Interaction of a supersonic beam of toluene with a resonant RF electric field

Deflection of a cold supersonic toluene beam seeded in He has been observed when these molecules interact with both a static and a resonant oscillating electric field. The toluene beam splits into two beams each one peaking at a deflection angle of 1 degree towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the toluene molecule is 1411 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the toluene dipole moment and the employed RF field gradient. Different hypothesis are suggested to explain the observed strong beam splitting including the possibility of transverse beam interferences induced by both the resonant RF field and the transverse uniform electric field. A theoretical model is presented based on molecular beam interferences induced by the resonant RF field which seems to account satisfactorily for the present observations.     

Interaction of polar molecules with a resonant RF electric field: strong deflection of a NO molecular beam

Deflection of a cold supersonic NO beam seeded in He has been observed when these molecules interact with both static and a resonant oscillating electric field. The NO beam splits into two beams each one deflecting about 0.5° towards the positive and negative direction of the Stark field when the employed resonant frequency between the two Stark levels of the NO molecule is 1515 kHz. This deflection angle is about four orders of magnitude higher than the value one would expect from the NO dipole moment and the employed RF field gradient. This phenomenon suggests the possibility of a significant translational motion perpendicular to the beam axis, which is induced by the resonant RF electric field on the cold and high-density supersonic beam.     

Resonant scattering of three-level Rydberg atoms in a microwave field

We examine the theory of potential scattering of Rydberg atoms in a microwave field. The model of a three-level atom is employed to calculate the radiative force emerging in the resonant coherent interaction with the microwave field for the case of a two-photon resonance and high intensities, using the method of quasienergies of the system consisting of the atom and the field. We determine the probabilities of Landau-Zener transitions in the spatial regions where under two-photon resonance conditions the quasienergies of the atoms approach one another by a small quantity. We also study the dynamics of the variation of the spatial profile of a beam of Rydberg atoms caused by resonant scattering. Finally, we give the results of the first experimental observation of the variation of the transverse beam profile when Rydberg atoms pass through a nonuniform microwave field formed in a rectangular waveguide and in resonance with the two-photon 36P–37P transition. Zh. éksp. Teor. Fiz. 111, 796–815 (March 1997)     

RF focusing of ion beams in the axisymmetric periodic structure of a linac

A new approach to the analysis of charge particle motion in periodic resonant RF accelerators is suggested. A three-dimensional equation of motion in the Hamiltonian form is derived. This equation makes it possible to carefully study the relationship between the transverse and the longitudinal dynamics of the ion beams at low initial energies. General conditions for RF focusing in ion linacs are formulated. Basic results are compared with numerical simulation data for the beam dynamics in the polyharmonic field of the accelerating cavity. A version of an RF-focusing proton accelerator in which the current transmission coefficient is close to that in an accelerator with radio frequency quadrupole is described.     

Transmission of ultrasound through a single layer of bubbles

We investigate, both experimentally and theoretically, the effect of coupling between resonant scatterers on the transmission coefficient of a model system of isotropic scatterers. The model system consists of a monodisperse layer of bubbles, which exhibit a strong monopole scattering resonance at low ultrasonic frequencies. The layer was a true 2D structure obtained by injecting very monodisperse bubbles (with radius a ∼ 100 μm) into a yield-stress polymer gel. Even for a layer with a low concentration of bubbles (areal fraction, n a ² , of 10-20%, where n is the number of bubbles per unit area), the ultrasonic transmission was found to be significantly reduced by the presence of bubbles (-20 to -50 dB) and showed a sharp minimum at a particular frequency. Interestingly, this frequency did not correspond to the resonance frequency of the individual, isolated bubbles, but depended markedly on the concentration. This frequency shift is an indication of strong coupling between the bubbles. We propose a simple model, based on a self-consistent relation, which takes into account the coupling between the bubbles and gives good agreement with the measured transmission coefficient.     

