A SIMPLIFIED MULTIWAVELENGTH ESPI CONTOURING TECHNIQUE BASED ON A DIODE-LASER SYSTEM

A simplified multi-wavelength ESPI contouring technique using a diode laser source has been demonstrated to be a useful tool in the shape measurement of an object. Unlike other type of two-wavelength ESPI contouring systems, the technique described in this paper does not required a master-wavefront illumination and the conjugate condition imposed on the reference beam, the experiment procedure is, therefore, considerably simplified. Instead of modulating the injection current of the diode laser, the alternation of wavelength is achieved by adjusting the temperatures applied to the laser diode so that the problem of visibility reduction due to intensity variations of speckle pattern can be overcome. In addition, the decorrelation effect due to the wavelength change in this specific ESPI contouring system is also analyzed quantitatively in order to show the limitations of this technique on practical applications. Contour fringes of a pyramid, as an example, are obtained from experiments, which are in agreement with the theoretical analysis.