纳秒脉冲放电紫外光纤阵列检测与定位方法

峰化电容作为电磁脉冲模拟器中用于陡化脉冲输出的关键部件,在实际工程应用中易发生沿面放电和击穿现象,采用光电检测系统可对绝缘沿面放电现象进行有效分析。针对峰化电容器沿面放电监测的技术难题,研制了一套绝缘沿面放电过程光电检测系统,对绝缘沿面放电现象进行光电检测。首先提出了绝缘介质沿面放电过程光电探测系统的设计方案;其次,对系统的时延性能进行了评价;最后,完成了绝缘介质沿面放电过程定位实验,验证了光电探测系统的可行性。实验表明,该系统能够实现对放电区域的有效定位。     

New high-spin microsecond isomers in 131Sb

In this work we have identified and studied the decay of two new microsecond isomers 19/2^- and 23/2⁺ in ¹³¹Sb. This neutron-rich nucleus was produced by thermal neutron-induced fission of ²⁴¹Pu. The detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble) and the γ-rays or conversion electrons from isomers. These new data on high-spin states complete the level scheme previously obtained from β-decay. A large fraction of the members of the πg _7/2ν(h _11/2 ^-1 d _3/2 ^-1) and πg _7/2νh _11/2 ^-2 multiplets are now known and were compared with a multi-particle shell model calculation. Received: 7 June 2000 / Accepted: 19 September 2000     

New microsecond isomers in 189, 190Bi

The ¹³⁷I nucleus, populated in the spontaneous fission of ²⁴⁸Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in ¹³⁷I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in ¹³⁷I deviates significantly from the shell model scheme. Received: 6 June 2001 / Accepted: 4 October 2001     

Two-dimensional pressure measurements with nanosecond time resolution

An optical setup for the measurement of acoustic shock waves is demonstrated experimentally. This sensor, which is based on surface plasmon excitation, provides ns time resolution as well as 7m lateral resolution. Initial experiments with laser-induced plasma generation in a water cell already show that in a simple geometry high lateral resolution gives new insight into the ongoing processes.     

High-efficiency nanosecond optical parametric oscillator with the stable ring configuration

High stability nanosecond OPO operation at 1.57 μm was realized based on the type II non-critically phase-matched (NCPM) KTP crystal by utilizing a single frequency Nd:YAG master oscillator power amplifier (MOPA) laser as pump source. Energy conversion efficiency of 18.1% was demonstrated with single-pass ring cavity which was approximately two times more than that of critical ring cavity. The highest slope efficiency of 37.76% and maximum signal pulse energy of 3.1 mJ were attained with the output reflectivity of R = 50% at the pulse repetition frequency of 100 Hz. Experimental results reveal that the nanosecond OPO with ring stable configuration is a promising design to meet the need of IPDA’s transmitter.     

Time-resolved imaging of latent fingerprints with nanosecond resolution

Imaging of latent fingerprints using time-resolved (TR) method offers a broader platform to eliminate the unwanted background emission. In this paper, a novel TR imaging technique is demonstrated and implemented, which facilitates the detection of latent fingerprints with nanosecond resolution. Simulated experiments were carried out with two overlapping fingerprints treated with two fluorescent powders having different lifetimes in nanosecond range. The dependence of the fluorescence emission intensity in nanosecond resolution of TR imaging is also revealed.     

Laser drilling of stainless steel with nanosecond double-pulse

Nanosecond double-pulse laser drilling is reported in this paper. The double-pulse herein represents two closely conjoint pulses with 21 ns pulse duration and about 52 ns interpulse separation, which are acquired by temporal pulse shaping. Percussion drilling with such double-pulse is performed in stainless steel samples with different laser fluences, sample's thickness, repetition rates and ambient pressures. The experimental results show that the drilling rates of double-pulse drilling are more than one order of magnitude higher than that of conventional single-pulse drilling in air. Differences in the processing results between single-pulse and double-pulse with various processing parameters are investigated. In addition the ablation mechanisms of the double-pulse drilling are discussed.     

Interaction of nanosecond laser pulses with plastic foams

Some results of an experimental and theoretical study of the interaction of laser pulses with plastic foams are reported. The propagation velocity of a hydrodynamic peturbation which was initiated in foam target under the action of a laser pulse with intensityq≈2·10¹³ W/cm² and the velocity distribution function of plasma ions were measured; the preliminary results of time-integrated spectroscopic measurements of an intense red-shifted signal are also reported. A self-consistent model of the foam target’s laser plasma formed in a hydrodynamic mode was derived. The predictions of this model are consistent with experimental results. A model of microprocesses of laser plasma formation in a structured material was also developed. The results of numerical simulations by 1D and 2D computer codes are also reported. Original article submitted in English May 25, 1997.     

New features of the Moon revealed and identified by CLTM-s01

Previous analyses showed a clear asymmetry in the topography, geological material distribution, and crustal thickness between the nearside and farside of the Moon. Lunar detecting data, such as topography and gravity, have made it possible to interpret this hemisphere dichotomy. The high-resolution lunar topographic model CLTM-s01 has revealed that there still exist four unknown features, namely, quasi-impact basin Sternfeld-Lewis (20°S, 232°E), confirmed impact basin Fitzgerald-Jackson (25°N, 191°E), crater Wugang (13°N, 189°E) and volcanic deposited highland Yutu (14°N, 308°E). Furthermore, we analyzed and identified about eleven large-scale impact basins that have been proposed since 1994, and classified them according to their circular characteristics.     

