Optical Cross-Sections of Soot Agglomerates: The model of the virtual refractive index and first-order multiple scattering

A new technique for the calculation of the optical properties of agglomerated spherical primary particles is presented. By means of the so-called virtual refractive index, the multiple scattering within the agglomerate is decribed by a modified Mie solution, thus avoiding restrictions with respect to the primary particle size. An additional benefit of the method is the small numerical expense required, permitting practical use for complex agglomerate structures such as real combustion aerosols. Utilizing this method, attention is focused on the calculation of the extinction cross-section of real combustion aerosols in order to discuss the results of multiple-wavelength extinction measurements within combustion systems. It is found that approximately the primary particle diameter is determined. Furthermore, the error that occurs can be avoided by means of the method presented without a detailed knowledge of the agglomerate size. Thus, the present work eliminates some current uncertainties inherent in optical combustion aerosol characterization.     

Algorithms to retrieve optical properties of three component aerosols from two-wavelength backscatter and one-wavelength polarization lidar measurements considering nonsphericity of dust

We developed backward and forward types of algorithms for estimating the vertical profiles of extinction coefficients at 532 nm for three component aerosols (water-soluble, dust, and sea salt) using three-channel Mie-scattering lidar data of the backscatter (β) at 532 and 1064 nm and the depolarization ratio (δ) at 532 nm. While the water-soluble and sea-salt particles were reasonably assumed to be spherical, the dust particles were treated as randomly oriented spheroids to account for their nonsphericity. The introduction of spheroid models enabled us to more effectively use the three-channel data (i.e., 2β+1δ data) and to reduce the uncertainties caused by the assumption of spherical dust particles in our previously developed algorithms. We also performed an extensive sensitivity study to estimate retrieval errors, which showed that the errors in the extinction coefficient for each aerosol component were smaller than 30% (60%) for the backward (forward) algorithm when the measurement errors were ±5%. We demonstrated the ability of the algorithms to partition aerosol layers consisting of three aerosol components by applying them to shipborne lidar data. Comparisons with sky radiometer measurements revealed that the retrieved optical thickness and angstrom exponent of aerosols using the algorithms developed in this paper agreed well with the sky radiometer measurements (within 6%).     

Retrieving the aerosol lidar ratio profile by combining ground- and space-based elastic lidars

The aerosol lidar ratio is a key parameter for the retrieval of aerosol optical properties from elastic lidar, which changes largely for aerosols with different chemical and physical properties. We proposed a method for retrieving the aerosol lidar ratio profile by combining simultaneous ground- and space-based elastic lidars. The method was tested by a simulated case and a real case at 532 nm wavelength. The results demonstrated that our method is robust and can obtain accurate lidar ratio and extinction coefficient profiles. Our method can be useful for determining the local and global lidar ratio and validating space-based lidar datasets.     

Sensitive and accurate dual-wavelength UV-VIS polarization detector for optical remote sensing of tropospheric aerosols

An UV-VIS polarization lidar has been designed and specified for monitoring aerosols in the troposphere, showing the ability to precisely address low particle depolarization ratios, in the range of a few percent. Non-spherical particle backscattering coefficients as low as 5×10^?8 m^?1?sr^?1 have been measured and the particle depolarization ratio detection limit is 0.6 %. This achievement is based on a well-designed detector with laser-specified optical components (polarizers, dichroic beamsplitters) summarized in a synthetic detector transfer matrix. Hence, systematic biases are drastically minimized. The detector matrix being diagonal, robust polarization calibration has been achieved under real atmospheric conditions. This UV-VIS polarization detector measures particle depolarization ratios over two orders of magnitude, from 0.6 up to 40 %, which is new, especially in the UV where molecular scattering is strong. Hence, a calibrated UV-VIS polarization-resolved time-altitude map is proposed for urban and free tropospheric aerosols up to altitude of 4 kilometers, which is also new. These sensitive and accurate UV-VIS polarization-resolved measurements enhance the spatial and time evolution of non-spherical tropospheric particles, even in urban polluted areas. This study shows the capability of polarization-resolved laser UV-VIS spectroscopy to specifically address the light backscattering by spherical and non-spherical tropospheric aerosols.     

