Electronic speckle pattern interferometry with a microstructured refractive optical element and compact interferometer based on this method

Electronic speckle pattern interferometry (ESPI) suits very well for nondestructive optical testing of products and components. Most of the currently existing methods and devices for out-of-plane sensitive ESPI require a big number of optical elements which are difficult to align. A novel method of ESPI for out-of-plane deformation and vibration measurements is introduced. In the proposed method a microstructured refractive optical element (MROE) is used which serves as beam combiner of object wave and reference wave guiding them inline, along the optical axis of the camera objective to the camera sensor. This MROE contains two groups of microstructures which deflect each ESPI wave (ESPI object and reference one) exactly on-axis (in one variant of the method only one group is sufficient). The reference wave is generated by reflective scattering of the laser radiation on an arbitrary surface. Different surfaces were tested in our experiments and in every case high quality ESPI evaluations were obtained. For example a simple sheet of white paper or a colour photograph serving as a reference surface suit very well. We present an innovative ESPI device utilizing a MROE and experimental results obtained by means of this device. The method and the device based on this method can be used among others in microelectronic industries in development and quality testing of components, integrated circuits and printed circuit boards.