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1.
The line-integrated optical measurement of impurity radiation profiles for the study of light impurity transport is performed in the HT-7 tokamak. The carbon impurity line emissivity is obtained by Abel inversion. The radial transport behaviours of carbon impurities at different central line averaged electron densities ne are investigated in ohmic discharges. The diffusion coefficient Dk(r), the convection velocity Wk(r) and the total flux of the impurity ions Fk decrease with the increase of ne, which shows a reduction in the impurity particle transport at higher electron densities. 相似文献
2.
Origination of gamma-ray burst pulses associated with the Doppler effect of spherical fireballs or uniform jet
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Ryde and Petrosian have pointed out that the rise phases of
gamma-ray burst (GRB) pulses originate from the widths of the
intrinsic pulses and their decay phases are determined by the
curvature effect of the expanding fireball surface based on their
simplified formula. In this paper we investigate in detail the issue
based on the formula in Ref.[20], which is derived based on a model
of highly symmetric expanding fireballs, where the Doppler effect is
the key factor to be concerned about, and no terms are omitted in
their derivation. Our analyses show that the decay phases of the
observed pulses originate from the contributions from both the
curvature effect of the expanding fireball and the two timescales of
the local pulses, and the rise phases of the observed pulses only
come from the two timescales of the local pulses. Associated with a
local pulse with both rise and decay portions, the light curve of
GRBs in the rise portion is expected to undergo a concave phase and
then a convex one, whereas that in the decay portion is expected to
evolve by an opposite process. And the ratio of the concave timescale
to the convex one in the rise phase of the observed pulse linearly
increases with the ratio of the rising timescale to the decay one of
the local pulse ($r_{\rm rd}$), whereas the ratio of the convex
timescale to the concave timescale in its decay phase linearly
decreases with $r_{\rm rd}$. The two correlations are independent of
the local pulse forms and the rest-frame radiation forms. But the
different forms of local pulses and the different values of $r_{\rm
rd}$ gives rise to the diversity of the light curve pulse shapes. We
test a sample of 86 GRB pulses detected by the BATSE instrument on
board the Compton Gamma Ray Observatory and find that the
characteristics do exist in the light curve of GRBs. 相似文献
3.
Nikolopoulos LA Benis EP Tzallas P Charalambidis D Witte K Tsakiris GD 《Physical review letters》2005,94(11):113905
Temporal widths of an attosecond (asec) XUV radiation pulse train, formed by the superposition of higher order harmonics, have been recently determined utilizing a 2nd order autocorrelation measurement. An assessment of the validity of the approach, for the broadband XUV radiation of asec pulses, is implemented through ab initio calculations modeling the spectral and temporal response of the two-XUV-photon He ionization detector employed. The measured width of the asec bursts is discussed in terms of the spectral phases of the individual harmonics, as well as in terms of the spatially modulated temporal width of the radiation, and is found in reasonable agreement with the expected duration. 相似文献
4.
J. Larsson A. Allen P.H. Bucksbaum R.W. Falcone A. Lindenberg G. Naylor T. Missalla D.A. Reis K. Scheidt A. Sjögren P. Sondhauss M. Wulff J.S. Wark 《Applied Physics A: Materials Science & Processing》2002,75(4):467-478
We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking
curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals
by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm2. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated,
monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter
X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent
phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping
the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central
energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent
diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the
unperturbed rocking-curve peak.
Received: 22 March 2002 / Revised version: 25 March 2002 / Published online: 6 June 2002 相似文献
5.
Ultra-short bursts of hard X-ray radiation are generated by interaction of high-contrast femtosecond laser pulses with a jet of liquid Ga. The X-ray emission shows a strong dependence on the angle of incidence and polarization of the laser beam, consistent with the processes of resonant absorption and vacuum heating. As much as 60% of the total X-ray emission consists of [Ga]K radiation (9.22–9.25 keV) with a photon flux of 6×109 photons/(ssrad). Using this novel X-ray source, static diffraction patterns from a GaAs(111) crystal were recorded with an acquisition time of 2 s. PACS 52.38.Ph; 52.59.Px; 52.50.Jm 相似文献
6.
介绍阿秒超紫外线(XUV)激发惰性气体原子产生光电子并在强激光电场中运动的半经典近似 方法,以及同时、直接、全面地测量阿秒XUV脉冲频率和强度时间分布的光电子能谱相位确定法. 采用飞秒超短脉冲激光和XUV间的交叉关联技术,从不同激光强度下、与激光线性极化方向成0°或180°方向上测得的光电子能量积分谱,可以重建XUV的频率和强度时间分布. XUV脉冲时间宽度的测量范围从1/4到1/2激光振荡周期,时间分辨率取决于激光束和XUV脉冲之间的相对延时控制精度和光路抖动时间. 所述方法可用于在阿秒尺度上的超快速测量,以及有关电子在原子和分子中运动的超快速动力学过程研究.