带超环面镜的掠入射光栅谱仪测试系统响应特性模拟分析

指出了文献[1]在物理概念上和公式推导中的错误,并在订正了这些错误之后,考虑了实际的激光等离子体光源的几何尺度和线状等离子体的安排,对在复合泵浦X激光增益实验中所使用的带超环面镜X光中继元件的掠入射光栅光谱仪系统进行了全面的模拟计算.结果表明,作者所使用的带超环面镜的X光增益测试系统,其因离焦而导致的非线性效应是完全可以忽略的,系统的空间分辨能力的下降也是非常小的,从而否定了文献[1]中的结论,表明作者在X激光增益测量实验中所使用的带超环面镜X光中继元件的掠入射光栅光谱仪系统是完全可靠的.     

A method for the calculation of Coulomb interference and rescattering corrections to total cross sections in pure spin states

We propose a dispersion theoretic approach to the calculation of Coulomb interference and rescattering corrections to total cross sections in pure spin states. Both types of corrections can be carried out only if the real parts of the forward amplitudes are known, which in general is not the case. However, we show that under some assumptions the unknown real parts enter linearly, which together with analyticity leads to a uniquely solvable integral equation. Our approach is particularly useful in pp and pd scattering where corresponding measurements have been or will be performed. Some applications are discussed.     

光镊技术在气溶胶物理化学表征中的应用

有机气溶胶的热/动力学研究是多学科交叉的前沿研究领域,其核心问题主要是非理想混合包括挥发性、液-液相分离、非平衡传质动力学等,精确测量这些过程相关理化参数是目前研究的瓶颈。光镊系统可以悬浮气溶胶单颗粒,获得高信噪比受激拉曼光谱,在研究气溶胶物理化学性质与其大气效应中具有独到优势。被广泛用于有机及其与无机混合体系气溶胶的吸湿性、挥发性、水传质动力学、液-液相分离过程研究中。本文综述了激光悬浮气溶胶单颗粒技术的研究进展,主要包括光镊技术的原理和技术手段,以及在气溶胶关键物理化学参数测量中的应用。通过光镊系统,一方面可以获得重要理化参数的精确结果,另一方面可以对实际环境中悬浮液滴的状态进行模拟测量,从而为大气科学的研究与污染治理提供重要支撑。     

On the impact of non-sphericity and small-scale surface roughness on the optical properties of hematite aerosols

We perform a comparative modelling study to investigate how different morphological features influence the optical properties of hematite aerosols. We consider high-order Chebyshev particles as a proxy for aerosol with a small-scale surface roughness, and spheroids as a model for nonspherical aerosols with a smooth boundary surface. The modelling results are compared to those obtained for homogeneous spherical particles. It is found that for hematite particles with an absorption efficiency of order unity the difference in optical properties between spheres and spheroids disappears. For optically softer particles, such as ice particles at far-infrared wavelengths, this effect can be observed for absorption efficiencies lower than unity. The convergence of the optical properties of spheres and spheroids is caused by absorption and quenching of internal resonances inside the particles, which depend both on the imaginary part of the refractive index and on the size parameter, and to some extent on the real part of the refractive index. By contrast, small-scale surface roughness becomes the dominant morphological feature for large particles. This effect is likely to depend on the amplitude of the surface roughness, the relative significance of internal resonances, and possibly on the real part of the refractive index. The extinction cross section is rather insensitive to surface roughness, while the single-scattering albedo, asymmetry parameter, and the Mueller matrix are strongly influenced. Small-scale surface roughness reduces the backscattering cross section by up to a factor of 2-3 as compared to size-equivalent particles with a smooth boundary surface. This can have important implications for the interpretation of lidar backscattering observations.     

Simultaneous forward- and backward-hemisphere elastic-light-scattering patterns of respirable-size aerosols

Two-dimensional angular optical scattering (TAOS) patterns of aerosols are measured simultaneously from the forward hemisphere 15 degrees < theta < 90 degrees as well as the backward hemisphere 90 degrees < theta < 165 degrees (detecting 63% of the 4pi sr of scattered light) by using an ellipsoidal reflector and an intensified CCD detector. TAOS patterns were obtained from polystyrene-latex spheres (individuals and aggregates) and from single Bacillus subtilis spores. These information-rich patterns, measured with a single laser pulse for individual particles on the fly, suggest that forward-TAOS and backward-TAOS measurements may be used for rapid classification of single aerosol particles.     

