Laser focal spot measurements

Abstract

The focal spot size for a high-powered neodymium laser has been determined by measuring the energy passing through pinholes of various sizes and also, by photographing the focused spot. A comparison of the two methods indicated that the photographic method could give misleading results. The spot size was also determined by measuring the absorbed energy by target pellets of various sizes. This method always gave a smaller value than the pinhole method. The difference was attributed to plasma effects.