GaAs在光通讯波段的超快非线性光学研究（英文）

采用Z-扫描和泵浦-探测技术,在光通讯波段对砷化镓(Ga As)单晶进行了非线性动力学以及非线性光学的实验研究。飞秒泵浦-探测实验结果表明,三阶非线性光学效应源于砷化镓单晶对飞秒激光的瞬态双光子吸收,而五阶非线性光学效应源于砷化镓单晶双光子吸收诱导的自由载流子吸收效应。通过Z扫描实验,得到了关于Ga As单晶所有的非线性光学参数,包括双光子吸收系数、三阶非线性折射系数、双光子吸收诱导的自由载流子吸收截面以及双光子吸收诱导的自由载流子折射截面。结果表明,砷化镓单晶在制造光限幅器件和光电探测器方面具有良好的发展前景。     

GaN晶体在飞秒紫外波段激发下的可变非线性吸收效应和光动力学过程研究

采用Z扫描和泵浦-探测技术研究了GaN薄膜在370 nm时的非线性光学效应和非线性光动力学过程。首先,基于GaN薄膜的透射光谱,结合线性光学理论分析得到了其在370 nm的线性折射率n₀、线性吸收系数α₀、光学带隙E_g等线性光学性质。采用飞秒激光Z扫描技术,得到了不同光强激发下的Z扫描实验响应结果,结合非线性光学理论提取出GaN薄膜可变的光学非线性吸收效应。在激发光子能量接近GaN带隙情况下,低光强时材料表现为饱和吸收而高光强时为反饱和吸收,这是因为低光强下单光子吸收占主导而高光强下以单光子感应自由载流子吸收为主。闭孔Z扫描测量得到了GaN薄膜的三阶非线性折射系数为n₂=-(1.0±0.1)×10-3 cm2·GW-1,它几乎比传统非线性介质的高出一个数量级。为了探究上述非线性过程的动力学弛豫时间以及进一步探究GaN薄膜非线性光动力学过程的深层物理机制,采用了交叉偏振飞秒退相泵浦探测技术观察GaN薄膜的光激发载流子动力学弛豫过程。实验结果表明,在低光强下,饱和吸收效应来源于瞬态单光子吸收,高光强下单光子感应自由载流子吸收为非瞬态光动力学过程,其自由载流子弛豫时间约为17 ps。该工作将为GaN薄膜在紫外非线性纳米器件应用以及GaN薄膜非线性过程的机制分析理解提供新的思路。     

一新型金属有机化合物在皮秒激光下的三阶非线性光学性质研究

利用皮秒激光光源,采用z扫描技术研究了一种新型金属有机化合物的三阶非线性光学性质以及光限幅特性.z扫描研究结果表明,这种化合物在1064 nm波长激光激发下的三阶非线性极化率χ(3)为3.8×１０-14 esu,并且存在双光子吸收.光限幅实验结果显示双光子吸收和非线性折射两种不同机制决定了该化合物的光限幅特性.     

水溶性CdTe量子点的三阶光学非线性极化特性

利用超短脉冲Z扫描技术和光学Kerr效应研究了以巯基丙酸为稳定剂的CdTe量子点水溶液的三阶光学非线性极化特性. 在532nm,30ps和800nm,130fs脉冲激光激发下, 发现分别具有正负相反取值的三阶光学非线性折射率,自由载流子吸收和双光子吸收分别是这两种脉冲激光激发下三阶光学非线性吸收的起因. 测量得到CdTe量子点的三阶光学非线性极化率约为CS₂的32倍, 在520—700nm光谱区的CdTe量子点的光学响应时间小于400fs. 关键词： CdTe量子点(QDs) Z扫描 三阶光学非线性极化特性 双光子吸收     

基于半导体光放大器四波混频原理的光采样

建立了可研究强超短光脉冲放大特性且包含自由载流子吸收、受激辐射、双光子吸收、光谱烧孔和超快非线性折射效应的半导体光放大器理论模型,用以建立脉冲四波混频模型,并进一步仿真了基于半导体光放大器的光采样过程,重点讨论了自由载流子吸收、双光子吸收效应对采样特性的影响。仿真结果与实验结果相符。     

InP纳米颗粒的超快动力学和光学非线性

通过飞秒泵浦-探测方法测量了波长为800 nm时InP半导体纳米颗粒激发态的瞬态动力学过程。观察到一个快速的光致漂白建立和一个漂白的恢复过程,分析饱和吸收的来源可能是带填充效应引起跃迁的饱和吸收。对于漂白恢复中的快过程是由于自由载流子的弛豫,而慢成分是由于光激发载流子在很短的时间内受陷于表面态形成的限域载流子的弛豫。通过飞秒光克尔效应(OKE)方法测量材料的超快非线性响应曲线,计算了材料的光学三阶非线性极化率,分析了非线性的来源。     

