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Enhanced transmission through sub-wavelength hole arrays and a single sub-wavelength aperture with periodic corrugations surrounded have been investigated extensively. We report the similar phenomenon through a funnel-type aperture with a sub-wavelength outlet in a thick silver film, which was obtained numerically by using finite-difference time-domain method. Properties of the transmission spectrum can be modulated by geometric parameters of the funnel-type aperture. With periodic grooves or dielectric gratings on the output surface of the structure, beaming light emission can be obtained.

The method for measuring second-order nonlinear optical coefficients based on well-known Z-scan is presented. The influence of linear absorption coefficients on normalized transmittance is discussed. Using this method, we obtained the second-order nonlinear coefficient d31(5%MgO:LiNbO3) = 4.5 × 10−12 m/v at 1064 nm, which agrees well with theoretical calculations and previous well-known values.

A finite-difference algorithm that combines the local one-dimensional approximation and the Douglas scheme is suggested to solve the three-dimensional non-linear Schrodinger equation. The truncation error in this scheme is reduced to O(Δ x ) 4 in the transverse direction, whereas that in the conventional local one-dimensional approximation is O(Δ x ) 2 . Using this scheme, the computational accuracy and computational efficiency can be improved drastically without the introduction of additional programming works and computational time. Numerical results obtained for an elliptic Gaussian beam propagating in non-linear medium verify the advantages of this method.

We report the experimental results on characteristics of co-existence of third-order and transient thermally induced optical nonlinearities using a nanosecond pulse laser and CS2 solutions of nigrosine. Results show that thermally induced optical nonlinearity is very sensitive to linear absorption, beam waist size and pulsewidth. Numerical simulations obtained by solving simultaneously acoustic and electromagnetic wave equations, agrees basically with experimental results. Meanwhile, the transition of optical nonlinearity from self-focusing pattern to self-defocusing pattern was observed when the contribution from thermally induced optical nonlinearity exceeds that from third-order optical nonlinearity.

We apply a new method consisting of a coordinate transformation and a coordinate mapping technique, to simulate numerically Z-scan measurements of a nonlinear medium. A comparison of numerical results obtained by this new method with those by conventional numerical method is made. Results show that the new scheme yields a large, orders-of-magnitude range improvement in computational speed and accuracy for the analyses of closed-aperture and open-aperture Z-scan measurements, compared with conventional numerical methods.

We report an extension of variational method to study the elliptic Gaussian beam propagation in a nonlinear medium with nonlinear refraction as well as nonlinear absorption. The results obtained by this method agree quantitatively with numerical solutions. Meanwhile, results also show that the variational method takes much less time than numerical simulations using the finite difference method for analysis of elliptic Gaussian beam propagation in a thick medium with nonlinear refraction and nonlinear absorption. The validity of the variational method is checked to be very good.

The characteristics of the laser pulses produced by Kerr-lens mode-locking (KLM) with a microdot mirror are analyzed in this paper by using beam propagation and self-consistency approaches. The characteristics of the pulsewidth, the intracavity power, the nonlinear reflectance change and of the gain versus size of the microdot mirror are obtained. The effect of the geometry arrangement of the microdot mirror on the mode-locking is analysed, and the optimum geometry arrangement is suggested.

Two modified Z -scan methods, in which the far-field on-axis aperture in common Z -scan is replaced by an off-axis aperture and a circular board, are suggested for measurements of n 2 with enhanced sensitivity. The calculated results show that with the increase of the distance from the off-axis aperture to the axis or the diameter of the circular board, the peak-valley normalised transmittance difference of Z -scan will increase rapidly. Also the Z -scan characteristics with a nonlinear absorption are analyzed.