A study of the optical absorption in CdTe by photoacoustic spectroscopy

We show that the Photo-Acoustic Spectroscopy (PAS) is an useful alternative method for the determination of the optical-absorption coefficient of CdTe thin films, in the spectral region near to the fundamental absorption edge, ranging from 1.0 eV to 2.4 eV, using an open cell in the transmission configuration. We applied this method to the optical characterization of CdTe layers for several values of their thickness. These CdTe samples were deposited by closed-space vapor transport (CSVT) technique under different growth conditions.     

VUV spectroscopy of wide bandgap materials

In this paper we will present VUV spectroscopy experiments performed at the Superlumi station of Hasylab, DESY, Hamburg, on samples of BaF₂ crystals activated with Ce and BaF₂, (Ba,La)F₂ crystals activated with Er. The results of these experiments include time resolved luminescence and luminescence excitation spectra obtained under wavelength selective VUV and UV excitation by pulsed synchrotron radiation.We will reveal the information provided by the VUV/UV excitation spectra of the Ce³⁺ 5d → 4f as well as Er³⁺ 4fⁿ⁻¹5d → 4fⁿ and 4fⁿ → 4fⁿ emissions on energy transfer mechanisms from the fluoride host to the rare earth ion. We will demonstrate that the fast energy transfer channels involve bound excitons while the generation of free electrons and holes leads to slower processes dependant on hole and/or electron trapping.We will demonstrate that differences between the excitation spectra of the 5d → 4f emission in Ce and 4f¹⁰5d → 4f¹¹ emission in Er activated BaF₂ are generated by the coupling of the 4f → 5d transition to the 4f¹⁰ core of the Er³⁺ ion. We will also identify the additional band, absent for Ce, which is due to the exchange split high spin (HS) state of the 4f¹⁰5d configuration responsible for the slow decay of the excited Er³⁺ ions in BaF₂ and (Ba,La)F₂.Finally we will provide evidence and explain why the dominant VUV 4f¹⁰5d → 4f¹¹ Er³⁺ emission in BaF₂ is spin-forbidden and slow while in the mixed (Ba,La)F₂ crystals it is spin-allowed and fast.     

Emission and absorption spectroscopy of magnetic materials

In recent years, optical methods have been accepted as a useful means for studying the magnetic properties in solids. In this paper it will be shown, from an introductory point of view, what kind of information optical studies can provide. The most numerous investigations have been performed with insulating materials. The observed phenomena can be divided into four types: first those where spectra can be described by a simple molecular field picture; second those where one incorporates small quantities of magnetic ions into a diamagnetic host and studies the spectra of various neighbour configurations; third those where one deals with the simultaneous excitation of states in the electronic system (excitons) and the spin system (magnons) which gives rise to the so-called magnon sidebands in absorption and emission spectra; and fourth those which deal with the exchange of energy between various magnetic sublattices by the magnetic interactions. Much less information is available on magnetic semiconductors. Yet here a very striking and perhaps technologically important effect has been observed, namely a considerable red shift of the absorption edge in going through the magnetic transition temperature, e.g., in EuO and EuS. In metals, so far only a few experiments have been performed, and only those on Ni and MnAg are mentioned here. In addition, the question of short-range correlations, which can be observed via optical spectra will be discussed. Finally, recent reviews in this field will be compiled to facilitate a deeper understanding.     

Time-resolved Fourier spectroscopy for activated optical materials

A low-cost add-on to commercial Fourier-transform spectrometers that have a continuously scanning Michelson interferometer has been developed for high-resolution, broadband, time-resolved spectroscopy. A number of innovations have been implemented to enable near-IR, visible, and UV photolumi-nescence studies. These include error correction and normalization of interferogram points to correct for laser intensity variations and missed shots, reduction of mirror-speed variations with recognition and avoidance of the timing mistakes they cause, and simple white-light-interferogram advancement optics that leave high-frequency modulation efficiency for the signal of interest unchanged in dynamically aligned systems. Application to energy-transfer phenomena in solid-state-laser media is described.     

Ground-based imaging differential optical absorption spectroscopy of atmospheric gases

We describe a compact remote-sensing instrument that permits spatially resolved mapping of atmospheric trace gases by passive differential optical absorption spectroscopy (DOAS) and present our first applications of imaging of the nitrogen dioxide contents of the exhaust plumes of two industrial emitters. DOAS permits the identification and quantification of various gases, e.g., NO2, SO2, and CH2O, from their specific narrowband (differential) absorption structures with high selectivity and sensitivity. With scattered sunlight as the light source, DOAS is used with an imaging spectrometer that is simultaneously acquiring spectral information on the incident light in one spatial dimension (column). The second spatial dimension is scanned by a moving mirror.     

