“黑青”“黑碧”的谱学鉴别特征探究

“黑青”指颜色近黑色,主要成分为透闪石的青玉。“黑碧”指颜色近黑色,主要成分为阳起石的碧玉。采用电子探针、激光剥蚀电感耦合等离子体质谱仪和红外光谱测试分析手段,确定“黑青”“黑碧”的矿物种属。采用拉曼光谱、显微紫外-可见分光光度计、红外光谱对“黑青”“黑碧”的谱学鉴别特征进行探究。“黑青”为标准透闪石拉曼谱峰,“黑碧”的谱峰位置与“黑青”存在几个波数的偏差,向波数小的方向移动。可见-近红外波段,“黑青”出现445 nm吸收峰,680和940 nm宽吸收带,为Fe2+和Fe3+作用;“黑碧”出现445 nm吸收峰,660和690 nm双吸收峰以及970 nm吸收峰,为Fe2+,Fe3+,Cr3+作用。显微紫外-可见光谱可分析到样品的近红外区,“黑青”在1 397,2 310,2 387和2 466 nm出现强吸收峰,1 915和2 120 nm出现弱吸收峰;“黑碧”在1 400,2 313和2 394 nm出现吸收峰。红外光谱分析“黑青”在5 225,4 738,4 692,5 349,4 317,4 190和4 064 cm-1存在吸收峰;“黑碧”在4 708,4 307,4 178和4 031 cm-1存在吸收峰。显微紫外-可见光谱与红外光谱分析结果虽然存在小的差异,但基本保持一致,以红外光谱分析结果为准。将透闪石质的“黑青”、阳起石质的“黑碧”、广西大化阳起石质玉进行对比,综合红外光谱和显微紫外-可见光谱分析结果得出“黑青”（透闪石）与“黑碧”（阳起石）近红外光谱的鉴别特征：“黑青”（透闪石）在4 800～4 600 cm-1存在两个吸收峰,4 350～4 300 cm-1存在分裂双吸收峰;“黑碧”（阳起石）在4 800～4 600 cm-1存在一个弱吸收峰,4 350～4 300 cm-1存在一个吸收单峰。且“黑碧”（阳起石）的近红外吸收峰相较于“黑青”（透闪石）整体向低波数方向移动。     

Radiative heat transfer analysis in pure water heater used for semiconductor processing

A simplified one-dimensional model is presented to analyze the non-gray radiative transfer in pure water heater used in the rinsing processes within semiconductor production lines, and the ray-tracing method is extended to simulate the radiative heat transfer. To examine the accuracy of the simplified model, the distribution of radiation absorption is determined by the ray-tracing method based the simplified model and compared with the data obtained by three-dimensional non-gray model in combination with Monte Carlo method in reference, and the effects of the water thickness on the radiation absorption are analyzed. The results show that the simplified model has a good accuracy in solving the radiation absorption in the pure water heater. The radiation absorption increases with the water thickness, but when the water thickness is greater than , the radiation absorption increases very slowly with the water thickness.     

New regime of inverse saturable absorption for self-stabilizing passively mode-locked lasers

The reflectivity of a semiconductor saturable absorber mirror (SESAM) is generally expected to increase with increasing pulse energy. However, for higher pulse energies the reflectivity can decrease again; we call this a roll-over of the nonlinear reflectivity curve caused by inverse saturable absorption. We show for several SESAMs that the measured roll-over is consistent with two-photon absorption only for short (femtosecond) pulses, while a stronger (yet unidentified) kind of nonlinear absorption is dominant for longer (picosecond) pulses. These inverse saturable absorption effects have important technological consequences, e.g. for the Q-switching dynamics of passively mode-locked lasers. A simple equation using only measurable SESAM parameters and including inverse saturable absorption is derived for the Q-switched mode-locking threshold. We present various data and discuss the sometimes detrimental effects of this roll-over for femtosecond high repetition rate lasers, as well as the potentially very useful consequences for passively mode-locked multi-GHz lasers. We also discuss strategies to enhance or reduce this induced absorption by using different SESAM designs or semiconductor materials. PACS 42.60.Fc; 42.70.Nq; 78.20.Ci     

Three-photon absorption and its limitation of third-order nonlinear optical effects in rutile

Three-photon absorption and three-photon-induced excited-state absorption of rutile are studied by transmission measurements using picosecond pulses of a mode-locked Nd: glass laser. The nonlinear absorption limits efficient stimulated Raman scattering. It reduces the efficiency of two-photon absorption of a picosecond probe continuum. Three-photon absorption coefficients, excited-state absorption cross sections, a Raman gain factor, and two-photon absorption cross-section spectra are determined. The arrangementsEc andE c are considered.     

