IOP PUBLISHING LASER PHYSICS LETTERS Laser Phys. Lett. 10 (2013) 035401 (5pp) doi:10.1088/1612-2011/10/3/035401 LETTER Impact of incorporated anatase nanoparticles on the second harmonic generation in KDP single crystals V Ya Gayvoronsky 1 , M A Kopylovsky 1 , M S Brodyn 1 , I M Pritula 2 , M I Kolybaeva 2 and V M Puzikov 2 1 Institute of Physics NAS of Ukraine, Kiev 03680, Ukraine 2 Institute for Single Crystals NAS of Ukraine, Kharkov 61001, Ukraine E-mail: vlad@iop.kiev.ua (V Ya Gayvoronsky) Received 15 March 2012, in final form 2 July 2012 Accepted for publication 11 July 2012 Published 11 January 2013 Online at stacks.iop.org/LPL/10/035401 Abstract The second harmonic generation efficiency was studied for the single crystalline potassium dihydrogen phosphate matrix with incorporated TiO 2 nanocrystals in the field of the mode-locked Nd:YAG laser pulses. For the first time the frequency conversion efficiency gain was observed for KDP:TiO 2 single crystal (SC) instead of KDP SC due to the internal self-focusing effect of the pump beam caused by the giant cubic nonlinear optical response of the embedded nanoparticles. 1. Introduction Potassium dihydrogen phosphate family crystals (KDP, DKDP, ADP) are widely used in nonlinear optics, optoelec- tronics and laser techniques due to their efficient quadric nonlinear optical (NLO) response, high resistance to laser induced damage and the possibility to grow large-size single crystals (SCs). At the present time, D(K)DP crystals are a unique material for the production of wide-aperture laser radiation frequency converters and Pockels cells for the new generation of ultra-power laser setups. The drawback of the material is a comparatively low magnitude of the d 36 nonlinear coefficient which determines second harmonic generation (SHG) efficiency versus the novel borate family materials. The main approach to improve the functional properties of the KDP family crystals is an embedding of the organic/inorganic additives at the stage of the growth process. There were many publications about the enhancement of the frequency conversion efficiency of KDP SCs doped with organic dyes [1, 2], potassium chloride/acetate/citrate [3, 4] and La 3+ ions [5]. However, nonisomorphic incorporations of dopants causes the creation of an essential local deformation of the crystal lattice. The incorporation of SiO 2 [6] and CdTe [7] nanoparticles (NPs) into the KDP matrix was realized in order to design novel lasing media. We have shown the possibility of growing KDP SCs with incorporated TiO 2 nanocrystals of the anatase modification [8]. According to the x-ray analysis data the TiO 2 NPs do not essentially distort the matrix structure of KDP:TiO 2 SCs. During the growth process of the mentioned crystals the NPs are rejected by the crystallization front and are then ‘captured’ by the boundaries of the growth layer stacks [9]. This leads to the formation of the 1D layered macroscopic structure KDP:TiO 2 :KDP with a spatial period of ⇠15–20 μm. The high optical quality of KDP:TiO 2 SCs was proved experimentally [10]. The presence of the anatase NPs in the crystal matrix caused the enhancement of the cubic NLO response and the sign change of the nonlinear refractive index of the composite system at picosecond pulse excitation at 1064 nm [11]. The effect has been explained by the giant NLO response of the anatase NPs due to the resonant excitation of their surface defect states under picosecond laser pulses [12]. 1 1612-2011/13/035401+05$33.00 c  2013 Astro Ltd Printed in the UK & the USA