Kerr Nonlinear Refractive Index Research Articles

Linear and nonlinear optical refractions of CR39 composite with CdSe nanocrystals

Hybrid composites of CdSe nanocrystals embedded in allyl diglycol carbonate (CR39) matrices have been prepared and characterized. The measurements show that the linear refractive index of the composite decreases as the CdSe nanocrystal’s weight-percentage concentration increases at the laser wavelengths of 632.8 nm and 532 nm. The room temperature nonlinear optical properties of the hybrid composites were investigated using a single-beam Z-scan technique with femtosecond laser pulses at the wavelengths of 794 nm and 397 nm. The experimental data reveals that the Kerr nonlinear refractive index n 2 of the composite increase at these wavelengths when the CdSe nanocrystal’s weight-percentage concentration increases. Also, the nonlinear refractive index n 2 of the CdSe/CR39 hybrid composites exhibit dispersion from a positive value at 794 nm (below the band gap) to a positive value at 395 nm (above the band gap). The measured dispersion of n 2 is roughly consistent with the Sheik-Bahae’s theory for the bound electronic nonlinear refraction resulting from the two-photon resonance.

Light Controlling Light with Enhanced Kerr Nonlinearity

The Kerr nonlinear index of refraction of a three-level atomic medium can be greatly enhanced by atomic coherence induced by two laser beams. Such electromagnetically induced transparency (EIT) media can be used to generate efficient nonlinear optical processes at low light intensities. Control and enhancement of Kerr nonlinearity in EIT media can be useful in all-optical communication, all-optical computing, and quantum information processing.

Atomic coherence induced Kerr nonlinearity enhancement in Rb vapour

The Kerr nonlinear index of refraction for rubidium atoms is measured by using an optical ring cavity with and without electromagnetically induced transparency (EIT). Significant enhancement and inhibition of the Kerr nonlinear index is observed near resonance with EIT. The nonlinear index of refraction is measured as functions of probe and coupling frequency detunings, respectively, with and without the presence of EIT. A simple theoretical calculation including Doppler broadening is presented and is found to be in good qualitative agreement with the experimentally measured results.

High-Order Two-Way Artificial Boundary Conditions for Nonlinear Wave Propagation with Backscattering

When solvinglinear scattering problems, one typically first solves for the impinging wave in the absence of obstacles. Then, using the linear superposition principle, the original problem is reduced to one which involves only the scattered wave (which is driven by the values of the impinging field at the surface of the obstacles). When the original domain is unbounded, special artificial boundary conditions (ABCs) have to be set at the outer (artificial) boundary of the finite computational domain in order to guarantee the reflectionless propagation of waves through this external artificial boundary. The situation becomes conceptually different when the propagation equation is nonlinear. In this case the impinging and scattered waves can no longer be separated, and the problem has to be solved in its entirety. In particular, the boundary on which the incoming field values are prescribed should transmit the given incoming waves in one direction and simultaneously be transparent to all the outgoing waves that travel in the opposite direction. We call such boundary conditions two-way ABCs. In the paper, we construct the two-way ABCs for the nonlinear Helmholtz equation, which models a continuous-wave laser beam propagation in a medium with a Kerr nonlinear index of refraction. In this case, the forward propagation of the beam is accompanied by backscattering, i.e., generation of waves in the opposite direction to that of the incoming signal. Our two-way ABCs generate no reflection of the backscattered waves and at the same time impose the correct values of the incoming wave. The ABCs are obtained in the framework of a fourth-order accurate discretization to the Helmholtz operator inside the computational domain. The fourth-order convergence of our methodology is corroborated experimentally by solving linear model problems. We also present solutions in the nonlinear case using the two-way ABC which, unlike the traditional Dirichlet boundary condition approach, allows for direct calculation of the magnitude of backscattering.

Enhanced Kerr nonlinearity via atomic coherence in a three-level atomic system.

We measure the Kerr-nonlinear index of refraction of a three-level Lambda-type atomic system inside an optical ring cavity. The Kerr nonlinearity is modified and greatly enhanced near atomic resonant conditions for both probe and coupling beams. The Kerr nonlinear coefficient n(2) changes sign when the coupling beam frequency detuning switches sign, which can lead to interesting applications in optical devices such as all-optical switches.

Degenerate four-wave mixing for characterization of thin-film waveguides

We demonstrate experimentally a degenerate four-wave mixing (DFWM) geometry in waveguides that permits the simultaneous determination of the optical Kerr nonlinear refractive index, the nonlinear absorption, and the nonlinear response time of thin-film materials. The geometry consists of two counterpropagating guided pump beams in a planar waveguide. The probe beam simply passes through the thin film and is not guided. By measuring the DFWM signal energy and the guided pump energy at the waveguide output, one can observe several effects simultaneously. Each effect has a different sensitivity to the nonlinearity and, used together, these effects increase the accuracy in determination of the complex n2. This technique was tested on dialkylaminonitrostilbene films. Good agreement was found between the numerical simulations and experimental data. Therefore the technique appears to be a useful characterization technique that yields, in a single setup with basic laboratory equipment, all the relevant parameters of the optical Kerr nonlinearity of thin-film planar waveguides.