Studies on satellite and ground-based measurements of aerosols over urban environment

EP/TOMS satellite-derived aerosol index (AI) data have been analyzed over typical tropical urban environment corresponding to Hyderabad, India to study seasonal and annual distribution of UV-absorbing aerosols. Observations reveal that UV-absorbing aerosol loading is highly seasonal. During the years 1987, 1991 and 1992 high concentration of UV-absorbing aerosols into the atmosphere over Hyderabad region has been observed. UV-absorbing aerosols are high during summer period. Ground-based measurements of aerosol optical depth (AOD) and satellite-derived AI showed good correlation with AOD at .     

Multiple-scattering effects of atmosphere aerosols on light-transmission measurements

Multiple-scattering effects of atmosphere aerosols are of interest for remote sensing, free-space communications, and atmosphere detection. In the present work, the multiple-scattering effects of atmosphere aerosols on light-transmission measurements are, for the first time, investigated through numerical simulations based on the Monte Carlo method. For different extinction coefficients of the atmosphere, the multiple-scattering effects are discussed with respect to the aerosol asymmetry factor and the intended optical system parameters such as the baseline length, the area of the photoelectronic detector, and the field of view. As the simulation results, the total photon energies of scattering of each order are demonstrated. It is shown that the multiple-scattering effects are influenced by all the mentioned factors, as expected. Our work is useful for improving the optical systems based on the light-transmission measurements that are widely employed in weather observation and aerosol characterizations.     

Temporal characterization of mid-IR free-electron-laser pulses by frequency-resolved optical gating

We performed what we believe are the first practical full-temporal-characterization measurements of ultrashort pulses from a free-electron laser (FEL). Second-harmonic-generation frequency-resolved optical gating (FROG) was used to measure a train of mid-IR pulses distorted by a saturated water-vapor absorption line and showing free-induction decay. The measured direction of time was unambiguous because of prior knowledge regarding free-induction decay. These measurements require only 10% of the power of the laser beam and demonstrate that FROG can be implemented as a pulse diagnostic simultaneously with other experiments on a FEL.     

Evaluation ofk ± p forward dispersion relations

Kaon-nucleon forward scattering amplitudes have been calculated from dispersion relations using recent experimental data on the total cross sections. In the unphysical region the analytical continuation of theK ^? p effective range theory has been done and for the asymptotic behaviour of the total cross sections a parametrization, suggested by the Regge-pole models, has been used. The calculated real parts of the scattering amplitude are compared with the existing experimental values, as found by the optical theorem and the extrapolation of the angular distribution to the forward direction.     

A review of optical measurements at the aerosol and cloud chamber AIDA

This paper provides a survey of recent studies on the optical properties of aerosol and cloud particles that have been conducted at the AIDA facility of Forschungszentrum Karlsruhe (Aerosol Interactions and Dynamics in the Atmosphere). Reflecting the broad accessible temperature range of the AIDA chamber which extends from ambient temperature down to 183 K, the investigations feature a broad diversity of research topics, such as the wavelength-dependence of the specific absorption cross sections of soot and mineral dust aerosols at room temperature, depolarization and infrared extinction measurements of ice crystal clouds generated at temperatures below 235 K, and the optical properties of polar stratospheric cloud constituents whose formation was studied in chamber experiments at temperatures well below 200 K. After reviewing the AIDA research activity of the past decade and introducing the optical instrumentation of the AIDA facility, this paper presents illustrative examples of ongoing and already published work on optical measurements of soot aerosols, mineral dust particles, and ice crystal clouds.     

基于粒子谱的多波长激光雷达近场大气光学参数校正方法

非同轴激光雷达由于存在发射激光与接收望远镜之间的不完全重叠区, 造成近场回波信号与真实大气信号不一致. 对于多波长激光雷达, 这种不一致更为突出和复杂. 然而, 近场大气是人类活动最集中的区域, 因此对多波长激光雷达近场信号进行校正, 对于了解和探究边界层大气具有十分重要的意义. 提出了一种利用粒子谱仪测量近地层气溶胶尺度谱分布并运用Mie 散射理论和低层大气指数衰减规律, 进而直接校正多波长激光雷达消光系数廓线近场信号的新方法. 通过对晴天、多云天气和雾天多波长气溶胶消光系数廓线近场信号的校正, 证明了该方法的可行性和实用性. 该方法着重考虑了多波长激光雷达比的波长依赖性和气溶胶粒子谱分布的天气相关性, 将该方法用于近地层大气消光系数廓线校正, 减少了由于不考虑这两个因素带来的消光系数廓线反演和校正的不确定性. 该方法对于研究不同天气情况下边界层内的大气气溶胶物理、光学特性具有一定的实用价值和借鉴意义.     

