Ba/Fe-堇青石固溶体(Ba0.05Fe0.1Mg)2Al4Si5O18的组合筛选及红外辐射性能优化

采用组合材料方法制备并筛选了具有高红外辐射性能的Ba/Fe共掺堇青石固溶体(Ba_0.05Fe_0.1Mg)₂Al₄Si₅O₁₈. 通过组合溶液喷射法,制备了7×7阵列的样品库,并在不同温度下进行热处理.通过X射线衍射、红外热成像等测试方法分析了Ba²⁺、Fe³⁺固溶对堇青石晶格畸变和红外辐射性能的影响. 经过放大制备实验的验证,确定了材料的最佳组分为5%Ba²⁺和10%Fe³⁺共固溶的堇青石. 最佳组分样品在100 oC时的红外辐射率在5-24 μm波段均高于0.8.     

Z→li±lj干 processes in the BLMSSM

In a supersymmetric extension of the Standard Model (SM) where baryon and lepton numbers are local gauge symmetries (BLMSSM), we investigate the charged lepton flavor violating (CLFV) processes Z→l_i^±l_j^干 after introducing new gauginos and right-handed neutrinos. In this model, the branching ratios of Z→l_i^±l_j^干 are around (10^-8-10^-10), which approach the present experimental upper bounds. We hope that the branching ratios for these CLFV processes can be detected in the near future.     

199Hg+光频标的黑体辐射频移

光学频率标准会受到环境温度的黑体辐射影响发生频移,进而影响其准确度. 本文估算了¹⁹⁹Hg⁺的超精细能级5d¹⁰6s²S_1/2 (F=0)和5d⁹6s^{2 2}D_5/2 (F=2)的极化率,得到了室温(300 K)下黑体辐射引起的相对频移为-5.4×10^-17, 最后讨论了低温环境下黑体辐射对¹⁹⁹Hg⁺光频标的影响.     

克里奇中间体CH2OO与CF3CF=CF2反应的动力学研究

本文使用OH激光诱导荧光方法研究了结构最简单的克里奇中间体CH₂OO和CF₃CF=CF₂的反应动力学. 在压强为10 Torr条件下，测量了温度在283，298，308和318 K的反应速率常数，分别为(1.45±0.14)×10^-13，(1.18±0.11)×10^-13，(1.11±0.08)×10^-13和(1.04±0.08)×10^-13 cm³·molecule^-1·s^-1. 根据阿伦尼乌斯方程，获得该反应的活化能为(-1.66±0.21) kcal/mol. 在6.3∽70 torr压力范围内，未观察到该反应的速率常数存在压力相关.     

LiNbO3和LiTaO3晶体Er3+/Yb3+掺杂水热外延层室温吸收光谱分析

本文引入与浓度和厚度有关的k_NL待定参数, 在J-O理论基础上, 对Er³⁺/Yb³⁺掺杂的LiNbO₃和LiTaO₃单晶衬底上 的多晶水热外延样品进行了基于吸收光谱的拟合计算. LiNbO₃:Ω₂=2.34× 10^-20 cm², Ω₄=0.77× 10^-20 cm², Ω₆=0.31×10^-20 cm², k_NL=4.32× 10^-2 mol·m^-2. LiTaO₃:Ω₂=1.68×10^-20 cm², Ω₄=0.84×10^-20 cm², Ω₆=0.45×10^-20 cm², k_NL=9.17×10^-3 mol· m^-2. 该方法可尝试推广到粉体或胶体等难以直接获得浓度和厚度数据的体系. 经上转换发光测试及光谱参数计分析认为Er³⁺/Yb³⁺离子的掺杂浓度比为1:1的情况下, 样品呈现绿色上转换发光光谱; 可尝试以降低基质声子能量的方法提高⁴I_13/2能级 对²H_11/2和⁴S_3/2能级的量子剪裁效率.     

