be used. Such media have constant valuesof their absorption coefficient and refractive index when exposed to low-intensity laser radiation and change their properties only when the threshold value is reached.The aim of this work was the study of the nonlinear optical properties of an aqueous dispersion of single-walled carbon nanotubes exposed to nano- and femtosecond radiation. For the characterization of the studied medium, Z-scan and fixed sample location experiments were used. The optical parameters were calculated using a threshold model based on the radiation transfer equation.As a result of the experiments, it was shown that the aqueous dispersion of single-walled carbon nanotubes is capable of limiting radiation with wavelengths from the visible and near-IR ranges: nano- (532, 1064 nm) and femtosecond (810 nm). A description of nonlinear optical effects was proposed for when a medium is exposed to radiation with a nanosecond duration due to reverse saturable absorption and two-photon absorption. When the sample exposed for a femtosecond duration the main limiting effect is spatial self-phase modulation. The calculated optical parameters can be used to describe the behaviour of dispersions of carbon nanotubes when exposed to radiation with different intensities. The demonstrated effects allow us to conclude that it is promising to use the investigated media as limiters of high-intensity laser radiationin optical systems to protect light-sensitive elements.

Diel transcriptional oscillations of light-sensitive regulatory elements in open-ocean eukaryotic plankton communities

The 24-h cycle of light and darkness governs daily rhythms of complex behaviors across all domains of life. Intracellular photoreceptors sense specific wavelengths of light that can reset the internal circadian clock and/or elicit distinct phenotypic responses. In the surface ocean, microbial communities additionally modulate nonrhythmic changes in light quality and quantity as they are mixed to different depths. Here, we show that eukaryotic plankton in the North Pacific Subtropical Gyre transcribe genes encoding light-sensitive proteins that may serve as light-activated transcription factors, elicit light-driven electrical/chemical cascades, or initiate secondary messenger-signaling cascades. Overall, the protistan community relies on blue light-sensitive photoreceptors of the cryptochrome/photolyase family, and proteins containing the Light-Oxygen-Voltage (LOV) domain. The greatest diversification occurred within Haptophyta and photosynthetic stramenopiles where the LOV domain was combined with different DNA-binding domains and secondary signal-transduction motifs. Flagellated protists utilize green-light sensory rhodopsins and blue-light helmchromes, potentially underlying phototactic/photophobic and other behaviors toward specific wavelengths of light. Photoreceptors such as phytochromes appear to play minor roles in the North Pacific Subtropical Gyre. Transcript abundance of environmental light-sensitive protein-encoding genes that display diel patterns are found to primarily peak at dawn. The exceptions are the LOV-domain transcription factors with peaks in transcript abundances at different times and putative phototaxis photoreceptors transcribed throughout the day. Together, these data illustrate the diversity of light-sensitive proteins that may allow disparate groups of protists to respond to light and potentially synchronize patterns of growth, division, and mortality within the dynamic ocean environment.

Editorial on Special Issue “The Advances and Applications of Optogenetics”

This Special Issue provides an update for the rapidly developing technology known as “optogenetics” that is the use of genetically encoded light-sensitive molecular elements (usually derived from lower organisms) to control or report various physiological and biochemical processes within the cell. Two ongoing clinical trials use optogenetic tools for vision restoration, and optogenetic strategies have been suggested as novel therapies for several neurological, psychiatric and cardiac disorders. The Special Issue comprises two reviews and seven experimental papers on different types of light-sensitive modules widely used in optogenetic studies. These papers demonstrate the efficiency and versatility of optogenetics and are expected to be equally relevant for advanced users and beginners who only consider using optogenetic tools in their research.

Hardware Realization of the Pattern Recognition with an Artificial Neuromorphic Device Exhibiting a Short-Term Memory.

