以慢原子束方式进行原子转移的双磁光阱系统

建立了一套用于玻色-爱因斯坦凝聚实验的铷原子双磁光阱装置.从低速强源中获得慢原子束，向超高真空磁光阱进行原子转移.低速强源磁光阱与超高真空磁光阱之间可维持3个量级的压强差,超高真空磁光阱的真空度最高可达1×10^-9 Pa. 慢原子束的束流通量达1×10⁹/s. 约4×10⁸个⁸⁷Rb原子被装载到超高真空磁光阱中.还讨论了两种典型情况下磁光阱中装载的最大原子数.     

小型自冷式油扩散泵

在真空实验中,要想使系统获得高真空(10~(-2)Pa以下的气压),除用机械泵对系统进行排气外还必须加高真空泵,其中最常用的就是扩散泵。一般商品扩散泵都是多级泵,是由几个单级泵串联而成。泵的外形有立式、卧式;泵体材料有玻璃的、金属的;使用的工作液有汞、油等。但它体积大、自身重、需水冷,如果被排气的系统或容器容积不大,使用这种扩散泵无论从经济上还是从实用上考虑都显得大才小用。我们在实验中使用自己设计制做的二级自冷卧式玻璃油扩散泵。它的结构如图1所示,此扩散泵     

大型油扩散泵的改进工作

在鉴定某工厂试制的、口径为500毫米的油扩散泵时,测得泵的抽速为4580升/秒,最高真空为8×10~(-6)毫米汞柱(功率为3000瓦)。同时发现装在泵上的测量罩较热。 一般认为,油扩散泵的抽速应为泵口径(厘米)平方的三倍,而且大型泵的抽速应高于这个指标。据此,上述500毫米口径扩散泵的抽速应不小于7500升/秒。泵的最高真空,在不加水冷或液体氮冷却的情况下,国外水平约为5×10~(-7)毫米汞柱。     

层子模型里介子的波函数和能级

本文利用Bethe-Salpeter型的方程处理了层子模型中的介子内部波函数,指出如果层子和反层子之间的作用可以用一个赝标型位阱来代表,那么0^-和1^-介子将满足相同的近似迳向波动方程,从而导致SU₆对称性。我们以前曾经证明赝标型位阱是唯一可以导致这个对称性的单一型位阱。我们的位阱是V=V₀+V₁,V₀代表一个超强的深位阱,它的作用是降低层子的原始质量M,使它的有效值M′变得很小,使得层子在强子内部的运动是相对论的。V₁代表数量级为1/M的简谐振子位阱,另外还引入一个张量力来解释自旋和轨道角动量相同态的能级分裂。我们得出基态和角动量激发态0^-和1^-介子的解,基本上解释了所有观察到的介子。我们的理论可以同样处理重子态,只要唯象位阱V₀只有介子的值的一半。     

气压对吸气式激光推进冲量耦合系数的影响

 保持CO₂激光的单脉冲能量为61.4~64.6 J，采用高精度冲击摆系统进行了不同气压下吸气模式激光推进冲量耦合系数的实验测试，分析了对应的高度特性。结果表明：气压为2.8×10⁴～1×10⁵ Pa，即距离地面0～10 km时，冲量耦合系数大约3.5×10^-4 N·s·J^-1，上下波动幅度低于5%；气压低于2.8×10⁴ Pa，即高度大于10 km时，冲量耦合系数呈二次曲线显著下降；当气压降至1×10³ Pa，即距离地面约31 km高度时，耦合系数仅为9.7×10-5 N·s·J^-1。     

环境气氛压强对熔石英紫外激光损伤阈值的影响

 利用1∶1, S∶1, R∶1方法,测试了不同真空度（10-3～105 Pa）和不同气氛（空气、氮气、氧气）环境下熔石英351 nm激光损伤阈值,测试结果表明,用1∶1, S∶1方法测试得到的阈值在不同气氛压强下几乎相等;R∶1损伤阈值受气压的影响较大,在小于等于10³ Pa气压下,较105 Pa气压的阈值降低28%～41%;但R∶1损伤阈值同气氛的关系不大,在同气压下差别小于10%,在测量值误差范围内。利用50%破坏几率对应的损伤阈值Fth（R∶1）一半的激光能量密度辐照样品,考察其抗多脉冲辐照的能力,分析表明,在同样的能量密度辐照下,10³ Pa空气及氮气环境和105 Pa氮气环境下同样具有高的寿命;而10^-3 Pa高真空环境下其寿命较短,在10^-1 Pa低真空环境下其寿命最短。     

用激光计数放射性氪原子

原子阱痕量分析是一种基于激光的新方法,能够对数微升氪气中丰度低至10^-14的⁸⁵Kr和⁸¹Kr原子进行计数测量．介绍了在合肥建成的痕量放射性氪同位素测量系统,包括ATTA装置、水中溶解气提取和氪气分离提纯的样品处理设备．利用该系统对国内多处大气中⁸⁵Kr浓度的测量结果为1.3～1.6 Bq/m³,与文献中北半球大气本底值相吻合．对华南和华北的几个浅层和深层地下水样品进行了⁸⁵Kr和⁸¹Kr测年,示范了该系统的应用．     

