Narrow Light Beam Research Articles

Inhomogeneity of the optical Magnus effect

An experimental investigation was made of the dependence of the angle of rotation of the speckle pattern of the radiation, transmitted by a fibre waveguide with a step refractive index profile, on the angle α of entry of a narrow light beam into the fibre. The magnitude of the optical Magnus effect depended on this angle as α2.

Multiple scattering of narrow light beams in aerosols

A multiple scattering propagation model of narrow light beams in aerosol media is described. It is based on a paraxial approximation of the radiative transfer equation in which the flux normal to the incident beam direction is modeled by a diffusion process. The model solutions are the forward- and backscattered intensity profiles for the specified geometry and receiver aperture and field of view. The required inputs are the system parameters, and the aerosol single scattering angular phase function and extinction and scattering coefficients which are allowed to vary along the beam axis. Good agreement is shown with measurements performed in the laboratory over scales ranging from a few tens of mm to a few m, and in the atmosphere over a scale of the order of 1 km. The solutions are valid for optical depths smaller than ≈ 10, for phase functions corresponding to average size parameters of order one or greater, and for off-axis positions not exceeding ≈ 25% of the reciprocal of the scattering coefficient.

Experiment to demonstrate diffusion doping

Single crystals of CdS possess a translucent yellow color but when indium is diffused into the crystal from the vapor in an evacuated silica capsule it becomes opaque. This type of diffusion is linearly dependent on the indium concentration and produces a sharp interface between the diffused and undiffused regions of the crystal. The process of diffusion doping can be demonstrated by studying the variation of the depth of the interface with anneal time and temperature, using an optical microscope. In addition, as CdS possesses a hexagonal crystal structure of the ‘‘wurtzite’’ type, this is a sensitive method for studying diffusion anisotropy along the two principal crystal directions, and the sharpness of the interface can be demonstrated by the dispersion produced by a narrow beam of white light. This article describes how these properties can be incorporated into an undergraduate student experiment, or an open ended project for demonstrating Fick’s laws and the process of diffusion doping.

Features of interaction of a narrow light beam with a smectic OCBP. Memory effect

1. A memory effect was observed in a smectic liquid crystal without artificially increasing its absorption in a wide temperature interval — from the nematic-phase temperature (t ≤ 35°C) to room temperature (t ⋍ 21–22°C).

Material properties, project design rules and performances of single and dual-axis a-Si:H large area position sensitive detectors

We have developed large area (up to 80mm×80mm) Thin Film Position Sensitive Detectors (TFPSD) based on hydrogenated amorphous silicon (a-Si:H). Although crystalline silicon PSDs have been realized and applied to optical systems, their detection area is small (less than 10mm×10mm), which implies the need of optical magnification systems for supporting their field of applications towards large area inspection systems, which does not happen by using a-Si:H devices. The key factors for the TFPSDs resolution are the thickness uniformity of the constituting layers, the geometry and the position of the contacts. In this paper we present data on single and dual-axis rectangular TFPSDs correlating, their performances with the different underlying lateral effects. For the single axis-detector, with two opposite extended contacts, the output photocurrent difference to sum ratio is a linear function of the position of a narrow incident light beam, even for low illumination levels (below 20 lux). For the dual-axis detector with extended contacts, at all four sides (except for small gaps at the vertices due to edge effects) an almost linear relation has been found between the incident light spot position along both axis and the corresponding output photocurrents.

Vincent J. Schaefer (1906–1993)

In 1946, Vincent Schaefer carried out two simple experiments, the results of which echoed around the world in the meteorological research community.As the afternoon temperatures in the General Electric Research Laboratory at Schenectady, N.Y., inched higher on a hot day in 1946, Schaefer noticed that his cold box (an ordinary home freezer he had lined with black velvet and into which was directed a narrow beam of light) was not as cold as usual, so he placed a block of dry ice in the bottom of the freezer. Within seconds the entire cloud of water droplets in the cold box was turned into millions of tiny, sparkling ice crystals. Serendipitously, Schaefer found the trigger that converted super‐cooled droplets into ice crystals.

Structural changes of the human embryonal cortex during explantation.

