Optical and structural studies on Ba(Mg1/3Ta2/3)O3 thin films obtained by radiofrequency assisted pulsed plasma deposition

Single-phase Ba(Mg_1/3Ta_2/3)O₃ thin films were prepared by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) starting from a bulk ceramic target synthesized by solid state reaction. Atomic force microscopy, X-ray diffraction and spectroscopic ellipsometry were used for morphological, structural and optical characterization of the BMT thin films. The X-ray diffraction spectra show that the films exhibit a polycrystalline cubic structure. From spectroscopic ellipsometry analysis, the refractive index varies with the thin films deposition parameters. By using the transmission spectra and assuming a direct band to band transition a band gap value of ≈4.72 eV has been obtained.     

Numerical simulation of a gradient-index fibre probe and its properties of light propagation

In order to verify the properties of the light propagating through a gradient-index (GRIN) fibre probe for optical coherence tomography (OCT), numerical simulation using the optical software GLAD is carried out. Firstly, the model of the GRIN fibre probe is presented, which is consisted of a single mode fibre (SMF), a no-core fibre (NCF), a GRIN fibre lens and an air path. Then, the software GLAD is adopted to numerically investigate how the lengths of the NCF and the GRIN fibre lens influence the performance of the Gaussian beam focusing through the GRIN fibre probe. The simulation results are well consistent with the experimental ones, showing that the GLAD based numerical simulation technique is an intuitive and effective tool for the verification of the properties of the light propagation. In this paper, we find that on the conditions of a constant GRIN fibre lens length of 0.1 mm and an NCF length of 0.36 mm, the working distance of the probe will be 0.75 mm and the focus spot size is 32 μm.     

Electronic structure and optical properties of BiSI crystal

Electronic structure and optical properties of BiSI crystal were investigated by the full potential linearized augmented plane wave (FL-LAPW) method with density functional theory (DFT). The complex dielectric function and optical constants, such as optical absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, were calculated. The optical properties of BiSI crystal were studied experimentally by spectroscopic ellipsometry. The experimental results were compared with the theoretical spectra of complex dielectric functions and with the spectra of a pseudo-dielectric function (PDF). This method shows that experimental spectra consist of four Laurence lines sum.     

适合于内窥成像的共路型光学相干层析成像系统

提出了一种采用光纤型迈克耳孙干涉仪进行光程补偿的菲佐型光学相干层析成像(OCT)系统.该系统的传感探头为共路干涉结构,以解决现有内窥光学相干层析成像系统中存在的探头运动导致图像失真、以及更换使用不同探头时需进行色散和偏振态调节等问题.光程补偿和振动干扰实验结果表明,光程补偿方法正确可行,系统对环境干扰不敏感.利用研制的系统对反射镜和近红外卡进行了成像实验,验证了系统的有效性.提出的方法非常适合于内窥成像,并给出了把系统扩展为内窥光学相干层析成像系统的具体实现过程.     

Induced focusing due to counter-propagation of a pair of bright and dark optical beams in self-defocusing Kerr media

We present two-dimensional numerical simulations of a nonlinear optical system made of a bright probe and a dark pump beam that counter propagate in a thin slice of self-defocusing Kerr media, simultaneously. The numerical results show that although the medium is self-defocusing to both pump and probe beam, a profile compression occurs under some conditions, and the weak bright probe beam is focused due to cross-phase modulation. The influence of the characteristics of beams and medium length on the probe beam compression is also investigated.     

UV–VIS and mid-IR ellipsometer characterization of layers used in OLED devices

We report on the analysis of layer materials commonly used for the fabrication of organic light-emitting diodes (OLEDs) by means of spectroscopic ellipsometry operating in the ultraviolet–visible (UV–VIS) and in the mid-infrared (mid-IR) range of the electromagnetic spectrum. On covering a wide spectral range, these non-destructive, non-contact techniques offer a huge potential in characterizing thin films in terms of layer thickness values, optical indices, absorption properties modified by incorporating optically active dopant molecules, and, finally, electrical layer properties. Individual absorption bands of single organic films can significantly affect the luminance and performance efficiency of OLEDs when building multi-layer stacks. Using mid-IR spectroscopic ellipsometry, the resistance of as-deposited and annealed indium–tin oxide (ITO) layers on glass is determined and compared with values obtained by four-point probe techniques.     

Vacuum ultraviolet ellipsometry investigation of ultrathin organic films and their heterostructures

Thin layers and multilayer structures of the DNA bases guanine and cytosine on ZnO substrates were prepared by organic molecular beam deposition under ultra-high vacuum conditions and measured in situ by means of vacuum ultraviolet spectroscopic ellipsometry at the synchrotron source BESSY. Using the dielectric function of the individual layers the optical response of the G/C and C/G heterostructures was modeled. Deviations between simulated and experimental data were mainly attributed to the ordering of cytosine over guanine in the G/C and C/G structures and to the influence of the substrate.     

