Surface contouring in a video frame by changing the wavelength of a diode laser

Two-wavelength surface contouring systems using either electronic speckle pattern interferometry (ESPI) or an electronic holography procedure by modulating directly the current of a laser diode are reported. Two states of the test object corresponding to each wavelength of the laser can be recorded in both fields of a single video frame. This is achieved by synchronizing the interline-transfer CCD (charge-coupled device) camera in a noninterlaced mode to the current modulation of the diode. Environmental disturbances at low frequencies such as air turbulence, slow object drift and stress in the object have no influence on the measurements. The test object does not need to be on a vibration isolated table. Quantitative experimental results are presented. (C) 1996 Society of Photo-Optical instrumentation Engineers.