Z-scan and spatial self-phase modulation of a Gaussian beam in a thin nonlocal nonlinear media

Abstract

Considering that the nonlinear photoinduced phase shift to a Gaussian beam in a thin sample of nonlocal nonlinear media can be modeled as a Gaussian function to some real power the far-field can be calculated using the Fraunhofer integral. In this paper we calculate numerically this integral to obtain the on-axis intensity in a Z -scan experiment or the intensity pattern in a self-phase modulation experiment. Experimental results of samples under cw illumination are fitted using the model with a good correspondence between experimental and numerical results. The model presented is adequate to describe samples with any magnitude of the maximum nonlinear photoinduced phase shift of purely refractive local or nonlocal nonlinear thin media.

Two nonlinear optical processes in Z-scan curves of a bleached photographic film

“…Besides, the optical nonlinear response is highly nonlocal with higher levels of power, this can be observed in the values of m obtained for the fit. It was established in [15] that a value of m = 2 the interaction is considered as local. The physical mechanism that creates such response can be of different origins: heat [20], charge carriers [21], atoms [22].…”

“…For the FLD model the values of s were integers, a value of 4 is associated to a Kerr mechanism of nonlinearity and 2 is associated to a thermal, a value of 3 has been associated to a reorientational mechanism [19]. For NL model values of m larger than 2 are associated with nonlinear phase changes that spatially are extended to region narrower than the incident intensity and values smaller than 2 extend in a broader region [15].…”

“…One of the models is based on the idea of that a lens is photoinduced in the samples with a focal length that depends on the incident beam radius to some power [14] but this power changes with the position of the sample. The second model is based on the nonlocality of the nonlinear response of the sample [15], that also can change with the position. In the next section we describe and reproduce the experimental results reported in [10].…”

The optical nonlinearity of gold nanoparticles prepared by bioreduction method

“…Several works have reported Z-scan curves of colloidal gold nanoparticles obtained and reproduced with thermal lens models [15,16], but the agreement between the results and the models is not always accurately, especially when the change of phase of the nonlinear response is larger [17]. The model, established in [9], considers a Gaussian beam propagating in the Z direction; at some distance z illuminates a thin nonlinear sample with field amplitude ( )…”

“…Also their nonlinear optical properties was investigated employing the Z-scan technique and a recent theoretical model that takes into account the non local response of the media [9]. yeast was purchased from Bioxon BD.…”