Experimental preparation of the initial state of Xe+-N laser-induced collisional charge transfer system: Multi-photon resonant ionization of xenon

A novel one-color Xe⁺-N laser induced collisional charge transfer system is proposed, and preparation of the initial state of the system, i.e., Xe⁺ is experimentally implemented through resonance enhanced multi-photon ionization (REMPI) by ～440 nm dye laser. The REMPI of Xe is experimentally investigated through time-of-flight (TOF) mass spectrometry and the intensity dependence of Xe⁺ is obtained, aiming at the preparation of Xe⁺. The resonant ionization spectra of Xe at ～440 nm under several different conditions are measured, showing the impacts of mode purification and source pressure on the resonant ionization spectrum. The results indicate the feasibility of preparing the initial state of the Xe⁺-N system by ～440 nm multi-photon resonant ionization, which prepares for a further experiment of laser-induced collisional charge transfer.     

Tunable phase-stabilized infrared parametric laser source

This paper reports that the tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800 nm pump source, the output idler pulses are tunable from 1.3 μm to 2.3 μm, and the maximum output energy of the idler pulses is higher than 1 mJ at 1.6 μm by using 6 mJ pump laser. A carrier-envelope phase fluctuation of ～ 0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer.     

Linear and nonlinear optical properties of ZnO nanorod arrays

Polarization-dependent linear absorption, second-harmonic generation （SHG） and 3rd-order nonlinearities of wellaligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0×10^4cm/GW at the wavelength -750nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.     

PM567-Doped solid dye lasers based on PMMA

Polymers are a kind of attractive hosts for laser dyes due to their high transparency in both pumping and lasing ranges and superior optical homogeneity. In this paper solid dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of 1, 3, 5, 7, 8 -pentamethyl-2, 6-diethylpyrromethene-BF$_{2 }$ (PM567) are prepared. The absorption, fluorescence and lasing spectra of the samples are obtained. Wide absorption and fluorescence bands are obtained and a red shift of the maxima of the lasing emission spectra is observed. With the second-harmonic generation of Q-switched Nd:YAG laser (532\,nm, $\sim $20\,ns) pumping the samples longitudinally, the slope efficiencies of the samples are obtained. There is an optimal dye concentration for the highest slope efficiency when the pumping energy is lower than some typical value ($\sim $250\,mJ), and the highest slope efficiency 35.6{\%} is obtained in the sample with a dye concentration of $2\times10^{ - 4}$\,mol/L. Pumping the samples at a rate of 10Hz with a pulse energy as high as 200\,mJ (the fluence is 0.2\,J/cm$^{2})$, the output energy drops to one-half of its initial value after approximate 15500 pulses and the normalized photostability is 5.17\,GJ/mol. A kind of solid dye laser which could have some applications is built.     

Judd-Oflet analysis of spectrum and laser performance of Ho：YAP crystal end-pumped by 1.91μm Tm：YLF laser

The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.     

Interaction of argon clusters with intense VUV-laser radiation: the role of electronic structure in the energy-deposition process

The response of Ar clusters to intense vacuum-ultraviolet pulses is investigated with photoion spec-troscopy. By varying the laser wavelength, the initial excitation was either tuned to absorption bands of surface or bulk atoms of clusters. Multiple ionization is observed, which leads to Coulomb explosion. The efficiency of resonant 2-photon ionization for initial bulk and surface excitation is compared with that of the nonresonant process at different laser intensities. The specific electronic structure of clusters plays almost no role in the explosion dynamics at a peak intensity larger than 1.8 x 10(12) W/cm(2). The inner ionization of atoms for resonant and nonresonant excitation is then saturated and the energy deposition is mainly controlled by the plasma heating rate. Molecular dynamics simulations indicate that standard collisional heating cannot fully account for the strong energy absorption.     

Continuous-wave mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate

This paper reports a continuous-wave (CW) mid-infrared intracavity singly resonant optical parametric oscillator based on periodically poled lithium niobate (PPLN) pumped by a diode-end-pumped CW Nd:YVO$_{4}$ laser. Considering the thermal lens effects, it adopted an optical ballast lens and the near-concentric cavity for better operation. At the PPLN's grating period of 28.5\,$\mu$m and the temperature of 140\du, the maximum idler output power of 155\,mW at 3.86\,$\mu$m has been achieved when the 808\,nm pump power is 8.5\,W, leading to an optical-to-optical conversion efficiency of 1.82{\%}.     

