19 July 1996 Computer-controlled active phase stabilization for electronic holography
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Electronic Holography or ESPI (electronic speckle pattern interferometry) is widely used for deformation analysis of complex, 3D surfaces. The sensitivity is well below 1 micron and deformations can be observed in real time. Any of those methods require either a constant phase between the interfering beams or a defined phase oscillation about a stable mean value or another controlled phase variation. The use of active control loops enhances the degree of phase constance, facilitates the defined variation of phase and permits a considerable reduction of cost for passive stabilizing installations, thus permitting the operation of an ESPI camera in an industrial production environment. By the use of a computer as active controller, autocalibration becomes feasible, a variety of stabilization parameters and algorithms can be tested easily, parameter optimization can be automized and phase perturbations can be recorded. User- guidance for failure diagnosis enhances further the user friendliness of the system. All this has been accomplished without any special or high-performance equipment, which allowed a relatively cheap realization. With an interferometer and photodiode amplifier as phase detector, a PC with a multi-I/O board and a piezo-mounted mirror with a simple, self-built driver as phase actuator, phase stabilization up to the kHz regime was demonstrated, limited by the mechanical resonances of the optical setup. The complete software has been developed by the author, using Oberon as language, operating system and development system.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Frank Hrebabetzky, "Computer-controlled active phase stabilization for electronic holography", Proc. SPIE 2861, Laser Interferometry VIII: Applications, (19 July 1996); doi: 10.1117/12.245162; https://doi.org/10.1117/12.245162


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