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1.
We have examined a number of candidates for the minimum-surface-energy arrangement of two-dimensional clusters composed of
N bubbles of area 1 and N bubbles of area λ ( λ≤1). These include hexagonal bubbles sorted into two monodisperse honeycomb tilings, and various mixed
periodic tilings with at most four bubbles per unit cell. We identify, as a function of λ, the minimal configuration for N → ∞. For finite N, the energy of the external (i.e., cluster-gas) boundary and that of the interface between honeycombs in “phase-separated” clusters have to be taken into account.
We estimate these contributions and find the lowest total energy configuration for each pair (N,λ). As λ is varied, this alternates between a circular cluster of one of the mixed tilings, and “partial wetting” of the
monodisperse honeycomb of bubble area 1 by the monodisperse honeycomb of bubble area λ.
Received 1 August 2002
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ID="a"e-mail: paulo@ist.utl.pt 相似文献
2.
For the first time, tunable lasing from a dye laser with an active polymer medium has been obtained using 1.06 μm pumping.
The conversion efficiency of 43% and the tunable range of Δλ=63 nm have been reached with the use of polymethine dye in a
polyurethane matrix.
Received: 20 April 2001 / Revised version: 16 July 2001 / Published online: 19 September 2001 相似文献
3.
The influence of an external field on photorefractive recording in Sn2P2S6 (SPS) crystals is studied. A large gain factor of more then 15 cm-1 is achieved for a grating spacing of 12 μm at λ=0.9 μm. For an applied field exceeding ±200 V/cm a switching of the beam
coupling direction is detected, exhibiting a pronounced hysteresis.
Received: 25 October 2000 / Revised version: 18 January 2001 / Published online: 21 March 2001 相似文献
4.
W. Shuicai H. Junfang X. Dong Z. Changjun H. Xun 《Applied physics. B, Lasers and optics》2001,72(7):819-821
We have constructed a three-wavelength Ti:sapphire femtosecond laser with an independent tunable wavelength (λ1) and two variable central wavelengths (λ2 and λ3) for use with the multi-excited photosystem II. Stable sub-40-fs pulses are generated. The λ1-wavelength pulses can be tuned independently from 750 nm to 850 nm. The center wavelengths λ2 and λ3 can be varied from 760 nm to 840 nm.
Received: 14 April 2000 / Revised version: 5 September 2000 / Published online: 27 April 2001 相似文献
5.
Single-frequency Ti:Er:LiNbO3 distributed Bragg reflector waveguide laser with thermally fixed photorefractive cavity 总被引:1,自引:0,他引:1
The first single-frequency Ti:Er:LiNbO3 distributed Bragg reflector waveguide laser with two thermally fixed photorefractive gratings as resonator mirrors is reported.
The optically pumped (λp=1480 nm,120-mW incident power) laser emits up to 1.1 mW at λs=1561.1 nm. The threshold pump power is 70 mW.
Received: 7 June 2001 / Published online: 30 October 2001 相似文献
6.
We describe a laser system that readily provides radiation tunable from 2 μm in the infra-red to 35 nm in the extreme ultraviolet
spectral range. The broad spectral range is covered through a range of non-linear processes such as Raman shifting and high-order
harmonic generation. Pulses with duration of tens of picoseconds are obtained. The relative bandwidth of the radiation is
δλ/λ=10-4, comparable with what can be achieved by using high-resolution monochromators at state-of-the-art synchrotron beamlines.
We discuss different methods for characterising the radiation in this wide wavelength regime. We also discuss the capabilities
of the system from the measured parameters.
Received: 12 December 2000 / Revised version: 8 March 2001 / Published online: 27 April 2001 相似文献
7.
We present comparative measurements of two Mach–Zehnder interferometers, one with Y-junction couplers and the other with MMI couplers, both developed in silicon-on-insulator technology and using plasma dispersion
effect for light phase modulation. Measurements of fiber-to-fiber losses, absorption coefficient, output intensity vs. time
and extinction ratio vs. frequency have been performed at λ=1.3 μm and at λ=1.55 μm. Results are reported and discussed in
this paper.
Received: 18 May 2001 / Revised version: 24 September2001 / Published online: 30 October 2001 相似文献
8.
