Wavelength Discrimination Research Articles

Voltage Controlled Amorphous Si/SiC Phototransistors and Photodiodes as Wavelength Selective Devices: Theoretical and Electrical Approaches

AbstractIn this paper single and stacked structures that can be used as wavelength selective devices, in the visible range, are analysed. Two terminal heterojunctions ranging from p-ií-n to p-i-n-p-i’-n configurations are studied. Three terminals double staked junctions with transparent contacts in-between are also considered to increase wavelength discrimination. The color discrimination was achieved by ac photocurrent measurement under different externally applied bias. Experimental data on spectral response analysis and current –voltage characteristics are reported. A theoretical analysis and an electrical simulation procedure are performed to support the wavelength selective behaviour. Good agreement between experimental and simulated data was achieved. Results show that in the single p-i-n configuration the device acts mainly as an optical switch while in the double ones, due to the self bias effect, the input channels are selectively tuned by shifting between positive and negative bias. If the internal terminal is used the inter-wavelength cross talk is reduced and the S/N increased.

Long-wave sensitivity in the masked greenling ( Hexagrammos octogrammus), a shallow-water marine fish

Microspectrophotometry (MSP) revealed that surprisingly for a “fully marine” species, in summer, photoreceptors of the nearshore scorpaeniform fish known as the masked greenling, Hexagrammos octogrammus, contained exclusively, or presumably, porphyropsin with a small admixture of rhodopsin. As a result of this, the λ max of the spectral sensitivity of the photoreceptors were significantly shifted to longer wavelengths as compared to the λ max typical of marine shallow-water fishes, showing about 530 nm for rods and single cones, and 570/625 nm for double-cone members. These unique spectral shifts would permit a cone-driven wavelength discrimination in spite of high-density orange corneal filters which block light at lower wavelengths.

The molecular basis of color vision in colorful fish: four long wave-sensitive (LWS) opsins in guppies (Poecilia reticulata) are defined by amino acid substitutions at key functional sites.

BackgroundComparisons of functionally important changes at the molecular level in model systems have identified key adaptations driving isolation and speciation. In cichlids, for example, long wavelength-sensitive (LWS) opsins appear to play a role in mate choice and male color variation within and among species. To test the hypothesis that the evolution of elaborate coloration in male guppies (Poecilia reticulata) is also associated with opsin gene diversity, we sequenced long wavelength-sensitive (LWS) opsin genes in six species of the family Poeciliidae.ResultsSequences of four LWS opsin genes were amplified from the guppy genome and from mRNA isolated from adult guppy eyes. Variation in expression was quantified using qPCR. Three of the four genes encode opsins predicted to be most sensitive to different wavelengths of light because they vary at key amino acid positions. This family of LWS opsin genes was produced by a diversity of duplication events. One, an intronless gene, was produced prior to the divergence of families Fundulidae and Poeciliidae. Between-gene PCR and DNA sequencing show that two of the guppy LWS opsins are linked in an inverted orientation. This inverted tandem duplication event occurred near the base of the poeciliid tree in the common ancestor of Poecilia and Xiphophorus. The fourth sequence has been uncovered only in the genus Poecilia. In the guppies surveyed here, this sequence is a hybrid, with the 5' end most similar to one of the tandem duplicates and the 3' end identical to the other.ConclusionEnhanced wavelength discrimination, a possible consequence of opsin gene duplication and divergence, might have been an evolutionary prerequisite for color-based sexual selection and have led to the extraordinary coloration now observed in male guppies and in many other poeciliids.

