Showing papers on "Collimated light published in 1995"

Laser Light Scattering

Abstract: This chapter provides introduction to both the classical and quasi-elastic forms of laser light scattering, which can serve as an introductory text for students and a reference for research workers. Classical light scattering studies are concerned with the measurement of the intensity of scattered light as a function of the scattering angle. Lasers produce collimated, quasi-monochromatic radiation having high intensity. In all but the least expensive lasers, the output is highly polarized. The chapter describes information that can be obtained from the various experiments rather than either presenting a comprehensive survey of the literature. The decrease in intensity may seem a nuisance, but it turns out to be a unique source of information pertaining to the size and shape of the particle. Inhomogeneity in either the size or shape of the particles leads to ambiguity in the interpretation of the angular dependence of the scattered intensity.

High-speed fluorescence scanner

Abstract: A high-speed fluorescence scanner for scanning a sample at equal angles has most of its optical components, including a light beam source (11), a detector (19), filters (18), lenses (17), and reflectors (15-16), in a fixed position (24), removed from the scan head (22). The lightweight scan head contains a single reflector (13) and lens (12) combination which is reciprocated rapidly along one axis to lengthen and shorten a region of the path of a collimated excitation beam (30) and to form a scan line (25-26) on a sample. The fluorescence emission is gathered by the lens (12) of the scan head and directed back, generally along the optical path of the excitation beam, to a detector. Another embodiment places the light source (43), in miniature form, directly on the scan head. The sample may be translated in an axis orthogonal to the scan line to stimulate fluorescent emission from two-dimensional portion of the sample.

Illumination system employing an array of microprisms

Abstract: An optical illumination system comprising a waveguide (16) that accepts light generated by a diffuse light source (14) and transmits the light via total internal reflection. Attached on one face of the waveguide is an array of microprisms (90), with each microprism (90) having a light input surface (92) parallel to a light output surface (94) and at least two sidewalls (96, 98) tilted at an angle from the direction normal to the surface of the waveguide (16) such that light escapes from the waveguide, reflects off the tilted sidewalls (96, 98) and emerges from the microprism (90) as a spatially directed light source. An array of microlenses (80) may be positioned to accept the output of the microprisms (90) so that the light exiting from the microlenses (80) is a substantially collimated light source. The optical illumination system is advantageous for any application that requires a non diffuse or substantially collimated that is both energy efficient and contained in a low profile assembly.

Atom interferometer based on Bragg scattering from standing light waves.

Abstract: We have constructed an atom interferometer by Bragg deflecting a collimated beam of metastable neon atoms from three parallel standing waves. Interference fringes have been observed using atoms Bragg scattered at up to the third order, giving a maximum of $6\ensuremath{\Elzxh}k$ transverse momentum difference between the two arms of the interferometer. In the first order case we have achieved a fringe contrast of 62% and a peak to peak signal of 1700 atoms/s. We believe this to be the highest fringe contrast that has been achieved in atom interferometers.

Apparatus for switching optical signals and method of operation

Abstract: The present invention provides an apparatus (74 and 200) for switching an optical signal from an input optical fiber (210) to one of a plurality of output optical fibers (214 and 216). The apparatus (74 and 200) includes a collimator (76) for collimating an input optical signal into a collimated beam (216) at an angle with respect to a reference and a decollimator (78) for focusing the collimated beam to an output optical signal (220). The present invention also includes a reflector (92, 208, 218 and 222) for reflecting the collimated beam. The reflector (92 and 208) has a plurality of positions for changing the angle of the collimated beam (216) with respect to the reference so that the output optical signal (220) is focused on one of the plurality of output optical fibers (214 and 216).

Method and apparatus for temporal and spatial beam integration

Abstract: A method and apparatus for providing sequential temporal and spatial integration of a collimated non-symmetrical excimer laser beam to optimize the temporal and spatial characteristics of the beam. The temporal integrator comprises a pair of cylindrical lenses spaced along the beam axis by a distance substantially equal to the sum of the focal length of both lenses, and a motor mechanism for rotating the two spaced cylindrical lenses about the beam axis. The spatial beam integrator includes a plurality of prisms distributed about a hollow center, the outlet face of each prism being angled with respect to the body axis of the spatial beam integrator so that portions of the laser beam passing through a given prism are refracted towards the center upon emergence from the outlet face. The spatial beam integrator is preferably rotated about the beam axis at twice the rotation rate of the cylindrical lenses so that the rotated beam emerging from the temporal beam integrator is stationary with respect to the spatial beam integrator. Alternatively, the spatial beam integrator may be rotated at the same rate as the cylindrical lenses, or may be maintained stationary, i.e., not rotated at all.

