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1.
A method of selecting molecules embedded in nanodroplets (clusters) of superfluid helium is proposed, which is based on the selective vibrational excitation of embedded molecules by intense IR laser radiation. This action leads to a significant decrease in size of the excited clusters, after which these clusters are separated with respect to size via scattering of the cluster beam on a crossing atomic beam. The method is described in detail and the possibility of selecting SF6 molecules in liquid helium nanodroplets using the excitation by CO2 laser radiation and the angular separation via scattering on a xenon atomic beam is demonstrated. The results show that, by using this technique, it is possible to separate molecules with respect to isotope (element) composition. Advantages and drawbacks of the method are analyzed. 相似文献
2.
B. Bescós R. Hoch H.-J. Schmidtke G. Gerber 《Applied physics. B, Lasers and optics》2000,71(3):373-379
Femtosecond-laser spectroscopy is used to study the photoionization and photofragmentation of large neutral silicon clusters
in a beam. Silicon clusters Sin with sizes up to n≈6000, corresponding to nanoparticles with diameters up to 6 nm, are generated in a laser vaporization
source. Nanosecond- and femtosecond-laser ionization are employed to characterize the free silicon nanoparticles. Excitation
with intense femtosecond-laser pulses leads to prompt formation of doubly and triply charged Sin clusters. Additionally, strong fragmentation of charged clusters occurs by Coulomb explosion, resulting in high released
kinetic energies. Multiply charged atoms up to Si4+ with initial kinetic energies in the range of 500 eV are observed for laser intensities of about 1013 W/cm2. Pump–probe spectroscopy yields decay times of the intermediate resonances of the nanoparticles.
Received: 22 January 2000 / Published online: 7 August 2000 相似文献
3.
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
4.
Titanium clusters are produced by laser vaporization of a metal wire in a helium gas pulse, stored in a Penning trap, size
selected and transformed into multiply charged anions by electron attachment. Both doubly and triply charged titanium clusters
are observed. For the first observation of photodetachment of electrons from metal cluster dianions, Ti
55
2-
clusters are selected and excited by a laser pulse, which leads to the emission of an excess electron: Ti
55
2-
→ e− + Ti
55
-
.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
T. Döppner J. P. Müller A. Przystawik J. Tiggesbäumker K.-H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):261-266
Silver clusters embedded in helium nanodroplets are
exposed to intense femtosecond laser pulses (1013 - 1016 W/cm2).
The signal of highly charged (q≤11) atomic fragments is maximized by
delayed plasmon enhanced ionization using stretched laser pulses. Further
details with respect to the dynamics of the charging process can be obtained,
when the intensity distribution within the laser focus is taken into
account. For the first time, the z-scan method is applied to clusters
which offers a route to investigate the explicit dependence of the ion signals
with respect to the laser intensity. By taking advantage of the volumetric
weighting effect ionization thresholds are determined, yielding values well
below 1014 W/cm2 for Agq+ ions with q≤11. 相似文献
6.
V. Dierolf A.B. Kutsenko A. Ostendorf W. von der Osten W. Sohler H. Suche 《Applied physics. B, Lasers and optics》2001,72(7):803-810
Starting from previous investigations in LiNbO3 bulk crystals, we studied the optical properties of Er3+ ions in Ti:LiNbO3 channel waveguides and investigated the waveguide-specific lattice environment of the Er3+ ions (“sites”) caused by the doping method used and the presence of a large number of Ti4+ ions. For that purpose the method of combined excitation–emission spectroscopy was applied for the first time to waveguides
at low temperatures. Comparing the spectroscopic results obtained for the green, red, and near-IR luminescence (λ≈550, ≈650
and ≈980 nm) under direct (450 nm), 2-step (980 nm), and 3-step (1.5 μm) laser excitation, we found several distinguishable
Er3+ sites which in terms of energy levels and relative numbers are similar to those in bulk material, but exhibit significantly
different up-conversion efficiencies and strongly inhomogeneously broadened transitions. Moreover, we were able to distinguish
isolated and cluster Er3+ sites by their characteristic excitation and emission transition energies and studied the respective excitation/relaxation
channels. The cluster sites are most efficient in the up-conversion process, especially under 3-step excitation. Using accepted
microscopic models for Er3+ and Ti4+ incorporation into the LiNbO3 crystal lattice, the site distribution and up-conversion mechanisms are elucidated and their consequences for laser applications
in different spectral regions are discussed.