Tetrachromacy in a butterfly that has eight varieties of spectral receptors

This paper presents the first evidence of tetrachromacy among invertebrates. The Japanese yellow swallowtail butterfly, Papilio xuthus, uses colour vision when foraging. The retina of Papilio is furnished with eight varieties of spectral receptors of six classes that are the ultraviolet (UV), violet, blue (narrow-band and wide-band), green (single-peaked and double-peaked), red and broad-band classes. We investigated whether all of the spectral receptors are involved in colour vision by measuring the wavelength discrimination ability of foraging Papilio. We trained Papilio to take nectar while seeing a certain monochromatic light. We then let the trained Papilio choose between two lights of different wavelengths and determined the minimum discriminable wavelength difference Deltalambda. The Deltalambda function of Papilio has three minima at approximately 430, 480 and 560nm, where the Deltalambda values approximately 1nm. This is the smallest value found for wavelength discrimination so far, including that of humans. The profile of the Deltalambda function of Papilio can be best reproduced by postulating that the UV, blue (narrow-band and wide-band), green (double-peaked) and red classes are involved in foraging. Papilio colour vision is therefore tetrachromatic.

Narrow bandwidth interference filter-stabilized diode laser systems for the manipulation of neutral atoms

We present and investigate different external cavity diode laser (ECDL) configurations for the manipulation of neutral atoms, wavelength-stabilized by a narrow-band high transmission interference filter. A novel diode laser, providing high output power of more than 1 W, with a linewidth of less than 85 kHz, based on a self-seeded tapered amplifier chip has been developed. Additionally, we compare the optical and spectral properties of two laser systems based on common laser diodes, differing in their coating, as well as one, based on a distributed-feedback (DFB) diode. The linear cavity setup in all these systems combines a robust and compact design with a high wavelength tunability and an improved stability of the optical feedback compared to diode laser setups using diffraction gratings for wavelength discrimination.

Detection of faint X-ray spectral features using wavelength, energy, and spatial discrimination techniques

We report here our methods and results of measurements of very low-signal X-ray spectra produced by highly charged ions in an electron beam ion trap (EBIT). A megapixel Si charge-coupled device (CCD) camera was used in a direct-detection, single-photon-counting mode to image spectra with a cylindrically bent Ge(2 2 0) crystal spectrometer. The resulting wavelength-dispersed spectra were then processed using several intrinsic features of CCD images and image-analysis techniques. We demonstrate the ability to clearly detect very faint spectral features that are on the order of the noise due to cosmic-ray background signatures in our images. These techniques remove extraneous signal due to muon tracks and other sources, and are coupled with the spectrometer wavelength dispersion and atomic-structure calculations of hydrogen-like Ti to identify the energy of a faint line that was not in evidence before applying the methods outlined here.

Photon detection with polarization discrimination

A simple and general method of using a photon detector to directly distinguish between two or three different polarizations is described. The method is suitable for a pre-selected limited wavelength region, for example as with encoded fibre optic communication. Alternatively, wavelength discrimination via wavelength selective polarization is possible.

The influence of darkness and visual contrast on oviposition by Anopheles gambiae in moist and dry substrates

The influence of substrate brightness (value), contrast and colour (hue) on oviposition is quantified under low night-light levels of 1.2 × 10−4 w m−2 in choice-tests using caged Anopheles gambiae sensu stricto laboratory strains and/or gravid An. gambiae sensu lato from a natural population in Western Kenya. Egg output increases as darkness of the substrate increases against a white background. Black substrates elicit the most oviposition by both laboratory and house-collected mosquitoes, whereas white elicits the least. Contrast between patches of substrate and background also influences egg placement. In four-choice tests, a black ovipositional dish against a white floor receives many more eggs than does black–black, white–white, and white–black dish vs. floor combinations. In a similar test presenting four grey vs. black combinations of dish vs. floor, females respond similarly to grey vs. black dishes and deposit nearly as many eggs on the dry floors as on wet dishes. Illumination at 2.1 × 10−3 w m−2, equivalent to late dusk and early dawn, improves discrimination between black dishes and grey floors. Under the experimental conditions, An. gambiae females respond almost equally to dishes of water placed over red, yellow, green, blue and purple paper disks matching the brightness and saturation values of their neutral (grey) counterparts. Thus, no evidence is found for wavelength discrimination on oviposition. It is concluded that visual contrast strongly influences the search patterns for prospective ovipositional sites whereas darkness of substrate and moisture are strong releasers of oviposition.

