Tuning the velocity and flux of a low-velocity intense source of cold atomic beam
Shu Chen(陈姝), Ying-Ying Li(李营营), Xue-Shu Yan(颜学术), Hong-Bo Xue(薛洪波), Yan-Ying Feng(冯焱颖) Citation:Chin. Phys. B . 2017, 26(11): 113703. doi: 10.1088/1674-1056/26/11/113703
Journal homepage: http://cpb.iphy.ac.cn; http://iopscience.iop.org/cpb
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Phys. B Vol. 26, No. 11 (2017) 113703
Tuning the velocity and flux of a low-velocity intense source of cold atomic beam∗
Shu Chen(陈姝)1, Ying-Ying Li(李营营)1, Xue-Shu Yan(颜学术)1, Hong-Bo Xue(薛洪波)2, and Yan-Ying Feng(冯焱颖)1,†
a)State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084, China b)State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
(Received 3 June 2017; revised manuscript received 3 August 2017; published online 30 September 2017)
We investigate experimentally and numerically the quantitative dependence of characteristics of a low-velocity inten- sity source (LVIS) of atomic beam on light parameters, especially the polarization of cooling laser along the atomic beam axis (pushing beam). By changing the polarization of the pushing beam, the longitudinal mean velocity of a rubidium atomic beam can be tuned continuously from 10 to 20 m/s and the flux can range from 3 × 108 to 1 × 109 atoms/s, corre- sponding to the maximum sensitivity of the velocity with respect to the polarization angle of 20 (m/s)/rad and the mean sensitivity of flux of 1.2 × 109 (atoms/s)/rad. The mechanism is explained with a Monte-Carlo based numerical simula- tion method, which shows a qualitative agreement with the experimental result. This is also a demonstration of a method enabling the fast and continuous modulation of a low-velocity intense source of cold atomic beam on the velocity or flux, which can be used in many fields, like the development of a cold atomic beam interferometer and atom lithography.
Keywords: atomic source, low-velocity intensity source (LVIS), laser cooling, light polarization PACS: 37.20.+j, 37.10.De DOI: 10.1088/1674-1056/26/11/113703
1. Introduction decrease in the beam brightness and phase space density. The other class of methods more recently adopted is to Since the first demonstration of a laser-cooled atomic use magneto-optic forces to first confine atoms in a vapor cell, beam by Phillips and Metcalf,[1] a bright and cold atom beam which form a reservoir from which atoms can be efficiently has become the basis of many precise measurements and atom ejected into a well-collimated beam. Vapor cells trade-off optic experiments, including ultra-high-resolution atomic and flux (about 109 − 1010 atoms/s) for the transverse compres- molecular spectroscopy,[2,3] atom frequency standards,[4,5] sion of the atomic beam, a decrease in the longitudinal ve- Bose–Einstein condensation (BEC) experiments,[6,7] atom locity of atoms and a reduced background of thermal atoms, interferometers,[8–12] atom lithography,[13] etc. The desirable but with similar flux density and a greater flexibility in de- features for a cold beam of neutral atoms are high flux at sign. The three most common vapor cell designs have been de- low average velocity, small divergence, tunability of flux and veloped according to different configurations of magnetic and velocity, and robustness and stability in the beam parame- optical fields, including two-dimensional (2D) MOT,[9,21–25] ters, which are especially important in our case, where a cold 2D+ MOT[26–33] and its variations,[34–39] and 3D MOT or the atomic beam of rubidium is directly used as a matter wave LVIS.[40–43] Both the 2D+ MOT and LVIS designs use cool- [14] source for an atom interferometer. ing and radiation force imbalance along the flux axis to pro- For obtaining a high-flux low-velocity atomic beam, duce a slow and narrow velocity distribution to several me- two classes can be generally identified among the different ters per second range, using a 2D and 3D quadrupole mag- schemes developed. One of the earliest methods is to start netic field, respectively. In the cases of the 2D MOT and 2D+ with a thermal beam and decelerate it along its propagation MOT design, the standard three-dimensional (3D) MOT ar- axis using radiation pressure in several methods, such as Zee- rangement in the source chamber is replaced by a 2D MOT man slower,[1,15,16] frequency-chirped laser radiation,[15,17,18] configuration, with (2D+ MOT) or without (2D MOT) push isotropic light slowing,[19] and wideband light slowing.[4,20] and cooling beam along the symmetry axis. These techniques Among these methods, Zeeman slowers are still widely used have been used for generating cold beams of different species to give a high flux of atoms (about 1011 −1012 atoms/s). How- of atoms and molecules from alkaline atoms (Li, Na, K, Rb, [44] [45] ever, the process of cooling by all these techniques is accompa- Cs) to the alkaline earths, metastable helium, and NH3 nied by associated photon heating, which induce unavoidable molecular.[46] increase in the transverse temperature of atoms and hence a The choice of the method for producing a cold atomic ∗Project supported by the National Natural Science Foundation of China (Grant Nos. 61473166 and 41404146). †Corresponding author. E-mail: [email protected] © 2017 Chinese Physical Society and IOP Publishing Ltd http://iopscience.iop.org/cpb http://cpb.iphy.ac.cn 113703-1 Chin. Phys. B Vol. 26, No. 11 (2017) 113703 beam depends on the specific requirements of the subsequent (MOT), is pumped to 2 × 10−9 Torr, and the other cham- experiment. Most of these continuous cold atomic beam are ber, working for the subsequent experiments, is pumped to eminently suitable for loading MOT, but are still very far from 8 × 10−10 Torr when the rubidium reservoir is turned off. The the ideal of a continuous beam with a controllable velocity, two chambers are separated by a λ/4 plate and a mirror, de- density, and temperature in the moving frame comparable to a noted as QWP1 and M1, respectively, each of which has a pulsed cold atomic source based on an MOT in the application hole of diameter 1.5 mm at its center (Fig.1). An LVIS of of an atom interferometer experiment. On one hand, flexible cold 87Rb atoms is generated from the first chamber in which velocity or flux tunability is important for getting precise con- cold atoms are prepared in a vapor-cell 3D MOT.