共查询到20条相似文献,搜索用时 62 毫秒
1.
N. Kolachevsky A. Akimov I. Tolstikhina K. Chebakov A. Sokolov P. Rodionov S. Kanorski V. Sorokin 《Applied physics. B, Lasers and optics》2007,89(4):589-594
We have studied possible candidates for laser cooling transitions in 169Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure
and rates of two nearly closed cycling transitions from the ground state 4f136s2(2F0)(Jg=7/2) to upper states 4f12(3H5)5d3/26s2(Je=9/2) at 410.6 nm and 4f12(3F4)5d5/26s2(Je=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates
from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that
the strong transition at 410.6 nm has an optical leak rate of less then 2×10-5 and can be used for efficient laser cooling of 169Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground
state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (Jg=7/2)↔(J’g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks.
PACS 32.70.Cs; 32.10.Fn; 32.80.Pj 相似文献
2.
D. Sukachev K. Chebakov A. Sokolov A. Akimov N. Kolachevsky V. Sorokin 《Optics and Spectroscopy》2011,111(4):633-638
We demonstrated laser cooling and trapping of thulium atoms at sub-Doppler temperatures in a magneto-optical trap (MOT). Up
to 3 × 106 thulium atoms were trapped in the MOT at temperatures down to 25(5) μK which is approximately 10 times lower than the Doppler
limit. The lifetime of atoms in the MOT varied between 0.3–1.5 s and was restricted mostly by optical leaks from the upper
cooling level. The lower limit for the leaking rate was estimated to be 22(6) s−1. Due to a big magnetic moment of Tm atoms, a part of them were trapped in a magnetic trap from the quadrupole field of the
MOT. We observed about 3 × 104 purely magnetically trapped atoms at temperature of 25 μK with a lifetime in the trap of 0.5 s. Also we set up a “dark” MOT
consisting of six crossed hollow beams which increased the number of trapped atoms by a factor of 5 leading to 1.5 × 107 atoms at the expense of higher temperature. 相似文献
3.
Cold atomic beam from a rubidium funnel 总被引:1,自引:0,他引:1
We report an experimental demonstration of a continuous, slow and cold beam of rubidium atoms from a two-dimensional magneto-optic
trap or atomic funnel. Typically 7.3(7)×108 atoms/s are ejected from the funnel with a variable velocity in the range 2–8 m/s and a temperature of 45–55 μK in the moving
frame. This represents the first demonstration of sub-Doppler laser cooling in an atomic beam and temperatures as low as ≈25 μK
have been observed.
Received: 30 September 1999 / Published online: 5 April 2000 相似文献
4.
Machi I. Z. Connell S. H. Sellschop J. P. F. Bharuth-Ram K. 《Hyperfine Interactions》2001,136(3-8):723-726
A preliminary study of the diamagnetic (μd) and the paramagnetic (Mu
T
) states in a synthetic 13C diamond has been performed using the Transverse Field Muon Spin Rotation method. This system could be used to verify the
quantum diffusion behaviour observed before, however, with a more reliable extraction of the hopping rate. The results were
obtained in an applied magnetic field of 7.5 mT and at sample temperatures of 10 K, 100 K and 200 K. The prompt fraction,
f, of the μd state remains constant at 22(5)% in the range 10–200 K; that of the Mu
T
state increases from 53(10)% at 10 K to 78(10)% at 200 K. The fractions of the two states add to 100% at 200 K, suggesting
non-population of the bond-centred state, MuBC, which is often observed in other diamond samples. The μd state has a spin relaxation rate of 0.20(5) μs−1, in contrast to the zero value obtained in type II diamond samples. This indicates appreciable interaction of the μd state with the 13C atoms. The Mu
T
state has a large spin relaxation rate ranging from 3.0(5) μs−1 at 10 K to 7.0(5) μs−1 at 200 K, consistent with values obtained in diamond samples with defects. This work is part of ongoing studies of muon/muonium-defect
interactions in diamonds.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
5.
