Speckle Interferometry Based On Speckle Correlation Modulation

As an important branch of optical measurement,speckle interferometry has been widely used in nondestructive testing of the surface deformation.When the deformation increases to a certain extent,the fringes contrast decrease,even the fringes disappear,which leads to the decorrelation phenomenon.The decorrelation phenomenon affects the measurement accuracy and measurement range of speckle interferometry,which restricts the application of speckle interferometry.The thesis presents a method based on speckle correlation modulation,which increases the correlation size,therefore improves the correlation of the speckle field,extends the longitudinal coherent area,restrains decorrelation phenomenon by placing the cubic phase mask in the speckle interferometry system.This thesis includes the following works:1.Presents the method using phase modulation to suppress the decorrelation phenomenon and demonstrate the feasibility.On the basic of analyzing the relationship between speckle correlation and speckle size,researches on how phase modulation extends the transverse and the longitudinal speckle size.Verifies that phase modulation improves the correlation of the speckle field by extending the speckle size,therefore suppresses the decorrelation phenomenon.Demonstrates phase modulation doesn't affect the measurement results at the same time.2.Researches on how phase modulation affects the correlation of the speckle field.Builds phase modulation speckle interferometry system,calculates the speckle field in the image plane according to the propagation rules of the light in free space and phase transformation of optical elements.Reaearches on the effects of phase modulation on the transverse and the longitudinal speckle size.Experiment results consistent with simulation results well.3.Designs an optical system to verify the use of phase modulation in speckle pattern interferometry.Builds speckle interferometry system based on a 4f system to detect the deformation of the rubber.The experiments results show that the phase modulated speckle interferometry system has a deeper longitudinal coherent area and better fringes contrast,therefore it can suppress decorrelation phenomenon to some extent.On the basic of this,discusses the influence of the parameters of the phase modulation system on modulation effects.