Image plane digital holographic microscope for the inspection of ferroelectric single crystals

Abstract. One of the most important characteristics in the research and application of ferroelectric materials is the appearance of the domain patterns, which take place in phenomena such as ferroelectric phase transitions or ferroelectric switching. The ability to visualize domains is the key factor that enables the progress in the research of these extremely interesting phenomena. However, the three-dimensional visualization of the ferroelectric domain patterns in the whole volume of the ferroelectric single crystal is not a straightforward task. We present the optical method, which allows the acquisition of quantitative and qualitative data substantial for the ferroelectric domain research. The principle of the method is based on image plane digital holographic microscopy (DHM). We used DHM setup outcomes from a Mach–Zehnder type of interferometer and phase-shifting digital holography. The studied specimen is a single crystal of barium titanate. It is demonstrated that the use of solid-state thin-film transparent electrodes of indium tin oxide greatly reduces the unwanted wavefront distortions, which are frequently produced in liquid electrodes. Using this approach, it is possible to greatly improve the DHM measurements in low applied electric fields. Thanks to the properties of the setup, real-time observation of domain walls growth or existing patterns of the ferroelectric crystal is possible.