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Plasma Science and Technology 2019年第3期21卷 98-107页

作者： Ying WANG Anmin CHEN Qiuyun WANG Dan ZHANG Laizhi SUI Suyu LI Yuanfei JIANG Mingxing JIN Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy (Jilin University)

In double-pulse laser-induced breakdown spectroscopy(DP-LIBS), the collinear femtosecond double-pulse laser configuration is experimentally investigated with different initial sample temperatures using a Ti:sapphire laser. The glass sample is ablated to produce the plasma spectroscopy. During the experiment, the detected spectral lines include two Na(I) lines(589.0 nm and 589.6 nm) and one Ca(I) line at the wavelength of 585.7 nm. The emission lines are measured at room temperature(22 ℃) and three higher initial sample temperatures(T_s?=?100 ℃, 200 ℃, and 250 ℃). The inter-pulse delay time ranges from-250 ps to 250 *** inter-pulse delay time and the sample temperature strongly influence the spectral intensity,and the spectral intensity can be significantly enhanced by increasing the sample temperature and selecting the optimized inter-pulse time. For the same inter-pulse time of 0 ps(single-pulse LIBS), the enhancement ratio is approximately 2.5 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. For the same inter-pulse time of 150 ps, the enhancement ratio can be up to 4 at T_s?=?200 ℃ compared with that obtained at T_s?=?22 ℃. The combined enhancement effects of the different initial sample temperatures and the double-pulse configuration in femtosecond LIBS are much stronger than that of the different initial sample temperatures or the double-pulse configuration only.

关键词： laser-induced breakdown spectroscopy femtosecond laser double pulse emission enhancement glass

Effect of lens focusing distance on laser-induced silicon plasmas at different sample temperatures

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Plasma Science and Technology 2019年第3期21卷 69-76页

作者： Dan ZHANG Anmin CHEN Qiuyun WANG Ying WANG Suyu LI Yuanfei JIANG Mingxing JIN Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy (Jilin University)

We investigated the dependence of laser-induced breakdown spectral intensity on the focusing position of a lens at different sample temperatures(room temperature to 300 ℃) in atmosphere.A Q-switched Nd:YAG nanosecond pulsed laser with 1064 nm wavelength and 10 ns pulse width was used to ablate silicon to produce plasma. It was confirmed that the increase in the sample's initial temperature could improve spectral line intensity. In addition, when the distance from the target surface to the focal point increased, the intensity firstly rose, and then *** trend of change with distance was more obvious at higher sample temperatures. By observing the distribution of the normalized ratio of Si atomic spectral line intensity and Si ionic spectral line intensity as functions of distance and temperature, the maximum value of normalized ratio appeared at the longer distance as the initial temperature was higher, while the maximum ratio appeared at the shorter distance as the sample temperature was lower.

关键词： laser-induced breakdown spectroscopy initial sample temperature distance between focal point and target surface

Ellipticity-dependent ionization/dissociation of carbon dioxide in strong laser fields

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Chinese Physics B 2015年第3期24卷 122-126页

作者：张军峰马日左万龙吕航黄红卫徐海峰金明星丁大军 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy Jilin University

Ionization and dissociation of linear triatomic molecules, carbon dioxide, are studied in 50-fs 800-nm strong laser fields using time-of-flight mass spectrometer. The yields of double charged ions CO2^2＋ and various fragment ions（CO^＋,O^n＋, and C^n＋（n = 1, 2）） are measured as a function of ellipticity of laser polarization in the intensity range from 5.0 ×10^13W/cm2 to 6.0 × 10^14W/cm^2. The results demonstrate that non-sequential double ionization, which is induced by laser-driven electron recollision, dominates double ionization of CO2 in the strong IR laser field with intensity lower than2.0 × 10^14W/cm^2. The electron recollision could also have contribution in strong-field multiple ionization and formation of fragments of CO2 molecules. The present study indicates that the intensity and ellipticity dependence of ions yields can be used to probe the complex dynamics of strong-field ionization/dissociation of polyatomic molecules.