It has been shown in numerous studies on the transplantation of neocortical anlagen of mammals that processes of cytodifferentiation proceed successfully in the grafts, but that the cytoarchitectonics are disturbed. This may be associated with the formation of closed cavities lined with neuroepithelium [12], the so-called rosettes, in the early period following transplantation. The rosettes become the centers of proliferation from which cells which have completed division diverge in all directions instead of migrating to the cortical plate [2]. Information regarding the initial stages of the formation of rosettes is lacking in the literature. The purpose of the present study was to investigate the early changes in areas of the wall of the telencephalic vesicle of human embryos and the formation in it of rosettes under the conditions of explantation. Materials and Methods. The material for explantation was taken from 7-11-week old human fetuses obtained following artificial interruption of pregnancy in the clinic. The possibility of the use of medium 199 for the study of the morphogenetic mechanisms during explantation to it of anlagen of the neural tube of chick embryos has been demonstrated by a number of authors [10, 11]. This medium has been used in this study as well. Whole embryos (7-8 weeks) or fragments of the telencephalon broken off during the abortion (9-11weeks) were placed in the medium, cooled to 0-4~ for transportation. The dorsolateral sections of the walls of the cerebral hemispheres were freed from the pia mater under laboratory conditions, cut into pieces, from 1 to 10 mm in diameter, which were transferred to a fresh portion of medium with the addition of penicillin and cultured at 37~ In the process each explant was placed into a drop of medium on a slide; after it was sucked up with a pipette, Bouin's fluid was applied to the preparation. The fixed material was treated by two methods. A portion of the material was used to obtain histological sections (thickness 7 ~rn, staining with hematoxylin-eosin). The other portion of the material, following a one-hour bath in distilled water, was embedded in a 1% solution of silver nitrate for one to two days, following which each of the pieces was treated with a standard solution of a developer for photographic film (the Ramon y Cajal method). The relief of the surface of the explant was clearly demonstrated using raking illumination from above. Side-lighting with a narrow beam of light was used for the intravital investigations of the explants. Investigation Results and Discussion. Numerous fissures on the ventricular surface were found in the initial material in the total preparations, both impregnated with silver nitrate (Fig. la), and in the intravital observations. The occurrence of fissures is apparently caused by manipulations during the interruption of pregnancy and during the opening of the brain vesicles during the preparation of the material for explantation. The fissures are observed in all of the fetuses from 7 to 11 weeks of development. At the same time, the surface facing the pia mater remains smooth. The depth of the fissures is varied (see Fig. lb): In some cases they penetrate only to the middle of the ependymal zone (of the neuroepithelium); in others, they reach the intermediate layer. Not infrequently, dead cells with pyknotic nuclei are found in the region of the fissures. Undamaged smooth sections of the ventricular surface of the neuroepithelium are visible between the fissures. In the number of instances the borders of such sections are raised above the general surface of the explant. Noticeable changes do not take place during the first hour of cultivation at 37~ The degeneration of neuroblasts in the cortical zone is observed only in some instances. After 3-6 h (see Fig. lc) the borders of the fissures are somewhat raised, forming ridges. It can be seen in the sections (see Fig. ld) that the free edges of the neuroepithelium which are everted toward the ventricular surface correspond to the ridges, while the fissures themselves begin to fill with cells probably arising from the intermediate zone. The degeneration of neuroblasts in the cortical and especially in the subcortical zones is well seen at this stage. After 12-24 h, the fissures gradually close over, while the ridges surrounding them reach maximal development (see Fig. le). Where the fissures are located close to one another, their

Non-invasive evaluation of the effects of opening & closing of eyes, and of exposure to a minute light beam, as well as to electrical or magnetic field on the melatonin, serotonin, & other neuro-transmitters of human pineal gland representation areas & the heart.