Machi I. Z. Connell S. H. Sellschop J. P. F. Bharuth-Ram K. 《Hyperfine Interactions》2001,136(3-8):727-730
We report on transverse field muon spin rotation measurements on a nitrogen-rich type Ia diamond, both before and after the
conversion of some of the aggregated nitrogen centres to nitrogen-vacancy complexes known as H2/H3-centres. The prompt fractions
f and the spin relaxation rates λ were determined for the diamagnetic (μd) and the paramagnetic (MuT) states in the temperature range 10–300 K. The production of the nitrogen-vacancy complexes had little effect on the parameters
of the MuT state for which f and λ remained unchanged at approximately 30% and 4 μs−1, respectively. For the μd state, on the other hand, the formation of the H2/H3-centres resulted in an increase of the prompt fraction from 10(2)% to
20(3)%, and (for the first time) the spin relaxation rate showed a non-zero value of 0.020(3) μs−1. These results show evidence of strong μd interactions with the nitrogen-vacancy complexes in diamond, and suggest a more complex structure for this state than a bare
μ+.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
6.
The results of an experiment on muon catalyzed dd-fussion in HD gas are presented. The experiment was performed at the muon beam of PSI using a high-pressure ionization chamber
filled with pure HD-gas of low D2 concentration on the level 1%, at temperatures 50, 150 and 300 K. The non-resonant character of ddμ-molecule formation on HD molecules was confirmed by measuring the ratio of yields of the two ddμ-fusion channels, R=Y(3He,n)/Y(3H,p), which proved to be close to unity. The ddμ formation rate was found to vary from λddμ-HD=0.05· 106 s-1 at T=50 K to λddμ-HD=0.12· 106 s-1 at T=300 K, in agreement with the theoretical prediction. A prominent peak at t<60 ns was observed in the time spectrum of fusion neutrons indicating a resonant contribution of ddμ formation from epithermal dμ atoms.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
We present new theoretical calculations of nuclear fusion rates λ
f
J
from the resonant states of the muonic molecular ion 3Hedμ
++ with total angular momenta J=0,1. As a byproduct, new very accurate variational wave functions for these states have been obtained. Using these wave functions,
the probability density |Ψ(R=0)|2 in a fusion region has been calculated by extrapolating the variational solution to small internuclear distances by means
of the multi-channel adiabatic solution. Calculated fusion rates for the states J=0 and J=1 are: λ
f
0
=1.9·105s-1 and λ
f
1
=0.65·103s-1, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
L. N. Bogdanova V. R. Bom A. M. Demin D. L. Demin C. W. E. van Eijk S. V. Filchagin V. V. Filchenkov N. N. Grafov S. K. Grishechkin K. I. Gritsaj A. D. Konin A. V. Kuryakin S. V. Medved’ R. K. Musyaev A. I. Rudenko D. P. Tumkin Yu. I. Vinogradov A. A. Yukhimchuk S. A. Yukhimchuk V. G. Zinov S. V. Zlatoustovskii 《Journal of Experimental and Theoretical Physics》2009,108(2):216-225
The muon-catalyzed fusion (μCF) process in tritium was studied by the μCF collaboration on the muon beam of the JINR Phasotron.
The measurements were carried out with a liquid tritium target at the temperature 22 K and density approximately 1.25 of the
liquid hydrogen density (LHD). Parameters of the μCF cycle were determined: the ttμ muonic molecule formation rate λ
ttμ = 2.84(0.32) μs−1, the ttμ fusion reaction rate λ
f
= 15.6(2.0) μs−1, and the probability of muon sticking to helium ω
tt
= 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique
experimental method.
The article is published in the original. 相似文献
9.
10.
B. Viaris de Lesegno J.C. Karam M. Boustimi F. Perales C. Mainos J. Reinhardt J. Baudon V. Bocvarski D. Grancharova F. Pereira Dos Santos T. Durt H. Haberland J. Robert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):25-34
A new Stern Gerlach interferometer operating with a nozzle beam of metastable argon atoms Ar* (3p5 4s, 3
P
2) is described. The selection of incoming (polarisation) and outgoing (analysis) Zeeman sublevels is achieved by use of laser
induced transitions at two wavelengths, 811.5 nm (closed J = 2 → J = 3 transition) and 801.5 nm (open J = 2 → J = 2 transition). Linear superpositions of Zeeman sublevels, just beyond the polariser and just before the analyser, are prepared
by means of two zones where Majorana transitions take place. In between, a controlled magnetic field configuration (the phase
object) is produced within a triple μ-metal shielding. Standard interference patterns are obtained by scanning the field and
detecting the atoms by secondary electron emission from a Faraday cup. When a static radial magnetic gradient is used, the
beam profile is modulated by interference. The transverse pattern, which can be translated at will by adding a homogeneous
field, is observed for the first time using a multi-channel electron multiplier followed by a phosphor screen and a CCD camera.
