Issue
Europhys. Lett.
Volume 76, Number 6, December 2006
Page(s) 1123 - 1129
Section Condensed matter: structural, mechanical and thermal properties
DOI http://dx.doi.org/10.1209/epl/i2006-10375-2
Published online 16 November 2006
Europhys. Lett., 76 (6), pp. 1123-1129 (2006)
DOI: 10.1209/epl/i2006-10375-2

Effect of local rotations on the optical response of $\chem{LiNbO_3}$: Application to ion-beam damage

G. García1, J. Olivares2, F. Agulló-López1, 3, A. García-Navarro1, F. Agulló-Rueda4, A. García-Cabañes3 and M. Carrascosa3

1  Centro de Microanálisis de Materiales (CMAM), Universidad Autónoma de Madrid (UAM) - Cantoblanco, 28049 Madrid, Spain
2  Instituto de Óptica, CSIC - c/ Serrano 121, 28006 Madrid, Spain
3  Departamento de Física de Materiales, Universidad Autónoma de Madrid (UAM) Cantoblanco, 28049 Madrid, Spain
4  Instituto de Ciencia de Materiales (ICMM), CSIC - Cantoblanco 28049 Madrid, Spain


received 11 August 2006; accepted in final form 17 October 2006
published online 16 November 2006

Abstract
The effect of local rigid rotations of the $\chem{LiNbO_3}$ structure on the optical response has been theoretically explored and compared to experimental data obtained after irradiation with F (20-22$\un{MeV}$), O (20$\un{MeV}$) and Mg (39$\un{MeV}$) ions. The calculations account for the main trends of the ordinary and extraordinary refractive indices measured after the initial stage of irradiation, namely, decrease in birrefringence and approximate invariance of the average refractive index. Moreover, experimental data are quantitatively consistent with a distribution function $\exp [-\theta/\theta_0]$ for the rotation angle with respect to the trigonal (Z-axis) and isotropic azimuthal angle $\phi$. The corresponding $\theta_0$ angle is in the range 4.6- $7.0^{\circ}$ depending on ion and energy (stopping power). The model also predicts a significant reduction in second-harmonic generation (SHG) yield with fluence, comparable although somewhat lower than found by experiment.

PACS
61.80.Az - Theory and models of radiation effects.
61.80.Jh - Ion radiation effects.
78.20.Ci - Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity).

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