Ultraviolet photovoltaic characteristic of MgB2 thin film

Fast photoelectric effects have been observed in MgB₂ thin film fabricated by chemical vapour deposition. The rise time was $\sim $10 ns and the full width at half-maximum was \sim185\,ns for the photovoltaic pulse when the film was irradiated by a 308\,nm laser pulse of 25\,ns in duration. X-ray diffraction and the scanning electron microscope revealed that the film was polycrystalline with preferred c-axis orientation. We propose that nonequilibrium electron--hole pairs are excited in the grains and grain boundary regions for MgB₂ film under ultraviolet laser and then the built-in electric field near the grain boundaries separates carriers, which lead to the appearance of an instant photovoltage.     

Cluster-assisted generation of multicharged ions in nanosecond laser ionization of carbon bisulfide clusters at 1064nm

The photoionization of seeded carbon bisulfide molecular beam by a 1064\,nm nanosecond Nd-YAG laser with intensities varying from $0.8\times10^{11}$ to $5.6\times10^{11}$\,W/cm$^{2}$ have been studied by time-of-flight mass spectrometry. Multiply charged ions of S$^{q + }$ ($q$ = 2--6) and C$^{q +}$ ($q$ = 2--4) with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS$_{2}$ neat clusters in the beam. An electron recolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.     

NO(3+1)共振增强的多光子离化谱

用皮秒脉冲高功率Nd∶YAG激光器抽运的光学参量发生/放大器作激发源,获得了NO分子在420～500 nm波长范围内的多光子离化谱,光谱图呈现分离谱的特征,表明在该波长区间NO分子以多光子共振方式离化。离化信号随激光强度的近四次方变化关系表明,在420～500 nm波长范围内NO分子吸收4个光子而离化。通过对谱线的标识,首次分离出NO分子以E 2Σ激发电子态为中间共振态的(3+1)多光子离化光谱序列,由谱线序列峰值波长得到NO分子E 2Σ电子态的振动常数,从而实现了采用多光子离化技术对该态能级结构的实验研究。     

Molecular dynamics study of ice structural evolution

Molecular dynamics simulation is employed to study the structural evolution of low density amorphous ice during its compression from one atmosphere to 2.5 GPa. Calculated results show that high density amorphous ice is formed at an intermediate pressure of -1.0 GPa; the O-O-O bond angle ranges from 83° to 113°, and the O-H… O bond is bent from 112° to 160°. Very high density amorphous ice is obtained by quenching to 80 K and decompressing the ice to ambient pressure from 160 K/1.3 GPa or 160 K/1.7 GPa; and the next-nearest O-O length is found to be 0.310 nm, just 0.035 nm beyond the nearest O-O distance of 0.275 nm.     

Effect of four-photon interactions on coherent population trapping in Λ-systems

The resonance fluorescence spectrum of a Λ-system excited by two resonant light fields is calculated using a Markov analysis. Analytical formulas are derived in the strong-field limit within and beyond the rotating wave approximation. It is shown that the resonance fluorescence of the system does not vanish during coherent population trapping. Its spectrum consists of two multiplets which are similar to a triplet in the resonance fluorescence spectrum of a two-level atom and lie at the electronic transition frequencies, together with two triplets located at the frequencies of four-photon processes involving the optical excitation fields. The latter are fundamental in character and impose limits on the lower bound of the dephasing rate for the Raman resonance owing to the effect of radiative decay of the dipole transitions on the dynamics of the ground state. The effect of four-photon dephasing on the absorption spectrum of a Λ-system is analyzed and found to lead to a substantial reduction in the depth of a dip in the absorption spectrum which vanishes as the laser field strength is increased. Zh. éksp. Teor. Fiz. 113, 144–167 (January 1998)     

Spectroscopic investigation of a new crystal： Nd^3＋,Yb^3＋：YVO4

The absorption and emission spectra of the YVO4 single crystal co-doped with 1 at.% Nd^3＋ and 1 at.% Yb^3＋ are investigated. The efficient Nd^3＋ → Yb^3＋ energy transfer and the back transfer （Yb^3＋ → Nd^3＋） are observed at room temperature. The fluorescence lifetime of the 4F3/2 level of Nd^3＋ in Nd,Yb：YVO4 is measured under 808 nm laser light excitation. The efficiency of Nd^3＋ → Yb^3＋ energy transfer in YVO4 is determined to be about 34%.     

Measurement of quantum defect of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

<正>This paper reports that ultracold atoms are populated into different nS and nD Rydberg states(n=25~52) by two-photon excitation.The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization.This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.     