激发态分子内质子转移有机分子HBT的三阶非线性光学特性

以532nm皮秒脉冲作抽运光,采用单光束Z-扫描技术对具有激发态分子内质子转移效应的有机分子2-(2′-羟基苯基)苯并噻唑(HBT)在其双光子吸收区的非线性光学特性进行了研究.实验结果表明,对532nm波长的光,HBT分子存在明显的双光子吸收.通过拟合开孔Z-扫描实验数据,求解了HBT分子在其双光子吸收区的非线性吸收系数,并探讨了抽运光强度对介质双光子吸收效应的影响.采用高斯分解法,通过拟合闭孔Z-扫描除以开孔Z-扫描数据,理论推导并计算了在介质对抽运光存在非线性吸收的情况下HBT分子的非线性折射率,以及不同入射光强度时HBT分子的三阶非线性极化率实部和虚部的值.计算结果表明,理论分析与实验结果较好地符合,这些结果为进一步研究和开发此类材料的应用提供了理论与实验依据.     

多晶金刚石窗口材料的双光子激发

在超短脉冲抽运光作用下,利用双光子激发研究了多晶金刚石非线性吸收和非线性折射的动力学演化过程。在非线性吸收动力学实验中,观察到了金刚石样品中被激发载流子的两个不同的复合过程,时间尺度分别在百皮秒量级和纳秒量级,精确得到了不同抽运光能量作用时两个过程各自的时间常数。在非线性折射动力学实验中,观察到了金刚石样品中由非简并双光子吸收过程所引起的正的非线性折射率变化,得到了样品的三阶非线性系数。     

FEL诱导半导体材料非线性光吸收

应用北京自由电子激光(BFEL)对典型的红外光电子材料Hg_1-xCd_xTe ,InSb和InAs进行了非线性光吸收研究.利用FEL的高光子密度和皮秒量级的短脉冲宽度特性，研究了双光子吸收(TPA)以及光生载流子吸收(FCA)共同作用机理，从实验上直接证实了在强入射能量下，FCA是不可忽略的光吸收过程，提取了精确的自由载流子吸收截面参数. 关键词： FEL 双光子吸收 光生载流子吸收 吸收截面 载流子寿命     

Au纳米颗粒阵列中双光子吸收的饱和过程

采用纳米球蚀刻法制备了Au纳米颗粒阵列.并通过扫描电子显微镜观测了其表面形貌,表明三角形的Au纳米颗粒呈阵列状分布.采用Z扫描方法(800 nm, 50 fs)测量了Au纳米颗粒阵列的三阶非线性光学特性.在较小的激发功率下,结果呈现出双光子吸收效应,随着激发功率不断增加,出现了双光子吸收饱和的过程;非线性折射则呈现出自散焦效应.这种高效率的非线性响应机理使得该种Au纳米颗粒阵列在高速全光开关中有潜在的应用价值. 关键词： 纳米球蚀刻技术 Au纳米颗粒 三阶光学非线性     

Measurements of dynamics of nondegenerate optical nonlinearity in ZnS with pulses from optical parameter generation

We expand the degenerate PO pump-probe technique to nondegenerate field and use it to investigate optical nonlinear dynamics in ZnS single crystal. Excited by 532-nm laser pulses with 21-ps duration, the temporal response of nondegenerate nonlinear absorption and nondegenerate nonlinear refraction are probed by laser pulses from optical parameter generation (OPG) at 600 and 680 nm with pulse width of 10 ps. Based on the theory of free-carrier optical nonlinearity, we study the pure free-carrier refraction in ZnS. By numerically fitting based on the nondegenerate pump-probe theory, the nondegenerate two-photon absorption coefficient, the free-carrier lifetime, the free-carrier absorptive cross section and refractive coefficient at both probe wavelengths are determined respectively. The dispersion of the free-carrier refractive coefficients is discussed.     

双光子激发ZnSe自由载流子超快动力学研究

采用Z扫描和抽运-探测实验技术, 在波长为532 nm、脉冲宽度为41 fs的条件下测得ZnSe晶体的双光子吸收系数, 并获得了不同激发光强下的自由载流子吸收截面、电子-空穴带间复合时间和电子-声子耦合时间. 研究发现, 随着激发光强的增大, 自由载流子吸收截面减小, 复合时间变短. 当激发光强增大导致载流子浓度大于10¹⁸ cm^-3时, 抽运-探测信号出现明显改变, 原因归结为强光场激发导致样品在短时间内带隙变窄和电子-空穴等离子体的形成.     

Investigation of optical nonlinearities in Pd(po)2 by Z-scan technique

With nanosecond scale at a 532 nm wavelength, we firstly measured the nonlinear optical absorption and refraction coefficients of Pd(po)₂ complex by using Z-scan technique, here Hpo=1-hydioxy-2-pyridone. We describe an empirical expression for the case when nonlinear refraction is accompanied by nonlinear absorption to separately evaluate the nonlinear refraction and the nonlinear absorption by performing straightforward measurements with the aperture removed. The nonlinear optical response of Pd(po)₂ was determined by the linear decreasing irradiance-dependence. The nonlinear absorption originates from the near resonant two-photon absorption while the mechanism of the nonlinear refraction is the near resonant two-photon absorption transition enhancement. The linear increasing dependences of the optical nonlinearities on the incident irradiance arise from the population redistribution due to the near resonant two-photon absorption.     

