Using a 4-f imaging system for nonlinear optical measurements we deal with multi-wave mixing experiments. The
complex degenerate four-wave mixing experimental setup is simplified in order to characterize nonlinear materials.
Moreover, a generalization of the I-scan method is studied by considering one, two, three and four waves mixing
experiments. The determination of the cubic optical nonlinearity is possible by providing quadratic relations that relate
the nonlinear phase shift to the measured signal. The sensitivities of the measurements are compared systematically
showing the same order of magnitude for all the studied configurations. Experimental and simulated images are
presented here to validate our approach.
Nonlinear index of refraction n2 of a series of organic solvents was measured by the nonlinear imaging (z-scan) technique. The results were compared with the values derived from the optical third harmonic generation (THG) done at the same (1064.2 nm) wavelength. The systematic differences between the values obtained from the z-scan measurements and from THG are attributed to mainly two factors: rotational contribution to n2 in z-scan measurements, where one measures the light induced birefringence and to the difference in dispersion for n2 derived from Kerr susceptibilities with respect to those derived from THG measurements. The difference is discussed in terms of a three level model for centrosymmetric structures. Applied to silica and benzene the model shows, at the measurements wavelength, a small difference between the two determinations in the case of silica and quite an important one in the case of benzene. A good agreement is observed for silica with the recently determined THG value.
In this paper the recent results of our studies of linear and nonlinear optical properties of a selected rotaxane are presented and discussed. The studied rotaxane can be processed into good optical quality thin films by vacuum evaporation. The linear optical properties of rotaxane solutions were studied by the UV-VIS spectroscopy and the nonlinear optical properties by the picosecond degenerate four wave mixing and Z-scan methods. The results show important rotational contribution to the nonlinear index of refraction.
Infrared chalcogenide glasses are studied with respect to their non linear optical properties. These glasses are sulfur or selenide glasses synthesized in the binary or ternary systems of the Ge-As-S-Se family and are transparent from the end of the visible region to wavelengths above 10 μm depending on the composition. The non linear optical characteristics are firstly determined through a spatially resolved Mach Zender interferometer with the help of a Nd-YAG laser at 1064 nm. Non linearities three order of magnitude above the non linearity of silica glass are achieved. Then, the non linear imaging technique has been used to characterize the glasses at the telecommunication wavelength of 1.55μm. This one shot technique has allow us to obtain values for the non linear refractive index n2 as high as 14 10-18 m2/W. The non linear absorption at 1.55 μm has also been evaluated and is below 1 cm/GW for all the glasses. These third order non linear optical properties make these glasses suitable candidates for integrated ultra fast all optical devices. On the basis of the GeSe4 vitreous composition, an optical fiber, single mode at 1.55 μm, is achieved.
We present an improved method to measure the third order nonlinearity of materials. The principle is based on a pump/probe experiment using a Mach-Zehnder interferometer coupled to a CCD camera. Experiments are performed with fluoride glasses (PZG) and chalcogenide glasses. A comparison with the nonlinear coefficients obtained with the Z-scan technique is done and has led us to improve the detailed analysis of the Z-scan technique.
Mach-Zehnder interferometric technique for nonlinearity measurements is briefly described. The optical setup is combined to a charge-coupled device image processing and allows to resolve the spatial profile of the complex nonlinear variation index with only one laser shot in the nonlinear material. Our experimental results in chalcogenide glasses clearly demonstrate the existence of an intensity dependent change of the sign in the nonlinear dephasing. It is shown that the nonlinear index coefficient cannot be correctly described with the usual cubic model. A more convenient theory is developed assuming a medium with two-photon nonlinear absorption and both cubic (n2) and quintic (n4) nonlinear index variations. The resulting closed-form expression for the effective nonlinear index allows to extract the cubic and quintic index coefficients.
We report on the different regimes observed in a bipolarized neodymium-doped fiber laser self Q-switched by a thin slice of a polymer-based saturable absorber. We demonstrate the interplay between the total losses and the loss anisotropy induced respectively by defocusing the saturable absorber and by tilting the cavity mirror. Starting from a global chaotic behavior for low-losses (i.e. good cavity) configuration, the system evolves toward n-periodic (n= 4,2 and 1) regime for increasing losses (bad cavity configuration). Stabilization of the regimes depends on the anisotropic losses introduced. These regimes have been identified as to be due to non-linear coupling through saturable absorber between two distinct polarized modes. These modes have been experimentally resolved. Simple model based on a bipolarized fiber laser reproduces such dynamics.
Chalcogenide glasses in the [Ge-Se-S-As] system have been synthesized and studied with respect to their nonlinear optical properties from third and second order. Z-scan and Mach Zehnder interferometry measurements of the nonlinear refractive index (n2) and nonlinear absorption ((beta) ) have been performed at 1064 nm. Some z-scan measurements have been also realized at 1430 nm. The results have been correlated to the structures of the glasses and the figure of merit has been calculated with the purpose of a potential utilization of these glasses in the realization of ultra- fast all-optical switches. Nonlinearities as high as 850 times the nonlinearity of silica glass have been obtained and some glasses exhibit at 1430 nm nonlinear optical characteristics suitable for telecommunication applications. The all-optical poling of a chalcohalogenide glass has been realized with a Q-switch mode-locked Nd:YAG laser at 1064 nm emitting 45 ps pulses at a repetition rate of 10 Hz with frequency doubling at 532 nm. A nonlinear coefficient deff equals 2.8 10-17 m/V similar to that of the reference glass Schott SF 57 has been obtained. The thermal poling of a chalcogenide glass also has been realized and a transient second order nonlinear susceptibility (chi) (2) has been observed.
This study deals with the simulation of the image formation involved by using a nonlinear image processor composed of a nonlinear medium placed at the common focus of a 4-f system. A simple linear model is developed taking into account the third-order optical nonlinearity of the medium and the optical transfer function f the 4-f system. The simulated images through the system are given for phase and/or amplitude rectangular objects. Our model and its corresponding simulation lead to optimize nonlinear parameters of the medium for this class of objects, whatever their transmittance is, in order to enhance the visibility in image processors.