Phase-Shifting Holography Using Bragg and Non-Bragg Orders in Photorefractive LiNbO3

The refractive index (RI) of a material can be changed due to several effects such as the optical Kerr effect and the photorefractive (PR) effect. The use of PR materials for implementing real time phase shifting holographic interferometry is discussed in this work. Holographic interferometry (HI) is an effective and rich method for measuring very small (order of a wavelength) displacements and it is widely used for non-destructive testing. Bragg and non-Bragg orders can be generated during two-beam coupling in a PR material due to the induced RI in the material and can be used to retrieve the phase information of the object, as well as the deformation of the object. In previous work, we have shown how object deformation can be determined from monitoring a Bragg order. Furthermore, we have reported on preliminary experiments for determining the depth profile of an object and provided approximate analytic solutions for the Bragg and non-Bragg orders for the case of interacting plane waves. In this work we numerically calculate the exact solutions for the intensities of the Bragg and non-Bragg (higher orders) orders for the case of two incident plane waves, as well as for the case when one of the incident fields is a profiled or image bearing beam. We show how the information from the diffracted order intensities can be used to determine the amplitude and phase of the 3D object. Similarities with phase shifting holography will be discussed. Numerical results are compared with experimental results performed using lithium niobate as the photorefractive recording material. Key words: Photorefractive materials, Photorefractive effect, Bragg and non-Bragg ordershttps://ecommons.udayton.edu/stander_posters/1486/thumbnail.jp