Sign of the dominant charge carriers in photorefractive crystals determined by a phase-locked holographic technique

This work presents a holographic method based on active feedback techniques for determining the sign of the dominant charge carriers in photorefractive materials. A two-step procedure is proposed: first off a stationary phase-locked hologram is recorded; an electric field normal to the grating layers is then applied to the material, thus producing a running hologram. The sign of the charge carriers is determined by comparing the direction of the applied field with the direction of the hologram movement, which is known through the automatically attached light pattern. The method can be applied from highly photoconductive to highly insulating materials. Furthermore, no information on any material parameter is required. The method is validated by a set of holographic experiments using a Bi<inf>12</inf>TiO<inf>20</inf> crystal that has electrons as the majority photocarriers.