Using the finite-difference time-domain(FDTD) method,we simulate the coupling between a gold nanorod and gold nanoparticles with different plasmonic resonant frequencies/volumes as well as that between the nanorod and a dielectric nanosphere.The influences of coupling with different nanoparticles on the excitation of a forbidden longitudinal surface plasmon mode of the nanorod under normal incidence are investigated.It is found that the cause of this excitation is the broken symmetry of the local electric field experienced by the nanorod resulting from the charge pileup on the other nanoparticle.This result is valuable for understanding the near-field optical characterization of plasmonic metal nanoparticles.
A tunable plasmonic waveguide via gold nanoshells immerged in a silica base is proposed and simulated by using the finite difference time-domain (FDTD) method. For waveguides based on near-field coupling,transmission frequencies can be tuned in a wide region from 660 to 900 nm in wavelength by varying shell thicknesses. After exploring the steady distributions of electric fields in these waveguides,we find that their decay lengths are about 5.948-12.83 dB/1000 nm,which is superior to the decay length (8.947 dB/1000 nm) of a gold nanosphere plasmonic waveguide. These excellent tunability and transmittability are mainly due to the unique hollow structure. These gold nanoshell waveguides should be fabricated in laboratory.
Femtoscience offers a unique way to understand the dynamics in physics, chemistry and biology. This subject focuses on the process happening at femto-to pico-second time scale by femtosecond optical methods. Widely used in chemistry it reveals chemical reactions, including bond breaking, forming, and stretching, which happens at an ultrafast time scale. Femtoscience is also important in the biological system, for example, light harvesting system and vision system. Femtoscience in physics is also widely used, but it is not studied in this paper. Instead, we report new advances in femtochemistry and femtobiology, including structural dynamics, coherent control, enzyme function dynamics and hydration in the protein system. We also introduce attosecond science, focusing on electron dynamics at an extreme short time scale.
A dual optical tweezers system,which consists of a doughnut mode optical tweezer (DMOT) with the azimuthally polarised trapping beam and a solid mode optical tweezer (SMOT) with the Gauss trapping beam was constructed to compare the axial trapping effect of DMOT and SMOT.The long-distance axial trapping of ST68 microbubbles (MBs) achieved by DMOT was more stable than that of SMOT.Moreover the axial trapping force measured using the viscous drag method,was depended on the diameter of the particle,the laser power,and the numerical aperture (NA) of the objective lens.The measurement of the axial trapping force and the acquisition of CCD images of trapping effect confirmed that the DMOT showed excellent axial trapping ability than SMOT.A simple and effective method is developed to improve axial trapping effect using the azimuthally polarized beam as trapping beam.This is helpful for the long-distance manipulating of particles especially polarised biological objects in axial direction.