The results satisfactorily agree with all theoretical predictions.
Received 27 June 2002 / Received in final form 20 September 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: perales@lpl.univ-paris13.fr
RID="b"
ID="b"UMR 7538 du CNRS 相似文献
11.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献
12.
S. Bhattacharyya S. G. Nakhate 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):9-15
We have observed superfluorescence (SF) on five atomic transitions at
visible wavelengths 633.58, 635.00, 640.09, 640.61 and 736.22 nm in Doppler
broadened gas of europium (Eu) atom. The nanosecond SF pulses were observed
by longitudinally pumping Eu vapor column with a pulsed dye laser to upper
states 4f65d6s2, 8D7/2at 346.79 nm and 4f75d6p,
10F5/2at 348.73 nm from the ground state 4f76s2,
8S7/2. High optical conversion efficiency ≈10% was
measured for these SF transitions. Our experiment deals with the large
sample multilevel SF in the regime where the length of the excited
column L is greater than the maximum value of the Arecchi-Courtens
length (Lc). The observed variation of SF peak intensity (Ifl) and time
delay for SF evolution (τD) with number of atoms in the excited
state (N) resemble theoretically predicted SF scaling laws for transverse
excitation, namely Ifl∝N and tD μ 1/?N\tau_D \propto 1/{\sqrt N} although the experimental condition
is similar to the swept excitation. This could be due to the Rabi frequency
associated with the pump transition which is comparable to the SF delay time
precluding the initiation of SF at different times along the sample and
results in transverse (instantaneous) excitation. The experimental τD
values were found to be in agreement with the quantum mechanical
calculations describing SF. 相似文献
13.
Yu. M. Smirnov 《Optics and Spectroscopy》2010,109(3):330-335
The excitation of odd levels of the thulium atom, spontaneous transitions from which terminate at the 4f
13(2
F
o)6s6p(3
P
o) (7/2, J
2) levels with J
2 = 0, 1, is studied by the method of extended crossing beams. Fifty four excitation cross sections are measured at an excitation
electron energy of 50 eV. Seven optical excitation functions are recorded in the electron energy range of 0–200 eV. 相似文献
14.
Summary In this work we report on the anisotropic physical properties of silver-sheathed Bi-2223 tapes fabricated by means of hot
extrusion and repeated pressing and sintering processes. The obtained Bi-2223/Ag short tapes, having critical current densitiesJ
c of 20–30 kA/cm2 at 77 K, 0 T, were measured in external magnetic fields up to 0.5T applied in two different orientations (i.e. μ0H‖(a,b)-planes and μ0H ⊥(a,b)-planes). The magnetic characterizations were performed in a wide range of temperatures and magnetic fields to study
the first magnetization curve of tapes evaluating the lower critical fields μ0Hc1⊥ab and ⊥0Hc1#x2016;ab and their dependences on temperature. TheJ
c values at different fields in the temperature range 4.6–90 K, calculated from the magnetization data by the critical state
model, are also presented.
Paper presented at the ?VII Congresso SATT?, Torino, 4–7 October 1994. 相似文献
15.
S. R. Kreitzman T. Pfiz S. Sun-Mack T. M. Riseman J. H. Brewer D. Ll. Williams T. L. Estle 《Hyperfine Interactions》1991,64(1-4):561-566
The ionization of muonium centers in Si and GaAs have been studied using radio frequency (RF) resonant techniques. In Si all
three muonic centers are detectable by RF. No evidence was found for delayed Mu and Mu* states at any temperature. However, our results on the diamagnetic final state (μ
f
+
) show that it is composed of prompt fractions (as seen by conventional μSR) and delayed fractions arising from the ionization
of Mu* and Mu. We observe a full μ
f
+
fraction at 317 K when the Mu relaxation rate is above 10 μs−1. GaAs differs from the situation in Si in that we observed only a partial conversion of Mu* and Mu to a μ+ final state up to 310 K in spite of the fact that the transverse field relaxation rates become very high at 150 and 250 K
respectively. 相似文献
16.
