Guangjiong Dong

East China Normal University, Shanghai, Shanghai Shi, China

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Publications (11)23.14 Total impact

  • Yongkai Zhao, Weiping Lu, P. F. Barker, Guangjiong Dong
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    ABSTRACT: We study optical cooling of a large ensemble of particles. We derive a new scaling law with respect to particle number and show a high density molecular cloud are cooled from 10 mK to 700 muK.
    01/2009;
  • Yongkai Zhao, Weiping Lu, P F Barker, Guangjiong Dong
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    ABSTRACT: We present an investigation of the dynamics of centre-of-mass of a neutral particle cloud in a cavity pumped by an optical field. We derive an expression for the pump threshold for spatial self-organization of the particles and analyze its scaling laws in terms of the system parameters. Using a newly developed statistical model, we simulate the dynamics of the particles and numerically obtain the scaling laws. We show good agreement between the analytic formulae and simulations. We further use the scaling relation to discuss the operating conditions for cavity cooling a large ensemble of particles. Finally, we study cavity cooling of an ensemble of molecules with an initial temperature of around 10 mK. We show that 35% of the molecules are trapped by the optical field intensity in the cavity and a final temperature below 1 mK is reached.
    Faraday Discussions 01/2009; 142:311-8; discussion 319-34. · 3.82 Impact Factor
  • Guangjiong Dong, Bambi Hu
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    ABSTRACT: We investigate the effect of the position-dependent s-wave scattering length (SSL) on Bose-Einstein condensate (BEC) dynamics. In particular, we study the propagation of a BEC within a finite regime where the SSL, tuned by a periodic magnetic or optical field, results in the Bragg scattering of the BEC. We have predicted a matter-wave optical limiting process and bistability, which have potential applications like a matter wave limiter, a BEC mirror or cavity, and an atomic switch. The first phenomenon is a direct result of this periodic spatial tuning, showing that the position-dependent tuning of the SSL has the potential to result in novel properties of ultracold atomic gases.
    Physical Review A 01/2007; 75(1). · 3.04 Impact Factor
  • Guangjiong Dong, Bambi Hu, Weiping Lu
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    ABSTRACT: In this paper, we explore a scheme to tackle a challenging problem of stable Bose-Einstein condensates (BECs) with attractive atom interactions. In this scheme, the s-wave scattering length is tuned in space, rather than in time as previously studied, by a far-off-resonant Gaussian optical field, from negative to positive in the center region of the potential well. We find that this tuning leads to coexisting repulsive and attractive interactions within a single atomic gas and consequently a stable BEC in the repulsive region. We investigate the ground-state properties of the tuned BECs and show them to exhibit a strikingly different spatial density distribution from a conventional one with a positive s-wave scattering length. The tuned BEC is formed only when the condensed number is less than a critical number. We derive a formula for the critical number.
    Physical Review A 01/2006; 74(6). · 3.04 Impact Factor
  • Guangjiong Dong, Bambi Hu
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    ABSTRACT: We have studied the propagation of coherent light through a passive optical power limiter (OPL) consisting of two alternating layers with different linear and nonlinear refractive indices. We have obtained general formulas for the transmittance and the optical limiting output power.
    Physica D Nonlinear Phenomena 01/2006; 216(1):90-94. · 1.67 Impact Factor
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    ABSTRACT: A matter wave mirror using a single, pulsed, super-Gaussian (SG) optical beam for specular reflection of neutral ground-state molecules is studied. The mirror has a high reflectivity close to 100% and nearly perfect specular reflection over a large incident angle. This mirror avoids the usual problems due to surface roughness and the van der Waals interactions that occur in conventional atomic mirrors. Further, it is capable of reflectance and transmittance with applications to velocity filtering and deceleration of cold molecules.
    Physical Review A 01/2005; 72(3). · 3.04 Impact Factor
  • Guangjiong Dong, Weiping Lu, P.F. Barker, M.N. Shneider
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    ABSTRACT: We review recent theoretical studies on the dynamics of molecules in pulsed optical lattices. These lattices are periodic potential wells formed by the interaction between two counter propagating far-off resonant optical fields and the molecules. We show that the molecules can be manipulated in both constant velocity and accelerating lattices for a number of applications. We first study a molecular optical mirror through the reflections of molecules by a stationary optical lattice and show that the reflectivity can be significantly improved by optimizing the pulse duration. When reflection occurs from a moving lattice, we show that molecules can brought to rest when the lattice velocity is half the molecular velocity, demonstrating a new and efficient method for creating slow cold molecules. We further describe a microlinear accelerator for molecules produced by an accelerating optical lattice, which is achieved by frequency chirping one of the two optical fields. The molecules trapped by the potential wells of the lattice are accelerated to high velocities (10–100 km/s) over micron-size distance within nanosecond time scales. When the lattice is decelerated, the trapped molecules can be slowed to zero velocity, offering an alternate method for producing slow cold molecules. Molecules that are not trapped in the accelerating lattice can be temporarily localized around a characteristic velocity, which is uniquely dependent on the mass-to-polarizability ratio. We show that this feature can be used for a new form of time-of-flight mass spectrometry for chemical analysis of a mixture.