薄膜型超导红外(光)探测器

在高Tc GdBaCuO超导薄膜上,采用光刻技术分别制成两种不同结构的辐射、热测量器件及2×4集成阵列式微桥器件红外(光)探测器.探测器芯片安装在STD-3型红外探测器杜瓦冷指上.用黑体及波长为0.6328μm的He-Ne激光器辐照器件,系统观测各种器件的特性,其中最好的结果:在10Hz时的噪音等效功率NEP(500,10,1)=3.6×10^-12 WH_z^1/2;探测率D^*(500,10,1)=1.6×10¹⁰ cmH_z^1/2W^-1;响应率R_v=8.2×103VW^-1.另外,多元串接微桥器件出现的多台阶式的特性,可望在红外探测计量及高频方面获得重要应用.     

HC2nO+ (n=3-6) 正离子的红外光解离光谱以及理论计算研究

本文利用脉冲激光溅射-超声分子束载带离子源在气相中产生了HC_2nO⁺ (n=3-6)正离子. 通过对贴附CO的络合物离子的红外光解离光谱实验获得了HC_2nO⁺正离子在1600∽3500 cm^-1范围内的红外光谱. 通过比较实验光谱和理论模拟光谱确定了HC_2nO⁺正离子具有端接氢和氧的直线型碳链衍生物结构,基态为三重态,单重态比三重基态能量高10∽15 kcal/mol. 成键分析表明HC_2nO⁺中的碳链具有连烯的结构特征.     

Cl/HN3/I2全气相化学激光体系的化学动力学模拟计算

 对Cl/HN₃/I₂产生NCl(a)/I激光的过程进行了化学动力学计算，主要考察了Cl,HN₃和I₂的初始粒子数密度及其配比对小信号增益系数的影响。结果发现,当温度为400K, 初始Cl粒子数密度为1×10¹⁵，1×10¹⁶和1×10¹⁷cm^-3时,小信号增益系数分别达到1.6×10^-4,1.1×10^-3和1.1×10^-2cm^-1，获得最佳小信号增益系数的HN₃和I₂的初始粒子数密度分别为初始Cl粒子数密度的1～2倍和2%～4%。同时，对Cl，HN₃和I₂配比对小信号增益系数和增益持续时间的影响进行了讨论。     

Er3+/Ce3+共掺碲铋酸盐玻璃的制备及光谱特性提高研究

采用高温熔融退火法制备了系列 80TeO₂-10Bi₂O₃-10TiO₂-0.5Er₂O₃-xCe₂O₃ (x=0,0.25, 0.5,0.75,1.0 mol%)和(80-y) TeO₂-10Bi₂O₃-10TiO₂-yWO₃-0.5Er₂O₃-0.75Ce₂O₃ (y=3,6,9,12 mol%)的碲铋酸盐玻璃.测试了玻璃样品400-1700 nm范围内的吸收光谱, 975 nm抽运下的上转换发光谱和1.53 μm波段荧光谱, 以及808 nm激励下的Er³⁺离子荧光寿命和无掺杂玻璃样品的Raman光谱, 并结合Judd-Ofelt理论和McCumber理论计算了Er³⁺离子光谱参数.结果表明, 在掺Er³⁺碲铋酸盐玻璃中引入Ce³⁺离子进行Er³⁺/Ce³⁺共掺, 通过Er³⁺离子⁴I_11/2能级与Ce³⁺离子²F_5/2 能级间基于声子辅助的能量传递过程,可以有效抑制Er³⁺离子上转换发光并明显增强其 1.53 μm波段荧光;同时,在现有Er³⁺/Ce³⁺共掺玻璃组分基础上引入WO₃, 可进一步提高1.53 μm波段荧光并展宽其荧光发射谱. 研究结果对于获取优异光谱特性的宽带掺Er³⁺光纤放大器玻璃基质具有实际意义.     