A. Guglielmetti R. Bonetti G. Ardisson V. Barci T. Giles M. Hussonnois J.F. Le Du C. Le Naour V.L. Mikheev A.L. Pasinetti H.L. Ravn S.P. Tretyakova D. Trubert 《The European Physical Journal A - Hadrons and Nuclei》2001,12(4):383-386
The branching ratio of 225Ac decay by emission of 14C was remeasured under improved experimental conditions by using a radioactive source produced at the ISOLDE mass-separator
at CERN and a nuclear track detector technique. The result, B = λ14C/λα = (4.5±1.4)10-12, is consistent with the anomalously high value obtained in the 1993 experiment, thus confirming the importance of nuclear-structure
effects in this exotic decay.
Received: 20 July 2001 / Accepted: 28 November 2001 相似文献
9.
A.E.R. Malins J.R. Neal T.-H. Shen W.Y. Liang 《Applied physics. B, Lasers and optics》2002,74(7-8):729-733
The spin asymmetry of internal photo-electron emission over Schottky barriers has been investigated for Fe/GaAs (001) having
close-to-ideal current–voltage characteristics. Using a low-power circularly polarised YAG laser operated at its fundamental
frequency (λ=1064 nm) as well as a visible diode laser (λ=670 nm) we demonstrate that, by eliminating the photo-current due
to inter-band transitions in GaAs with the infrared source, a significant enhancement to the magnetic asymmetry could be achieved.
The bias dependence of the asymmetry was also measured. It was found that the values were considerably different for the photo-electrons
traversing the barriers in opposite directions.
Received: 15 November 2001 / Revised version: 23 March 2002 / Published online: 2 May 2002 相似文献
10.
G. Seifert M. Kaempfe K.-J. Berg H. Graener 《Applied physics. B, Lasers and optics》2001,73(4):355-359
By repetitive irradiation of pico- or femtosecond laser pulses on glasses containing silver nanoparticles, dichroitic areas
can be produced with different optical properties depending on the actual irradiation parameters. This effect, which is nanoscopically
caused by permanent deformation of the initially spherical particles to non-spherical shapes and an additional formation of
a halo of very small particles, is studied as a function of polarization and number of the applied pulses using two different
laser systems (Ti:sapphire, λ=400 nm, tp=150 fs; Nd:YLF, λ=523.5 nm, tp=4 ps). A very special diffraction grating produced by this local deformation, which has strongly polarization- and wavelength-dependent
features, is introduced and discussed.
Received: 20 July 2001 / Published online: 10 October 2001 相似文献
11.
Analysis of THz-wave surface-emitted difference-frequency generation in periodically poled lithium niobate waveguide 总被引:1,自引:0,他引:1
It was shown that the periodically poled LiNbO3-waveguide with period of poling λ≈λ/ng (λ is the wavelength of emitted THz-wave, ng is a refractive index corresponding to optical group velocity) emits THz-wave difference-frequency generation (DFG) in the
direction normal to the surface of the planar waveguide. The 5% distinction between the manufactured and required periods
of gratings results only in a small deflection (∼6°) of the output THz-beam from the normal direction. The dependence of DFG
efficiency on mode size is analyzed. The output THz power at λ=150 μm is estimated as 2 mW, taking into account imperfections
in coupling incident beams with guided modes. It was shown that the efficiency of THz-wave DFG in surface-emitting geometry
is more than for collinear geometry in bulk crystal, especially in the high-absorption wavelength region.
Received: 16 May 2001 / Revised version: 13 August 2001 / Published online: 2 November 2001 相似文献
12.
A miniaturized, high repetition rate, picosecond all solid state photo-induced distributed feedback (DFB) polymer-dye laser
is described by applying a passively Q-switched and frequency-doubled Cr4+:Nd3+:YAG-microchip laser (pulse width Δτ=540 ps, repetition rate ν=3 kHz, pump energy Epump=0.15 μJ) as a pump source. A poly-methylmethacrylate film doped with rhodamine B dye serves as active medium. The DFB-laser
pulses are temporally and spectrally characterized, and the stability of the thin polymer/dye film at high repetition rates
is analyzed. The shortest DFB-laser pulses obtained have a duration of 11 ps. After the emission of 350000 pulses the intensity
of the DFB-laser output has decreased by a factor of two and the pulse duration has increased by a factor of 1.2. For single
DFB-laser pulses of 20-ps duration the spectral bandwidth is measured to be Δλ=0.03 nm, which is only 0.005 nm above the calculated
Fourier limit assuming a Gaussian profile for the temporal shape of the pulses. Coarse wavelength tuning of the DFB laser
between 590 and 619 nm is done by turning the prism. Additionally, a fine tuning of the DFB-polymer-laser wavelength is achieved
by changing the temperature of the polymer/dye layer (=-0.05 nm/°C) in the range from 20 to 40 °C.
