共查询到20条相似文献,搜索用时 31 毫秒
1.
Understanding the effects of cold nuclear matter on J/ψ production is a key requirement for interpreting the J/ψ suppression
reported in heavy-ion collisions. Based on a Glauber model, the J/ψ–nucleon inelastic cross section is determined from a statistical
analysis of the J/ψ world data on nuclear targets. The global fit of all data gives σJ/ψN = 3.4 ± 0.2 mb, significantly smaller than previous estimates, yet the χ2 of the fit is pretty large, χ2/ndf=1.5. A similar value, σJ/ψN = 3.5 ± 0.2 ± 1.7 mb, is obtained when the De Florian–Sassot modifications of the nuclear parton densities are included in
the analysis, although we emphasise that the present uncertainties on gluon (anti-) shadowing do not allow for a precise determination
of σJ/ψN. Finally, the possible energy dependence of the J/ψ–nucleon inelastic cross section is investigated within this framework.
No significant energy dependence of the J/ψ–N interaction is observed.
PACS 25.75.-q; 14.40.Gx; 24.85.+p 相似文献
2.
M. Takai P. H. Tsien S. C. Tsou D. Röschenthaler M. Ramin H. Ryssel I. Ruge 《Applied Physics A: Materials Science & Processing》1980,22(2):129-136
CW CO2-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry,
and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods
was made. The laser annealing was done with power densities of 100 to 640 W cm−2 for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser
annealing with a power density of 500 W cm−2 and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×1015 cm−2 was obtained for 1×1016 cm−2 implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min. 相似文献
3.
A nonlinear optical method has been proposed for probing the evolution of a plasma and energy transfer processes in the microvolume
of a transparent dielectric using the third-harmonic probe signal. The electron self-trapping time has been estimated as t = 150 ± 80 fs. A decrease in the third-harmonic probe signal has been detected at the picosecond time scale; this decrease
can be attributed to a change in the third-order susceptibility χ(3) of a fused silica sample modified by laser radiation. 相似文献
4.
Large third-order nonlinear optical susceptibility of Au-Al2O3 composite films near the resonant frequency 总被引:2,自引:0,他引:2
2 O3 composite films with high Au concentrations (30%–60% in volume fraction) were prepared by reactive co-sputtering and post
rapidly thermal annealing. The structure of the films and the size distributions of the Au nanoclusters were examined by TEM,
and the third-order nonlinear optical susceptibility χ(3) was measured by degenerated four-wave mixing using a 70-ps pulse laser at 532 nm. The maximum value of the χ(3) was about 1.2×10-6 esu in the annealed films and occurred at around 45% Au concentration. The figure of merit, χ(3)/α (α is the absorption coefficient), has a value of 7×10-12 esu cm over a wide range of Au concentrations.
Received: 23 July 1997 相似文献
5.
Hollow cathode (HC) lasers usually operate in a single axial mode without any optical selection. This is attributed to the
large homogeneous linewidth of the gain curve due to the relatively high filling pressure of these lasers. Collisional and
Doppler broadening (ΔνC and ΔνD) of the Cd+ 636 nm and Cd+ 538 nm lines (laser transitions of the HeCd+ laser) excited in a HC discharge tube were determined using a Fabry–Perot interferometer technique. It was found that in
the pressure range 7–25 mbar ΔνD was nearly constant, while, as expected, ΔνC increased linearly with pressure. The broadening constants were α(636 nm)= (47±2) MHz/mbarand α(538 nm)=(11.8±0.5) MHz/mbar.
The first constant is large enough to explain single-mode operation of the red HeCd+ laser; but in the case of the green laser, the exact reason for the single-mode operation remained unclear.
Received: 23 November 2000 / Revised version: 30 March 2001 / Published online: 7 June 2001 相似文献
6.
A.R. Präg F. Löwenthal R. Tommasini J.E. Balmer 《Applied physics. B, Lasers and optics》1998,66(5):561-566
2 . By using a 0.7% prepulse that precedes the main pulse by 5 ns and applying a total pump energy of 100 J or less, the J=0-1
lasing is at least one order of magnitude higher than the non-lasing background. For the 32.6-nm line of Ti, the 25.5-nm line
of Fe, and the 23.1-nm line of Ni, gain coefficients of (±) 4.20.4cm-1, (±) 3.90.3cm-1, and (±) 3.60.6cm-1, respectively, were measured for 2.4-cm-long curved targets, resulting in gain–length products of ∼10. Angle-resolved spectra
indicate a beam divergence of 3 mrad (FWHM), typically. The space-resolved spectra show that the J=0-1 lasing lines are emitted
from an approximately 60-μm-wide (FWHM) plasma region, whereas the nearby continuum emission is produced in a considerably
broader plasma region of ∼250 μm. Lasing at 25.5 nm in neon-like iron was observed at a pump power as low as 180 GW (∼9 TW/cm2), with, however, considerable shot-to-shot scatter in the absolute laser output.