Spin dynamics at low microwave frequencies in crystalline Fe ultrathin film double layers using co-planar transmission lines

Magnetic damping has been studied in magnetic double layers using a network analyzer (NA) with a coplanar transmission line. The magnetic films consisted of ultrathin crystalline films of Fe separated by an Au spacer. The films were deposited on GaAs(0 0 1) substrates using the molecular beam epitaxy (MBE) technique. NA-ferromagnetic resonance (NA-FMR) measurements were carried out along the magnetic hard axis, allowing one to follow the frequency FMR linewidth down to the 1 GHz range of frequencies. It will be shown that the FMR linewidth in the NA-FMR measurements is not entirely described by Gilbert damping. The additional contribution in the frequency linewidth increases with decreasing frequency, and is most likely caused by dipolar fields associated with an inhomogeneous RF field around the coplanar transmission line.     

重离子治癌装置4 MeV/u IH型漂移管直线注入器的动力学设计

基于KONUS束流动力学理论,完成了一台工作频率为162.5 MHz、占空比为1%的交叉指型漂移管直线注入器（IH-DTL）的动力学设计。该IH-DTL内置两套三组合四极透镜,共有41个加速单元,可为同步加速器提供流强400 eμA、能量4 MeV/u的C4+束流。在动力学设计过程中着重对每个加速间隙的同步能量偏差、注入相位和间隙电压等参数进行优化,使得该IH-DTL的横向归一化RMS接收度达到0.24 πmm·mrad,且横纵向归一化发射度增长小于10%,有利于提高同步环的注入效率。然后根据动力学设计的结构参数进行IH-DTL的高频仿真计算,将得到的三维电磁场分布导入PIC粒子跟踪程序中进行束流动力学模拟。动力学模拟结果显示,束流在IH-DTL出口的横向自然发射度小于13 πmm·mrad,达到了同步环的注入要求,而且在7%的垂直二极场分量下,束流中心的横向偏移在±0.5 mm以内,整体的束流传输效率高于99%。An interdigital H-mode drift tube linac (IH-DTL) with KONUS beam dynamic has been designed, which operation frequency was chosen 162.5 MHz. This IH-DTL consists of 41 accelerating cells and two quadrupole magnets triplets, can provide the C4+ with the current of 400 eμA and energy of 4 MeV/u for the synchrotron. In the beam dynamic design, the synchronous particle energy, inject RF phase and the acceleration voltage of each gap are optimized carefully to make the transverse normalized RMS acceptance of the IH-DTL to be 0.24 πmm·mrad and the beam emittance growth small than 10%. Then the RF structure was designed and the 3D electromagnetic field was imported into the PIC particle tracking code for the beam dynamic simulation. The transverse beam emittance at the exit of the IH-DTL is small than 13πmm·mrad which meets the injection requirement of the synchrotron. What is more, under the 7% vertical dipole fields component, the offset between the beam center and the drift tube's axis is ±0.5 mm at most. The transmission efficiency of the IH-DTL is higher than 99% for the whole beam in the acceptance.     

Characterization of an oriented metastable atom source based on a magnetic hexapole

The M_J-state selection of the metastable rare-gas (Rg*) was achieved by a magnetic hexapole that is composed of permanent magnets. The performance of the magnetic hexapole was examined by characterizing the velocity distribution and the spatial profile of the state selected Rg* beam. The characterization was carried out using position resolved time-of-flight analysis and its trajectory simulation. The magnetic hexapole enhanced the beam intensity at least one order of magnitude owing to the focusing effect. In addition, the magnetic hexapole was found to act as a good velocity selector.     

