Real-time double-exposure interferometries using a self-pumped conjugator with Cu:KNSBN crystal

Abstract

We describe real-time double-exposure interferometies with an internally self-pumped conjugator employed by a photorefractive crystal Cu:KNSBN. The device offers many advantages as a nondestructive testing device: elimination of the effects of turbulence or optical distortion, self-alignment, high reflectivity, and so on. In our experiment, an argon ion laser beam at 0.515 μm is expanded and collimated to a 4-cm diameter beam size. The collimated beam passes through a transparent test object and is focused into a photorefractive crystal Cu:KNSBN with 51% phase-conjugate reflectivity. A beam splitter separates the conjugate beam generated by the self-pumped conjugator, and a CCD camera receives the output interfering fringes formed in double exposure. In the first exposure, the image of the test object is conjugated by the self-pumped conjugator. Applying force to the test object, an internal shape change occurs. The image that its phase has changed is written in the crystal again. Th-en the interfering fringes are received by the CCD camera and are analyzed by a computer. Using this device, the defects of the test object can be inspected in real-time.