Coarse Gratings Research Articles

Sensing the structural characteristics of surfaces: texture encoding by a bottom-dwelling fish.

The texture of contacted surfaces influences our perception of the physical environment and modulates behavior. Texture perception and its neural encoding mechanisms have traditionally been studied in the primate hand, yet animals of all types live in richly textured environments and regularly interact with textured surfaces. Here we explore texture sensation in a different type of vertebrate limb by investigating touch and potential texture encoding mechanisms in the pectoral fins of fishes, the forelimb homologs. We investigated the pectoral fins of the round goby (Neogobius melanostomus), a bottom-dwelling species that lives on substrate types of varying roughness and whose fins frequently contact the bottom. Analysis shows that the receptive field sizes of fin ray afferents are small and afferents exhibit response properties to tactile motion that are consistent with those of primates and other animals studied previously. In response to a periodic stimulus (coarse gratings), afferents phase lock to the stimulus temporal frequency and thus can provide information about surface texture. These data demonstrate that fish can have the capability to sense the tactile features of their near range physical environment with fins.

Understanding diffraction grating behavior: including conical diffraction and Rayleigh anomalies from transmission gratings

With the wide-spread availability of rigorous electromagnetic (vector) analysis codes for describing the diffraction of electromagnetic waves by specific periodic grating structures, the insight and understanding of nonparaxial parametric diffraction grating behavior afforded by approximate methods (i.e., scalar diffraction theory) is being ignored in the education of most optical engineers today. Elementary diffraction grating behavior is reviewed, the importance of maintaining consistency in the sign convention for the planar diffraction grating equation is emphasized, and the advantages of discussing “conical” diffraction grating behavior in terms of the direction cosines of the incident and diffracted angles are demonstrated. Paraxial grating behavior for coarse gratings (<italic>d</italic> ≫ λ) is then derived and displayed graphically for five elementary grating types: sinusoidal amplitude gratings, square-wave amplitude gratings, sinusoidal phase gratings, square-wave phase gratings, and classical blazed gratings. Paraxial diffraction efficiencies are calculated, tabulated, and compared for these five elementary grating types. Since much of the grating community erroneously believes that scalar diffraction theory is only valid in the paraxial regime, the recently developed linear systems formulation of nonparaxial scalar diffraction theory is briefly reviewed, then used to predict the nonparaxial behavior (for transverse electric polarization) of both the sinusoidal and the square-wave amplitude gratings when the +1 diffracted order is maintained in the Littrow condition. This nonparaxial behavior includes the well-known Rayleigh (Wood’s) anomaly effects that are usually thought to only be predicted by rigorous (vector) electromagnetic theory.

Form vision from melanopsin in humans

Detection and discrimination of spatial patterns is thought to originate with photoreception by rods and cones. Here, we investigated whether the inner-retinal photoreceptor melanopsin could represent a third origin for form vision. We developed a 4-primary visual display capable of presenting patterns differing in contrast for melanopsin vs cones, and generated spectrally distinct stimuli that were indistinguishable for cones (metamers) but presented contrast for melanopsin. Healthy observers could detect sinusoidal gratings formed by these metamers when presented in the peripheral retina at low spatial (≤0.8 cpd) and temporal (≤0.45 Hz) frequencies, and Michelson contrasts ≥14% for melanopsin. Metameric gratings became invisible at lower light levels (<1013 melanopsin photons cm−2 sr−1 s−1) when rods are more active. The addition of metameric increases in melanopsin contrast altered appearance of greyscale representations of coarse gratings and a range of everyday images. These data identify melanopsin as a new potential origin for aspects of spatial vision in humans.

Discrete dipole approximation simulation of bead enhanced diffraction grating biosensor

We present the discrete dipole approximation simulation of light scattering from bead enhanced diffraction biosensor and report the effect of bead material, number of beads forming the grating and spatial randomness on the diffraction intensities of 1st and 0th orders. The dipole models of gratings are formed by volume slicing and image processing while the spatial locations of the beads on the substrate surface are randomly computed using discrete probability distribution. The effect of beads reduction on far-field scattering of 632.8nm incident field, from fully occupied gratings to very coarse gratings, is studied for various bead materials. Our findings give insight into many difficult or experimentally impossible aspects of this genre of biosensors and establish that bead enhanced grating may be used for rapid and precise detection of small amounts of biomolecules. The results of simulations also show excellent qualitative similarities with experimental observations.

