Self-defocusing

Z-scan8 is a technique used to derive the nonlinear refractive index intensity coefficient n2 (from which 3) and y can be determined) by examining self-focusing or self-defocusing phenomena in a nonlinear material. Using a... 

The detailed physical properties of glassy molecular materials based on methine dyes is given in Sect. V. Some special photophysical, and optical phenomena such as complementary grating competition, self-defocusing, and optical instability are discussed. 

The large index modulation also leads to a large self-defocusing of light beams. The intensity distribution and the propagation dispersion of the output... 

Nonlinear refi"action of the composite materials results from different mechanisms such as the Kerr effect and thermal focusing [5]. Taking into account that the laser intensity and repetition rate were large enough, the speed of MN hyperpolarizability causing Kerr-induced self-defocusing should overlap the thermal focusing mechanism. 

A quantitative study of the role played by the laser wavefront curvature and other geometrical/optical parameters on the transmitted far-field intensity profile [3] demonstration of self-defocusing effect for optical limiting application [4]. 

While self-focusing and self-defocusing are manifestations of the refractive part of the degenerate cubic optical nonlinearity, the absorptive part results in variation of the total power of the beam transmitted through the sample as a function of z. This can be monitored with a detector that integrates the power in the whole beam, and the changes of such power as a function of z (in the so-called open-aperture scan) can be directly related to the nonlinear absorption coefficient of the sample, a2. 

Self-action effects Self-focusing Self-defocusing... 

Disturbance of phase-matching conditions Self-focusing or self defocusing... 

The real part of the nonlinear susceptibility in Eq. (48) gives rise to the spatial effects of self-focusing and self-defocusing, spectral broadening, and changes in the polarization vector. The imaginary part of the susceptibility causes nonlinear absorption. 

Self-defocusing results from a combination of a negative value of 2 and a beam profile that is more intense at the center than at the edge. In this situation the refractive index is smaller at the center of the beam than at the edges, resulting a shorter optical path for rays at the center than... 

The nonlinear optical properties and the role of the surface plasmon resonance (SPR) in optical limiting (OL) properties of Ag-Cu nanoclusters co-doped in Si02 films were investigated [322]. These films show a self-defocusing nonlinearity and the nonlinear refractive index decreased with decreasing particle size, whereas the nonlinear absorption increased with an increase in Cu concentration. 

The Z-scan technique is a very simple and convenient way of investigating self-focusing or self-defocusing phenomena as well as nonlinear absorption in a nonlinear material. Z-scan has been used for the measurement of the cubic NLO... 

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