Parallel-beam coupling into channel-cut monochromators using curved graded multilayers

Abstract: Parabolically bent multilayers with laterally graded period were applied as condensing reflectors to convert divergent X-rays from laboratory X-ray sources into a parallel beam. Two different modes of coupling such a collimated beam into multi-reflection channel-cut monochromators for high-resolution X-ray diffractometry were tested. (i) Parallel coupling (the scattering vector of the mirror reflection is in the plane of the scattering vectors of the monochromator and the sample) enables one to exploit a wider solid angle range of the X-ray source and to gain nearly two orders of magnitude in intensity. (ii) Crossed coupling (the scattering vector of the mirror reflection is perpendicular to the scattering vectors of the monochromator and the sample) delivers a beam with much reduced vertical divergence. This eliminates the line broadening in rocking curve measurements even for strongly tilted samples.

A Monte Carlo estimation of tissue optical properties for use in laser dosimetry.

Abstract: In certain clinical situations, such as photodynamic therapy, light dosimetry should be considered. The propagation of light in tissues is influenced by fundamental or microscopic optical properties, namely absorption mu a, and scattering mu s coefficients, refractive index n and anisotropy factor g. These optical parameters can be determined experimentally by direct and/or indirect methods when tissue macroscopic properties, such as reflectance, transmittance or collimated transmittance from a tissue slab, are measured. The method described in this work provides graphical, and in simple cases analytical, 'inverse' solutions to determine tissue microscopic properties from measured macroscopic parameters. The graphs necessary for this inversion have been calculated and are provided. The method can be applied in either direct or indirect techniques and it does not depend on limitations introduced by assumptions and approximations when using theoretical models. It can also be applied for any tissue type, detector geometry and experimental apparatus. The accuracy of the method is very good over a wide range, unlimited in practice, of values of optical properties. Finally, the results of this work are in good agreement with theoretical and experimental results of other investigators.

Collimator scatter in photon therapy beams.

Abstract: A model for collimator photon scatter calculations is presented. The scatter from a collimating block is separated into two categories, one being the scatter released from photons entering the block through the surface facing the source, and one from photons striking the block tangentially through the side tangential to the beam. Both sources of scatter are analyzed by means of scatter kernels, defined as the scatter fluence distribution from a narrow line beam striking a collimator block. Kernels for both cases are calculated analytically using first scatter models based on Klein-Nishina cross sections including corrections for binding effects and coherent scattering. For 1-MeV primary photons, Monte Carlo calculations (EGS4) are used to show that the collimator scatter is dominated by first scatter. The kernels for the two types of scattering geometries are shown to be related and thus the total collimator scatter kernel can be derived from the kernel for the photons which have entered the block through the source facing side. Using a set of photon beam spectra, the kernels are parameterized as functions of beam energy in a form suitable for implementation in treatment planning systems. The parameterization is used to derive collimator scatter distributions for broad beam geometries of clinical interest. It is shown that scatter from the primary collimator, due to its location close to the beam source, is a major source of scatter that amounts to several percent of the primary fluence. The scatter from beam shaping collimators, however, generally accounts for less than 1% of the primary fluence. Although the beam-shaping collimators generate little scatter, the model used to calculate the resulting dose component is simple to implement and separates the different sources of scattered photons from the accelerator head. The latter provides generality and accuracy in dose per monitor unit calculations in treatment planning. Due to the low magnitude of collimator scatter it is recommended to use the phrase "head scatter" instead of "collimator scatter" when addressing the overall subject of extra-focal radiation from medical accelerators.

Homogenizer formed using coherent light and a holographic diffuser

Abstract: A homogenizer for incident light including: a sheet of embossable material including a one micro-sculpted surface relief structure that (i) controls the direction in which light propagates and (ii) homogenizes light with directionality has been formed by replicating in the sheet of embossable material another micro-sculpted surface structure that (i) controls the direction in which light propagates and (ii) homogenizes light with directionality, the another micro-sculpted surface structure having been formed in a photosensitive medium having a refractive index by: (a) generating random, disordered and non-planar speckle in the photosensitive medium using coherent light, the coherent light having been diffused through a holographic diffuser, so as to define non-discontinuous and smoothly varying changes in the refractive index of the photosensitive medium, the smoothly varying changes scattering collimated light into a controlled pattern with smooth brightness variation; and (b) developing the photosensitive medium. Light that is incident on and directed from the homogenizer is directed to an output area, the homogenizer controlling the direction of light that is emanating from the homogenizer to the output area so as to increase brightness in the output area relative to an area outside the output area.

