Infrared Spectra of Hydrogenated C60, Carbon Nanotubes,and Nanofibers

Abstract

Hydrogenated C₆₀, carbon single‐wall nanotubes (SWNT) and nanofibers (NF) were studied by means of IR transmittance spectroscopy of polycrystalline samples, of powder pressed in KBr pellets (TPKBr) and diffuse reflection (DR). Diffuse reflection was found to be a preferable method. Hydrogenation reduces the high‐frequency conductivity σ of the free carriers by 10 and 30 times in SWNT and NF, respectively, and results in the appearance of a C–H vibrational mode. This mode disappears and σ restores partially after an annealing of the samples at 700°C.     

The optical properties of hot-pressed magnesium fluoride and single-crystal magnesium fluoride in the 0.1 to 9.0 μm range

A polycrystalline high-density magnesium fluoride, fabricated into plates or shapes by hot-pressing, exhibits high in-line transmittance from 2.5 to 6.0 m, and single-crystal magnesium fluoride extends from 0.1 to 6.0 m. The ultimate and practical transmittance of hot-pressed magnesium fluoride using intrinsic and extrinsic reflectance, absorptance and scattering mechanisms, are investigated. The intrinsic scattering mechanism due to the polycrystalline structure is basically responsible for the tremendous difference in transmittance in the short wavelength region of the spectrum. The in-line transmittance of polycrystalline and singlecrystal MgF₂ is discussed in terms of sample thickness.     

Testing the radiometric accuracy of Fourier transform infrared transmittance measurements

We have investigated the ordinate scale accuracy of ambient temperature transmittance measurements made with a Fourier transform infrared (FT-IR) spectrophotometer over the wavelength range of 2-10 mum. Two approaches are used: (1) measurements of Si wafers whose index of refraction are well known from 2 to 5 mum, in which case the FT-IR result is compared with calculated values; (2) comparison of FT-IR and laser transmittance measurements at 3.39 and 10.6 mum on nominally neutral-density filters that are free of etaloning effects. Various schemes are employed to estimate and reduce systematic error sources in both the FT-IR and laser measurements, and quantitative uncertainty analyses are performed.     

Design and fabrication of thin film optical filters to replace fiber Bragg grating in Yb-doped fiber laser

Thin film optical filters were designed and fabricated on the end-side of the fiber as the end pumping and out coupler devices to replace the fiber Bragg grating in Yb-doped fiber laser system. It was found that the average transmittance of the end pumping device in the laser pumping wavelength (900-985 nm) is around 95.2%, and the average reflectance in the laser irradiation wavelength (1065-1085 nm) is 99.72%. The average reflectance of the out coupler device is 99.7% (900-1035 nm), and the average transmittance is 20% (1065-1085 nm), respectively.     

Fabrication of KTa0.65Nb0.35O3 film by pulsed laser deposition on glass substrate with various buffer layers

KTa_0.65Nb_0.35O₃ (KTN) thin films were deposited on amorphous glass substrates using a range of single buffer layers such as indium tin oxide (ITO), zinc oxide (ZnO), 3 at% Al-doped ZnO (AZO), and 3 at% Ga-doped ZnO (GZO), as well as a variety of multi-buffer layers such as SrTiO₃ (STO)/ITO, STO/ZnO, STO/AZO, and STO/GZO using a pulsed laser deposition system. All films showed a polycrystalline perovskite phase with the exception of all single buffer layers and STO/ITO multi-buffer layers. The STO buffer layer is important for crystallizing KTN films due to the similar lattice constant and same crystal structure. The optical transmittance of all films exhibited a transmittance ?90% in the wavelength range.     

Characterization for imperfect polarizers under imperfect conditions

The principles for measuring the extinction ratio and transmittance of a polarizer are formulated by use of the principal Mueller matrix, which includes both polarization and depolarization. The extinction ratio is about half of the depolarization, and the contrast is the inverse of the extinction ratio. Errors in the extinction ratio caused by partially polarized incident light and the misalignment of polarizers can be corrected by the devised zone average method and the null method. Used with a laser source, the null method can measure contrasts for very good polarizers. Correct algorithms are established to deduce the depolarization for three comparable polarizers calibrated mutually. These methods are tested with wire-grid polarizers used in the 3-5-mum wavelength region with a laser source and also a lamp source. The contrasts obtained from both methods agree.     