Materials exhibiting memory or those capable of implementing certain learning schemes are the basic building blocks used in hardware realizations of the neuromorphic computing. One of the common goals within this paradigm assumes the integration of hardware and software solutions, leading to a substantial efficiency enhancement in complex classification tasks. At the same time, the use of unconventional approaches towards signal processing based on information carriers other than electrical carriers seems to be an interesting trend in the design of modern electronics. In this context, the implementation of light-sensitive elements appears particularly attractive. In this work, we combine the abovementioned ideas by using a simple optoelectronic device exhibiting a short-term memory for a rudimentary classification performed on a handwritten digits set extracted from the Modified National Institute of Standards and Technology Database (MNIST)(being one of the standards used for benchmarking of such systems). The input data was encoded into light pulses corresponding to black (ON-state) and white (OFF-state) pixels constituting a digit and used in this form to irradiate a polycrystalline cadmium sulfide electrode. An appropriate selection of time intervals between pulses allows utilization of a complex kinetics of charge trapping/detrapping events, yielding a short-term synaptic-like plasticity which in turn leads to the improvement of data separability. To the best of our knowledge, this contribution presents the simplest hardware realization of a classification system capable of performing neural network tasks without any sophisticated data processing.

A Ferroelectric/Electrochemical Modulated Organic Synapse for Ultraflexible, Artificial Visual‐Perception System

Human eyes undertake the majority of information assimilation for learning and memory. Transduction of the color and intensity of the incident light into neural signals is the main process for visual perception. Besides light-sensitive elements that function as rods and cones, artificial retinal systems require neuromorphic devices to transform light stimuli into post-synaptic signals. In terms of plasticity timescale, synapses with short-term plasticity (STP) and long-term potentiation (LTP) represent the neural foundation for experience acquisition and memory formation. Currently, electrochemical transistors are being researched as STP-LTP devices. However, their LTP timescale is confined to a second-to-minute level to give unreliable non-volatile memory. This issue limits multiple-plasticity synapses with tunable temporal characteristics and efficient sensory-memory systems. Herein, a ferroelectric/electrochemical modulated organic synapse is proposed, attaining three prototypes of plasticity: STP/LTP by electrochemical doping/de-doping and ferroelectric-LTP from dipole switching. The device supplements conventional electrochemical transistors with 10000-second-persistent non-volatile plasticity and unique threshold switching properties. As a proof-of-concept for an artificial visual-perception system, an ultraflexible, light-triggered organic neuromorphic device (LOND) is constructed by this synapse. The LOND transduces incident light signals with different frequency, intensity, and wavelength into synaptic signals, both volatile and non-volatile.

Phase-Slip Phenomena in Proximitized NbN/NiCu Superconducting Nanostripes

Ultrathin superconducting/ferromagnet (S/F) nanostripes are very interesting systems to investigate both the physics involved on nanoscale size and as light sensitive elements for superconducting single photon detectors. The electrical transport properties of NbN(8 nm)/NiCu(10 nm) nanostripes are presented down to a temperature of 4.2 K. A number of voltage steps were observed on the current-voltage characteristics, and they were investigated at different temperatures. A possible explanation in terms of active phase-slip phenomena has been proposed on the basis of the time-dependent Ginzburg-Landau theory, leading to an estimation of the inelastic electron-phonon relaxation time around 0.8 ps. The latter value was found to be in good agreement with a relaxation time, independently measured by femtosecond transient optical reflectivity experiments performed on the same bilayer.

(Invited) Carbon Nanotubes: Towards an Advanced Material for Energy and Electronic Applications

Ever since their discovery, carbon nanotubes (CNTs) have been touted as a material of the future and a lengthy list of possible applications are often cited in the literature. However, the realization of these applications have so far been hindered by exactly the property which made CNTs so attractive in the first place, namely their varying optical and electronic properties. In order to become a true advanced material of the future it is necessary to develop techniques to prepare CNTs with defined length, wall number, diameter, electronic and optical property on the large scale. Furthermore, in addition to simply having large quantities, it is important that strategies for their incorporation into large-area devices are developed. In our work we address these issues with the use of aqueous gel based sorting techniques to routinely prepare milligram quantities of metallic and semiconducting, single chirality and even double walled carbon nanotubes with defined outer-wall electronic type. This ‘toolbox’ of available CNTs is then used for the realization of CNT based devices with applications to energy. For example CNT:Fullerene solar cells, CNT:Si solar cells and CNT based light sensitive elements. In addition to being of fundamental scientific interest these applications also provide us the opportunity to address the challenges of controlling this 1 D nanomaterial on the macro-scale. To this end we prepare inks from sorted CNT material and look at strategies to align them in thin films over large areas. [1] K. E. Moore, M. Pfohl, D. D. Tune, F. Hennrich, S. Dehm, V. S. K. Chakradhanula, C. Kuebel, R. Krupke, B. S. Flavel, ACS Nano 9 (2015) 3849-3857. [2] D. D. Tune, A. J. Blanch, C. J. Shearer, K. E. Moore, M. Pfohl, J. G. Shapter, B. S Flavel, Applied Materials & Interfaces (2015) 10.1021/acsami.5b08212. [3] M. Pfohl, K. Glaser, J. Ludwig, D. D. Tune, S. Dehm, C. Kayser, A. Colsmann, R. Krupke, B. S Flavel, Advanced Energy Materials (2015) 10.1022/aemn.201501345. [4] B. S. Flavel, K. E. Moore, M. Pfohl, M. M. Kappes, F. Hennrich, ACS Nano 8 (2014) 1817-1826.

