纳秒强激光场中甲醇光电离产生高价离子的研究

利用25ns脉冲Nd YAG 532nm的激光，在1011 W·cm-2的光场强度下，利用飞 行时间质谱对He, N2, Ar载气条件下甲醇的激光电离过程进行了研究.发现当利用氩作为 载气时，除观察到一般多光子电离所产生的离子和碎片离子外，还观察到很强的Cq+(q=2-4)和Oq+(q=2—4)高价离子.这些离子都有很高的平动能，通 过改变载 气种类和压力以及使用不同延迟条件的脉冲电场的实验，可以认为这些高价离子来源于含甲 醇团簇的库仑爆炸过程.这些实验结果为发展库仑爆炸理论研究提供新思路. 关键词： 甲醇 纳秒激光 高价离子 库仑爆炸     

纳秒强激光中乙腈团簇增强的高价电离研究

利用脉宽为25 ns的脉冲:Nd:YAG 1064 nm的激光,在1010～1011 W·cm-2的强度下,用飞行时间质谱对乙腈分子束激光电离过程进行了研究.实验中利用氦气作为载气,乙腈分子束采用扩散和脉冲两种方式进样,当扩散束进样时,乙腈分子的谱峰可用多光子电离来解释,而当脉冲分子束进样时,实验中产生了外层价电子高剥离的Nq (q=2～5)和Cq (q=1～4)信号谱.实验中同时发现,激光波长增大时,高价离子的谱强度也趋向于增大.激光延迟及谱峰的相关性分析表明,这些高价离子可能来源于乙腈团簇的库仑爆炸过程.提出一个多光子电离引发,逆韧致吸收加热一电子碰撞电离模型来解释高价离子的产生,对高价离子伴随的波长效应也给出了较为合理的解释.     

N_2O~ 离子A~2Σ~ 电子态的光解动力学研究

用一束波长为 36 0 5 5nm的激光 ,通过N2 O分子的 (3 1 )共振多光子电离 (REMPI)过程制备纯净且布居完全处于X2 Π(0 0 0 )态的母体离子N2 O ,然后用另一束波长在 2 75— 32 8nm范围内的可调谐激光将制备的N2 O 离子激发至预解离电子态A2 Σ .实验发现 ,由于解离碎片NO 所具有的一定的反冲速度 ,其TOF质谱峰明显比N2 O 母体宽 .通过分析NO 碎片TOF质谱峰形状 ,得到了解离产物的总平均平动能〈ET〉 ;通过考察〈ET〉随光解能量的变化 ,发现光解能量在 32 0 0 0cm- 1 附近约 2 5 0cm- 1 的变化范围内 ,〈ET〉值由约 80 0 0cm- 1 突然减小至约 1 6 0 0cm- 1 .通过分析 ,在光解能量小于 32 0 0 0cm- 1 的区域 ,解离通道为NO (X1 Σ ) N(4 S) ;而在光解能量大于 32 0 0 0cm- 1 的区域 ,另一个具有较高解离限的解离通道 ,NO (X1 Σ ) N(2 D) ,开启并完全取代N(4 S)通道成为解离的惟一通道 .根据实验结果 ,对在所研究的光解能量范围内的N2 O 离子A2 Σ 电子态预解离机理进行了探讨     

N2O+离子A2∑+电子态的光解动力学研究

用一束波长为360.55nm的激光,通过N2O分子的(3+1)共振多光子电离(REMPI)过程制备纯净且布居完全处于X2Ⅱ(000)态的母体离子N2O+,然后用另一束波长在275-328nm范围内的可调谐激光将制备的N2O+离子激发至预解离电子态A2∑+.实验发现,由于解离碎片NO+所具有的一定的反冲速度,其TOF质谱峰明显比N2O+母体宽.通过分析NO+碎片TOF质谱峰形状,得到了解离产物的总平均平动能;通过考察随光解能量的变化,发现光解能量在32000cm-1附近约250cm-1的变化范围内,值由约8000cm-1突然减小至约1600cm-1.通过分析,在光解能量小于32000cm-1的区域,解离通道为NO+(X1∑+)+N(4S);而在光解能量大于32000cm-1的区域,另一个具有较高解离限的解离通道,NO+(X1∑+)+N(2D),开启并完全取代N(4S)通道成为解离的惟一通道.根据实验结果,对在所研究的光解能量范围内的N2O+离子A2∑+电子态预解离机理进行了探讨.     