[40] Standard trol or modulation on parameters of a matter-wave source for a 3D MOT optics with the retro-reflective configuration are im- 87 2 well-defined de Broglie wavelength. On the other hand, these plemented with the cooling light tuned to the Rb 5s S1/2, 2 0 factors may lead to the instability of beam parameters of an F = 2 →5p P3/2, F = 3 allowed transition with a typical red atomic source, which induces phase noise of an atom inter- detuning of δ = 4–5Γ (where Γ = 2π × 6 MHz is the nat- ferometer. Several methods have been demonstrated for con- ural linewidth of 87Rb) and the repumping light tuned to the trolling the flux of an atomic beam and correspondingly the 2 2 0 5s S1/2, F = 1 → 5p P3/2, F = 2 allowed transition. The longitudinal velocity by changing the detuning of the cooling total power of cooling beams is 150 mW with each pair of [47,48] beam, using separate “pushing” and “retarding” beams 45 mm waist beam corresponding to 4.5 mW/cm2 peak inten- [27] [36] along the flux axis, or two-color pushing beams. sity. The repumping light of 12 mW total power is overlapped In this paper, we study the characteristics of an LVIS atom with transverse cooling beams. To trap the atoms, a pair of beam as a function of light beam parameters, especially the anti-Helmholtz coils oriented along the z-axis is used to gener- 87 pushing light polarization. A Rb atomic beam is prepared ate a quadrupole magnetic field with a transverse field gradient and experimentally measured for this aim and a numerical sim- of about 15 G/cm. Using the holes drilled in QWP1 and M1, ulation based on the Monte Carlo method is used to explain our one pair of cooling beams, here denoted as pushing beam, is results qualitatively. Results show that pushing beam polariza- produced along the z-axis by retro-reflection of the light beam. tion angle may influence the longitudinal velocity and flux of This generates a dark channel along the z-axis and allows cold an LVIS atomic beam with the sensitivity of 20 (m/s)/rad and atoms to leak out continuously from the MOT chamber be- 9 1.2×10 (atoms/s)/rad, respectively. This also presents a sim- cause of the unbalanced radiation pressure. The continuous ple method which enables fast modulation of an LVIS atomic cold atomic beam then enters the next chamber with no fur- beam on the longitudinal mean velocity ranging continuously ther cooling or collimation. from 10 to 20 m/s by changing the polarization of the pushing The longitudinal velocity and flux of the cold atomic beam. beam are measured by the time-of-flight (TOF) method, re- alized by switching off the atomic beam using a plug beam. 2. Experimental setup The fluorescence of atoms, induced by a probe laser beam, is A diagram of the experimental setup is shown in Fig.1. collected by a photomultiplier tube (PMT, H7422-50, Hama- The vacuum system consists of two chambers, each of which matsu, Japan) in a distance of 0.7 m from the plug beam. Both is pumped with a single ion pump. One chamber, working for the plug beam and probe beam are tuned to the F = 2 → F0 = 3 an imbalanced three-dimensional (3D) magneto-optical trap resonance.
(a) (b) ω1&ω 2 M |e> QWP QWP3 probe beam for |2> plug ∆ beams 1&2 1&2 beams
pushing I beam pumping optical raman raman beam1 beam2 cold 87Rb beam M1 ω2 π/2 π/2 atom beam ω1
87 |2> |1> Rb QWP1 QWP4 lens δD HWP QWP2 |2> ω0 X ω1 g coils M M |1> Z ω2 PMT Y cooling beams Fig. 1. (color online) (a) Schematic of the experimental layout for the LVIS system of 87Rb atoms. M: mirror; HWP: half-wave plate; QWP: quarter-wave plate; PMT: photomultipliers. (b) Level diagram for the ground states |1i and |2i and the excited state |ei. The frequencies ω1 and ω2 are used to induce Raman transitions between the two ground states.
113703-2 Chin. Phys. B Vol. 26, No. 11 (2017) 113703
The transverse velocity distribution of the cold atomic the background vapor in a 3D MOT, form into a beam un- beam is measured by the two-photon velocity-selective Ra- der the imbalanced radiation pressure, and then pass through a man transitions.[49] When a pair of counter-propagation Ra- hole into the next UHV chamber where the beam flux is mea- man beams, in Doppler-insensitive geometries, meet at right sured. angle with the atomic beam, the detuning frequency of Raman For the description of motion of atoms in an MOT, we beam, δD, is related to the transverse velocity vx, consider the scattering force on atoms in the low-intensity limit. The total scattering force on an atom is given by + − δD = keff · vx, (1) σ σ FMOT = Fscatt + Fscatt, where where keff = k1 − k2 is the effective wave vector, ki = ωi/c, σ ± hk¯ Γ s Fscatt = ± 2 , (2) i = 1,2 is the wave vector of Raman beams, ωi, i = 1,2 the an- 2 1 + s + (2δ±/Γ ) gular frequency of Raman beams, and c the velocity of light. where Γ is the natural linewidth of atomic transition and hk¯ the By sweeping the detuning frequency δD and getting spectrum momentum of photons. s = I/Isat is the on-resonance satura- of the stimulated Raman transition, we can make measure- tion parameter for the cooling laser, where I is the laser beam ments of transverse velocity distribution of the atomic beam intensity and Isat is the saturation intensity for the atomic tran- from Eq. (1). 