Divergent Light Research Articles

Making fast cylindrical gradient-index lenses diffraction limited by using a wave-front-correction element

A wave-front-correction element (WFCE) is produced to make a cylindrical Ag-ion-exchanged gradient-index (GRIN) lens with a high numerical aperture (0.53) diffraction limited (wave-front error, 0.02lambda rms). The wave-front aberrations of the cylindrical GRIN lens are measured by a phase-shifting shearing interferometer, with a conventional microscope objective used as a compensation lens. The continuous surface relief of the WFCE is produced by a lithographic process. The wave-front-corrected GRIN lens is applied to collimate the strongly divergent light (57 degrees full diverging angle measured at 1/e(2) of maximum intensity) emitted by a high-power diode laser. The power irradiated into a full angle of 2 mrad can be enhanced by a factor of 1.8 with the WFCE.

Characteristic features of light scattering by a thick volume hologram

A mathematical model is proposed for the optical transfer function of a thick two-dimensional volume hologram bounded by a rectangular periphery. It is shown that the hologram is made up of two parts. The first part is formed by a point reference beam which reads out the hologram through the longitudinal boundary, while the second part is formed when it is read out through its transverse boundary. It is established that the principal features of light scattering by a thick hologram involve the second component of the optical transfer function. It is shown that under conditions of phase detuning the angular dependence of this component fails to coincide with the corresponding dependence of the first part, and this greatly complicates the structure of the angular intensity of the reconstructed light beam. This conclusion is confirmed by the experimental results given which were obtained when investigating holograms of a divergent light beam recorded in a lithium niobate photorefractive crystal. The results are given of a calculation using the mathematical model discussed as applied to the experimental situation considered.

Dependence of output properties on ridge structures and asymmetric facet reflectivity in 0.98-μm InGaAs-InGaAsP-InGaP SQW FP-LDs

The dependence of output performances on the waveguide structures and the facet reflectivity of 0.98-/spl mu/m Al-free InGaAs-InGaAsP-InGaP ridge waveguide single-quantum-well Fabry-Perot laser diodes are investigated theoretically and experimentally. In our analysis, lateral and longitudinal spatial hole-burning, carrier-density-dependent optical loss in the well, and gain saturation are considered simultaneously. Permissible ranges of the ridge width, the InGaP cladding thickness, and the front facet reflectivity are presented in conjunction with the desired performance parameters such as maximum kink-free output power, beam divergence, and peak light density at the front facet.

Limitations in mixed-mode stress intensity factor evaluation by the method of caustics

Evaluation of stress intensity factors in crack problems by the method of caustics is complicated due to the changing state of stress in the neighborhood of the crack tip. Near the tip the state of stress is plane straina while at a critical distance from the tip it can be approximated as plane stress. Between the two regions the stress field is three-dimensional. The type of the state of stress has a tremendous effect on the values of stress-optical constants which enter into the evaluation equations of stress intensity factors. In almost all cases the assumption of plane stress is involved, which infers that the initial curve of the caustic should lie in the region where plane stress conditions dominate. This imposes limitations on the values of the applied loads, specimen dimensions and characteristic lengths of the optical arrangements for the correct application of the method. In the present work a thorough investigation of the limits of applicability of the method of caustics for the evaluation of mixed-mode stress intensity factors is undertaken. The case of an inclined crack in a uniaxial tensile stress field is studied in detail. Results are given for the selection of material, load level, specimen size and optical arrangement when the specimen is illuminated by a parallel, divergent or convergent light beam. It is shown that mixed-mode loading conditions impose more severe limitations on these quantities as compared to opening-mode loading.

On the feasibility of employing gradient crystals for high resolution synchrotron optics

Abstract We present first experimental data on a novel type of optical element for synchrotron radiation applications in the X-ray region: namely laterally-graded aperiodic crystals on the basis of Si 1− x Ge x alloys. The lattice parameter of such gradient crystals containing up to some atomic % in Si 1− x G x crystal changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated for. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical divergence without a collimating premirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si-crystal monochromator.

Compact dielectric reflective elements I Half-sphere concentrators of radially emitted light

Optical designs of aspheric internally reflective concentrators of divergent light emitted within a spatial angle of 2n sr are proposed and discussed. Four types of solid transparent element are considered: the divergence angle reducer, the small-spot illuminator, the point focuser, and the collimator. The output beam aperture in all cases is comparable with the light-source external dimensions. Expressions describing the profiles of beam-transforming surfaces and results from experiments with model devices are presented.

Application of a divergent laser beam in a grating interferometer for high-resolution displacement measurements

A grating interferometer for high-resolution displacement measurements is presented. To decrease interferometer sensitivity to inaccuracy of the grating guide, application of divergent light beam is proposed. The effect of the interferometer geometry on the direction and constant of fringes is analyzed. Comparison is drawn between results of applying plane and spherical wavefronts. The advantages of spherical wavefront application are theoretically evaluated and experimentally proved. An acceptable value of the angular instability of the grating illuminated by spherical wavefront is equal to about ±3 arcmin.