关键词： laser ellipticity strong field ionization and dissociation carbon dioxide

Field-free orientation of diatomic molecule via the linearly polarized resonant pulses

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Chinese Physics B 2015年第10期24卷 213-217页

作者：李苏宇郭福明王俊杨玉军金明星 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy Jilin University

We propose a scheme to coherently control the field-free orientation of NO molecule whose rotational temperature is above 0 K. It is found that the maximum molecular orientation is affected by two factors： one is the sum of the population of M = 0 rotational states and the other is their distribution, however, their distribution plays a much more significant role in molecular orientation than the sum of their population. By adopting a series of linearly polarized pulses resonant with the rotational states, the distribution of M = 0 rotational states is well rearranged. Though the number of pulses used is small, a relatively high orientation degree can be obtained. This scheme provides a promising approach to the achievement of a good orientation effect.

关键词： orientation diatomic molecule linearly polarized pulses coherent control

A tunable XUV monochromatic light source based on the time preserving grating selection of high-order harmonic generation

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Chinese Physics B 2017年第7期26卷 194-198页

作者：牛永梁红静刘燚刘方圆马日丁大军 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy Jilin University

We accomplish a laboratory facility for producing a femtosecond XUV coherent monochromatic radiation with a broad tunable spectral range of 20 eV-75 eV. It is based on spectral selected single-order harmonics from intense laser driven high harmonic generation in gas phase. The time preserving for the selected harmonic radiation is achieved by a Czerny-Turner type monochromator designed with a conical diffraction grating mount for minimizing the time broadening caused by grating diffraction and keeping a relatively high diffraction efficiency. Our measurement shows that the photon flux of the 23-order harmonic（H23） centered at 35.7 eV is 1×10~9 photons/s approximately with a resolving power E/？E ≈ *** source provides an ultrashort tunable monochromatic XUV beam for ultrafast studies of electronic and structural dynamics in a large variety of matters.

关键词： high harmonic generation conical diffraction time preserving monochromator femtosecond extreme ultraviolet pulse

Ionizations and fragmentations of benzene, methylbenzene, and chlorobenzene in strong IR and UV laser fields

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Chinese Physics B 2015年第11期24卷 212-216页

作者：张军峰吕航左万龙徐海峰金明星丁大军 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy Jilin University

Ionizations and fragmentations of benzene, methylbenzene, and chlorobenzene are studied in linearly polarized 50-fs, 800-nm and 400-nm strong laser fields using a time-of-flight mass spectrometer. It is shown that at low laser intensity, the parent ions are dominant for any one of the molecules in an 800-nm strong laser field, while extensive fragmentation is observed in a 400-nm laser field, which can be understood by the resonant photon absorption of molecular cations. The ratio of the yield of the parent ion to the yield of the total ion for each molecule is measured as a function of laser intensity in a range from 1.0 × 1013 W/cm2 to 4.0 × 1014 W/cm2, in either the 800-nm or 400-nm laser field. The results show that the fragmentation of the aromatic molecules increases significantly as the laser intensity is increased. Possible mechanisms for fragmentation in strong laser fields are discussed. Finally, the saturation intensity of ionization of the titled molecules is also determined.

关键词： strong field ionization fragmentation benzene substitute benzene

Defocusing role in femtosecond filamentation: Higher-order Kerr effect or plasma effect?

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Chinese Physics B 2015年第11期24卷 54-58页

作者：李苏宇郭福明杨玉军金明星 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy (Jilin University)

The femtosecond filamentation in the classical and high-order Kerr （HOK） models is numerically investigated by adopting multi-photon ionization （MPI） cross section with different values. It is found that in the case that the MPI cross section is relatively small, there exists a big difference between the electron density as well as clamped intensity calculated in the classical model and those calculated in the HOK one, while in the case that the MPI cross section is relatively large, the electron density and clamped intensity calculated in the two models are nearly in agreement with each other, and under this circumstance, even if the higher-order nonlinear terms do exist, the free-charge generation and the associated defocusing in a filament are enough to mask their effects. The different behaviors of the maximum intensity and on-axis electron density at the collapse position with the pulse duration provides an approach to determine which effect plays the dominant defocusing role. These results demonstrate that it is ionization that results in the difference between the two models.

