Optical absorptions of a biexciton quantum dot

A investigation of the linear and nonlinear optical properties for intersubband electronic transitions associated with a biexciton in a quantum dot has been performed by using the method of few-body physics. The optical absorption coefficients and the refractive index changes have been examined based on the computed energies and wave functions. It is over two orders of magnitude higher than that obtained in an exciton quantum dot. The results show that the optical absorption saturation intensity can be controlled by the confinement potential frequency and the relaxation time.     

单层膜体吸收与界面吸收研究

采用热透镜测量方法进行了SiO₂和HfO₂单层膜的体吸收与界面吸收分离研究.首先推导了光从薄膜侧及基底侧入射时单层膜内的驻波场分布,给出了单一厚度薄膜分离体吸收和界面吸收的计算方程式以及求解薄膜消光系数的方法.利用电子束蒸发工艺制备了半波长光学厚度(λ=1064 nm)的SiO₂和HfO₂单层膜,通过热透镜的测量数据实际分离了两种薄膜的体吸收和界面总吸收.计算结果表明,对于吸收小至10^{-6关键词： 驻波场理论 光热技术 薄膜吸收 消光系数}     

Intersubband optical absorptions of a two-electron quantum ring

In this Letter, the optical properties of a quantum ring with two electrons are studied. Its effective-mass Hamiltonian matrix was diagonalized with numerical methods, followed by the calculations of a number of optical quantities. We have found that the intersubband optical absorptions strongly depends on the ring radius, electron-electron interaction, and the incident optical intensity. We also found that the spin-singlet states are more sensitive to ring radius than the spin-triplet states.     

单层与双层石墨烯的光学吸收性质研究

采用紧束缚模型分别描述单层、双层石墨烯的能带结构, 利用光子-电子相互作用的二阶微扰理论分别计算单光子和双光子吸收系数.计算结果表明: 单层石墨烯单光子吸收系数为常数, 约为6.8×10⁷ m^-1, 即单层石墨烯对入射光的吸收率约为2.3%; 双层石墨烯的单光子吸收比单层石墨烯的单光子吸收强, 且随入射光波长呈分段性变化.单层石墨烯的双光子吸收系数与波长λ⁴成正比; 双层石墨烯双光子吸收系数在红外波段(～ 3100 nm处)有一个很强的共振吸收峰. 研究结果可为石墨烯材料在光电子器件的研究和制作方面提供指导. 关键词： 石墨烯 光学吸收 紧束缚模型     

Photo-acoustic and photo-refractive detection of small absorptions in liquids

The sensitivities of pulsed photo-acoustic and photo-refractive (e.g., thermal lensing) techniques for the measurement of small absorptions in liquids have been evaluated both theoretically and experimentally. Electrostriction limits the sensitivity of both techniques, this limitation is less severe for the photo-refractive technique. The minimum absorption constants observed experimentally, for a 200-μm laser spot size in liquid N₂, are 4 × 10^-5 cm^-1 for the photo-acoustic measurement and 6 × 10^-7 cm^-1 for the photo-refractive measurement. The calculated electrostrictive limits are 2 × 10^-5 cm^-1 and 7 × 10^-11 cm^-1, respectively.     

Terahertz field-induced modulations of intersubband absorptions in quantum wells

Nonlinear optical properties of intersubband electrons in a 3-level quantum well under intense terahertz field are investigated by using a density matrix approach. The results show that the terahertz fields with different frequencies cause the distinct modulations of the intersubband absorptions. The terahertz-induced sideband and Autler--Towns splitting in the absorption spectrum are obtained, respectively for the terahertz-photon energy below and close to the transition energy between the ground and first excited state.     

Optical absorptions in ZnO/a-Si distributed Bragg reflectors

The distributed Bragg reflectors (DBRs) consisting of alternating layers of ZnO and heavy doped amorphous silicon (a-Si) have been fabricated by magnetron sputtering. It is novel to find that the optical absorptions exist in the stopband of the DBRs, and that many discrete strong optical absorption peaks exist in the wavelength range of visible to near-infrared. The calculated results by FDTD show that the absorptions in the stopband mainly exist in the first a-Si layer, and that the light absorbed by other a-Si layers inside contributes to the two absorption peaks in near-infrared range. The strong absorptions ranged from visible to infrared open new possibilities to the enhancement of the performance of amorphous silicon solar cells.

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New resonant absorptions in liquids - local lattice modes

It is shown conclusively that the far infrared spectra of liquids (polar and non-dipolar) are composed of sharp resonant absorptions which may be compared directly with the lattice modes resolved in the solid. This is an unexpected discovery which shows that local molecular structure is preserved on passing from the solid state into the liquid. The observations have wide ranging consequences for condensed state physics which demands we reappraise some of the most basic concepts on which our classical theories of liquid state matter are based.     

