共查询到20条相似文献,搜索用时 31 毫秒
1.
R. R. Letfullin 《Journal of Russian Laser Research》2002,23(3):252-273
Huge energy gain is detected theoretically in a pulsed chemical laser-amplifier based on a photon-branched chain reaction initiating in a gaseous disperse medium composed of H2–F2–O2–He and Al particles by focused external infrared radiation. It is shown that this effect is observed due to the other optical effect of diffractive multifocal focusing of the input radiation on a certain type of bicomponent optical system coupled structurally with the input mirror of an unstable telescopic laser cavity. Such a relatively simple bicomponent diffraction system, consisting of two plane screens with circular apertures on a given optical axis, enables one to focus the input beam without using classical refraction elements such as lenses and prisms. The focusing of the input signal ensures the minimization of the initially excited volume of the laser active medium and the appropriate sharp lowering of the necessary energy of the input pulse up to 10-6 J. This enables the laser system to reach a high value of the energy gain of 109. The huge laser energy gain allows us to use a master oscillator in the form of a small microjoule laser powered by an accumulator, and consequently makes it possible to construct a completely self-contained compact pulsed chemical HF-laser. 相似文献
2.
V. K. Rai 《Applied physics. B, Lasers and optics》2009,95(2):329-333
Upconversion luminescence in triply ionized praseodymium-doped TeO2–Li2O glass using excitation at ∼590 nm into the 1D2 level from a dye laser pumped with the second harmonic of a pulsed Nd:YAG laser has been reported. The mechanism involved
in the upconversion emission observed at ∼480 nm indicates that the most important contribution is energy transfer among praseodymium
ions in pairs followed by the dipole–dipole interaction. The rate-equation model for the emission at ∼480 nm that provides
direct information to determine the energy-transfer rates containing the pair of states involved in the upconversion process
has been explored. 相似文献
3.
A. Liem D. Nickel J. Limpert H. Zellmer U. Griebner S. Unger A. Tünnermann G. Korn 《Applied physics. B, Lasers and optics》2000,71(6):889-891
We report on a high-gain diode-pumped ytterbium-doped fiber-amplifier system delivering pulse energies in the 100-μJ range
at high repetition rates (32 kHz) with nearly-diffraction-limited beam quality (M2∼1.7) at a 1060-nm center wavelength. Femtosecond seed-laser pulses are stretched in a commercially available single-mode
fiber and compressed after amplification to subpicosecond pulse duration. In a multimode Yb-doped fiber amplifier we have
demonstrated average powers of up to 22 W and single-pulse energies of up to 130 μJ.
Received: 16 August 2000 / Revised version: 4 September 2000 / Published online: 8 November 2000 相似文献
4.
R.P. Singh R.K. Bhowmik S.S. Ghugre S.B. Patel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):35-40
High spins states in 99Rh were populated via the 66Zn(37Cl, 2p2n)99Rh reaction at an incident beam energy of 130 MeV. Seventeen new transitions have been observed in the present study and the
level scheme has now been extended up to a spin of J∼ 25ħ and an excitation energy of about E
x∼ 10 MeV. The observation of a positive parity E2 cascade based on the 9/2+ isomeric level is suggestive of collective behaviour in this nucleus up to high spins. Spherical shell model (within restricted
model space) and Cranked shell model calculations were performed to obtain an insight into the observed level structure. The
new collective band observed up to a spin of J∼ 25ħ is suggested to be based on (πg
9/2
3) ⊗ (νg
7/2
2) quasi-particle excitations.
Received: 12 July 1999 / Revised version: 14 September 1999 相似文献
5.
M. Stanislawki J. Meister T. Mitra M.M. Ivanenko K. Zanger P. Hering 《Applied physics. B, Lasers and optics》2001,72(1):115-120
The Er:YAG and the CO2 laser are competitors in the field of hard tissue ablation. The use of Er:YAG lasers (2.94 μm, pulse length
L of 100 to 200 μs) show smaller areas of thermal defects then ‘‘superpulsed’’ CO2 lasers with pulse lengths of approximately 100 μs. Only the development of a Q-switched CO2 laser (9.6 μm, τL=250 ns) allowed for similar results. In this paper new results for the Er:YAG and the Q-switched CO2 laser under the influence of water spray will be presented. Several parameters are of special interest for these investigations:
the specific ablation energy, which shows a minimum for the CO2 laser at an energy density of 9 J/cm 2 and a broad shallow minimum in the range of 10 to 70 J/cm2 for the Er:YAG laser, and comparison of the cut-shape and depth. Surface effects and cutting velocity are discussed based
on SEM pictures.