A study of optical absorption in 9,10-anthraquinone crystals

Single crystals of 9,10-anthraquinone having dimensions 5 mm × 5 mm × 1.5 mm were grown from the melt using the Bridgeman technique. The starting material was purified by sublimation and zone-refining techniques in specially, designed crystal-growth tubes. The crystals were transparent and yellow in colour, and could be cleaved easily along ab-, bc-planes and poorly along the ac-planes of the crystal. Thin layer chromatography of the final crystals was performed, and no impurity was detected in these crystals by this technique. The cleaved crystals were found to have a surface photocurrent of 10^–11 A, which increased non-linearly with the increasing voltage at room temperature. This is attributed to the formation of triplets in the bulk of the crystal which migrate and dissociate at the surface of the crystal. The optical absorption spectrum in benzene and ether solutions were found to exhibit similar behaviour in the visible range, i.e. 320–450 nm. From the optical absorbance data, the optical band gap was found to be 3.4 eV.     

Time-resolved diffuse optical spectroscopy: a differential absorption approach

A method is presented for the estimate of spectral changes in the absorption properties of turbid media from time-resolved diffuse optical spectroscopy. The method relies on the hypothesis of constant scattering over the wavelength range of interest, but no limitations come from the sample size and shape as the method is derived directly from the Beer-Lambert law. The effects of a moderate spectral dependence of the scattering properties and of the non-ideal instrument response function were investigated theoretically, and the results were confirmed experimentally, showing that the method can be profitably applied in cases of practical interest.     

X射线吸收精细结构谱在材料科学中的应用

简单介绍了X射线吸收精细结构谱的物理基础,数据处理方法,讨论了X射线吸收精细结构谱在元素组成,价态和结构环境方面的分析结果。结果显示,在钠钙硅酸盐平板玻璃中,二价铁离子和三价铁离子同时存在。在Ag-Na离子交换后,二价铁离子被银离子氧化成三价铁离子。当Ti2O3和锐钛矿被分别掺入硼硅酸盐玻璃后,钛离子主要以四价存在,Ti^4＋离子占据五重配位点。在玻璃中同时掺入锐钛矿和还原剂C,诱导三价钛离子生成,三价钛离子占据八面体配位点,使得Ti K边预边峰高度降低。包裹在钠钙硅酸盐玻璃中的银纳米颗粒界面存在张应力,使得银晶格膨胀,银原子存在两种结构环境：Ag-O配位和Ag-Ag配位。孤立银原子的存在,使得最近邻Ag-Ag配位数显著降低。     

A study of optical absorption in tellurite and tungsten-tellurite glasses

A series of glass specimens was prepared from TeO₂ glass and from the binary tungsten tellurite glasses (TeO₂-WO₃) and their densities, optical absorption edges and infrared absorption spectra were measured. It was found that the fundamental absorption edge is a function of glass composition, and absorption in this region is due to indirect electronic transitions in k-space. The main infrared absorption bands in the TeO₂-WO₃ glasses are related to those characteristics of the TeO₂ component.     

非线性吸收激光光限幅材料研究进展

介绍了基于非线性吸收原理的新型光限幅材料及其研究进展。主要是反饱和吸收机制和双光子吸收机制的材料。     

Time-resolved optical emission spectroscopy of pulsed RF plasmas with copper magnetron sputtering

Time-resolved optical emission spectroscopy is used to investigate the discharge of the RF pulse sputtering of copper. The time integrated emission of a neutral copper atom in RF pulse sputtering was found to be superior to emission in continuous mode. The increase stemmed from the concentration of the power in the sharp pulse at the breakdown of the discharge. The integrated emission reached its maximum at 50% duty ratio. A sudden drop in the copper emission in continuous mode from that of a 98% duty ratio was correlated with an absence of the power peak of the pulse mode.     

Tunable diode laser absorption spectroscopy in coiled hollow optical waveguides

We demonstrate tunable diode laser absorption spectroscopy of CO2 and NH3 near 1.5 microm using a distributed feedback diode laser in conjunction with hollow optical waveguides as long-path sample cells. The waveguides are coiled to reduce the physical extent of the system. The small volume of the waveguide provides rapid instrument response to changes in gas concentration. To reduce the pressure drop associated with long lengths and high flow rates, we perforate the waveguides in a novel geometry providing parallel pneumatic paths while maintaining optical path length. A minimum detectable absorbance of 3.5 x 10(-5) in a 3-m section of waveguide is demonstrated.     

差分吸收光谱法在线测量排放烟气浓度研究

介绍了差分吸收光谱(DOAS)在线测量系统,分析了DOAS的光谱处理方法.研究了SO2气体浓度的DOAS测量方法,可以实现排放烟气中SO2的在线测量.DOAS法利用数学方法将吸收光谱分解成快变和慢变部分,他利用快变部分计算气体成分的浓度,这使得烟尘干扰和光源强度变化不影响烟气浓度测量精度.DOAS法用线测量代替点测量,可获得区域内更具有代表性的数据,能更准确的反映烟气排放情况;可同时对多种污染物的进行定性、定量分析;是非接触性测量,无需采样.     