2 sition (Isat for the D2 resonance line in Rb is 1.6 mW/cm ). As shown in Fig.1, the Raman beam 1 with crossed The frequency detuning from resonance, δ±, for each linear polarization is converted into opposite circular polar- laser beam is given by izations using a quarter-wave plate (QWP3). After passing 0 through the atomic beam, the light fields are linearized by δ± = δ0 ∓ 푘 · 푣 ± µ B/h¯, (3) another quarter-wave plate (QWP4), and ω1 and ω2 are spa- where δ is the laser frequency detuning from resonance, v tially separated by a polarizing beam splitter (PBS). Only 0 q the velocity of atoms, and B = B2 + B2 + B2 the magnitude the ω1 beam is retro-reflected back through the atomic beam. x y z The counter-propagating Raman laser beams are generated for of local magnetic field produced by the anti-Helmholtz coils. 0 Doppler-sensitive Raman transitions in the form of σ +–σ + µ ≡ (geme − ggmg)µB is the effective magnetic moment for or σ −–σ − transitions. Removing the QWP3 and blocking the transition used, subscripts g and e refer to ground and ex- the retro-reflected beam allows Raman transitions in Doppler- cited states, respectively, gg,e is the Lande g factor, µB is the insensitive geometries, which forms a Raman–Ramsey inter- Bohr magneton, and mg,e is the magnetic quantum number. 0 ferometer along with the Raman beam 2.[50] Raman beams are The third term of Eq. (2), +µ B/h¯ is caused by the Zeeman ef- + 0 generated based on a sideband injection-locking technique us- fect. Figure2 shows δ corresponding to +|µ B/h¯| for z < 0 − 0 ing a fiber electro-optical modulator (FEOM).[51] To detect the and δ to +|µ B/h¯| for z > 0. signals of the stimulated Raman transitions and the Raman– Energy Ramsey fringes, Raman detuning is adjusted by sweeping the Me=+1 RF signal driving the Raman optics. Before interacting with the Raman beams, the atoms ini- σ-(−|µ′B/h|) σ+(−|µ′B/h|) Me=0 - B h tiated in the F = 2 ground state need to be state-prepared to σ+(+|µ′B/h|) σ (+|µ′ / |) the magnetically insensitive |F = 1,mF = 0i ground state by Me=-1 a combination of optical pumping beams 1 and 2, which are 0 0 M tuned to F = 2 → F = 2 allowed transition and F = 1 → F = e=0 Position ± 0 in σ transitions (linear polarization orthogonal to the mag- Fig. 2. Arrangement for the LVIS along the cold atom beam. The hor- netic field), respectively. In addition, a constant magnetic bias izontal axis represents the laser frequency seen by an atom at rest in field is applied throughout the length of the second chamber to the center of the trap. The pushing beam and its retro-reflected beam are elliptical, and it can also be seen as the composition of σ + and σ − define a quantization axis, horizontally in the direction of the transition. Both of the cooling beams along the cold atomic beam can Raman beams, with a four-conductor magnetic field assembly work with both of the Me = +1 and Me = −1. running inside the vacuum chamber (not shown in Fig.1). Equation (2) is based on a pure σ + −σ − transition, which corresponds to right circularly polarized pushing beam. When 3. Numerical simulation rotating the λ/4 wave plate denoted as QWP2 in Fig.1, the po- A numerical simulation based on the Monte Carlo method larization of the pushing beam can be changed to be elliptical. is carried out to model the atomic beam characteristics in a Considering the x linearly polarized wave of initial Jones vec- et al.[33] Ax 1 similar approach used by Chaudhuri The simulation tor with expansions in linearly polarized basis J0 = [ Ay ] = [ 0 ], considers motion equations of atoms, which are captured from the final Jones vector of the light wave J after passing through 113703-3 Chin. Phys. B Vol. 26, No. 11 (2017) 113703 the λ/4 wave plate with its fast axis along an arbitrary direc- 3D MOT with 1000 atoms tion at an angle θ 0 with the x axis given with expansions in 0.10 circularly polarized basis: 0.06 AR J = z S AL 0.02 1 cos2 θ 0 − cosθ 0 sinθ 0 + j(sin2 θ 0 − cosθ 0 sinθ 0) = √ , (4) -0.02 2 cos2 θ 0 + cosθ 0 sinθ 0 + j(sin2 θ 0 + cosθ 0 sinθ 0) where AR and AL are right and left circularly polarized compo- S nents, respectively. Thus, the intensity component of the right y Sx circularly polarized light IR with respect to the total intensity Fig. 3. Simulated trajectories of 1000 atoms captured in the vapor cell I of the light is given by 3D MOT and transferred to an atomic beam (length in meters).
2 0 IR |AR| 1 − sin2θ 2 4. Results and discussion = 2 2 = = cos θ, (5) I |AR| + |AL| 2 We simulate numerically and measure experimentally 0 where θ ≡ θ − π/4. θ = 0 corresponds to right circularly various beam characteristics of atoms, especially the atomic + polarized light which means pure σ transition in our case. beam flux and longitudinal velocity as functions of the cool- Combining Eq. (2) with Eq. (5) and ignoring the influence of ing beam detuning or the pushing beam polarization. One − + σ − σ transition pairs, the scattering force along the longi- simulated velocity distribution of an atomic beam extracted tudinal axis becomes Eq. (5) from the LVIS and the corresponding experimental result are 2 shown in Fig.4. The simulated mean longitudinal veloc- σ ± hk¯ Γ cos θs Fscatt = ± 2 2 . (6) 2 1 + cos θs + (2δ±/Γ ) ity is 7.3 m/s with a distribution of 3 m/s in full width at half maximum (FWHM), compared to the experimental mean Equation (6) is the basis for numerical simulation of the longitudinal velocity of 12 m/s with an FWHM of 3.5 m/s. LVIS source. Initial positions of atoms are chosen randomly Generally, atom numbers with low longitudinal velocity in the from the 3D cooling chamber. Initial velocities are chosen experiments will be underestimated compared to those in the according to the Maxwell–Boltzmann distribution at 300 K simulation because atoms with low longitudinal velocity tend using the Monte Carlo method. Trajectories of atoms are to