Compact holographic sight

Abstract: A holographic sight (20) which includes a base (24) having at least one connector (25) for mounting the base (24) on a small arm (22), and a hologram (30) of a reticle pattern, a compact laser light source (32) for illuminating the hologram (30), and a power source (38) for the laser diode (32), each mounted on the base (24). The sight (20) also includes an achromatizer (36) supported in the path of the light beam for reducing shifts in the position of the reticle pattern due to variations in the wavelength of the light beam emitted from the laser diode (32). The sight (20) may further include means for circularizing the elliptical beam emitted from the laser diode (32) to provide a uniform illumination pattern for the hologram (30). A brightness adjuster (44) and position adjuster (40), for varying the brightness and relative position of the reticle, respectively, may also be provided.

Illumination system employing an array of multi-faceted microprisms

Abstract: An optical illumination system comprising a waveguide (16) that accepts light generated by a light source and transmits the light via total internal reflection. Attached on one face of the waveguide is an array of microprisms (28), with each microprism having a light input surface, a light output surface and at least one sidewall (33a) which is tilted at an angle ς from the direction normal to the surface of the waveguide (16) and further comprising at least two planar faces (31, 31a) such that light escapes from the waveguide (16), reflects off the tilted sidewalls (33a) and emerges from the microprism as a spatially directed light source. An array of microlenses may be positioned to accept the output of the microprisms (28) so that the light exiting from the microlenses is a substantially collimated light source. The optical illumination system is advantageous for any application that requires a non diffuse or substantially collimated light source that is both energy efficient and contained in a low profile assembly.

Fluorescence detection apparatus

Abstract: A fluorescence analysis system detects light transmitted from wells in a sample plate One embodiment of the system includes a single light detector A reflector is capable of receiving light from any one of several detection emitters and of reflecting the light toward the light detector One reflector includes a prism which is mounted on a stepping motor The prism is selectively rotated so that it faces each detection emitter in turn The light from several wells in a row is directed toward the light emitter by rotating the prism to face, one-by-one, each of the emitters corresponding to the wells The detection emitters include one end of an optical fiber bundle The other end of each bundle is positioned near the wells, with each bundle positioned by a different well to carry light from that well to the corresponding emitter A collimating lens is positioned between each detection emitter and the rotating prism to focus light from the emitter onto the prism A baffle is positioned between the light detector and the prism Light from a xenon arc excitation lamp is carried by optical fiber bundles toward the sample wells A computerized controller coordinates light detection with the activities of an automated liquid handling system

HeNe-Laser Light Scattering by Human Dental Enamel

Abstract: Knowledge of the optical properties of tooth enamel and an understanding of the origin of these properties are necessary for the development of new optical methods for caries diagnosis and the measurement of tooth color. We measured the scattering intensity functions for HeNe-laser light of 80- to 100- micrometers-thick human dental enamel slabs. The asymmetry factors were calculated to be g = 0.68 at 633 nm. By measuring the collimated beam attenuation, we determined the scattering coefficient to be s = 6.6mm(-1). From Fraunhofer diffraction patterns, obtained from transmission of the laser beam, we calculated the periodicity of the prismatic structure as 5.4 micrometers. We present a model containing scattering by crystals and by prisms. It shows that the prisms are the most important scatterers but that the crystals are responsible for the back-scattering.

Collimation of emissions from a high-power multistripe laser-diode bar with multiprism array coupling and focusing to a small spot

Abstract: Twelve beams emitting from twelve stripes, with 200-microm apertures spaced 800 microm apart, of a 1-cm linear diode array were collimated by a multiprism array consisting of fourteen 800-microm-wide prismlets. The spatial intensity distribution of each beam was twisted around its optical axis through three total reflections in a prismlet, transforming a series arrangement of emitters into a parallel arrangement to prevent overlap of adjacent beams. Collimated beams were focused to a spot of ~200 microm (FWHM).

Catadioptric system and exposure apparatus having the same

Abstract: This invention relates to a catadioptric optical system in which, a large numerical aperture is attained on the image side and, while securing a sufficient working distance, the size of the beam splitter is reduced, thereby attaining a resolution of a quarter micron unit, and an exposure apparatus using the same. In order to form a reduced image of a pattern of a first surface on a second surface, this catadioptric optical system comprises, at least, a first lens group, a beam splitter, a concave mirror having an enlarging magnification, and a second lens group. These constitutional elements of the catadioptric optical system are disposed such that light from the first surface passes through the first lens group, the beam splitter, the concave mirror, the beam splitter, and the second lens group in this order. In particular, the rear-side principal plane of the second lens group is on the second surface side with respect to a light-entering surface of the second lens group on which the light having passed through the beam splitter is incident. In addition, the concave mirror functions to collimate the light having passed through the beam splitter and then make thus collimated light re-enter the beam splitter.