CMOS 32-APS linear array for high-sensitivity, low-resolution spectrophotometry

This paper presents a CMOS 32-APS (active pixel sensor) linear array for high-sensitivity, low-resolution micro spectrophotometer. The APS employs a buried double junction (BDJ) detector, which has an improved spectral response when compared to the use of a CMOS photodiode, and allows wavelength discrimination for instrumental auto-calibration. The sensitivity is enhanced by using large pixel and small extra integration capacitor, with implementation of high-gain charge amplifier to minimize effects of detector's junction capacitors. The APS features two channels: well channel and diffusion one. Each channel performs charge amplification and correlated double sampling (CDS) with buffered output. The well channel is read for photometric measurement, while both channels are exploited for wavelength detection. The in-pixel CDS circuits allow synchronous sampling of all APS, which improves readout rate. The fabricated linear array in a 0.8-μm CMOS process has been tested. The evaluated sensitivity of the APS is about 14 V/lx s @ 555 nm for the well channel. Under a 3.3 V supply, the dynamic range (DR) of the APS for a fixed integration time is about 50 dB for both channels. By varying integration duration, a DR over 130 dB for both channels can be reached. For photometric measurement, the minimum detectable signal using 125 s integration is about 1 μlx @ 555 nm.

Generalization and categorization of spectral colors in goldfish I. Experiments with one training wavelength

Goldfish have a tetrachromatic color vision with a high discrimination ability for spectral colors as well as for object colors. We investigate the question whether goldfish organize the high number of discriminable colors in terms of color categories, i.e. in a few larger groups of colors independent of wavelength discrimination. Twenty-four goldfish were trained with food reward, each fish on one out of 13 wavelengths between 371 nm and 630 nm. In transfer tests two different wavelengths were presented, one shorter and one longer than the training wavelength, and the choice behavior was determined. Choice frequencies of >or=50% were assumed to indicate similarity to the training color. The wavelength ranges >or=50% were about 100 nm and twice as large as the just noticeable differences measured in wavelength discrimination tests (Fig. 7). The ranges were surprisingly about the same for all training wavelengths, provided the data were plotted on a wavelength scale weighted according to discrimination ability (Fig. 4). Thus, with the training method chosen goldfish showed a kind of categorization which, however, depends on training wavelength and discrimination ability. Generalization tests in which training wavelength and test wavelengths were shown separately for 2 min each gave the same results as wavelength discrimination tests (Figs. 5 and 6) and are, therefore, not indicative for color categories.

Infrared Radiation Sensors of <I>Melanophila acuminata</I> (Coleoptera: Buprestidae): A Thermopneumatic Model

A description of the fine structure of the infrared radiation (IR) sensor of Melanophila acuminata (De Geer) and of the role of the wings during flight in mechanically modulating incoming IR into on and off pulses, supports a thermopneumatic model of IR perception by this insect. The model postulates that pulsed IR, corresponding to wavelengths emitted by fires, enters an enclosed, airtight, thick-walled cavity in each sensor through an apical epicuticular waveguide and is absorbed by a thin, chitinous endocuticular lamella of the cavity wall. The lamella is heated and in turn heats and expands the enclosed air that then compresses a basal cuticular cap that displaces the tubular body of the sensor, triggering a dendritic impulse and transducing an action potential in the neuron. This process is possible because of the absorption by the chitinous lamella of the wavelengths of IR emitted by fires resulting in extraordinary IR wavelength discrimination, radiant energy sensitivity, and rapid response time. These properties distinguish the sensor from temperature sensors of insects, sometimes erroneously designated as IR sensors, that respond relatively slowly to broadband wavelength radiation.