Manipulating light flow with one-dimensional photonic crystals of an electromagnetically induced transparency medium

The band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dielectric medium, can be dramatically changed by tuning the coupling field intensity (or coupling Rabi frequency, CRF) of the EIT medium. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. The behavior of a Gaussian beam (probe light) obliquely incident on such an EIT PC slab is simulated numerically. The probe light beam transmitted from the slab can be shifted transversely in a large range, and negative refraction enhances this effect. The present scenario can be applied in some areas such as quantum optical and photonic device designs.     

采用APD阵列的共口径激光成像光学系统设计

针对机载平台激光3D成像系统的轻小型需求,设计了采用APD阵列的共口径激光收发光学系统。在分析激光成像系统照明方式及其光学系统结构的基础上,给出了激光3D成像光学系统结构框图:激光经衍射元件实现分束照明,采用双工反射镜实现收发光路的耦合。该光学系统用于2 km以内的目标三维成像,根据激光测距方程,确定了接收光学系统的参数以获得满足信噪比的回波能量。为避免造成像素之间串扰,设计了5倍扩束比的发射光学系统。最后,采用偏振片与1/4波片相结合的方式消除杂光,降低了发射光路对接收光路的影响。设计结果表明:接收光学系统弥散斑直径小于120μm,畸变小于0.2%。该光学系统体积小、重量轻,成像质量良好,可为同类激光成像光学系统提供借鉴参考。     

Far-infrared dielectric functions and phonon spectra of alloys determined by spectroscopic ellipsometry

We have used spectroscopic ellipsometry to determine the complex dielectric function of a series of ternary Be_xZn_1−xTe thin films grown by molecular beam epitaxy. The II–VI semiconductor alloys were grown on InP substrates that had an InGaAs buffer layer. After the growth, X-ray diffraction experiments were performed in order to determine the alloy concentration. A standard inversion technique was used to obtain the dielectric functions from the measured ellipsometric spectra, obtained between 2000 nm (5000 cm⁻¹) and 40,000 nm (250 cm⁻¹). By modelling the dielectric function as a collection of oscillators, representing longitudinal and transverse optical phonons of the Be_xZn_1−xTe lattice, we were able to recover the phonon spectra for this alloy system. It is argued that the additional phonon modes that are obtained from ellipsometry are best understood from the recently-proposed percolation model.     

Gas spectroscopy and optical path-length assessment in scattering media using a frequency-modulated continuous-wave diode laser

Simultaneous assessment of the spectroscopic absorption signal of gas enclosed in a scattering medium and the corresponding optical path length of the probing light is demonstrated using a single setup. Sensitive gas absorption measurements are performed by a tunable diode laser using wavelength-modulation spectroscopy, while the path length is evaluated by the frequency-modulated cw technique commonly used in the field of telecommunication. Proof-of-principle measurements are demonstrated with water vapor as the absorbing gas and using polystyrene foam as an inhomogeneously scattering medium. The combination of these techniques opens up new possibilities for straightforward evaluation of gas presence and exchange in scattering media.     

基于全息光学元件的光纤光谱仪的光路设计

基于全息光学理论分析了全息光学元件的高斯成像性质,包括光焦度、成像位置、衍射效率以及作为光纤光谱仪光栅元件的可行性,并以全息光栅的成像理论以及光谱仪工作原理为基础,设计了光谱仪器光学系统的各个参数,通过Zemax软件的仿真、像质评价及优化,得出最终的参数和模拟结果。所使用的全息光栅记录波长为575 nm,记录光束之间的夹角为10,一束为平面波,一束为球面波,焦距40 mm,使用+1级衍射光,光栅孔径为10 mm。光谱仪的工作波长范围为400 nm～800 nm,体积140 mm*30 mm*40 mm,谱面展宽29.1 mm。通过在光学平台上搭建光路,利用已研发完成的电路系统及光谱仪软件,针对汞灯光谱进行了试验,光谱分辨率优于8 nm,测量得到的汞灯光谱与标准汞灯光谱一致,表明了所设计的基于全息元件的光纤光谱仪光学系统是可行的。     

High performance liquid chromatography with on-line dual quantum cascade laser detection for the determination of carbohydrates, alcohols and organic acids in wine and grape juice

In the present study the simultaneous use of two quantum cascade lasers (QC-lasers) was investigated for the on-line detection in high performance liquid chromatography (HPLC). An optical set-up based on three gold mirrors and a ZnSe beam splitter was used to direct the emitted laser light trough a liquid flow cell with an optical path length of 52 μm onto a mercury-cadmium-telluride (MCT) detector. Using the separation of eight components of wine and grape juice as an example, on-line dual QC-laser detection in HPLC could be shown successfully for the first time.     