Optoelectric transducer system for stringed instruments

A pick-up apparatus for a string instrument comprising an array of supports for positioning an array of detectors, each of which monitors strings' vibrations and generates electrical signals, each of the supports straddling a string of the stringed instrument. The detectors include a sensor mount, a divergent light source, and first and second optical sensors which receive light simultaneously when the light source is illuminated and generates an electrical analog output signal.

Grating couplers as chemical sensors: a new optical configuration

An optical configuration is proposed that allows the determination of the coupling angle of an integrated optical grating coupler by means of a very simple set-up. The sensor head is small and no moving parts are required. A convergent (or divergent) light beam is directed onto the grating. The intensity distribution of the light reflected by the sample is analysed. Because of the coupling into the waveguide, at the coupling angle a dark line occurs in the reflected beam. The position of this line, which may be evaluated with a photodetector array, is a measure of the effective refractive index of the waveguide. From this, the quantity to be measured is derived.

Limits of applicability of the method of caustics in crack problems

The state of stress in the neighborhood of the crack tip changes from plane strain very close to the tip to plane stress further away from the tip through an intermediate region where the stress field is three-dimensional. This situation complicates the experimental determination of stress intensity factors in crack problems by the method of caustics, since the values of the stress-optical constants entering into the evaluation equations change drastically when the stress state changes from plane strain to plane stress. In the present study a thorough investigation of the limits of applicability of the method of caustics in crack problems under conditions of plane stress is undertaken. The fact that the generatrix curve of the caustic, the so-called initial curve, should lie in the plane stress region introduces restrictions on the values of the applied loads, specimen dimensions and characteristic lengths of the optical arrangement for the correct application of the method. The limiting values of these quantities are defined when the specimen is illuminated by a parallel, divergent or convergent light beam. It is shown that direct application of the method may give erroneous results if certain conditions are not satisfied. Thus, the experimentalist following the results of the present study can safely apply the method of caustics to determine stress intensity factors in crack problems.

Inducible in vivo DNA footprints define sequences necessary for UV light activation of the parsley chalcone synthase gene.

We began characterization of the protein--DNA interactions necessary for UV light induced transcriptional activation of the gene encoding chalcone synthase (CHS), a key plant defense enzyme. Three light dependent in vivo footprints appear on a 90 bp stretch of the CHS promoter with a time course correlated with the onset of CHS transcription. We define a minimal light responsive promoter by functional analysis of truncated CHS promoter fusions with a reporter gene in transient expression experiments in parsley protoplasts. Two of the three footprinted sequence 'boxes' reside within the minimal promoter. Replacement of 10 bp within either of these 'boxes' leads to complete loss of light responsiveness. We conclude that these sequences define the necessary cis elements of the minimal CHS promoter's light responsive element. One of the functionally defined 'boxes' is homologous to an element implicated in regulation of genes involved in photosynthesis. These data represent the first example in a plant defense gene of an induced change in protein--DNA contacts necessary for transcriptional activation. Also, our data argue strongly that divergent light induced biosynthetic pathways share common regulatory units.

Laser angioplasty: controlled delivery of argon laser energy.

A laser catheter system that integrates balloon and fiberoptic technologies was evaluated. In vitro tissue studies were conducted to compare the tissue response to laser irradiation from a bare optical fiber (undiverged light beam) and from a fiber with an optical assembly (diverged light beam). An in vivo study of occluded and unoccluded canine femoral arteries examined coaxial alignment of the diverged light beam and the resultant thermal effects. In the in vitro studies, a diverged laser light beam effected maximum tissue ablation (mean crater diameter, 1.81 mm +/- 0.44) at a distance of only 3 mm from the optical fiber tip. The in vivo study demonstrated the ability of a specially designed balloon catheter to align the diverged laser beam coaxially within the arterial lumen. This laser catheter system successfully avoids the risks of inadequate tissue removal and perforation.

ブロッホラインメモリーの最近の進展

新概念メモリーであるブロッホラインメモリーは, 1cm2にGbit程度の情報を記憶できる全固体の不揮発性メモリーとして注目されている.現在までに, ブロッホライン対の書込み, 転送, 読出しの一連の動作を実現し, メモリーとしての可能性が具体的に示されている.今後, 実用化を目指した研究の加速が期待される.

Diffusive transport of light in sea ice

A new experimental technique has been developed and tested in McMurdo Sound, Antarctica for the in situ measurement of the diffusive transport of light through sea ice. A weakly divergent monochromatic light source is placed on the surface of the ice, and the emergent radiation field is measured at both the top and bottom surfaces. The spatial and angular distribution of the emergent radiance, combined with the results of Monte Carlo simulations, has given a simple and direct measurement of the light scattering length, inhomogeneity, and anisotropy in this very complex material.