Asymmetric Response in a Line of Optically Driven Metallic Nanospheres

We describe the dipole-dipole interactions between a linear array of optically driven silver metallic nanospheres (MNSs). These model calculations incorporate the full electric field generated by an oscillating dipole and predict several interesting effects due to the retardation of the field. The distribution of the power associated with MNSs along the array shows a strong variation on a scale smaller than the wavelength of the driving light. For a given geometry, there is a small range of frequencies where the relative power in the last MNS compared to the first dramatically changes, suggesting a simple device for wavelength discrimination in this frequency range. Moreover, small changes in the driving frequency can completely change the direction of the scattered light when only a single nanosphere is driven.

Intensity-referenced and temperature-independent curvature-sensing concept based on chirped fiber Bragg gratings

An intensity-referenced temperature-independent curvature-measurement technique that uses a smart composite that comprises two chirped fiber Bragg gratings is demonstrated. The two gratings are embedded on opposite sides of the composite laminate and act simultaneously as curvature sensors and as wavelength discriminators, enabling a temperature-independent intensity-based scheme to measure radius of curvature. Also, the system's performance is independent of arbitrary power losses that are induced in the lead fibers to the sensing head. It is demonstrated that the measurement range depends on the relative positions of the chirped fiber Bragg gratings and on their spectral bandwidths. By using two chirped fiber Bragg gratings with bandwidths W1 = 2.8 nm and W2 = 3.7 nm and with central wavelengths at lambda 01 = 1560.3 nm and lambda 02 = 1563.7 nm, we obtained a resolution of 1.6 mm/square root of Hz for the measurement of the radius of curvature (approximately R = 350 mm) over the measurement range 190 mm < R < infinity.

Homogeneity and diversity of color-opponent horizontal cells in the turtle retina: Consequences for potential wavelength discrimination.

Color information processing in fish and turtles starts with the transformation of the tetra-chromatic cone system into two types of color-opponent horizontal cells (C-type). Few studies reported on large variability between C-type horizontal cells of the same class, suggesting it might improve color vision. However, such variability is contradictory with the tight coupling between horizontal cells that tends to average intercellular differences. We addressed this apparent discrepancy, and studied the spectral properties of C-type horizontal cells in the turtle retina. Photoresponses were recorded in the eyecup preparation, using light stimuli of different wavelengths and intensities. The spectral properties of each cell were defined by the neutral points (wavelengths at which response polarity reversed), which were derived from sensitivity data and from large-amplitude photoresponses. For each C-type horizontal cell, a linear relationship between log stimulus intensity needed for polarity reversal and wavelength was found. With this definition, homologous C-type horizontal cells from the same retina were practically identical in their spectral properties, indicating that the averaging effects of the horizontal cell syncytium eliminated any intercellular variability. In contrast, C-type horizontal cells of the same class exhibited large inter-retina variability. We tested the potential for wavelength discrimination by applying the line element theory to the action spectra of the two chromatic (Red/Green & Yellow/Blue) horizontal cell channels, and found good agreement with behavioral data from a similar species of turtles.

Multiphoton-excited luminescence of a lanthanide ion in a protein complex: Tb(3+) bound to transferrin.

The Tb(iii) complex of the iron-transport protein transferrin (Tb(2)-Tfr) exhibits strongly sensitised, sharp line luminescence from f-f states following multiphoton excitation via two tyrosinate residues directly co-ordinated to the lanthanide ion. Using an ultrafast Ti:sapphire laser system, a quadratic dependence of the Tb(iii) luminescence intensity was observed on excitation with photons at 503 and 566 nm, and a cubic dependence with photons at 800 nm. The two-photon cross-sections at 503 and 566 nm are 7.4 x 10(-50) and 0.37 x 10(-50) cm(4) s photon(-1) mol(-1), respectively, which compare favourably with values reported for the green fluorescent protein. Three-photon excitation at 800 nm gives rise to a Tb(iii) emission spectrum with excellent signal to noise ratios. These results lead to a proposal that if a Tb(iii)-protein complex with similar luminescent properties could be formed in vivo, an intra-cellular imaging system that uses multiphoton-excited, long-lived lanthanide ion luminescence could be developed. This offers the prospect of multiphoton imaging in tight focal planes using sharp line emission with long lifetimes for wavelength and time discrimination against background fluorescence.

