Laser cavity power increases caused by reflections from workpiece surfaces

Abstract

Inconsistent increases in laser power were observed during laser brazing studies conducted on high reflectivity materials. These increases are due to reflected laser light reentering the lasing cavity. A high-speed pyrometer recorded the energy passing through the 99% reflecting rear mirror of the laser cavity. With no surface melting occurring, the main variables affecting this phenomenon are reflectivity of material, angle of incidence between surface and laser beam, position of focal point, energy density at workpiece, and surface roughness. A molten aluminum surface reflected significant amounts of laser light back into the lasing cavity while mild steel did not.