Collimated light

About: Collimated light is a research topic. Over the lifetime, 17272 publications have been published within this topic receiving 180982 citations.

The trouble with CTD100.

Abstract: The computed tomography dose index (CTDI100) is typically measured using a 100 mm long pencil ion chamber with cylindrical polymethyl methacrylate (PMMA) dosimetry phantoms. While this metric was useful in the era of single slice CT scanners with collimated slice thicknesses of 10 mm or less, the efficiency of this metric in multi-slice CT scanners with wide (40 mm) collimated x-ray beams is unknown. Monte Carlo simulations were used to assess the efficiency of the CTDI100 parameter for wider beam collimations. The simulations utilized the geometry of a commercially available CT scanner, with modeled polyenergetic x-ray spectra. Dose spread functions (DSFs) were computed along the length of 12.4 mm diam rods placed at several radii in infinitely long 160 mm diam (head) and 320 mm diam (body) PMMA phantoms. The DSFs were used to compute radiation dose profiles for slice thicknesses from 1 to 400 mm. CTDI00 efficiency was defined as the fraction of the dose along a PMMA rod collected in a 100 mm length centered on the CT slice position, divided by the total dose deposited along an infinitely long PMMA rod. For a 10 mm slice thickness, a 120 kVp x-ray spectrum, and the PMMA head phantom, the efficiency of the CTDI00 was 82% and 90% for the center and peripheral holes, respectively. The corresponding efficiency values for the body phantom were 63% and 88%. These values are reduced by only 1% when a 40 mm slice thickness was studied, so the use of CTDI00 for 40 mm wide x-ray beams is no less valid than its use for 10 mm beam widths. However, these data illustrate that the efficiency of the CTDI100 measurement even with 10 mm beam widths is low and, consequently, dose computations which are derived from this metric may not be as accurate as desirable.

An interferometer for atoms.

Abstract: We have demonstrated an interferometer for atoms. A three-grating geometry is used, in which the interfering beams are distinctly separated in both position and momentum. We used a highly collimated beam of sodium atoms with a de Broglie wavelength of 16 pm and high-quality 0.4-\ensuremath{\mu}m-period free-standing gratings which we fabricated using a novel method. The interference signal is 70 counts/s, which allows us to determine the phase to 0.1 rad in 1 min. Applications of atom interferometers are briefly discussed.

Design and performance of a refractive optical system that converts a Gaussian to a flattop beam.

Abstract: A system of two aspheric lenses is described, which efficiently converts a collimated Gaussian beam to a flattop beam. Departing from earlier designs, both aspheric surfaces were convex, simplifying their fabrication; the output beam was designed with a continuous roll-off, allowing control of the far-field diffraction pattern; and diffraction from the entrance and exit apertures was held to a negligible level. The design principles are discussed in detail, and the performance of the as-built optics is compared quantitatively with the theoretical design. Approximately 78% of the incident power is enclosed in a region with 5% rms power variation. The 8-mm-diameter beam propagates approximately 0.5 m without significant change in the intensity profile; when the beam is expanded to 32 mm in diameter, this range increases to several meters.

LED collimation optics with improved performance and reduced size

Abstract: An LED module that includes an LED (light-emitting diode) and a rotationally symmetrical, bowl-shaped collimator lens is provided. The collimator lens has an inner refractive wall, an outer reflective wall, a first surface having an entrance aperture with a recess in which the LED is situated and which collimator lens is also provided with a second surface from which light generated by the LED emerges, the normal to the surface extending substantially parallel to the axis of symmetry of the lens, and the LED module also includes one or more of the following structures: (1) a conic wall portion of the recess of the inner refractive wall at the entrance aperture that includes a curved portion, and an outer reflective wall so configured in accordance with the structure of the inner refractive wall to achieve substantial collimation of a source of light at the entrance aperture; and/or (2) a first surface of the lens that is recessed away from the LED source; and/or (3) two surfaces of said refractive wall between which the refractive function of said refractive wall is divided. The LED module offers an improvement in the performance of the Flat top Tulip Collimator disclosed and claimed in our co-pending application Ser. No. 09/415,833 in terms of reduced size, beam divergence, beam uniformity, and to some degree efficiency. Moreover, it allows a wider variety of choices in optimizing various performance characteristics, and this in turn allows more flexibility in the structure design.

A High Intensity Source for the Molecular Beam. Part I. Theoretical

Abstract: In a standard molecular beam source the maximum attainable intensity in the collimated beam is limited first by the effusion rate through the oven slit, which must be made sufficiently narrow to attain free molecule flow, and second by unfavorable geometrical factors encountered in selecting a collimated beam from random initial velocities. This paper will propose that the first slit be placed in the flow from a miniature high velocity nozzle coaxial with the final beam. The nozzle converts part (∼¾ for a Mach number of 4 in the design for air to be presented) of the random translational and internal energy of the oven gas into directed mass motion. The mass motion provides an initial rough collimation, which improves both the effusion rate and the geometrical factors, indicating a considerable possible beam intensification (by a factor of ∼75 in the sample design). The velocities of the molecules in the final beam are grouped about the initial mass velocity which provides a partial velocity selection.In ...