Frequency stabilization of laser diodes using 1.51-1.55 μm absorption lines of 12C2H2 and 13C2H2

Frequency stabilization of an 1.5 μm distributed feedback laser diode (DFB-LB) is demonstrated using a vibrational-rotational absorption of acetylene ¹²C₂H₂ and ¹³C₂H₂ molecules (VRAM). Frequency stability within 2 MHz peak-to-peak fluctuation can be achieved in the wavelength region of 1.51-1.55 μm. Frequency-stabilized distributed feedback (DFB) laser compact modules have been constructed. When the fiber-pigtail-type acoustic optical modulator was used for small laser frequency scanning, frequency stability within 3 MHz peak-to-peak fluctuation was achieved without any broadening of laser spectral linewidth. In addition, temperature and pressure dependencies of the acetylene absorption lines are characterized.     

Na_2CaSiO_4:Sm~(3+),Eu~(3+)荧光粉的发光特性和能量传递

利用高温固相法合成Na_2CaSiO_4:Sm~(3+),Eu~(3+)系列荧光粉末,研究了Sm~(3+)和Eu~(3+)掺杂对Na_2CaSiO_4晶体结构的影响、材料发光特性以及存在的能量传递现象.X射线衍射结果表明Sm~(3+)和Eu~(3+)单掺及共掺样品均为单相的Na_2CaSiO_4结构,晶体结构没有改变.Na_2CaSiO_4:Sm~(3+)荧光样品在404 nm激发波长下呈现峰峰值为602 nm的橙红色荧光,来源于~4G_(5/2)→~6H_(7/2)跃迁.Na_2CaSiO_4:Eu~(3+)荧光样品在395 nm激发波长下发射出峰峰值为613 nm的红色荧光.对光谱和荧光寿命的测试和分析结果表明Sm~(3+)与Eu~(3+)之间存在能量传递,通过理论计算得到Sm~(3+)和Eu~(3+)之间的能量传递临界距离为1.36 nm,相互作用形式为电四极-电四极相互作用.随着Eu~(3+)掺杂浓度的增加,能量传递效率也逐渐提高至20.6%.     

Projectile coulomb excitation of Ne and Ne

The static quadrupole moments of the first excited J^π = 2⁺ states in ²⁰Ne and ²²Ne and the reduced electric quadrupole transition probabilities of these states to the ground states were measured via projectile Coulomb excitation. The quadrupole moments were deduced from the shapes of γ-ray angular distributions. The results are: Q(²⁰Ne, 2⁺) = −0.20±0.05 b and Q(²²Ne, 2⁺) = −0.11±0.05 b. The transition strengths were deduced from yield measurements and by comparison with the yields of target γ-rays. The results are: B(E2; 0⁺ → 2⁺, ²⁰Ne) = 0.037±0.003 e² · b² and B(E2; 0⁺ → 2⁺, ²²Ne) = 0.025±0.002 e²· b². The results for the transition strengths are consistent with the results of accurate timing methods and resolve discrepancies between previous experiments. The results for the quadrupole moments are consistent with earlier measurements, although the mean values we obtain are slightly lower. The experimental measurements are compared with theoretical predictions and a detailed discussion is given of corrections to this type of reorientation experiment.     

层状二硫化钼研究进展

近年来,层状二硫化钼由于其特殊的类石墨烯结构和独特的物理化学性质已成为国内外研究的热点.本文综述了层状二硫化钼的物理结构、价带结构和光学性质;介绍了制备方法,包括生长制备和剥离制备.生长制备的原料包括四硫代钼酸铵((NH4)_2MoS_4)、钼(Mo)和三氧化钼(MoO_3)等.剥离制备包括微机械剥离、液相超声法、锂离子插层法和电化学锂离子插层法等.归纳了层状二硫化钼在场效应晶体管、传感器和存储方面的应用,展望了层状二硫化钼的研究前景.     

调制激光场中Rydberg原子的电磁感应透明

本文主要研究了调制探测激光场中铯Rydberg 原子阶梯型三能级系统的电磁感应透明(EIT) 效应. 铯原子基态6S_1/2, 第一激发态6P_3/2 和Rydberg 态形成阶梯型三能级系统, 探测光作用于6S_1/2 (F = 4)→6P_3/2(F' = 5) 的跃迁, 耦合光在Rydberg 跃迁线6P_3/2→49S_1/2 附近扫描, 形成Rydberg 原子EIT. 当对探测光频率施加一个几kHz 的调制时, 调制解调后的EIT 信号分裂为两个峰, 双峰间距与调制频率无关,而与调制幅度导致的失谐量大小(频率调制幅度) 成正比, 双峰间隔的一半等于探测光频率调制幅度的λ_p/λ_c = 1.67 倍. 实验结果与理论计算相一致. 本文的研究结果可应用于激光线型和频率抖动的实时监测.     