N2O+离子A2∑+电子态的光谱研究

用一束波长为360.55 nm的激光,通过N2O分子的(3+1)共振增强多光子电离过程制备纯净的母体离子N2O+X2Ⅱ3/2,1/2(000).用另一束可调谐激光将N2O+离子激发至预解离态A2Σ+,利用飞行时间质谱检测解离碎片NO+离子强度随光解光波长的变化,在278-328 nm波长范围内获得了光解碎片的激发(PHOFEX)谱.观测到了N2O+离子A2Σ+←X2Ⅱ电子跃迁较丰富的振动谱带.通过对PHOFEX光谱的标识,获得了A2∑+态较准确和全面的分子光谱常数.     

纳秒激光电离分子团簇产生高价离子实验研究

 利用飞行时间质谱仪，研究了功率密度为10⁹~10¹¹ W/cm²，波长为532 nm 的纳秒激光对苯、呋喃、甲醇及碘甲烷分子团簇的激光电离过程。实验观察到了高平动能的高价离子C^q+(q≤3)，O^q+(q≤3)和I^q+(q≤4)，该过程经历了以“初始的多光子电离引发-逆轫致吸收加热-电子碰撞电离模式”为主的激光团簇作用过程，后期经历了团簇的库仑爆炸过程。实验发现：即使激光能量变化一个量级以上时，主要高价离子的种类及占全部离子产物的比率也没有明显的变化，但是高价离子的初始平动能随激光强度的增大而增加；分子中含有较多个外壳层电子的氧、碘原子更容易电离产生高价离子，而碳离子的价态和强度相对较低。     

飞秒强激光脉冲中氩团簇库仑爆炸特性研究

利用Bathe模型，理论模拟了氩团簇在飞秒强激光中(100 fs, 1016 W/cm2)的电离和爆炸过程.研究结果显示，在团簇尺寸较小时，离子平均能量与团簇初始半径平方成正比，爆炸机制为典型的库仑爆炸.随着团簇尺寸的增加，能量增加的速度趋缓并在一定团簇尺寸后趋于饱和.模拟结果与实验数据有较好的吻合.     

Fragmentation of N2 in 410 nm Intense Femtosecond Laser Field

用速度成像技术研究了氮分子在410和820 nm线偏振飞秒激光场中(1014 W/cm2)碎片化过程．N2在410 nm激光场中碎片化行为与820 nm激光场中不同,碎片离子的能量分布和角分布不随410 nm激光场强明显变化．氮分子在410 nm激光场中的碎片化过程主要是由垂直激发导致的非库仑态解离引起的．     

高电荷态Arq+与Ne碰撞中入射离子电荷交换截面的研究

报道Arq++Ne(q=8, 9, 11, 12)碰撞体系中多电子转移过程,得到了多组实验测量电荷交换截面数据,讨论入射离子电荷交换截面、反冲离子产生截面与入射离子电荷态、能量以及散射离子电荷态的关系,并且将实验结果与Arq++Ar碰撞体系进行对比研究.在修正分子库仑过垒模型的基础上,对实验现象做了合理的解释.     

CH_3I~(2+)的二体、三体解离过程的理论研究

采用密度泛函和耦合簇理论从过渡态的观点对CH_3I~(2+)离子的解离过程进行了计算和分析.优化得到了CH_3I,CH_3I+和CH_3I~(2+)的稳定结构及解离过渡态的几何构型并给出了相应能量,计算的第一、二电离能与实验结果符合.基于母体离子、过渡态和解离碎片的几何结构和能量,对CH_3I~(2+)的两体解离过程和三体解离过程进行了详细分析和讨论.给出了二体、三体解离的可能解离通道,并分析了实验上观测到的解离碎片离子的产生机制.计算结果表明,三重和单重绝热势能面上的一些解离过程表现出明显的差异.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.