fall down under the action of gravity before they reach the numerically simulated in the presence of velocity-dependent forces imparted by four transverse cooling laser beams and a pair of longitudinal cooling beams with a dark column along 800 (a) the velocity distribution in simulation the atomic beam axis, and position-dependent forces induced Gauss fit of the velocity distribution by a quadrupole magnetic field produced by anti-Helmholtz 600 coils. All laser beams are chosen to have Gaussian intensity 400 profiles truncated to the size of AR-coated windows of the chamber along with appropriate polarizations and directions 200 for magneto-optical trapping. We ignore the heating due to numbers/a.u. Atom spontaneous emission and dipole forces on atoms since these 0 0 4 8 12 16 20 24 effects on atomic motions are much smaller than radiation Velocity/mSs-1 pressure forces. Collisional losses due to collisions with back- 7 (b) ground rubidium atoms and cold collisions between atoms in 6 the cold atomic beam are also ignored. When moving into the 5 dark column region, an atom is acted by transverse cooling 4 atoms/m) light beams and only the pushing light beam in the +z direc- 7 tion, which creates a radiation imbalance in that region. 3 Starting with an initial sample of 1×107 atoms, we com- 2 Flux/(10 pute their individual trajectories and obtain the fraction of 1 atoms being captured and transferred into the atomic beam. 0 4 8 12 16 20 24 28 Trajectories of 1000 atoms calculated by a 3D numerical sim- Velocity/mSs-1 ulation are shown in Fig.3. To calculate the atomic beam flux, Fig. 4. (color online) (a) Numerical result of the longitudinal velocity the initial atom number are scaled up according to the rubid- distribution of an atomic beam, the mean velocity is 7.3 m/s with an FWHM of 3 m/s. (b) The corresponding experimental result, and the ium vapor pressure in the 3D cooling chamber. mean velocity is 12 m/s with an FWHM of 3.5 m/s. 113703-4 Chin. Phys. B Vol. 26, No. 11 (2017) 113703 detection region at a distance of 0.7 m from the ejection hole tivity of 8.3×107 (atoms/s)/rad, compared to the experimental and have not been counted in the experiment. Therefore, the results with a mean sensitivity of 1.2×109 (atoms/s)/rad. This longitudinal velocity distribution in the simulation will totally can be explained by considering the influence of gravity when move towards the lower side compared to that in the exper- low-velocity atoms fly through a long distance and fall down iment under the same conditions. Numerical results show a before they reached the detection region and hence cannot be qualitative agreement with experimental results, but are help- measured in the experiments. Experimental and numerical re- ful to understand the mechanism for tuning the beam charac- sults show that changing the push beam polarization can be teristics. an effective method to tune the velocity and flux of an LVIS atomic beam source. 22 The variation of atomic beam characteristics is also stud- -1 experiment s (a) S 20 simulation ied as a function of frequency detuning of the transverse cool- 18 ing laser. Experimental and numerical data are shown in
16 Fig.6. The change in the mean longitudinal velocity is about 1.1 m/s when the transverse cooling detuning is changed by 14 1Γ , as shown in Fig. 6(a), and the corresponding atomic beam 12 flux is changed and has the maximum flux when the detuning 10 is −4Γ . Although changing the frequency detuning of trans- 8 verse cooling beams is also an effective method for tuning the
Mean longitudinal velocity/m longitudinal Mean [47] 6 velocity and flux of the LVIS beam, but in some cases it is -4 -2 0 2 4 Polarization of the pushing beam/(π/16 rad) not convenient to adjust the frequency of a cooling beam with- out the power fluctuation of the cooling beam, for example experiment when using a single pass AOM for tuning the light frequency. 4.0 (b) simulation
24 (a) experiment
-1 atoms/s)
3.0 s 8 S simulation 20 2.0 16 1.0 12
0 Atomic beam flux/(10 beam Atomic 8 -4 -2 0 2 4 Polarization of the pushing beam/(π/16 rad)
Mean longitudinal velocity/m longitudinal Mean 4 Fig. 5. (color online) Experimental and simulation data showing the depen- -8 -6 -4 -2 0 dence of atomic beam characteristics on polarization of the pushing beam. (a) Mean longitudinal velocity versus polarization of the pushing beam. (b) Detuning of the transverse cooling beam, δ/Γ Atomic flux versus polarization of the pushing beam. The black rectangles are the experimental results and the red circles the numerical results. The hor- izontal axis represents the polarization angle of the pushing beam in the unit 4.0 (b) experiment + simulation of π/16 rad and with the zero angle corresponding to a pure σ transition. 3.5
atoms/s) 3.0 Atomic beam characteristics generated in the LVIS are 8 2.5 studied with respect to variation of the pushing beam polar- ization by rotating the quarter-wave plate QWP2. Experimen- 2.0 tal and simulation results are shown in Fig.5. Here, the zero 1.5 polarization angle of the pushing beam is corresponding to a 1.0 pure σ + transition. Data are measured and numerically calcu- 0.5
Atomic beam flux/(10 beam Atomic 0 lated when QWP2 is rotated every π/16 rad within the range -8 -6 -4 -2 0 of ±π/4 rad. The mean longitudinal velocity of the atomic Detuning of the transverse cooling beam, δ/Γ beam is sensitive to the variation of polarization of the push- Fig. 6. (color online) Experimental and simulation data showing the ing beam both in experiments and simulations. The maximum dependence of atomic beam characteristics on the transverse cooling sensitivity of the mean longitudinal velocity with respect to the beams detuning. (a) Mean longitudinal velocity versus detuning. (b) Atomic beam flux versus detuning. The black rectangles and red circles polarization angle can be up to 20 (m/s)/rad. However, the cor- are the experimental and numerical results respectively. The horizontal responding simulated atomic beam flux show a weaker depen- axis represents the frequency detuning of the transverse cooling laser dence on the polarization of the push beam with a mean sensi- in the unit of the dimensionless parameter δ/Γ , referred to the natural linewidth of the 87Rb atomic transition. 113703-5 Chin. Phys. B Vol. 26, No. 11 (2017) 113703
