Narrow Light Beam Research Articles

Study of the spreading of a finite beam transmitted through a scattering layer

The propagation of a narrow beam of light in a scattering medium is one of the central problems in the optics of scattering media. It is clear that not enough experimental data have been published [1-9] in order to check the results of well-known theories (see, for example, [10-16] as well as the review in Chapter 3 of [6]) and to obtain convenient and reliable empirical approximations, describing the behavior of the propagation of a narrow beam in a scattering medium for practical use. In this work, we present the results of an experimental study of the spreading of a finite beam in a plane which is the bounding surface of a plane-parallel scattering layer and which is perpendicular to the axis of the incident beam. The features of the experiment are as follows: The energy characteristics of the radiation transmitted through the layer and not inside the layer are studied; media in which the photon survival probability A is close to i (I -A < 2.10-~), with extremely strong elongation of the scattering function of an elementary volume (the asymmetry coefficient is not less than 250), are studied; the scattering layers have a comparatively high optical thickness ~ (14 ~ ~ 580) and are illuminated by a beam with a variable optical diameter 2~r (r is the geometrical radius of the illuminating beam; e is the attenuation coefficient of the medium), whose values vary in the range 3-1100 (the indicated values of the optical thickness of the layers indicate that, for all practical purposes, direct transmission in them did not occur); the scattering layers have boundaries which reflect and refract the light beams in accordance with Snell's law and Fresnel's formulas. The indicated characteristics are determined by the properties of the material used to fabricate the objects used for the experimental study: plane-parallel polished samples of light-scattering glasses [17, 18], primarily MS23 glass. The measured quantity was the luminosity of the scattered radiation passing through the sample and propagating along the axis of the illuminating beam, i.e., along the normal to the surface of the layer. At the same time, photometric measurements were performed on the flux from a limited section of the surface of the sample, which had the form of the circle with radius R centered on the axis of the illuminating beam (see Fig. I). Successive measurements were performed for a series of values of Ri. The difference J(Ri+~) -J(Ri) gives the magnitude of the luminosity of the light scattered by an annular zone bounded by the radii Ri+, and Ri. In addition, dividing this difference by the area of the ring we obtain the average brightness L of the radiation emerging at a distance (Ri+~ + Ri)/2 from the axis of the illuminating beam. To perform the measurements, we used the setup described in [19], where a luminosity measuring head (the optical setup that realizes the conditions for measuring the luminosity according to the body-centered method) was placed in front of the photometer. The measurements were performed at ~ = 546 nm and aperture angles of the illuminating beam and the observed beam equal to 4 and i ~ respectively. In addition, pointwise probing of the surface of the samples with the help of the luminosity measuring head was also

Ultrasonic Light Diffraction Using a Narrow Light Beam –Transition from Diffraction to Deflection–

Theoretical results of ultrasonic light diffraction using a narrow light beam whose intensity profile is Gaussian or square are described. As the beam width becomes narrower, instantaneous diffraction patterns for square beams show a complicated transition procss from diffraction to deflection, as compared with a smooth transition for Gaussian beams. Using a very narrow light beam, the angle of beam deflection cannot be determined from the time-averaged diffraction pattern, but can be determined from the instantaneous diffraction pattern.

Blue- and red-light action in photoorientation of chloroplasts in Adiantum protonemata

An action spectrum for the low-fluencerate response of chloroplast movement in protonemata of the fern Adiantum capillus-veneris L. was determined using polarized light vibrating perpendicularly to the protonema axis. The spectrum had several peaks in the blue region around 450 nm and one in the red region at 680 nm, the blue peaks being higher than the red one. The red-light action was suppressed by nonpolarized far-red light given simultaneously or alternately, whereas the bluelight action was not. Chloroplast movement was also induced by a local irradiation with a narrow beam of monochromatic light. A beam of blue light at low energy fluence rates (7.3·10(-3)-1.0 W m(-2)) caused movement of the chloroplasts to the beam area (positive response), while one at high fluence rates (10 W m(-2) and higher) caused movement to outside of the beam area (negative response). A red beam caused a positive response at fluence rates up to 100 W m(-2), but a negative response at very high fluence rates (230 and 470 W m(-2)). When a far-red beam was combined with total background irradiation with red light at fluence rates causing a low-fluence-rate response in whole cells, chloroplasts moved out of the beam area. When blue light was used as background irradiation, however, a narrow far-red beam had no effect on chloroplast distribution. These results indicate that the light-oriented movement of Adiantum chloroplasts is caused by red and blue light, mediated by phytochrome and another, unidentified photoreceptor(s), respectively. This movement depends on a local gradient of the far-red-absorbing form of phytochrome or of a photoexcited blue-light photoreceptor, and it includes positive and negative responses for both red and blue light.

