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1.
In this letter, we discuss the increase in the average cluster size by lowering the stagnation temperature of the methane (CH4) gas. The Coulomb explosion experiments are conducted to estimate the cluster size and the size distribution. The average CH4 cluster sizes Nay of 6 230 and 6 580 are acquired with the source conditions of 30 bars at 240 K and 60 bars at 296 K, respectively. Empirical estimation suggests a five-fold increase in the average size of the CH4 clusters at 240 K compared with that at room temperature under a backing pressure of 30 bars. A strong nonlinear Hagena parameter relation (Г^*∝ T0^-3.3) for the CH4 clusters is revealed. The results may be favorable for the production of large-sized clusters by using gases at low temperature and high back pressures. 相似文献
2.
Trends in ultrashort and ultrahigh power laser pulses based on optical parametric chirped pulse amplification 下载免费PDF全文
Since the proof-of-principle demonstration of optical parametric amplification to efficiently amplify chirped laser pulses in 1992,optical parametric chirped pulse amplification(OPCPA)became the most promising method for the amplification of broadband optical pulses.In the meantime,we are witnessing an exciting progress in the development of powerful and ultrashort pulse laser systems that employ chirped pulse parametric amplifiers.The output power and pulse duration of these systems have ranged from a few gigawatts to hundreds of terawatts with a potential of tens of petawatts power level.Meanwhile,the output pulse duration based on optical parametric amplification has entered the range of fewoptical-cycle field.In this paper,we overview the basic principles,trends in development,and current state of the ultrashort and laser systems based on OPCPA,respectively. 相似文献
3.
Laser wakefield accelerators(LWFAs)are compact accelerators which can produce femtosecond high-energy electron beams on a much smaller scale than the conventional radiofrequency accelerators.It is attributed to their high acceleration gradient which is about 3 orders of magnitude larger than the traditional ones.The past decade has witnessed the major breakthroughs and progress in developing the laser wakfield accelerators.To achieve the LWFAs suitable for applications,more and more attention has been paid to optimize the LWFAs for high-quality electron beams.A single-staged LWFA does not favor generating controllable electron beams beyond 1 Ge V since electron injection and acceleration are coupled and cannot be independently controlled.Staged LWFAs provide a promising route to overcome this disadvantage by decoupling injection from acceleration and thus the electron-beam quality as well as the stability can be greatly improved.This paper provides an overview of the physical conceptions of the LWFA,as well as the major breakthroughs and progress in developing LWFAs from single-stage to two-stage LWFAs. 相似文献
4.
A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated.A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier.After the amplified pulses pass through the LBO crystal,the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA).The 850-nm chirped signal light gain from the stretcher is 1.5×10 4 in the first-stage OPA while it is 120 in the second-stage OPA.The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8×10 6. 相似文献
5.
Surface-enhanced resonance Raman scattering (SERRS) of
Rhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied.
Based on the great enhancement of the Raman signal and the quench of the
fluorescence, the SERRS spectra of R6G were recorded for the samples of dye
colloidal solution with different concentrations. Spectral inhomogeneity
behaviours from single molecules in the dried sample films were observed with
complementary evidences, such as spectral polarization, spectral diffusion,
intensity fluctuation of vibrational lines and even ``breathing' of the
molecules. Sequential spectra observed from a liquid sample with an average of
0.3 dye molecules in the probed volume exhibited the expected Poisson
distribution for actually measuring 0, 1 or 2 molecules. Difference between
the SERRS spectra of R6G excited by linearly and circularly polarized light
were experimentally measured. 相似文献
6.
Study on the interaction of intense femtosecond laser pulses with nanometre-sized hydrogen clusters 下载免费PDF全文
The interaction of intense femtosecond laser pulses with hydrogen clusters
has been experimentally studied. The hydrogen clusters were produced from
expansion of high-pressure hydrogen gas (backed up to 8\tm106Pa) into vacuum
through a conical nozzle cryogenically cooled by liquid nitrogen. The
average size of hydrogen clusters was estimated by Rayleigh scattering
measurement and the maximum proton energy of up to 4.2keV has been obtained
from the Coulomb explosion of hydrogen clusters under 2×1016 W/cm2 laser irradiation. Dependence of the maximum proton energy on cluster size and laser intensity was
investigated, indicating the correlation between the laser intensity and the
cluster size. The maximum proton energy is found to be directly proportional
to the laser intensity, which is consistent with the theoretical prediction. 相似文献
7.
Accurate determination of the absolute phase and temporal-pulse phase of few-cycle laser pulses 下载免费PDF全文
A Fourier analysis method is used to accurately determine not
only the absolute phase but also the temporal-pulse phase of an
isolated few-cycle (chirped) laser pulse. This method is
independent of the pulse shape and can fully characterize the
light wave even though only a few samples per optical cycle are
available. It paves the way for investigating the absolute
phase-dependent extreme nonlinear optics, and the evolutions of
the absolute phase and the temporal-pulse phase of few-cycle
laser pulses. 相似文献
8.
Characteristics of ultrafast K line hard x—ray source from femtosecond terawatt laser—produced plasma 下载免费PDF全文
Theoretical studies and analytical scalings were carried out to find the optimized laser parameters and target conditions so that ultrashort hard x-ray pulses and high x-ray power could be achieved.The dependence of laser intensity and wavelength on the yield of K-shell x-ray emission was studied.We propose an optimal design for a foil target for producing high-yield hard x-ray pulses of customizing duration. 相似文献
9.
10.
三、带前置轮胎镜的反射式光栅谱仪 从前文的讨论已看出,在光路中加上针孔时,尽管能改善空间分辨,但谱仪的集光能力较差,使用时受到一定的限制.为了克服这一缺点,1981年意大利帕多代大学根据几何光学的消象散原理,在掠入射光栅光谱仪前加入一个轮胎型反射镜,成功地看到了 BeIV L 线和BeIV的1S2-1s2P共振线在远离靶≥2mm处对称地劈裂成两部分[1].谱仪工作波段在20—300A之间,其基本结构见图 5. 图5中A是光源,M是前置反射镜,G是凹面光栅,B是集光点,S是狭缝.轮胎镜M的顶点和曲率中心位于光栅G子午面(x-y面)内,轮胎镜在这平面上的主曲率… 相似文献