New isomers and their decay in odd-odd neutron-deficient cesium isotopes

By a systematic on-line cesium mass separation fromA=122 toA=132 and subsequent gamma and electron decay spectroscopy at very low energy, new isomers have been precisely identified:^122m Cs (T _1/2=0.36±0.02 s),^124m Cs (T _1/2=6.3±0.2 s) and^130m Cs (T _1/2=3.46±0.06 min). Detailed level schemes are given for both^124m Cs and^130m Cs. Comparison of excited levels known in the odd-odd nuclei of the same region shows that more experimental informations are needed to propose a clear and realistic picture of the nuclear states structure. Radioactivity:^{122m, 124m, 130m} Cs [from La or Ce,³Hexn]-measuredT _1/2,E _γ,I _γ,E _CE ,I _CE ,γ-γ-t, γ-ce coinc.; deduced ICC,^{124, 130}Cs deduced levels,J, π. Online mass separated sources, Ge(Li), intrinsic Ge, Si(Li), magnetic electron selector.     

Experimental mathematical model of nanosecond laser interaction with material

Interaction of nanosecond pulsed lasers with material was studied from thermal point of view using experimental techniques and theoretical approach of dimensional analysis. Experimental data of laser heating, melting and plasma formation on metallic samples and silicon, presented mainly in previous publication and partly in this paper, were used for formation of experimental mathematical model in the form of criteria equations of laser-material interaction process. Four different criteria equations were created: for maximum surface temperature increase, melting threshold, melting duration and plasma formation threshold. Two equations account for changes of thermal properties with temperature. The value of latent heat of fusion was found to have almost no influence on melting duration. The presented model showed good agreement with the measured results. The criteria equations can be used for approximate prediction of laser pulse effects on materials without creating an exact mathematical or numerical model and for control of technological processes.     

Low-threshold lasing in stimulated Raman lasers with nanosecond pumping

We have studied the conditions resulting in maximum lowering of the excitation threshold for pulsed stimulated Raman (SRS) lasers. It has been shown theoretically that in order to achieve the lowest possible values of laser radiation pulse energy needed to excite lasing in SRS lasers, we need high reflection of the cavity mirrors and low losses at the wavelength of the 1st Stokes component, high reflection of the output mirror at the wavelength of the pump radiation, and also matching of the confocal parameters for the exciting laser radiation and the cavity with each other and with the length of the Raman-active medium. The experimentally achieved excitation threshold for an SRS laser based on a barium nitrate crystal was 6 μJ, which quantitatively corresponds well to the calculation results. Lasing of up to five Stokes components simultaneously occurred. The efficiency for conversion of the laser radiation to one component was as high as 39%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 284–290, March–April, 2008.     

Interdiffusion studies in Bi-based layered systems with nanosecond laser pulses

Interdiffusion processes are induced by nanosecond laser pulses from an excimer laser. The Bi-based systems studied are formed by a Bi layer and a Sb or Ge layer. Configurations with Bi at the surface layer or at the innermost layer are both studied. Real-time reflectivity measurements are performed during the irradiation to determine the process kinetics and times and Rutherford backscattering spectrometry is used to obtain the concentration depth profiles. It will be shown that there is an interfacially initiated diffusion process in the Bi-Sb system and that the diffusion coefficients of this system within the liquid phase are in the 10^–5–10^–6 cm²/s range. The Bi-Ge system shows instead little mixing, the diffusion coefficients of the system within the liquid phase being at least two orders of magnitude lower. The differences observed when Bi is the surface layer or the innermost one are related to the different thermal responses of the system.     

Dynamics of laser hole drilling with nanosecond periodically pulsed laser

Results are presented on the dynamics of the laser drilling process for a single hole using a periodically pulsed nanosecond laser with a repetition rate up to 60 kHz. The intensity dependence of drilling velocity was determined by measuring the delay time between the beginning of exposure and the moment when the hole opens. The hole collapse phenomenon was observed in our experiments. The competition process between material ejection and the flow of the liquid phase into the ejected area is supposed to be responsible for the hole collapse.     

Widely tunable narrow-linewidth nanosecond optical parametric generator with self-injection seeding

This paper reports a widely tunable narrow-linewidth nanosecond optical parametric generator (OPG) with a pulse-repetition rate of 10 kHz. The OPG consists of a 55-mm-long periodically poled lithium niobate crystal with a domain period of 29.5 m. At an average pump power of 2.0 W the OPG emitted 0.33 W of signal power and 0.17 W of idler power. The wavelength and spectral width of the OPG are controlled by self-injection seeding. For this purpose, a small fraction of the OPGs pulsed signal radiation is used as seed radiation for the next OPG pulse. In order to overlap in time the seed pulse with the succeeding pump pulse, the seed pulse is delayed by a 22-km-long single-mode fiber. For narrowing the spectrum of the seeded OPG output, the seed radiation is spectrally filtered by a tunable fiber Fabry–Perot interferometer (FFPI). The OPG signal radiation could be tuned from 1547 to 1605 nm by changing the OPGs crystal temperature and by tuning simultaneously the FFPI. The corresponding idler wave tuned from 3157 to 3413 nm. Within the whole tuning range, the linewidth of the signal wave was less than 185 MHz. Compared to the 240-GHz linewidth of the free-running OPG, the linewidth of the seeded OPG is thus narrowed by more than three orders of magnitude. By tuning the FFPI, continuous wavelength tuning has been demonstrated within the gain spectrum of the OPG over a range of 820 GHz. PACS 42.65.Yj; 42.79.Nv; 42.79.Qx