Dust aerosol forward scattering effects on ground-based aerosol optical depth retrievals

Monte Carlo radiative transfer calculations are performed to examine the forward scattering effects on retrievals of dust aerosol optical depth (AOD) from ground-based instruments. We consider dust aerosols with different AOD, effective radius and imaginary refractive index at 0.5 μm wavelength. The shape of dust aerosols is assumed to be spheroids and the equivalent spheres that preserve both volume and projected area (V/P) are also considered. The single-scattering albedos and asymmetry factors of spheroids and V/P-equivalent spheres have small differences, but the scattering phase functions are very different for the scattering angle range ∼90-180°. The relative errors of retrieved AOD caused by forward scattering effects due to the differences between the single-scattering properties of spheroids and spheres are similar. It is shown that at solar zenith angle (SZA) smaller than ∼70° the effect of the forward scattering is generally small although the relative errors in retrieved AOD can be as large as −10% when r_e=2. However, the largest relative errors, which can reach −40%, appear at high SZA (>∼70°) with AOD larger than 1. This is not caused by the increase of forward scattering intensity, but is due to the strong attenuation of solar direct beam.     

Investigation of the nonlinear optical characteristics of composite materials based on sapphire with silver, copper, and gold nanoparticles by the reflection Z-scan method

The nonlinear optical characteristics of silver, copper, and gold nanoparticles synthesized in a sapphire matrix by ion implantation are studied. The measurements are performed by the RZ-scan method with optical reflection at the radiation wavelength of a picosecond Nd:YAG laser (λ = 1064 nm). The nonlinear refractive indices and the real parts of the third-order nonlinear susceptibility of the composites are determined. It is shown that the nonlinear refraction in the samples is caused by the Kerr effect.     

Optical Emission Diagnostic of a Low Pressure Planar Microwave Discharge for Plasmachemical Deposition

Low pressure microwave plasmas are of growing interest for plasmachemical applications since they have special and in some cases unique advantages with respect to other plasma excitation methods. Subject of this paper are spatially resolved measurements of the optical emission of a special planar microwave plasma source utilized to investigate different plasmachemical processes. The optical emission spectroscopy (OES) is used as a tool to get information concerning the spatially distribution of reactive atom and molecule concentration by actinometry and concerning the neutral gas temperature by measurements of Doppler line broadening. The results refer to hydrocarbon containing hydrogen plasmas which gas pressures above 100 Pa. Surprisingly measurements confirm an earlier developed simplified two layer model consisting of a preferentially physically active plasma layer near the microwave window followed by a preferentially chemically active decaying region. They give evidence that this model is more adequate to the real physical situation as assumed until now.     

Characterization of excimer laser ablation generated pepsin particles using multi-wavelength photoacoustic instrument

Preparation of organic thin layers on various special substrates using the pulsed laser deposition (PLD) technique is an important task from the point of view of bioengineering and biosensor technologies. Earlier studies demonstrated that particle ejection starts during the ablating laser pulse resulting in significant shielding effects which can influence the real fluence on the target surface and consequently the efficiency of layer preparation. In this study, we introduce a photoacoustic absorption measurement technique for in-situ characterization of ablated particles during PLD experiments. A KrF excimer laser beam (λ=248 nm, FWHM=18 ns) was focused onto pepsin targets in a PLD chamber; the applied laser fluences were 440 and 660 mJ/cm². We determined the wavelength dependence of optical absorption and mass specific absorption coefficient of laser ablation generated pepsin aerosols in the UV–VIS–NIR range. On the basis of our measurements, we calculated the absorbance at the ablating laser wavelength, too. We demonstrated that when the laser ablation generated pepsin aerosols spread through the whole PLD chamber the effect of absorptivity is negligible for the subsequent pulses. However, the interaction of the laser pulse and the just formed particle cloud generated by the same pulse is more significant.