Time-resolved UV absorption of polyimide

The 355-nm transient absorption of polyimide thin films has been measured following excitation withsubablative, 24-ps long, 355-nm laser pulses. The 355-nm absorption increases by 25% following 355-nm, 20 mJ/cm² excitation and recovers with a fast time constant 34 ps, and a slow time constant which is much longer than 6 ns. The data are fitted by a three-level rate equation model incorporating the temperature dependence of the ground state absorption coefficient. The fast component is attributed to the decay ofS ₁ and the slow component results from increased ground state absorption caused by a laser-induced temperature rise. The nonlinear intensity dependence is attributed to excited state (S ₁) absorption. These results indicate the importance of considering the dynamic absorption in modelling ablation.     

Photoacoustic X-ray absorption fine-structure spectroscopy of the NiK-edge

The X-ray absorption in a 5 m thick Ni foil for energies from 8.2 keV to 8.8 keV was measured by the photoacoustic method using a gas-microphone-cell. Results are presented for both photoacoustic amplitude and phase as a function of incident photon energy. The absorption fine structure above the NiK-edge is clearly resolved. The data are compared with a simple theory for the signal generation, and discrepancies are explained by discussing the various energy dissipation channels following the X-ray absorption.     

俄罗斯“绿龙晶”的成分和结构特征研究

随着近几年文玩市场的兴起,"绿龙晶"成为人们喜爱的一类新兴的宝玉石品种。目前对于"绿龙晶"的主要矿物组成的认识仍存分歧。采用常规宝石学仪器测试、电子探针、红外吸收光谱和X射线粉晶衍射测试方法对产自俄罗斯的"绿龙晶"玉的基本性质、化学成分、红外吸收光谱及矿物组成特征等进行了较为详细的研究分析。结果显示:俄罗斯"绿龙晶"玉主要为深绿至灰绿色,表面具有特殊的放射状花纹及典型的丝绢光泽,折射率约为1.57,密度为2.61g·cm-3。"绿龙晶"中SiO2的含量为36.177%~36.651%,MgO含量为36.439%~36.730%,Al2O3含量为11.961%~12.318%,FeO含量为2.304%~2.853%,具富镁贫铁特点。样品中Al/(Al+Mg+Fe)为0.185 3~0.215 9,推测其为镁铁质岩蚀变成因。样品中的Si=3.10~3.40,Fe~(2+)/R~(2+)=0~0.024 8,属叶绿泥石类型。"绿龙晶"的红外吸收光谱为特征的绿泥石振动谱峰,高频区3 673cm~(-1)附近的吸收峰为OH伸缩振动所致,1 400cm~(-1)附近吸收峰属OH弯曲频率,1 000cm~(-1)附近的三个吸收峰由Si—O伸缩振动致,400~600cm~(-1)之间的吸收谱带属于Si—O弯曲振动。其中中频区1 000cm~(-1)附近分裂的三个吸收峰1 051,1 006和968cm~(-1)可作为鉴定其为叶绿泥石的关键证据。X射线粉晶衍射分析结果与化学成分及红外吸收光谱分析结果一致,显示"绿龙晶"中的主要组成矿物为叶绿泥石,非斜绿泥石。     

The relationship between absorption coefficient and temperature and their effect on the atmospheric cooling rate

Several approaches are considered to determine the temperature effect on the absorption coefficient within a correlated k-distribution method. Taking in the 610- region for example, the absorption coefficients and atmospheric cooling rates calculated using these approaches are compared with line-by-line integration. It is emphasized in this paper by numerical calculation that the effect of pressure on absorption coefficient is related to temperature and vise versa; the larger the pressure, the larger the effect of temperature on absorption coefficient. Results show that the temperature effect must be considered in radiative calculations although its effect on the absorption coefficient is much smaller than that of pressure.     

Fast method for calculating infrared spectral transmittances in the wings of absorption lines

When performing line-by-line simulations of atmospheric high-resolution infrared spectra, a large portion of the computation time is spent in the calculation of the absorptions by the far wings of the absorption lines. For applications in which one is interested mainly in evaluating the effective absorption in a microwindow, a computationally less expensive method has been developed. The method is faster than the explicit line-by-line calculation by a factor proportional to the number of line wings that contribute to the absorption in the simulated microwindow. This paper presents the method and demonstrates its performances in the 700- infrared band. Typically one obtains a gain in computation time of order 25.     

Tunable laser radiation,nonlinear absorption,and “anti-stokes” luminescence of color centers in α-Al2O3

This work investigates the generation of laser radiation by color centers of leucosapphire, nonlinear absorption, and the excitation mechanism of UV-luminescence. It is shown that UV-luminescence from color centers, excited in the 0.68 m absorption band, is caused by a two-staged excitation mechanism. The optical characteristics of the color centers are measured and calculation is made of the variation of the absorption coefficient with laser pulse's duration.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 41–46, October, 1987.     

