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  1. Abstract

    The manipulation of magnetization through optically generated ultrafast spin currents is a fascinating area that needs a thorough understanding for its potential future applications. In this work, a comprehensive investigation of helicity‐driven optical spin‐orbit torque in heavy metal/ferromagnetic metal heterostructures is presented, specifically cobalt capped with gold or platinum, subject to laser pumping at different wavelengths. The results demonstrate up to tenfold enhancement in optical spin‐orbit torque quantum efficiency for gold compared to platinum of the same thickness when pumped with a visible laser. Additionally, the study provides the first experimental analysis of the photon energy dependence of optical spin‐orbit torque and derives the optical spin orientation spectra for both gold/cobalt and platinum/cobalt heterostructures. A key insight gained from the study is the impact of photon energy‐dependent spin transport in the system, which suggests the use of a high photon energy pump for efficient spin transport. These findings highlight the potential of spin current generation and manipulation in gold/ferromagnet heterostructures for a wide range of applications such as all‐optical magnetization switching, spin‐wave generation and control, and spintronic terahertz emission.

     
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    Free, publicly-accessible full text available October 18, 2024
  2. Non-Hermitian meta-gratings enable unidirectional excitation and reflection of optical surface waves at the nanoscale. 
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  3. Engineered noise can increase the channel capacity for polarization multiplexing with a metasurface hologram. 
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  4. Abstract

    Manipulation of nanoparticles by light induced forces is widely used in nanotechnology and bioengineering. In normal cases, when a nanoparticle is illuminated by light waves, the transfer of momentum from light to the nanoparticle can push it to move along the light propagation direction. On the other hand, the lateral optical force can transport an object perpendicular to the light propagation direction, and the optical pulling force can attract an object toward the light source. Although these optical forces have drawn growing attention, in situ tuning of them is rarely explored. In this paper, tuning of both lateral optical forces and optical pulling forces is numerically demonstrated via a graphene/α‐phase molybdenum trioxide (α‐MoO3) bilayer structure. Under plane‐wave illumination, both the amplitude and direction of the optical forces exerted on a nanoparticle above this bilayer structure can be tuned in the mid‐infrared range. The underlying mechanism can be understood by studying the corresponding isofrequency contours of the hybrid plasmon‐phonon polaritons supported by the graphene/α‐MoO3bilayer. The analytical study using the dipole approximation method reproduces the numerical results, revealing the origin of the optical forces. This work opens a new avenue for engineering optical forces to manipulate various objects optically.

     
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  5. Abstract

    On the basis of the Jones matrix, independent control over the amplitude and phase of light has been demonstrated by combining several meta‐atoms into the supercell of a metasurface. However, due to the intrinsic limitation of a planar achiral structure, the maximum number of independent, complex elements in one Jones matrix is three, giving rise to up to three‐channel amplitude and phase control. In this work, more Jones matrices corresponding to different angles of incidence are proposed to add, so that the degrees of freedom in the amplitude and phase control can be further increased. The supercell of the designed metasurfaces consists of three dielectric nanoblocks with predefined rotation angles and displacements in the 2D space, which can be inversely determined with the help of the genetic algorithm. Empowered by the ability to realize four‐ or even eight‐channel amplitude and phase control, the generation of multiple structured light, including two independent perfect Poincaré beams, two double‐ring perfect Poincaré beams, two perfect Poincaré beam arrays, and four vector vortex beam arrays, is numerically demonstrated. Such novel designs are expected to benefit the development of modern optical applications, including but not limited to optical communications, quantum information, and signal encryption.

     
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