Horizontal, vertical and oblique eye movements in infants to single- and double-step target displacements

AOptix Technologies, a laser communication systems provider, has closed an $18m Series B round of financing, co_led by Lehman Brothers and 3i. The round also included participation from existing investors Kleiner Perkins Caufield & Byers and Clearstone Venture Partners. As part of the financing, Brian Paul of Lehman Brothers and David Aslin of 3i have joined AOptix’s Board of Directors. AOptix’s Lasercom systems are built upon an entirely new and radically different core technology called Adaptive Optics (AO). By combining wavefront sensors, deformable mirrors, extremely narrow light beams and precision beam tracking, AO dynamically corrects signal distortions caused by turbulent air and office windows. In addition, AO makes it possible to create an all_optical Lasercom system without traditional optical_to_electrical conversions.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.

Does light enhance calcification in hermatypic corals?

Calcification rates in different fragments along branches of the hermatypic coral Stylophora pistillata were tested in the laboratory using a new technique, the “optic glassfiber” method. By this method, the tested colony remains constantly in dark conditions while a narrow beam of light, transferred through the optic fiber, illuminates a small distinct point of coral tissue (on a branch tip or base). The selected illuminated portion of the branch serves as the experimental fragment, while all the other parts of the same colony serve as the dark controls. The results indicate that significantly more calcium is incorporated in the tip fragments than in the bases, both in light and in dark conditions (4.1 to 13.2 times more). Illumination of the tips or the bases did not stimulate or enhance the calcification rates of these fragments. Thus, in all colonies tested, the calcification rates of the illuminated fragments were not significantly different from the average rates of other similar, non-illuminated fragments of the same colony. It is suggested that light does not directly enhance calcification in hermatypic corals, but rather, that light enhances O2 production, which consequently stimulates coral metabolism. Our preliminary results indicate that calcification rates recorded in aerated dark experiments are significantly higher than calcification rates of non-aerated dark controls.

Distribution of the irradiance from a narrow light beam in a turbid atmosphere

Distribution of the irradiance from a narrow light beam in a turbid atmosphere

A Whole-Field Interferometric Scheme for Measuring strain and Flow Rates of Glacier and Other Natural Surfaces

AbstractThe flow of glacier ice is mapped using high-resolution photography and non-coherent-light speckle interferometry. Young’s fringe patterns result when a double-exposed photoplate image of the straining surface is illuminated by a narrow beam of coherent light. Geometry gives a relationship between the ice surface displacement vector and the interference fringe patterns. This displacement vector is corrected for rigid-body (camera) movement and projected onto the ice surface using topological maps. The strain during the time-lapse interval is thus known. Comparison with data acquired by surveying techniques at Nisqually Glacier, Washington, U.S.A., is limited because of small overlap of the surface studied. In the areas for which results can be compared, our experiments yield a flow of 0.6 m/d where conventional methods yield about 0.4 m/d.

A Whole-Field Interferometric Scheme for Measuring strain and Flow Rates of Glacier and Other Natural Surfaces

AbstractThe flow of glacier ice is mapped using high-resolution photography and non-coherent-light speckle interferometry. Young’s fringe patterns result when a double-exposed photoplate image of the straining surface is illuminated by a narrow beam of coherent light. Geometry gives a relationship between the ice surface displacement vector and the interference fringe patterns. This displacement vector is corrected for rigid-body (camera) movement and projected onto the ice surface using topological maps. The strain during the time-lapse interval is thus known. Comparison with data acquired by surveying techniques at Nisqually Glacier, Washington, U.S.A., is limited because of small overlap of the surface studied. In the areas for which results can be compared, our experiments yield a flow of 0.6 m/d where conventional methods yield about 0.4 m/d.

