E. Reynoso Lara

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

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.

Analytical expressions for z-scan with arbitrary phase change in thin nonlocal nonlinear media

Analytical expressions for the normalized transmittance of a thin material with simultaneous nonlocal nonlinear change in refraction and absorption are reported. Gaussian decomposition method was used to obtain the formulas that are adequate for any magnitude of the nonlinear changes. Particular cases of no locality are compared with the local case. Experimental results are reproduced (fitted) with the founded expressions.

Neither Kerr Nor Thermal Nonlinear Response of Dye Doped Liquid Crystal Characterized by the Z-Scan Technique

In the experimental characterization of the nonlinear optical properties of dye-doped liquid crystals by the Z-scan technique with CW lasers it is rather common to assign it a Kerr or thermal nonlinear response. In this work, we demonstrate that neither of them correctly describes all features of the Z-scan obtained in planar samples of methyl red doped 5CB liquid crystal using He-Ne CW illumination, where a strong nonlinear optical response is observed. The Z-scan curves depend strongly on the input polarization of the beam obtaining negative and positive nonlinear response for polarizations parallel and orthogonal to the director vector. We discuss and compare the effect of an additional incoherent linearly-polarized beam and plain heating source on Z-scan experiments. A theoretical model, valid for small and large phase modulation, is proposed based on the assumption that the sample can be considered as a thin lens with a photoinduced focal length dependent on the Gaussian beam radius ω m (where m is an integer), obtaining good agreement with the experimental curves for m = 3, which is neither a Kerr nor thermal nonlinearity.

A model for light transmission through a thin nonlocal-nonlinear media

The transmission of an intense light beam through a thin nonlinear sample has been extensively studied, like in self phase modulation experiment and Z-scan technique, with different approaches: the Gaussian decomposition method, the Huygens-Fresnel principle, the diffraction theory, etc., The nonlocality in the response of the media in general leads to solve more than one differential equation. In this work we present a simple model to calculate, in a numerical way, the on axis far field intensity in a Z-scan experiment or the far field pattern in spatial self phase modulation experiment by means of the diffraction theory and taking into account the locality of the thin nonlinear media. The obtained results show that the peak-valley separation distance and the transmittance difference in a Z-scan experiment and the number of rings, size and intensity distribution of the far field pattern in the spatial self phase modulation experiment are functions of the locality in the nonlinear response of the media. The proposed model describes in good approximation experimental results for samples, like absorbing liquids, liquid crystals, metal nanoparticles, etc., with different kind of nonlinear response. This model is valid for any value of the nonlinear phase shift.

Discrete optical fiber microsensor of immicible liquid interfaces

We demonstrate and present a novel semidrop optical fiber refractometric microsensor, which by contact is capable to distinguishing immiscible liquid interfaces. Microsensor consists of a couple of 8.3/125 monomodal fibers, parallel placed, and with one pair of their ends are joined by electrical arch fusion. In this junction we shaped a glass semidrop, as a half ldquodonutrdquo. 1.55 mum laser beam was injected by one of fiber ends, propagating and reflecting across the semidrop/surrounding media interface, up to reaching another ends of the fiber. Output power value depends on refractive index of surrounding media, in according to Fresnel theory.

Autobalanced photoreceiver based on erbium CdS doped thin films

By employing chemical bath deposition, polycrystalline thin films of CdS were grown on glass substrates. During the process of growth relative volumes of nitrate of erbium penta- hydrate (Er(NO3)35H2O) were added in aqueous solution of CdS in order to obtain different levels of doping, the samples obtained by this method were electrically and optically characterized determining the dark conductivity, and photoconductivity in the 590 to 451 nm range respectively, afterwards, the most suitable sample with optimal electrical and optical characteristics was chosen to develop an autobalanced photo receiver which uses the photoconductive properties of CdS for electronically auto compensate the intensity difference between the signal and reference sensor.

Automated Z‐Scan to Distinguish Different Types of Nonlinearity Without Proposing it

Z‐scan technique is powerful method to obtain both the sign and magnitude of the complex nonlinear refractive index [1,2]. However, in order to obtain the magnitude of the nonlinear refractive index is necessary to know what type of nonlinearity present the material. In this work, we have built an all‐automated z‐scan system that is able to measure a sample under z‐scan technique and give the better numerical curve, which fits to experimental curve. The numerical z‐scan curve is obtained through one model that considers all parameters of the experimental apparatus, and especially considers to the sample like a photoinduced lens; the focal length of it has a dependence of some power m of the incident beam radius. This model is based on the propagation of Gaussian beams and in the approximation of thin lens and small distortion for the nonlinear sample. As it has been demonstrated [3] the peak and valley position difference depend of the value of m. Since each value of m correspond to a type of nonlinearity...