Photochemistry of solid C60 with tunable infrared radiation

60 with trains of picosecond infrared (IR) pulses, tuned over the 8–15 μm range, is studied. At some specific wavelengths, white-light emission as well as ejection of ionic species from the solid is observed. The spectral characteristics of the white-light emission resemble those of a black body. The mass distribution of the ejected ionic species shows substantial amounts of C₆₀ coalescence products. Unexpectedly, all these processes only occur at wavelengths where solid C₆₀ is relatively transparent. No white-light emission nor ejection of ionic species is observed when being resonant with an IR-allowed transition of C₆₀. It is concluded that regular C₆₀ is not the chromophore for the observed processes, and that sequential absorption of single photons by a strong absorber that is dilute in the crystal takes place. Plausible chromophores are sites that are intercalated with alkali metals. Accumulation of energy at these sites leads to fullerene coalescence in the solid, ion ejection, and white-light emission, ultimately resulting in the destruction of the C₆₀ molecules. Received: 14 April 1998/Accepted: 22 April 1998     

Effect of diffusion on absorption and saturation of infrared radiation in molecular gases

Effect of diffusion on absorption of infrared radiation and saturation of absorption in molecular gases is considered. Incorporating the diffusion term, a theory is developed from multi-level rate equations, both for homogeneous and inhomogeneous broadening cases. It is shown that the effect of diffusion is characterized by a diffusion functionK'(k ₂ a), which varies inversely with the radius of the laser beam at low pressures and small beam sizes. Experimental results with seven molecular gases pumped by the CO₂ laser beam around 10.6 μm are reported.     

Atomic line radiation in the infrared

The present paper considers atomic infrared line emission from states of high angular momentum, which should be significally populated in a high-temperature, equilibrium (LTE) gas. Such states are shown to give rise to a “universal” series of strong lines, the first member of which is at ～4μ, and corresponds to the puzzling 4 μ-feature by Taylor and Caledonia.Several of the higher members of the predicated series are found in cesium spectra taken in our laboratory.     

On quantum effects on the surface of solid hydrogen

The low-frequency spectrum of hypothetical superfluidity on the free surface of a quantum crystal of hydrogen is determined. In the quantum-rough state of the surface, crystallization waves with a quadratic spectrum should propagate. In the atomically smooth state, the spectrum is linear. Crystallization waves propagating along elementary steps are also considered.     

Two-dimensional hydrogen behaviors on solid surfaces studied by hydrogen microscope

Recently, much work has been done to study hydrogen behavior on solid surfaces for applications in fuel cells, semiconductor devices, and diamond-like carbon films. We have developed a hydrogen microscope making use of electron stimulated desorption (ESD) spectroscopy. A thermal-field emission type electron gun set to a low-energy range (<1 keV) is used to obtain a beam size less than 100 nm in diameter. A pulsed beam has been used to measure the time-of-flight (TOF) to detect desorbed ions from specimen surfaces. Scanning the pulsed beams across solid surfaces, a two-dimensional distribution image of hydrogen atoms can be obtained. This paper reviews some capabilities of the hydrogen microscope and a chemical state analysis for H and O adsorbed by different elements on a surface.     

Generation of high-energy negative hydrogen ions upon the interaction of superintense femtosecond laser radiation with a solid target

The formation of a high-energy (～35 keV) beam of negative hydrogen ions was observed in the expanding femtosecond laser plasma produced at the surface of a solid target by radiation with an intensity of up to 2× 10¹⁶ W/cm². The energy spectra of the H⁺ and H^?-ions show a high degree of correlation.     

Influence of infrared radiation on the excitonic absorption edge of CuCl

We report changes in the excitonic absorption edge of CuCl caused by intense CO₂ laser radiation at 10.6 m, a wavelength which lies in the infrared (ir) transparency region of CuCl. With an ir intensity of 0.4 GW/cm² we observe a 100% absorption increase for the Kr⁺ laser probe wavelength of 406.7nm. The effect scales linearly with ir intensity but does not depend on relative polarization. We explain the effect by laser field induced electroabsorption of the exciton. The magnitude of the effect is closely related to electroabsorption induced by static external fields and by internal electric fields from optical phonons.     