Received: 5 September 1997/Revised version: 10 November 1997 相似文献
7.
M.L. Ndawana R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):399-407
We compute the number level variance Σ
2 and the level compressibility χ from high precision data for the Anderson model of localization and show that they can be
used in order to estimate the critical properties at the metal-insulator transition by means of finite-size scaling. With
N, W, and L denoting, respectively, linear system size, disorder strength, and the average number of levels in units of the mean level
spacing, we find that both χ(N, W) and the integrated Σ
2 obey finite-size scaling. The high precision data was obtained for an anisotropic three-dimensional Anderson model with disorder
given by a box distribution of width W/2. We compute the critical exponent as ν≈ 1.45±0.12 and the critical disorder as W
c≈ 8.59±0.05 in agreement with previous transfer-matrix studies in the anisotropic model. Furthermore, we find χ≈ 0.28±0.06
at the metal-insulator transition in very close agreement with previous results.
Received 1st November 2001 and Received in final form 8 March 2002 Published online 6 June 2002 相似文献
8.
The experimental results of a high-power tunable mid-IR laser are presented. The optical parametric oscillator (OPO) with
a 3-mm-thick PPMgCLN crystal was pumped by a 1.064 μm pulse laser. When the pump power of the 1.064 μm laser was 151 W at
10 kHz, and the operating temperature of the PPMgCLN with 5% MgO doping was 100°C, average output power of 23.7 W at 3.91
μm was obtained with a slope efficiency of 18.2% for the idler resonant OPO. The variation of the 3.91 μm output power was
about ±4% in 10 min continuous operation. The beam quality factor M
2 was less than 2.6. The average output power of 27.4 W at 3.91 μm was also obtained with 151 W pump power and the slope efficiency
of 20.9% for the signal resonant OPO by changing the coating parameters of the OPO cavity mirrors. The mid-IR wavelength tunability
of 3.7–4.0 μm can be achieved by adjusting the temperature of a 29 μm period PPMgCLN crystal from 200 to 30°C. 相似文献
9.
Harold Jones 《Applied Physics A: Materials Science & Processing》1978,15(3):261-264
A tunable microwave frequency was added to, or subtracted from fixed frequency13C16O2 and12C18O2 laser lines using the nonlinearity of molecular absorptions. In this way the frequency of 30 transitions of the ν2-band of ammonia were measured with an accuracy of ±0.0005 cm−1. A further four transitions were measured with an accuracy of ±0.0001 cm−1 by saturating the two-photon transition and observing the Lamb dip. For laser lines up to 11 GHz off-resonant with in frared
transitions Doppler-limited signals were observed with microwave power densities of only 10 mW/cm2 using a wide-band intracavity cell. 相似文献
10.
A. P. Bogatov 《Journal of Russian Laser Research》1994,15(5):417-453
The electromagnetic field inside a nonlinear active medium of a laser is considered as a system of counterpropagating waves.
Such an approach changes radically an earlier studied behavior of the lateral field instability due to self-deformaion (or
self-focusing). In our calculations we used an expression for a laser field in the form of two “strong” counterpropagating
waves whose complex amplitudes have weak perturbations. Amplitude perturbations of each of the “strong” waves can be presented
by two spatial harmonics corresponding to two weak perturbation waves with wave vectors making some tilted angle ±φ with the
cavity axis. Thus six waves would participate in the interaction: two counterpropagating strong waves and two pairs of weak
waves. Using this approach, we have developed a theory for the propagation of four “weak” perturbation waves in a nonlinear
amplifying medium in the presence of two counterpropagating “strong” waves. It is shown that perturbation waves with tilted
angle φ⋍0.5–1.2° inside the active region, and respecively, with the side lobes of the far-field pattern at ∼1.7–4°, have
the greatest growth increment. These perturbation waves produce lateral intensity modulation with period 10–30 μm for the
0.85 μm lasing wavelength. The appearance of such waves corresponds to the instability threshold of a homogeneous lateral
distribution of optical power in a diode laser.