关键词:
阿秒测量
光电子能谱
相位确定法
超紫外线
频率和强度时间分布 相似文献
7.
H. Lemke 《Annalen der Physik》1974,486(3):287-292
It is assumed that in an inelastic collision of two particles at high energy fireballs are created, the decay of which produces the observed particles. The fireball distribution results from the decay of the primary hadron system into a leading fireball and a rest system, which can decay further. The decay is assumed to behave according to a bootstrap condition, making the fireball distribution, that results from the rest system in its rest frame, equal to the fireball distribution in the total collision in the c.m. frame. This bootstrap condition leads to an integral equation. Approximate solutions of this integral equation in the scaling limit are discussed. 相似文献
8.
Fen Lyu Yan-Zhi Meng Zhen-Fan Tang Ye Li Jun-Jie Wei Jin-Jun Geng Lin Lin Can-Min Deng Xue-Feng Wu 《Frontiers of Physics》2021,16(2):24503
There are some similarities between bursts of repeating fast radio bursts (FRBs) and giant pulses (GPs) of pulsars. To explore possible relations between them, we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar. We find that the power-law slope of GPs (with fluence≥130 Jy·ms) is 2.85±0.10. The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function. For the bursts of FRB 121102 above the break energy (1.22 ×1037 erg), the best-fitting slope is , similar to the index of GPs at the same observing frequency (∼1.4 GHz). We further discuss the physical origin of the repeating FRB 121102 in the framework of the super GPs model. And we find that the super GPs model involving a millisecond pulsar is workable and favored for explaining FRB 121102 despite that the magnetar burst model is more popular. 相似文献
9.
We have experimentally investigated the supercontinuum (SC) generation based on high-energy Gaussian-spectrum pulses emitted
from an erbium-doped fiber laser with large-anomalous dispersion. The pulses exhibit rectangular shape in temporal domain
with the pulse duration of about 16 ns. When the amplified pulses propagate through 10-km single-mode fiber, the SC ranged
from 1530 to 1750 nm arises from the stimulated-Raman-scattering effect and the pulses break up due to the modulation instability.
Comparatively, when the amplified pulses propagate through a segment of highly-nonlinear zero-dispersion-flattened photonic
crystal fiber, super-broad SC beyond the range of 1300–1750 nm is generated due to strong four-wave mixing effect, whereas
the pulses almost maintain their shapes. 相似文献
10.
Sansone G Benedetti E Caumes JP Stagira S Vozzi C Pascolini M Poletto L Villoresi P De Silvestri S Nisoli M 《Physical review letters》2005,94(19):193903
By using a self-referencing technique, we have experimentally measured the influence of the carrier-envelope phase of femtosecond light pulses on the phase of the electric field of the radiation produced by high-order harmonic generation. We show that, in particular experimental conditions, the temporal evolution of the electric field of the attosecond pulses, is directly controlled by the carrier-envelope phase of the driving pulses. 相似文献
11.
O. A. Bukin A. A. Il'in S. S. Golik I. G. Nagornyi F. P. Yarovenko 《Journal of Applied Spectroscopy》2003,70(4):599-604
The results of investigation of the dynamics of the emission spectra of a plasma generated at the surface of liquid and solid targets by a laser pulse of a complex time form are presented. It is shown that the shock wave arising as a result of breakdown on the surface of the solid and developing to heights of the order of 4 mm is a laser-supported detonation shock wave. In the case of solid targets, we recorded additional laser plasma light pulses coming after the main pulse. Two additional light pulses have been recorded for the emission line AlI 396.1 nm. In the case of the liquid, we have not detected additional pulses for the investigated emission lines of the elements at the laser radiation power densities used. 相似文献
12.
M. A. Kazaryan N. P. Korotkov S. E. Skipetrov S. D. Zakharov 《Journal of Russian Laser Research》1998,19(2):186-189
Backscattering of high-power laser pulses in a randomly inhomogeneous media containing microparticles suspended in a liquid is treated theoretically. Relationships for the temporal correlation function of multiply scattered radiation, which account for acceleration of particles in the field of optical radiation, sure derived for the first time. A new method for determination of particle velocities based on correlation properties of scattered light is proposed. 相似文献
13.
The effect of the second-order dispersion on the spatiotemporal dynamics of ultrashort pulses in nonlinear waveguides with infinite parabolic and stepped profiles of the refractive index is studied. It is shown that the leakage of radiation from the core to the cladding of step-index waveguides prevents the formation of a steady spatiotemporal distribution of the field. The possibility of compressing light pulses in a dielectric waveguide with a positive group-velocity dispersion is discussed. 相似文献
14.
