用于原子能级结构研究的激光共振电离光谱系统

激光共振电离光谱技术是一种利用一路或多路激光将待测原子选择性共振激发与电离,通过测量离子信号来研究原子能级结构的光谱技术。研建了一套激光共振电离光谱装置,用于原子高激发态能级结构参数的测量。分别从该装置的总体结构、关键技术和应用实例等方面进行了详细介绍。该套装置主要包括高调谐精度的染料激光器系统、高效的激光离子源系统和高分辨率的飞行时间质量分析器。染料激光器系统包括3台多纵模可调谐染料激光器和1台单纵模可调谐染料激光器,均为脉冲工作方式,重复频率为10 kHz,泵浦源均为532 nm的Nd∶YAG固体激光器。激光离子源系统包括原子化源、激光与原子相互作用区和离子光学透镜组三部分组成,样品在原子化源中被电加热实现原子化,喷射出的原子被激光选择性激发、电离,产生的离子被离子传输透镜整形成能量分散小、束窄的离子束。飞行时间质量分析器采用了反射式结构设计、脉冲垂直推斥技术和偏转板调节技术。利用此装置,实验测定了U原子的自电离态光谱,获得了U原子一条较佳的三色三光子共振电离路径,对应激光的波长分别为591.7,565.0和632.4 nm。此系统还可用于测量同位素位移和原子超精细结构等参数。另外,由于此系统中联用了质量分析器,因此可用于样品多元素分析、痕量元素分析、同位素丰度分析。     

用激光增强电离光谱(LEIS)方法进行钠原子的灵敏检测

用脉冲可调谐染料激光共振激励火焰中的钠原子。通过测量钠原子的激光增强电离光谱(LEIS)信号进行钠原子的灵敏检测,实际的检测限可达10~(-11)g/ml。     

碘原子共振多光子电离光谱研究

用可调谐的染料激光(4600～5000(?)),共振(3+2)和(4+1)多光子电离探测了I(5p~2P_(3/2)~0)和1~#(5p~2P_(1/2)~0).碘原子是由碘分子(I_2)经激光解离而产生的.在上述激光波段中共观察到12个原子跃迁,其中,(4+1)多光子电离跃迁是首次观察到的.     

锌掺杂半导体材料的共振电离质谱分析

本文简要地描述了激光共振电离质谱的实验装置和测量方法,给出了用共振电离质谱方法对锌掺杂化合物半导体材料进行分析的光谱和质谱图,并估计了用这种方法进行痕量分析可能达到的检测限.     

NO分子共振增强的多光子离化机制

用皮秒Nd：YAG激光器泵浦光学参量发生／放大器做激发源,获得了420～480nm波长范围内NO分子的多光子离化谱。通过对谱线的归属,分析确定了NO分子的离化为以A^2∑为中间共振态的(2 2)共振增强的多光子离化过程。以速率方程为基础,利用激光脉宽较窄(35ps)的条件,推导出离化信号随激光强度呈近四次方变化关系,与实验测量结果相符,这可为用共振增强多光子离化(REMPI)光谱技术探测污染物NO分子提供实验参考。     

Fe（CO）5双色共振增强多光子电离研究

利用超声分子束、强激光多光子电离和飞行时间质谱探测装置研究了Fe(CO)_5分子在355nm、532nm和355nm+532nm单、双色激光作用下的多光子电离质谱.实验结果证明了双色激光的共振增强电离作用.由飞行时间质谱的展宽峰型结构估算了Fe(CO)_5等分子的光解离寿命与Fe~+和Fe(CO)_5离子分子反应截面.     

镥的激光共振电离同位素选择性研究

本文在速率方程基础上通过数值模拟方法 ,对镥的激光共振电离通道 :5d6s2 2 D3 /2 (5 73.6 5 5nm)→5d6s6 p4F3 /2 (6 4 2 .5 18nm)→ 6s6 p2 4P1/2 (6 4 3.5 4 8nm)→Autoionizationstate的激光诱导同位素选择性进行了研究。在实际实验条件下用这一方法计算得到的激光波长对激光诱导同位素选择性的关系与实验结果相符合。探讨了在偏振激光作用的情况下各种激光参数 (波长、带宽和激光强度 )对激光诱导同位素选择性的影响 ,并提出了在一定实验条件下激光共振电离质谱计较为准确地测定同位素比值的方法。这一理论方法 ,同样适用于研究其它元素的激光共振电离同位素选择性和选择激光同位素分离电离通道     