The present theory makes it possible to investigate the stability of the homogeneous lateral optical intensity distribution
in a diode laser of any design. This allows one to choose a suitable design of a laser with a homogeneous lateral distribution
at high radiation power.
Translated from Preprint No. 43 (1992) of the Lebedev Physics Institute, Russian Academy of Sciences. 相似文献
11.
A two-channel photo-acoustic spectrometer (PA spectrometer) with a near infrared diode laser was used for taking measurements
of a high resolution ethylene absorption spectrum. A semiconductor TEC-100 laser with an outer resonator generates a continuous
single-frequency radiation in the range 6030–6300 cm-1. A newly designed model of photo-acoustic detector (PAD) in the form of a ring type resonator provides for measurement of
weak absorption cross-section equal to 4×10-23 cm2/mol at a laser radiation power of 3 mW. The PAD threshold sensitivity is 2×10-9 cm-1 Hz-1/2 W, when the signal to noise ratio equals to 1.
The ethylene absorption spectrum within the range 6035–6210 cm-1 was measured for the first time with a spectral resolution of 10 MHz. The reported line centre positions have an uncertainty
of ± 0.0005 cm-1. The precise measurements of ethylene absorption cross-sections were carried out using the mixture of high purity ethylene
and broadening gas (nitrogen) at the mixture ratio 1:50–1:200. Measurements were carried out at a mixture pressure of about
4.2 kPa.
PACS 42.62.Fi; 42.55.Px 相似文献
12.
Sara N. Mendiara R. P. Baquero M. R. Katunar A. Y. Mansilla L. J. Perissinotti 《Applied magnetic resonance》2009,35(4):549-567
Ultraviolet and visible spectroscopy was applied to characterize and to measure the concentration of β-carotene dissolved
in a dioxane and water mixture. The reaction of β-carotene in the presence of nitrite anion and acid medium was studied at
different temperatures. The reaction systems were homogeneous and were kept anaerobic. Pseudo-first-order rate constants in
respect of β-carotene were measured in the range from 293 to 313 K and pH 5.8 ± 0.2. The energy of activation was calculated
to be E
a = 67.2 ± 3.4 kJ/mol. We interpolate a value that may have biological interest, k
β-carotene(310 K) = (9.70±0.78) · 10−3 s−1, in the presence of 9.3 · 10−3 M nitrite anion. Electron paramagnetic resonance spectroscopy was applied to characterize and quantify a persistent intermediate
radical generated in the reaction system described. The recorded spectra showed triplet-type signals with a peak-to-peak value
of 12.7 G. Nearly the same triplet radical-type intermediates were detected when studying the following reaction systems in
pure dioxane: nitrogen dioxide (NO2)/β-carotene, nitric oxide (NO)/β-carotene and NO/NO2/β-carotene. Therefore, we proposed that the nitrogen oxides have also been intermediates in the reaction system of β-carotene,
nitrite anion and acid medium, in the dioxane and water mixture. A mechanism was proposed and checked by employing the chemical
kinetics simulation. The explanations developed would lead to a better understanding of the behavior of carotenoids in the
presence of nitrite anion and nitrogen oxides. 相似文献
13.
S. Vanishri J.N. Babu Reddy H.L. Bhat S. Ghosh 《Applied physics. B, Lasers and optics》2007,88(3):457-461
We report the surface laser damage threshold in sodium p-nitrophenolate dihydrate, a nonlinear optical crystal. The experiment
is performed with a pulsed Nd:YAG laser in TEM00 mode. The single shot damage thresholds are 11.16±0.28 GW cm-2 and 1.25±0.02 GW cm-2 for 1064 nm and 532 nm laser wavelengths respectively. A close correlation between the laser damage threshold and mechanical
hardness is observed. A possible mechanism of laser damage is discussed.
PACS 42.70.Mp; 61.80.Ba; 81.10.Dn 相似文献
14.
A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface
(GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study
of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have
been performed for a Gaussian laser beam of peak intensity 5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 1 × 1019 cm − 3, and for a Gaussian laser beam of peak intensity 1.5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 3.5 × 1019 cm − 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the
plasma density is 1 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV.
On the other hand, when the plasma density is 3.5 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV. 相似文献
15.
