Photons, nonlinear light interaction

Nonlinear light-matter interactions have been successfully applied to create new visualization contrast mechanisms for optical microscopy. Nonlinear optical microscopy employs femtosecond and picosecond lasers to achieve a high photon flux density by focusing the beam onto a sample with a high numerical aperture (NA) microscope... 

This chapter is devoted to describe the impact of metallic nanosphere to the multi-photon excitation fluorescence of Tryptophan, and little further consideration to multi-photon absorption process will be given, as the reader can find several studies in [11-14]. In section II, the nonlinear light-matter interaction in composite materials is discussed through the mechanism of nonlinear susceptibilities. In section III, experimental results of fluorescence induced by multi-photon absorption in Tryptophan are reported and analyzed. Section IV described the main results of this chapter, which is the effect of metallic nanoparticles on the fluorescent emission of the Tryptophan excited by a multi-photon process. Influence of nanoparticle concentration on the Tryptophan-silver colloids is observed and discussed based coi a nonlinear generalization of the Maxwell Garnett model, introduced in section II. The main conclusion of the chapter is given in secticHi IV. 

Menzel, Ralf. Photonics Linear and Nonlinear Interactions of Imsct Light and Matter. 2d ed. Berlin Springer-Verlag, 2007. For the advanced student, covers how light interacts with matter, both for linear and nonlinear cases. The bibliography contains an enormous set of references. 

Characterization of Molecular Hyperpolarizabilities Using Third Harmonic Generation. Third harmonic generation (THG) is the generation of light at frequency 3co by the nonlinear interaction of a material and a fundamental laser field at frequency co. The process involves the third-order susceptibility x 3K-3 , , ) where —3 represents an output photon at 3 and the three s stand for the three input photons at . Since x(3) is a fourth (even) rank tensor property it can be nonzero for all material symmetry classes including isotropic media. This is easy to see since the components of x(3) transform like products of four spatial coordinates, e.g. x4 or x2y2. There are 21 components that are even under an inversion operation and thus can be nonzero in an isotropic medium. Since some of the terms are interrelated there are only four independent terms for the isotropic case. 

Molecular nonlinear optics is the description of the change of the molecular optical properties by the presence of an intense light field. Since light either can be considered a classical electromagnetic wave or as a stream of photons, we may describe the interaction between light and matter in two apparently different ways, and we will start by considering how linear and nonlinear optical phenomena can be described in these two frameworks. 

It is clear that the route followed hitherto can be extended to an arbitrary order in the perturbation, and thus provide the description of general multi-photon interactions. However, since very high light intensities are needed in order to observe tlie nonlinear responses, the predominant interest in optics are focused at processes incorporated in the linear polarizability and the first- and second-order hyperpolarizability. The expression for the general-order nonresonant response... 

---