Excited-state absorptions of an exciton confined in a quantum dot

The optical absorptions of an exciton with the higher excited states in a disc-like quantum dot are investigated. Calculations are made by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. With typical semiconducting GaAs based materials, the linear, third-order nonlinear, total optical absorption coefficients and refractive index changes have been calculated for the s–p, p–d, and d–f transitions. The results show that as the angular momentum quantum number of transitions increases, the absorption peaks shift towards lower energies and the absorption intensities increase.     

Near-infrared LIF spectroscopy of HfF

The molecular ion HfF⁺ is the chosen species for a JILA experiment to measure the electron electric dipole moment (eEDM). Detailed knowledge of the spectrum of HfF is crucial to prepare HfF⁺ in a state suitable for performing an eEDM measurement [1]. We investigated the near-infrared electronic spectrum of HfF using laser-induced fluorescence (LIF) of a supersonic molecular beam. We discovered eight unreported bands, and assign each of them unambiguously, four to vibrational bands belonging to the transition [13.8]0.5 ← X1.5, and four to vibrational bands belonging to the transition [14.2]1.5 ← X1.5. Additionally, we report an improved measurement of vibrational spacing of the ground state, as well as anharmonicity ω_ex_e.     

稀土-PAN配合物的近红外发光研究

金属指示剂1－（2－吡啶偶氰）－2－萘酚（PAN）对Ln^3 (Ln^3 -Yb^3 ,Nd^3 和Er^3 )的近红外发光有不同的敏化作用，不论在固体还是在溶液中，PAN分子都可显著地敏化Yb^3 离子的发光，对Er^3 离子的发光也有一定的敏化作用，但不能敏化Nd^3 离子的发光，溶剂的种类对配合物溶液的近红外发光强度有非常明显的影响，根据配体三重态能级与Ln^3 的发射能级匹配的原理和浓度猝灭效应，对不同条件下Ln-PAN配合物的近红外发光行为进行了解释。     

Determination of free-carrier and phonon-assisted absorptions for Si-doped GaSb thin layers

Photothermal deflection spectroscopy is used in order to investigate near- and sub-band gap absorption of Si-doped GaSb epilayers deposited by MBE on a semi-insulating GaAs substrate. The optical absorption spectra show an extra absorption on the transparency region below the bandgap due to free-carrier absorption. However, for energies above the gap, we notice a linear behavior of the square root of the absorption coefficient versus the heating beam energy, which is attributed to phonon-assisted absorption. From interpolation of the phonon absorption to low energies we have determined the free-carrier absorption that is found to follow the Drude law.     

飞秒激光所致金纳米粒子析出的玻璃非线性吸收

依据Z-scan技术,使用波长532nm的纳秒脉冲,研究了通过聚焦的飞秒脉冲诱导并辅以热处理得到的金纳米粒子析出的玻璃的非线性吸收.观察到金纳米粒子析出的玻璃具有饱和吸收特性.根据局域场效应,对实验结果拟合,得到在接近表面等离子体共振激发情况下,金纳米粒子三阶极化率虚部分别为Imχ(3)m=57×10-7esu.玻璃样品中金纳米粒子的非线性响应主要起源于热电子贡献. 关键词： 带内跃迁 带间跃迁 热电子贡献     

The theory and experiment of solute migration caused by excited state absorptions

Nonsymmetrical transition from reverse-saturable absorption (RSA) to saturable absorption (SA) caused by excited state absorption induced mass transport of the CuPcTs dissolved in dimethyl sulfoxide is observed in an open aperture Z-scan experiment with a 21-ps laser pulse. The nonsymmetrical transition from RSA to SA is ascribed neither to saturation of excited state absorption nor to thermal induced mass transport, the so-called Soret effect. In our consideration, strong nonlinear absorption causes the rapid accumulation of the non-uniform kinetic energy of the solute molecules. The non-uniform kinetic field in turn causes the migration of the solute molecules. Additionally, an energy-gradient-induced mass transport theory is presented to interpret the experimental results, and the theoretical calculations are also taken to fit our experimental results.     

Parameters-dependent nonlinear absorptions in InGaN/GaN MQW and GaN film

The optical nonlinearities of an InGaN/GaN multiple quantum well (MQW) and a GaN film were experimentally investigated by using femtosecond Z-scan method in this paper. It was observed that the InGaN/GaN MQW displays a nonlinear saturable absorption (SA) effect and the nonlinear absorption coefficient β was determined to be ; and the GaN film shows a reverse saturable absorption (RSA) effect and the β is . It is also found that the absorption cross sections and quantum confinement effect (QCE) give an influence on the SA of the InGaN/GaN MQW structure.     

Remark on the conductivity sum rule for the optical absorptions of alkali metals

In reference to the optical absorption data for K, Rb, and Cs, it is shown that, when an optical coupling between conduction and core electrons is strong, the Pauli-forbidden transitions of conduction electrons to occupied core states play an important role in the sum rule applied restrictively to the conduction electron system.     

近红外技术在物理特性领域的应用

介绍了近红外光谱分析技术的原理及特点,综述了近红外分析技术在制药、纺织、石化、农业、烟草、木材等行业物理特性领域的应用,认为该技术的应用将会越来越宽广,并对该技术在物理特性领域的应用进行了展望.