Study of sequential two photon absorption and conduction band electrons absorption in ZnSe

Using the Z-scan technique and pump–probe technique with 130 fs laser pulses at 800 nm, we verify that an intraband one-photon absorption follows the interband two photon absorption. Particularly, we find that there is an intraband relaxation interspersed between these two absorption processes for some of the conduction band electrons but not all of them. In this study, we measure the interband two photon absorption coefficient and the absorptive cross sections associated with both excitation pathways within the conduction band. In addition, we estimate the time for relaxation of electrons within the conduction band to be 250 fs.     

Photoassociation of ultracold RbCs molecules into the （2）0- state （v = 189,190） below the 5S1/2 ＋ 6P1/2 dissociation limit

Ultracold polar RbCs molecules are produced via photoassociation in a laser-cooled mixture of 85Rb and 133Cs atoms. The a 3Σ+ state molecules which decay from electronically excited (2)0- state RbCs molecules are detected by resonance-enhanced two-photon ionization. The new rovibrational levels (v = 189, 190) in the (2)0- state are also observed, which exist in theory and have not been observed in experiments yet. The corresponding rotational constants are measured by photoassociation spectroscopy, which are consistent with theoretical calculations using a nonrigid rotor model.     

分子光学及其应用前景

随着原子光学的快速发展，一门新兴的有关研究中性分子与电场、磁场和光场等物质相互作用及其冷却、囚禁、操控与应用的学科——“分子光学”正在逐步形成．文章首先就分子光学的学术内涵及其研究内容作一简单类比与讨论；其次，就冷分子束的产生与超冷分子样品的实验制备、超冷分子物理与光谱学、非线性与量子分子光学的研究及其最新进展进行简要综述．最后，就分子光学的应用前景进行了展望．     

Half-Width Integral Method for Gas Concentration Measuring in Tunable Diode Laser Absorption Spectroscopy

ABSTRACT

We analyze the influence of random errors and absorption shape fitting errors on gas concentration measurement in tunable diode laser absorption spectroscopy. We then propose a new data processing method according to the characteristic of random errors and fitting absorption shape. This method only uses the integral value within the half width at half maximum of the fitting absorption shape to determine the gas concentration in actual measurements. Meanwhile, the O₂ transition at 13,150.197 cm^?1 is selected to measure the O₂ concentration using this method. Compared with the traditional method, the method established in this paper can accurately measure O₂ concentration.     

Characterization of X‐ray gas attenuator plasmas by optical emission and tunable laser absorption spectroscopies

X‐ray gas attenuators are used in high‐energy synchrotron beamlines as high‐pass filters to reduce the incident power on downstream optical elements. The absorption of the X‐ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X‐ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X‐ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2p excited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1s₅ state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X‐ray transmission. The results showed a plasma confined around the X‐ray beam path, its size determined mainly by the spatial dimensions of the X‐ray beam and not by the absorbed power or the gas pressure. In addition, the X‐ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X‐ray beam plays an essential role in the X‐ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators.     

从光晶格中释放的超冷玻色气体密度-密度关联函数研究

利用量子旋转场理论详细研究了从光晶格中释放的超冷玻色气体的空间密度-密度关联函数.由于量子旋转场理论充分考虑了光晶格中冷原子气体的粒子数涨落和相位效应,该理论能有效应用于具有强相互作用的冷原子系统,从而光晶格处于超流态到绝缘态逐渐过渡过程中的超冷原子气体的关联特性在这一理论体系下都得到了很好的描述.结果表明:随着超冷玻色气体逐渐从绝缘态向超流态过渡,其密度-密度关联图样中连续对角斜线也逐渐向分散的尖峰过渡,理论结果与目前实验观测到的结果符合.除此以外,上述密度-密度关联的结果中还包含了超冷原子系统量子耗散效应,相关结论与目前已有的理论和实验一致.     