Using the Bi-Digital O-Ring Test electromagnetic resonance phenomena between 2 identical substances, first the pineal gland representational (rep.) areas were localized on the 5 different locations on the surface of the head using microscope slides of the pineal gland or Melatonin (while the eyes are closed) as a reference control substance. The 3 pineal rep. areas along the mid-line of the head always showed two lobes connected as a "Dumbbell" shape, with one round or oval area at each side of the mid-line. From each side of the head, anterior and superior to the ear, it appeared in a shape resembling the side view of a pineal gland. When both eyes were open, Melatonin, Norepinephrine (NE), and Acetylcholine (ACh) markedly decreased, while Serotonin, Dopamine, and GABA increased significantly in the outer part of the pineal gland rep. areas. When both eyes were closed, Melatonin, NE and ACh increased markedly, with marked decrease in Serotonin, Dopamine and GABA in the outer part of the pineal gland rep. areas. However, in the inner core of the pineal gland rep. area, an opposite response was found. Thus, the pineal gland has 2 main lobes, and functionally each lobe seems to have two concentric areas with an inverse relationship, i.e., a "Functional Cortex" area and a "Functional Core" area. The biochemical changes between the cortex and the core are in an inverse relationship. Melatonin was also found in the S-A node & right side of normal heart when the eyes were closed. When the eyes were open, Melatonin was found in the left side of the heart, as well as the salivary glands, stomach, colon, etc. While both eyes were closed, when a weak light beam was exposed at different parts of the body, such as any part of the upper and lower extremities, Melatonin, NE, and ACh decreased, with an increase in Serotonin, GABA and Dopamine only in the functional cortices of the pineal gland lobes on the same side of the body. Even when both eyes were open, if a very weak narrow beam of light was exposed on any part of the body, Melatonin, NE and ACh decreased, while Serotonin, Dopamine and GABA increased compared with pre-exposure level in only the functional cortices of the pineal gland lobes in the same side of the light exposure, and the opposite effect was also observed in the functional core of the light exposed side only.(ABSTRACT TRUNCATED AT 400 WORDS)

Densitometry on Thin-Layer Chromatographic Plates by Fourier Transform Near-Infrared Spectrometry

Direct measurement by Fourier transform near-infrared (FT-NIR) spectrometry on thin-layer chromatographic plates is described. Zones separated on a high-performance thin-layer chromatographic plate fixed on the sample stage of a microscope linked with an FT-NIR spectrometer were scanned with a narrow beam of light (0.4-mm square). The NIR chromatogram and spectra of the separated zones were then obtained by the diffuse transmission method. Three kinds of phospholipids that have essentially no absorption bands in the ultraviolet and visible regions but that do have native absorption bands in the NIR region were used to evaluate the usefulness of this method. The limit of detection for phosphatidylcholine was under 1 μg, and the correlation coefficient of the calibration curve obtained from derivative spectra was 0.998 for amounts from 1.25 to 10 μg.

Vectorial Analysis of the Gaussian Beams of Light

The scalar theory of Gaussian beams is an approximation to describe narrow beams of light. A vectorial analysis is required to describe the electromagnetic fields in the focal region with a small spot size. Maxwell's equations are solved to obtain the longitudinal as well as the transversal components of field vectors in a beam of light propagating along an axis. Solutions of the electromagnetic fields of either the plane-polarized-electric (and magnetic) or the transeverse-electric (and magnetic) modes are expressed in terms of Hermite-Gaussian functions. Magnitudes of the longitudinal field components in these modes are evaluated in particular.

Vectorial Analysis of the Gaussian Beams of Light

The scalar theory of Gaussian beams is an approximation to describe narrow beams of light. A vectorial analysis is required to describe the electromagnetic fields in the focal region with a small spot size. Maxwell's equations are solved to obtain the longitudinal as well as the transversal components of field vectors in a beam of light propagating along an axis. Solutions of the electromagnetic fields of either the plane-polarized-electric (and magnetic) or the transeverse-electric (and magnetic) modes are expressed in terms of Hermite-Gaussian functions. Magnitudes of the longitudinal field components in these modes are evaluated in particular.

