Abstract We propose a tightly focused hollow beam to trap cold molecules by using a metasurface grating, which has a hybrid phase with focusing and completely destructive interference functions. The intensity distributions of the hollow beam in free space concerning different structural parameters of the grating are theoretically studied in detail. The influences of both the discrete and continuous phases of the grating on the intensity distribution of the modulated optical field are compared. Our theoretical study shows that such a blue-detuned beam can provide a deep potential to trap cold molecules with a low photon scattering rate and a long trap lifetime. Our studies suggest that the metasurface-based optical chip is applicable to trap molecules and can be an ideal platform for building a robust quantum laboratory.
Abstract We propose a tightly focused hollow beam to trap cold molecules by using a metasurface grating, which has a hybrid phase with focusing and completely destructive interference functions. The intensity distributions of the hollow beam in free space concerning different structural parameters of the grating are theoretically studied in detail. The influences of both the discrete and continuous phases of the grating on the intensity distribution of the modulated optical field are compared. Our theoretical study shows that such a blue-detuned beam can provide a deep potential to trap cold molecules with a low photon scattering rate and a long trap lifetime. Our studies suggest that the metasurface-based optical chip is applicable to trap molecules and can be an ideal platform for building a robust quantum laboratory.
A scheme for storage of cold molecules in a hollow optical ring generated by a metasurface grating is proposed. The characteristics and intensity distribution related to the ring’s structural parameters and fabrication error tolerance are theoretically studied. The optical potential and dipole force required for the ring to trap magnesium monofluoride (MgF) molecules are also calculated. The dynamic behavior of MgF molecules in the storage ring is simulated by a Monte Carlo method, which shows that a metasurface-based optical storage ring can be used to trap molecules and is an interesting platform for research into ultracold quantum gases and their quantum-state manipulation.
We propose a new scheme to guide cold atoms (or molecules) by using a one-dimensional (1D) array of focused hollow-beam pipes generated by the combination of a binary phase grating and a 1D array of micro-cylindrical lenses on the substrate surface. We also calculate the intensity distribution of the focused hollow-beam pipe array and its optical potential for 85 Rb atoms. The result shows that when the blue detuning of the incident beam and its intensity are 10 GHz and 7.0×10 3 W/m 2 respectively, the horizontal dark spot size of each focused hollow-beam pipe and the efficient optical potential are 4.4 μm and ~0.23 mK, which is high enough to guide cold 85 Rb atoms (~20 μK) from a standard optical molasses and then to realize the 1D array of surface atomic waveguides on an atom chip.
An enhanced or improved far-field-diffracted optical dipole trap with a red or blue detuning for cold atoms or molecules on an optical chip is proposed, and our trap scheme is formed by an optical system composed of a binary phase plate and a circular aperture illuminated by a plane light wave. The relative radial and axial intensity distributions of the far-field optical trap and its optical potentials for 87Rb atoms are calculated, and the dependences of the relative intensity of the far-field optical trap and its well depth on the modulated phase φ of the phase plate are studied. Also, the feasibility of our enhanced far-field optical trap is analyzed, and some potential applications of our optical trap are briefly discussed. Our research shows that some geometric and optical parameters of the far-field optical trap can be greatly improved, and the evolution of the far-field optical trap from a red-detuned optical trap to a blue-detuned one can be realized by using our proposed binary phase plate. Particularly, with the change of the modulated phase φ from 0 to −π, the maximum intensity (i.e., the well depth) of the far-field optical trap and its trapping volume will be increased by about four and eight times, respectively. While the modulated phase φ of the phase plate is changed from 0 to π, a red-detuned optical trap will be evolved as a blue-detuned one, and the corresponding trapping intensity and volume will be enhanced by about 4 times. So such an enhanced far-field optical trap scheme has some important applications in the fields of laser cooling and trapping; atomic, molecular, and optical physics; integrated atom or molecule optics; quantum information science; and so on.
We propose a new scheme to form 1D or 2D arrays of hollow optical microtraps for cold atoms, molecules, or microscopy particles on a chip by using an optical system composed of a four-step phase grating and a 2D array of microlenses. We calculate the intensity distribution of the 2D array of the hollow optical microtraps and its optical potential for 85Rb atoms and discuss its potential applications in atom and molecule optics. Our study shows that when our optical system is illuminated by a 1 W Ti:Sapphire laser, 103 hollow optical microtraps can be generated. Each optical microtrap has a small trapping volume and a high effective intensity, and its intensity gradient and the optical dipole potential for 85Rb atoms can reach 167 μK. Characteristic parameters of each optical microtrap can be changed by adjusting the parameters of our optical system, which can be used to satisfy real needs of various experiments to manipulate and control cold atoms, molecules, or microscopy particles.
We report the generation of a crossed, focused, optical vortex beam by using a pair of hybrid holograms, which combine the vortex phase and lens phase onto a spatial light modulator. We study the intensity distributions of the vortex beam in free propagation space, and the relationship of its dark spot size with the incident Gaussian beam’s waist, the lens’s focal length, and its orbital angular momentum. Our results show that the crossed, focused, vortex beam’s dark spot size can be as small as 16.3 μm and adjustable by the quantum number of the orbital angular momentum, and can be used to increase the density of trapped molecules. Furthermore, we calculate the optical potential of the blue-detuned, crossed vortex beam for MgF molecules. It is applicable to cool and trap neutral molecules by intensity-gradient-induced Sisyphus cooling, as the intensity gradient of such vortex beam is extremely high near the focal point.
In this paper, we propose a new scheme to form an array of surface hollow optical micro-traps for cold atoms (or molecules) by using a phase grating with four phase steps and an array of microlens, study the intensity distribution of 2D array of surface hollow optical micro-traps, and calculate the corresponding optical potential for cold 85Rb atoms, and discuss some potential applications of our hollow micro-trap array in atom and molecule optics. Our study shows that when our grating-lens system is illuminated by YAG laser with a power of 1W, a 2D array of surface hollow optical traps with 104 micro-wells will be generated in an area of 1cm2. Each optical trap has some novel characteristics, such as smaller trapping volume, higher effective intensity and its intensity gradient. The corresponding optical potential for trapped 85Rb atoms can reach 190μK, which is high enough to trap cold atoms or cold molecules, and can be used to realize an all-optical atomic and molecular Bose-Einstein condensations, even to prepare novel optical lattices, and so on.