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1.
We have measured the absorption of the 19.47-nm neon like bromine (J=2–1) X-ray laser line in low-pressure helium. The experiment
was motivated by the coincidence of this line with the low-absorption wing of an autoionizing transition in helium. We observe
that, with 1 mbar of helium, the continuum background and another bromine X-ray laser line at 19.82 nm are strongly reduced,
enhancing the relative strength of the 19.47-nm laser line. Increasing the helium pressure to 1.5 mbar makes the continuum
virtually disappear, resulting in an almost monochromatic emission of the X-ray laser line. An estimate of the absorption
cross section for the 19.47-nm line is given as ≈3.9×10-19 cm2 and for the nearby continuum as 0.9–1.3×10-18 cm2.
Received: 8 March 1999 / Revised version: 26 April 1999 / Published online: 11 August 1999 相似文献
2.
J. A. Koch R. W. Lee J. Nilsen J. C. Moreno B. J. MacGowan L. B. Da Silva 《Applied physics. B, Lasers and optics》1994,58(1):7-11
We point out that existing Ne-like X-ray lasers have sufficient brightness to be used as pump sources in resonant pump-fluorescence experiments, and we discuss some of the potential benefits and limitations of such experiments. In preliminary experiments, we have measured the line overlap of the Ne-like yttrium X-ray laser near 155 with 4f–3d transitions in H-like Na and He-like Mg. These experiments used a high-resolution grating spectrometer, and calibrated the wavelength of the yttrium laser by comparison against lines of known wavelength. The results indicate that the wavelength of the yttrium laser is 154.985 ± 0.025 , a factor of 2–4 improvement in precision over previous calibrations. We find that the yttrium laser is 100 m to the long-wavelength side of both the He-like Mg line and the H-like Na line, so that neither resonance is perfect; however, Stark broadening could improve the overlap in the latter scheme, and bulk Doppler shifting could improve both resonances. We also find a good resonance between the yttrium laser and an un-identified transition which we tentatively attribute to copper. 相似文献
3.
We investigate the electronic and ionic dynamics of Na clusters under the influence of a laser pulse in the range 100 femtoseconds
to picoseconds. The dynamics is described by means of the time-dependent local-density approximation coupled to ionic molecular
dynamics (TDLDA-MD). Variation of pulse length allows us to explore the time scales of ionic motion in a manner similar to
pump and probe experiments. Resonant enhancement of electron emission serves as a measure for the time scale of Coulomb explosion.
Received: 3 July 2001 / Published online: 10 October 2001 相似文献
4.
Analytic expressions are obtained for the saturation intensity in X-ray laser schemes based on short-pulse high-intensity drivers. For field-ionized plasma schemes, the specific mean saturation intensityJ
sat is time independent and depends only on atomic transition probabilities, level degeneracies, and transition energies. The analytic expression is found to be in good agreement with a detailed numerical calculation. Integrating over space and frequency gives a saturation intensityI
sat of order 2 × 1011 W/cm2 for lasing in Li-like Ne at 98 . The low input energy requirements for this scheme (< 1 J), associated with using a confocal geometry, give energy efficiencies of order 10–6 and greater. For inner-shell photo-ionization schemes, an accurate expression for a time-dependent saturation intensity is obtained. This scheme is calculated to have high saturation intensities,I
sat 1013 W/cm2, at short wavelengths (5–15 ). The requirement of a line focus geometry leads to higher input energies (5 J) and the short duration of lasing (50 fs) results in lower energy efficiencies ( 10–7). Repetition rates are important in determining appropriate applications for both schemes. 相似文献
5.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《Applied physics. B, Lasers and optics》2001,73(4):411-416
The pathway competition between neutral monomer and neutral dimer evaporation from optically excited odd-size gold cluster
ions Au+
n, n=7–15, has been investigated as a function of cluster size and excitation energy. Gold cluster ions of these sizes are
the only ones to show observable pathway competition while all other sizes exclusively evaporate either neutral monomers or
neutral dimers. The investigation has been performed by photoexcitation of stored size-selected gold cluster ions with a single
10-ns laser pulse. Subsequent time-resolved observation of the delayed dissociation allows us to quantitatively determine
the relative fragment yields of the respective decay channels as a function of excitation energy. Contrary to theoretical
expectations, the dimer-to-monomer branching ratio of evaporated particles is found to decrease monotonously with increasing
excitation energy for all cluster sizes under investigation. Possible explanations for this behaviour are discussed.
Received: 9 July 2001 / Revised version: 24 September 2001 / Published online: 15 October 2001 相似文献
6.
7.