Propagation of narrow light beams in rain

Propagation of narrow light beams in rain

Propagation of a narrow modulated light beam in a scattering medium with fluctuations of the photon pathlengths in multiple scattering

Propagation of a narrow modulated light beam in a scattering medium with fluctuations of the photon pathlengths in multiple scattering

Intercellular power transmission along trichomes of cyanobacteria

An attempt at demonstrating lateral power transmission over millimeter distances along a coupling membrane has been undertaken. Trichomes of the multicellular filamentous cyanobacteria Phormidium uncinatum were illuminated with a very narrow light beam forming a light spot that covered only 4–5% of a 1–2 mm long cyanobacterial trichome. Such illumination was found to support motility (gliding along agar surface) of the trichome under conditions when the light was the only energy source. It was also shown that illumination with the light spot caused rotation of rings of slime (accompanying the operation of the ‘motors’ responsible for the motility of cyanobacteria) not only in the illuminated, but also in the distal, nonilluminated part of the trichome. Electric potential transmission along trichomes was revealed by means of the extracellular electrode technique. The light spot was found to induce generation of an electric potential difference between two electrodes in the dark region of the trichomes, which were placed at different distances from the illuminated end. Cutting the trichomes between the light spot and the closest ‘dark’ electrode abolished this effect. Valinomycin + K + and carbonyl cyanide p-trifluoromethoxyphenylhydrazone affected the potential difference formation between two ‘dark’ electrodes much stronger than that between a light and a dark electrode. All the light spot-induced effects develop in the seconds time scale. Both the amplitudes and the kinetics of the potential difference measured with four electrodes placed along the trichome prove to be in good agreement with the theoretical curves computed on the basis of the electric cable equation. It is concluded that transcellular power transmission in the form of Δψ takes place along trichomes of cyanobacteria. This confirms the hypothesis about the biological function of Δψ as a transportable form of energy.

Analytical aspects of absorption spectroelectrochemistry at a platinum electrode—II Quantitative basis and study of organic compounds

The theoretical basis for a new spectroelectrochemical technique, in which a narrow light-beam is passed at grazing incidence over a plane electrode surface, has been derived. Agreement between theoretical and experimental behaviour has been obtained for a number of organic molecules with well-defined redox behaviour. The advantages of this technique over other spectroelectrochemical techniques are discussed with respect to potential applications in quantitative analysis and electrochemical studies.

Wide-Field High-Intensity Lantern: An Affordable Night Mobility Aid

Individuals with disorders such as retinitis pigmentosa or severe glaucoma often have difficulty ambulating at night, not only because they have lost rod vision, but because flashlights do not help. The problem is that ordinary flashlights produce a very narrow beam of light (only about 3°) which is hard to follow with tunnel vision. To eliminate this problem, we have designed a relatively inexpensive lantern which produces a bright wide beam of light. It can greatly enhance the night mobility of patients with severe field constriction or night blindness.

Theory of the propagation of a narrow light beam in a stratified scattering medium

Theory of the propagation of a narrow light beam in a stratified scattering medium

Interpretation of light diffraction by cross‐striated muscle as Bragg reflexion of light by the lattice of contractile proteins.

1. The diffraction spectrum obtained by illuminating a cross-striated muscle fibre with a narrow beam of monochromatic light generally shows asymmetry of light intensity between left and right spectral lines. 2. The asymmetry of light intensity in left and right spectral lines is reversed when the fibre is rotated by 180 degrees. This indicates that intensities of the spectral lines are determined more by Bragg reflexion than by simple diffraction as in a plane grating. Populations of myofibrils with differing tilt of lattice planes must exist in each illuminated fibre segment to account for simultaneous Bragg reflexion to the left- and right-hand sides. 3. The light intensity of spectral lines shows a complicated dependence on the angle at which the incident beam is directed against the fibre. This 'intensity distribution' seems to reflect the specific myofibrillar arrangement at the site of illumination. 4. The intensity distributions of the left and right first order lines show close correlation if the deflexion of the incident beam differs by twice the Bragg angle. 5. The deflexion angle of the incident beam at which maximum intensity in spectral lines is obtained depends on sarcomere length as predicted by Bragg's formula. 6. Intensities of the first and second order lines are little correlated when recorded at the same beam deflexion, but are well correlated when recorded at beam deflexions calculated from Bragg's formula. 7. When a diffraction line is scanned perpendicularly to the meridional plane, the light intensity shows fluctuations resembling those obtained by beam deflexion within the meridional plane.