反常吸收与高质量的远红外光谱

在水汽含量恒定但相对湿度较大的情况下,远红外光谱仪得不到理想的100%线。这表明过高的水汽含量将会导致反常吸收现象。反常吸收的出现将严重影响远红外光谱的质量。研究了光谱仪内部空气相对湿度和光谱分辨率对反常吸收的影响,发现降低水汽含量和采用适当光谱分辨率可以有效抑制反常吸收现象,对获得高质量的远红外光谱很有益处。在无反常吸收现象发生的实验条件下,采用"湿度中和法"在空气湿度波动的情况下也可以得到理想的100%线,这为快速获得高质量的远红外光谱提供了新测量方法。     

Absorption of external thermal radiation in asymmetrically illuminated droplets

A theoretical model of thermal radiation absorption in semi-transparent droplets at the surface and inside a fuel spray is presented. Asymmetry of droplet illumination is taken into account. Results of Mie calculations of thermal radiation absorption inside large spherical droplets illuminated from a hemisphere are presented. Simple approximations for the angular and radial dependencies of the absorbed radiation power are suggested. These approximations are generalisations of the approximations suggested earlier by the authors for the case of symmetric illumination of droplets. They predict the results close to those which follow from the Mie calculations. Results of approximate calculations for a typical diesel fuel droplet at the periphery of the spray are presented. As in the case of symmetrical droplet illumination, an increased absorption of thermal radiation in the central area of the droplet is predicted. Also, at the illuminated side of the droplet, the absorption of radiation in a thin layer near the surface of the droplet is predicted, as in the case of symmetrical droplet illumination. Absorption of radiation in the central area of the droplet is related to the contribution of radiation in the spectral ranges of semi-transparency. The maximum of radiation absorption near the droplet surface is linked to the contribution of radiation in the vicinity of the diesel fuel absorption peak .     

Method of Eliminating Systematic Errors of Atomic Absorption Analysis in Atomization of a Material in a Graphite Furnace

By taking as an example the obtaining of the spectra of the gas phase over alkali metal iodides and calcium fluoride, we show the possibility of eliminating systematic errors of atomic absorption analysis which are due to nonselective absorption of light. It is been suggested that it makes sense to create a database that would contain molecular absorption spectra of the most abundant substances and would be intended for use by chemistsanalysts.     

Multichannel selective femtosecond coherent control based on symmetry properties

We present and implement a new scheme for extended multichannel selective femtosecond coherent control based on symmetry properties of the excitation channels. Here, an atomic nonresonant two-photon absorption channel is coherently incorporated in a resonance-mediated (2+1) three-photon absorption channel. By proper pulse shaping, utilizing the invariance of the two-photon absorption to specific phase transformations of the pulse, the three-photon absorption is tuned independently over an order-of-magnitude yield range for any possible two-photon absorption yield. Noticeable is a set of "two-photon dark pulses" inducing widely tunable three-photon absorption.     

Nonlinear absorption measurements in proustite (Ag3AsS3) and CdSe

Nonlinear absorption has been observed in proustite at 694 nm; however at 1.06m, in contrast to previous results, no nonlinear absorption could be detected at intensities up to the damage threshold. Measurements on CdSe at 1.06m and 1.32m show that the nonlinear absorption mechanism is two photon absorption followed by absorption by the photo-induced carriers. The implications of this for nonlinear mixing applications are discussed.     

In situ measurement of the effective nonlinear absorption order in multiphoton photoresists

Knowledge of the order of the effective nonlinear absorption in multiphoton photoresists is a key element in the development of improved materials for multiphoton absorption polymerization (MAP). The direct measurement of this nonlinearity has proven challenging. A new technique called 2‐beam initiation threshold (2‐BIT) is presented that allows for the unambiguous, in situ measurement of the order of the effective nonlinear absorption using a simple optical arrangement that can be employed with virtually any MAP setup. This technique is benchmarked using three common commercial photoinitiators that have been used previously in MAP and one common dye that acts as a photoinitiator. The linear absorption spectrum is demonstrated to be a poor predictor of the effective order of nonlinear absorption at a given wavelength. Surprisingly, for two of these initiators the effective nonlinear absorption process is dominated by 3‐photon absorption in the 800 nm wavelength range, suggesting that 2‐BIT is a valuable means of identifying initiators that can improve the resolution of MAP.

