Michael W. Sasnett

Beam characterization and measurement of propagation attributes

Beam waist size, waist location and the times-diffraction-limit number, M2, are the most basic and fundamental parameters describing the propagation characteristics of laser beams. This information is useful in the engineering development of lasers and beam delivery systems, and provides a meaningful way to monitor, compare and control quality both in the manufacture and in the application of laser devices. An instrument that allows real-time access to this information is described.

Techniques for measuring the moments of laser beam irradiance distributions

Methods for determining the position and diameter of a laser beam are discussed. Of particular interest is a method that makes use of optical filters having transmittance that varies with one or more spatial coordinates. With the appropriate distribution of transmittance, a simple measurement of the fractional power transmitted by a particular filter can, after proper scaling, directly give beam position and beam diameter.

Effect of pump laser mode quality on the mode quality of the cw dye laser

Measurements with a beam propagation analyzer of the mode characteristics of the cw dye laser as a function of pump laser input power and mode quality, indicate that the thermal lens (of cylindrical form, induced by pump absorption in the flowing dye) controls the dye beam mode quality. At high pump power, if the dye laser resonator is adjusted for maximum output power, a degraded quality dye mode results, which is lower for lower quality pump modes. When the dye resonator is adjusted for maximum output power density (a direct output of the analyzer), typically a 12% power drop is sufficient to produce a nearly perfect beam quality (M2 < 1.1) and a +27% increase in beam power density for a multimode pumped dye laser.

In-situ measurement of output coupler absorption using a beam propagation analyzer

Optical characteristics of the output coupler in a high-power CO2 laser can be measured while the optic is in the laser and functioning normally. This is done by using a beam propagation analyzer to measure the rate at which the beam waist location changes with increasing beam power. The characteristics that can be measured with this technique include the fraction of beam power absorbed by the optic and its radius of curvature.