The optical properties of alkali nitrate single crystals

Absorption of non-polarized light by a uniaxial crystal has been studied. The degree of absorption polarization has been calculated as a function of the ratio of optical densities in the region of low and high absorbances. This function is proposed for analysis of the qualitative and quantitative characteristics of uniaxial crystal absorption spectra. Non-polarized light spectra of alkali nitrate single crystals, both pure and doped with thallium, have been studied. It is shown that the absorption band at 300 nm is due to two transitions, whose intensities depend on temperature in various ways. There is a weak band in a short wavelength range of the absorption spectrum of potassium nitrate crystal, whose intensity increases with thallium doping. The band parameters of alkali nitrate single crystals have been calculated. Low-energy transitions in the nitrate ion have been located.     

Study of band structure of one-dimensional photonic crystal composed of dispersive and nonlinear dielectric materials

The analysis of band structure of one-dimensional (1-D) photonic crystal containing dispersive and non-linear dispersive materials has been presented. The band spectra for the different combination of photonic crystals have been calculated by the well-known plane wave expansion method. The effect of the dispersive and non-linear materials on the band structures has been determined. The third-order nonlinearity has been considered in the non-linear material, and Lorentz–Drude model has been taken for dispersive material. The band gaps of considered photonic crystal are affected by the nonlinearity in the presence of dispersive material like gold. We have observed that the normalized frequency difference between photonic bands decreases on increasing intensity of input beam. This work may be useful in optical switching devices.     

Self-induced Temperature Profile and Inhomogeneity Effect on Second Harmonic Generation Using Focused Laser Beam

The behaviour of optical second harmonic due to crystal inhomogeneity and self-induced thermal effect has been considered for a focused laser beam. Temperature profile created due to a fundamental laser beam along the crystal length shows an increase in temperature band width for various values of focusing parameter. Normalized second harmonic power in inhomogeneous crystals increases up to an optimum value of focusing parameter. Utility of focusing is limited due to formation of filament in crystal for higher values of focusing parameter.     

Effect of gamma irradiation on the optical properties of CR-39 polymer

The UV-Visible absorption spectra of virgin and gamma irradiated (20–800 kGy) CR-39 polymer have been deduced by using Shimadzu Double beam Double Monochromator UV-Visible Spectrophotometer (UV-2550). The existence of the peaks, their shifting and broadening as a result of gamma irradiation has been discussed. Finally the indirect and direct band gap in virgin and gamma irradiated CR-39 has been determined. The values of indirect band gap have been found to be lower than the corresponding values of direct band gap.     

Negative refraction in the visible range in water-infiltrated opal photonic crystals

A negative refraction effect has been found in opal photonic crystals in the visible range. We have calculated the dispersion branches of a photonic crystal and determined the position of its photonic band gap. The frequency range has been identified where the refractive index of the opal is negative. An experimental arrangement is proposed for focusing a light beam by passing it through a plane-parallel opal photonic crystal and experimental evidence is presented in favor of negative refraction in the visible range.     

Dynamics of Changes in the Infrared Spectrum of Distilled and Heavy Water upon Exposure to an Electron Beam of Nanosecond Duration

The absorption spectra of distilled and heavy water upon exposure to an electron beam of nanosecond duration are investigated. The changes in the absorption spectrum of distilled water after exposure to an electron beam are that the absorption band of valence vibrations of the OH groups becomes broadened, the amplitude of the valence asymmetric band increases, and a shift of the absorption maximums toward shorter wavelength frequencies and an increase in the amplitudes with insignificant band broadening are observed for absorption bands comprised of the sum of deformation and libration vibrations of water molecules and the deformation band of water. The changes in the absorption spectrum of heavy water after its irradiation with an electron beam consist in that the band of valence vibrations of the OH groups of the H₂O and HDO molecules is broadened, while the absorption band of the OH overtones of the deformation vibrations of the HDO molecule becomes stronger and the absorption range is preserved. A shift of the absorption maximum toward higher frequencies is observed for the deformation vibrations of the H₂O and HDO molecules of heavy water, and the maximum of deformation vibrations of the D₂O molecules remains unchanged.     

Study of nonlinear optical properties of organic dye by Z-scan technique using He–Ne laser

Laser induced nonlinear absorption coefficient of Brilliant Green solution was measured by single beam open aperture Z-scan technique using a continuous wave He–Ne laser at the wavelength of 632.8 nm. It was found that the material exhibits multiphoton absorption type optical nonlinearity. Significant optical nonlinearity is an indicative that Brilliant Green dye is prominent material for low power nonlinear applications. Ultraviolet–visible and photoluminescence (PL) spectra of Brilliant Green solutions are also recorded. A strong linear absorption band with a peak at 625 nm has been observed, while the PL intensity was found to decrease due to quenching effect on increasing the concentration.     

