极性分子HC2n+1(n=2,3,4)强场搜寻态减速

Laser-assisted Stark deceleration scheme was proposed to decelerate the high-field-seeking molecule ICl in its rovibronic ground state. However, the laser intensity of 1.0×10¹⁰ W/cm² is hard to realize in experiment. The time-of-flight signals of HC_2ⁿ+1N (n=2, 3 and 4) by three-dimensional Monte-Carlo simulation suggest that deceleration of such molecules is more feasible experimentally as only one-tenth laser intensity is needed.     

Efficient second, third, fourth, and fifth harmonic generation of a Yb-doped fiber amplifier

We report generation of the second, third, fourth, and fifth harmonics of the output of a Yb-doped fiber amplifier seeded by a passively Q-switched Nd:YAG microchip laser. We obtained high conversion efficiencies using a simple optical arrangement and critically phase-matched nonlinear crystals. Starting with 320 mW of average power at 1064 nm (86 μJ per pulse at a 3.7 kHz repetition rate), we generated 160 mW at 532 nm, 38 mW at 355 nm, 69 mW at 266 nm, and 18 mW at 213 nm. The experimental results are in excellent agreement with calculations.     

Strictly all-fiber picosecond ytterbium fiber laser utilizing chirped-fiber-Bragg-gratings for dispersion control

A compact, strictly all-fiber, picosecond pulse source based on ytterbium (Yb) doped fiber is described. Stable solitary mode-locking is obtained in a fiber-oscillator utilizing a carefully designed chirped fiber-Bragg-grating (C-FBG) for both dispersion control and spectral filtering. Self-starting is assured through the use of a fiber-coupled semiconductor-saturable-absorber-mirror (SESAM). The oscillator’s 50 MHz 3.8 ps pulse-train output at 1064 nm wavelength is amplified to 1.2 W average power by an Yb-doped fiber-amplifier, yielding 6.45 ps parabolic pulses. Numerical simulations of the fiber-oscillator design based on the modified nonlinear Schrödinger equation (NLSE), agree well with the experimental results.     

Passively mode-locked ytterbium fiber laser utilizing chirped-fiber-Bragg-gratings for dispersion control

A robust, self-starting picosecond pulse source based on ytterbium (Yb³⁺) doped fiber laser is described. Utilizing a chirped-fiber-Bragg-grating (C-FBG) for dispersion control, solitary mode-locking is obtained without bulk dispersion compensation elements. A semiconductor saturable absorber (SESAM) is used for stable self-starting. 3.6 ps pulses are produced, with 45 MHz basic repetition-rate and mW scale average output power at 1060 nm. Detailed numerical simulations based on the modified nonlinear Schrödinger equation agree well with the experimental results and are used as a design tool for the solitary mode-locked picosecond laser. The presented design can be simply employed in an all-fiber environmentally-stable system.     

Experimental and theoretical studies on ytterbium sensitized erbium-doped fiber amplifier

The performance of a high power erbium-ytterbium doped fiber amplifier (EYDFA) is investigated experimentally and theoretically. The EYDFA provides a flat gain with an output power higher than 23 dBm in the wavelength region from 1541 to 1565 nm using a multimode pumping at 927 nm. In the theoretical analysis, the rate and power propagation equations are solved to examine the effect of fiber length on the bandwidth of the gain spectra. In the C-band region, the small signal gain of the EYDFA varies from 30 to 34 dB with 10 m long erbium-ytterbium doped fiber (EYDF) while the 927 nm pump power is fixed at 3.5 W. It is shown that the calculated output power is in good agreement with the experimental results, verifying the feasibility of our theoretical model. However, the experimental result shows a relatively lower gain compared to the theoretical result due to the spurious reflection in the cavity and the insertion loss of the EYDF which were neglected in our theoretical model.     

