Stark ladder resonances for small electric fields

We prove the existence of resonances in the semi-classical regime of smallh for Stark ladder Hamiltonians in one-dimension. The potentialv is a real periodic function with period which is the restriction to of a function analytic in a strip about . The electric field strengthF satisfies the bounds |v|>F>0. In general, the imaginary part of the resonances are bounded above by, for some 0<1, where _T h ^-1 is the single barrier tunneling distance in the Agmon metric forv+Fx. In the regime where the distance between resonant wells is , we prove that there is at least one resonance whose width is bounded above byce ^–/F , for some ,c>0 independent ofh andF forh sufficiently small. This is an extension of the Oppenheimer formula for the Stark effect to the case of periodic potentials.Partially supported by NSF Grant DMS-8911242     

Absolute detector calibration using twin beams

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.     

托卡马克等离子体被动光谱诊断的绝对标定

综述了托卡马克装置几套常规被动光谱诊断的绝对标定方法以及利用基于碰撞辐射模型的原子数据库诊断出粒子密度以及通量等物理量的方法。其中诊断系统包括可见波段具有高时空分辨的光电二极管阵列、具有高时间分辨的光电倍增管,具有二维空间分辨的高速相机,具有时空分辨和高谱分辨的光谱仪;极紫外波段具有时空分辨的光谱仪等。     

利用分支比法作真空紫外单色仪灵敏度的绝对校准

本实验利用托卡马克的高温等离子体作光源,采用分支比法对掠入射真空紫外单色仪在150(?)～1640(?)波段的灵敏度作了绝对校准.文章对该方法的技术问题也作了讨论.     

High resolution submillimetre Stark spectroscopy using an HCN maser

High resolution Stark spectra have been observed for the pure rotation transition of D₂O which lies very close to the 337 µm HCN maser emission. The assignment of the transition is confirmed as 6₂₄-6₁₅ and the frequency separation as approximately 370 Mhz on the low frequency side of the maser emission.

Stark spectra have been observed for several other gases but due to the large number of Stark components complete resolution was not achieved. However, it is shown that even in these cases some information can be gained about the type of pure rotation transition responsible for the absorption.     

Coherent NMR Stark spectroscopy

We demonstrate phase-coherent Stark effects from a radiofrequency E field at twice the NMR frequency (2ω(0)) of (69)Ga in GaAs. The 2ω(0) phase (?(E)) selects component responses from the nuclear quadrupole Hamiltonian (H(Q)). This is possible by synchronizing few-μs 2ω(0) pulses with an NMR line-narrowing sequence, which averages the Stark interaction to dominate spectra on a background with 10(3)× enhanced resolution. Spectra vs ?(E) reveal relative sizes of tensorial factors in H(Q). Comparative modeling and numerical simulations evaluate spectral features unexplained by average Hamiltonian theory, and suggest improvements for quantitative calibration of individual response components. Application of this approach to bulk samples is of value to define Stark responses that may later be used to interrogate the internal electrostatics of structured samples.     

Absolute work function measurement by using photoelectron spectroscopy

Work function (WF) of a material is not only an intrinsic characteristic of bulk but also a surface property. The measurement and control of WF have been of great concern in many electronic and optical devices as the WF governs charge transfer and charge injection/collection efficiency at interfaces and emission characteristics of conventional charged particle emitters. Photoelectron spectroscopy (PES) has been mainly used to determine surface electronic structure and chemical composition. Despite the common use of this technique to measure WF, there has been a lack of discussion on how to use the PES and what to be considered to determine the absolute WF. The main contribution of this review lies in the discussion of the causes of errors when measuring WF, and provides a guide for reliable WF measurement. Along with the limitations of current measurement technology, we propose future directions for absolute WF measurement.     

Laser Stark spectroscopy of FCN

Using a CO₂ laser, Stark shifted resonances have been measured for the CF stretching fundamental (ν₃) of FCN near 9.3 μm, and for two nearby “hot” bands. The band centers measured are 1076.492007 ± 0.000013 cm^?1 for 00⁰1-00⁰0, 1085.741046 ± 0.000050 cm^?1 for 01¹1-01¹0, and 1091.16222 ± 0.00015 cm^?1 for 02⁰1-02⁰0. The ground state dipole moment of FCN is found to be 2.1203 ± 0.0010 D and dipole moments are also given for the other states observed. Values are given for the rotational constant and l-doubling constant for the 01¹1 state.     

Nonlinear spectroscopy of barium in parallel electric and magnetic fields

We report on the experimental spectral observations of barium in parallel electric and magnetic fields. The laser pulse is linearly polarized along or perpendicular to the fields, leading to the states m = 0 and the states m = -t-1 populated, respectively, by one photon excitation. By sweeping the electric field, we observe the linear and nonlinear splitting of the diamagnetic spectrum as the electric field increases. The spectral anticrossing is induced by the atomic core effect. The Stark spectrum also shows an obvious nonlinear quadratic behavior when the applied magnetic field varies strongly. All spectra are well explained by the full quantum calculation after taking the quantum defect effects of the channel ns up to nf into account.     