Green and red up-conversion emissions and thermometric application of Er3+-doped silicate glass

The green and red up-conversion emissions centred at about 534, 549 and 663\,nm of wavelength, corresponding respectively to the ${^{2}}H_{11 / 2} \to {^{4}}I_{15 / 2}$, ${^{4}}S_{3 / 2} \to {^{4}}I_{15 / 2}$ and ${^{4}}F_{9 / 2} \to {^{4}}I_{15 / 2}$ transitions of Er$^{3 + }$ ions, have been observed for the Er$^{3 + }$-doped silicate glass excited by a 978\,nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296--673\,K, which shows that Er$^{3 + }$-doped silicate glass can be used as a sensor in high-temperature measurement.     

Electron spin resonance study of the Ba-doping manganite Nd0.5Sr0.5MnO3

We have performed magnetization measurements and electron spin resonance （ESR） on polycrystalline manganites of Nd0.5Sr0.5-xBaxMnO3 （x = 0.1）. Phase separation and phase transitions are observed from the susceptibility and the ESR spectra data. Between 260 K （～ Tc） and 185 K （～ TN）, the system coexists of the paramagnetic phase and the ferromagnetic （FM） phase. Between 185 K and 140 K, the system coexists of the FM phase and the antiferromagnetic （AFM） phase. These results indicate that the system has a very complex magnetic state due to the origin of the instability stemming from manganite Nd0.5Sr0.4Ba0.1MnO3 by partially substituting the larger Ba^2＋ ions for the smaller Sr^2＋ ions.     

Vibration properties of low-fraction hydrogen in deuterium ices

Inelastic incoherent neutron scattering spectra of D2O high-density amorphous （hda） ice, ice-Ⅷ and ice-Ⅱ mixed with small amount of H2O （（5%） have been measured recently on high-energy transfer spectrometer at Rutherford Appleton Laboratory （UK）. The hydrogen atom on D2O ice lattices has three distinguished vibrational modes, two bending at low frequencies and one stretching at high frequencies, and their frequencies are slightly different for different phases of ice. It was found that the lower one of the bending modes is located at -95 meⅤ for hda-ice, at -95 meⅤ for ice-Ⅷ and at -96 meⅤ for ice-Ⅱ and they are all lower than the value of 104 meⅤ for ice-Ih. It was also measured that the O-D and O-H covalent bond stretching modes of ice-Ⅷ are at -315 and -425 meⅤ, ice-Ⅱ at 307 and -415 meⅤ, hda-ice at 312 and -418 meⅤ, respectively. They are significantly higher than the values of ice-Ih at -299 and -406 meⅤ, respectively.     

适用于ppb量级NO_2检测的低功率蓝光二极管光声技术研究

在405 nm处基于低功率蓝光二极管光声技术探测ppb量级NO_2浓度系统,获取了NO_2有效吸收截面,探讨了水蒸气等气体的测量干扰,通过频率扫描拟合得到了1.35 kHz的谐振频率.采用内部抛光的铝制圆柱空腔作为光声谐振腔(内径为8 mm,长为120 mm),系统优化了腔体、窗片和电源等影响因素,分析了降低本底噪声、提高信噪比的方法,噪声信号可降至0.02μV.设计了两级缓冲结构,显著抑制了流量噪声的影响,提高了系统的稳定性.系统的标定梯度曲线经过线性拟合后的斜率为0.016μV/ppb, R~2为0.998,在60 s平均时间下,系统NO_2探测限为3.67 ppb(3σ).为了证实系统的测量结果,将其与二极管激光腔衰荡光谱系统同步对比测量大气NO_2浓度,二者线性拟合后的斜率为0.94±0.009,截距为1.89±0.18,相关系数为0.87,一致性较好.实验结果表明,该系统实现了ppb量级NO_2浓度的低成本在线探测,可用于NO_2浓度外场的实时检测.     

Green and red up-conversion emissions and thermometric application of Er^3＋-doped silicate glass

The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, have been observed for the Er^3＋-doped silicate glass excited by a 978 nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296-673 K, which shows that Er^3＋-doped silicate glass can be used as a sensor in high-temperature measurement.     

Judd--Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the Tm^3＋：Lu2SiO5 （Tm：LSO） crystal is grown by Czochralski technique. The roomtemperature absorption spectra of Tm：LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Ω2=9.3155×10^-20 cm^2, Ω4=8.4103×10^-20 cm^2, Ω6=1.5908×10^-20 cm^2, the fluorescence lifetime is calculated to be 2.03 ms for ^3F4 → ^3H6 transition, and the integrated emission cross section is 5.81×10^-18 cm^2. Room-temperature laser action near 2μm under diode pumping is experimentally evaluated in Tm：LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuouswave maximum output power of 0.67 W. The emission wavelengths of Tm：LSO laser are centred around 2.06μm with spectral bandwidth of -13.6 nm.