掺铍GaAs量子阱的光致荧光

测量了掺铍的,阱宽约为10nm的GaAs量子阱在4.2K的光致荧光。掺杂浓度分别为1×10¹⁷和5×10¹⁸cm^-3。测量结果表明:对于无规掺杂,局域在阱中心的铍的状态密度与导带电子从n=1量子能级到阱中心中性铍的跃迁概率的乘积大于对应于介面铍的乘积。另外,实验结果也表明:当掺杂浓度升高时,由于带隙收缩的影响,阱中心铍的电离能减小。     

感应磁场压缩下氢等离子体中巴耳末系谱线的斯塔克加宽

本工作研究感应磁场压缩下,氢等离子体中的巴耳末系谱线的斯塔克加宽。电容器对围绕在放电管外部的线圈放电,产生交变轴向磁场,使放电管中氢气离化、压缩与加热。放电周期14微秒,放电电压20千伏,最大电流165千安,初始工作气压2.0×10^-1毫米汞高。用照相方法研究H_β和H_γ的轮廓。这些谱线有显著的加宽。在整个发光阶段中,H_β的平均半宽度为14—16(埃),H_γ为18—19(埃),相应的离子密度为1.7—2.5×10¹⁶厘米^-3。实验轮廓与Griem,Kolb和Shen的理论较为接近,与Holtsmark理论相差较远。光电测量进一步表明:H_β的轮廓随着时间而改变,相应的离子密度亦在改变。在放电的第三半周期初级电流极大时,离子密度最大,达到3.2×1O¹⁶厘米^-3,为初始氢原子密度的2.2倍。     

射频电子枪中LaB6阴极的研究

 一种用于射频电子枪中的LaB₆热阴极已经研制成功。分别研究了(100)、 (110)、(111) 晶向LaB₆单晶的热发射特性。选用(100)晶向的LaB₆单晶材料作为发射体并用铼做基底材料。试验表明,在1823K工作条件下,其热发射电流密度达到 30A/cm²;在真空条件为5×10^-5Pa下,寿命已达10000小时以上。在室温下反复多次暴露大气后,其发射性能保持不变。     

Low gas pressures obtained by means of sorbents

The paper describes the use of active charcoal and a 13X molecular sieve at 78°K to pump all-glass apparatuses with a small volume (up to 5000 cm³) from atmospheric pressure to a pressure region of 10^–2 mm Hg. At this pressure an outgassed second pumping stage (also sorbent) permits pressures from 10^–6 to 10^–7 mm Hg to be obtained. Active charcoal was also used as a two-stage fore pump (p=10^–6 mm Hg) for a one-stage mercury diffusion pump and in this system pressures of 5 to 10×10^–10 mm Hg were achieved.     

Spectroscopic and chemical reactivity analysis of D-Myo-Inositol using quantum chemical approach and its experimental verification

Glow discharge conditioning (GDC) has long been accepted as one of the basic wall conditioning techniques for achieving ultrahigh vacuum in an unbaked chamber. As a part of this fundamental experimental study, a test chamber has been fabricated from stainless steel 304 L with its inner surface electropolished on which a detailed investigation has been carried out. Both helium and hydrogen gases have been employed as discharge cleaning medium. The discharge cleaning was carried out at 0.1 A /m ² current density with working pressure maintained at 1.0 × 10 ^-2 mbar. It was experimentally observed that the pump-down time to attain the base pressure ~10 ^-8 mbar was reduced by 62% compared to the unbaked chamber being pumped to this ultimate vacuum. The results were similar irrespective of whether the discharge cleaning medium is either hydrogen or helium. It was also experimentally established that a better ultimate vacuum could be achieved as compared to theoretically calculated ultimate vacuum with the help of discharge cleaning.     

Study of the CdS crystal evaporation kinetics by laser step atomic photoionization

Laser resonant multistep atomic photoionization is employed to measure evaporation rates and saturated vapor pressures of cadmium sulfide and pure cadmium in temperature ranges of 585–950 and 350–535 K, respectively. It is shown that CdS thermally dissociates into Cd atoms and S₂ molecules. The photoionization of cadmium atoms follows the scheme

$5s^1 S_0 \xrightarrow{{\lambda _1 = 326.1nm}}5p^3 P_1 \xrightarrow{{\lambda _2 = 479.9nm}}6s^3 S_1 \xrightarrow{{\lambda _3 = 488.1nm}}17p^3 P_2 + (\varepsilon = 12kV/cm) \to Cd^ + + e^ - .$

.

The minimal pressure of pure cadmium is found to be 10^?11 mm Hg.     

