Cone Of Light Research Articles

Limitation in the Cone of Light through GRIN Lenses: Stops, Pupils and Vignetting

This work deals with the limitation in the extents of the light beams through GRIN lenses by analyzing the stops, pupils and vignetting. The obtained results will be applied to the particular case of Selfoc lenses.

Vision-Aided Robotic Welding: An Approach and a Flexible Implementation

Conventional, nonadaptive, robot welding systems can only be used when the workpieces are highly repeatable and well fixtured. An approach for vision-aided adaptive robotic weld ing and an implementation of a flexible, sensory-controlled robotic welding system are presented in this paper. Structured lighting, in the form of a steerable cone of laser light, and machine vision are used for sensing of the weld joint location and determining the detailed three-dimensional weld joint surface geometry ahead of the welding torch. This sensory feedback is used for the off-line detection of large fixturing errors before welding starts (part finding); the real-time cor rection of robot paths to compensate for thermal distortion and loose part tolerances during single- and multipass weld ing (seam tracking); and the in-process adjustment of weld ing conditions to correct for weld joint shape variations (adaptive welding). A general approach for modeling and calibration of the novel cone-of-light structured lighting sensor is presented. Robust vision-processing schemes for the detec tion and recognition of laser stripe features in noisy images are developed and implemented using a pipelined processing architecture. Three-dimensional (3D) offsets from the taught path are computed in real time along the actual path, and a 3D surface model is developed and used to determine user- defined joint cross-sectional features and dimensions during welding. Approaches are proposed and implemented for incorporating the visually determined offsets in robot path planning and control and for controlling the welding process parameters on the basis of the monitored cross-sectional dimensions.

Three dimensional surface shape measurment method by multiple image processing using lighting equipment composed of optical fiber cables.

In this paper, we first propose a design method of lighting equipment using an optical fiber cable that projects a half cone of light on an object and relieves the heating of this object. A sharp edge defined by the line between the lighted section and the dark shaded area can be easily detected by the first order differential procedure of image processing. second, we construct the three dimensional shape measurement equipment which is composed of the proposed luminaire, two cameras and an object table. The outer shape of the object is measured from the multiple images detected by the cameras under the condition that the object table can be rotated, inclined and turned over.

Two-beam cross coupling from mutually incoherent lasers

The cross coupling of two mutually incoherent sources in photorefractive materials is described. It is shown that when there are two mutually incoherent pump beams that are not counterpropagating, the respective outputs are cones of light whose parameters depend on the interaction angle of both pump beams. The phase-matching equations are solved, and the cones are analytically represented. Additionally, the coupled-wave equations are solved to give the intensity of light along the coordinates of the cones. These cones are experimentally observed as ellipses on a screen. Preliminary experiments are reported in which the intensities of the cones are measured and compared with theory. How this applies to other cases of mutually incoherent two-beam cross coupling is discussed.

Refractive index of some mammalian tissues using a fiber optic cladding method

The index of refraction n of the many mammalian tissues is an important but somewhat neglected optical constant. Archival and oral papers have quoted the use of values of n for tissue generally ranging from 1.35 to 1.55. However, these values are frequently without experimental basis. They have arbitrarily used values near that of water, which is a major component of mammalian tissue, or have calculated a theoretical n from the weighted elemental composition of tissue. Since these values have not been precise and little information is available on specific indices for each tissue, a study was undertaken to develop a simple, rapid, and reliable method for the experimental determination of n. This was done using the ubiquitous quartz optical fiber. By substituting the usual cladding found on commercial quartz optics by the tissue in question and utilizing the principle of internal reflection, the value of n for the specific tissue can be calculated. This is done by utilizing the known indices for air and quartz and measuring the angle of the emergent cone of light from the output of the optical fiber. A number of indices for mammalian tissue (bovine, porcine, canine, and human) have been determined at 632.8 nm. With few exceptions, for tissues at this wavelength, n was in the 1.38-1.41 range. The species type did not appear to be a factor. Bovine muscle showed normal dispersion characteristics through the visible wavelengths. The denaturation of tissue was shown to alter significantly the refractive index.