HF/DF激光传输的大气衰减特性

 大气中的水汽对DF激光主要强线的吸收相对较小，而HF激光的大多数谱线受水汽和CO₂分子等的吸收较大。利用较新的HITRAN96数据库和我国不同地区的气象资料，采用逐线积分法计算了HF/DF 激光的大气衰减情况。所选的谱线中，在合肥地区（年平均）， HF的水汽吸收系数最大值可达到10km^-1的数量级，二氧化碳吸收系数最大可达10^-4~10^-3km^-1量级，P2(8)线吸收最弱；DF激光水汽吸收系数最大值可达到10^-1km^-1,比HF低2个量级，且随高度衰减很快，10km处就到10^-5~10^-4km^-1量级，P2(8)线吸收最弱。在我国，由南向北，由夏季到冬季，水汽浓度减少，大气对HF/DF激光的吸收率也相应地递减。     

Comparison of cw and pulsed operation with a TE-cooled quantum cascade infrared laser for detection of nitric oxide at 1900 cm-1

A quantum cascade laser operating near room temperature with thermoelectric (TE) cooling has been used in both continuous-wave (cw) mode (-9 °C) and pulsed mode (+45 °C) to detect atmospheric nitric oxide using spectral lines at 1900.07 cm^-1 (5.3 μm). The totally non-cryogenic spectrometer integrates the laser with a 69-m astigmatic multi-pass cell and a TE-cooled infrared detector to enable operation for extended time periods without operator attention. The pattern of reflections on the astigmatic cell mirrors has been designed to minimize optical interference fringes, which are substantially greater with cw mode than with pulsed operation. The detection method uses direct absorption with rapid- scan sweep integration to achieve sub-second time response. Detection precision for NO in air of 0.5 parts in 10⁹ Hz^-1/2 (1σ) is obtained in pulsed mode with an Allan variance minimum corresponding to 0.1 parts in 10⁹ after 30-s averaging time. The precision in cw mode improves to 0.1 parts in 10⁹ Hz^-1/2 and 0.03 parts in 10⁹ after 30-s averaging, corresponding to an absorbance per unit path length of 2×10^-10 cm^-1. The advantages and disadvantages of cw compared to pulsed operation are discussed. PACS 07.88.+y; 42.62.Fi; 82.80.Gk; 92.60.Sz     

Cavity-enhanced absorption: detection of nitrogen dioxide and iodine monoxide using a violet laser diode

We present an application of cavity-enhanced absorption spectroscopy with an off-axis alignment of the cavity formed by two spherical mirrors and with time integration of the cavity-output intensity for detection of nitrogen dioxide (NO₂) and iodine monoxide (IO) radicals using a violet laser diode at λ=404.278 nm. A noise-equivalent (1σ≡ root-mean-square variation of the signal) fractional absorption for one optical pass of 4.5×10^-8 was demonstrated with a mirror reflectivity of ∼0.99925, a cavity length of 0.22 m and a lock-in-amplifier time constant of 3 s. Noise-equivalent detection sensitivities towards nitrogen dioxide of 1.8×10¹⁰ molecule cm^-3 and towards the IO radical of 3.3×10⁹ molecule cm^-3 were achieved in flow tubes with an inner diameter of 4 cm for a lock-in-amplifier time constant of 3 s. Alkyl peroxy radicals were detected using chemical titration with excess nitric oxide (RO₂+NO→RO+NO₂). Measurement of oxygen-atom concentrations was accomplished by determining the depletion of NO₂ in the reaction NO₂+O→NO+O₂. Noise-equivalent concentrations of alkyl peroxy radicals and oxygen atoms were 3×10¹⁰ molecule cm^-3 in the discharge-flow-tube experiments. Received: 4 February 2003 / Revised version: 10 March 2003 / Published online: 12 May 2003 RID="*" ID="*"Corresponding author. Fax: +44-1865/275-410, E-mail: vlk@physchem.ox.ac.uk     

电磁脉冲在实验室等离子体中传播时间的实验研究

利用矢量网络分析仪，对频域9—11 GHz的电磁脉冲在实验室稳态无磁场等离子体中传播时间的问题进行了实验研究.实验发现当等离子体密度在0.65—1.43×10¹¹ cm^-3范围内时，电磁脉冲通过该等离子体传播的时间将会小于该电磁脉冲在真空中传播同样距离所需要的时间，在密度约为1.10×10¹¹ cm^-3时，这两个时间差会出现一个极值.进一步的研究表明在此密度范围内，非磁化Xe等离子体中的电磁波色散关系将不再成立. 关键词： 电磁脉冲 脉冲传播时间 等离子体密度 色散关系     