Special features of the periodic-pulse-train laser radiation confinement in doped gallium arsenide and zinc selenide

Experimental data on the pulsed laser radiation confinement in compensated GaAs and ZnSe with deep impurity levels are reported for the laser wavelength λ=1.55 μm and a pulse repetition frequency of up to 100 kHz. It is demonstrated that an increase in the pulse repetition rate is accompanied by a decrease in the energy confinement threshold and by an increase in the radiation attenuation coefficient. These effects are explained by the accumulation of nonequilibrium charge carriers related to a dependence of the recombination time constant on the concentration of free impurity centers.     

Electrorheological Fluids Based on Titania Particles Coated with Silica and Their Application in Smart Windows

The electrorheological (ER) fluids are colloidal suspension of highly polarizable particles in a non-conducting solvent.Chains of submicron-sized particles formed along an applied DC electric field by the so-called electrorheological effect.According to the obvious change of transmittance of the ER fluids in a DC electric field when the polarized particles arranged along the field,the model of smart window was proposed by sandwiching the ER fluids based on titania particles coated with silica between a pair of In-Sn oxide (ITO) coated glasses.The solar transmittance change as much as 48.0% was obtained with the wavelength of 500 nm at the maximum on applying and removing the electric field of 500V/mm.     

Transparent Conducting ZnO:A1 Films on Different Organic Substrates Deposited by r.f. Sputtering

Transparent conducting ZnO:AI films with good adhesion, low resistivity and high transmittance have been prepared on polyptopylene adipate (PPA), polyisocyanate (PI) and polyester substrates by r.f. magnetron sputtering. The structural, electrical and optical properties of the obtained films were studied. The polycrystalline ZnO:AI films with resistivity as Iow as 5.76×10-4 Ω·cm,carrier concentration 9.06×1020 cm-a and Hall mobility 11.98 cm2 V-1s-1 were produced on PPA substrate by controlling the deposition parameters. The average transmittance of films on PPA is ～80% in the wavelength range of visible spectrum. The films on PPA substrates have better electrical and optical properties compared with the filmson other kinds of substrates.     

Remote sensing of crop parameters with a polarized, frequency-doubled Nd:YAG laser

Polarized laser remote-sensing measurements that correlate the yield, the normalized difference vegetation index, and the leaf area index with the depolarized backscattered radiation from corn plots grown with eight different nitrogen fertilization dosages are presented. A polarized Nd:YAG laser emitting at 1064 and 532 nm is used. Depolarization increased significantly with increasing fertilization at the infrared wavelength, and there was a decrease in the depolarization at the green wavelength. The depolarization spectral difference index, defined as the absolute difference in the depolarization at the two wavelengths, is introduced as a parameter that is an indicator of the condition of the internal leaf structure.     

Structural and optical properties of ZnO thin films prepared by laser ablation using target of ZnO powder mixture with glue

ZnO thin films were deposited on ITO/glass substrates by pulsed laser deposition (PLD) using two different kinds of targets. One of the targets was made of pure ZnO powder and the other one consisted of a mixture of ZnO powder with cyanoacrylate glue. The structural and morphological properties of the films obtained using both targets were compared, in order to determine which one produces samples with properties more suitable for their use as buffer and antireflective layer in CdTe-based solar cells, also different heterostructures were deposited to study the optical properties of the obtained thin films and their utility in the applications mentioned before. The films deposited with the mixture powder target were polycrystalline with preferential orientations in the planes (100) and (101) with a high transmittance in the range of 70–90% in the 540–850 nm wavelength region and showed a high resistivity of \({\sim }1.30 \times 10^{2} \,\Omega \hbox { cm}^{-1}\), such properties are considered to be appropriate for thin films that are wanted to be used as a buffer and antireflective layer in CdTe solar cells.     

凝胶冷冻干燥法制备透明氧化钇陶瓷

采用凝胶冷冻干燥法, 在--50℃、8Pa的真空度下制备了碱式硝酸钇前驱体. 干燥后前驱体呈疏松片状堆积, 比烘箱干燥样品具有更为清晰的轮廓. 经过1100℃煅烧后, 凝胶冷冻干燥处理的粉体具有较细的颗粒, 颗粒尺寸分布均一, 并且具有较大的比表面积. 该粉体经过干压型, 于1700℃真空保温4h烧结后得到晶粒大小均匀的致密多晶透明陶瓷, 平均晶粒尺寸在40μm左右, 样品相对密度达99.6%. 样品经抛光后可见光400nm波长透过率达60%, 并且在紫外波段也具有类似于氧化钇单晶的高透过率.     