High-resolution photoassociation spectroscopy of ultracold Cs2 long-range 0g- state：The external well potential depth

High-resolution photoassociation spectroscopy is reported using a modulation spectroscopy technology in a cesium atomic magneto-optical trap. The two lowest vibrational levels have been experimentally observed which have been theoretically predicted in [Phys. Rev. A 75 052501(2007)]. A new potential curve is obtained by using the Rydberg–Klein–Ress method with a well depth of 82.384±0.026 cm-1, which is deeper than the result of previous experiment( 77.909 cm-1) and the theoretical prediction( 81.6445 cm-1).     

Photoacoustic detection of two photon absorption in formaldehyde using pulsed dye laser

Absorption spectra of formaldehyde molecule in the gas phase have been recorded using photoacoustic (PA) technique with pulsed dye laser at various power levels. The spectral profiles at higher power levels are found to be different from that obtained at lower laser powers. Two photon absorption (TPA) is found to be responsible for the photoacoustic signal at higher laser power while the absorption at lower laser power level is attributed to one photon absorption (OPA) process. Probable assignments for the different transitions are given in this paper.     

飞行时间质谱探测磁光阱中超冷分子离子的实验研究

利用飞行时间质谱探测了由磁光阱中的俘获光和 再泵浦光光缔合作用形成的超冷基态铯分子, 研究了微通道板工作电压、加速电场强度和加速电场持续时间对铯分子离子信号强度的影响. 实验结果与理论模型的拟合一致; 获得了适合实验条件的最优化实验参数, 为进一步研究超冷分子的光缔合光谱和光电离光谱奠定了实验基础.     

磁光阱中超冷钠-铯原子碰撞的实验研究

研究了磁光阱中异核超冷钠铯原子的碰撞机理, 测量了超冷钠原子的碰撞损失率, 得到了钠-铯原子的碰撞损失系数β_Na-Cs与钠原子俘获光强度之间的关系. 利用多普勒模型计算了不同俘获光强度下的钠原子磁光阱的阱深, 得到了临界光强的理论值, 与实验结果符合得较好.     

The status of strontium in biological apatites: an XANES/EXAFS investigation

Osteoporosis represents a major public health problem through its association with fragility fractures. The public health burden of osteoporotic fractures will rise in future generations, due in part to an increase in life expectancy. Strontium‐based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk but the molecular mechanisms of the action of these Sr‐based drugs are not totally elucidated. The local environment of Sr²⁺ cations in biological apatites present in pathological and physiological calcifications in patients without such Sr‐based drugs has been assessed. In this investigation, X‐ray absorption spectra have been collected for 17 pathological and physiological calcifications. These experimental data have been combined with a set of numerical simulations using the ab initioFEFF9 X‐ray spectroscopy program which takes into account possible distortion and Ca/Sr substitution in the environment of the Sr²⁺ cations. For selected samples, Fourier transforms of the EXAFS modulations have been performed. The complete set of experimental data collected on 17 samples indicates that there is no relationship between the nature of the calcification (physiological and pathological) and the adsorption mode of Sr²⁺ cations (simple adsorption or insertion). Such structural considerations have medical implications. Pathological and physiological calcifications correspond to two very different preparation procedures but are associated with the same localization of Sr²⁺versus apatite crystals. Based on this study, it seems that for supplementation of Sr at low concentration, Sr²⁺ cations will be localized into the apatite network.     

Fundamental Studies of Photon Migration in Biological Tissues and Their Application to Optical Tomography

This paper reviews the studies of photon migration in biological tissues and its application to optical tomography which were conducted in the Mechanical Engineering Laboratory of Japan’s Ministry of International Trade and Industry. The research subjects range from theoretical and experimental studies of photon migration in random media to the development of image reconstruction algorithms and experiments for optical tomography. The most fundamental theoretical study of the photon diffusion equation has proved that the photon diffusion coefficient is independent of the absorption coefficient while the conventional one is dependent on the absorption coefficient. Experimental studies included the time-resolved spectroscopy and the fabrication of realistic human head phantoms which have five tissue types with different optical properties. Several types of reconstruction algorithms have been developed and verified experimentally. These investigations are pioneering work in the field of biomedical optics in Japan.