Differential optical absorption spectroscopy system used for atmospheric mercury monitoring

A high-resolution differential optical absorption spectroscopy (DOAS) system for long-path atmospheric pollution monitoring is described. The system, consisting of a broadband lamp and a dispersive, fast-scanning optical receiver, separated by a few kilometers, was used in measurements of different pollutants, highlighted by the monitoring of the local concentration of atomic mercury. Mercury levels in the ppt (1:10(12)) range were assessed by comparisons with laboratory measurements.     

Differential optical absorption spectroscopy instrument for stratospheric balloonborne trace-gas studies

A newly developed UV-visible instrument for differential optical absorption spectroscopic measurements of atmospheric trace gases from balloon platforms is described. Direct solar light at daytime in the near-ultraviolet (320.6-422.6-nm) and the visible (417.6-670.7-nm) spectral ranges can be simultaneously analyzed for the atmospheric column abundances or profiles of O(3), NO(2), NO(3), BrO, OClO, O(4), H(2)O, and possibly other species (HNO(2), IO, CH(2)O). Compared with previously used balloonborne UV-visible spectrometers, the instrument has the superior properties of low mass (42 kg), low power consumption (30 W), decreased spectral drift that is caused by temperature and pressure changes, low detector dark current, and low spectrometer stray light. The three last-named characteristics are achieved by enclosure of the entire spectrometer in a pressurized and thermostated container and by inclusion of separately thermostated photodiode array detectors. The optical setup is simplified to reduce its weight. The spectral stray light is reduced by suppression of the higher-order and zero-order grating reflections by use of light traps and in the UV by addition of a dispersive prism preanalyzer. The major instrumental design characteristics and the instrumental performance as tested in the laboratory and during several stratospheric balloon flights are reported.     

Operator representation as a new differential optical absorption spectroscopy formalism

UV-visible absorption spectroscopy with extraterrestrial light sources is a widely used technique for the measurement of stratospheric and tropospheric trace gases. We focus on differential optical absorption spectroscopy (DOAS) and present an operator notation as a new formalism to describe the different processes in the atmosphere and the simplifying assumptions that compose the advantage of DOAS. This formalism provides tools to classify and reduce possible error sources of DOAS applications.     

Characterization of bismuth tri-iodide single crystals for wide band-gap semiconductor radiation detectors

Bismuth tri-iodide is a wide band-gap semiconductor material that may be able to operate as a radiation detector without any cooling mechanism. This material has a higher effective atomic number than germanium and CdZnTe, and thus should have a higher gamma-ray detection efficiency, particularly for moderate and high energy gamma-rays. Unfortunately, not much is known about bismuth tri-iodide, and the general properties of the material need to be investigated. Bismuth tri-iodide does not suffer from some of the material issues, such as a solid state phase transition and dissociation in air, that mercuric iodide (another high-Z, wide band-gap semiconductor) does. Thus, bismuth tri-iodide is both easier to grow and handle than mercuric iodide. A modified vertical Bridgman growth technique is being used to grow large, single bismuth tri-iodide crystals. Zone refining is being performed to purify the starting material and increase the resistivity of the crystals. The single crystals being grown are typically several hundred mm³. The larger crystals grown are approximately 2 cm³. Initial detectors are being fabricated using both gold and palladium electrodes and palladium wire. The electron mobility measured using an alpha source was determined to be 260±50 cm²/Vs. An alpha spectrum was recorded with one of the devices; however the detector appears to suffer from polarization.     

Improvement of differential optical absorption spectroscopy with a multichannel scanning technique

Differential optical absorption spectroscopy (DOAS) of atmospheric trace gases requires the detection of optical densities below 0.1%. Photodiode arrays are used more and more as detectors for DOAS because they allow one to record larger spectral intervals simultaneously. This type of optical multichannel analyzer (OMA), however, shows sensitivity differences among the individual photodiodes (pixels), which are of the order of 1%. To correct for this a sensitivity reference spectrum is usually recorded separately from the trace-gas measurements. Because of atmospheric turbulence the illumination of the detector while an atmospheric absorption spectrum is being recorded is different from the conditions during the reference measurement. As a result the sensitivity patterns do not exactly match, and the corrected spectra still show a residual structure that is due to the sensitivity difference. This effect usually limits the detection of optical densities to approximately 3 × 10(-4). A new method for the removal of the sensitivity pattern is presented in this paper: Scanning the spectrometer by small wavelength increments after each readout of the OMA allows one to separate the OMA-fixed pattern and the wavelength-fixed structures (absorption lines). The properties of the new method and its applicability are demonstrated with simulated spectra. Finally, first atmospheric measurements with a laser long-path instrument demonstrate a detection limit of 3 × 10(-5) of a DOAS experiment.