Surface roughness is commonly used to characterize material microstructure during processing, and accurate measurement of surface roughness is the premise and foundation of machining. Therefore, online non-destructive measurement of surface roughness based on the laser speckle method has become a hot issue in recent research. The improvements in surface roughness measurements based on the laser speckle method are systematically reviewed. Theory of speckle formation is introduced. The statistical properties of the speckle patterns including first-order statistical properties and second-order statistical properties are directly related to surface roughness. Surface roughness measurements based on the laser speckle method are roughly divided into the speckle contrast method, speckle correlation method, and fractal method. The three methods are described in detail, and an extensive comparison among all the methods is presented. The recent progresses and application of surface roughness measurements are reviewed. Finally, surface roughness measurements based on the laser speckle method are prospected and summarized.

Surface roughness is commonly used to characterize material microstructure during processing, and accurate measurement of surface roughness is the premise and foundation of machining. Therefore, online non-destructive measurement of surface roughness based on the laser speckle method has become a hot issue in recent research. The improvements in surface roughness measurements based on the laser speckle method are systematically reviewed. Theory of speckle formation is introduced. The statistical properties of the speckle patterns including first-order statistical properties and second-order statistical properties are directly related to surface roughness. Surface roughness measurements based on the laser speckle method are roughly divided into the speckle contrast method, speckle correlation method, and fractal method. The three methods are described in detail, and an extensive comparison among all the methods is presented. The recent progresses and application of surface roughness measurements are reviewed. Finally, surface roughness measurements based on the laser speckle method are prospected and summarized.