Sn激光共振电离质谱分析中电离通道理论探讨

Sn激光共振电离质谱同位素分析中电离通道的选择非常关键.采用Dirac–Hartree–Fock(MCDHF)方法和相对论组态相互作用的Grasp VU原子结构计算程序,计算了Sn、Te原子的低激发态能级结构、光谱跃迁几率.通过对Sn质谱分析用灯丝样品进行热蒸发实验,确定了Sn原子在蒸发条件下基态能级粒子布局.结合理论计算跃迁数据和布局数据,从选择性电离角度出发,推荐了Sn激光共振电离质谱分析中Sn电离光谱通道.     

Ti原子315nm-321nm区（1+1）共振增强多光子电离谱的实验研究

结合激光烧蚀、超声射流技术,在实验上制备了高浓度的Ti原子自由原子束源,测定了315nm-321nm光谱区过渡金属Ti原子的(1+1)共振增强多光子电离谱,并对光谱结构进行了归属.     

三氯乙烯分子的多光子电离解离研究

用可调谐染料激光器 ,在 4 5 0— 4 75 nm范围内 ,在飞行时间质谱仪上研究了三氯乙烯分子的共振增强多光子电离解离过程。研究表明 ,在此实验波段内三氯乙烯分子经历了从 π到 3d里德堡态的 (3 1 )多光子过程 ,可以用母体离子阶梯开关模型对三氯乙烯的电离解离过程进行解释 ,并对振动能级进行了标识 ,对振动频率进行了计算     

Tunable resonance fluorescence monochromator with sub-Doppler spectral resolution

A cesium-based resonance fluorescence monochromator with a spectral resolution of 200 MHz and a tunable response over the D(2) absorption line of cesium (380 MHz) is described. The narrow spectral response is achieved through excitation of a monokinetic population of the 6(2)P(3/2)( degrees ) state by arrangement of the excitation lasers in either a copropagating or a counterpropagating orientation. The narrow spectral response of the detector allows for excitation of specific hyperfine components involved in the 6(2)P(3/2)( degrees ) (F=3-5) to 6(2)D(5/2) (F=2-6) transition (917.23 nm). The selectivity gained through resolving specific hyperfine transitions allows for a photon detector that is both spectrally tunable and narrow. We report the sub-Doppler linewidths achieved through various laser beam orientations. We also describe how these beam geometries can be applied to spectrally narrow and tunable image detection.     

Two photon resonant third harmonic generation in calcium vapour

We have generated ultraviolet picosecond pulses by frequency tripling a mode locked dye laser in calcium vapour. Saturation of third harmonic generation is observed when the dye laser is turned to a two photon resonance. Peak powers of 100 kW, tunable around 200 nm are achieved at fundamental powers of 250 MW.     

All fiber tunable- or dual-wavelength Yb-doped fiber laser covering from dissipative soliton to dissipative soliton resonance

In this Letter, a simple and passively mode-locking Yb-doped all fiber laser using a nonlinear polarization rotation technique operating under dissipative soliton(DS) or dissipative soliton resonance(DSR) conditions is proposed, furthermore, using a combination of a bandpass filter and a Loyt filter, tunable single-wavelength or dual-wavelength operation under two different conditions is realized, respectively. The tunable single?wavelength DS laser has a 5 nm tuning range from 1029 to 1034 nm with a pulse width of 110 ps. The tunable single-wavelength DSR operation laser has a range of 4 nm. In-depth research on the mechanism of the con?version between DS and DSR is carried out. Particularly, under dual-wavelength DSR operation, the obtained step-like pulses consist of two rectangular pulses with different energies. This work could help give a deeper insight into normal dispersion pulses.     

