Image formation, filtering and applications to third order nonlinear measurement techniques

Date du colloque&nbsp;: 10/2011</p

Kerr-induced nonlinear focal shift measurements

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Nonlinear Characterization Techniques inside a 4f System

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Kerr-induced nonlinear focal shift in presence of nonlinear absorption

We report a theoretical formulation for the nonlinear Kerr-induced focal shift of converging lenses in a high intensity regime. A numerical relation expressing the on-axis intensity of a focused Gaussian beam is derived in the case of a nonlinearly absorbing and diffracting lens induced in a medium. The concept of an effective Fresnel number is used to provide a simple linear relationship between the focal displacement and the nonlinear phase distortions. The influence of nonlinear absorption on the sensitivity of the focal shift measurements is also discussed

Linear optical characterization of transparent thin films by the Z-scan technique

We report experimental characterization of a very small rectangular phase shift (&lt;0.3 rad) obtained from the far-field diffraction patterns using a closed aperture Z-scan technique. The numerical simulations as well as the experimental results reveal a peak-valley configuration in the far-field normalized transmittance, allowing us to determine the sign of the dephasing. The conditions necessary to obtain useful Z-scan traces are discussed. We provide simple linear expressions relating the measured signal to the phase shift. A very good agreement between calculated and experimental Z-scan profiles validates our approach. We show that a very well known nonlinear characterization technique can be extended for linear optical parameter estimation (as refractive index or thickness)

Robust self-trapping of vortex beams in a saturable optical medium

We report the first observation of robust self-trapping of vortex beams propagating in a uniform condensed medium featuring local saturable self-focusing nonlinearity. Optical vortices with topological charge m=1, that remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At larger intensities, the vortex beams lose their stability, spontaneously breaking into two fragments. Numerical simulations based on the nonlinear Schr\"odinger equation including the three-photon absorption and nonpolynomial saturation of the refractive nonlinearity demonstrate close agreement with the experimental findings.Comment: 27 pages, 7 figures,to be published in Phys. Rev. A (2016

Spatially resolved phase objects using Mach–Zehnder interferometry

Phase characterization with a good spatial resolution is crucial for focused beams in nonlinear media. The phase-shifting interferometry technique, using the least-squares error criterion for several interferograms, is implemented using a reflective spatial light modulator (SLM). The method provides a convenient calibration for any phase-shift steps. The reliability of the proposed method is checked by direct comparison with results obtained by the Fourier transform method as well as using a previously characterized circular phase object

Fifth-order nonlinear susceptibility: Effect of third-order resonances in a classical theory

We compute the fifth-order nonlinear susceptibility in the frame of a classical model based on an anharmonic oscillator, taking into account the local field corrections. A third-harmonic resonance is evidenced, which explains the strong enhancement of some measured values of the corresponding nonlinear index and its sign changes with the wavelength. The ratio between the fifth-order nonlinear index and the fifth-order nonlinear absorption is computed and is in good agreement with experimental data measured in carbon disulfide CS2

Optimization of Z-scan technique inside a 4f system

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