<title>Speckle reduction methods for laser line gages</title>

Abstract

Speckle caused by the use of laser sources is a well known phenomena. For some applications, the presence of the speckle is used as part of the method, but in others it is purely a source of noise. In the case of line based laser gages, speckle is typically of considerable concern. Certainly, using white light sources or LEDs with short coherence is one way around this problem, but such methods also loose some of the valuable properties of laser line projection such as very narrow lines, the ability to create multiple lines by diffraction, and high signal to background through the use of bandpass filters to view only the laser wavelength. There have been a number of valuable tools introduced that help reduce the problem of speckle from laser sources, without giving up all the advantages of the laser itself. This paper reviews the pros and cons of a number of these methods, and suggests a specific set of tools that are specific to laser line projection.