Observation of resonance electronic and non‐resonance‐enhanced vibrational natural Raman optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low‐lying electronic transition is reported. These new phenomena were measured using the rare‐earth complex Eu(tfc)₃ (+)‐tris[3‐trifluoroacetyl‐D ‐camphorato]europium(III), where electronic resonance occurs between the 532‐nm laser excitation and the ⁷F₁ → ⁵D₁ transition of the Eu³⁺ metal center. Electronic Raman spectra involve the Raman transitions terminating on the low‐lying electronic states of Eu(tfc)₃. The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)₃ to its low‐lying electronic states with significant magnetic‐dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance‐enhanced since the 532‐nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064‐nm laser excitation. Copyright © 2010 John Wiley & Sons, Ltd.     

铕（Eu）原子的激光增强电离光谱的研究

本文从激光增强电离光谱的速率方程和ＬＥＩ光谱加宽理论出发，得到ＬＥＩ光谱信号和光谱轮廓的表达式，在紫外区测得铕的三条ＬＥＩ谱线。并用计算机模拟光谱的方法给出这三条谱线的轮廓，与实验所得的谱图一致。     

Observation of 280 nm and 298 nm ultraviolet emissions in sodium vapor

Dye laser output around 578 nm is utilized to pump sodium vapor confined in a heatpipe. Fixed wavelength ultraviolet emissions at 280 nm and 298 nm are observed for the first time and can be explained by anti-Stokes Raman scattering and two photon emission respectively. In addition, there are tunable emission lines around 280 nm and 298 nm, the frequencies of which vary with pump laser wavelength. These tunable lines can be explained by four-wave mixing schemes.     

2080 nm long-wavelength,high-power dissipative soliton resonance in a dumbbell-shaped thulium-doped fiber laser

We demonstrate a 2080 nm long-wavelength mode-locked thulium(Tm)-doped fiber laser operating in the dissipative soliton resonance(DSR) regime. The compact all-fiber dumbbell-shaped laser is simply constructed by a 50/50 fiber loop mirror(FLM), a 10/90 FLM, and a piece of large-gain Tm-doped double-clad fiber pumped by a 793 nm laser diode. The 10/90 FLM is not only used as an output mirror, but also acts as a periodical saturable absorber for initiating DSR mode locking. The stable DSR pulses are generated at the center wavelength as long as 2080.4 nm, and the pulse duration can be tunable from 780 to 3240 ps as the pump power is increased. The maximum average output power is 1.27 W, corresponding to a pulse energy of 290 nJ and a nearly constant peak power of 93 W. This is, to the best of our knowledge, the longest wavelength for DSR operation in a mode-locked fiber laser.     

Three-dimensional memory effect in fluorescent photosensitive glass activated by europium and cerium

The persistent extinction of fluorescence emission of Eu(3+) in glasses activated with europium and cerium is reported for the first time to the authors' knowledge. The glass samples containing Eu(3+) and Ce(3+) were initially colorless and transparent and exhibited intense emission peaks at 592 and 612 nm assigned to the (5)D(0)-(7)F(1, 2) transitions of Eu(3+). The complete extinction of the Eu(3+)-ion emission was obtained as an effect of multipulse excimer-UV-laser (lambda = 248 nm, tau(FWHM) >/= 20 ns) irradiation of the glass samples. Fluorescence microscopy, M?ssbauer spectrometry, and electron spin resonance were applied for investigation of the modifications induced by the laser treatment. As a decisive proof of the extinction of fluorescence we succeeded in recording three-dimensional fluorescent photographic patterns within the activated samples.     

Xe-Kr laser induced collisional ionization system and experimental preparation of its initial state: Four-photon resonant excitation

This paper proposes a novel one-colour Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction--the four 4f levels with even J of Xe-can be prepared through method of four-photon resonant excitation by dye laser with wavelength of -440 nm. Absorption of an additional photon （the transfer laser） of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at -440nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of -440 nm four-photon resonant excitation of the initial 4f state of the Xe Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization.     

Stochastic resonance in single-mode semiconductor lasers

Owing to the considerable virtues of semiconductor lasers for applications, they have become the main optical source for fiber communication systems recently. The behavior of stochastic resonance (SR) in direct-modulated semiconductor laser systems is investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the modulated laser system were calculated using the linear approximation method. We found that the SR always appears in the dependence of the SNR upon the bias current density, and is strongly affected by the cross-correlation coefficient of the carrier and photon noises, the frequency of modulation signal and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated semiconductor laser systems and improve the quality of optical communication.