Ultra-sensitive ambient ammonia detection using CO<Subscript>2</Subscript>-laser-based photoacoustic spectroscopy

An ambient trace-ammonia sensor that uses resonant photoacoustic spectroscopy and a line-tunable CO₂ laser has been developed. This system achieves a 1 replicate precision of 32 parts-per-trillion (ppt) with an averaging time of 5 s and a total measurement time of 40 s. This 32-ppt precision corresponds to a minimum detectable fractional absorbance of 8.8×10^-9, a minimum detectable absorption coefficient of 9.6×10^-10 cm^-1, and a minimum path-length-normalized detectivity of 1.1×10^-8 Wcm^-1/Hz^1/2. Background interference from CO₂, H₂O, and cell-window absorption were subtracted by switching to a neighboring off-resonance laser wavelength . PACS 42.62.Fi; 82.80.Gk; 82.80.Kq     

乙烯着火延迟的激波管测量与分子碰撞理论分析

在75%和96%两个不同的稀释度下,测量了乙烯/氧气/氩气混合气的着火延迟时间,实验当量比为1,压力为1.3-3.0 atm,温度为1092-1743 K.实验结果表明,着火延迟时间的对数与温度倒数呈良好的线性关系,在两个稀释度下,着火延迟时间随着温度增加而减少.通过回归分析,得到了乙烯着火关联式.计算得乙烯着火延迟在96%稀释度时是75%稀释度的5倍.采用分子硬球碰撞模型,计算了不同稀释度下,乙烯与氧分子的碰撞次数,在96%稀释度下,乙烯与氧气分子碰撞次数为1.53×10²⁹/（s·cm³）,而在75%稀释度下,该碰撞次数增加为5.99×10³⁰/（s·cm³）,约为前者40倍,而着火延迟时间的差异在两条件下仅为5倍的关系,可能由于位阻因子的影响所致.     

Study of the Correlation between Low-Frequency Noise and the Current-Voltage Characteristic of a GaAs Schottky-Barrier Diode

Correlation between low-frequency (1/f) noise and the current-voltage (I-V) characteristic of a beam-lead GaAs Schottky-barrier diode (SBD) is studied. It is shown that the ideality factor n of the I-V characteristic (and its increase) in the current range 10^-4-10^-3 A has the maximum correlation (the correlation coefficient k_cor>0.9) with low-frequenvy noise measured at the same currents at frequencies 8-10 KHz, i.e., n is most sensitive to the series resistance of an SBD. At the same time, the values of n in the 10^-6-10^-5 A range usually do not exceed 1.1 and do not show correlation with low-frequency noise. The correlation is explained predominantly by the barrier-height nonuniformity over the Schottky-barrier contact.     

Off-axis continuous-wave cavity-enhanced absorption spectroscopy of narrow-band and broadband absorbers using red diode lasers

We present an application of continuous-wave (cw) cavity-enhanced absorption spectroscopy (CEAS) with off-axis alignment geometry of the cavity and with time integration of the cavity output intensity for detection of narrow-band and broadband absorbers using single-mode red diode lasers at λ=687.1 nm and λ=662 nm, respectively. Off-axis cw CEAS was applied to kinetic studies of the nitrate radical using a broadband absorption line at λ=662 nm. A rate constant for the reaction between the nitrate radical and E-but-2-eneof (3.78±0.17)×10^-13 cm³ molecule^-1 s^-1 was measured using a discharge-flow system. A nitrate-radical noise-equivalent (1σ≡ root-mean-square variation of the signal) detection sensitivity of 5.5×10⁹ molecule cm^-3 was achieved in a flow tube with a diameter of 4 cm and for a mirror reflectivity of ∼99.9% and a lock-in amplifier time constant of 3 s. In this case, a noise-equivalent fractional absorption per one optical pass of 1.6×10^-6 was demonstrated at a detection bandwidth of 1 Hz. A wavelength-modulation technique (modulation frequency of 10 kHz) in conjunction with off-axis cw CEAS has also been used for recording 1f- and 2f-harmonic spectra of the ^RR(15) absorption of the b¹Σ_g ⁺-X³Σ_g ^- (1,0) band of molecular oxygen at =14553.947 cm^-1. Noise-equivalent fractional absorptions per one optical pass of 1.35×10^-5, 6.9×10^-7 and 1.9×10^-6 were obtained for direct detection of the time-integrated cavity output intensity, 1f- and 2f-harmonic detection, respectively, with a mirror reflectivity of ∼99.8%, a cavity length of 0.22 m and a detection bandwidth of 1 Hz. Received: 24 June 2002 / Revised version: 12 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: vlk@physchem.ox.ac.uk     

