A Holographic Interferometer For The Study Of Transparent Media

Holographic optical elements (HOEs)are more and more commonly used in all kind of optical design. When used in interferometry, holographic optics not only make it possible to avoid the use of expensive optical precision components, but allow under certain conditions a "holographic null correction" for all optical aberrations. In OIP, a holographic interferometer was built with the aim of studying transparent media. Convection phenomena in transparent fluida can be observed in real time; when using a complementary pair of lenses, deviations of a copy lens from a master one can be visualized. The interferometer can have a rather large visualization area (almost 100mm x 100mm), and has the possibility to zoom in onto the object. The image may be visualized by means of a CCD-camera. The interferometer operates entirely with HOE-technology, no conventional lens or beamsplitter is used, with exception for the microscope objective to produce a diverging laser beam. Four HOEs in dichromated gelatine are used to realize interferograms in a Mach-Zehnder configuration. The first acts as a holographic beamsplitter to produce a reference and an object beam; the second and the third are diffraction elements which convert the diverging object beam into a collimated one and back into a converging beam. On the last HOE a rest pattern has been recorded. The interference of an "active" object beam with the holographic "reconstructed" one produces the real-time interferogram corrected for optical aberrations of the system. The interferometer operates with an Ar-laser (λ=514nm) at this moment but will be modified to operate with a small built-in HeNe-laser.