Infrared holographic recording in lithium tantalate crystals by means of the pyroelectric effect

Abstract

Infrared holographic recording in a two-step process is demonstrated in stoichiometric iron-doped lithium tantalate crystals. Through absorption of two intersecting infrared pulses (A = 1064 nm) a temperature grating and thus a modulated pyroelectric field build up. Free electrons, excited by homogeneous light of a shorter wavelength (lambda = 532 nm) drift in this field, and a phase hologram is stored that can be read nondestructively. The change in refractive index depends mainly on the absorption coefficient at the wavelength of the recording light and on the intensity of the infrared light. The proposed method may be extended to telecommunication wavelengths by choice of suitable dopants.

Defect–Domain Wall Interactions in Trigonal Ferroelectrics

“…Li -based polaron hopping has an activation energy between 0.49-0.9 eV (68-72) for LiNbO 3 and between 0.5-0.90 eV for LiTaO 3 (73,74). Ionic conductivity becomes prominent at higher temperatures (∼125 • C), with an activation energy of ∼1.1-1.23 eV (75,76).…”

Two-Step Recording in Photorefractive Crystals

“…However, the relatively large optical activation energy of small polarons is a serious difficulty. For this reason, a further method has been suggested based on the pyroelectric effect [31]. As demonstrated earlier [32], this effect also provides a charge driving force which may be utilized for two-step processes.…”

“…To obtain sufficiently large pyroelectric fields, a considerable absorption at the IR recording wavelength is required. The method has been demonstrated with stoichiometric LiTaO 3 : Fe crystals that contain only very few Nb 4þ Li polarons [31]. IR pulses of a Nd:YAG laser (duration 7 ns, l ¼ 1:06 mm) generate the pyroelectric field and a homogeneous green pulse (second harmonic generation, l ¼ 0:53 mm) excites electrons.…”