Monolithic integration of vertical-cavity laser diodes with refractive GaAs microlenses

Abstract: Beam collimation and focusing, necessary for practical use of vertical-cavity laser diodes, is achieved by the monolithic integration of lasers with refractive microlenses etched on the back side of the GaAs substrate. For 7 mu m diameter lasers, an original beam divergence of 6.5 degrees was reduced to 1.9 degrees and increased to 12.3 degrees with lenses of focal lengths approximately 220 mu m, and approximately 60 mu m, respectively.

Focussed beam reflectometer for solid and liquid surfaces

Abstract: Neutron reflectometry from liquid surfaces implies reflection in a vertical plane at variable angles and/or variable wavelengths. The TOF wavelength-scan method conventionally used for this kind of geometry offers many technical advantages, but it requires an end position on a beam tube/guide delivering a white beam. Due to space restrictions the reflectometer V6 at BENSC had to be installed using a crystal monochromator. In order to allow variable angle reflection on a horizontal sample surface, a 10-cm high curved monochromator crystal assembly is used. The polarized monochromatic beam is focussed in the vertical plane to the sample at some 3 m distance (angular range of grazing incidence ∼ 1.9°, i.e. a q range of 0–0.09 A −1 at 4.75 A wavelength). The instrument can be used in different modes of operation: (1a) Fixed collimated narrow beam: the beam is defined by two 0.1–1 mm wide horizontal slits between monochromator and sample. (1b) Fixed collimated, wide beam: for small area samples the slit close to the sample is opened up, so that the beam width is determined by the projection of the sample surface. (2) Collimated beam with the beam direction scanned via moving slits: for liquid surfaces. (3) Focussed, fan-like incoming beam and simultaneous observation of the specular reflections with multidetector bank. Modes (1a), (lb) and (2) allow for the investigation of diffuse scattering effects by the use of the multidetector, too.

Optical element and optical device

Abstract: An optical element of this invention converts incident light having a predetermined shape and a predetermined intensity distribution into output light having a desired shape and a uniform intensity distribution. Furthermore, in an optical device of this invention, which has this optical element as a first optical element, a light source radiates a light beam having the predetermined beam shape and the predetermined intensity distribution, the first optical element shapes the beam shape of the incident light beam into one of rectangular, circular, and elliptic shapes having a uniform intensity distribution, and a second optical element gives a collimation to the incident shaped light beam.

Apparatus and method for optically measuring concentrations of components

Abstract: An apparatus and method for optically measuring concentrations of components allow enhancement in measurement accuracy of concentration. The apparatus includes a cell, a light irradiator, a photodetector, and an arithmetic unit. The cell presents different optical path lengths at different locations and is to contain a sample therein. The light irradiator, which includes a variable-wavelength laser generator and a measuring system composed of convex lenses, outputs a collimated, enlarged laser beam, and makes the laser beam incident upon the cell. The photodetector comprises a multiplicity of photodetectors arranged in parallel to the surface of the cell, so that it can detect intensity of rays of transmitted light that have traveled over different optical path lengths at positions of an equal distance from the cell. The arithmetic unit, receiving a signal from the individual photodetectors, calculates concentrations of components in the sample based on optimum optical path lengths for different wavelengths and values of transmitted light at positions of the optimum optical path lengths, and further outputs calculation results.

Packaged optical amplifier assembly

Abstract: A packaged optical amplifier assembly includes an erbium doped silica based optical amplifying fibre (330) co-pumped and counter-pumped by a pair of laser diodes (336) as optical pumps. The optical pumps (336) are each coupled to an end (332, 340) of the fibre (330) by reflection from a dichroic mirror (328), the optical signal being collimated and arranged to propagate unguided between the input (306) and the first end (332), and the second end (340) and the output (346), and optical pump light from each optical pump (336) being collimated and arranged to propagate unguided between the optical pump (336) and the end of the fibre (332, 340) to which it is coupled.

X-Ray focal spot movement compensation system

Abstract: An apparatus for compensating for drift of the focal spot (42) of an x-ray radiation source (118) used in a tomography system is disclosed so as to maintain a primary collimated beam (70) of radiation emanating from the focal spot aligned with target detectors (50) of the tomography system. A second collimated beam (170) of radiation is produced from the same focal spot and directed along a different axis from the first beam. An array (180) of detectors tracks the movement of the second collimated beam and produces signals which are used to reposition the collimators used to collimate the primary beam so as to maintain the primary beam substantially aligned with the target detectors.

