激光加热微管靶在软X射线波段观察很高的粒子数反转

本文分析在软X射线区获得粒子数反转的几种实验后,提出激光加热微管靶方案。并从实验上观察到Mg的ls3p和ls4p能级与ls5p和ls5p能级间很高的粒子数反转,对其中物理机制作了分析。 关键词：     

Mg原子3p3/2nd系列自电离分支比的研究

利用多通道量子亏损理论(MQDT),结合已知的K矩阵,研究了受实验条件限制目前无法得到的Mg原子3p3/2nd(J=1,3)系列的自电离分支比,同时对3pnd系列的部分自电离光谱作了计算,并取得了和实验比较吻合的结果。结合分支比研究结果探讨了Mg原子的能级结构特点及粒子数反转的可能性     

Ne空阴极放电中l_(S_2)-2p反常脉冲光电流信号的研究

本文报道利用YAG倍频激光泵浦的脉冲可调谐染料激光器在Ne-Nd空心阴极放电中测定Nels_2—2p态跃迁及ls_2-2p-5s′_1态二级级联跃迁的光电流信号实验,并介绍了我们对此进行的理论计算.结果表明,Ne ls_2—2p态跃迁的反常光电流信号起因不在于能级间粒子数反转.     

无粒子数反转激光研究的进展

概括地介绍了无粒子数反转光放大与无粒子数反转激光的基本概念和原理，讨论了这种类型激光对激光科学发展的重要意义，叙述了自１９６２年以来科学家们所提出的几种实现无粒子数反转光放大及无粒子数反转激光的主要的理论模型和有关的实验进展，最后介绍了钠原子蒸汽中首次观察到无粒子数反转光放大的实验装置和实验结果。     

MgⅪ 1s3p-1s4p能级间平均高温及高密度条件下的粒子数反转

采用最新设计带侧向喷口的微管靶,当微管内壁平均激光辐照强度约为3.5×10¹³W·cm^-2时,观察到沿整个喷口1s3p ¹P₀⁰和1s4p ¹P₀⁰能级间强烈的粒子数反转。测得相应环境等离子体平均电子温度470—520eV,密度约为2×10²⁰cm^-3。分析了可能导致高温条件下粒子数反转的机制。 关键词：     

在低价氮离子中实现3s-2p软X射线的最佳条件研究

从实现离子的基态和激发态之间粒子数反转的主要参量入手，数值计算了基态的 粒子数密度、上能级和下能级的统计权重之比、三体复合速率和自发辐射衰减速率之比等每个参量对反转粒子数密度的影响，并且以基于光场感生电离（OFI）复合机制B－likeN系统为例对实际系统进行分析讨论，给出了实现基于光场感生电离B-like N45.21nm3s-2p跃迁激光放大的最大激光功率密度。     

类Li钙离子精细结构能级和软X射线光谱的理论计算

用多组态HFR方法计算了类Li等电子序列钙(Ca,Z=20)离子1s~2nl(n=2～6,l=0～5)组态的所有能级和电偶极跃迁的软X射线光谱,其中4f→3d,5f→3d及5d→3p、4d→3p由于其下能级跃迁速率较大,容易形成粒子数反转因而可作为激光跃迁,5f→3d、6f→3d跃迁已处于“水窗”波段,而4f→3d的激光跃迁(5.77nm)已为我们最近的实验所证实.并将我们的计算结果与其它理论计算和实验数据进行了比较.     

声光调Q衍射效率对脉宽压缩的影响研究

通过对衍射效率和反转粒子数密度的关系,反转粒子数密度和脉冲宽度的关系的分析,得出当通过提高泵浦速率来压缩脉宽时,衍射效率必须与泵浦速率和重复频率相匹配.并提出了匹配条件,从匹配条件出发又得到了衍射效率与泵浦速率和重复频率的匹配关系式.关系式中的衍射效率即为能够有效地压缩脉宽的最小衍射效率.实验结果与理论分析符合较好.     

X射线激光器研究初步结果

利用等离子体复合抽运X射线激光器模型和四能级速率方程,我们导出了在激光等离子体体系中发生位子数反转所须满足的条件。在这个基础上,通过分析不同结构靶的等离子体性质,我们发现当激光辐照复合镁靶时,在镁的类氦离子1S4P-1S3P能级间的粒子数反转。另外,我们在中等Z系例元素等离子体中也得到类氖离子系统粒子数反转证据并证明这些现象主要是由等离子体复合而引起的。 上述实验证明了我们的理论计算结果。     

X射线激光器研究初步结果

利用等离子体复合抽运X射线激光器模型和四能级速率方程,我们导出了在激光等离子体体系中发生位子数反转所须满足的条件。在这个基础上,通过分析不同结构靶的等离子体性质,我们发现当激光辐照复合镁靶时,在镁的类氦离子1S4P-1S3P能级间的粒子数反转。另外,我们在中等Z系例元素等离子体中也得到类氖离子系统粒子数反转证据并证明这些现象主要是由等离子体复合而引起的。 上述实验证明了我们的理论计算结果。     

Characterization of compact bright soft X-ray source based on picosecond laser plasma

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 10¹⁴ W/cm² was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density N_e=(1-1.9)×10²¹ cm^-3 and the electron temperature T_e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. PACS 41.50.+h; 52.25.Os; 52.50.Jm     

Generation and characterization of a bright X-ray source using picosecond laser

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N _e=(1?1.9)×10²¹ cm^?3 and the electron temperature T _e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.     