Received: 16 November 2000 / Published online: 21 March 2001 相似文献
7.
S. Dobosz M. Schmidt M. Perdrix P. Meynadier O. Gobert D. Normand K. Ellert T. Blenski A. Ya. Faenov A. I. Magunov T. A. Pikuz I. Yu. Skobelev N. E. Andreev 《Journal of Experimental and Theoretical Physics》1999,88(6):1122-1129
The x-ray spectra of a plasma generated by heating CO2 and Ar clusters with high-intensity femtosecond laser pulses with q
las≃1018 W/cm2 are investigated. Spatially resolved x-ray spectra of a cluster plasma are obtained for the first time. Photoionization absorption
is observed to influence the spectral line profiles. The recorded features of the x-ray emission spectra definitely indicate
the existence of a large relative number of excited ions (≃10−2–10−3) with energies of 0.1–1 MeV in such a plasma. Possible mechanisms underlying the acceleration of ions to high energies are
discussed. It is shown that the experimental results can be attributed to the influence of ponderomotive forces in standing
waves generated by the reflection of laser radiation from the clusters.
Zh. éksp. Teor. Fiz. 115, 2051–2066 (June 1999) 相似文献
8.
K. G. Shaynurova S. A. Bakhramov A. M. Kokhkharov U. K. Makhmanov E. A. Zakhidov 《Journal of Applied Spectroscopy》2012,78(6):802-810
Features of light pulse propagation and nonlinear optical transformation of the spectrum generated by titanium-sapphire laser
pulses (τ0.5 = 27 fs, λ0 = 790 nm) have been studied experimentally in a 50-cm cylindrical hollow waveguide (microcapillary with 280-μm diameter core)
filled with gaseous molecular nitrogen and helium. Stable guided propagation of light pulses with an intensity of ~1.5⋅1014 W/cm2 in the fundamental EH11 mode of the gas-filled capillary has been demonstrated. Exact focusing of the laser light made it possible to obtain rather
high relative (≥95%) and absolute (~60%) energy transmission efficiencies for the pulses at gas pressures equal to or lower
than 760 Torr. A method to determine the nonlinear phase shift of the pulses has been proposed. Values of the nonlinear refractive
index n2 ≈ 4.5⋅10–23 cm2/(W⋅Torr) (N2) and n2 ≈ 2.8⋅10–23 cm2/(W⋅Torr) (He) have been found. A short-wavelength shift in addition to the Kerr nonlinearity has been shown to be contributed
by the generated electron plasma at high pulse intensities (≥1014 W/cm2). 相似文献
9.
X. J. Kuang X. Q. Wang G. B. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):71-80
An all-electron scalar relativistic calculation on
Au
n
NO (n = 1–10) clusters has been performed by using density functional
theory with the generalized gradient approximation at the PW91 level. The
small gold cluster would like to bond with nitric and the nitric monoxide
molecule prefers to occupy the on-top and single fold coordination site. The
Au
n
structures in all Au
n
NO clusters are only distorted slightly
and still keep the planar structures. With the bend of Au-N-O bond, the
structures of Au
n
NO clusters evolve from the 2D structure to 3D
structure. The most favorable adsorption between small gold cluster and
nitric monoxide molecule takes place in the case that nitric monoxide
molecule is adsorbed onto an odd-numbered pure Au
n
cluster and becomes
odd-numbered Au
n
NO cluster with even number of valence electrons. The
scalar relativistic effect strengthens the Au–Au, Au–N interaction and
weakens the N–O interaction, appearing as the shorter Au–Au, Au–N
bond-length and the longer N–O bond-length. The differences between our work
and previous work are believed to be the reflection of the scalar
relativistic effect. 相似文献
10.
B. Klipp M. Grass J. Müller D. Stolcic U. Lutz G. Ganteför T. Schlenker J. Boneberg P. Leiderer 《Applied Physics A: Materials Science & Processing》2001,73(5):547-554
A PACIS (pulsed arc cluster-ion source) developed for high average cluster-ion currents is presented. The performance of the
PACIS at different operational modes is described, and the suitability for cluster-deposition experiments is discussed in
comparison with other cluster-ion sources. Maximum currents of mass-selected cluster ions of 3–6 nA of small Sin
- (n=4–10) clusters and 0.3–0.5 nA of large Aln
+/- (n=20–70) clusters are achieved. The mass-selected cluster ions are soft-landed on a substrate at residual kinetic energies
lower than 1 eV/atom, and the samples are characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy.