Performance characteristics of a dual head SPECT scanner with PET capability

Abstract: Using a dual detector scanner in coincidence avoids many of the factors leading to poor performance in a SPECT system collimated for 511 keV. On the other hand, it would be unrealistic to expect the same good performance achieved with a dedicated PET scanner. It was therefore the goal of the present investigation to develop an ECT scanner which provides the same performance achieved with present SPECT scanners when operated as a SPECT system for imaging single photon emitters and which provides clearly superior performance to a 511 keV collimated SPECT scanner when operated in the coincidence mode.

Astigmatic gradient-index elements for laser-diode collimation and beam shaping

Abstract: For the conversion of light from edge-emitting laser diodes into symmetric laser beams two main tasks have to be performed: collimation and beam shaping. Generally these two jobs are performed separately. Because of the inherently different divergence angles of the emitted light, collimation with astigmatic lenses generally results in a beam with an elliptically shaped amplitude distribution. This asymmetry has to be compensated for by an anamorphic imaging step to obtain the desired spherical beam profile. It can be advantageous to combine both jobs in one element. We demonstrate the design, the fabrication, and the application of refractive gradient-index elements, which allow one to perform both jobs with a single element. Our astigmatic lenses were fabricated by silver–sodium ion exchange in glass.

Optical head device

Abstract: A light beam emitted from a semiconductor laser (114) element is collimated by a collimating lens (102), and is applied to an optical disk (105) through a polarizing holographic beam splitter (181), a λ/4 plate (115) and an objective lens (103), a light beam reflected by the optical disk is applied to the polarizing holographic beam splitter and is diffracted Diffracted light beams of +1st order and -1st order are applied to two photodetectors (191, 192), and a focus error signal is obtained on the basis of the diffracted light beam of +1st order and a tracking error signal is obtained on the basis of the diffracted light beam of -1st order

Fluorescence imaging system employing a macro scanning objective

Abstract: Fluorescence imaging system includes objective (21) which is achromatic and has an external entrance pupil (29), serves as a condenser for the system, and positioned above sample (23) in close proximity to one another. Laser (18) directs collimated light (19) to scan device (20) located at entrance pupil (29). Scan device (20) reflects, refracts, or diffracts light through objective (21) to illuminate a spot (22) on the sample's surface, and illuminates a line or an area on the sample surface by varying the angle of laser light into objective (21). Sample (23) emits fluorescent light (24) in response to the illumination. The fluorescent light (24) is collected by objective (21) and passes through the system along the path of the illumination light. Wavelength-discriminating dichroic filter (25), placed along the optical axis between laser (18) and objective (21), directs fluorescent light (24) onto photodetector (26) to produce a signal representing the sample surface emitting the fluorescent light. Display (37) displays the digitized data in a raster format.

Threaded parts inspection device

Abstract: An opto-electronic, threaded parts inspection device The device includes a source for generating a thin, planar beam of collimated light which is disposed on one side of a parts carrier The laser light beam is rotatable about two axes, normal to one another and both normal to the longitudinal axis of parts passing through the beam A sensor unit is disposed on the other side of the parts carrier so that the light beam falls thereupon The threaded parts inspection device can be adjusted to pass light over different features of the threaded parts as they are moved past the inspection device by the parts carrier By measuring how much of the light is interrupted by the profile of the passing threaded parts, it is possible to detect deviations in the pitch angle and major and minor diameters of the threaded workpieces

Laser surgical probe for use in intraocular surgery

Abstract: A novel microfocusing laser surgical probe for use in intraocular surgery combines a high power laser with a gradient index (GRIN) lens to provide sufficient energy density at a focal point inside the eye to achieve laser induced breakdown and destroy fibrovascular membranes resulting from diabetes and other diseases. The gradient index lens steeply focuses the light close to its end so that the energy density of the light widely diverges beyond the focal point to reduce the potential for damage to the underlying retina. The gradient index lens also focuses the light far enough from the end of the lens to prevent damage to the lens itself. In a first embodiment, an open transmission line couples a YAG laser to a gradient index lens so that the light is still collimated when it strikes the lens. This first probe may be articulated by the use of mirrors or other optical devices. In a second embodiment, a tapered optical fiber couples a YAG laser to a gradient index lens to increase the maneuverability of the probe. An air gap separates the end of the optical fiber from the lens to better couple the light energy output from the optical fiber to the lens.