Received: 19 July 2000 / Revised version: 1 November 2000 / Published online: 30 November 2000 相似文献
6.
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
7.
F. Liu W. Wang W. Zheng Y. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(3):435-440
In this study, spatially resolved measurements of the
emission intensity of OH (A2Σ↦X2Π, 0-0) and the
vibrational temperature of N2 (C) have been performed during a positive
pulsed streamer discharge with a wire-plate electrode configuration at
atmospheric pressure. The effects of pulse peak voltage, pulse repetition
rate and the added O2 flow rate on the spatial distributions of the
emission intensity of OH (A2Σ↦X2Π, 0-0) and the
vibrational temperatures of N2 (C) perpendicular to the wire in the
direction towards the plate (in the radial direction) are investigated. It
has been found that the emission intensity of OH (A2Σ↦X2Π, 0-0) increases with increasing pulse peak voltage and pulse
repetition rate and decreases with increasing the distance from the wire
electrode. When the different oxygen flows are added in N2 and H2O
mixture gas, the emission intensity of OH (A2Σ↦X2Π, 0-0) decreases with increasing the flow rate of oxygen. The
vibrational temperature of N2 (C) is nearly independent of pulsed peak
voltage and pulsed repetition rate, but increases with increasing the added
O2 flow rate and keeps almost constant in the radial direction under
the present experimental conditions. This measurement plays a crucial role
in understanding the discharge characters of pulsed streamer discharge and
establishing the molecule reaction dynamics model of pulsed streamer
discharge. 相似文献
8.
E.T. Seppälä M.J. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):407-424
We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with
random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type
of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics
argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE
1∼L
θ[ln(L
z
L
- ζ)]-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and Lz is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility
of the manifolds ∼L
2D + 1 - θ[(1 - ζ)ln(L)]1/2. We also present a mean field argument for the finite size scaling of the first jump field, h
1∼L
d - θ. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium
surface growth are discussed.
Received December 2000 and Received in final form April 2001 相似文献
9.
E. Jahier J. Guéna Ph. Jacquier M. Lintz M.A. Bouchiat 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):221-229
We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium
vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment.
We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse
duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×1014 at/cm3 without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further
improvements obtained with sapphire cells are also presented.
Received 15 September 2000 相似文献
10.
S.I. Dolgaev S.V. Lavrishev A.A. Lyalin A.V. Simakin V.V. Voronov G.A. Shafeev 《Applied Physics A: Materials Science & Processing》2001,73(2):177-181
The formation and development of the large-scale periodic structures on a single crystal Si surface are studied upon its evaporation
by pulsed radiation of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns). The development of structures
occurs at a high number of laser shots (∼104) at laser fluence of 1–2 J/cm2 below optical breakdown in a wide pressure range of surrounding atmosphere from 1 to 105 Pa. The structures are cones with angles of 25, which grow towards the laser beam and protrude above the initial surface
for 20–30 μm. It is suggested that the spatial period of the structures (10–20 μm) is determined by the capillary waves period
on the molten surface. The X-ray diffractometry reveals that the modified area of the Si substrate has a polycrystalline structure
and consists of Si nanoparticles with a size of 40–70 nm, depending on the pressure of surrounding gas. Similar structures
are also observed on Ge and Ti.
Received: 12 February 2000 / Accepted: 28 March 2000 / Published online: 20 June 2001 相似文献
11.
C. Monthus T. Garel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):39-45
The directed polymer in a 1+3 dimensional
random medium is known to present a disorder-induced phase
transition. For a polymer of length L, the high temperature
phase is characterized by a diffusive behavior for the end-point
displacement R2 ∼L and by free-energy fluctuations of order
ΔF(L) ∼O(1). The low-temperature phase is characterized by
an anomalous wandering exponent R2/L ∼Lω and
by free-energy fluctuations of order ΔF(L) ∼Lω
where ω∼0.18. In this paper, we first study the scaling
behavior of various properties to localize the critical temperature
Tc. Our results concerning R2/L and ΔF(L) point towards
0.76 < Tc ≤T2=0.79, so our conclusion is that Tc is equal
or very close to the upper bound T2 derived by Derrida and
coworkers (T2 corresponds to the temperature above which the ratio
remains finite as L ↦
∞). We then present histograms for the free-energy, energy and
entropy over disorder samples. For T ≫Tc, the free-energy
distribution is found to be Gaussian. For T ≪Tc, the free-energy
distribution coincides with the ground state energy distribution, in
agreement with the zero-temperature fixed point picture. Moreover the
entropy fluctuations are of order ΔS ∼L1/2 and follow a
Gaussian distribution, in agreement with the droplet predictions,
where the free-energy term ΔF ∼Lω is a near
cancellation of energy and entropy contributions of order L1/2. 相似文献
12.
