红外发射率控制方法及机理研究

红外发射率的控制具有广泛的用途,根据电磁波理论,讨论了物体表面的发射率与折射率的关系,折射率大的物体发射率低.电致变色材料是一种可控制其表面折射率和发射率的材料.以氧化钨为例探讨了发射率的控制方法.利用电场对三氧化钨薄膜进行离子和电子的共注入和共抽取,三氧化钨中的载流子浓度发生了变化,折射率和红外发射率也发生了变化.     

红外发射率调制技术研究

物体红外发射率的调制具有广泛的应用前景.从理论上研究了红外发射率的调制机理,给出了三种调制发射率的技术途径:机械式、半导体载流子调制和电化学式.机械式发射率调制技术是利用不同发射率的材料组合来进行调制,通过调整不同材料在表面所占比例来调整发射率.半导体材料可通过调制PN结中的自由电子浓度实现红外发射率的调节.电化学式调制可通过多层薄膜实现.通过电场控制器件中变发射率薄膜层的离子和电子浓度,实现器件红外发射率的调制.     

MOCVD生长的GaN膜的光学性质研究

本文报道（0001）晶向蓝宝石衬底上金属有机化学气相淀积（MOCVD）方法生长的单晶六角GaN薄膜室温光学性质．由光吸收谱和488umAr+激光激发的光调制反射光谱（PR）确定的禁带宽度分别为3．39和3．400eV，从光吸收谱得到了GaN薄膜的折射率随光谱能量的变化关系．对PR谱的调制机理进行的分析，发现信号来自缺陷作用下的表面电场调制．应用喇曼光谱研究了GaN薄膜中的声子模，通过对LO声子-等离激元的耦合模散射峰的研究，得到了材料中的载流子浓度和等离激元阻尼常数．     

太赫兹时间分辨系统研究有机卤化物钙钛矿薄膜的超快太赫兹调制

研究了利用太赫兹时间分辨系统研究有机卤化物钙钛矿薄膜(CH_3NH_3PbI_3 and CH_3NH_3PbI_(3-x)Cl_x)的皮秒尺度的超快太赫兹调制特性.在光激发作用下出现了太赫兹透射波的瞬时下降.相比于CH_3NH_3PbI_3薄膜,在光激发作用下CH_3NH_3PbI_(3-x)Cl_x薄膜展现了更高的调制深度(10%).通过测算材料的电导率及载流子浓度,其调制机理为瞬态光激发载流子浓度上升.实验结果表明,CH_3NH_3PbI_(3-x)Cl_x薄膜可作为一种高效超快太赫兹调制器件.     

太赫兹时间分辨系统研究有机卤化物钙钛矿薄膜的超快太赫兹调制（英文）

研究了利用太赫兹时间分辨系统研究有机卤化物钙钛矿薄膜(CH_3NH_3PbI_3 and CH_3NH_3PbI_(3-x)Cl_x)的皮秒尺度的超快太赫兹调制特性.在光激发作用下出现了太赫兹透射波的瞬时下降.相比于CH_3NH_3PbI_3薄膜,在光激发作用下CH_3NH_3PbI_(3-x)Cl_x薄膜展现了更高的调制深度(10%).通过测算材料的电导率及载流子浓度,其调制机理为瞬态光激发载流子浓度上升.实验结果表明,CH_3NH_3PbI_(3-x)Cl_x薄膜可作为一种高效超快太赫兹调制器件.     

溅射压力对制备a-GaAs1-xNx 薄膜光学常数的影响

采用反应磁控溅射法在室温条件下制备了a-GaAs_1-xN_x 薄膜。实验测定了薄膜厚度、氮含量、载流子浓度和光学透过率及并研究了其随溅射压的变化。系统研究了溅射压对所制备薄膜的光学带隙、折射率和色散参数的影响。所制备的薄膜为直接带隙材料,利用Cauchy和Wemple模型能够很好地拟合所制备薄膜的折射率色散曲线。     

基于标准黑体的物体表面发射率计算方法研究

红外测温仪器的精度和被测物体表面的发射率对测量物体红外辐射特性的准确性影响很大。为了提高物体表面发射率的计算精度,先通过标准黑体对红外热像仪进行标定。然后,利用标定好的红外热像仪测量温度,计算出被测物体表面的发射率。将基于神经网络的红外热像仪标定方法应用到目标发射率的求解方法中,有效地消除了热像仪的系统误差。测试装置简单,测试结果准确。同时,温度和发射率的精确测量为红外隐身材料的研制奠定了基础。     

负折射率半透明薄膜的热发射特性研究

根据传输矩阵法和基尔霍夫定律研究了负折射率薄膜的热发射特性.较为系统地考察了相关参数对热辐射s偏振波的影响.研究结果表明,负折射率材料的热发射率随角频率的变化呈现复杂的振荡现象.同时也发现,它的发射率峰值有时在远离法线的区域.     

