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2Features of the Bragg diffraction on the regular domain structures with inclined walls in MgO:LiNbO3
E. Savchenkov'*, A. Dubikov1, D. Belskaya1, S. Shandarov1, M. Chuvakova2,
A. Akhmathanov2, V. Shur2
1- Tomsk State University of Control Systems and Radioelectronics, Tomsk, Russia 2- Ural Federal University, Ekaterinburg, Russia
Controlling the parameters of laser beams in the temporal and spatial regions on the base of Bragg diffraction of light waves in ferroelectric crystals on regular domain structures (RDS) formed in them is the important task for different applications [1-5]. The RDS in MgO:LiNbO3 crystals have domain walls characterized by an inclination to the polar axis at the angle ±a = 0.2° and more [6,7]. The features of the distribution of light intensity in Bragg maxima, which are to correspond to various spatial harmonics in disturbances of the optical properties of a 5%MgO:LiNbO3 crystal created by RDS with inclined walls, have been studied in [6] for a cylindrical probing Gaussian beam with a radius of ro ~ 0.16 mm. In this report the results of experimental studies and theoretical analysis of Bragg diffraction of light on RDS with inclined domain walls in a 5%MgO:LiNbO3 sample for an elliptical probing laser beam with a waist of 2zo ~ 25 ^m at different positions of its center along the polar axis Z are presented.
The examined RDS having a spatial period A = 8.79 ^m has been formed in a 5%MgO:LiNbO3 crystal with dimensions of 40^2^1 mm3 along theX, Yand Zaxes, respectively. The domain walls RDS of the Y-type in this sample described earlier in [6] had an inclination to the polar Z-axis at the angle a = ±0.31°. The sample was placed on a turntable, which allowed to specify the Bragg angle in the XY plane to observe diffraction in the first order. The probing Gaussian beam of a He-Ne laser with an extraordinary polarization, wavelength X = 632.8 nm, power 22.5 mW and aperture r0 = 0.7 mm was focused on the input face of the crystal y = 0 by a cylindrical lens with a focal length of 95 mm in the form of a narrow elliptical Gaussian light spot with an aperture of 2200x25 ^m2 along the X and Z axes, respectively. The dependence of diffraction efficiency n(z) on the position of the probing beam shifted along the Z axis by a micrometer system at spacing of 25 ^m. It has been found that n(z) is characterized by nonmonotonic behavior and reached the minimum value n = 0.02 for z = 0.45 mm as well as two maxima: n = 0.11 for z = 0.19 mm and n = 0.15 for z = 0.80 mm.
The approach developed earlier in [6] for a probing Gaussian beam with a narrow angular spectrum was used in the theoretical analysis of the diffraction efficiency and intensity distribution in diffraction maxima for elliptical probing Gaussian beam under study. The integral expressions to be allowed to describe both the dependences of n(z) and the intensity distribution of Idm(z) in the Bragg diffraction maxima corresponding to spatial harmonics with number m in the distribution of optical disturbances created by RDS with different parameters of domain walls have been obtained. Numerical calculations have demonstrated satisfactory agreement between the theoretical dependences for n(z) and Idm(z) and the relevant experimental data.
This study was funded by the Ministry of Science and Higher Education of the Russian Federation in the framework of the state assignment for 2023-2025 (job-order FEWM-2023-0012).
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