Measurement of the three-dimensional velocity distribution of Stark-decelerated Rydberg atoms

The full three-dimensional velocity distributions of decelerated and accelerated particles in a Stark decelerator for Rydberg atoms and molecules have been measured. In the experiment, argon atoms in a supersonic beam are excited to low-field and high-field seeking Stark states with principal quantum number in the range n=15 to 25 and are decelerated in a 3 mm long decelerator consisting of four electrodes on which time-dependent voltages are applied. The time dependence of the resulting inhomogeneous electric field is chosen such that the decelerating force acting on the high-field seeking states is maximized at each point along the trajectories. The three-dimensional velocity distribution of the atoms before and after the deceleration is determined by measuring times of flight and two-dimensional images of the atomic cloud on the detector. Under optimal deceleration conditions, the decrease in kinetic energy in the longitudinal dimension amounts to 1.0×10^-21 J and the increase in mean kinetic energy in the transverse dimensions is only 1.0×10^-23 J. The corresponding temperatures of 100 mK and 300 mK in the two transverse dimensions are sufficiently low that trapping can be envisaged. The possibility of focusing a Rydberg atom beam is demonstrated experimentally.     

Analysis of open resonators

A multiple reflection approach is employed to examine the properties of the lowQ open resonators commonly used in high power gyrotrons. The resonant frequency, diffractionQ, and RF field profile are derived in closed forms in the lowQ limit. Formation of the eigenmode in the resonator is shown as the result of constructive wave interference. The lower limit ofQ in the context of a conventional definition ofQ is derived.     

Measurement of electric field strengths in a waveguide by means of the dynamic Stark effect in hydrogen and neutral helium spectral lines

The dynamic Stark effect of the spectral lines H_β and of the neutral helium lines λ=402.6 nm (2³ P ⁰−5³ D) and λ=438.8 nm (2¹ P ⁰−5¹ D) emitted from a discharge tube was used for probing rf electric fields in a transverse waveguide. Calculations accounting for the pertubation of the atomic states by strong unidirectional fields prove to be suitable in order to interprete the main experimental results. If the waveguide is terminated with a metallic reflector and the plasma in the discharge tube becomes overdense—then representing a slightly permeable mirror—a resonant enhancement of the electric field strength may be achieved by tuning. This enhancement is well recognizable in the spectral line contours.     

Chaos synchronization in semiconductor lasers with polarization-rotated optical feedback

Chaotic oscillations of the transverse magnetic (TM) mode, which is not a common lasing mode, are excited by using polarization-rotated optical feedback from the transverse electric (TE) mode in a semiconductor laser. In our previous paper, we found that the dynamics were strongly dependent on their RF components under the condition of moderate optical feedback from the TE mode to the TM mode and that they were divided into three RF regions; low-pass filtered signals with a lower frequency than the laser relaxation oscillation frequency, intermediate RF components including the relaxation oscillation frequency, and high-pass filtered signals with a higher frequency higher than the relaxation oscillation frequency. Depending on the frequency bands, the laser outputs showed different correlations. In the present study, using such schemes, the polarization-rotated beam from a transmitter laser (i.e., the rotated TE-mode beam of a transmitter laser) is injected into a receiver laser. We experimentally observe chaos synchronization in accordance with the dynamics of RF components on the transmitter laser side. We also perform numerical calculations using a model and obtain good agreement between the theoretical and experimental results.     

Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X²Π-A²Σ⁺ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO⁺ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.     

Coupling of Acoustical Plane p-Wave to a Cased Borehole

Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot＇s theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.     

射频场控制的磁子能级中单色激光吸收抑制

理论上研究了射频场作用下多塞曼能级系统中单色激光的吸收抑制现象.一束单色线偏振或者椭圆偏振的激光作用于铷原子两能级间,线或椭圆偏振矢量方向与磁场方向垂直.在磁场中冷铷原子能级发生分裂,通过一个射频场将这些磁子能级耦合起来.当扫描射频场频率时,计算表明原子对单色光的吸收谱中出现了透射峰,类似于电磁诱导透明现象,光吸收减弱,光场透射增强.对于线性偏振或者椭圆偏振的单色光均能得到透射增强的结果 .这种现象完全不同于通常光泵磁共振实验中射频场与磁子能级谐振时光被吸收最多的现象.这种扫描射频场频率时单色光的透射增强现象来自于磁子能级间的相干效应.计算表明在扫描射频场频率时单色光吸收谱中出现的透射峰与射频场的拉比频率和椭圆偏振光的左旋和右旋圆偏振成分相关.这种射频场控制的单色光透射增强效应在磁场测量,光信息处理等领域有潜在的应用价值.     