氮化铝薄膜的椭偏法研究

文章采用真空磁过滤电弧离子镀法在单晶Si(100)基片上成功制备了氮化铝(AlN)薄膜,并利用椭偏法对AlN膜进行了研究.根据沉积方法的特点,建立合适的膜系进行拟合,得到薄膜的折射率、消光系数和几何厚度;分析薄膜与基片之间的附着方式为简单附着,以及引起薄膜材料比块体材料折射率偏小的原因为:薄膜中含有空隙,Al/N不符合化学剂量比,薄膜表面形成了Al2O3钝化层.     

有机半导体薄膜的光学和电学性质研究

采用真空热蒸镀技术制备了NPB有机半导体薄膜和单层夹心结构器件,通过透射谱测量研究了薄膜的光学能隙、折射率和消光系数等光学性质,结果表明有机半导体薄膜具有直接带隙半导体的光学性质,并且其折射率色散性质遵循单振子模型.另外,通过分析器件的电流-电压特性研究了薄膜的电导率、载流子迁移率和载流子浓度等电学性质.这些实验结果对于有机光电子器件的结构设计具有一定的参考价值.     

Control of Refractive Index Distribution for High-Bandwidth Graded Index Plastic Optical Fiber

The graded index plastic optical fiber (GI-POF) has been proposed as the transmission medium to realize high-speed information transmission. We have succeeded in fabricating a GI-POF by the coextrusion process, a method that allows continuous fabrication of GI-POF. Although it has been indicated that the refractive index distribution of GI-POF fabricated by this process is formed by Fick diffusion with diffusion coefficient dependent on dopant concentration, the method to control it remains unknown. The purpose of this paper is to establish the technology of controlling refractive index distribution in GI-POF fabricated by the coextrusion process. Therefore, we investigate the physical mechanism of the dependency of diffusion coefficient on dopant concentration. It has become clear that the dependency is affected by the decrease of glass transition temperature and the nonlinear increase of melt flow rate. Moreover, through simulation of dopant diffusion by our originally developed program, it has become evident that changing the molecular weight of the core and cladding material allowed control of fabricating a GI-POF with optimal refractive index distribution by this fabrication method.      

二维非线性梯度折射率介质的热辐射特性研究

发展了二维梯度折射率介质热辐射传递的数值求解方法,研究了非线性折射率介质的表观方向发射率.研究结果表明,采用本文方法计算二维梯度折射率介质的表观方向发射率,最大相对误差小于1.6%.通过研究发现,二维非线性梯度折射率介质的热辐射能够呈现非常明显的定向辐射的特征,我们定义这种现象为类相干发射.     

离子交换单模玻璃平面波导折射率分布的确定

用Ag-Na离子交换技术制备了玻璃平面波导.求解扩散方程得到Ag离子在玻璃内部浓度分布.使用一次多项式模拟的方法求解折射率变化与Ag离子浓度变化之间的关系,从而得到了单模平面波导的折射率分布,并验证其与同等实验条件(离子交换时间除外)的多模波导获得的折射率分布函数基本一致.     

A digital signal-processing analysis technique for the infrared reflectivity characterization of ion implanted silicon

A new method for the characterization of ion-implanted silicon is proposed. It is based on analysis of the Fourier spectrum of bilinearly transformed infrared reflectance versus wavenumber data of ion-implanted samples. This non-destructive technique has been applied to previously published infrared reflectance data of 〈111〉 and 〈100〉 oriented Si samples which had been implanted with 2.7 MeV phosphorus and 380 keV silicon ions, respectively, and annealed at 500° C for various lengths of time. The refractive index and thickness of the amorphous layer of the as-implanted samples can be measured directly by means of this technique. The position of boundaries between the amorphous, recrystallized and substrate zones, as well as the position of the carrier concentration peak can be determined for the various annealing times. Depending on the annealing time, the recrystallized layer in 〈111〉 silicon has a refractive index which is between 2% and 4% higher than the substrate refractive index, while the difference in refractive index between the amorphous and recrystallized layers is in the order of 5%. In contrast to these results, the presence of the substrate/recrystallized material interface could not be detected in partially recrystallized 〈100〉 silicon by this method, implying that the refractive index step at the substrate/recrystallized material interface is less than 1%. The step in refractive index at the crystalline/amorphous interface in 〈100〉 silicon implanted with a dose of 0.5 x 10¹⁶ cm⁻² silicon ions, was measured to be 12%, and it is reduced to 8% after partial regrowth has occurred. These results confirm the data obtained by a model-based least-squares analysis.     