S. Basu P. L. Hagelstein J. G. Goodberlet M. H. Muendel S. Kaushik 《Applied physics. B, Lasers and optics》1993,57(5):303-307
We identified for the first time the 3d
94d
1
S – 3d
94p
1
P line in Ni-like Nb at 204.2 Å that was predicted to show gain. When pumped with a train of pulses containing less than 1 J per pulse, significant emission was recorded at 204.2 Å following the second and the third pulses. We measured the small signal gain coefficient per Joule of incident laser energy to be 1.49±0.42 cm–1 J–1 for this laser transition, which is higher by several orders of magnitude than that reported for other collisional laser systems in this wavelength range. 相似文献
8.
K. Gäbel Ch. Bergmann E. Fill E. Förster I. Uschmann 《Applied physics. B, Lasers and optics》1993,56(1):3-7
Photo-resonant pumping of X-ray lasers requires close coincidence of a strong emission line with a suitable absorbing transition. We use a high-resolution crystal spectrometer to verify five coincidences, one of which has apparently not yet appeared in published work. All but one of the coincidences are found to lie within one linewidth. With respect to X-ray laser photo-pumping three of the five coincidences seem to be promising candidates. 相似文献
9.
Population-rate equations are analytically solved for constant pump rates. Conditions for population inversions are developed for this simplified case. Numbers appropriate for inner-shell photo-ionization of magnesium and neon are used. These allow back-of-the envelope calculations for predicting lasing duration. Pump-rate thresholds are also given which permit lasing for the duration of the pumping. Blackbody-source temperatures associated with such pump rates are calculated. A method of using the solution of the small-signal population-rate equations to determine the saturated intensity when the lower lasing level has a decay channel is given. This method is applied to the case of constant pump rates. An analytic expression for the saturated intensity is developed for this case. 相似文献
10.
R. Schlipper R. Kusche B. v. Issendorff H. Haberland 《Applied Physics A: Materials Science & Processing》2001,72(3):255-259
Positively charged sodium clusters can be easily ionized by a fs laser pulse of relatively low intensity (<1010 W/cm2), if the laser is in resonance with the plasmon excitation of the cluster. This ionization process was investigated in detail
by measuring the kinetic energy distribution of electrons emitted from a size-selected Na93
+ as a function of the fs laser intensity. In all cases pure Boltzmann-like energy distributions were observed. A comparison
with statistical theory shows that the emission is a purely thermal process. It is different to normal thermionic emission
insofar as the electrons are emitted from a hot electron system which is only weakly coupled to a cold ionic background. The
results demonstrate purely statistical behaviour of a small fermionic system even for very high excitation energy.
Received: 25 May 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
11.
Accepted: 6 March 1997 相似文献
12.
Demonstration of Mo Soft X-Ray Lasers with a Grazing Incidence Pumping Scheme in the XL-II Facility
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A Ni-like Mo soft x-ray laser (SXRLs) operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120m^3 in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5-3cm^-1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4× 10^14 W/cm^2 of the 200fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent. 相似文献
13.
M.E. Garcia H.O. Jeschke I. Grigorenko K.H. Bennemann 《Applied physics. B, Lasers and optics》2000,71(3):361-371
We present a theoretical study of the short-time relaxation of clusters in response to ultrafast excitations using femtosecond
laser pulses. We analyze the excitation of different types of clusters (Hgn, Agn, Sin, C60 and Xen) and classify the relaxation dynamics in three different regimes, depending on the intensity of the exciting laser pulse.
For low-intensity pulses (I<1012 W/cm2) we determine the time-dependent structural changes of clusters upon ultrashort ionization and photodetachment. We also study
the laser-induced non-equilibrium fragmentation and melting of Sin and C60 clusters, which occurs for moderate laser intensities, as a function of the pulse duration and energy.
As an example for the case of high intensities (I>1015 W/cm2), the explosion of clusters under the action of very intense ultrashort laser fields is described.
Received: 26 November 1999 / Published online: 2 August 2000 相似文献
14.
A. McPherson T. S. Luk B. D. Thompson K. Boyer C. K. Rhodes 《Applied physics. B, Lasers and optics》1993,57(5):337-347
The development of a unified picture of short-pulse high-intensity multiphoton processes, embracing atoms, molecules, and solids, appears possible through the study of clusters. Of particular significance are possible intra-cluster processes that can influence the mechanism of ionization and lead to the production of inner-shell vacancies. Inner-shell excitation leading to prompt X-ray emission is specifically considered and the treatment leads to the definition of a critical cluster size n
c representing the achievement of maximal X-ray emission from the ensemble. These results suggest the possibility of designing a new class of molecular materials optimized for the efficient production and amplification of X-rays. 相似文献
15.
R. Thissen P. Lablanquie R.I. Hall M. Ukai K. Ito 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):335-342
Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron
and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence
states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve
as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer,
the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the
class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that
loses its innershell electron to its neutral partner.
Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998 相似文献
16.