M. Jackson E.M. Telles M.D. Allen K.M. Evenson 《Applied physics. B, Lasers and optics》2001,72(7):815-818
A significantly improved far-infrared laser has been used to generate optically pumped laser emissions from 26 to 150 μm for
CD3OH. Using an X–V-pumping geometry, several new laser emissions have been found for CD3OH. In addition, an increase in power, by factors from 10 to 1000, for many of the previously known shorter-wavelength laser
lines, below 100 μm, has been observed. Frequency measurements for several lines have also been performed and have been reported
to a fractional uncertainty up to ±2×10-7, permitting the spectroscopic assignment of the laser transition. One of the frequency-measured lines, 44.256 μm observed
using the 10R34 pump, has confirmed the assignment of the previously reported FIR emission (n,K;J)=(1,7;20)?(0,8;20)A in the
ground vibrational state.
Received: 26 October 2000 / Published online: 7 February 2001 相似文献
16.
G. V. Danilyan J. Klenke V. A. Krakhotin V. V. Novitsky V. S. Pavlov P. B. Shatalov 《Physics of Atomic Nuclei》2010,73(7):1116-1118
The results of an experiment aimed at searches for formally T-odd correlations in the angular distribution of prompt neutrons from the fission of 235U nuclei are presented. The experiment was performed in the MEPHISTO polarized cold-neutron beam from the Munich FRMII reactor.
The correlation coefficient proved to be (−3.5 ± 3.4) × 10−5 for a three-vector correlation (TRI effect) and (−5.0 ± 3.4) × 10−5 for a five-vector correlation (ROT effect). This means that no significant effects were discovered within the measurement
errors. A comparison with the analogous effects in the ternary fission of 235U nuclei was performed. The values of the corresponding correlations in the angular distribution of prompt fission gamma rays
were refined. 相似文献
17.
Chu Liu Fan Zhang Chun-can Wang Yu-chun Lu Rui Geng Shui-sheng Jian 《Optical Review》2009,16(5):529-532
A new method for the wavefront measurement of high power laser diode array with large dynamic ranges is presented. The wavefront
sensor has a large dynamic range of −π/2 to π/2 and high precision on the measured wavefront slopes (±1′). According to the measurements of the slopes and intensity of
the high power laser diode array, complex amplitudes can be obtained and the wavefront can be reconstructed. The reconstructed
wavefront of high power laser diode array can be used in designing a laser beam shaping system in future work. 相似文献
18.
M. Inguscio P. Minguzzi A. Moretti F. Strumia M. Tonelli 《Applied Physics A: Materials Science & Processing》1979,18(3):261-270
The operation of a cw FIR laser in the presence of a strong electric field is described. A hybrid metal-dielectric waveguide
is used and the cavity length is scanned to study how the frequency and power of the laser depend on the field strength. The
results have also been checked by heterodyning with a conventional reference laser. We report the results obtained for the
496 μm line of CH3F and the 70.5 μm and 119 μm lines of CH3OH. A large frequency tunability of almost ±40 MHz is obtained in the best case with power levels in the mW range. A very
simple theoretical model accounts for the experimental results. We also report the appearance of a new FIR line at about 204
μm when CH3OH is pumped by the 9 μmP(34) of CO2 in the presence of an electric field larger than 1.2 KV/cm. 相似文献
19.
X. Y. Tao I. Fsaifes V. Koncar C. Dufour C. Lepers L. Hay B. Capoen M. Bouazaoui 《Applied Physics A: Materials Science & Processing》2009,96(3):741-749
Indium tin oxide (ITO) thin films prepared by the sol–gel method have been deposited by the dip-coating process on silica substrates. CO2 laser is used for annealing treatments. The electrical resistivity of sol–gel-derived ITO thin films decreased following
crystallization after exposure to CO2 laser beam. The topological and electrical properties of the irradiated surfaces have been demonstrated to be strongly related
to the coating solution and to the laser processing parameters. Optimal results have been obtained for 5 dip-coating layers
film from 0.4 mol/l solution irradiated by 0.6 W/m2 laser power density. In this case, homogeneous and optically transparent traces were obtained with a measured sheet resistance
of 1.46×102 Ω/□. 相似文献
20.
G. Schreiber H. Suche Y.L. Lee W. Grundkötter V. Quiring R. Ricken W. Sohler 《Applied physics. B, Lasers and optics》2001,73(5-6):501-504
Using an FM-mode-locked Ti:Er:LiNbO3 waveguide laser as the fundamental source, wavelength conversion by cascaded χ(2):χ(2)-difference frequency generation with a conversion efficiency of up to +3(-4.6) dB was demonstrated at a pulse repetition
rate of about 2 (10) GHz. In addition, multi-channel conversion was demonstrated with a fully packaged wavelength converter
using a continuous fundamental source.
Received: 29 May 2001 / Revised version: 10 August 2001 / Published online: 2 November 2001 相似文献