R. Tremblay

Linear, annular, and radial focusing with axicons and applications to laser machining

New optical combinations of axicons and axicons with spherical mirrors and lenses suitable for laser machining are presented. Linear and annular focusing, coaxially and radially to the laser beam, are possible. Most combinations allow continuous adjustment of exit beam parameters, focal line length, focal ring diameter, and magnification, by varying the relative position of one of the axicons. Potential new laser applications are also discussed in relation to these optical devices.

Mechanical properties and microstructure of new magnesium-lithium base alloys

Magnesium-lithium base alloys containing aluminum, silicon and rare-earth additions have been prepared by melting and solidification in a low-carbon steel crucible, homogenized at 350°C and extruded at the same temperature. The distribution of alloying elements in homogenized specimens was determined and the microstructure of these alloys characterized. The mechanical properties were measured and compared with those of similar alloys.

Focal depth of a transmitting axicon

The transmitting axicon is examined for the axial field distribution of a regular axicon when the incident wave is plane and uniform, and when it has a gaussian irradiance distribution. In the microwave region, the focal depth of an axicon does not differ very much from that of a perfect lens. In the visible region, the axicon possesses a much greater focal depth, which can be greatly changed by changing the curvature of the slanting side of the axicon. For an axicon with a straight slanting side and small height, when a gaussian incident wave is used, the irradiance at the principal focus varies inversely with the focal length.

CdS microcrystallites‐doped thin‐film glass waveguides

Thin films of Corning 7059, glass doped with CdS (2%–4% by weight) microcrystallites, with diameters presumably larger than 6 nm, were fabricated using rf sputtering technique. Sharp optical cutoff near 500 nm is visible on the absorption spectra of the films. Both Raman and absorption spectra presumably reveal the presence of size effects. At λ=632.8 nm the refractive index of the films varies from 1.55 to 1.69 depending on rf power. Propagation losses for TE0 guided mode are about 10 dB/cm.

Nonlinear optical properties of thin‐film waveguides deposited onto semiconductor‐doped glasses

We report the fabrication procedure and properties of optical nonlinear guided wave structures consisting of a thin film of Corning 7059 glass deposited on the surface of CdSxSe1−x doped glass. The limiting action in power‐dependent prism coupling in the structures produced is described. The nonlinear prism coupling is used to evaluate both the sign and the steady‐state value of the intensity‐dependent refractive index of the substrate. For the glass used the nonlinearity is negative and its value is in the range of 10−10 m2/W.

Influence of the divergence of a laser beam on the axial intensity distribution of an axicon

Abstract The importance of the laser pulses wavefront divergence on the intensity distribution of the focalized energy along the axicons axis is emphasized by solving the Kirchkoff-Fresnel integral. Furthermore, results of these calculations suggest a simple mean to vary this intensity distribution.

Characterization of SiCp/2024 aluminum alloy composites prepared by mechanical processing in a low energy ball mill

Abstract In the present work, SiC p /2024 composite powders were produced by low energy ball milling a mixture of centrifugally atomized 2024 particles and β -SiC reinforcements having a size range between 2 and 6 μm. The experimental parameters studied were the milling time (between 1 and 24 h) and the volume proportion of β -SiC in the starting powder mixture (between 5 and 35%). These SiC p /2024 composite powders were consolidated by hot extrusion using optimized processing parameters. The microstructure of the extruded composites showed a uniform distribution of β -SiC particles in the 2024 aluminum matrix. Moreover, the mechanical properties (yield strength and Young’s modulus) improved with the SiC content although some reduction in ductility was observed.

Boundary-Diffraction-Wave Theory of Cascaded-Apertures Diffraction*

Systems of cascaded circular apertures may be built to focus electromagnetic waves if the difference (d) between the Fresnel numbers of any two apertures pertaining to two points (A and B) is an even number. With a point source at A, the spherical incident wave will be focused to B. In general, the irradiance at B (principal focus) is roughly proportional to (n±1)2 where n is the number of apertures; the plus sign is used when the Fresnel numbers are odd integers, and minus when even. A system of a few apertures with d = 0 can focus waves over a wide range of frequencies, though the actual irradiance at the principal focus is a function of frequency. A condition to maximize the irradiance at the principal focus has been found. Theoretically such systems have been analyzed by the boundary-diffraction-wave theory generalized by Miyamoto and Wolf. Analytical expressions for the diffraction wave amplitude have been obtained for axial and off-axial points. when the iteration method of Fox and Li is also applicable, the two theoretical results agree very well with each other. Experimental data obtained agree well with the theoretical results.

Guiding of atoms in a travelling-wave laser trap formed by the axicon

Abstract The possibility of collimation and guiding of atomic beams in the radiation-pressure trap formed by the laser field focused by the glass cone is examined. We conclude that such configuration could be used for guiding collimated beams and acts as the velocity selector for atoms. This is due to the long focal line of a small diameter produced by the axicon.

SiCp/Mg composites made by low-energy mechanical processing

AbstractComposite powders containing 10, 20 and 30 vol% SiCp particulates in a Mg matrix were produced using mechanical processing. A small laboratory ball mill was used to achieve a uniform distribution of the reinforcements in the Mg matrix. The particle size distribution and the microstructure of the composite powders were studied as a function of processing time. Based on these observations, four successive stages of processing were identified. It was shown that a homogeneous distribution of SiC in a Mg matrix may be obtained under low-energy milling conditions. The influence of milling time and concentration of SiCp on tensile strength, stiffness, elongation and impact properties of rods extruded from the resulting composite powders were investigated. The hardness of SiCp/Mg composites was also evaluated to determine the influence of SiCp content.