吡喃酮类化合物与镱配合物的红外和拉曼光谱研究

采用非水体系中牺牲金属阳极的电化学方法分别合成了稀土金属镱与 3 羟基黄酮及 3 羟基 2 甲基 γ 吡喃酮的配合物。对配合物进行了IR和Raman光谱测定。两种光谱提供了互为补充的信息 ,配体经配位后—OH的伸缩振动谱峰消失 ,部分相关的谱峰频率发生了明显位移 ,特别是羰基伸缩振动红移十分明显 ,在Raman光谱的低波数区间检测到可指认为金属和配体键合的伸缩振动。根据这两种光谱的研究结果推断了所得配合物的可能结构。     

Frequency ratios of Sr,Yb, and Hg based optical lattice clocks and their applications

This article describes the recent progress of optical lattice clocks with neutral strontium (⁸⁷Sr), ytterbium (¹⁷¹Yb) and mercury (¹⁹⁹Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on an Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an optical frequency comb, the ratios of the clock frequencies are determined with uncertainties smaller than possible through absolute frequency measurements. Finally, we describe a synchronous frequency comparison between two Sr-based remote clocks over a distance of 15 km between RIKEN and the University of Tokyo, as a step towards relativistic geodesy.     

电场中里德伯原子动力学性质的半经典理论研究

利用闭合轨道理论和Poincaré截面两种方法研究了鞍点附近电场中高里德伯态Li原子的动力学性质.由于原子实的作用,体系是混沌的,闭合轨道和周期轨道在混沌体系中并存,但二者在Poincaré截面上的反映是不同的.讨论了两种半经典理论在研究混沌体系时的联系,得到了仅靠闭合轨道理论得不到的信息. 关键词： Poincaré截面 回归谱 Stark效应     

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.     

火焰原子吸收光谱法测定光学新材料钛酸钡锶中钡和锶

本文介绍了火焰原子吸收光谱法测定光学新材料钛酸钡锶中钒和锶，研究样品制备、测试条件和共存元素干扰，本法的准确度和精密度均满意。     

Minibands of p-type δ-doping superlattices in GaAs

A microscopic theory is presented for high-field miniband transport in a two-dimensional superlattice. The energy transfer to the lateral electron motion is taken into account as well as scattering on polar optical phonons. Oscillatory current anomalies appear when the optical phonon frequency is a multiple of the Bloch frequency. The current oscillations, which are due to Wannier–Stark localization, are much more pronounced in a two-dimensional than in a three-dimensional system with a superlattice structure in one direction.     

On the vibrational behaviour of cyanide adsorbed at Pt(1 1 1) and Pt(1 0 0) surfaces in alkaline solutions

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(1 1 1) and Pt(1 0 0) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C-N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(1 1 1)-CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C-N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.     

Magneto-spectroscopy studies of graphite nanoplatelet films

The magneto-optical properties of graphite nanoplatelet films in the THz frequency range have been investigated. The room-temperature THz spectrum of graphite nanoplatelets shows a free carrier absorption at zero frequency with an electronic scattering rate of 175 cm⁻¹ (3.3×10¹³ rad/s) and plasma frequency of 1675 cm⁻¹. The lack of a major change in Drude plasma frequency down to 4.2 K implies that any band gaps in graphite nanoplatelets are less than 1 meV. The 300 K magneto-transmission contrast is as large as 60% near 1 THz at 10 T. The results are potentially useful for magnetic memory applications away from the dc limit.     

使用斯塔克展宽计算大气压射频介质阻挡放电氮气等离子体的电子密度

大气压射频等离子体是近几年发展起来的一种新型非平衡等离子体。以氮气掺杂少量氩气为放电气体,实现了大气压射频介质阻挡放电。利用发射光谱对放电进行在线诊断研究,并分析谱线线型,从中分离出谱线的Stark线型,从而计算出放电通道的电子密度。研究了单个放电通道中电子密度的空间分布并测量了通道同一位置的电子密度随放电输入功率的变化。结果显示,在放电通道中部,当放电输入功率由138W增加至248W,电子密度由4.038×1021 m-3升高至4.75×1021 m-3。     

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.     