Photorefractive conical diffraction in BaTiO 3

A laser beam incident on BaTiO 3 can cause a cone of light to exit the crystal. If the incident beam is polarized as an extraordinary ray, the cone of light is formed by ordinary rays. The cone angle is fixed by a phase-matching condition for the incident and cone beams. Measurement of this cone angle as a function of the incident angle is a simple and sensitive method for determining the birefringence of a BaTiO 3 crystal over the entire range of wavelengths where the sample is photorefractive.

The Vertical Component of Plant Species Diversity in Temperate and Tropical Forests

Forests are widely observed to contain two or more discrete superimposed strata of plants. In the eastern United States, deciduous forests growing between 30⚬ and 42⚬ north latitude are commonly constructed of three strata: a high canopy of sun-adapted trees, a shade-tolerant herbaceous ground layer, and a midstory of shrubs or small trees, of which the flowering dogwood (Cornus florida) is a prime example. Flowering dogwoods and other woody species occupying ecologically equivalent positions in the forest midstory must depend heavily on sunflecks because up to 80% of the light penetrating the forest interior is this kind of direct-beam illumination. The light field in the forest interior is simply modeled. Immediately beneath the canopy, the light field (integrated over the daily sun cycle) is characterized by a high horizontal variance, because any point is either in a gap and directly illuminated or under a crown and continuously shaded. Farther down in the forest interior the horizontal variance becomes greatly diminished because the expanding cones of light beneath each gap eventually intersect. Where the cones of light from alternate gaps intersect, the light field becomes horizontally uniform. Plants of the woody middle stratum should grow up to, but not exceed, the upper limit of the horizontally uniform light field. The position of the upper limit of the horizontally uniform light field can be predicted from measurements of the canopy and the angular distribution of light gaps overhead. Such predictions for five climax stands in the southeastern United States agreed quite closely with the median height of trees composing the midstory of these stands. Finally, the shapes of tree crowns can be expected to vary adaptively with the systematic latitudinal decrease in the angle of the sun above the horizon. Consequently, tree crowns at high latitudes are narrowly conical in profile, but those in tropical latitudes tend to be planar or shallowly dome-shaped. As a result, direct light is admitted to high-latitude forests only at sharply inclined angles that do not permit the establishment of a woody midstory. By contrast, light is able to penetrate the canopy of tropical forests at relatively shallow angles, allowing the development of a second tree layer closely beneath the crowns of the first. The vertical dimension of plant species diversity thus seems to be controlled by adaptive responses to physical parameters of the latitudinal gradient.

Imaging of birefringent objects in scanning microscopes

A method is described whereby the effective detector sensitivity function can be modified in a scanning optical microscope by placing a polarizer in front of a photodetector. The technique relies on the polarizer being placed in a divergent cone of light. The technique is powerful as birefringent information from the specimen may be obtained simultaneously. Examples of amplitude and differential phase contrast images are presented.

Photoradiation of rabbit ocular malignant melanoma sensitized with hematoporphyrin derivative.

Photoradiation therapy (PRT) against the Greene-Harvey amelanotic malignant melanoma on the rabbit iris was effectively used to cause tumor regression. A dose of 2.5 mg/kg of hematoporphyrin derivative (HPD) given intravenously, followed by photoradiation at a wavelength of 632 nm and a power density as low as 71 mW/cm2 for 24 minutes (102 J/cm2) was found to be lethal for tumors 4 mm in diameter with an acceptable level of reversible toxicity to the surrounding tissues. This was best accomplished with a dye laser as the source of light because of its very narrow expanding cone of light, as emitted from a fiber optic. A 1000 Watt xenon arc lamp was also effective but not as efficient. Because of this tumor's exceptionally rapid growth rate, it was necessary to compromise one important variable - the 3 to 4 day period between injection of HPD and photoradiation to allow for HPD depletion from normal tissues. Thus, the best tumor death responses were achieved when the light was given 1 to 16 hours after administering HPD. It is surmised that with this rapidly growing tumor, new cell progeny possess insufficient concentrations of HPD to be killed by the radiant energy. At such a short delay period, toxicity to normal tissues was observed mainly as conjunctivitis and conjunctival chemosis. A dose level of HPD at 5 mg/kg was very close to the threshold where minor increases in light intensity would cause strong inflammatory reactions. Higher doses, at 7.5 and 10 mg/kg were excessive. A dose of 23 mg/kg accompanied by mild light energy exposures, even after 30 days, caused massive damage to normal tissues.