逆正向蒙特卡罗方法及应用

在打破传统蒙特卡罗方法在光线跟踪计算时各个子过程连贯性的基础上,发展了灵活的逆正向蒙特卡罗法,进而利用该方法研究了介质的矢量辐射传输问题。通过建立一维梯度折射率半透明介质模型,模拟了大气层折射率分布,得到了考虑偏振时介质自身的Stokes矢量。研究结果表明,梯度折射率介质不同表面的发射率存在一定的区别,散射性介质在考虑偏振时表面发射率的结果与标量方法存在一定的差异。逆正向蒙特卡罗方法可用以解决矢量辐射传输这类复杂问题。     

Iterative simplex-finite difference method for the characterizationof optical waveguides

A new method is presented for reconstructing smooth refractive index profiles of optical waveguides from measured effective indexes. It is based on the semivectorial finite difference method to solve the polarized wave equation for a given refractive index profile. An iterative simplex algorithm is used to find the best refractive index parameters that give, as a solution, effective indexes close to the measured ones. The method is applied successfully to Ag⁺-Na ⁺ ion-exchanged glass slab waveguides and to diffused Mg/Ti:LiNbO₃ slab waveguides. Dopant concentration profiles are obtained by using secondary ion mass spectrometry. The relationship between the refractive index change and the dopant concentration is determined for both cases. The iterative simplex algorithm-finite difference method (ISA-FDM) is compared to other index profile reconstruction methods, and the advantages with respect to WKB-based methods are pointed out     

Calculation of emissivity of Si wafers

A computer-software, Emissivity, has been developed to calculate the emissivity (ɛ) of silicon wafers of any surface morphology, for a given temperature and dopant concentration. The software uses a combination of ray- and wave-optics approaches to include the interference and the polarization effects necessary for multilayer surface coatings and multi-reflections within thin wafers. The refractive index and the absorption coefficient are calculated as a function of temperature and dopant concentration using an empirical model for an indirect bandgap semiconductor. The results of this model are compared with conventional emissivity calculations and experimental data.     

Chaotic self-pulsation and cross-modulation in awavelength-selective external-cavity laser diode

Chaotic self-pulsation in a single wavelength external-cavity laser diode is observed. It is shown that the self-pulsation is caused by interdependencies between the optical output power and the compound cavity losses through the refractive index of the laser diode material. Refractive index changes result in a detuning between the externally selected wavelength and the weak internal-mode structure of the anti-reflection coated laser diode. This detuning is directly related to the compound cavity losses. On the one hand, a change in optical output power results in a change of the refractive index via the carrier density. On the other hand, it results in a change of refractive index via temperature changes. Compared to the carrier induced refractive index change, the temperature induced refractive index change is opposite in sign, a factor of ~10² smaller and slower. The switch-on and switch-off time of the self-pulsation is governed by the carrier life time. The repetition rate of the self-pulsation is governed by the thermal time constant and is in the megahertz region. Cross-modulation resulting from the thermal induced refractive index change is demonstrated. In a two-wavelength double external-cavity laser diode, optical power at one wavelength effects the optical power at the other wavelength. This cross-modulation is shown to be related to previous experiments on a laser neural network. A novel technique is introduced to measure the thermal impedance of a laser diode that is based on the cross-modulation     

Index sensing characteristics of the plasmonic sensor based on metal-insulator-metal waveguide-coupled structure

A plasmonic refractive index sensor based on metal-insulator-metal(MIM) waveguide-coupled structure is proposed and demonstrated in this paper.The physical mechanism of the device is deduced,and the finite difference time domain(FDTD) method is employed to simulate and study its index sensing characteristics.Both analytic and simulated results show that the resonant wavelength of the sensor has a linear relationship with the refractive index of material under sensing.Based on the relationship,the refractive index of the material can be obtained from the detection of the resonant wavelength.The results show that the sensitivity of the sensor can exceed 1600 nm/RIU,and it can be used in chemical and biological detections.