Comparison of CW High-power Nd:YAG Lasers and Beam Characterization Methods

摘要

Good process control in laser materials processing demands quantitative knowledge of how laser and optics-delivery designs vary beam characteristics; that is, how does spotsize vary with changes in laser power, lens types and sizes, fiber diameter and type, and laser system. Laser beam power, spot diameter, minimum focus location and mode structure are related to surface absorption, temperature and process quality, affecting average irradiance and focusing of the spot. Beam stability during power changes has consequences in closed loop process control and automation. Continuous wave Nd: YAG lasers from different manufacturers, with different resonator design, using both hard optics and fiber delivery were characterized using Prometec and Precitec scanning profilometers and additional analog spotsize measuring methods. Focused spot size, depth of focus, effective focal lengths and beam quality (M~2) were measured for various power levels, lens and focal lengths. Results for the different laser systems are presented and compared. Comparative measurements between beam profilers and additional beam characterization methods and their relative merits are discussed. Power related changes in spot size are quantified; impact on laser materials processing qualification, process quality, and control are discussed.