An inexpensive, versatile sample illuminator for photo-CIDNP on any NMR spectrometer

Photochemically induced dynamic nuclear polarization (photo-CIDNP) of proteins requires the introduction of ca. l-7 W of 488 nm light directly into NMR samples (1). This has been previously accomplished by a number of configurations: directing the light beam via an optical bench and mirrors through the bottom of the supercon NMR probe to a flat-bottom NMR sample tube; or, alternatively, focusing the light through a cylindrical quartz rod with a 45” polished end to convey a diverged light beam to the side of a spinning sample tube in the rf coil (2). In both cases, costly probe modifications are necessary, including removal or alteration of the variable temperature control apparatus. Laser beam alignment (into a mirror at the magnet base) can also be awkward and time consuming. Lerman and Cohn (3) illuminated samples by inserting a coupled optical fiber directly into the NMR sample solution. Kaptein and Dykstra (personal communication) have fixed a prism at the end of an optical fiber and situated it between the rf coil windings of a modified Bruker 360 MHz proton probe. We report here an alternative modification utilizing fiber optics illumination. Coupling to the laser was accomplished with a Newport Corporation (Fountain Valley, Calif.) model F-LFI-CO-25 ($850.00) fiber optics coupler laser head mount (universally mounts to any laser bezel mount) with 25 ft of 200 p fiber in place of the standard 10 ft length and armored handpiece. The free output end was stripped free of cladding (l-2 cm length) and inserted into a 2 mm stem coaxial insert (Cat. No. 5203, Wilmad Glass Company, Inc., Buena, N.J.) which fits snuggly into a 5 mm sample tube (Fig. 1). Maximal illumination was observed when the fiber tip was positioned in the center of the rf coil region. The laser light probe was introduced by triggering an inexpensive solenoid mounted to the coupling head slide shutter under computer control. Light coupling was fine tuned with x, y, and z adjustments on the coupling head. For maximal efficiency the fiber must be cut perfectly flat and well polished. Coupling efficiencies of up to 90% were typically measured. In a nonspinning sample of 1 mA4 tyrosine (pH 7.0) and 0.4 r&4 ‘?N-carboxyethyllumiflavin, the tyrosyl 3,5 protons were enhanced (light intensity-dark intensity)/ (dark intensity) 1Zfold at 500 MHz on an NTC spectrometer with a Spectra Physics 165-9 argon ion laser operating at 7.0 W (all lines). Figure 2 displays the light-dark

Monophasic synovial sarcoma, epithelioid sarcoma and chordoid sarcoma: ultrastructural evidence for a common histogenesis, despite light microscopic diversity.

Ultrastructural examination of six rare sarcomas--four monophasic spindle cell tumours, one epithelioid sarcoma, one chordoid sarcoma--has revealed marked similarities at the electron microscopic level despite widely divergent light microscopic appearances. These features consisted of: 1 the presence of two cell types, viz. a clear cell and a cell resembling the fibroblast; 2 pseudoglandular spaces with projecting microvilli or filopodia, and with related tight junctions; 3 an amorphous intercellular ground substance with focal condensation into recognizable basement membrane. The findings suggest a common maturation of these diverse tumours to synovial-like tissue, and support the proposal of Hajdu Shiu & Fortner (1977) that these be considered variants of synovial sarcoma. Published ultrastructural studies of synovial, epithelioid and chordoid sarcoma are reviewed in the light of these findings. The ultrastructural differentiation of synovial sarcoma from extraskeletal myxoid chondrosarcoma, chordoma and the spectrum of malignant spindle cell tumours is discussed.

A Study on the Moire Topography : An Accurate Theory and the Applicable Limit of the Divergent Light Ray Method

A Study on the Moire Topography : An Accurate Theory and the Applicable Limit of the Divergent Light Ray Method

Deformed boundaries determined by the method of caustics

The caustics formed by illuminating straight deformable boundaries by a parallel, convergent or divergent light beam were used to determine the load distribution along these boundaries. A universal method based on the characteristic geometric elements of the corresponding caustics (pseudocaustics) was developed. This method leads to a system of singular integral equations, which was solved numerically by a collocation method of successive approximations. The singular points of the integrals were removed by integrating along regular paths determined by the optically obtained pseudocaustics. This procedure constitutes a new combined numerical-experimental method for solving singular integral equations with singularities of the Cauchy type. Several examples are given to show the potentialities of the method.

Stress intensity factors in cracked cylindrical shells under tension

The singular stress field at the tip of a circumferential crack in a cylindrical shell under axial tension was studied by the optical method of caustics. The material of the shell was considered as linearly elastic and optically anisotropic. A complete study of the influence of the optical anisotropy of the material of the shell, the shell curvature and the characteristics of the optical set-up, on the shape and size of the caustics formed by illuminating the shell by a divergent or parallel light beam was undertaken. The stress intensity factor for the crack tip was evaluated by interrelating this quantity with the geometric characteristics of the caustics. Stress intensity factors evaluated experimentally on shells made either of an optically inert material (plexiglas) or of an optically active material (polycarbonate) compared favorably with the already existing theoretical solutions.

The use of divergent beam interferometry in the measurement of small displacements: an application to the measurement of the thermal expansion of copper up to 1200K

From an original suggestion of Tolansky (1943) an interferometer system is described capable of high absolute accuracy in the measurement of small linear displacements. Because divergent light beams are used a great simplification may be made in the optical train and the use of a laser light source permits automatic fringe detection and recording against high background light intensities. An apparatus is described for the absolute measurement of the thermal expansion of copper to 1200K and it is pointed out that the apparatus is capable of measurements to still higher temperatures.