Hologram recording via spatial density modulation of NbLi4+/5+ antisites in lithium niobate

Abstract

Hologram recording is studied in thermally reduced, nominally undoped lithium niobate in the time domain from 10 ns to 100 s by means of intense ns pump laser pulses (λ = 532 nm) and continuous-wave probe light (λ = 785 nm). It is shown that mixed absorption and phase gratings can be recorded within 8 ns that feature diffraction efficiencies up to 23 % with non-exponential relaxation and lifetimes in the ms-regime. The results are explained comprehensively in the frame of the optical generation of a spatial density modulation of Nb(Li)(4+/5+) antisites and the related optical features, i.e. absorption as well as index changes mutually related via the Kramers-Kronig-relation. Implications of our findings, such as the electrooptical properties of small bound Nb(Li)(4+) polarons, the optical features of Nb(Li)(4+):Nb(Nb)(4+) bipolarons, Nb(Nb)(4+) free polarons and O-hole-polarons, the impact of light polarization of pump and probe beams as well as of the polaron density are discussed.

Z-scan study of nonlinear absorption in reduced LiNbO3 crystals

“…The magnitude of the measured NLA is considerably different from the reported Z-scan results obtained in as-grown LiNbO 3 . The positive sign of NLA obtained with the red light has been related to the generation of the small bound polarons absorbing in red and near-IR ranges.…”

“…[12][13][14]20 Besides, photorefraction can be controlled (strongly suppressed) by introducing certain dopants (like Mg, Zn, or In), 7,12 or by periodic poling. 13 For example, in the as-grown Mg-doped congruent LiNbO 3 , with a Mg concentration ! 5 mol.…”

“…1,2 Besides of fundamental aspects, polarons are very perspective entities for practical purposes, e.g., the polarons can be used in the holography as intrinsic photorefractive centers in undoped and doped LiNbO 3 crystals, including chemically reduced nominally pure ones. 2,3 There are many hints that short-living small polarons strongly influence the photorefractive sensitivity. Furthermore, it has been shown that small bound polarons may act as intermediate shallow traps in a multi-step recording scheme for phase holograms featuring non-destructive read-out.…”

“…Furthermore, it has been shown that small bound polarons may act as intermediate shallow traps in a multi-step recording scheme for phase holograms featuring non-destructive read-out. 3,4 To optimize the crystal properties for photorefractive holography, it is necessary to study the efficiency of single polarons excitation. We propose to use the open-aperture Z-scan method, as it has been established 3 that the photorefractive sensitivity is proportional to the light-induced absorption.…”

“…Z-scan study of nonlinear absorption in reduced LiNbO 3 The nonlinear absorption (NLA) was studied by open-aperture Z-scan experiments in the chemically reduced nominally pure LiNbO 3 crystals at cw-illumination with the red (644 nm) and green (514.5 nm) laser beams. The magnitude of the measured NLA is considerably different from the reported Z-scan results obtained in as-grown LiNbO 3 .…”