Improved measurement characteristics in collimation testing using Lau interferometry and Fourier fringe analysis technique

We demonstrate an automated procedure for the detection of collimation position of an incoherent beam in Lau interferometry using Fourier fringe analysis technique. The experimental arrangement consists of a Lau based interferometer in which light from a source grating illuminates a set of two coarse gratings separated by self imaging distance. Direct phase measurement using Fourier Transform Method (FTM) has been used to obtain the slope map of the wavefront and hence the detection of collimation position is undertaken advantageously. The experimental arrangement is simple and interferometric noise is lower. Detailed uncertainty analysis has also been reported. The technique is fully automatic and provides good accuracy and high precision.

Real-time slope mapping and defect detection in bent plates using Talbot interferometry

We demonstrate a simple method for obtaining slope contours of bent plates using Talbot interferometry. The technique has been used to map slope contours of polymethyl methacrylate specimens of different shapes. The Talbot image of a coarse grating is projected onto a specimen such that the self-image is backreflected onto the same grating again. As a Talbot interferometer is basically a grating shearing interferometer, it results in the generation of characteristic slope maps of the specimen under test. Results of the investigation match well with other slope-mapping techniques. Validation of experimental results with theoretical predictions in the case of a cantilever beam specimen has been undertaken. Accuracy of about 4.7% with respect to theoretical predictions is obtained.

Automated collimation testing in Lau interferometry using phase shifting technique

We demonstrate an automated procedure for detection of collimation position of an incoherent beam in Lau interferometry using phase shifting technique. The experimental arrangement consists of a Lau-based interferometer in which light from a source grating illuminates a set of two coarse gratings separated by self-imaging distance. Phase shifting procedure is incorporated by translating the detector grating, corresponding to different positions of the collimating lens. The phase map is plotted corresponding to each position. The slope of the phase map is indicative of the collimation position of the optical beam. The technique is fully automatic and provides good accuracy and high precision.

AQUEOUS EXTRACTION OF SOLUTES FROM FENNEL (FOENICULUM VULGARE) ASSISTED BY PULSED ELECTRIC FIELD

ABSTRACT Aqueous nonthermal extraction was performed from thin and coarse fennel gratings of seven different sizes in order to obtain extracts, which could be used as natural food preservatives (antioxidants). A moderate pulsed electric field (PEF) with different intensities, E = 0–600 V/cm, and number of pulses, n = 0–850, was used to electropermeabilize the cell membranes and to accelerate the following extraction. The optimal parameters of PEF were found for each size of grating to maximize the yield of solutes. Extract turbidity and color were evaluated. Additionally, the thermal extraction from coarse gratings was studied at different temperatures (60–90C). The concentration of vitamins C and E in extracts, obtained with thermal and PEF treatments, was estimated. The PEF treatment was more effective for coarse gratings (the juice yield increased from 60 to 98%, and the obtained extracts were less turbid and less colored) than for thin gratings. Furthermore, extracts obtained from coarse gratings treated by PEF contained more vitamins C and E than extracts obtained by thermal extraction. PRACTICAL APPLICATIONResearches presented in this article should find their entire practical application in the field of food industries. They will permit preparation of fennel extracts, used as food preservatives (antioxidants), by PEF‐assisted aqueous extraction, which preserves better antioxidant substances. Extracts should be of good quality and the energy consumption should be reasonable.

Blindsight

Blindsight

Multi-PON access network using a coarse AWG for smooth migration from TDM to WDM PON

An interoperable access network architecture based on a coarse array waveguide grating (AWG) is described, displaying dynamic wavelength assignment to manage the network load across multiple PONs. The multi-PON architecture utilizes coarse Gaussian channels of an AWG to facilitate scalability and smooth migration path between TDM and WDM PONs. Network simulations of a cross-operational protocol platform confirmed successful routing of individual PON clusters through 7 nm-wide passband windows of the AWG. Furthermore, polarization-dependent wavelength shift and phase errors of the device proved not to impose restrain on the routing performance. Optical transmission tests at 2.5 Gbit/s for distances up to 20 km are demonstrated.

Defect suppression in liquid crystal filled polymer devices

Liquid crystal filled polymer structure (LiCFiPS) devices consist of a polymer structure, which performs the desired spatial phase modulation of the incident light, the spaces within which are filled with liquid crystal to permit modulation of this optical function. Potentially, fabrication of this type of device may be carried out at very low cost using established polymer hot rolling or embossing techniques. In previous work on coarse gratings liquid crystal defects have been observed when the alignment direction of the liquid crystal is perpendicular to the grating ruling direction. These give rise to spurious diffraction peaks. The models of this type of device suggest that these defects might be suppressed if the dimensions of the liquid crystal region are small. Measured diffraction patterns show that for devices with smaller liquid crystal region dimensions, diffraction free of spuriae is in fact observed. Being fixed function, such devices might not offer the ultimate versatility of matrix addressed SLM devices; they do however offer electronic control of diffractive optical devices at very low cost.

