Nanooptics and photonics
Characterization of the nonlinear
optical properties of ZnO nanoparticles
V.V. Multian1,2, R. Le Dantec2, Y. Mugnier2, 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

Harmonic Nanoparticles (HNPs) are a new family of bio-markers for multiphoton imaging [1,2] exerting the optical contrast by the second, the third and higher optical harmonics generation. The simultaneous detection of these signals with an additional tunability of response can be used for sensing and imaging to increase selectivity against background. In this work the microscopy studying of the efficiencies of second (SH) and third harmonic (TH) generation under femtosecond laser excitation in range 900–1300 nm were used for HNPs diagnostics [1,2]. The comparison of SH, TH and photoluminescence (PL) of separate ZnO HNPs with different sizes (~40 nm, 100 nm and 150 nm) was done. The impacts of ZnO HNPs agglomeration and their orientation were studied. 
Studied ZnO nanoparticles are demonstrating high PL signal at about 380 nm and SH signal under excitation wavelengths <1000 nm. For longer excitation wavelengths ZnO NPs show strong THG signal with maximum at the excitation wavelength about 1100 nm. This effect can be explained by the three-photon resonant enhancement of THG.
The obtained results indicate that the applied approach can be used for single HNPs characterization. 

1.	Riporto J., Demierre A., Kilin V., Dantec R., Wolf J-P., Mugnier Y., Bonacina L. et al., Bismuth ferrite dielectric nanoparticles excited at telecom wavelengths as multicolor sources by second, third, and fourth harmonic generation. Nanoscale – 2018. 
2.	Schmidt C., Riporto J., Uldry A., Rogov A., Mugnier Y., Dantec R., Wolf J-P. and Bonacina L., Multi-Order Investigation of the Nonlinear Susceptibility Tensors of Individual Nanoparticles. Sci. Rep.  – 2016, -6, 25415.
3.	Multian V., Dantec R. and Gayvoronsky V., Characterization of colloidal nanoparticle suspensions using the third harmonic generation at interfaces. UJPO – 2018, -19, 92-98.