J.W. Walewski J.A. Filipa C.L. Hagen S.T. Sanders 《Applied physics. B, Lasers and optics》2006,83(1):75-79
High-pulse-energy super-continua featuring an M2 of one were generated in standard single-mode fibers. The highest pulse energy achieved was ∼600 nJ and the pulse duration
was ∼1 ps. The spectral width of the generated continua extended over up to 35% of the pump wavelength.
PACS 42.65.-k; 42.81.-i; 42.79.Nv 相似文献
13.
The selective ablation of thin (∼100 nm) SiO2 layers from silicon wafers has been investigated by applying ultra-short laser pulses at a wavelength of 800 nm with pulse
durations in the range from 50 to 2000 fs. We found a strong, monotonic decrease of the laser fluence needed for complete
ablation of the dielectric layer with decreasing pulse duration. The threshold fluence for 100% ablation probability decreased
from 750 mJ/cm2 at 2 ps to 480 mJ/cm2 at 50 fs. Significant corruption of the opened Si surface has been observed above ∼1200 mJ/cm2, independent of pulse duration. By a detailed analysis of the experimental series the values for melting and breaking thresholds
are obtained; the physical mechanisms responsible for the significant dependence on the laser pulse duration are discussed. 相似文献
14.
Robert Lloyd Amin Abdolvand Marc Schmidt Philip Crouse David Whitehead Zhu Liu Lin Li 《Applied Physics A: Materials Science & Processing》2008,93(1):117-122
Utilising a Nd:YVO4 laser (wavelength of 532 nm, pulse duration of 8 ns, repetition rate of 30 kHz) and a Nd:YAG laser (wavelength of 1064 nm,
pulse duration of 7 ns, repetition rate of 25 kHz), it was found that during the pulsed laser ablation of metal targets, such
as stainless steel, periodic nodular microstructures (microcones) with average periods ranging from ∼30 to ∼50 μm were formed.
This period depends on the number of accumulated laser pulses and is independent of the laser wavelength. It was found that
the formation of microcones could occur after as little as 1500 pulses/spot (a lower number than previously reported) are
fired onto a target surface location at laser fluence of ∼12 J/cm2, intensity of ∼1.5 GW/cm2. The initial feedback mechanism required for the formation of structures is attributed to the hydrodynamic instabilities
of the melt. In addition to this, it has been shown that the structures grow along the optical axis of the incoming laser
radiation. We demonstrate that highly regular structures can be produced at various angles, something not satisfactorily presented
on metallic surfaces previously. The affecting factors such as incident angle of the laser beam and the structures that can
be formed when varying the manner in which the laser beam is scanned over the target surface have also been investigated. 相似文献
15.
Spectroscopic concentration measurements of ammonia and ethylene were done with a pulsed, distributed feedback (DFB) quantum
cascade (QC) laser centered at 970 cm−1. An astigmatic Herriot cell with 150 m path length was employed, and we compare the results from experiments using inter-
and intrapulse techniques, respectively. The measurements include the detection of ammonia in breath with these methodologies.
In the interpulse technique, the laser was excited with short current pulses (5–10 ns), and the pulse amplitude was modulated
with an external current ramp resulting in a ∼0.3 cm−1 frequency scan. A standard amplitude demodulation technique was implemented for extracting the absorption line, thus avoiding
the need for a fast digitizer or a gated integrator. In the intrapulse technique, a linear frequency down-chirp is used for
sweeping across the absorption line. A 200 ns long current pulse was used for these measurements which resulted in a spectral
window of ∼1.74 cm−1 during the down-chirp. The use of a room temperature mercury-cadmium-telluride detector resulted in a completely cryogen
free spectrometer. We demonstrate detection limits of ∼3 ppb for ammonia and ∼5 ppb for ethylene with less than 10 s averaging
time with the intrapulse method and ∼4 ppb for ammonia and ∼7 ppb for ethylene with the interpulse technique with an integration
time of ∼5 s. 相似文献
16.