A History of Thermo Jarrell Ash Corporation and Spectroscopist Richard F. Jarrell

This paper chronicles the career of Richard F. Jarrell and the developments in atomic emission spectrochemical analysis during the period following that covered by Jarrell in his presentation at this symposium.In the 1950s dedicated computers calculated concentrations, reduced analytical times by a single operator for a standard analytical program to 10-20 min. In the 1960s computers made it possible to time analysis in microseconds, after spark backgrounds had largely disappeared, to improve detection limits by 10% or more. The 1980s and 1990s introduced the use of array detectors and coarse gratings with crossed prisms and computer readouts to measure desired "pixels" and returned spectrochemical analysis to the versatility of spectrographs, with the speed and accuracy of analysis of direct readers.

Vernier and grating acuity in adult hooded rats: The influence of sex.

Although morphological sex differences are pervasive in the primary visual cortex of hooded rats, it is not known whether sex differences occur in vision in these rats. In this study, grating acuity was measured in a forced-choice Y maze and a jumping stand in adult hooded rats, and vernier acuity thresholds were established in the jumping stand. With a criterion of 34 correct/50 trials, the number of correct choices for both sexes was high (1.0-1.6 cycles per degree [c/deg]) for spatial gratings. Female rats made more correct identifications of the coarse gratings (0.125 and 0.25 c/deg) than male rats, but no sex differences were found for higher spatial frequencies. In contrast, male rats were better at detecting smaller vernier offsets in both the individual criterion and group averages than female rats, and all of the rats detected vernier misalignments at 34.1 min (equivalent to 1.75 c/deg), which is above their grating acuity. Vernier acuity may mirror some sex differences in visual cortex anatomy.

Does local or global orientation determine the McCollough effect?

In this research, the McCollough effect was observed by using an ambiguous test pattern of coarse gratings made out of fine gratings. Coarse gratings meet at right angles to fine gratings. The global features (coarse gratings) in the test pattern became more salient if the test pattern was blurred, and the frequency of the McCollough effect, corresponding to the global orientation of the test pattern, increased with the increase of the extent of blur. The McCollough effects corresponding to the local orientation of the test pattern occurred frequently if the subjects adapted to fine gratings before viewing the test pattern, whereas the McCollough effects corresponding to the global orientation of the test pattern occurred frequently if the subjects adapted to coarse gratings. Our results indicate that the perceptual organization is an important determinant in the McCollough effect.

Vernier and grating acuity in adult hooded rats: the influence of sex.

Although morphological sex differences are pervasive in the primary visual cortex of hooded rats, it is not known whether sex differences occur in vision in these rats. In this study, grating acuity was measured in a forced-choice Y maze and a jumping stand in adult hooded rats, and vernier acuity thresholds were established in the jumping stand. With a criterion of 34 correct/50 trials, the number of correct choices for both sexes was high (1.0-1.6 cycles per degree [c/deg]) for spatial gratings. Female rats made more correct identifications of the coarse gratings (0.125 and 0.25 c/deg) than male rats, but no sex differences were found for higher spatial frequencies. In contrast, male rats were better at detecting smaller vernier offsets in both the individual criterion and group averages than female rats, and all of the rats detected vernier misalignments at 34.1 min (equivalent to 1.75 c/deg), which is above their grating acuity. Vernier acuity may mirror some sex differences in visual cortex anatomy.

The role of striate cortex in visual function of the cat

We examined the contribution of area 17 to visual function in two cats whose fixation was monitored by means of scleral search coils. Ibotenic acid lesions were made within the physiologically identified representation of the lower left visual field of area 17. In a detection task in which the cats simply indicated the presence or absence of a vertical grating, contrast sensitivity loss was greatest at middle spatial frequencies with no loss in spatial resolution. However, when cats were required to discriminate between vertical and horizontal gratings, sensitivity loss was profound at both middle and high spatial frequencies with an octave loss of spatial resolution. This greater loss was not due to disrupted orientation discrimination since sensitivity to the orientation of coarse gratings was unaffected in the lesioned hemifield. We also found deficits in the ability to discriminate the direction of grating motion, but only at higher spatial and lower temporal frequencies. The role of area 17 in perceiving the global motion of complex patterns was also studied with high contrast, dynamic random dots drifting at high speeds. Paradoxically, area 17 lesion improved the perception of global motion. This improvement was eliminated by spatially filtering the dot patterns to remove high spatial frequencies, suggesting that the lesion has enhanced performance by interfering with masking by high spatial frequencies. Our results demonstrate that the performance of traditional detection tasks may be insensitive to the effects of area 17 lesions. Discrimination tasks, on the other hand, revealed that area 17 neurons play a major role in the perception of higher spatial frequency stimuli as long as they move or flicker at low rates, but contribute little to these functions when the stimuli are coarse and move at high speeds.