Transverse velocity spread is measured by the Doppler- (a) sensitive Raman transition spectrum. The Doppler-sensitive 6 Raman transition spectra driven by the first π/2 Raman pulse 4 by blocking the Raman beam 2 shown in Fig.1. The velocity- sensitive Raman transition spectrum is shown in Fig.7. The 2 transverse velocity spread of the atomic beam is approxi- mately ± 6.5 cm/s (FWHM), which can be estimated from 0 Eq. (1) with the ∼ 336 kHz linewidth of velocity-sensitive Ra- man transition. This corresponds to the transverse temperature -4 -2 0 2 4 Raman-Ramsey fringe/arb. units fringe/arb. Raman-Ramsey Raman detuning/kHz of 177 µK (Doppler cooling limit is 142 µK and 11.8 cm/s for 87Rb atoms) and the divergence of 8.6 mrad. Here the longitu- (b) dinal velocity of the atomic beam is v = 15.0 m/s and the lon- z0 1.4 gitudinal velocity spread is δvz = 3.5 m/s. Doppler-insensitive Raman transitions are driven by residual co-propagating Ra- 1.2 man lasers, and are shifted from the peaks by tilting the Raman beams from the orthogonal propagation. 1.0
2.0 0.8 residual Dopplerinsensitive units fringe/arb. Raman-Ramsey -4 -2 0 2 4 Raman transition Raman detuning/kHz 1.5 Fig. 8. (color online) (a) Raman–Ramsey fringes with a linewidth of 395 Hz (FWHM) for the central fringe and corresponding free evolution time of 1.3 m/s when the longitudinal mean velocity of the cold atomic 1.0 FWHM beam is 15 m/s. (b) The Raman–Ramsey fringes with a linewidth of 13 cm/s 500 Hz (FWHM) for the central fringe and corresponding free evolu- tion time of 1.0 m/s when the longitudinal mean velocity of the cold 0.5 atomic beam is 19 m/s. sensitive Raman transition/V Raman sensitive
0 5. Conclusion -20 -10 0 10 20
Doppler Transverse velocity/cmSs-1 In conclusion, we study experimentally and numerically Fig. 7. (color online) Doppler-sensitive Raman transition spectrum for the quantitative dependence of an LVIS of atomic beam on measuring transverse velocity spread. the polarization of the pushing light beam. Results show that the pushing light polarization is an important factor to in- fluence the flux and velocity of an LVIS atomic beam, with The tunability of the velocity and flux of a continuous maximum sensitivity with respect to the polarization angle of LVIS atomic beam are demonstrated in a Raman–Ramsey 1.2 × 109 (atoms/s)/rad and 20 (m/s)/rad, respectively. For atomic interferometer by changing the polarization of the an atom interferometer rotating at an angular velocity Ω, the pushing beam. With the π/2–π/2 pulse sequence, we ob- 2 phase shift can be written as ∆Φ = 푘eff ·[(2푣 ×훺)T ], where tain the Raman–Ramsey fringes with an interaction-zone sep- Ω 푣 and T are the initial velocity of atoms and interference time, aration of L = 19 mm and an interaction-zone width of d = respectively. The scale factor and its stability of an atom in- 1 mm. The Raman–Ramsey fringes with different longitu- terferometer gyroscope are dependent on the initial velocity dinal velocity of the atomic beam are shown in Fig.8. As of atoms and its stability, respectively. For an atom inter- shown in Fig. 8(a), the linewidth of the central fringe is ferometer gyroscope based on an LVIS of atomic beam, the δRamsey = vp/(2L) = 395 Hz, corresponding to an interroga- pushing light polarization instability can contribute a lot to tion time of 1.3 ms, where the longitudinal mean velocity is the phase noise of the interferometer and active stabilization 15 m/s. The fourth order of the interference fringe, where on it should be implemented. Take for example an atomic n = vp/∆v = 4, can be clearly identified against the veloc- beam interferometer gyroscope using two-photon Raman tran- ity averaging effect.[52] As shown in Fig. 8(b), the Ramsey sition for coherent manipulation of the matter-wave packet, fringes with a linewidth of 500 Hz (FWHM) for the central the shot-noise-limited rotation sensitivity ∆Ω near zero rota- [53] √ v fringe is observed when the longitudinal mean velocity of the tion rate Ω = 0 can be given as ∆Ω = 2 , where η 2NkeffL cold atomic beam is adjusted to vp = 19 m/s. Correspondingly, v is the mean longitudinal velocity, η the contrast of the in- the free evolution time of the cold atomic beam is T = 1.0 ms. terferometer signal, N the number of atoms contributing to 113703-6 Chin. Phys. B Vol. 26, No. 11 (2017) 113703 the interferometer signal, L = vT the interferometer length. [16] Yang W, Sun D L, Zhou L, Wang J and Zhan M S 2014 Acta Phys. Sin. For a typical cold atomic beam interferometer gyroscope (tak- 63 153701 (in Chinese) [17] Ertmer W, Blatt R, Hall J L and Zhu M 1985 Phys. Rev. Lett. 54 996 8 ing N = 1 × 10 atoms/s, η = 50%, L = 0.3 m, v = 20 m/s, [18] Truppe S, Williams H J, Fitch N J, Hambach M, Wall T E, Hinds E A, k = 1.6 × 107 m−1 for 87Rb atoms), the shot-noise-limited Sauer B E and Tarbutt M R 2017 New J. Phys. 19 022001 eff √ . × −9 [19] Ketterle W, Martin A, Joffe M A and Pritchard D E 1992 Phys. Rev. sensitivity of rotation is 1 95 10 rad/s/ Hz and the fluc- Lett. 69 2483 tuation of sensitivity due to the velocity variation of each [20] Zhu M, Oates C W and Hall J L 1991 Phys. Rev. Lett. 67 46 10% or the flux variation of each 10% can be calculated to [21] Riis E, Weiss D S, Moler K A and Chu S 1990 Phys. Rev. Lett. 64 1658 √ √ −10 −11 [22] Swanson T B, Silva N J, Mayer S