Beyond the Fringe: Diffraction as seen by Grimaldi, Fabri, Hooke and Newton

Beginning his third ‘Account of a Book’ in no.79 of his Philosophical Transactions (22 January 1671/2) Henry Oldenburg wrote: ‘This learned Treatise was not to be altogether omitted in these Philosophical Transactions though an Account of it hath been deferr’d (too long), it being but lately fallen into the Publisher's hands.’ (1) The work in question was Francesco Maria Grimaldi’s Physico-Mathesis de Lumine (Bologna, 1665); Oldenburg accorded it a moderately long review of almost three pages. He noted that Grimaldi had introduced a fourth manner of propagation of light, that is, ‘not only directly, and by refraction , and reflexion , but also by diffraction ’ thus coining a new technical word for the English language. But alas! the account leaves the new phenomenon very obscure, for Oldenburg continues: ‘which last, according to him, is done, when the parts of Light, separated by a manifold dissection, do in the same medium , proceed in different ways.’ The essence of a typical 17th century diffraction experiment - a narrow beam of light partially obstructed by a sharp edge - is not mentioned.

A narrow beam of light: A reading of two novels by André Brink

A narrow beam of light: A reading of two novels by André Brink

An Optical Method for Determining Bubble Size Distributions—Part I:Theory

A new optical technique is developed to determine the size distribution of bubbles in a two-phase flow. Implementation involves passing a narrow beam of light through the bubbly flow and monitoring the transmitted light intensity. The basic units of data are the rate at which each bubble blocks off the beam and the duration of blockage. Adding the hypothesis that the distance of closest approach between a bubble’s center and the beam axis is randomly distributed, a statistical analysis yields the bubble size distribution.

Multiscattering model for propagation of narrow light beams in aerosol media

An approximation to the radiative transfer equation is derived for the propagation of narrow light beams. The main feature is the representation of the power flux in the direction normal to the propagation axis by a diffusion process. Coupled partial differential equations are obtained for the forward and backward flux densities. They are valid in the paraxial approximation. The solutions are written in general analytic formulas applicable to inhomogeneous aerosol media. Comparisons with Monte Carlo calculations and laboratory data reported in a companion paper [Appl. Opt. 27, 2485 (1988)] show very good agreement over a wide range of extinction coefficients, scattering albedos, and particle size parameters.

Whole-Field Measurement of Ice Displacement and Strain Rates

The flow of glacier ice is mapped using high-resolution photography and noncoherent light speckle interferometry. Time-lapse, double-exposures of a straining surface yield Young’s fringes when the resulting image is interrogated by a narrow beam of coherent light. Such fringe patterns, when corrected for camera motion, are indicative of the surface displacement occurring between exposures. Results of glacier field experiments are consistent with those garnered by conventional methods at the Nisqually Glacier, Washington. The interferometric method seems amenable to other geophysical applications, such as mapping sea ice flow, using terrestrial or space-based camera platforms.

Feeling our way in the dark

The papers by Pontecorvo et al., Kesner and Altman and Normile are considered with regard to their illuminating potential in an area dark and murky with research issues. While each of these papers contributes an interesting perspective and narrow beam of light, the collective darkness dissipated by their work remains small.

Spherical reflectors as laser-beam expanders

Lasers emit a narrow beam of light which, for many applications, is often required to be expanded and then collimated. A common type of device used for this purpose is a lens telescope in which a pin-hole is placed at the common focal point of the two lenses. In dye laser cavities, dispersion through a number of prisms gives an expanded beam. The divergence of a laser beam can also be achieved by a convex reflecting surface like a polished steel ball. Here the capability of a small steel ball as an inexpensive, simple and convenient laser-beam expander has been investigated experimentally. It has been shown, with the help of shearing interferograms and Ronchigrams, that the aberrations introduced from on-axis as well as off-axis illumination of the ball are less than 1/4 of a fringe.

87:6102 Monte Carlo calculation of the structure of a narrow nonstationary light beam in seawater at large optical depths: Zakharov, A.K. and Yu.A. Gol'din, 1986. Izv. Atmos. Ocean Phys. (a translation of Fiz. Atmos. Okeana), 22(5):403–408

87:6102 Monte Carlo calculation of the structure of a narrow nonstationary light beam in seawater at large optical depths: Zakharov, A.K. and Yu.A. Gol'din, 1986. Izv. Atmos. Ocean Phys. (a translation of Fiz. Atmos. Okeana), 22(5):403–408

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.