Received: 1 March 2001 / Revised version: 23 May 2001 / Published online: 18 July 2001 相似文献
13.
T. Rothacher W. Lüthy H.P. Weber 《Applied Physics A: Materials Science & Processing》2001,73(2):133-136
According to UN estimations there are between 80 and 115 million activated landmines worldwide. These mines, or other unexploded
ordnance (UXO), can be triggered accidentally and kill or injure more than 2000 civilians per month. The most common explosive
in these mines is trinitrotoluene (TNT). In this paper, the potential of some of the most promising lasers for mine neutralisation
is investigated, namely an ArF laser, a KrF excimer laser and a Nd:YAG solid-state laser. We have studied the interaction
between laser beams emitting at λ=193 nm, 248 nm and 1060 nm and a bare solid sample of TNT of approximately 15 mg. Using
pulsed excimer radiation at λ=193 nm, with an energy density up to 1 J/mm2, ablation of the TNT without any deflagration has been achieved. At λ=248 nm, using the KrF excimer laser with a pulse duration
of 30 ns and a repetition rate of 5 Hz, the TNT sample started melting and burning after an irradiation of 10 s. Preliminary
results with the Nd:YAG solid-state laser operating in cw emission have shown that the irradiated sample exhibits the desired
burning behaviour even after the exposure is stopped.
Received: 14 December 2000 / Accepted: 18 December 2000 / Published online: 20 June 2001 相似文献
14.
L. Menzel A.A. Kosterev R.F. Curl F.K. Tittel C. Gmachl F. Capasso D.L. Sivco J.N. Baillargeon A.L. Hutchinson A.Y. Cho W. Urban 《Applied physics. B, Lasers and optics》2001,72(7):859-863
Two configurations of a continuous wave quantum cascade distributed feedback laser-based gas sensor for the detection of NO
at a parts per billion (ppb) concentration level, typical of biomedical applications, have been investigated. The laser was
operated at liquid nitrogen temperature near λ=5.2 μm. In the first configuration, a 100 m optical path length multi-pass
cell was employed to enhance the NO absorption. In the second configuration, a technique based on cavity-enhanced spectroscopy
(CES) was utilized, with an effective path length of 670 m. Both sensors enabled simultaneous analysis of NO and CO2 concentrations in exhaled air. The minimum detectable NO concentration was found to be 3 ppb with a multi-pass cell and 16 ppb
when using CES. The two techniques are compared, and potential future developments are discussed.
Received: 1 November 2000 / Revised version: 19 January 2001 / Published online: 20 April 2001 相似文献
15.
R. Dandoloff A. Saxena 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):265-267
For a spin-polarized electron gas on an elastic cylinder in an external axial magnetic field and an axial electric field we
find that the corresponding Euler-Lagrange equation is the double sine-Gordon (DSG) equation with an exact 2π-skyrmion solution.
The DSG skyrmion is stabilized, without Coulomb repulsion, by the curvature of the cylinder. It adopts a characteristic length
ξ which is smaller than the radius of the cylinder. For an elastic cylinder this mismatch of length scales causes a deformation
of the cylinder in the region of the skyrmion.
Received 23 October 2001 / Received in final form 8 March 2002 Published online 2 October 2002
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ID="a"e-mail: rossen.dandoloff@ptm.u-cergy.fr 相似文献
16.
E.G. Gamaly A.V. Rode A. Perrone A. Zocco 《Applied Physics A: Materials Science & Processing》2001,73(2):143-149
We present two sets of experimental results on the ablation-rate decrease with increase of the number of consecutive laser
pulses hitting the same spot on the target surface. We have studied laser ablation of a carbon target with nanosecond pulses
in two different interaction regimes: one with a XeCl laser (λ=308 nm) and the other with a Nd:YAG laser (λ=1064 nm), in both
cases at the intensity ∼5×108 W/cm2 Two different mechanisms were found to be responsible for the ablation-rate decrease; they are directly related to the two
different laser–matter interaction regimes. The UV-laser interaction is in the regime of transparent vapour (surface absorption).
