Nonlinear refraction and absorption of Mg doped stoichiometric and congruent LiNbO3

Abstract

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO 3 in the THz rangeThe light induced change of refraction is studied in pure and Mg doped LiNbO 3 with congruent and stoichiometric compositions by the Z-scan method using all-lines visible argonion laser, up to MW/cm 2 intensity level. In Mg-doped congruent and stoichiometric crystals with Mg concentrations above threshold a positive change in the refractive index was found, in contrast to all other cases where beam fanning and negative change of the refractive index were observed. The beam distortion in the samples doped above threshold was related to thermal lensing, while below it to the photorefractive effects. It was also shown that for thermal lensing nonlinear absorption plays a dominant role. The Z-scan method was found to be an alternative technique to decide whether the Mg dopant level is above or below the photorefractive threshold. The damage resistance of the Mg doped samples above threshold was higher for the stoichiometric crystal than for the congruent one and increased with the amount of the built-in Mg concentration.

Z-scan study of nonlinear absorption in reduced LiNbO3 crystals

“…5 mol. %, and in periodically poled undoped crystals, the b values are lower by three orders of magnitude at similar experimental conditions (sample thickness and laser power) 12,13,22 that indeed confirms our conclusion on origin of the marked variation of data on b values in as-grown LiNbO 3 crystals at cw-illumination.…”

“…20,21 Such an influence is the inherent factor for undoped as-grown crystals. [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 !…”

“…Such a shape of the optical response is typical for open-aperture Z-scan measurements in the as-grown nominally pure and doped LiNbO 3 crystals. [12][13][14][15] In this case called reverse saturable absorption (RSA), 16 the sample experiences the strongest I at focus (I ¼ I 0 at z ¼ 0); therefore, it absorbs the most energy and allows least transmittance. Away from the focus in the directions of both increasing and decreasing z, transmittance increases evenly because the irradiance decreases symmetrically about the focus.…”

NMR Analysis of Mg Ion Localization in LiNbO3Crystal

“…It has been established too, that the value of a quadrupole coupling constant C z of 7 Li nuclei, for all investigated crystals, within an error coincides with well-known value C z = (55.0 ± 0.5) kc [19] at the keeping of axial symmetry of EFG tensor at site of 7 Li nuclei. Dependences of the spectrum central line width (δν 0 ) and quadrupole satellites width (δν 1 ) on the general relative defects quantity of the crystal at θ = 0 • are the most informative results, obtained during 7 Li NMR experiments (θ is the angle between the direction of magnetic field B 0 and axis c of the crystal). Respondent results are illustrated in Fig.…”

“…The analysis of Mg 2+ ions localization in LN structure was made by many researchers and it has been shown that at MgO concentration less than threshold, Mg 2+ ions usually occupy positions of Li + -ions, preventing the appearance of antisite Nb Li ions [5][6][7][8][9]. However, when MgO concentration is above the threshold there are different models of Mg 2+ ions localization in LN crystal: 3.…”