Lasers and Optics The role of carrier mobility in holographic recording in LiNbO3

Abstract. We investigate the role of carrier mobility in holo-graphic recording in LiNbO3 crystals. Both normal holo-graphic recording (single wavelength, single trap) and two-center recording are considered, and the differences between the performances of the two methods are explained. We show that increasing mobility by using stoichiometric crystals or by doping with Mg does not improve sensitivity considerably, but does reduce M/ # by at least one order of magnitude. PACS: 42.40.-i; 42.40.Pa; 42.40.Ht Volume holographic storage systems are tried and tested with photorefractive crystals as the recording medium [1]. In such systems, the inhomogeneous illumination created by the interference of the reference and signal beams excites charge carriers from impurity levels into the conduction or va-lence bands, the charge carriers migrate and they are trapped by empty impurities elsewhere. A space-charge field builds up and modulates the refractive index via the electro-optic effect. The important material properties are sensitivity (S), dy-namic range (M/#) and persistence (or non-destructive read-out). For several years, lack of persistence was the major drawback of holographic storage in photorefractive crys-tals, and several methods (thermal fixing [2], electrical fix-ing [3], two-photon recording [4], frequency-difference holo-grams [5] and readout with wavevector spectra [6] ) were proposed to solve this problem. More recently, two-center holographic recording was proposed and demonstrated [7, 8]. Two-center recording makes storage of persistent holograms possible without sacrificing the dynamic range and sensitiv-ity considerably [9]. The sensitivity of the widely used con-gruently melting LiNbO3 crystals, however, is still not very ∗Corresponding author