Bioluminescent bioreporter integrated circuits: potentially small, rugged and inexpensive whole-cell biosensors for remote environmental monitoring.

1. SUMMARYA bioluminescent bioreporter integrated circuit (BBIC) is anovel whole-cell biosensor that combines the environmentalmonitoring capabilities of genetically engineered biolu-minescent micro-organisms (bioreporters) with optical appli-cation-specific integrated circuits. A BBIC device consistsof bioreporters sustained within a micro-environment, theintegrated circuit microluminometer, and a light-tightenclosure. The bioreporter typically contains the luxCDABEreporter genes encoding the enzymes required for biolumin-escence. In the presence of a targeted analyte, a gene(transcriptional) regulatory system induces the expressionof the luxCDABE genes. Analytical benchmark data forexposure of the bioreporter Pseudomonas fluorescens 5RLto salicylate was determined using a flow-through testsystem. The detection limit (after a 45 min exposure) wasca 50 lgl

A simple fiber‐Bragg‐grating sensor system based on a linear‐cavity fiber laser

AbstractA simple fiber‐Bragg‐grating (FBG) sensor system based on a linear‐cavity fiber laser is proposed and experimentally demonstrated. The lasing wavelength shift resulting from the temperature variation on this sensing element is discriminated by two FBGs. These two FBGs, acting as wavelength discriminators, are used to increase the real‐time measurement range for monitoring the temperature variation. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 15–17, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10810

α/β radiation detector using wavelength and delayed fluorescence discrimination

This paper describes a novel two-layer radiation detector for α/β simultaneous counting for dust radiation monitoring in nuclear power plants. For α/β discrimination, wavelength and delayed fluorescence discrimination techniques were newly developed. To establish the wavelength discrimination, we adopted a two-layer scintillator consisting of the plastic scintillator (NE-111A) and Y 2O 2S(Eu) whose emission spectra are quite different. To reject the mixed β signal in the α detection layer, we used the delayed fluorescence characteristics of Y 2O 2S(Eu) in the signal processing. We manufactured the detector and tested its feasibility and the detection performance for dust radiation monitoring. Finally, we concluded that the performance of this new α/β detector using the new discrimination methods is suitable for dust radiation monitoring.

Influence of material properties on the performance of diamond photocathodes

Variations in photoyield at 186 and 252 nm have been measured from CVD diamond photocathode materials grown on silicon substrates, as the growth conditions and surface termination were changed. The photoyield increased rapidly for short growth times when the surface comprised a mixture of diamond and non-diamond phases in intimate contact, but this increase occurred at both wavelengths, so poor spectral selectivity resulted. Further growth caused the photoyield to decay as the diamond content of the film improved, before rising again at longer growth times, whence improved wavelength discrimination was also observed. Caesiation enhanced the photoyield observed compared to hydrogenated interfaces.

Instrumentation for fast functional optical tomography

In this article, we describe the design rationale and performance features of an integrated multichannel continuous wave (cw) near-infrared (NIR) optical tomographic imager capable of collecting fast tomographic measurements over a large dynamic range. Fast data collection (∼70 Hz/channel/wavelength) is achieved using time multiplexed source illumination (up to 25 illumination sites) combined with frequency encoded wavelength discrimination (up to four-wavelength capability) and parallel detection (32 detectors). The described system features a computerized user interface that allows for automated system operation and is compatible with various previously described measuring heads. The results presented show that the system exhibits a linear response over the full dynamic measuring range (180 dB), and has excellent noise (∼10 pW noise equivalent power) and stability performance (&amp;lt;1% over 30 min). Recovered images of laboratory vessels show that dynamic behavior can be accurately defined and spatially localized.