掺镁近化学计量比LiNbO3晶体的生长

利用提拉法，从掺入11mol％K2O和1mol％MgO的化学配比LiNbO3熔体中生长了高质量的掺镁近化学计量比LiNbO3晶体．与同成分LiNbO3晶体相比，紫外吸收边发生明显蓝移，OH^-红外吸收峰的位置和波形也发生了显著的变化，初步断定晶体中Mg^2 的掺杂浓度已达到抗光伤阈值浓度．酸腐蚀结果表明，晶体具有区域性单畴结构。     

Laser pulsing of field evaporation in atom probe tomography

The processes by which field evaporation in an atom probe is momentarily stimulated by impingement of a laser beam on a specimen are considered. For metals, the dominant and perhaps only sensible mechanism is energy absorption leading to thermal pulsing, which has been well established. The energy of a laser beam is absorbed in a thin optical skin depth on the surface of the specimen. For materials with a band gap such as semiconductors and dielectrics, it is found that energy absorption in a thin surface layer dominates the process as well and leads to similar thermal pulsing. The relative amount of surface absorption versus volume absorption can strongly influence the heat flow and therefore the mass spectrum of the specimen. Thus it appears for very different reasons that all materials behave similarly in response to laser pulsing in atom probe tomography.     

Properties of the 4.45 eV optical absorption band in LiF:Mg,Ti

The optical absorption (OA) and thermoluminescence (TL) of dosimetric LiF:Mg,Ti (TLD-100) as well as nominally pure LiF single crystal have been studied as a function of irradiation dose, thermal and optical bleaching in order to investigate the role of the 4.45 eV OA band in low temperature TL. Computerised deconvolution was used to resolve the absorption spectrum into individual gaussian bands and the TL glow curve into glow peaks. Although the 4.45 eV OA band shows thermal decay characteristics similar to the 4.0 eV band its dose filling constant and optical bleaching properties suggest that it cannot be associated with the TL of composite peaks 4 or 5. Its presence in optical grade single crystal LiF further suggests that it is an intrinsic defect or possibly associated with chance impurities other than Mg, Ti.     

周期声学黑洞结构弯曲波带隙与振动特性

作为一种被动型波操控结构,声学黑洞能对弯曲波起到较好聚集作用,再结合阻尼层能更好抑制结构振动波的传播。从声子晶体角度通过周期性排列构造一种声学黑洞结构与基体结合的一维声子晶体结构,选取合适的晶胞,采用有限元法对周期排列的声学黑洞结构弯曲波带隙特性进行研究,对比分析8周期声子晶体梁与等长度的恒定截面梁及周期楔形梁的振动位移传递函数,讨论黑洞区域材料变化对带隙的影响。结果表明:该声学黑洞结构具有较好弯曲波带隙,在对应带隙及附近频带区间振动位移响应出现较大衰减,表明其抑制振动效果明显;在黑洞区域选择合适的材料可以使带隙向低频移动,同时使得带隙区间增多。     

Optical absorption edge in rare earth sesquisulfides

Optical absorption edge spectra have been measured by diffuse reflectance spectroscopy on a complete suite of rare earth sesquisulfide compounds of varying structure type. Optical band gaps were extracted from these data. The observed band gaps tend to vary with crystal structure type but many compounds with the same structure have similar band gaps independently of the particular rare earth ion. The ordered α-structure has a substantially lower band gap than the defect γ-structure for all compounds examined except for La₂S₃.     

Investigation on the growth and structure of Fe-doped near-stoichiometric LiNbO3 crystal

The Fe-doped near-stoichiometric LiNbO₃ crystal has been grown from the Li-rich melt by Czochralski method. The UV-Vis absorption spectra, IR transmittance spectra and X-ray diffraction were measured and used to study the defect structure of the crystal. Compared with that of congruent Fe:LiNbO₃, in near-stoichiometric Fe:LiNbO₃, the lattice parameter reduces, the basal absorption edge shifts towards shorter wavelength, and the OH stretching vibration absorption band shifts towards the lower wavenumber side (3466 cm^–1) in the Fe-doped near-stoichiometric LiNbO₃.     