Synthesis and optical properties of Er and Eu doped SrAl2O4 phosphor ceramic

We report, for the first time on luminescence from a Er³⁺ doped SrAl₂O₄ phosphor. Effects of Eu³⁺ doping were also studied. The influence of rare-earth doping in crystal structure and its optical properties were analysed by means of X-ray diffraction (XRD), Raman scattering, optical absorption, excitation and emission (PL) spectroscopy, thermally stimulated luminescence (TSL) and scanning electron microscope (SEM). Luminescence spectra and luminescence decay curves for Er³⁺ transitions in the near infrared region were recorded. The PL maximum for Eu doped SrAl₂O₄ is obtained at 620 nm and corresponds to the orange region of the spectrum. Diffraction patterns reveal a dominant phase, characteristic of the monoclinic SrAl₂O₄ compound and the presence of dopants has no effect on the basic crystal structure of SrAl₂O₄. The shapes of the glow curves are different for each dopant irradiated with either a ⁹⁰Sr-⁹⁰Y beta source, or UV light at 311 nm, and in detail the TL signals differ somewhat between Er and Eu dopants.     

以MgO为缓冲层的硅基铌酸锶钡薄膜取向特性与其波导结构的设计研究

采用溶胶－凝胶法在Si(100)基片上制备出择优取向的MgO薄膜,随后在其上生长出具有择优取向的铌酸锶钡铁电薄膜.实验发现,MgO缓冲层的应用可以大大提高SBN薄膜的择优取向性能.同时,用五层对称理想波导耦合模理论,以SBN为波导层,分析了波导损耗与厚度的关系. 通过对计算出的理想结果与实际相结合,以及对SBN在生长过程工艺与损耗关系的研究,制备出高质量、低损耗的SBN薄膜,为其在电光波导调制器等微系统中的应用打下良好的基础.     

Pulsed laser deposition and characterization of nitrogen-substituted SrTiO3 thin films

Nitrogen-substituted cubic perovskite-type SrTiO₃ thin films were deposited in a one-step process using pulsed reactive crossed beam laser ablation (PRCLA) and RF-plasma assisted pulsed laser deposition (RF-PLD). Both techniques yield preferentially oriented films on SrTiO₃(0 0 1), LaAlO₃(0 0 1) and MgO(0 0 1) substrates with the unit cell parameters within 0.390(5) < a < 0.394(9) nm. The nitrogen content is higher in films deposited by PRCLA (0.84-2.40 at.%) as compared to films deposited by RF-PLD with nitrogen plasma (0.10-0.66 at.%). PRCLA with an ammonia gas pulse leads to a higher nitrogen content compared to the films grown with a nitrogen gas pulse, while films deposited by RF-PLD with ammonia plasma reveal only minor nitrogen contents (<0.10 at.%). The amount of the incorporated nitrogen can be tuned by adjusting the deposition parameters. Films deposited by PRCLA have a lower roughness of 1-3 nm compared to 12-18 nm for the films grown by RF-PLD. PRCLA yields partially reduced films, which exhibit electronic conductivity, while films deposited by RF-PLD are insulating. There is also a pronounced influence of the substrate material on the resistivity of the films deposited by PRCLA: films grown on SrTiO₃ substrates exhibit a metallic-like behaviour, while the corresponding films grown on MgO and LaAlO₃ substrates reveal a metal-to-semiconductor/insulator transition. Nitrogen incorporation into the SrTiO₃ films results in an increased optical absorption at 370-500 nm which is associated with N(2p) localized states with the energy about 0.7 eV higher than the valence band energy in strontium titanate. The optical band gap energies in the studied N-substituted SrTiO₃ films are 3.35-3.40 eV.     

The applications of the stark effect to the stabilization of the CO2 laser and the submillimeter laser

Methods based on the Stark effect are described for dither-free frequency stabilization of the optically pumped submm laser. The CO₂ pump laser was stabilized using a Stark Lamb dip signal of the submm lasant in an external Stark cell. An estimated frequency stability (f/f) better than ±1.4×10^–8, for one hour recording, was obtained by this method. The frequency of the submm laser was stabilized using the d.c. and a.c. Stark effects for a metal-dielectric rectangular waveguide laser. An estimated frequency stability of ±6×10^–8 was obtained for 119 m line of CH₃OH laser for one hour recording.