Extinction of light in Brewster polarizers: a shadowlike phenomenon

A Brewster polarizer in this study is any dielectric plane reflecting surface reflecting light at or near the Brewster angle of incidence. In this paper, we consider an interesting phenomenon observed when we use an extended source of light or a cone of light with its axis incident on the plane surface at the Brewster angle. The resulting reflected light is viewed (a) through an ordinary sheet polarizer and (b) after reflection from another Brewster polarizer. The extinction pattern of light by such a system is in the form of an elongated black shadow in (a) and a nearly circular shadow in (b), respectively. These shadows are explained on the basis and use of the familiar Fresnel equations at a plane interface between two dielectric media. Photographs of the shadows are also presented.

Quantiative Interference Microscopy: Effect of Microscope Aperture

Quantitative microscope interferometry has, until recently, been limited to observations at small apertures with, consequently, limited image brighteness and resolution. Also, in the beam splitting comparison techniques, specimen shape and area are necessarily limited because of the requirement for an adjacent background reference area. We have previously described a quantitative finite aperture theory (FAT) for incident light interferometry which avoids these endemic problems and operates with cones of incident light having included angles between 30° and 105°. In addition to determining thicknesses, it is possible to derive film refractive index by making measurements at several different apertures, a unique feature among optical methods because it is capable of measuring over areas less than 0·05 wm2. We report here new measurements which confirm the correctness of finite aperture theory to a high level of precision.

THE STUDY OF SHG IN THE POLYDOMAIN STRIAE REGION OF LiNbO<sub>3</sub> SINGLE CRYSTAL

Using acousto-optic Q-switched Nd3+: YAG laser as a source of fundamental beam, we measured the SHG scan vs temperature in LiNbO3 and BNN single crystals. There are usually two peaks appearing on the SHG scan curves for the striae region, at the same time two NPM hollow cones of SHG light may be observed in one to one correspondence.One of the two peaks in the polydomain striae region of LiNbO3 disappeared after the crystal was completely polarized. The occurrence of this peak was analyzed.The SHG power in the polydomain region of LiNbO3 is usually several times larger than that of single domain region. We attributed the enhancement mechanism to the stress relaxation occurring with the formation of insular 180°domains.

Interference reflection microscopy. A quantitative theory for image interpretation and its application to cell-substratum separation measurement

We propose a quantitative theory of microscope interferometry where the specimen is illuminated by a cone of monochromatic light of solid angle 0 - 100 degree, corresponding to an illuminating numerical aperture of 0 to approximately 1.2. Computed results compare favorably with photometric measurements of fringe irradiance for a water wedge 0 - 2,000-nm thick. The interpretation of cell-substratum interference images is discussed in relation to the theory. We conclude that in assessing cell-glass separation, the cytoplasmic thickness does in general contribute significantly to the final image, but this contribution is minimized at high illuminating apertures. In these circumstances, however, normal incidence theory is inapplicable and the theory for finite illuminating aperture is essential. Neglect of this fact can lead to errors of up to 100% in estimated cell-glass separation.