关键词： high-order Kerr model plasma defocusing filamentation

Rydberg excitation of neutral nitric oxide molecules in strong UV and near-IR laser fields

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Chinese Physics B 2015年第6期24卷 284-287页

作者：吕航张军峰左万龙徐海峰金明星丁大军 Institute of Atomic and molecular Physics Jilin University Jilin Provincial Key Laboratory of Applied Atomic and molecular spectroscopy(Jilin University)

Rydberg state excitations of neutral nitric oxide molecules are studied in strong ultraviolet （UV） and near-infra-red （IR） laser fields using a linear time-of-flight （TOF） mass spectrometer with the pulsed electronic field ionization method. The yield of Rydberg molecules is measured as a function of laser intensity and ellipticity, and the results in UV laser fields are compared with those in near-IR laser fields. The present study provides the first experimental evidence of neutral Rydberg molecules surviving in a strong laser field. The results indicate that a rescattering-after-tunneling process is the main contribution to the formation of Rydberg molecules in strong near-IR laser fields, while multi-photon excitation may play an important role in the strong UV laser fields.

关键词： strong laser fields neutral Rydberg excitation nitric oxide

Controllable double electromagnetically induced transparency in a closed four-level-loop cavity-atom system

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Chinese Physics B 2017年第7期26卷 117-122页

作者：郭苗迪苏雪梅 Key Laboratory of Coherent Light Atomic and Molecular Spectroscopy (Ministry of Education) and College of Physics Jilin University

We present a theoretical study of an optical cavity coupled with single four-level atoms in closed loop formed via applied control lasers. The transmitted probe field from the cavity is analyzed. We show that the electromagnetically induced transparency（EIT） in the cavity and the normal mode splitting will be very different with changing the closed interaction phase and the intensity of the free-space control laser. This coupled cavity-atom system presents a variational double-EIT that comes from modulating the splitting of the dark state, which means that we could realize the gradual transfer between one EIT peak and two EIT peaks by adjusting the applied control lasers, and the normal mode splitting sidebands will shift slightly by changing the free-space control laser. This means that we could control the output cavity probe field more freely and it is easer to realize optical switch controlled by more parameters. We also depict the angular dispersion of the intracavity probe field in different free-space control laser. The large phase shift（-π → π） of the reflected intracavity probe field will be very useful for optical temporal differentiation and quantum phase gate.

关键词： cavity quantum electrodynamics double electromagnetically induced transparency all optical switch cross phase modulation

Numerical simulation of end-pumped CW Nd^(3+):GdVO_4 laser at 1063nm

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Chinese Physics B 2008年第5期17卷 1809-1816页

作者：祖宁宁孙桂娟戴振文 Department of Physics Jilin University Key Laboratory of Coherent Light Atomic and Molecular Spectroscopy Ministry of Education

A theoretical model to simulate an end-pumped CW Nd^3＋：GdVO4 laser at 1063 nm is presented. Its essence is to use the propagation equations to demonstrate the spatial evolutions of the pump and the laser powers in the cavity, hence it is applicable to both low and high gain lasers. The simulation results obtained by this model are in good agreement with the experimental observations reported in the literature for a Ti：sapphlre-pumped Nd^3＋：GdVO4 laser. Moreover, some parameters, such as the reflectivity of output coupler, the spot size of laser beam and the crystal length, are discussed with a view to optimizing the laser performance.

关键词： end-pumped Nd^3+:GdVO4 1063nm laser