Multi-wavelength excimer ultraviolet sources from a mixture of krypton and iodine in a dielectric barrier discharge 总被引:1,自引:0,他引:1
New ultraviolet (UV) sources (excimer lamps) have been demonstrated using mixtures of krypton and iodine in a high-pressure
dielectric barrier discharge to provide intense multi-wavelength radiation at λ=183 nm (atomic iodine line, 4
P
5/2?2
P
3/2), 191 nm (KrI*, B
1/2?X
1/2), 206 nm (atomic iodine line, 2
P
3/2?2
P
1/2), and 342 nm (I*
2, D
1/2?X
1/2). The characteristics of the optical emission spectra of the atomic species and the excited dimers (excimers) formed for
different total gas pressures and in the presence of a buffer gas have been investigated. The highest intensity, at 183 nm,
is obtained at pressures up to 1 bar while the overall emission spectra can be controlled by adjusting the total pressure.
The results show that these strong multi-wavelength lamps offer an interesting alternative to conventional UV sources.
Received: 1 March 2000 / Revised version: 5 April 2000 / Published online: 30 June 2000 相似文献
17.
T. Döppner S. Teuber M. Schumacher J. Tiggesbäumker K.H. Meiwes-Broer 《Applied physics. B, Lasers and optics》2000,71(3):357-360
Clusters of heavy metal atoms in strong femtosecond laser-light fields undergo multi-ionization with the loss of hundreds
of electrons. The cross section largely exceeds that of corresponding isolated atoms, which leads in the case of PbN to a complete ionization of the 4f shell with a light intensity of 1.2×1015 W/cm2. Experimental investigations on Pb and Pt clusters with variable pulse widths and, for the first time, with the pump&probe
technique give insight into the dynamics of the coupling of electromagnetic radiation into the clusters. Both approaches support
the picture according to which, after an initial charging, the clusters expand due to Coulomb forces. This expansion is accompanied
by a reduction of the electron density and at the same time by an increase of the optical sensitivity. Once the plasmon energy
of the diluted nanoplasma approaches the photon energy, the charging efficiency increases significantly. The experimental
observations are confirmed by random-phase approximation (RPA) calculations of the optical response, including molecular-dynamics
simulations of the expanding systems.
Received: 11 November 1999 / Published online: 13 July 2000 相似文献
18.
M.E. Garcia 《Applied Physics A: Materials Science & Processing》2001,72(3):261-271
A theoretical study of different ultrafast nonequilibrium processes taking place during and after ultrashort excitation of
clusters is presented. We discuss similarities and differences for several processes involving nonequilibrium ultrafast motion
of atoms and electrons. We study ultrashort relaxation of clusters in response to excitations produced by femtosecond laser
pulses of different intensities. We show how different relaxation processes, such as bond breaking, melting, fragmentation,
emission of atoms, or Coulomb explosion, can be induced, depending on the laser intensity and laser pulse duration. We also
discuss processes involving nonequilibrium electron dynamics, such as intraband Auger decay in clusters and ultrafast electronic
motion during collisions between clusters and surfaces. We show that this electron dynamics leads to Stückelberg-like oscillations
of measurable quantities, such as the electron emission yield.
Received: 4 April 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
19.
R. Ohmukai H. Imajo K. Hayasaka U. Tanaka M. Watanabe S. Urabe 《Applied physics. B, Lasers and optics》1997,64(5):547-551
1 S0→1P1 and 1P1→1D2 transitions were employed in this scheme. This method enabled precise measurement of the velocity distribution with the isotope
selection and a higher resolution than our previous measurements using only the 1S0→1P1 transition. This technique was applied to the measurement of the Yb atomic beam whose velocity distribution was optically
perturbed and compressed by radiation pressure.
Received: 10 June 1996/Revised version: 19 July 1996 相似文献
20.
K. Matsubara U. Tanaka H. Imajo S. Urabe M. Watanabe 《Applied physics. B, Lasers and optics》2003,76(3):209-213
We have laser-cooled all even isotopes of Zn+ ions confined in a linear radio-frequency ion trap, and measuredoptical isotope shifts in the 4s 2
S
1/2-4p 2
P
3/2 transition. Tunable continuous-wave coherent light near 202 nm was generated for this experiment by means of frequency conversion
of light from diode and solid-state lasers. The measured isotope shifts are as follows: 66Zn+-64Zn+, 0.676(6) GHz; 68Zn+-66Zn+, 0.670(4) GHz; and 70Zn+-68Zn+, 0.568(10) GHz. In all cases, the transition line of the heavier isotope was observed at the higher frequency. The mass and
the field shifts were estimated using a King plot. This is the first isotope-shift measurement in the transition involving
the ground (4s 2
S
1/2) state of Zn+ ions.
Received: 18 July 2002 / Revised version: 20 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +81-42/327-6694, E-mail: matubara@crl.go.jp Present address: Communications Research Laboratory,
4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795, Japan 相似文献