Megabar-pressure infrared study of hydrogen deuteride

Solid hydrogen deuteride (HD) has been studied to a pressure of 159 GPa and to low temperatures using near infrared spectroscopy. Of the two high pressure phases observed in hydrogen and deuterium, known as the BSP (broken-symmetry phase) and the A phase, only the BSP had been observed in the lower pressure region of the phase line of HD and it was unusually different from the homonuclear diatomic species with a reentrant behavior. In this Letter the BSP phase line is identified to its maximum pressure of 159 GPa. Infrared absorption reveals a transition to the A phase, observed for the first time in HD with onset at 157+/-3 GPa. A new phase of electric dipolar order that should occur at low temperature is discussed.     

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO₂ lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO₂ lasers. Using the combination of lines from a waveguide CO₂ laser, with its larger tuning range, with lines from CO₂, N₂O, and CO₂ isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm^–1) with stepwise-tunable cw radiation.Contribution of the National Bureau of Standards, not subject to copyright     

红外辐射场理论模拟中的普适性模型研究

在现有海面目标红外辐射场理论建模工作的基础上建立了具有普适性意义的海面目标红外辐射场理论建模通用框架,重点对建立目标的几何构型、适用于各种微元的物理模型、及通用的三维数据场可视化这三个问题进行了叙述。所得结果不仅对海面各种目标红外辐射场的计算机模拟研究具有普遍的意义,且对空中、陆地及其他场景中目标的红外辐射场理论建模研究也有一定的借鉴作用。     

基于图像的飞行器红外辐射特性测量

通过将目标在一定波段内的红外辐射等效为红外成像系统前一定距离下黑体在对应波段内的红外辐射,建立了等效辐射方程。根据黑体辐射定标实验数据,利用非线性回归方法确定了在不同的积分时间条件下红外凝视成像系统输出红外图像的灰度值与在一定距离下的黑体温度之间的定量关系,建立了辐射定标方程。在Visual C++6.0平台下,在对红外目标图像进行SUSAN滤波等预处理后,分析了已知目标距离的红外图像的灰度均值。首先根据辐射定标方程计算出目标等效为黑体的温度,然后利用等效辐射方程反推目标的红外辐射强度,以达到根据跟踪的红外图像确定红外目标辐射特性的目的。此项研究不仅可以为目标识别提供目标分类、识别和辨认所必需的光谱数据库,而且还可以为红外预警提供重要的参考数据。     

Effect of a magnetic field on the radiation emitted by a nonequilibrium hydrogen and deuterium plasma

Radiative transfer in a nonequilibrium plasma in an external electric field is considered. The system of kinetic equations determining the populations of atomic levels is written taking into account the combination of collision and radiative processes and is solved together with the kinetic equation for photon of various frequencies, which are emitted and absorbed in the radiative transitions from the states of the continuous and discrete spectra. The shape of spectral lines is determined from the solution of the quantum-mechanical problem on the emission of an atom in the electric field of the plasma and an external magnetic field, taking the Doppler effect into consideration. The developed approach is used in the model calculation of radiative transfer under the conditions corresponding to the edge plasma in a tokamak, which is simulated by a homogeneous plane layer of a deuterium plasma. It is shown that the joint action of the external magnetic field and the electric plasma fields considerably affects the spectral and integrated characteristics of the radiation.     

Characterization of solid hydrogen targets

In experiments using the TRIUMF solid hydrogen target system, the knowledge of the target thickness and uniformity is often essential in order to extract physical parameters from the data. We have characterized the thickness and uniformity of frozen targets using the energy loss of alpha particles. An accuracy of 5% was achieved, a limit imposed by the uncertainty in the stopping powers: The details of the method are described, and the thickness calibration of the target is presented.     

基于光学厚度的云红外辐射计算

 为了研究不同物理厚度和不同波段下云的红外辐射特性,提出了基于光学厚度的云红外辐射计算方法。综合考虑云的红外辐射的各个因素,建立了较为完善的云的红外辐射模型,引入光学厚度经验计算公式,并根据光学厚度针对中波和长波红外分别计算了云的发射率、反射率和透过率,进而得到云的红外辐射亮度分布。利用该计算方法,计算了中波和长波红外云的辐射亮度数值,计算结果表明：随着光学厚度增大,云的发射率和反射率增大,探测器接收到的云红外辐射增强。比较发现,该计算结果与实测数据有较好的一致性,该计算模型可以为云背景的红外特性分析、探测及仿真提供参考数据。