Spotsize measurements of a focused CW Nd:YAG laser

The minimum spotsize, beam quality or M{sup 2}, and Strehl ratio of a focused laser beam provide different measures of the performance of the laser/optic system. Focusing lenses typically used to provide irradiances sufficient to cause melting and/or vaporization of metals or ceramics typically exhibit considerable spherical aberration, and thus limit the minimum spotsize attainable for a given lens at a specific laser power. The purpose of this work is to quantify the increase in the minimum spotsize and decrease in Strehl ratio of a focused materials processing CW Nd:YAG laser caused by laser cavity heating and spherical aberration introduced by the focusing lens. Minimum spotsize was determined by making several measurements of spotsize along the propagation direction using a scanning aperture system, and fitting the data to the laser propagation equation. These measurements were performed for 6 plano-convex lenses of different focal lengths, using laser powers ranging from 500 to 1500 watts. A nonlinear variation of spotsize with laser power and with focal length was observed for the lenses and power levels tested

Two powder stream diagnostics for laser deposition processes

The velocity, density, and mass flow of particles suspended in a subsonic gas stream are important aspects of plasma spray and laser deposition processes. This paper will focus on two optical diagnostic techniques applied to the metal powder streams out of a powder feeder and into a new nozzle developed specifically for such applications. An important characteristic of the new powder nozzle is that it produces a very small column (approximately I mm diameter) of powder which can be used for small focus laser deposition and cladding processes. Laser Doppler Velocimetry (LDV) was applied to the nozzle`s output to better understand the kinetic parameters (velocity and spatial density) of exiting particles. Optical scattering of the powder stream was used to measure the total mass flow into the nozzle. Different light scattering detector scenarios applied to the input powder stream were used to identify signals useful for mass flow feedback control. Both of these techniques have the advantages of being fast, noninvasive diagnostics of the powder flow characteristics, and with a well established theoretical framework. Together, or individually, these diagnostics can provide real-time control or post-process analysis of the powder stream