Absorption measurements by laser calorimetry

A solution to the heat equation is given which describes a cylindrical body uniformly heated along its axis. The application considered is the determination of bulk and surface absorption coefficients of the sample material from temperature-vs-time measurements when the heat source is a weakly absorbed narrow light beam. Under certain conditions, the full solution can be greatly simplified and the inference of absorption coefficients thus facilitated; these conditions are discussed and specified quantitatively. Equivalent results for rectangular samples are also given. The utility of the analysis is illustrated by several experimental examples.

Apical growth of protonemata inAdiantum capillus-veneris

Action spectra for the induction of apical swelling in red-light-grown single-celled protonemata of the fernAdiantum were determined by continuous irradiation with monochromatic light for 5 hr. The resultant action spectra showed a sharp peak at 480 nm with a broad plateau in the region of blue and near ultraviolet light. Wave-lengths longer than 520 nm had no effect.When the tips of filamentous protonemata were irriadiated with a narrow beam (20 μm in width) of blue light for 3 hr, apical swelling and apical growth inhibition obviously took place in all protonemata tested, while no significant effect was observed when any other regions than the tip were irradiated. Polarized blue light vibrating parallel with the developmental axis of protonemata induced apical swelling and also prevented apical growth as effectively as non-polarized light, but that vibrating in a normal direction was significantly less effective.

Effects of narrow-beam irradiations with blue and far-red light on the timing of cell division in Adiantum gametophytes

Protonemata of the fern Adiantum capillusveneris L., grown as single-cell filaments under continuous red light, were irradiated with a narrow beam of blue light. Only irradiation of the region containing the nucleus induced cell division. Beams of 30 μm in width, which corresponds to the diameter of the nucleus, or wider, were equally effective; beams 10 μm wide or less were less effective. The results indicate that the nuclear region is the site of the blue- and near ultraviolet-light-absorbing pigment (PB-NUV) which mediates the timing effect of cell division. In contrast, the effect of a narrow beam of far-red (FR) light, which delays the onset of the blue-light-induced cell division, was found to be present along the entire length of the protonema cell, including the largely vacuolated basal region of the latter. Polarized FR light having the electrical vector parallel to the protonema axis was less effective than that vibrating in other directions. These observations support the hypothesis that the phytochrome controlling the timing effect is localized in the plasma membrane.

Single- and dual-axis lateral photodetectors of rectangular shape

A 2-dimensional diffusion model of rectagular single-and dual-axis, lateral photodiodes is analyzed and the different underlying lateral effects are discussed for the small-signal (unbiased) and fully reverse-biased modes, with either infinite terminating impedances at midlateral point contacts or zero loading impedances at extended lateral contacts. For the single-axis detector with two opposite extended contacts, previous results of the 1-dimensional model appear to remain valid, and the output current difference to sum ratio in the fully reverse-biased mode is a linear function of the position of a narrow incident light beam. For the dual-axis detector with extended contacts at all four sides--except for small gaps at the vertices--an approximately linear relation has been found between the light spot position along an axis and the log ratio of the corresponding output currents. The transient responses of these configurations are discussed, and the utility of operation in the small-signal mode is illustrated with some typical parameter values.

Apparent Rotational Amplification in Measurement Systems

The rotation of a shaft is sometimes measured by detecting the position of a narrow beam of light, reflected by a mirror rigidly mounted to the shaft. For small angles of rotation, a centering detector can be used to determine the position or the change in position of the beam. One type of centering detector is comprised of two photo-detectors each having the shape of a hemi-disc. These hemi-discs are placed close to each other so that their straight edges are aligned parallel. If a radially symmetric beam of light is incident on two such detectors with equal sensitivity, their electrical output signals will be of equal magnitude when the beam center coincides with the geometric center of symmetry of the pair. If the beam is displaced, the detector outputs are no longer equal, and the unbalance is related to the magnitude of the displacement.