Biaxial behaviour of an optical waveguide fabricated by ion implantation in a uniaxial BaTiO3 substrate

Biaxial behaviour has been observed in a waveguide fabricated by the technique of ion-beam implantation (H⁺ ions: 1 MeV at a rather high dose of 6 × 10¹⁶ ions/cm²) in a uniaxial BaTiO₃ single crystal. For the first time to our knowledge this phenomenon has been connected to the elasto-optic properties of the material. The index profile reconstructions both for TE and TM modes are led with two methods and we compare the results. The computation technique to connect the latter with the elasto-optic properties is presented. Then the calculations are successfully compared with the measured values.     

A study of atomic iodine and molecular thallium iodide by X-ray photoelectron and auger electron spectroscopy

The I3d5/2 binding energy has been measured in atomic iodine, thallium iodide and cesium iodide by high temperature gas-phase photoelectron spectrscopy using Al K (1486.6 eV) X-rays. The iodine M₅N_4,5N_4,5 (¹G₄) Auger energies for TlI and CsI have also been measured and combined with binding energies to yield extra-atomic relaxation energies of 0.5 and O.3 eV, respectively, after corrections are applied to the Auger parameter. Charges were calculated using the simple potential model, which was also used to obtain an estimate of the atomic T14f binding energy. Two other estimates of the atomic T14f7/2 binding energy have also been calculated, both based on Dirac-Fock ΔSCF binding energies. The results of the three methods suggest a value of 125.3 ± 0.2 eV for T14f7/2.     

低温燃烧合成法制备的氧化铝陶瓷粉体的发光特性

α-Al₂O₃∶C单晶具有优良的热释光特性,被用做热释光剂量计,但α-Al₂O₃∶C晶体剂量计的形状不易加工,生产成本高且碳在晶体中难以掺杂均匀。采用低温燃烧合成法以无水乙醇为溶剂,尿素为染料,硝酸铝为反应物制备少团簇、分散均匀的片状α-Al₂O₃∶C陶瓷粉体。探讨不同点火温度和不同退火温度对其光致发光特性的影响,不同退火温度对热释光特性的影响以及热释光与辐射剂量(90Sr β)的关系。通过分析α-Al₂O₃∶C陶瓷粉体的光致发光光谱得出：α-Al₂O₃∶C陶瓷粉体的发射波长在395 nm附近,点火温度T≤800℃时,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体的光致发光强度最强;在相同点火温度T=500 ℃下,经不同温度退火制备α-Al₂O₃∶C陶瓷粉体,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体经1 000 ℃退火后光致发光强度最强。通过分析α-Al₂O₃∶C陶瓷粉体的热释光曲线得出：退火后的α-Al₂O₃∶C陶瓷粉体在200 ℃左右的热释光峰值占主导,900 ℃退火的α-Al₂O₃∶C陶瓷粉体在200 ℃附近的热释光峰值最强;通过峰高法对900 ℃高温退火处理后的α-Al₂O₃∶C陶瓷粉体位于200 ℃左右的热释光峰做剂量响应曲线,可以看出,在1～50 Gy剂量范围内具有良好的热释光剂量线性响应关系,在50～200 Gy剂量范围内出现超线性响应关系。与α-Al₂O₃∶C晶体(1～10 Gy)和多孔Al₂O₃∶C薄膜(1～10 Gy)相比,α-Al₂O₃∶C陶瓷粉体的线性剂量响应范围明显扩大。此研究可为提高氧化铝陶瓷粉体的热释光性能提供思路。     

Study of ion desorption induced by a resonant core-level excitation of condensed H2O using Auger electron photo-ion coincidence (AEPICO) spectroscopy combined with synchrotron radiation

