We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum(LSAM)in optical tweezers by tightly focusing the first-order spirally polarized vector(SPV)beams wi...We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum(LSAM)in optical tweezers by tightly focusing the first-order spirally polarized vector(SPV)beams with zero intrinsic angular momentum into a refractive index stratified medium.The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers,with off-axis intensity lobes in the radial direction possessing opposite LSAM(helicities corresponding toσ=+1 and−1)compared to the beam center.We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane and observe particles spinning in opposite directions depending on their location.The direction of rotation depends on the particle size with larger particles spinning either clockwise or anticlockwise depending on the direction of spirality of the polarization of the SPV beam after tight focusing,while smaller particles spin in both directions depending on their spatial locations.Numerical simulations support our experimental observations.Our results introduce new avenues in spin-orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers.展开更多
Propagation of electromagnetic waves in one-dimensional(1-D)stratifiedchiral structures is described by the 4X4 transfer-matrix method.The photonic bandgap(PBG)properties in 1-D periodical chiral media are investigate...Propagation of electromagnetic waves in one-dimensional(1-D)stratifiedchiral structures is described by the 4X4 transfer-matrix method.The photonic bandgap(PBG)properties in 1-D periodical chiral media are investigated.The relation between PBGand chiralityadmittance has been analyzed.Under proper operating parameters,quite perfect multichannelfiltering properties can be obtained with the periodic structure.The photonic bandgap properties ofone-dimensional layered periodical structures that include of double negative(DNG)medium,so-called backward-wave(BW)medium are investigated.The simulation results show that the width ofthe PBG in the structure composed of chiral medium and BW medium is larger then that composed ofchiral medium and usual medium.Our analysis has shown that the usage of the negative material makesit possible to dramatically widen the band gap of one-dimensional photonic crystal.展开更多
The transmission and negative refractive index(NRI) of metal–dielectric–metal sandwiched metamaterials perforated with di?erent filling media of holes are numerically studied. Results indicate that filling the appro...The transmission and negative refractive index(NRI) of metal–dielectric–metal sandwiched metamaterials perforated with di?erent filling media of holes are numerically studied. Results indicate that filling the appropriate medium in rectangular holes can enhance transmission. The NRI and frequency bandwidth of NRI decrease with increased relative permittivity of the filling medium. A stronger magnetic response that contributes to the dual NRI metamaterials is found.展开更多
基金the SERB,Department of Science and Technology,Government of India(Project No.EMR/2017/001456)aIISER Kolkata IPh.D fellowship for research.
文摘We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum(LSAM)in optical tweezers by tightly focusing the first-order spirally polarized vector(SPV)beams with zero intrinsic angular momentum into a refractive index stratified medium.The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers,with off-axis intensity lobes in the radial direction possessing opposite LSAM(helicities corresponding toσ=+1 and−1)compared to the beam center.We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane and observe particles spinning in opposite directions depending on their location.The direction of rotation depends on the particle size with larger particles spinning either clockwise or anticlockwise depending on the direction of spirality of the polarization of the SPV beam after tight focusing,while smaller particles spin in both directions depending on their spatial locations.Numerical simulations support our experimental observations.Our results introduce new avenues in spin-orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers.
基金Supported by the NationaI Natural Seience Foundation of China(40374059)
文摘Propagation of electromagnetic waves in one-dimensional(1-D)stratifiedchiral structures is described by the 4X4 transfer-matrix method.The photonic bandgap(PBG)properties in 1-D periodical chiral media are investigated.The relation between PBGand chiralityadmittance has been analyzed.Under proper operating parameters,quite perfect multichannelfiltering properties can be obtained with the periodic structure.The photonic bandgap properties ofone-dimensional layered periodical structures that include of double negative(DNG)medium,so-called backward-wave(BW)medium are investigated.The simulation results show that the width ofthe PBG in the structure composed of chiral medium and BW medium is larger then that composed ofchiral medium and usual medium.Our analysis has shown that the usage of the negative material makesit possible to dramatically widen the band gap of one-dimensional photonic crystal.
基金supported by the National Natural Science Foundation of China(No.60778041)the Graduate Education Innovation Project of Jiangsu Province(No.CXLX13_39)
文摘The transmission and negative refractive index(NRI) of metal–dielectric–metal sandwiched metamaterials perforated with di?erent filling media of holes are numerically studied. Results indicate that filling the appropriate medium in rectangular holes can enhance transmission. The NRI and frequency bandwidth of NRI decrease with increased relative permittivity of the filling medium. A stronger magnetic response that contributes to the dual NRI metamaterials is found.