Multilayer-coated echelle gratings for soft x rays and extreme ultraviolet

Mechanically ruled or ion-etched blazed diffraction gratings can be coated with multilayer reflectors to increase their on-blaze efficiency in the soft x-ray and extreme ultraviolet (EUV) spectral regions. The quality of the groove facets produced by these conventional manufacturing techniques precludes their use in high spectral orders to achieve high resolving power, i.e., as echelles. However, coarse gratings fabricated in crystalline silicon by orientation-dependent etching have excellent groove profile and extremely smooth facets, which make them ideal for coating with multilayers for use as echelles at short wavelengths. Such a grating was coated with tungsten-carbon multilayers for use at soft x-ray wavelengths near the carbon K edge. It was evaluated using both a reflectometer based on a laser-produced plasma source and with synchrotron radiation. In the 50–220 Å wavelength region, diffraction orders up to the 61st were observed, allowing the grating performance to be compared with theoretical predictions. Such multilayer-coated echelles offer the possibility of extremely high spectral resolving power in the EUV and soft x-ray region.

Responses of the starburst amacrine cells to moving stimuli.

1. Rabbit retinas were isolated from the eye and incubated in the presence of 3H-choline. Samples of retina taken from a defined midperipheral eccentricity were spread over the domed end of a fiberoptic bundle that formed the floor of a superfusion chamber. The rate of release of labeled acetylcholine by the starburst amacrine cells was studied. 2. When the retina was stimulated by moving gratings, the cells vigorously increased their secretion of acetylcholine. Responses were observed when the bars were as small as 60 microns in width. Systematically varying the spatial and temporal frequency of stimulation revealed that temporal frequency was the dominant variable: the cells responded best to stimuli of 1-4 Hz, whether those stimuli were flashing lights, fine gratings moving slowly, or coarse gratings moving rapidly. 3. With temporal frequency constant, the cells' responses decreased as the spatial frequency of the grating increased. The decreased response to fine gratings is most likely due, at least in part, to lateral interactions that become stronger as the light and dark bars become more closely spaced. These could occur in either the outer or inner retina. 4. The velocity tuning curve for the starburst cells' release of acetylcholine matched fairly well the velocity tuning of ON-OFF directionally selective cells in the rabbit. It did not correspond at all well with the tuning curve for the ON directionally selective cells. If the ON cells receive input from the starburst cells, that input appears to be quite indirect.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of grating spacing on the Ronchi test

For the Ronchi test, the phase of the Ronchigram can be retrieved very accurately with the aid of a phase-reduction algorithm originally designed for phase-shift interferometry. The simplest algorithm to reproduce the test wave front is the integration of the Ronchigram phase. However, the accuracy of integration depends heavily on the grating spacing. The effects of grating spacing is discussed using actual test results and mathematical simulation. The results indicate that coarse gratings, which benefited from the accuracy of phase-reduction techniques and qualified for integration in retrieving wave fronts, may be the better choice for the Ronchi test.

Multichord spectroscopy of the DIII-D divertor region

A multichannel spectrometer with high spectral resolution (0.01 nm) and high temporal resolution (0.5 ms) has been configured to collect data simultaneously from eight viewchords spanning the divertor region of DIII-D. Fiber optically coupled to a wide-field lens with a vertical view of the vessel floor, the instrument will be capable of differentiating the behavior of impurity line emission at the inner and outer divertor strike points, on and off the Advanced Divertor Program ring, on the face of the Divertor Material Exposure System probe, and in the region of the lower centerpost. Used with a coarse grating (300 grooves/mm), spectral coverage of each spatial channel is 15 nm with 0.3 nm resolution; used in high order with a 1200 groove/mm grating, the instrument is capable of resolving Doppler profiles. Spatial variation of gas recycling and impurity influx will be studied for both single- and double-null divertor configurations in low and high density operating regimes.