We demonstrate burst-mode operation of a polarization-maintaining Yb-doped fiber amplifier. Groups of pulses with a temporal spacing of 10?ns and 1?kHz overall repetition rate are amplified to an average pulse energy of ~20?μJ and total burst energy of 0.25?mJ. The pulses are externally compressed to ~400?fs. The amplifier is synchronously pulsed-pumped to minimize amplified spontaneous emission between the bursts. We characterize the influence of pump pulse duration, pump-to-signal delay, and signal burst length. 相似文献
15.
The electric field profiles of broad-bandwidth coherent terahertz (THz) pulses, emitted by laser-wakefield-accelerated electron bunches, are studied. The near-single-cycle THz pulses are measured with two single-shot techniques in the temporal and spatial domains. Spectra of 0-6 THz and peak fields up to approximately or = 0.4 MV cm(-1) are observed. The measured field substructure demonstrates the manifestation of spatiotemporal coupling at focus, which affects the interpretation of THz radiation as a bunch diagnostic and in high-field pump-probe experiments. 相似文献
16.
Mihail Alfimov 《International Journal of Theoretical Physics》2010,49(9):2215-2229
Cherenkov radiation in uniformly moving homogeneous isotropic medium without dispersion is studied. Formula for the spectrum
of Cherenkov radiation of fermion was derived for the case when the speed of the medium is less than the speed of light in
this medium at rest. The properties of Cherenkov spectrum are investigated. 相似文献
17.
V. A. Dranevich V. N. Gartmanov 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(4):416-418
Light curves of 115 bright gamma-ray bursts with known cosmological distances z from sources detected by the BAT telescope on board the Swift spacecraft in four energy channels are analyzed. An averaged curve describing the shift of the light curves is obtained that depends on the energy of the channels in the coordinate system associated with the source. The results are compared to similar detailed curves for individual gamma-ray bursts detected in a wider range of energies by the BATSE (CGRO) and GBM (FERMI) telescopes. The divergence of curves in the region of low energies for some gamma ray bursts indicates the existence of an additional radiation source. 相似文献
18.
Development of the spectrum of gamma-ray burst pulses influenced by the intrinsic spectral evolution and the curvature effect
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The spectral evolution of gamma-ray burst pulses assumed to arise from
the emission of fireballs is explored. It is found that due to the
curvature effect, the integrated flux is well related to peak energy
by a power law in the decaying phase of pulses, where the index is
about 3, which does not depend on intrinsic emission and the Lorentz
factor. The spectra of pulses in the decaying phase are slightly
different from each other when different intrinsic spectral
evolution patterns are considered, indicating that it is dominated
by the curvature effect. In the rising phase, the integrated flux
keeps increasing whilst the peak energy remains unchanged when the
intrinsic emission bears an unchanged spectrum. Within this phase,
the flux decreases with the increase of the peak energy for a
hard-to-soft intrinsic spectrum, and for a soft-to-hard-to-soft
intrinsic spectrum, the flux generally increases with the increase
of the peak energy. An intrinsic soft-to-hard-to-soft spectral
evolution within a co-moving pulse would give rise to a pulse-like
evolutionary curve for the peak energy. 相似文献
19.
López-Martens R Varjú K Johnsson P Mauritsson J Mairesse Y Salières P Gaarde MB Schafer KJ Persson A Svanberg S Wahlström CG L'huillier A 《Physical review letters》2005,94(3):033001
We report the generation, compression, and delivery on target of ultrashort extreme-ultraviolet light pulses using external amplitude and phase control. Broadband harmonic radiation is first generated by focusing an infrared laser with a carefully chosen intensity into a gas cell containing argon atoms. The emitted light then goes through a hard aperture and a thin aluminum filter that selects a 30-eV bandwidth around a 30-eV photon energy and synchronizes all of the components, thereby enabling the formation of a train of almost Fourier-transform-limited single-cycle 170 attosecond pulses. Our experiment demonstrates a practical method for synthesizing and controlling attosecond waveforms. 相似文献
20.
A novel algorithm for the discrimination of neutron and γ -ray events with wavelet transform modulus maximum (WTMM) in an organic scintillation has been investigated. Voltage pulses arising from a BC501A organic liquid scintillation detector in a mixed radiation field have been recorded with a fast digital sampling oscilloscope. The WTMM method using frequency-domain features exhibits a strong insensitivity to noise and can be used to discriminate neutron and γ -ray events based on their different asymptotic decay trend between the positive modulus maximum curve and the negative modulus maximum curve in the scale-space plane. This technique has been verified by the corresponding mixed-field data assessed by the time-of-flight (TOF) method and the charge comparison (CC) method. It is shown that the characterization of neutron and γ ray achieved by the discrimination method based on WTMM is consistent with that afforded by the TOF method and better than the CC method. Moreover, the WTMM method itself has presented its ability to eliminate the noise without any pretreatment to the pulses. 相似文献