Dielectric Layer Transfer by Low-Temperature Wafer Bonding for Optical Characterization

The optical properties of dielectric layers on top of photodiodes processed in mixed signal CMOS processes significantly influence the characteristics of these light sensitive elements. This paper describes the transfer of this type of layer from silicon to a quartz wafer, in order to allow their optical characterization.

Visual pathways serving motion detection in the mammalian brain.

Motion perception is the process through which one gathers information on the dynamic visual world, in terms of the speed and movement direction of its elements. Motion sensation takes place from the retinal light sensitive elements, through the visual thalamus, the primary and higher visual cortices. In the present review we aim to focus on the extrageniculo-extrastriate cortical and subcortical visual structures of the feline and macaque brain and discuss their functional role in visual motion perception. Special attention is paid to the ascending tectofugal system that may serve for detection of the visual environment during self-motion.

Phthalocyanines and related compounds as switchable materials upon strong irradiation: the molecular engineering behind the optical limiting effect

The possibility of varying the optical properties of materials in a controlled fashion constitutes an appealing objective, which represents the necessary starting point for the development of those advanced technologies designated to exploit the energy of the luminous radiation into a desirable way. Usually, in electrochromic, thermochromic or photochromic processes, the reversible switching of the material absorbance or reflectance in the UV–vis–NIR spectrum is accompanied by reversible variations of the material chemical composition. This is followed by mostly redox, dimerization or isomerization reactions which are induced by temperature changes or slowly and rapidly variable electric fields. Other means of varying the optical properties of materials are offered by nonlinear optical (NLO) processes in which the intensity of the light modifies absorptive and refractive properties of the irradiated material within the limits of its photochemical stability (photochromic effect). Among various nonlinear optical phenomena, the optical limiting (OL) effect represents an important one for its possible exploitation in the protection of light-sensitive elements which must operate below a safety threshold of light intensity. In the present contribution, the optical limiting effect generated by different classes of phthalocyanine-based materials is described and analyzed in terms of those molecular features which are associated with the better optical limiting performances.

Optoelectronic monitoring of individual whisker movements in rats

We describe two systems for the real-time recording and display of individual vibrissa movements in head-fixed rats. Both systems utilize high-speed, linear image sensors, each composed of an array of light sensitive elements (CCDs). Uniform illumination of the array generates a constant baseline voltage in each element. The shadow produced by the movement of a whisker interposed between the light source and the sensors produces a voltage shift in a subset of elements. The successive position of the shift is linearly related to the momentary whisker position. Associated software/hardware scans the array at regular intervals to identify the successive positions of voltages above a preset threshold and outputs the data to a microprocessor for computation of the whisker movement trajectory. In both systems, movements of a single whisker may be monitored ‘on-line’ with high spatial and temporal resolution; in one case with, in the other without the presence of neighboring whiskers. Optoelectronic monitoring facilitates rapid and efficient (computer-assisted) acquisition and analysis of data on rodent whisking behavior.

Colour in photography

Colour photography uses films and printing papers that incorporate gelatin dispersions of silver halide crystals as light-sensitive elements. About one micrometer in size, these crystals are insensitive at wavelengths greater than approximately 500 run and require development to reveal the effects of exposure. This paper describes methods by which photographic materials can ‘see’ most of the visible spectrum, how colours of subjects are analysed and how final images are synthesised, all within layers a few microns thick.