K, Maki J J and McIntyre D H 1996 1.95 × 10 rad/s/ Hz or 9.8 × 10 rad/s/ Hz, respec- J. Opt. Soc. Am. B 13 1833 tively. [23] Weyers S, Aucouturier E, Valentin C and Dimarcq N 1997 Opt. Com- Although we have demonstrated that the pushing beam mun. 143 30 [24] Schoser J, Batr A, Lw R, Schweikhard V, Grabowski A, Ovchinnikov polarization is one of the important factors that influence the Y B and Pfau T 2002 Phys. Rev. A 66 023410 characteristics of an LVIS of an atomic beam, the improve- [25] Wang X L, Cheng B, Wu B, Wang Z Y and Lin Q 2011 Chin. Phys. Lett. 28 053701 ment of the stability of an LVIS of atomic beam depends on [26] Dieckmann K, Spreeuw R J C, Weidemller M and Walraven J T M the systematic optimization involving many experimental pa- 1998 Phys. Rev. A 58 3891 rameters like light intensity, frequency detuning, etc. Con- [27] Conroy R S, Xiao Y, Vengalattore M, Rooijakkers W and Prentiss M 2003 Opt. Commun. 226 259 cerned with the pushing beam polarization, one can make the [28] Ovchinnikov Y B 2005 Opt. Commun. 249 473 LVIS source operate in the polarization-insensitive range or [29] Catani J, Maioli P, De Sarlo L, Minardi F and Inguscio M 2006 Phys. take some active method for stabilizing the polarization. On Rev. A 73 033415 [30] Ramirez-Serrano J, Yu N, Kohel J M, Kellogg J R and Maleki L 2006 the other hand, one can fast tune the velocity and flux of an Opt. Lett. 31 682 LVIS-based atomic beam by simply changing the polarization [31] Kellogg J R, Schlippert D, Kohel J M, Thompson R J, Aveline D C and Yu N 2012 Appl. Phys. B 109 61 of the pushing light for actively stabilizing the atomic beam [32] Rathod K D, Singh A K and Natarajan V 2013 EPL 102 43001 source or amplitude modulating and demodulating the phase [33] Chanu S R, Rathod K D and Natarajan V 2016 Phys. Lett. A 380 2943 of an atomic beam interferometer to get interferometer signal [34] Chaudhuri S, Roy S and Unnikrishnan C S 2006 Phys. Rev. A 74 023406 with higher signal-to-noise ratio. [35] Fang J, Qi L, Zhang Y, Wang T, Li H, Hu Z and Quan W 2015 J. Opt. Soc. Am. B 32 B61 [36] Park S J, Noh J and Mun J 2012 Opt. Commun. 285 3950 Acknowledgment [37] Pruvost L, Marescaux D, Houde O and Duong H T 1999 Opt. Commun. The authors thank Jiaqiang Huang, Chi Xu, and Lijun 166 199 [38] Carrat V, Cabrera-Gutirrez C, Jacquey M, Tabosa J W, de Lesegno B V Wang for helpful discussion. and Pruvost L 2014 Opt. Lett. 39 719 [39] Huang J Q, Yan X S, Wu C F, Zhang J W and Wang L J 2016 Chin. Phys. B 25 063701 References [40] Lu Z T, Corwin K L, Renn M J, Anderson M H, Cornell E A and Wie- [1] Phillips W D and Metcalf H 1982 Phys. Rev. Lett. 48 596 man C E 1996 Phys. Rev. Lett. 77 3331 [2] Wineland D J, Itano W M, Bergquist J C and Hulet R G 1987 Phys. 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113703-7 Chinese Physics B
Volume 26 Number 11 November 2017
TOPICAL REVIEW — ZnO-related materials and devices 117101 The p-type ZnO thin films obtained by a reversed substitution doping method of thermal oxidation of
Zn3N2 precursors Bing-Sheng Li, Zhi-Yan Xiao, Jian-Gang Ma and Yi-Chun Liu 118102 One-dimensional ZnO nanostructure-based optoelectronics Zheng Zhang, Zhuo Kang, Qingliang Liao, Xiaomei Zhang and Yue Zhang
TOPICAL REVIEW — Magnetism, magnetic materials, and interdisciplinary research 117502 Anisotropic nanocomposite soft/hard multilayer magnets Wei Liu and Zhidong Zhang
REVIEW 114302 Review on second-harmonic generation of ultrasonic guided waves in solid media (I): Theoretical analy- ses Wei-Bin Li, Ming-Xi Deng and Yan-Xun Xiang
RAPID COMMUNICATION 113202 Velocity-selective spectroscopy measurements of Rydberg fine structure states in a hot vapor cell Jun He, Dongliang Pei, Jieying Wang and Junmin Wang 117802 Nano-infrared imaging of localized plasmons in graphene nano-resonators Jiahua Duan, Runkun Chen and Jianing Chen
GENERAL 110301 Parallel propagating modes and anomalous spatial damping in the ultra-relativistic electron plasma with arbitrary degeneracy H Farooq, M Sarfraz, Z Iqbal, G Abbas and H A Shah 110302 Simple and practical method of characterizing the parametric down-conversion source Dong Wang, Juan Wu, Liang-Yuan Zhao, Xue-Bi An, Zhen-Qiang Yin, Wei Chen, Zheng-Fu Han and Qin Wang 110303 Quantum coherence preservation of atom with a classical driving field under non-Markovian environ- ment De-Ying Gao, Qiang Gao and Yun-Jie Xia 110304 Balancing four-state continuous-variable quantum key distribution with linear optics cloning machine Xiao-Dong Wu, Qin Liao, Duan Huang, Xiang-Hua Wu and Ying Guo 110305 Performance optimization for quantum key distribution in lossy channel using entangled photons Yu Yang, Luping Xu, Bo Yan, Hongyang Zhang and Yanghe Shen
(Continued on the Bookbinding Inside Back Cover) 110501 Effect of plasma on combustion characteristics of boron Peng Zhang, Wenli Zhong, Qian Li, Bo Yang, Zhongguang Li and Xiao Luan 110502 Multi-scroll hidden attractors and multi-wing hidden attractors in a 5-dimensional memristive system Xiaoyu Hu, Chongxin Liu, Ling Liu, Yapeng Yao and Guangchao Zheng 110503 Free-matrix-based time-dependent discontinuous Lyapunov functional for synchronization of delayed neural networks with sampled-data control Wei Wang, Hong-Bing Zeng and Kok-Lay Teo 110504 Nonlinear density wave and energy consumption investigation of traffic flow on a curved road Zhizhan Jin, Rongjun Cheng and Hongxia Ge 110505 Empirical topological investigation of practical supply chains based on complex networks Hao Liao, Jing Shen, Xing-Tong Wu, Bo-Kui Chen and Mingyang Zhou
