Beam Propagation In The Material And Periodic Micro-structure Materials And Application Research

In this dissertation, we investigate the beam propagation in bulk materials, photonic band gap materials, and metamaterials, as well as their applications from theoretical and experimental aspects. We organize them by two clues. One focuses on materials, and developes from bulk materials, photonic band gap materials to metamaterials. The other pays more attation to their applications, such as, Z-scan, optical limiting/all-optical switching, local electric field enhancement and electromagnetic resonance. Chapter 4 is the intersection of the two clues. The details are descripted as follows:1. Using Gaussian decomposition method, we study the characteristics of Z-scan for a thin nonlinear medium with large nonlinear phase shift induced by a pulsed laser. It has been verified that the Gaussian decomposition method is still valid for analyses of Z-scan measurements with large nonlinear phase shift, and is better than some others. By comparing the peak-valley configuration of Z-scan curves for large nonlinear phase shift induced by pulsed with that by CW laser, we find that some peak-valley features of Z-scan curves appear as aperture size or light intensity increases in the case of large nonlinear phase shift. Meanwhile, we carry out the Z-scan experiments of pure CS₂ by a picosecond pulsed laser to verify the theoretical calculations in the case of large nonlinear phase shift.2. 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 obtain the second-order nonlinear coefficient d₃₁(5%MgO:LiNbO₃) =4.50×10^-12m/v at 1064 nm, which agrees well with theoretical calculations and previous well-known values.3. We propose a novel Z-scan theory for one-dimensional nonlinear photonic band gap materials. The Z-scan characteristics for this material are analyzed. Results show that the Z-scan curves for photonic band gap materials with nonlinear refraction are similar to those of uniform materials exhibiting both nonlinear refraction and nonlinear absorption simultaneously. Effect of optical gain and induced absorption on Z-scan results is also discussed. Finally, we discuss the Z-scan results for photonic band gap material with defected mode. The nonlinear optical properties of the defect material are the main contribution to the Z-scan results near the defect mode frequency.4. Based on the Pade approximation and multistep method, we propose an implicit high-order unconditionally stable complex envelope algorithm to solve the time-dependent Maxwell's equations. Unconditional numerical stability can be achieved simultaneously with a high-order accuracy in time. As we adopt the complex envelope Maxwell's equations, numerical dispersion and dissipation are very small even at comparatively large time steps. To verify the capability of our algorithm, we compare the results of the proposed method with the exact solutions.5. A surface-enhanced Raman scattering fiber sensor with chessboard nanostructure on a cleaved fiber facet is studied by finite-difference time-domain method. Surface plasmons at the metal coated nanostructured fiber facet can be effectively excited and strong local electric field enhancement is obtained. Studies on the influence of light polarization demonstrate a large polarization dependence of the field enhancement factor while the polarization effects on the plasmon resonance wavelength are relatively small.6. We propose two metamaterials with sub-wavelength double-slots -single-side double-slot metamaterial and double-side double-slot metamaterial. The dependence of the electromagnetic resonances and local intensity enhancements on the structural parameters is studied by the finite-difference time-domain method and the finite element method. Results show that the central-arm of a double-slot structure strongly influences frequency and local intensities at both high- and low-frequency resonances. Very strong field localization can be achieved at the high-frequency resonance and its particular distribution can be well controlled by the width of the central-arm. A double-side double-slot structure can be utilized to further enhance the high-frequency resonance, while suppressing the low-frequency resonance.