Continuous-wave laser spectrometer automatically aligned and continuously tuned from 11.8 to 16.1 microm by use of diode-laser-pumped difference-frequency generation in GaSe

We report a fully automated mid-IR difference-frequency spectrometer with a spectral resolution under 70 MHz pumped by a pair of conventional room-temperature 800-900-nm diode lasers. 0.1 muW of tunable cw radiation is produced from incident-diode powers of 120 and 75 mW. The system has computer-controlled beam alignment with compact CCD cameras, motorized mirrors and positioners to obtain 0.01 degrees crystal-angle positioning, 4-mum beam overlap at the nonlinear crystal, and automated diode laser beam collimation. Computer-operated frequency control uses temperature tuning and current tuning of the free-running diode lasers. The system has been demonstrated by successfully scanning, without any human intervention, 64 randomly selected acetylene absorption lines between 12 and 15 mum. Spectral scans of ammonia are also presented. This mid-IR spectrometer is suitable for fully automated spectroscopy of an unlimited list of mid-IR frequencies and has the potential to detect any trace gas that has an acceptable absorption line within the large tuning range.     

Optical absorption in current-blackened yttria-stabilized zirconia

The nature of the blackening caused by high-temperature electrolysis of 8 and 12 mol % yttria-stabilized zirconia single crystals has been investigated by studying the optical absorption between 260 and 700 nm. In the early stages the band edge remained at 271 nm, the crystal became red and the transmission showed a broad minimum centred at 480 nm; in the later stages the crystal became black and the transmission was reduced drastically over the whole visible range. The low transmission was shown, by integrating sphere measurements, to be due to absorbing centres. These were attributed to the formation of vacancy aggregates which ultimately produced colloidal metallic particles.     

掺氮碳化硅晶体的近红外光谱研究

分别用红外光谱测量系统和双光束分光光度计研究了室温下碳化硅单晶的光学性质,测得碳化硅晶体的透射率和反射率随波变化的关系.通过掺氮与非掺杂碳化硅各种光谱的比较,发现掺氮不仅使近红外透射率降低,也导致反射率下降,掺氮碳化硅晶体在可见光部分出现了比较明显的吸收带.此外,利用透射谱还获得非掺杂6H-SiC晶体的折射率.     

Photoluminescence in fast-response Bi2Al4O9 and Bi2Ga409 oxide scintillators

The bulk bismuth aluminate Bi₂Al₄O₉ and gallate Bi₂Ga₄O₉ scintillative crystals have been grown from a high temperature self-flux solution adopting a top seeded technique. The lattice parameters and density of the compounds have been appropriately determined based on single crystals and powder pattern technique as well. The reflectivity, absorption and photoluminescence spectra of as grown crystals are reported. Green-yellow and red emission bands for both compounds have been readily recorded at 300 K, while the red luminescence can be sufficiently effective excited by high energy electron beam. The difference of excitation band position for crystals studied is evidently presented. Two decay time components equal 25 and 155 ns for Bi₂Al₄O₉ crystal have been detected at room temperature.     

快重离子辐照对氧化锌材料内部结构特性的影响

使用拉曼光谱和透射电镜等分析手段研究了高能快重离子辐照对ZnO单晶内部结构特性的影响。结果表明,经过快重离子辐照后,在ZnO单晶的拉曼光谱中出现了两个新的振动吸收峰。采用不同轴向的拉曼入射光表征方法,证实了位于576 cm^-1的振动吸收峰与氧空缺位(V₀)密切相关。经离子辐照后透射电镜图像显示出现了许多间隙原子、空位和位错等缺陷,而电子衍射图表明试样没有出现明显的非晶化。这个结果表明,较高的能量和辐照剂量对氧化锌的整体结构和性能几乎没有影响,也充分证明ZnO单晶具有良好的抗辐照性能。     

Neutron transmission measurements of zinc and lead single crystals

Neutron transmission measurements of zinc and lead single crystals have been carried out in a neutron wavelength band from 0.03 to 0.55 nm at different orientations of the crystal with regard to the beam direction. The measurements were performed using both time-of-flight and fixed-angle scattering spectrometers installed in front of the ET-RR-1 reactor horizontal channels. It was found that the position of the observed dips in the neutron transmission measurements corresponded to the reflections from the (hkl) planes of the hexagonal zinc single crystal which was cut along the (002) plane, while in the case of lead, the single crystal was cut perpendicular to the (311) plane. The reflectivity from the (002) plane of zinc was determined using both transmission and reflection methods. The maximum reflectivity was found to be 55% when the zinc crystal was orientated at 45° to the beam direction. The wavelength spread of the observed reflectivity curve was found to be in agreement with the calculated one, taking into consideration the spectrometer's resolution and the crystal mosaic spread.     

Photoluminescent properties of ZnS:Mn nanoparticles with in-built surfactant

Mn-doped ZnS nanoparticles, having average diameter 3–5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV–Visible absorption spectra.