ATOMIC AND MOLECULAR PHYSICS 113201 Rubidium-beam microwave clock pumped by distributed feedback diode lasers Chang Liu, Sheng Zhou, Yan-Hui Wang and Shi-Min Hou 113401 Helium nano-bubble bursting near the nickel surface Heng-Feng Gong, Min Liu, Fei Gao, Rui Li, Yan Yan, Heng Huang, Tong Liu and Qi-Sen Ren 113701 Combination of multiple tools for surface manipulation of polar molecules Qiang Wang, Bin Wei, Heng-Jiao Guo, Sheng-Qiang Li, Shun-Yong Hou and Jian-Ping Yin 113702 Deterministic loading of an individual atom: Towards scalable implementation of multi-qubit Jun He, Bei Liu, Jie-Ying Wang, Wen-Ting Diao, Gang Jin and Jun-Min Wang 113703 Tuning the velocity and flux of a low-velocity intense source of cold atomic beam Shu Chen, Ying-Ying Li, Xue-Shu Yan, Hong-Bo Xue and Yan-Ying Feng
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS 114101 An electrically tunable metasurface integrated with graphene for mid-infrared light modulation Zongpeng Wang, Ya Deng and LianFeng Sun 114102 Ultra-broadband and polarization-independent planar absorber based on multilayered graphene Jiao Wang, Chao-Ning Gao, Yan-Nan Jiang and Charles Nwakanma Akwuruoha 114103 Tunable coupling of a hybrid plasmonic waveguide consisting of two identical dielectric cylinders and a silver film Benli Wang, Han Liang and Jiafang Li 114201 Characteristics of photonic nanojets from two-layer dielectric hemisphere Yunyue Liu, Xianchao Liu, Ling Li, Weidong Chen, Yan Chen, Yuerong Huang and Zhengwei Xie 114202 Quantum statistical properties of photon-added spin coherent states G Honarasa 114203 Different influences of u-InGaN upper waveguide on the performance of GaN-based blue and green laser diodes Feng Liang, De-Gang Zhao, De-Sheng Jiang, Zong-Shun Liu, Jian-Jun Zhu, Ping Chen, Jing Yang, Wei Liu, Xiang Li, Shuang-Tao Liu, Yao Xing, Li-Qun Zhang, Mo Li and Jian Zhang
(Continued on the Bookbinding Inside Back Cover) 114204 Low-repetition-rate, all-polarization-maintaining Yb-doped fiber laser mode-locked by a semiconductor saturable absorber Xiao-Sheng Xiao
114205 2-µm mode-locked nanosecond fiber laser based on MoS2 saturable absorber Xiao-Fa Wang, Xiao-Ling Peng, Qiu-Xia Jiang, Xiao-Hui Gu, Jun-Hong Zhang, Xue-Feng Mao and Su-Zhen Yuan 114206 Two-color laser wavelength effect on intense terahertz generation in air Shufen Li, Chenhui Lu, Chengshuai Yang, Yanzhong Yu, Zhenrong Sun and Shian Zhang 114207 A new method of calculating the orbital angular momentum spectra of Laguerre–Gaussian beams in channels with atmospheric turbulence Xiao-zhou Cui, Xiao-li Yin, Huan Chang, Zhi-chao Zhang, Yong-jun Wang and Guo-hua Wu 4 4 3+ 114208 Intensities and spectral features of the I13/2– I15/2 potential laser transition of Er centers in CaF2–
CeF3 disordered crystal Qing-Guo Wang, Liangbi Su, Jun-Fang Liu, Bin Liu, Feng Wu, Ping Luo, Heng-Yu Zhao, Jiao-Jiao Shi, Yan-Yan Xue, Xiao-Dong Xu, Witold Ryba-Romanowski, Piotr Solarz, Radoslaw Lisiecki, Zhan-Shan Wang, Hui-Li Tang and Jun Xu 114209 Photonic crystal fiber polarization filter with two large apertures coated with gold layers Jun-Jun Wu, Shu-Guang Li, Qiang Liu and Min Shi 114210 Angular-modulated spatial distribution of ultrahigh-order modes assisted by random scattering Xue-Fen Kan, Cheng Yin, Tian Xu, Fan Chen, Jian Li, Qing-Bang Han and Xian-Feng Chen 114211 Gamma-radiation effects in pure-silica-core photonic crystal fiber Wei Cai, Ningfang Song, Jing Jin, Jingming Song, Wei Li, Wenyong Luo and Xiaobin Xu 114212 Analysis of proton and γ-ray radiation effects on CMOS active pixel sensors Lindong Ma, Yudong Li, Qi Guo, Lin Wen, Dong Zhou, Jie Feng, Yuan Liu, Junzhe Zeng, Xiang Zhang and Tianhui Wang 114301 Three-dimensional parabolic equation model for seismo-acoustic propagation: Theoretical development and preliminary numerical implementation Jun Tang, Sheng-Chun Piao and Hai-Gang Zhang 114303 Theoretical analysis of interaction between a particle and an oscillating bubble driven by ultrasound waves in liquid Yao-Rong Wu and Cheng-Hui Wang 114304 Broadband acoustic focusing by symmetric Airy beams with phased arrays comprised of different num- bers of cavity structures Jiao Qian, Bo-Yang Liu, Hong-Xiang Sun, Shou-Qi Yuan and Xiao-Zhu Yu 114401 Modified Maxwell model for predicting thermal conductivity of nanocomposites considering aggregation Wen-Kai Zhen, Zi-Zhen Lin and Cong-Liang Huang 114701 Establishment of infinite dimensional Hamiltonian system of multilayer quasi-geostrophic flow & study on its linear stability Si-xun Huang, Yu Wang and Jie Xiang
(Continued on the Bookbinding Inside Back Cover) 114702 Aerodynamic measurement of a large aircraft model in hypersonic flow Bao-Qing Meng, Gui-Lai Han, De-Liang Zhang and Zong-Lin Jiang 114703 Instabilities of thermocapillary–buoyancy convection in open rectangular liquid layers Huan Jiang, Li Duan and Qi Kang
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES 115101 Effect of aperture field distribution on the maximum radiated power at atmospheric pressure Pengcheng Zhao and Lixin Guo 115201 Effect of driving frequency on electron heating in capacitively coupled RF argon glow discharges at low pressure Tagra Samir, Yue Liu, Lu-Lu Zhao and Yan-Wen Zhou 115202 Tunneling dynamics of a few bosons with both two- and three-body interactions in a double-well potential Na-Na Chang, Zi-Fa Yu, Ai-Xia Zhang and Ju-Kui Xue 115203 Toroidal rotation induced by 4.6 GHz lower hybrid current drive on EAST tokamak Xiang-Hui Yin, Jun Chen, Rui-Ji Hu, Ying-Ying Li, Fu-Di Wang, Jia Fu, Bo-Jiang Ding, Mao Wang, Fu-Kun Liu, Qing Zang, Yue-Jiang Shi, Bo Lu,¨ Bao-Nian Wan and EAST team 115204 Acceleration and radiation of externally injected electrons in laser plasma wakefield driven by a Laguerre–Gaussian pulse Zhong-Chen Shen, Min Chen, Guo-Bo Zhang, Ji Luo, Su-Ming Weng, Xiao-Hui Yuan, Feng Liu and Zheng- Ming Sheng 115205 Measurement of iron characteristics under ramp compression H G Wei, E Brambrink, N Amadou, A Benuzzi-Mounaix, A Ravasio, G Morard, F Guyot, T de Resseguier,´ N Ozaki, K Miyanishi, G Zhao and M Koenig