Bird Versus Bats: Behavioral Interactions at a Localized Food Source

During June and July 1976, we investigated the foraging behavior and interactions of bats and common nighthawks (Chordeiles minor) at a localized food source in Columbus, Ohio. The patch consisted of insects attracted to a cone of light produced by six large (1000 W) spotlights illuminating a sign. While foraging in the light cone members of both taxa engaged in both intra— and interspecific chases. Seventy—five percent of the bat—initiated and 94% of the nighthawk—initiated chases had nighthawk targets. The smaller bats appeared to dominate the larger birds in all individual aggressive encounters. Members of both taxa foraged differently while using the patch. When either birds or bats foraged in the absence of members of the other taxon, they foraged low in the light cone. When birds and bats were present simultaneously, the aggressive interactions conditioned their foraging behavior. When together, bats remained in the lower zone of the light cone, while some nighthawks rose into the upper zones. When foraging in these upper zones, nighthawks suffered a decrease in foraging efficiency based on energetic considerations. They missed more prey per attempted capture, and either increased the time between captures or increased their foraging speed in the upper zones. In any case, more energy was expended by nighthawks foraging in the presence of bats than when they were alone. The expanded pattern of patch used by the larger yet socially subordinate nighthawks in the presence of bats supports Morse's (1974) hypothesis. Morse predicted that social dominance would be more important than body size in determining resource use in communities where interspecific aggression and dominance is important in resource partitioning.

Orientation of retinal rod photoreceptor membranes in the intact eye using X-ray diffraction

An unusual distortion of the X-ray diffraction spots obtained from in vivo retinal rod outer segments of the frog ( Rana pipiens) has been interpreted in terms of an asymmetric disorientation of the outer segments in the intact eye. Proof of this interpretation is presented here, along with evidence that the asymmetric disorientation is not a dissection artefact. The asymmetry is found on the peripheral retina and not near the center of the retina. It is conjectured that the retinal rods, or their photoreceptor membranes, orient towards the light and indicate the shape of the incident cone of light on the retina.

Observation of the simultaneous emission of roughness-coupled and optical-coupled surface plasmon radiation from silver

The optical excitation and decay of surface plasmons on Ag films is reported. The optical decay is observed as an annular cone of light when the substrate is in the form of a hemisphere. The polarization and angular distribution of this cone radiation is presented and compared to the roughness-coupled surface plasmon radiation simultaneously emitted from the Ag.

Electromagnetic field near focus as seen by a moving particle*

In a number of recent experiments, moving atoms are allowed to interact with the focused light from a resonant-dye laser. In such cases the frequency content of the light seen by the atom depends on its trajectory. The electromagnetic field produced by a laser beam near the focus of an ideal aplanatic lens has been calculated in the frame of a nonrelativistic particle moving at right angles to the optic axis. The frequency content of this field can be approached in two different ways—via its power spectrum, and via an envelope representation that yields the instantaneous frequency as a function of time. Both quantities have been evaluated for a number of different trajectories, and are found to be entirely different, in general. Whereas the power spectrum falls to zero for frequency deviations in excess of the maximum Doppler shift associated with the converging cone of light, there is no corresponding limit to the excursions of the instantaneous frequency.

Noncollinear-Phase-Matching Effects in Lithium Niobate

Hollow cones of second-harmonic light may, under certain conditions, be produced in nonlinear crystals in the process of optical second-harmonic generation. This effect is caused by the mixing of the central laser beam with a weak off-axis radiation field of the same frequency. Under these conditions noncollinear phase matching (NPM) occurs in a locus of directions defining a hollow cone. Equations have been developed describing NPM in negative uniaxial crystals, and the NPM hypothesis has been verified experimentally. A technique is described for characterizing the phase-matching properties of materials based on this result.

Photometer for Measurement of the Light Scattered by Large Submicron Cylinders at Both Perpendicular and Oblique Incidence

A light scattering photometer is described which is capable of viewing the periphery of the cone of light scattered by a cylinder tilted obliquely to the incident beam. The special case of perpendicular incidence can also be handled. Experimental data with a Pyrex cylinder show excellent concordance with theoretical calculations for a cylinder with a diameter of 525 mμ.

MEASUREMENT OF ABSORPTION SPECTRA OF CHLOROPHYLL IN ALGAL CELL SUSPENSIONS*

SummaryThe effects of instrumental geometry on the measurement of absorption spectra of scattering suspensions are considered. It is shown that the resolution of absorption spectra of cell suspensions is not improved by opal glass if a spectrophotometer receiving a large cone of light is used.The scattering of light by suspensions of several algae is found to be approximately proportional to the fourth power of the frequency, as would be expected if the scattering is due to small particles.