Detector array for measurement of high-frequency fluctuations in visible and near-UV emission from tokamaks

We developed an imaging detector to measure high-frequency fluctuations in visible and near-UV emission from tokamaks. The detector is intended for the study of plasma turbulence, mhd phenomena, and edge-localized modes. Particularly in the first two applications, it will complement existing techniques by providing higher spatial resolution as well as measurement capability in otherwise inaccessible regions of the plasma. The device consists of an optical system, a linear array of 32 photodiodes, and an amplifier for each photodiode. The amplifiers have a transimpedance gain of 105–106 and the frequency response is flat to 100 kHz. Experience with this device has shown that optical imaging systems can be easily designed and tailored to a specific measurement because of the small size and close spacing of the individual light-sensitive elements. The device has been successfully tested on TEXT-U in measurements of Hα fluctuations.

Maize rbcS promoter activity depends on sequence elements not found in dicot rbcS promoters.

Although the molecular mechanisms of dicot photosynthetic gene regulation have been pursued actively, comparable studies of monocot regulation have been slow to come forth. We show here that monocot (maize and wheat) but not dicot (pea, tobacco, and Arabidopsis) ribulose-1,5-bisphosphate carboxylase small subunit (rbcS) gene promoters are active in maize mesophyll protoplasts. The evolutionarily conserved GT and G boxes of dicot rbcS promoters are not essential for light-responsive expression in monocot leaf cells. Instead, at least six constitutive and light-sensitive regulatory elements are likely important for maize rbcS expression. Synergism between upstream and downstream promoter elements is required. Whereas in dicots, light triggers coupled leaf development and photosynthetic gene expression, in monocots, light regulation of rbcS is uncoupled from leaf development. Light regulation of maize rbcS may be divided into direct and indirect contributions mediated by different regulatory elements. Because wheat and maize rbcS promoters show sequence homologies and similar expression patterns in monocot and dicot leaf cells, it appears likely that monocots share conserved regulatory elements irrespective of whether they utilize the C3 or C4 pathway for carbon fixation.

The silver halide photographic process

Abstract The light-sensitive elements of conventional photographic materials are crystallites principally of the bromide or chloride salts of silver. Certain chemical modifications employing sulphur and gold compounds are used to maximize the response, and organic dyes are adsorbed to provide sensitivity throughout the visible spectrum. Absorption of a few photons results in the reductive formation of one or more clusters of silver or gold atoms on the surface. These clusters act as catalysts to promote further reduction of the host crystallites during photographic development. The success of the system depends upon the particular physical properties of the silver halides, such as their bonding and electron structure, the dielectric properties, the point defect structure, and the electronic transport characteristics. These are all reviewed, and the ways in which they interact to lead to the favourable photodecomposition are followed in some detail. A nucleation-and-growth mechanism operates to provide several of the favourable features of the process, and the chemical treatments used optimize the competition between these desirable steps and the unwanted recombination of electronic carriers.

Position determination of automatically guided vehicles

The realising of the great benefits of odometrically-controlled, freeranging, automatically guided vehicles has been prevented by the lack of an adequate secondary ‘absolute’ vehicle location technique, required to overcome the cumulative errors inherent in odometry. In this paper the sources of odometric error are discussed, and the resulting positional uncertainties investigated. The dominant amongst these is identified as being the uncertainty in the lateral location of the vehicle, and this is quantified as a function of odometric error. A location technique addressed specifically at this uncertainty has been devised and constructed, employing linear arrays of light sensitive elements and a narrow light beam. This system and its associated electronics and software is described.

The effect of inhibition of endothelial cell cyclooxygenase on arterial thrombosis

Arterial platelet thrombosis was induced in vivo in a branch of the mesenteric artery of the white Wistar rat by topical superfusion by adenosine diphosphate following local de-endothelialization of the dissected segment by means of a small electrical current. Detection of the thrombotic phenomena was performed by projection of the arterial segment onto a set of light sensitive elements, wich allows the registration of several discriminating parameters. The addition of arachidonic acid to the superfusing mixture results in an increase in thromboformation; this increasing effect can be blocked completely by prior inhibition od the vessel wall cyclooxygenase activity by inhibitors such as flurbiprofen or indomethacin. We therefore concluded that the arachidonate cascade, triggered within the endothelial cells, is involved in platelet-vessel wall interaction leading ultimately to local thrombosis.