射频场控制的磁子能级中单色激光吸收抑制

理论上研究了射频场作用下多塞曼能级系统中单色激光的吸收抑制现象.一束单色线偏振或者椭圆偏振的激光作用于铷原子两能级间,线或椭圆偏振矢量方向与磁场方向垂直.在磁场中冷铷原子能级发生分裂,通过一个射频场将这些磁子能级耦合起来.当扫描射频场频率时,计算表明原子对单色光的吸收谱中出现了透射峰,类似于电磁诱导透明现象,光吸收减弱,光场透射增强.对于线性偏振或者椭圆偏振的单色光均能得到透射增强的结果.这种现象完全不同于通常光泵磁共振实验中射频场与磁子能级谐振时光被吸收最多的现象.这种扫描射频场频率时单色光的透射增强现象来自于磁子能级间的相干效应.计算表明在扫描射频场频率时单色光吸收谱中出现的透射峰与射频场的拉比频率和椭圆偏振光的左旋和右旋圆偏振成分相关.这种射频场控制的单色光透射增强效应在磁场测量,光信息处理等领域有潜在的应用价值.     

矩形波导中超短脉冲电子束的相干同步辐射

考虑了当射频调制的超短脉冲电子束径向长度远小于辐射波长时，将其理想化为δ时间函数，提出了用波导本往模展开的方法来计算矩形波导中超短脉冲电子束的相干同步辐射及其频率特性。结果表明：（１）当谐振频率等于调制电子束微脉冲时间隔的射频的整数倍时，辐射模式表现为“纯”的波导本征模。（２）波导效应使得超短脉冲电子束在两个频率处发生相干同步辐射，而且低频支的辐射功率高于高频支的。最后指出波导自由电子激光器单横模     

ZnSe-ZnTe应变层超晶格远红外反射谱

本文首次报道室温下测量的分子束外延生长的ZnSe-ZnTe应变层超晶格的远红外反射谱.得到了ZnSe、ZnTe横光学声子摸.用长波长超晶格介电理论和多层吸收薄膜理论进行曲线拟合,确定Ⅱ-Ⅵ族ZnS、eZnTe材料的一些基本材料参数,如横光学声子频率、模衰减常数、模振荡强度、高频介电常数等.本文首次报道这些参数.     

Alignment-orientation conversion in molecules in an external magnetic field caused by a hyperfine structure

The paper presents a discussion on the problem of alignment-orientation conversion in an excited state of molecules. It is shown that a rather strong alignment-orientation conversion effect in the excited molecular state can be caused by a joint action of an external magnetic field and hyperfine interaction. The orientation thus created is transverse, i.e. perpendicular to the direction of the external magnetic field. The magnitude of this effect is analyzed as dependent on molecular parameters. Received 15 July 1999 and Received in final form 17 November 1999     

均匀横向磁场条件下抛物量子阱结构中的共振隧穿

采用简单的数值计算方法研究了均匀横向磁场条件下通过抛物量子阱结构的共振隧穿。计算了几种GaAs-AlxGa1-xAs-GaAs抛物阱结构的透射系数。结果表明：磁场增加时，共振峰向高能区移动，新的共振峰出现；同时讨论了回旋中心在不同位置时，抛物阱结构的J-V 特性。我们发现回旋中心在抛物阱中心时更有助于解释实验，并且能够得到和实验一致的结果：磁场增加，电流峰值减少且向高偏压移动。