激子效应对双曲型量子线中非线性光学吸收率的影响

本文研究了双曲型量子线的三阶非线性光学吸收率,着重研究了激子对其影响,并且利用密度矩阵算符理论导出了三阶非线性光学吸收率的解析表达式。最后,以A1GaAs/GaAs双曲型量子线为例作了数值计算。数值结果表明,当线宽增加时,激子效应对三阶非线性光学吸收率的影响越来越弱,特别是,当线宽接近于扩散长度时,激子效应将显着减弱。     

The nonlinear optical response of new organometallic compounds under picosecond excitation

The nonlinear optical response of three new organometallic compounds was studied by z-scan method under picosecond excitation at 1064 and 532 nm. The compounds showed self-focus effect at both wavelengths, and effective reverse saturation absorption at 532 nm and strong two-photon absorption at 1064 nm occurred. Through calculating and comparing the nonlinear optical indexes of the compounds, we found that the third-order nonlinear susceptibility was enhanced by two-fold for one photon transition resonant effect, and incorporating different heavy metal atoms in the delocalized organic system slightly influenced the nonlinear optical indexes.     

Low power continuous wave laser induced optical nonlinearities in saffron (<Emphasis Type="Italic">Crocus Sativus</Emphasis> L.)

We report on the low power CW laser induced nonlinear optical responses of Saffron (stigmata of Crocus Savitus L.) ethanol and methanol extracts. The optical nonlinearities were investigated by performing Z-scan measurements at 470 and 535 nm wavelengths. At both wavelengths the material has a strong nonlinear refraction, mainly of thermal origin. However, only at 470 nm wavelength the material exhibit pronounced saturable nonlinear absorption. Long-term (70 days) stability measurements indicated that the nonlinearities in the Saffron extracts are due to their nonvolatile components. This study shows that there is great potential for Saffron extracts to be used in nonlinear photonic applications.     

硒化镉载流子的超快动力学研究

硒化镉是一种可用于X射线全光分幅相机和全光条纹相机的重要探测材料。用基于相位物体的泵浦探测方式,研究了硒化镉在1030nm波长,飞秒脉冲下的载流子超快动力学和非线性光学特性。得到了双光子吸收系数、载流子吸收截面、载流子复合时间等参数。实验表明,硒化镉载流子的动力学和非线性特性是由束缚电子和载流子共同决定的。束缚电子的克尔效应和双光子激发都是瞬态的,而载流子复合持续了较长时间。这些参数和载流子图像的的获得,为X射线超快探测器件的设计和改进提供了参考。     

Fe2O3纳米微粒溶胶非线性光学特性的Z-扫描研究

利用Z扫描技术在透明区域研究了Fe₂O₃纳米微粒水溶胶和表面包覆有机溶胶的非线性光学特性，给出了非线性折射率γ、双光子吸收系数β、自由载流子折射系数σ_r和自由载流子吸收截面σ_ab等重要物理参数，讨论了自由载流子效应对Fe₂O₃纳米微粒非线性特性的影响 关键词：     

The nonlinear refraction and absorption dependence on the thermal effect for 4 ns pulse duration in binuclear Zn(II) phthalocyanine solution

The influence of thermal effect on the third-order nonlinear optical properties of binuclear Zn(II) phthalocyanine in chloroform solution was studied. The nonlinear refraction and absorption of the sample was measured by using Z-scan technique with 4 ns laser pulses at 532 nm wavelength. The opposite signs of the effective nonlinear refraction index were observed by changing the focal length of focusing lens from 10 cm to 20 cm in the experimental setup. Changing the focusing lens increased the beam waist radius from 7 μm to 20 μm. The nonlinear absorption coefficient was reduced about 200 times based on changing the fluence or beam waist radius. The drastic changes in the third-order nonlinear optical parameters were attributed to thermal effect. To investigate the role of thermal effects even further the effective nonlinear refraction and absorption coefficients were studied by using different repetition rates, input powers and concentrations.     

Nonlinear optical properties of [（CH3）4N]Au（dmit）2 using Z-scan technique

The third-order optical nonlinearities of [（CH3）4N]Au（dmit）2 （dmit = 4,5-dithiolate-1,3-dithiole-2-thione） at 532 nm and 1064 nm are investigated using the Z-scan technique with pulses of picoseconds duration. The Z-scan spectra reveal a strong nonlinear absorption （reverse saturable absorption） and a negative nonlinear refraction at 532 nm. No nonlinear absorption is observed at 1064 nm. The molecular second-order hyperpolarizability γ for the [（CH3）4N]Au（dmit）2 molecule at 532nm is estimated to be as high as （2.1 ±0.1） × 10^-31 esu, which is nearly three times larger than that at 1064 nm. The mechanism responsible for the difference between the results is analysed. Nonlinear transmission measurements suggest that this material has potential applications in optical limiting.