光束在体材料和周期性微结构材料中的传播及应用研究

【作者】 陈树琪；

【导师】 田建国；

【作者基本信息】 南开大学 ， 光子学与技术， 2009， 博士

【摘要】 本论文从理论和实验上对光束在体材料、光子带隙材料和Metamaterials（MMs）中的传播及应用进行了系统地分析和研究。我们分两条主线撰写,第一条主线是从体材料、光子带隙材料到MMs材料角度发展;第二条主线是从Z扫描、光限制/全光开关到局域场增强和电磁谐振的应用角度发展;其中第四章光子带隙材料的Z扫描及应用是这两条主线的交点。主要研究内容包括:1.我们应用高斯分解法对由脉冲电场诱导的大非线性相移下的Z扫描进行了研究。证明了高斯分解法仍然可以用来分析大非线性相移下的Z扫描理论,并且优于其它方法。我们对入射激光分别为连续和脉冲情况下的大非线性相移Z扫描曲线的峰谷结构进行了比较,发现在大非线性相移的情况下,Z扫描曲线的峰和谷随透过光阑或光强的变化表现出来某些新的特性。采用皮秒脉冲激光下的纯二硫化碳实验对理论分析加以验证。2.基于测量三阶非线性系数的Z扫描测量方法,我们提出了二阶Z扫描的理论,讨论了线性吸收系数对Z扫描曲线的影响。应用这种方法,我们测量了在1064 nm下,5%MgO:LiNbO₃的二阶非线性系数d₃₁=4.50×10^-12m/v,这一结果同先前用不同测量方法得到的结果符合得很好。3.我们提出了一种理想的一维非线性光子带隙材料的Z扫描理论。分析了一维周期性非线性光子带隙材料Z扫描曲线特征,结果表明只含非线性折射的一维非线性光子带隙材料的Z扫描曲线与同时包含非线性折射和非线性吸收的体材料Z扫描曲线相似。同时,分析了光学增益和诱导吸收对开孔和闭孔Z扫描曲线的影响。最后,我们还分析了具有缺陷的一维非线性光子带隙材料Z扫描结果,在缺陷模频率处,缺陷材料的非线性光学性质对Z扫描结果起决定作用。4.基于Pade近似和多步法,我们提出了一种无条件稳定隐格式高阶复包络算法求解时间依靠的Maxwell方程。无条件稳定和时间上高阶精度可以同时达到。由于我们采用复包络Maxwell方程,即使在相当大的时间步长下,数值色散和耗散都非常小。为了验证这种无条件稳定时域有限差分法的兼容性,我们比较了提出算法同准确解的结果。5.应用时域有限差分法,我们研究了在光纤末端具有棋盘状微结构的表面增强拉曼探测器。覆盖在微结构光纤端面金属上的表面等离子体可以被有效地激发,并且可以得到强烈的局域电场增强。对激发光偏振影响的研究表明,局域场增强因子对激发光偏振具有很强的依靠性,但是偏振效应对等离子体谐振波长几乎没有影响。6.我们提出了两种由亚波长小孔构成的MMs周期性结构——单侧双孔MM和双侧双孔MM。应用时域有限差分法和有限元法,我们研究了结构参数对这两种MMs的电磁谐振和局域场强度增强的影响。结果表明双孔结构的中臂强烈地影响着低频和高频谐振的频率和局域场强度。通过改变中臂的宽度,在高频谐振处可以得到非常强的局域场增强,并且很容易地控制局域场的分布。双侧双孔MM可以进一步用来增强高频谐振,同时削弱低频谐振。更多还原

【Abstract】 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.更多还原