     

A combination of laser-induced grating and transient-absorption experiments for investigation of laser pulse properties and fast molecular relaxation processes

A repetitive low-power laser-pulse apparatus has been developped which allows both absorption relaxation and light-induced grating experiments without changing geometry or components. The influence of pulse width and coherence time on the diffracted intensity correlation function is discussed for a weak amplitude grating in terms of a simplified theory. From the corresponding absorption relaxation signals including the coherent coupling contribution some easy ways for detecting vibronic-relaxation, intersystem-crossing and orientational-relaxation times are deduced. The advantage of the in-situ measurement of the amplitude grating autocorrelation function leads to a precise zero-delay calibration of the transient absorption equipment. Furthermore one gets the response function for the absorption experiments from the grating experiments, if stable mode-locking operation of the argon laser is reached. This condition can be controlled either by the time course of the absorption or grating signals. A surprisingly short coherence length is detected for the cavity-dumped laser beam. A reliable check of the coherent-coupling theory confirms the theoretical assumptions incorporated into the fast-relaxation signal analysis. Experiments on dye molecules show high triplet yield of heavy-atom substituted dyes and fast rotational diffusion of oblong molecular rotors.     

融入可见光-近红外高光谱吸收特征的新型植被指数估算天然草地FAPAR

考虑到植被可见光-近红外的光谱吸收特征与光合有效辐射吸收率(fraction of absorbed photosynthetically active radiation,FAPAR)有很好的关联,综合“高光谱曲线特征吸收峰自动识别法”与“光谱吸收特征参量化法”,提取对FAPAR敏感的高光谱吸收特征参数,借鉴可见光-近红外植被指数的数学形式,尝试用优化组合后的可见光-近红外光谱吸收特征参数替代光谱反射率,构建新型植被指数估算植被FAPAR,并利用2014年和2015年内蒙古自治区中部与东部地区天然草地典型群落冠层实测光谱数据进行FAPAR估算建模与验证。结果表明: 新型植被指数“SAI-VI”不仅有效提高了单个光谱吸收特征参数在高、低覆盖区域估算FAPAR的精度,而且相比五种与FAPAR有较好相关性的具有不同作用类型的可见光-近红外植被指数,其与FAPAR值的相关性更高(存在最大相关系数=0.801),以其为变量的指数模型预测FAPAR精度更高且稳定性较好(建模与检验的判定系数均最高且超过0.75,标准误差与平均误差系数也相应最小)。研究表明：融入可见光-近红外高光谱吸收特征的新型植被指数“SAI-VI”,强化了可见光波段与近红外波段光谱吸收特征的差别,相较单一光谱吸收特征参数,在降低土壤背景影响的同时增强了对FAPAR变化的敏感度。同时,“SAI-VI”有效综合了对植被FAPAR敏感的光谱吸收特征信息,相较原始光谱反射率,能表达植被光合有效辐射吸收特征的更多细节信息,可作为植被冠层FAPAR反演的新参数,一定程度上弥补当前植被指数法估算FAPAR的不足。     

Switching from "absorption within transparency" to "transparency within transparency" in an electromagnetically induced absorption dominated transition

The absorption of a resonant coupling laser driving a closed degenerate two-level system in an atomic cesium beam was investigated as a function of the detuning of a second laser probing the same transition. The measurements were performed for four different polarization combinations of the two laser beams. Except for the beams of counterrotating polarizations all coupling-laser absorption profiles showed "absorption within transparency," i.e., the absorption in the region around the two-photon resonance was smaller than the absorption corresponding to the one-photon transition induced by the coupling laser, and an extra absorption peak was observed on this curve at the two-photon resonance. With regard to the beams of counterrotating polarizations we observed a switch from absorption within transparency to "transparency within transparency" when the probe-laser power exceeded the constant coupling-laser power. In other words, the cesium ensemble became mostly transparent to the coupling-laser beam at the two-photon resonance.     

Solar absorption by Mie resonances in cloud droplets

Recent studies suggest that resonant absorption of sunlight by cloud droplets may constitute a significant and unaccounted-for solar energy sink in the atmosphere. We spectrally resolve, for the first time, all solar absorption, including sharp resonances, in typical liquid water clouds. Resolving all sharp resonances requires a resolution in size parameter χ=2πr/λ (r—droplet radius, λ—incident wavelength) of about 10^-7. The canonical integration resolution Δχ≈10^-1 produces absorption biases up to 70% over 10 nm spectral bands. Hence, neglecting Mie resonances may cause substantial biases in radiance-based retrievals from sensor channels where atmospheric absorption is particle dominated.The canonical resolution produces broadband solar mean and RMS absorption coefficient biases of about 0.02% and 4%, respectively. Self-cancellation of the pseudo-randomly distributed biases explains why the mean bias is much smaller than the RMS bias. Exceeding 1% RMS accuracy in solar absorption requires Δχ<10^-5. Increased cloud heating due to resolving all resonant absorption is less than 0.1%, equivalent to about global annual mean heating. Overlap of droplet and water vapor absorption within clouds helps diminish the net enhanced absorption by sharp resonances. Hence, the heretofore unrepresented absorption is negligible for global climate, though very important for narrow spectral regions. These results apply to homogeneous liquid water clouds and aerosols.