光谱型椭偏仪对各向异性液晶层的测量

探讨了利用普通光谱型椭偏仪对各向异性液晶层进行综合性测量的可行性. 并利用法国Jobin Yvon公司的UVISEL SPME(Spectroscopic Phase Modulated Ellipsometer)光谱型椭偏仪测量了光学各向异性液晶层的折射率n_o和n_e及液晶层厚d，进一步利用椭偏仪在透射方式下测量了平行排列液晶层的光延迟特性Δnd，二者取得了很好的一致性，说明利用光谱型椭偏仪可以实现对光学单轴性液晶层及其他材料的测量，测厚精度为纳米量级. 关键词： 光谱型椭偏仪 各向异性 折射率 相位延迟     

Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O3 films obtained by pulsed laser deposition

The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance.     

用于实现散射介质中时间反演的数字相位共轭的相干性

抑制散射介质对光的散射,调控光在散射介质中的传输,是光通信、生物光子学、光镊等领域的重要课题.设计并实现了基于宽谱光源和数字相位共轭的可调控光在散射介质中传输的时间反演实验系统.实验获取了不同相干长度下物光和参考光束之间的光程差与干涉图样、相位图及时间反演信号之间的关系,分析了光源相干性对调控光在散射介质中传输的影响.实验结果表明,基于宽谱光源的相干特性和数字相位共轭技术,通过调节光程差能选择性获取同一散射角度及相同传输路径的光束的相对相位,再利用空间光调制器对参考光束进行调控,实现光束的反向传播,从而选择性实现对同一散射角度及相同传输路径的光的时间反演.     

Influence of acoustic leakage at fluid–solid interface on interferometric detection of surface acoustic wave

When using laser interferometer to detect surface acoustic wave at fluid–solid interface, there are two factors which will cause the optical path length variation of the probe laser beam: interface deformation, and refractive index changes in fluid induced by acoustic leakage. Influence of acoustic leakage on laser interferometric detection for surface acoustic wave is researched here. A metal plate immersed in an infinite fluid is used as a physical model. Interface deformation due to laser-induced acoustic wave and pressure in fluid due to acoustic leakage are computed for select cases by finite element method. The optical path length variation caused by the two factors are calculated respectively and compared. The results show that the influence of acoustic leakage increases with the increasing acoustic impedance matching of fluid and solid, the peak-to-peak of influence degree increases linearly with the increasing acoustic impedance of fluid, and that decreasing the distance between the interferometer and interface can effectively reduce the influence of acoustic leakage.     

Analysis of properties of krypton ion-implanted Zn-polar ZnO thin films

The optical properties of materials are of great significance for their device applications. Different numbers of krypton ions are doped into high-quality Zn-polar Zn O films fabricated by molecular beam epitaxy(MBE) on sapphire substrates through ion implantation. Krypton is chemically inert. The structures, morphologies, and optical properties of films are measured. The x-ray diffraction(XRD) spectra confirm the wurtzite structures of Zn-polar Zn O films. Atomic force microscopy(AFM) results show that the films have pit surface structure and higher roughness after Kr ion implantation. A detailed investigation of the optical properties is performed by using the absorption spectrum, photoluminescence(PL), and spectroscopic ellipsometry(SE). The absorption spectrum is measured by UV-visible spectrophotometer and the bandgap energy is estimated by the Tauc method. The results show that the absorption increases and the bandgap decreases after Kr ion implantation. Moreover, the Kr ion implantation concentration also affects the properties of the film. The ellipsometry results show that the films' refractive index decreases with the Kr ion implantation concentration increasing. These results can conduce to the design and optimization of Kr ion-implanted polar Zn O films for optoelectronic applications.     

Tetracene film morphology: Comparative atomic force microscopy, X-ray diffraction and ellipsometry investigations

X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response.     

反光板(合作目标)反射率测量仪

本文介绍了反光板（合作目标）反射率测量仪的研制。仪器采用对称双光路比较测量法，给定两束相等光通量的光束，分别作为参考光束和测试光束，并用分束器实现原光路取样，从而解决了合作目标反光板入射光线与反射光线重合不能用常规测试方法来检测的难题。由于采用对称双光路的方法，入射光通量是相对恒定的，不受外界因素影响，从而使反射率测量仪达到精度高、重复性好和环境要求低的设计要求。