Behavior of nuclear matter under extreme conditions in fission

The spontaneous fission of ²⁵²Cf has been studied via γ-γ-γ coincidence and γ-γ light charged particle coincidence with Gammasphere. The binary fission yields of correlated Mo?Ba pairs with 0–10 neutron emission have been remeasured. The existence of “hot” fission mode with 8–10 neutron emission seen previously in the Mo?Ba split is confirmed but with lower intensities. By gating on the light charged particles detected in ΔE-E detectors and a γ ray in one partner, the relative yields of correlated pairs in alpha ternary SF with zero to 6n emission are observed for the first time with the distribution peaked at 2.5n. New correlated pairs are identified in ¹⁰Be ternary SF. We observed essentially only cold, On ¹⁰Be and little, if any, hot, xn ¹⁰Be. New γ-γ-γ data with 2.3 times the total events show weak non-Doppler broadened high energy peaks in coincidence with transitions in correlated pairs in ¹⁰Be SF shifted by the same 6,1 to 26 keV from the 2-0 energy in ¹⁰Be as seen earlier.     

Gamma-ray solid laser: ion-optical system for fasthigh-quality focusing of powerful non-paraxial ion beams of largeformat enriched with excited nuclei

An ion-optical system (IOS) for fast high-quality focusing of powerful paraxial ion beams of large format is suggested. Such beams could be enriched in excited short-lived (10^-4-10^-6 s) laser-active nuclei (ELAN). To increase the beam power, ions are collected from the visible surface (10-10⁴ cm²) of an intermediate target (converter). The full converter surface is enhanced by a factor of 10²-10⁴ by a special micro-relief and achieves 10³-10⁷ m². The toms containing ELAN are created in the converter by a powerful radiation source using neutrons, γ quanta, charged particles, etc. Those ELAN atoms are emitted from the converter surface and selectively ionized by a dye laser just above the surface. Using a specially chosen emitter (converter) shape, a paraxial ion beam is formed. This is due to the micro-relief structure of the emitter surface, its high-quality orientation, and cylindrical (instead of spherical) ion optics. In the vicinity of an active medium (AM) for a gamma-ray laser, the ions are decelerated so that they can penetrate only into 1-3 outer layers of the host matrix, e.g., diamond. This makes heating of the AM by the ion beam negligible in comparison to self-heating due to internal conversion. Analytical and numerical estimation of the IOS aberrations have shown that the compression of the ion beam exceeds10⁵-10⁶, and that a considerable part (10%) of the ELAN reach the AM in a time as short as10^-7 s. This ensures the rapid and controllable deposition of ELAN into an AM within a gamma-laser system based on existing techniques without using nuclear explosions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron paramegnetic detection of ionic motional effects in the super ionic conductor β-sodium gallate

The EPR spectra of Cu²⁺, Mn²⁺ and Eu²⁺, incorporated into the conducting mirror planes of β-sodium gallate, have been studied. For all three impurities, the EPR spectra at or near room temperature show pronounced relaxation effects caused by the motion of the ions. From the relaxation effects the correlation time of the motion is found to be of the order of 10^-11 sec. This time corresponds to a residence time for the paramagnetic ion at a lattice site in the conducting plane. From this time and the thermal activation energy an attempt frequency of 10¹² Hz is determined.