X光激光研究中的等离子体状态诊断

在预作X光激光增益介质的中Z靶(象锗靶)中均匀掺人少量的低Z元素(象铝),利用后者的类氦谱线强度比确定了等离子体状态;同时还在PLTE近似下由锗线的强度比确定了等离子体状态,二者基本吻合。     

用He-like离子特征谱线测量等离子体电子温度和电子密度

本文详细叙述了利用He-like离子的特征谱线诊断等离子体的电子密度和电子温度的方法,给出了共振线与双电子伴线的强度比随电子温度的变化曲线和共振线与互组合线的强度比随电子密度的变化曲线。并且根据实验测得的上述两组谱线的强度比,定出激光产生等离子体的电子温度和电子密度。     

Energy Spectrum and Charge Composition of Ions of Laser-Produced Gd and Al Plasmas

The energy spectrum and the distribution of the total charge over the ion energy are studied for plasma produced by partially coherent radiation of the neodymium glass laser with a power density of ~10¹³ W/cm² in the focusing spot incident on continuous gadolinium (Gd) and aluminum(Al) plates. The spectra of plasma ions for gadolinium and aluminumtargets are presented at laser radiation energies of 2, 7, 20 J and 1 J, respectively. For the gadolinium target, an increase in the peak amplitudes in ion spectra with increasing influencing radiation energy and manifestations of higher-energy ions are observed. The difference in the ion emission for gadolinium and aluminum targets is also recorded at close radiation energies of 2 and 1 J, respectively.     

Spectral analysis of K-shell X-ray emission of magnesium plasma produced by ultrashort high-intensity laser pulse irradiation

Spectral analysis of K-shell X-ray emission of magnesium plasma, produced by laser pulses of 45 fs duration, focussed up to an intensity of ～10¹⁸ W cm^?2, is carried out. The plasma conditions prevalent during the emission of X-ray spectrum were identified by comparing the experimental spectra with the synthetic spectra generated using the spectroscopic code PrismSPECT. It is observed that He-like resonance line emission occurs from the plasma region having sub-critical density, whereas K-α emission arises from the bulk solid heated to a temperature of 10 eV by the impact of hot electrons. K-α line from Be-like ions was used to estimate the hot electron temperature. A power law fit to the electron temperature showed a scaling of I ^0.47 with laser intensity.     

Orbital Electron Capture Rate and Time Modulation of H- and He-like Ions in a Storage-Ring

We have studied in a heavy ion storage ring the orbital electron capture decays of H- and He-like ¹⁴⁰Pr and ¹⁴²Pm ions and found that the H-like ions with one electron in the K-shell decay 1.49(8) and 1.44(6) times faster, than the corresponding He-like ions with two electrons in the K-shell. This result is explained by spin statistics due to the hyperfine structure of the H-like ions.     

Application of snow nanograin targets for the generation of fast ions in femtosecond laser plasma

We have measured the energy of the directed motion of multiply charged ions produced when solid targets are exposed to low-contrast (10^?3–10^?2) femtosecond laser pulses with intensities 10¹⁵–10¹⁶ W cm^?2. The measurements are based on the recording of spatially resolved X-ray spectra for H-and He-like oxygen ions in the target plane. Analysis of the He_β and Ly_α line profiles has revealed fractions of accelerated ions in plasma with energies from several to several tens of kiloelectronvolts. We show that using a layer of frozen nanometer-size water droplets as the targets leads to an effective absorption of laser pulses and a twofold rise in the energy (to 0.1 MeV) of He-like oxygen ions compared to the use of solid targets.     

X-ray spectroscopy diagnostics of a recombining plasma in laboratory astrophysics studies

The investigation of a recombining laser plasma is topical primarily because it can be used to simulate the interaction between plasma jets in astrophysical objects. It has been shown that the relative intensities of transitions of a resonance series of He-like multicharged ions can be used for the diagnostics of the recombining plasma. It has been found that the intensities of the indicated transitions for ions with the nuclear charge number Z _n ~ 10 are sensitive to the plasma density in the range N _e ~ 10¹⁶–10²⁰ cm^–3 at temperatures of 10–100 eV. The calculations performed for the F VIII ion have determined the parameters of plasma jets created at the ELFIE nanosecond laser facility (Ecole Polytechnique, France) in order to simulate astrophysical phenomena. The resulting universal calculation dependences can be used to diagnose different recombining plasmas containing helium-like fluorine ions.     

Observation of dielectronic satellites in the K-spectrum of argon ions in plasma produced by femtosecond laser pulses

The satellite structure of 1s2p ^1,3 P ₁-1s ²¹ S ₀ lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.