The increase of the neutral vapour density in the crater produced by the preceding laser pulses is the main reason for the
decrease of ablation rate. With the IR laser each single laser pulse interacts with a partially ionised plume. With increase
of the number of pulses hitting the same spot on the target surface, the laser–matter interaction regime gradually changes
from the near-surface absorption to the volume absorption, resulting in the decrease in absorption in the target and thus
in the decrease in the ablation rate. The change in the evaporation rate was considered for both vacuum and reactive-gas environments.
Received: 21 February 2001 / Accepted: 26 February 2001 / Published online: 23 May 2001 相似文献
17.
A simple method for patterning of thin (15–650 nm) aluminum films on glass substrates by direct, low-power, laser-thermal
oxidation in water under common laboratory conditions is demonstrated. Local heating of the metal film enhances the formation
of aluminum oxide (hydrargillite, Al2O3–3H2O) and provokes breakdown of the passivation layer followed by local corrosion at temperatures close to the boiling point
of water. Moving the focus of an Ar-ion laser (λ=488 nm) over the aluminum film with a speed of several μm/s yields grooves
flanked by hydrargillite. Upon through oxidation of the metal these structures act as electrically insulating domains. Depending
on the film thickness, the minimum width of the line structures measures between 266 nm and 600 nm. The required laser irradiation
power ranges from 1.7 mW to 30 mW. It is found that the photo-thermal oxidation process allows for writing of two-dimensional
electrode patterns.
Received: 16 July 2001 / Accepted: 23 July 2001 / Published online: 2 October 2001 相似文献
18.
Q.S. Hu H. Zheng 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):255-262
A new perturbation approach is developed for single- and many-electron Holstein model in one-, two-, and three-dimension.
The results show that this approach has a good agreement with the Migdal theory in the adiabatic regime when the coupling
is moderate (λ < 1), but with the Lang-Firsov theory in the antiadiabatic regime ( ω/W≫ 1). In the intermediate region, our approach can describe the transition from a large-polaron Fermi-liquid to the small-polaron,
and this transition may be discontinuous in adiabatic regime, which means a phase transition appears in many-electron system.
In single-electron case, we eliminate the abrupt transition using the degenerate perturbation theory, and the calculated ground
state energy and effective mass are successfully compared with those of previous authors. Besides, the method has the advantage
of requiring little computational effort.
Received 27 December 2001 / Received in final form 8 April 2002 Published online 31 July 2002 相似文献
19.
B. Pura J. Petykiewicz M. Wierzbicki R. Cio lek Z. Wrzesiński 《Applied physics. B, Lasers and optics》2002,75(4-5):549-551
By ellipsometric measurements we have observed the polarization variations of the primary light beam, with wavelength λ1=5145 ?, interacting with the secondary light beam of controlled variable polarization, transmitted through a TGS crystal
layer. We present a theoretical explanation based on the second-order optical nonlinearity of TGS.
Received: 4 December 2001 / Revised version: 28 May 2002 / Published online: 25 October 2002
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ID="*"Corresponding author. Fax: +48-22/660-5447, E-mail: petyk@if.pw.edu.pl 相似文献
20.
R.K. Varma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):211-218
It has been shown earlier [3,6] that matter waves which are known to lie typically in the range of a few angstrom, can also
manifest in the macrodomain with a wave length of a few centimeters, for electrons propagating along a magnetic field. This
followed from the predictions of a probability amplitude theory by the author [1,2] in the classical macrodomain of the dynamics
of charged particles in a magnetic field. It is shown in this paper that this case constitutes only a special case of a generic
situation whereby composite systems such as atoms and molecules in their highly excited internal states, can exhibit matter
wave manifestation in macro and mesodomains, in one-dimensional scattering. The wave length of these waves is determined,
not by the mass of the particle as in the case of the de Broglie wave, but by the frequency ω, of the classical orbital motion
of the internal state in the correspondence limit, and is given by a nonquantal expression, λ = 2πv/ω, v being the velocity of the particle. For the electrons in a magnetic field the frequency corresponds to the gyrofrequency,
Ω and the nonquantal wave length is given by λ = 2πv
|| /Ω; v
|| being the velocity of electrons along the magnetic field.
Received 29 September 2001 / Received in final form 23 May 2002 Published online 19 July 2002 相似文献