First results on the soft landing of “magic” Si4
- clusters on graphite are presented.
Received: 30 May 2001 / Accepted: 14 June 2001 / Published online: 2 October 2001 相似文献
11.
L. A. Surin 《JETP Letters》2013,97(1):57-65
The studies of small helium clusters (up to 100 atoms) and molecular-hydrogen clusters (up to 20 molecules) that are formed in a supersonic gas jet and are coupled by the weak van der Waals interaction with a linear chromophore molecule are reviewed The shift of the frequency of the fundamental vibration of the chromophore, as well as a change in the moment of inertia of a cluster with its growth, has been detected by their rotational and vibrational-rotational spectra. A nonclassical behavior of the moment of inertia manifested in its decrease beginning with a certain number of attached He atoms (H2 molecules) has been revealed. This behavior indicates that a part of a cluster is decoupled from the rotational motion of a molecule. The key question of these studies is whether such behavior of the moment of inertia is the manifestation of the super-fluidity of helium and hydrogen at microscopic level. The results are compared to the spectroscopy of molecules and hydrogen clusters in liquid-helium nanodroplets. 相似文献
12.
V. I. Dashkevich A. A. Bui V. A. Lisinetskii A. P. Shkadarevich R. V. Chulkov V. A. Orlovich 《Journal of Applied Spectroscopy》2007,74(3):390-395
We present the characteristics of an optical parametric oscillator based on a KTP crystal, pumped with noncritical phase matching
by a pulsed Ti3+:Al2O3 laser, tunable in the range 677–970 nm. Tunable generation of signal and idler waves is obtained in the ranges 1030–1390
nm and 2690–3050 nm respectively. The efficiency of conversion of the pump to the signal wave is ≈23%, which for pulses of
duration ≈8 nsec ensures an energy in the range 1.0–11.5 mJ. The width of the emission spectrum for the signal wave is within
the range 0.8–1.8 nm and is predominantly determined by the linewidth of the Ti3+:Al2O3 pump laser.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 351–356, May–June, 2007. 相似文献
13.
N. Pontius P.S. Bechthold M. Neeb W. Eberhardt 《Applied physics. B, Lasers and optics》2000,71(3):351-356
A femtosecond photo-electron experiment is described which provides excellent conditions for measuring time-resolved photo-electron
spectra of free, monodispersed cluster anions using repetition rates up to 100 Hz. Cluster anions are synthesized in an electric
arc and subsequently cooled in a helium carrier gas. A time-of-flight spectrometer is used for mass separation of the negatively
charged clusters. The kinetic energy of the photo-electrons is analyzed by a magnetic-bottle time-of-flight spectrometer,
which guarantees a maximum collection efficiency. Femtosecond laser pulses are generated by a seeded regenerative Ti:Sa amplifier,
which is externally pumped with the second harmonic of a diode-pumped solid-state Nd:YAG laser. A retroreflector mounted on
a computer-controlled translation stage serves as a reproducible time delay of the probe pulse. The high energy output of
the laser pulses (∼3 mJ) in combination with the variable repetition rate and the high stability of the amplified pulses provide
excellent conditions for recording pump-probe photo-electron spectra of mass-separated cluster anions even at the fairly low
ion density of pulsed plasma cluster sources. First results on the electron dynamics of the Pt3
- cluster demonstrate the reliability of the whole system. Further experimental investigations will concentrate on electron-relaxation
processes in transition- and noble-metal clusters as well as on the nuclear and transition-state dynamics of chemically reacted
adsorbate clusters.
Received: 7 January 2000 / Published online: 7 August 2000 相似文献
14.
S. Dobosz M. Schmidt M. Perdrix P. Meynadier O. Gobert D. Normand Ya. Faenov A. I. Magunov T. A. Pikuz I. Yu. Skobelev N. E. Andreev 《JETP Letters》1998,68(6):485-491
The x-ray spectra of a plasma produced by heating CO2 clusters with intense femtosecond laser pulses with λ=0.8 μm and λ=0.4 μm are investigated. Spatially resolved x-ray spectra
of the cluster plasma are obtained. The observed characteristic features of the x-ray emission spectra show unequivocally
that such a plasma contains quite a large relative number of ions (≃10−2–10−3) with energies of 0.1–1 MeV. The contour of the OVIII Lyα line is found to have characteristic features that are especially conspicuous when the clusters are heated with second-harmonic
pulses. These features cannot be explained by any mechanisms known to the authors.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 454–459 (25 September 1998) 相似文献
15.