Stark mixing spectroscopy in cesium

We present a new technique for selectively populating excited states which are inaccessible by dipole excitation from the ground state. The method uses a static electric field to introduce a component of a dipole-allowed state into the state of interest. We have applied the method to cesium to measure lifetimes and a Stark mixing coefficient. The results are $\text{τ(6}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=64(2) ns}$, $\text{τ(7}{}^2\text{D}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{)=92.5(15) ns}$, and <6²D_{$\text{5}\text{2}$}|;ez |7²P_{$\text{3}\text{2}$}>/(E_7P?E_6D)=0.7(3)×10^?3 where is in kV/cm. 141     

Forming concentric double-emulsion droplets using electric fields

Double-emulsion droplets may be assembled into highly concentric shells using a uniform AC electric field to induce dipole/dipole interactions. The resulting force centers the inner droplet with respect to the outer shell if the outer droplet has a higher dielectric constant than the ambient, suspending liquid. The dielectric constant of the inner droplet does not influence this condition. Applying an electric field >10⁴ V_rms/m achieves centering of approximately 3–6 mm diameter droplets suspended in ～10 centipoise liquids within ～60 s. If the outer shell is electrically conductive, the effect depends strongly on frequency. In the case of the monomer-containing liquids requisite to forming foam shells for laser target fabrication, the electrical field frequency must be ～10 MHz or higher. Because of very stringent requirements imposed on the concentricity and sphericity of laser targets, electric field induced droplet distortion must be minimized. Consequently, the liquid constituents must be matched in density to ～0.1%.     

Absolute measurement of sputtered ion fractions using matrix isolation spectroscopy

Sputtering yields for neutrals and ions have been measured by collecting the sputtered species in a noble gas matrix and determining their amounts from optical absorption spectroscopy. The atomic ion fractions for Ti and Zr bombarded by O₂⁺ at 2 keV are 0.8 and 0.4, respectively, whereas TiO and ZrO are sputtered largely as neutrals. Neutral sputtering yields from Ar⁺ bombardment arc consistent with previous measurements. The experimental results are compared with various theoretical models for the sputtering process.     

Time-resolved Stark effect in rapidly varying fields

The cycle-averaged ac Stark effect associated with the ^[ A _]2Σ⁺v^′=2?^[ X _]2Π1/2v^′=0 two-photon absorption of NO at intensities between 7.7 and 15.2 TW cm^-2 has been characterized in real time through a synergic combination of bichromatic laser experiments and quantum-dynamics calculations. Measurements of the fluorescence emitted by the Rydberg ^[ A _]2Σ⁺v^′=2 level as a function of time between Stark and probe components of a bichromatic field exhibit a characteristic evolution in temporal peak structure with Stark-field intensity, which is interpreted in terms of a time-dependent Floquet analysis of the laser–matter interaction. The experimental observations are consistent with a dynamic Stark shift of Δε_s(ω₁,ω₂)≤0.23 eV of the optical transition at these intensities. Received: 18 January 2002 / Revised version: 6 March 2002 / Published online: 24 April 2002     

Compression of positron clouds using rotating wall electric fields

An asymmetric dipolar rotating electric field can be used to compress a trapped cloud of positrons when applied with a frequency close that of their axial bounce, and in the presence of a low pressure molecular gas to provide cooling. Measurements of the compression rate and associated parameters are presented and compared with results of a theory we have developed. The latter treats positron behaviour in a perfect Penning trap potential, in the presence of the rotating field, with the cooling modelled in the Stokes viscous drag approximation. Good agreement between the theory and experiment has been found, which has allowed us to identify the phenomenon as a new form of sideband cooling.     

成像光谱仪绝对辐射定标技术研究

为了实现成像光谱仪绝对辐射定标,以高稳定均匀光源为基础,结合单色仪、大口径平行光管和标准辐射计,建立了一套绝对辐射定标系统。在绝对辐射定标系统上采用替代法标准辐射计标定出被测成像光谱仪入瞳面上的光谱辐射照度,通过获得被测成像光谱仪各像元的输出信号,计算得到各像元的光谱辐射照度响应度,从而实现成像光谱仪可见到远红外波段范围内的绝对辐射定标。实验验证成像光谱仪绝对辐射定标的不确定度优于5%。     

Surface structuring of particle laden drops using electric fields

Emulsion drops readily adsorb particles at their surfaces, which may lead to a fluid or solid layer encapsulating the drop, known as an armored drop. In this review, we discuss how electric fields can be used to manipulate colloidal surface structures, by dielectrophoretic or electro-hydrodynamic mechanisms and we also compare this to related phenomena in lipid bilayer vesicles. The phenomena discussed are important for a wide range of uses of particle laden drops, including emulsion stabilization, Janus or patchy mesocapsule-, scaffold- or other materials-production.     

Possibility for separation of polarizable molecules using electric fields

The motion of polarizable molecules in the presence of nonuniform electric fields is analyzed. The separation of molecular flows in the presence of such fields is theoretically demonstrated. Angular dispersions are estimated for endofullerene (Sc@C₈₂, Y@C₈₂, La@C₈₂, and Gd@C₈₂) and fullerene (C₆₀, C₇₀, C₈₂, and C₈₄) molecules in the presence of the field that is generated by a system of parallel charged wires using the known dipole moments and polarizabilities. The numerical simulation shows that a separator of polarizable molecules can be constructed using such fields.