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES 116101 Novel conductance step in carbon nanotube with wing-like zigzag graphene nanoribbons Hong Liu 116102 Slip on the surface of silicon wafers under laser irradiation: Scale effect Zhi-Chao Jia, Ze-Wen Li, Jie Zhou and Xiao-Wu Ni
116103 Ab-initio investigation of 퐴GeO3 (퐴 = Ca, Sr) compounds via Tran Blaha-modified Becke Johnson exchange potential Rasul Bakhsh Behram, M A Iqbal, Muhammad Rashid, M Atif Sattar, Asif Mahmood and Shahid M Ramay
116201 Ce Co-doped BiFeO3 multiferroic for optoelectronic and photovoltaic applications Jyoti Sharma, Deepak Basandrai and A K Srivastava
116202 Exploring the compression behavior of HP-BiNbO4 under high pressure Yin-Juan Liu, Jia-Wei Zhang, Duan-Wei He, Chao Xu, Qi-Wei Hu, Lei Qi and A-Kun Liang 116501 First-principles calculations of structural and thermodynamic properties of β-PbO Vahedeh Razzazi and Sholeh Alaei 116502 High-temperature thermodynamics of silver: Semi-empirical approach R H Joshi, B Y Thakore, P R Vyas, A R Jani and N K Bhatt
(Continued on the Bookbinding Inside Back Cover) 116503 Thermal transport in twisted few-layer graphene Min-Hua Wang, Yue-E Xie and Yuan-Ping Chen 116504 Temperature-induced effect on refractive index of graphene based on coated in-fiber Mach–Zehnder interferometer Li-Jun Li, Shun-Shun Gong, Yi-Lin Liu, Lin Xu, Wen-Xian Li, Qian Ma, Xiao-Zhe Ding and Xiao-Li Guo 116801 Structural characterization of indium-rich nanoprecipitate in InGaN V-pits formed by annealing Junjun Xue, Qing Cai, Baohua Zhang, Mei Ge, Dunjun Chen, Ting Zhi, Jiangwei Chen, Lianhui Wang, Rong Zhang and Youdou Zheng 116802 Formation of high-Sn content polycrystalline GeSn films by pulsed laser annealing on co-sputtered amor- phous GeSn on Ge substrate Lu Zhang, Hai-Yang Hong, Yi-Sen Wang, Cheng Li, Guang-Yang Lin, Song-Yan Chen, Wei Huang and Jian- Yuan Wang 116803 Improvement of sensitivity of graphene photodetector by creating bandgap structure Ni-Zhen Zhang, Meng-Ke He, Peng Yu and Da-Hua Zhou
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTI- CAL PROPERTIES 117001 Enhancement of electroluminescent properties of organic optoelectronic integrated device by doping phosphorescent dye Shu-ying Lei, Jian Zhong, Dian-li Zhou, Fang-yun Zhu and Chao-xu Deng 117201 Uncertainties of clock and shift operators for an electron in one-dimensional nonuniform lattice systems Long-Yan Gong, You-Gen Ding and Yong-Qiang Deng
117202 Biaxial strain-induced enhancement in the thermoelectric performance of monolayer WSe2 Wanhuizi Shen, Daifeng Zou, Guozheng Nie and Ying Xu 117203 Spin transport in a chain of polygonal quantum rings with Dresselhaus spin–orbit coupling Han-Zhao Tang, Xiao-Teng Yao and Jian-Jun Liu 117301 Band structure and edge states of star-like zigzag graphene nanoribbons Hong Liu 117302 Photon-assisted electronic and spin transport through two T-shaped three-quantum-dot molecules em- bedded in an Aharonov–Bohm interferometer Jiyuan Bai, Li Li, Zelong He, Shujiang Ye, Shujun Zhao, Suihu Dang and Weimin Sun 117401 Fluctuating specific heat in two-band superconductors Lei Qiao, Cheng Chi and Jiangfan Wang
117501 Observation of giant magnetocaloric effect under low magnetic fields in EuTi1−xCoxO3 Qi-Lei Sun, Zhao-Jun Mo, Jun Shen, Yu-Jin Li, Lan Li, Jun-Kai Zhang, Guo-Dong Liu, Cheng-Chun Tang and Fan-Bin Meng 117503 Effects of dipolar interactions on magnetic properties of Co nanowire arrays Hong-Jian Li, MingYue, Qiong Wu, Yi Peng, Yu-Qing Li, Wei-Qiang Liu, Dong-Tao Zhang and Jiu-Xing Zhang
(Continued on the Bookbinding Inside Back Cover) 117701 On the parameters for electrocaloric effect predicted by indirect method Hong-Bo Liu 117801 Resonant magneto–optical Kerr effect induced by hybrid plasma modes in ferromagnetic nanovoids Xia Zhang, Lei Shi, Jing Li, Yun-Jie Xia and Shi-Ming Zhou
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
118101 Effects of Al particles and thin layer on thermal expansion and conductivity of Al–Y2Mo3O12 cermets Xian-Sheng Liu, Xiang-Hong Ge, Er-Jun Liang and Wei-Feng Zhang
118103 An easy way to controllably synthesize one-dimensional SmB6 topological insulator nanostructures and exploration of their field emission applications Xun Yang, Hai-Bo Gan, Yan Tian, Ning-Sheng Xu, Shao-Zhi Deng, Jun Chen, Huanjun Chen, Shi-Dong Liang and Fei Liu 118104 Improvement of laser damage thresholds of fused silica by ultrasonic-assisted hydrofluoric acid etching Yuan Li, Hongwei Yan, Ke Yang, Caizhen Yao, Zhiqiang Wang, Chunyan Yan, Xinshu Zou, Xiaodong Yuan, Liming Yang and Xin Ju 118401 Sampled-data modeling and dynamical effect of output-capacitor time-constant for valley voltage-mode controlled buck-boost converter Shu-Han Zhou, Guo-Hua Zhou, Shao-Huan Zeng, Min-Rui Leng and Shun-Gang Xu 118501 A phenomenological memristor model for synaptic memory and learning behaviors Nan Shao, Sheng-Bing Zhang and Shu-Yuan Shao 118502 An improved memristor model for brain-inspired computing Errui Zhou, Liang Fang, Rulin Liu and Zhenseng Tang 118503 Luminescent properties of thermally activated delayed fluorescence molecule with intramolecular π–π interaction between donor and acceptor Lei Cai, Jianzhong Fan, Xiangpeng Kong, Lili Lin and Chuan-Kui Wang 118701 Improved simultaneous multislice magnetic resonance imaging using total variation regularization Ya-Jun Ma, Sha Li and Song Gao 118702 Wavelet optimization for applying continuous wavelet transform to maternal electrocardiogram compo- nent enhancing Qiong Yu, Qun Guan, Ping Li, Tie-Bing Liu, Jun-Feng Si, Ying Zhao, Hong-Xing Liu and Yuan-Qing Wang
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS 119201 Image of local energy anomaly during a heavy rainfall event Shuai Yang, Qunjie Zuo and Shouting Gao
RETRACTION 113301 Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis Zhi-Chao Ding, Jie Yuan, Hui Luo and Xing-Wu Long