A. Heidenreich I. Last J. Jortner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):195-202
We present a theoretical and computational study of the properties and the
response of the nanoplasma and of outer ionization in Xen clusters (n =
55–2171, initial cluster radius R0 = 8.7–31.0 ?) driven by
ultraintense near-infrared laser fields (peak intensity IM = 1015–1020 Wcm-2, temporal pulse length τ= 10–100 fs, and frequency ν= 0.35 fs-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of
the fs laser pulse and can either be persistent (at lower intensities of IM = 1015–1016 Wcm-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities
of IM = 1018–1020 Wcm-2 and/or for smaller cluster sizes). The nanoplasma is depleted by outer ionization that was semiquantitatively described by
the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity and pulse length
dependence of the outer ionization yield. The electrostatic model was further utilized for estimates of the laser intensity
and pulse
width dependence of the border radius R0
(I) for the attainment of complete outer ionization at
,
while at R0 > R0
(I) a persistent nanoplasma prevails. R0
(I)
establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense
laser-cluster interactions. 相似文献
16.
The methods of selective laser spectroscopy applied at 1.8–10 K to a glass-forming tetrahydrofuran-toluene (3∶1) mixture have
revealed that in the dimers of tetrapyrrole compounds (ethane-bis-octaethylporphyrins, ethane-bis-Zn-octaethylchlorins, heterodimers
of Zn-cyclopentane porphyrins) the exciton interactions (V12≈118 cm−1) and S-S-transfer of energy (of probability F≈11 sec−1) are implemented under conditions of substantial inhomogeneous broadening (δF1/2≈50 cm−1). Upon excitation of a donor component in the dimers, one observes a strong quenching of its emission, the disappearance
of the fine structure in the fluorescence spectra, a decrease in the efficiency of spectral hole burning by, approximately,
an order of magnitude, and a 12-fold increase in their halfwidth.
To whom correspondence should be addressed.
Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 500–504, July–August, 1999. 相似文献
17.
A. N. Chumakov S. A. Petrov N. A. Bosak E. N. Shcherbakova 《Journal of Applied Spectroscopy》2012,79(4):664-669
We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm2. We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films. 相似文献
18.
S. Yu. Bogdanov V. B. Burilina A. G. Frank 《Journal of Experimental and Theoretical Physics》1998,87(4):655-662
The possibilities of current-sheet formation in two-dimensional magnetic fields with a null line as well as the characteristic
features of the plasma dynamics under high initial pressure conditions (helium, P
0≈300 mtorr) are investigated for the first time. It is shown that current-sheet formation and efficient compression of the
plasma into a sheet require that the magnetic field gradient be sufficiently large. A brightly emitting compact region with
electron density N
e∼9×1016 cm−3, an order of magnitude higher than the gas atom density, was observed to form at the center of the layer.
Zh. éksp. Teor. Fiz. 114, 1202–1214 (October 1998) 相似文献
19.
Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N
q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments
(FF). Emission of (LiF)
n
Li+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for N
q+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and
(ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative
cluster ions (LiF)
n
F− closely resembles that of the positive secondary (LiF)
n
Li+ ions. The desorption yields of positive ions scale as Y(n) ∼ q
5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S
e
3 with the electronic stopping power S
e
, as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering).
We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions. 相似文献
20.
M. Theisen F. Lackner F. Ancilotto C. Callegari W. E. Ernst 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(2):403-408
We present the first sequential laser excitation of atom-doped helium nanodroplets. Rubidium atoms on the
surface of helium nanodroplets are selectively excited with a continuous wave laser to the 52P1/2
state so as not to desorb from the nanodroplets. From there they are excited by a laser pulse to the 52D
state; a laser-induced fluorescence (LIF) spectrum is recorded by monitoring the
62P ?\rightarrow 52S1/2 emission. The LIF spectrum differs from that of the two-photon one-color
direct excitation spectrum 52D ?\leftarrow 52S1/2, indicating that the system does relax vibrationally
during the lifetime of the 52P1/2 state. To model the LIF spectra we use calculated energy levels of the
Rb atom as a function of its distance R from the center of the helium nanodroplet. The Franck-Condon factors of
the resulting potential energy curves agree with the experimental spectra. In the future the 52P1/2 state
can be used as a springboard to reach high-lying 2S and 2D states, and possibly create an artificial
super-atom. 相似文献