Al2O3/SiO2 and HfO2/SiO2 dichroic mirrors for UV solid-state lasers

HfO₂/SiO₂ and Al₂O₃/SiO₂ multilayers to be employed as high reflectance end mirrors in Cerium-doped fluoride solid-state lasers were produced by radio frequency sputtering. The components were designed to have high transmittance at the pumping wavelength and high reflectance in a wavelength band corresponding to the active medium emission. A photoacoustic beam deflection technique and inspection of the irradiated area under a microscope were used to measure the laser induced damage threshold of the mirrors at the pumping wavelength. These coatings were tested in a laser cavity.     

Optical power limiting with photoinduced anisotropy of azobenzene films

We study the power-limiting properties of photoanisotropic azobenzene films with low-power laser. The trans-cis photoisomerization and molecular reorientation of azobenzene molecules induced by polarized laser beams result in intensity-dependent anisotropic effects. Consequently, the transmittance of the input beam that passes through the film between two crossed polarizers becomes enhanced at low intensities and clamped at high intensities. The limiting threshold is adjustable by changing the intensity of excitation beam.     

Transparent conducting ZnO : Al films on different organic substrates deposited by r.f. sputtering

1. IntroductionThansparellt conducting zinc oxide films have beenextensively studied in recede years, because of theirlow material cost, relatively low deposition temperature and stability in hydrogen plasma compared withITO and SnOZ films[1]. These adVatages are of considerable interest for electrrvoptical conversion device.Compared with undoped ZnO, Al-doped ZnO filmshave lobed resistivity and better stability. nansparellt conducting films deposited on organic substrateshave many lments…     

Optically driven nanorotors: experiments and model calculations

We show that asymmetric nanorods rotate under the laser radiation pressure, irrespective of the polarization of the light, when trapped in laser tweezers. If a nanorod is not quite transparent to the trapping laser radiation, the radiation pressure force generates a non zero torque on the asymmetric nanorods making them rotate at a moderate speed. Our experimental observations on radiation pressure driven rotations of MgO and Si nanorods in optical trap show that the efficiency of the rotors depends directly on their transmittance at the trapping wavelength. We propose theoretical models to estimate the rotational speed at different laser powers for a rotor with shape asymmetries or surface irregularities.     

新型体全息窄带滤光器的光学特性研究

用紫外/可见分光光度计测定由DCG记录的透射式体全息窄带带阻滤光器的光谱特性,分析其滤波特性。测量结果分析表明,滤光器有较窄的带宽,其半宽度小于13nm,1/10宽度小于19nm。在400-800nm可见光区域,对其主谱线的相对透过率小于2%,其它谱线的相对透过率大于85%。对半导体泵浦激光器主谱线532.0nm有优良的滤光特性。     

硫系Ge-As-S玻璃和薄膜的特性

用差热分析，X射线衍射分析和透射光谱分析等手段研究了硫系Ge-As-S玻璃和薄膜的性能，结果表明，Ce-As-S体系的成玻能力较强在空气中自然冷却就能成玻，其（Tg-Tc)/Tg值为0.127-0.289，经激光辐射后的Ge-As-S玻璃薄膜的透射光谱曲线向短波方向移动，且平移的大小随激光功率的增加而增加，薄膜的透射光谱线的平移表明激光辐射导致薄膜光致结构变化，利用电子束辐射极化，通过Maker条纹测试方法在Ge-As-S玻璃中观察到二次谐波。     

Generation of radially polarized beams with an image-rotating resonator

We show how a passive image-rotating optical resonator can be used to convert a linearly polarised, lowest-order Gaussian beam into a radially polarized beam. The image and polarization rotation of the cavity removes the frequency degeneracy of the modes, making it possible to select the radially polarized mode by cavity tuning. With the addition of gain, the same cavity should operate as a radially polarized laser when injection seeded at the proper wavelength.     

Elimination of interference effects from photoinduced-transmission decay curves of thin silicon films

The effects of interference on the photoinduced-absorption signals of thin absorbing films have been studied by recording the picosecond photoinduced-absorption decay curves of an amorphous and a polycrystalline silicon film and applying various probe-beam wavelengths and angles of incidence. The normalized decay curves measured at close to normal incidence have been found to depend strongly on the probe-beam wavelength. By contrast the decay curves obtained at the Brewster angle of incidence have shown a satisfactory coincidence. Theoretical calculations for the photoinduced changes of the transmittance of the film have been performed. These calculations prove that at normal incidence the contributions of the photoinduced changes of the absorption coefficient Δα and of the refractive index Δn to the change in the transmittance Δ T are comparable, whereas when the Brewster angle arrangement is employed, Δ T is proportional to Δα and the effect of the change in the refractive index is negligible.