UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-23 18:33
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Conference: Bucharest University Faculty of Physics 2009 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Surface Enhanced Second Harmonic Generation


Authors:
Iulian Ionita


Affiliation:
University of Bucharest


E-mail
iulian.ionita@g.unibuc.ro


Keywords:
Harmonic generation, microscopy


Abstract:
Nonlinear microscopy can be extended to the use of multi-harmonic light wherein the energy of the incident photons is scattered via a process of harmonic up-conversion, instead of being absorbed by a molecule. Second Harmonic Generation (SHG) is a second-order nonlinear optical process and thus requires an environment without a center of symmetry, such as an interfacial region, to produce a signal. Over the last two decades SHG has been widely used as a spectroscopic tool in a variety of interfacial studies, including liquid-solid, liquid-air, and liquid-liquid interfaces. Applications have included probing equilibrium properties such as the absolute orientation of molecule at surface, structural phase transitions and electrochemical potential. Many of the approaches used to probe bulk interfacial properties can be extended to microscopy. Because of the interfacial specificity of the process, SHG is an ideal approach for studying the biophysics of model membranes, and the physiology of membranes in living cells. In particular, some dye molecules with large Hyper-Rayleigh scattering efficiency get aligned in the membrane and coherently produce large amounts of Second Harmonic Generation (SHG) signals. In general, randomly oriented molecules produce SHG incoherently, and the total generated SHG power simply scales as the number of radiating molecules, as in the case of standard fluorescence. We have built-up an original SHG microscope which is presented in detail. We report also an interesting phenomenon, consisting in enhancing the intensity of the SH emission near the surface of the material irradiated by ultra-short pulses of light.