I. N. Ogorodnikov N. E. Poryvay I. N. Sedunova A. V. Tolmachev R. P. Yavetskiy 《Physics of the Solid State》2011,53(2):263-270
The thermally stimulated recombination processes and luminescence in crystals of the lithium borate family Li6(Y,Gd,Eu)(BO3)3 have been investigated. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence spectra), the temperature
dependences of the X-ray luminescence intensity, and the glow curves for the Li6Gd(BO3)3, Li6Eu(BO3)3, Li6Y0.5Gd0.5(BO3)3: Eu, and Li6Gd(BO3)3: Eu compounds have been measured in the temperature range 90–500 K. In the X-ray luminescence spectra, the band at 312 nm
corresponding to the 6
P
J
→ 8
S
7/2 transitions in the Gd3+ ion and the group of lines at 580–700 nm due to the 5
D
0 → 7
F
J
transitions (J = 0–4) in the Eu3+ ion are dominant. For undoped crystals, the X-ray luminescence intensity of these bands increases by a factor of 15 with
a change in the temperature from 100 to 400 K. The possible mechanisms providing the observed temperature dependence of the
intensity and their relation to the specific features of energy transfer of electronic excitations in these crystals have
been discussed. It has been revealed that the glow curves for all the crystals under investigation exhibit the main complex
peak with the maximum at a temperature of 110–160 K and a number of weaker peaks with the composition and structure dependent
on the crystal type. The nature of shallow trapping centers responsible for the thermally stimulated luminescence in the range
below room temperature and their relation to defects in the lithium cation sublattice have been analyzed. 相似文献
17.
I. N. Ogorodnikov N. E. Poryvai I. N. Sedunova A. V. Tolmachev R. P. Yavetskiy 《Optics and Spectroscopy》2011,110(2):266-276
The luminescence and thermally stimulated recombination processes in lithium borate crystals Li6Gd(BO3)3 and Li6Gd(BO3)3:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences
of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds
have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the 6
P
J
→ 8
S
7/2 transitions in Gd3+ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at
400–420 nm, which is due to the d → f transitions in Ce3+ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100
to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation
with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160
K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals
studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation
with defects in the lithium cation sublattice are discussed. 相似文献
18.
G. Fabritius G. Flik J. Golczewski D. Herlach G. Jünemann M. Krenke K. Maier A. P. Pathak H. Rempp A. Seeger W. Sigle E. Widmann D. W. Cooke 《Hyperfine Interactions》1986,31(1-4):229-234
By means of π+/μ+ channelling, positive pions (π+) implanted intoTa, Mo, andW are investigated up to high temperatures. A striking observation is that the channelling effect disappears in a rather narrow
temperature interval centred at 0.26 (Ta) to 0.51 (W) of the melting temperature. From studies of π+ trapping by oxygen atoms inTa estimates for the low-temperature π+ diffusivity inTa [D
π(23K)=1.4·10−10±0.3 m2s−1,D
π(47K)=5.7·10−10±0.3 m2s−1] as well as for the binding enthalpy of π+ to 0 atoms (H
B=7·10−2 eV) have been obtained. The diffusion data are in reasonable agreement with the theory of phonon-assisted tunnelling. 相似文献
19.
R. Cywinski S. H. Kilcoyne S. F. J. Cox C. A. Scott O. Schärpf 《Hyperfine Interactions》1991,64(1-4):427-433
Neutron polarisation analysis measurements reveal antiferromagnetic spin correlations persisting to temperatures of 120 K
in Pauli paramagnetic Y(Mn1−x
Fe
x
)2, 0.03≤x≤0.05. The mean moment at the Mn(Fe) site is found to be 0.2μ
B. Transverse field μSR is characterised by weak exponential damping with a rate of 0.02 μs−1 at 300 K increasing according to the power lawT
−0.75 to only 0.16μ
S
−1
at 12 K. It is suggested that these results are consistent with a slowing down of longitudinal spin fluctuations at the Mn
site as temperature decreases. 相似文献