Optimization of magnetron deposition process for formation of high-quality oriented ZnO films

The thickness distribution and structure of ZnO films deposited by DC-magnetron sputtering of a zinc target in argon-oxygen gaseous medium at substrate temperature of 27°C and gas pressure in the chamber within 5×10^?3 ? 5×10^?2 mm Hg was investigated. It was revealed that the use of a target with a certain depression in the sputtering zone allows depositing high quality c-oriented films at lower gas pressure than with a flat target. The dependence of film quality on geometric factors is interpreted on the basis of theoretical computations with the assumption that the film structure is improved when the flux of deposited Zn particles decreases while their energy increases.     

A continuous cold atomic beam from a magneto-optical trap

We have developed and characterized a new method to produce a continuous beam of cold atoms from a standard vapour-cell magneto-optical trap (MOT). The experimental apparatus is very simple. Using a single laser beam it is possible to hollow out in the source MOT a direction of unbalanced radiation pressure along which cold atoms can be accelerated out of the trap. The transverse cooling process that takes place during the extraction reduces the beam divergence. The atomic beam is used to load a magneto-optical trap operating in an ultra-high vacuum environment. At a vapour pressure of 10^-8mbar in the loading cell, we have produced a continuous flux of 7×10⁷atoms/s at the recapture cell with a mean velocity of 14 m/s. A comparison of this method with a pulsed transfer scheme is presented. Received 19 February 2001     

Controlled discharge in a vacuum gap switched by 1 Mc current pulses of up to 150 kA

The firing delay time, the rise time of the current up to its maximum, and the primary current amplitude of a controlled discharge in a vacuum gap are considered, for a voltage range of 10–80 kV, with a residual gas pressure in the chamber of 10^–4–10^–5 mm of mercury. The gap is switched by a damped oscillatory current pulse with a frequency of 1.25 Mc and a maximum amplitude of about 150 kA. The discharge is started by either one or three triggering devices.     

Auger spectroscopy of the electron-stimulated absorption of oxygen on surfaces of polycrystalline aluminum

Electron spectroscopic analysis of oxygen absorption on aluminum is performed at a partial oxygen pressure of ～10^?6 mm Hg, with and without external impact (electron bombardment). It is shown that under these conditions, an aluminum surface oxidizes in the time required for the content of an oxide film affected by Al radiation with electrons having an energy of 800 eV to stabilize.     

Magneto-optical trapping of neutral mercury

We report on the cooling of neutral mercury in a magneto-optical trap utilizing the spin forbidden ¹S₀ → ³P₁ transition at 253.7 nm. We trapped two Hg isotopes, i.e. the bosonic ²⁰²Hg and the fermionic ¹⁹⁹Hg isotope, respectively. The temperature of the cold atom cloud was determined to be approximately 300 μK using a modified TOF-method. It is currently limited by the quality of the laser lock. Trapped neutral Hg has many interesting avenues such as a time standard and high precision measurements. Here, we discuss the possibilities of photo-association spectroscopy and the generation of ultra-cold Hg₂ dimers.     

Characterization of vacuum evaporated In - Se thin films

The InSe films of different thicknesses (290–730 mm) were deposited onto glass substrates under a pressure of 3×10^?5 Torr by vacuum evaporation method. The composition (In=53.50%, Se=46.50%) of this film was confirmed using Auger Electron Spectroscopy (AES). Thicknesses of the deposited films have been measured using a Multiple Beam Interferometry. The amorphous nature of the film is confirmed with X-ray diffractogram. From the transmittance spectra in the range of 500 nm-1200 nm, it is observed that the film showed direct allowed transition. Effect of thickness on the optical parameters such as the fundamental band gap, absorption constant, refractive index of InSe thin films are reported. Under low electric field (～ 1.5×10⁵ Vcm^?1), the results of DC conductivity measurements revealed that the variable range hopping is the dominant conduction mechanism. The values of localized states density, localization radius and hopping energy of this film are estimated as 5.57×10²⁰ cm^?3eV^?1, 0.84 Å and 0.247 eV, respectively.     

Wide transparency range and high refractive index lead–niobium-germanate glass thin films

Lead–niobium-germanate glass thin films have been produced by pulsed laser deposition in a broad O₂ pressure range (10^-6–10^-1 mbar). The cation composition in the films approaches that of the glass target for a pressure of 10^-2 mbar. The oxygen content is only close to or above that of the glass for a pressure close to 10^-1 mbar, for which a Pb enrichment is also observed. Films grown in vacuum are highly absorbing, whereas transparent films with an absorption edge shifted to the UV with respect to the bulk glass are produced for pressures higher than 10^-2 mbar. The evolution of the optical energy gap and the refractive index of the films with the oxygen pressure is correlated to the changes observed in the film composition and discussed in terms of the features of the deposition process, the role of oxygen in the formation of the glass network and the progressive increase of the oxidation state of the cations as the oxygen pressure is increased. PACS 81.05.Kf; 78.20.Ci; 81.15.Fg