Temporal, spatial and spectral characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with
laser-produced plasma as cathode are presented. Electrons from a laser-produced aluminium plasma were accelerated towards
a conical point tip titanium anode to generate K-shell x-ray radiation. Approximately 1010 photons/pulse were generated in x-ray pulses of ∼18 to ∼28 ns duration from a source of ∼300 μm diameter, athυ = 4.51 keV (K
α emission of titanium), with a brightness of ∼1020 photons/cm2/s/sr. This was sufficient to record single-shot x-ray radiographs of physical objects on a DEF-5 x-ray film kept at a distance
of up to ∼10 cm. 相似文献
17.
Triglycine sulfate (TGS) films have been prepared by evaporation from a saturated aqueous solution on substrates of fused
quartz coated by a layer of thermally deposited aluminum (Al/SiO2) and white sapphire (α-Al2O3) on whose surface interdigital electrodes have been deposited by photolithography. The TGS films have a polycrystalline structure
made up of blocks measuring 0.1–0.3 mm (Al/SiO2) and 0.1 × 1.0 mm (α-Al2O3). The polar axis in the blocks is mostly confined to the substrate plane. The temperature dependences of the capacitance
and dielectric losses normal to and in the film plane have maxima at the temperature coinciding with that of the ferroelectric
phase transition in a bulk crystal, T
c
. The low-frequency conductivity G in TGS/Al/SiO2 structures displays a frequency dispersion described by the relation G ∼ ω
s
(s ≈ 0.82). The conduction can be tentatively ascribed to the hopping mechanism involving localized carriers with a ground state
energy of 0.8–0.9 eV. At temperatures above and below T
c
, the low-frequency conductivity in TGS/α-Al2O3 films operates through a thermally-activated mechanism with an activation energy of 0.9–1.0 eV. At the phase transition,
an additional contribution to conductivity appears in TGS/α-Al2O3 films with a dispersion G ∼ ω0.5, which can be associated with domain-wall relaxation. 相似文献
18.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):161-167
The parameters of the σ-ω-ρ model in the relativistic mean-field theory with nonlinear σ-meson self-interaction are determined
by nuclear-matter properties, which are taken as those extracted by fits to data based on nonrelativistic nuclear models.
The values of the relevant parameters are C
σ
2∼ 94, C
ω
2∼ 32, C
ρ
2∼ 26, b∼ - 0.09, c∼ 1, and the σ-meson mass m
σ∼ 370 MeV, while the value of the calculated nuclear- surface thickness is t∼ 1.4 fm. The field system is shown to be stable, since the σ-meson self-interaction energy is a lower bound in this whole
parameter region with positive c. On the other hand, the effective nucleon mass M* is larger than 0.73M, if the symmetry incompressibility Ks is assumed to be negative and the nuclear-matter incompressibility K0 is kept less than 300 MeV.
Received: 27 June 2001 / Accepted: 5 October 2001 相似文献
19.
V. D. Zvorykin A. O. Levchenko A. G. Molchanov I. V. Smetanin N. N. Ustinovskii 《Bulletin of the Lebedev Physics Institute》2010,37(2):60-64
The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small
easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular
laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ
mw
∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor
of 6 in comparison with propagation in free space. 相似文献
20.
A. Ya. Faenov S. A. Pikuz A. G. Zidkov I. Yu. Skobelev P. S. Komarov O. V. Chefonov S. V. Gasilov A. V. Ovchinnikov 《JETP Letters》2010,92(6):375-378
The characteristics of X rays of a laser plasma generated in the interaction of a femtosecond pulse with solid targets in
an air atmosphere have been investigated. It has been shown that the mechanism for the generation of X rays in the interaction
of short intense laser pulses with solid targets in a gas atmosphere is attributed to the generation of fast electrons in
the region of the filamentation of a laser pulse. It has been proven experimentally that under such conditions, the solid
target irradiated by laser radiation of even a low density of about 1015 W/cm2 very efficiently emits ∼10-keV photons. It has been shown theoretically that the maximum energy of accelerated electrons
can reach ɛmax ∼ 100–200 keV under these conditions. This means that the proposed method can provide characteristic radiation with the energy
of photons much higher than 10 keV. 相似文献