Nanooptics and photonics
Effect of the second and the third optical harmonics generation efficiencies enhancement in KDP single crystals due to incorporation of anatase nanoparticles
V.V. Multian1,2, A.V. Uklein1, O. O. Svistunov3, I.M. Pritula3, R. Le Dantec2, V.Ya. Gayvoronsky1
1 Institute of Physics NAS of Ukraine. Pr. Nauki, 46, Kiev 03028, Ukraine 
E-mail: vlad@iop.kiev.ua
2 Université Savoie Mont Blanc, SYMME, F-74000 Annecy, France
3Institute for Single Crystals of NASU, Nauky ave. 60, Kharkov 61072, Ukraine

Potassium dihydrogen phosphate (KDP) single crystals are widely used due to their nonlinear optical (NLO) and electro-optical properties. Within extremely high structural and optical perfection the crystals have relatively low magnitude of the quadratic NLO susceptibility. Since KDP family crystals contain a developed hydrogen bonds network, they can effectively capture impurity centers of a different nature. A promising trend in the development of up-to-date functional optical materials is an incorporation of tailoring impurities into the KDP crystalline matrix. Our previous study has shown promising results for KDP: TiO2  single crystals with incorporated anatase nanoparticles (NPs) within pulsed picosecond range and CW laser radiation. 
Recently the impact of TiO2 NPs incorporation in KDP matrix on quadratic and cubic NLO response of composite was studied by multiphoton microscopy technique under femtosecond laser excitation in range 710-1300 nm. It was shown the SHG and THG efficiency enhancement up to 10 and 5 times correspondingly versus the nominally pure KDP matrix. Observed harmonics generation enhancement is in a good agreement with previous study of self-action and SHG effects [1], and supercontinuum generation [2] and can be explained by self-action effects manifestation and nonlocal photoinduced proton network rearrangement via excitation of the intrinsic defects of TiO2 NPs and KDP crystalline matrix.

1. A.S.Popov A, A.V.Uklein, V.V.Multian et al. Nonlinear optical response of the KDP single crystals with incorporated TiO2 nanoparticles in visible range: effect of the nanoparticles concentration. Functional Materials 24 (2017) 5–10.
2. A.V.Balakin, L.A.Golovan, I.A.Ozheredov et al. Enhancement of Super- continuum Generation in KDP Crystals Incorporated with Anatase Nanoparticles. OSA Nonlinear Optics Tech. Digest (2013) doi: 10.1364/NLO.2013.NW4A.11