Ion desorption induced by a resonant excitation of O 1s of condensed amorphous H₂O has been studied by total ion and total electron yield spectroscopy, nonderivative Auger electron spectroscopy (AES) and Auger electron photo-ion coincidence (AEPICO) spectroscopy. The spectrum of total ion yield divided by total electron yield exhibits a characteristic threshold peak at hν = 533.4 eV, which is assigned to the 4a₁ ← O 1s resonant transition. The AES at the 4a₁ ← O 1s resonance is interpreted as being composed of the spectator-AES of the surface H₂O, and the normal-AES of the bulk H₂O, where the 4a₁ electron is delocalized before Auger transitions. H⁺ is found to be the only ion species in AEPICO spectra measured at the 4a₁ ← O 1s resonance and at the O 1s ionization (hν = 560 eV). The electron kinetic energy dependence of the AEPICO yield (AEPICO yield spectrum) at the 4a₁ ← O 1s resonance is found to be greatly different from that at the O 1s ionization. The peak positions of the AEPICO yield spectrum at the 4a₁ ← O 1s resonance are found to correspond to those of the spectator-AES of the surface H₂O, which is extracted from the AES at the 4a₁ ← O 1s resonance. Furthermore, the AEPICO yield is greatly enhanced at the 4a₁ ← O 1s resonance as compared with that at the O 1s ionization. On the basis of these results, a spectator-Auger-stimulated ion desorption mechanism and/or ultra-fast ion desorption mechanism are concluded to be responsible for the H⁺ desorption at the 4a₁ ← O 1s resonance. The enhancement of the H⁺ yield is ascribed to the O---H anti-bonding character of the 4a₁ orbital.     

不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

Response of thermoluminescent detectors to charged particles and to neutrons

Thermoluminescent detectors (TLDs) are widely used for the dosimetry of photons and electrons. They are less used for the radiation with higher linear energy transfer (LET). One of the reasons for that is that their TL relative efficiency η decreases for the most of them with increasing LET.

The paper presents first a review of author's experimental results in which η was established for charged particles having LET of the order from 1 to 100 keV/μm in tissue. Among TLDs studied were known materials like LiF:Mn; Ti; Al–P glass; CaSO₄:Dy; Al₂O₃:Na; and Al₂O₃:C. It was found that the dependence of their η on LET is not the same for all TLDs studied.

The response of the same materials to neutrons was also studied. It was found that both η as the relative response (RR) defined in terms of absorbed dose in tissue are different, they depend critically also on the composition. When a TLD contains nuclei like ⁶Li and ¹⁰B, their RR would be rather high. As far as η is concerned, the same tendencies were observed as for charged particles, i.e. when average LET of secondary particles formed in a TLD increases, their η generally decreases.     

氘氘-塑料靶丸变收缩比内爆物理实验研究

在神光III原型装置上利用8路6400 J/1 ns激光注入Φ1100 μm×1850 μm的黑腔内产生约200 eV的高温辐射场均匀辐照填充氘氘燃料的靶丸实现内爆. 实验中, 保持靶丸的内径一致, 通过改变靶丸烧蚀层厚度的方式实现不同收缩比的内爆. 通过闪烁体探测器、分幅相机等多套诊断设备获取了中子产额、X光bang-time (聚变反应产生X光时刻)、飞行轨迹、热斑形状等关键内爆参数. 结合一维数值模拟表明: 对于小收缩比内爆, 受到非一维因素的影响小, 其YOC_1D(实验测量中子产额与干净一维数值模拟计算结果之比)可以达到34%; 对于中等收缩比内爆, 受到非一维因素的影响显著, 其YOC_1D仅仅为2.3%.     

Observations on the role of MgCl2 in the Weissler reaction

Aqueous solutions of Nal containing CCl₄ and MgCl₂ at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I₃⁻ was determined. The yield was not affected by MgCl₂ at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl₂ concentration of 2.5 × 10⁻³M, the yield decreased to 60% at 1 M MgCl₂, the reason being the lower solubility of CCl₄ at high MgCl₂ concentrations. In the absence of CCl₄, another dependence on the MgCl₂ concentration was observed: the yield was not affected up to 1 M, and at higher MgCl₂ concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles.     

Radioluminescence (RL) behaviour of Al2O3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al₂O₃:C) TL dosimeter material (TLD-500) was investigated using a ¹³⁷Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s⁻¹). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al₂O₃:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.     