    Progress in Quantum Electronics. 01/2005;
  • Guangjiong Dong, Weiping Lu, P. F. Barker
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    ABSTRACT: We investigate the deceleration and bunching of cold molecules in a pulsed supersonic jet using a far-off-resonant optical lattice traveling with a constant velocity. Using an analytical treatment, we show that by choosing the lattice velocity equal to half the supersonic beam velocity and by optimizing the pulse duration, a significant fraction (∼33%) of translationally cold (1 K) CO molecules from a supersonic molecular beam can be decelerated to zero velocity, and simultaneously bunched in velocity space. Due to the large difference of polarizability to mass ratio between the buffer gas and the CO molecules in the pulsed jet, the buffer gas can be precluded from the fraction of stationary molecules by choosing a suitable pulse duration. Furthermore, we find that spatial bunching within the optical lattice is induced and the position of the bunch within the lattice can be chosen by varying the lattice velocity.
    Physical Review A 01/2004; 69(1). · 3.04 Impact Factor
  • Guangjiong Dong, Weiping Lu, P F Barker
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    ABSTRACT: We present an analytical solution to the collisionless Boltzmann equation for describing the distribution function of molecular ensembles subject to an external periodic traveling force of pulsed optical fields. We apply our solution to study a pulsed standing wave mirror for neutral molecules, recently proposed [P. Ryytty et al., Phys. Rev. Lett. 84, 5074 (2000)]. Using our analytical solution we study the effects of the anharmonicity of optical potential on the reflectivity of the molecular mirror and the corresponding optimal pulse duration. We demonstrate that the reflectivity of the molecular mirror can be significantly improved by optimizing the pulse duration of the external optical fields when taking into account the anharmonicity of molecular motion.
    Physical Review E 08/2003; 68(1 Pt 2):016607. · 2.31 Impact Factor
  • Guangjiong Dong, Weiping Lu, P. F. Barker
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    ABSTRACT: We investigate the dynamics of untrapped molecules within a far-off resonant accelerating optical lattice. Our analysis shows that untrapped molecules can be temporarily transported by the lattice, and those that are transported for the longest time reach a unique, well-defined critical velocity that depends on the mass to polarizability ratio of the molecular species. We show that this species-dependent critical velocity leads to a velocity dispersion for different species within a gas mixture. Our numerical simulations show that the velocity distribution of a multicomponent gas evolves to form well-separated peaks in velocity space for each species. We propose a time-of-flight analysis technique that transforms the velocity dispersion to a temporal separation of different species, even for small differences in the mass to polarizability ratio. Separation utilizing this concept is demonstrated for atmospheric species and isotopes of nitrogen. Finally, we present an extension of this concept for both temporal and angular dispersion. © 2003 American Institute of Physics.
    The Journal of Chemical Physics 01/2003; 118(4):1729-1734. · 3.16 Impact Factor
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    ABSTRACT: This work presents the proposed schemes for decelerating cold molecules created in pulsed supersonic expansions using pulsed optical lattices. The first scheme relies on the application of a decelerating optical lattice with a dipole-potential well depth of approximately 1 K, created by rapidly chirping medium-intensity fields in the 10 W/cm2 range. This scheme is an optical analog of the Start decelerator that has been successfully used to slow a range of polar molecules. A significant fraction (about 10%) of the very heavy I2 molecules in an Ar buffer gas is shown to be slowed by using this method over sub-microsecond time scales. In the second technique, an optical lattice with larger well depth in the 100 K range travelling at half the supersonic beam velocity is used to trap a significant fraction of the cold, high-velocity molecules. This technique is developed based on the property of periodic motion of the trapped molecules in the optical lattice; the molecules reverse their initial (relative) velocities in the lattice reference frame after half a period. Using this method the cold molecules can be transferred from high speed to zero velocity on nanosecond time scales. As an example, 33% of a CO molecule beam (1 K) with a velocity of 230 m/s is slowed utilising optical intensities of less than 1012 W/cm2.
    01/2003;

Publication Stats

82 Citations
23.14 Total Impact Points

Institutions

  • 2009
    • East China Normal University
      • State Key Laboratory of Precision Spectroscopy
      Shanghai, Shanghai Shi, China
  • 2003–2009
    • Heriot-Watt University
      • Department of Physics
      Edinburgh, SCT, United Kingdom
  • 2006
    • Hong Kong Baptist University
      • Department of Physics
      Chiu-lung, Kowloon City, Hong Kong
  • 2005
    • Mid Sweden University
      Härnösand, Västernorrland, Sweden