The role of excitons and substrate temperature in low-energy (5–50 eV) electron-stimulated dissociation of amorphous D2O ice

We have studied the interaction of low-energy (5–50 eV) electrons with nanoscale (10 ML) ice films by probing the yields and quantum-state distributions of the neutral dissociation products using laser resonance-enhanced multiphoton ionization spectroscopy. In particular, we have observed the electron-stimulated desorption (ESD) of D (²S), O (³P₂) and O (¹D₂) from amorphous D₂O films. These products are observed at threshold energies (relative to the vacuum level) between 6.5–7 eV and desorb with low kinetic energies (60–85 meV) which are independent of the incident electron energy. We associate the ESD of atomic fragments from ice with dissociation of Frenkel-type excitons of 4a₁ character which are near the bottom of the ice conduction band. These excitons are created either directly or via electron-ion recombination. Changing the surface temperature from 88 to 145 K results in an increase in the thermal component of the time-of-flight (kinetic energy) distributions and an overall increase in the neutral fragment yield. We suggest that the change in neutral yield with substrate temperature results from a combination of: (1) increased electron-ion recombination; (2) exciton transport to the near-surface region; and (3) dissociation followed by inelastic scattering and desorption.     

Non-proportional response of scintillation crystals to X-rays and γ-rays

Data are presented on the relative photon yield of Lu₂SiO₅(Ce³⁺), Cd₂SiO₅(Ce³⁺), CdWO₄, BaF₂, YAlO₃(Ce³⁺) and Lu₃Al₅O₁₂(Sc³⁺) scintillation of crystals on absorption of X-ray and γ-ray photons at energies ranging from 5 keV to beyond 1 MeV.     

Muonic Au: A test of the weak-coupling model

We report the measurement of the energies of various muonic atomic transitions above 500 keV in ¹⁹⁷Au. We have used the weak-coupling model in order to analyze the hyperfine structure of ¹⁹⁷Au. Using transitions to and from the 1s, 2s 2p and 3p levels as well as the fine structure of the 2p states and hyperfine splittings of the 2p, 3p and 3d states we have fitted our data to two deformed Fermi distributions: one with a constant skin thickness, the other with a skin thickness which varies. Both yield equally good fits. We have determined the quadrupole moment of ¹⁹⁷Au to be 0.547±0.016 b. The model dependence of our results is discussed. The weak coupling parameters of de-Shalit Ω_p, Ω₂₂, Ω₂₀ and A² have been determined and are in fair agreement with Coulomb excitation results. There is also good agreement between our results and those of electron scattering.     

Ion-implantation-induced structural modifications in Y1Ba2Cu3O7−δ superconductor

Ion-implantation-induced structural modifications in Y₁Ba₂Cu₃O_7−δ superconductor are examined by a grazing angle X- ray diffraction technique. By employing a range of grazing angles from 0.3° to 10° it is shown that 100 KeV Ar⁺ inplantation of the superconductor leads to amorphization as well as modification of grain size and orientation at dose values lower than 10¹⁶ ions/ cm². At the dose of 5 × 10¹⁶ ions/ cm² the X-ray diffraction intensity is a factor of 6 less as compared to the original pellet, though the lines themselves are sharp. This shows coexistence of perovskite grains and amorphous matrix.     

Al2O3吸附[Cu(H2O)6]2+基团的自旋哈密顿参量和四角畸变

采用微扰方法和对角化完全能量矩阵法计算了Al₂O₃粉末吸附的四角对称[Cu(H₂O)₆]²⁺基团的自旋哈密顿参量（g因子g∥,g_⊥和超精细结构常数A_∥和A_⊥）. 计算结果表明用这两种理论方法计算的自旋哈密顿参量很接近,并且都与实验结果比较一致. 表明这2种方法都可用于晶体中3d9离子基团的自旋哈密顿参量的研究,通过计算,我们还获得了[Cu(H₂O)₆]²⁺基团四角畸变的大小,并对结果进行了讨论.     

SeOx(x=1,2)的从头算势能曲线和光谱常数

采用从头算的多种方法和基组优化计算SeO_x(x=1,2)自由基的基态结构、谐振频率及离解能,优选出QCISD(T)/6-311+G(2df)、B3LYP/6-311G(3d2f)方法分别对SeO、SeO₂自由基进行计算,计算结果与实验结果吻合很好.对SeO自由基拟合出Murrell-Sorbie势能函数参数,计算出SeO自由基的光谱常数和力常数.计算出SeO₂自由基力常数,导出SeO₂自由基的多体展式势能函数,发现SeO₂自由基对称伸缩振动势能图中在对称的O+SeO→SeO₂反应通道上有一鞍点,其活化能约为48.24 kJ·mol^-1,O原子需要越过0.5 eV的能垒才能生成SeO₂的稳定结构.