Jia Wang

Manipulation and arrangement of biological and dielectric particles by a lensed fiber probe

An optical trapping system with a single-mode lensed fiber probe inserted at an angle is built; this system is simpler and more flexible than conventional optical tweezers. Two lasers, with 632.8- and 1550-nm wavelengths, are employed to trap and manipulate yeast cells and polystyrene microspheres. Nine yeast cells are manipulated to form a letter T. Finally, the manipulation performed with various inclination angles, particle materials, laser wavelengths, and laser powers is analyzed experimentally.

A design methodology for directional beaming control by metal slit-grooves structure

A design method is proposed for directional beaming control by a subwavelength metal slit surrounded with grooves. With the approach of modulating the phases of the radiation light decoupled by the surrounding grooves from surface plasmon polariton waves, the wavefronts of the radiation light from both sides of the slit are controlled in the beam toward specific directions. The design formulae of the plasmonic structures for directional beaming are deduced based on Huygens principle. Besides the grating equation being derived, the design requirement for the grating positions is determined. The transmitted field distributions through the designed structures are calculated by the finite-difference time-domain method. The results show that the transmitted light can be directionally beamed efficiently and the beam angle can be controlled accurately within the region of ± 20°.

Holographic plasmonic lenses for surface plasmons with complex wavefront profile

We present a direct-method solution toward the general problem of plasmonic wavefront manipulation and shaping to realize pre-designated functionalities based on the surface-wave holography (SWH) method. We demonstrate theoretically and experimentally the design and fabrication of holographic plasmonic lenses over surface plasmons with complex wavefront profiles. We show that visible light at 632.8 nm transmitting through a high-aspect-ratio slit or a micro-rectangle hole in a silver film can be focused to a preset three-dimensional point spot in free space via appropriately manipulating the interaction of excited surface plasmons with the nanoscale groove pattern of the holographic lens. The experiment results of scanning near-field optical microscopy for measuring the three-dimensional optical field distribution agree well both with designs and with numerical simulations, and this strongly supports the effectiveness and efficiency of the SWH method in the design of plasmonic devices that can fulfill manipulation and transformation of complicated-profile surface plasmons.

A nano-confined source based on surface plasmon Bragg reflectors and nanocavity

A type of nano-confined light source based on SPP Bragg reflectors and a nanocavity has been realized. The structures consisting of a nanocavity surrounded by annular grooves are used to obtain a single, localized and non-radiating central peak, which can be used as a nano source. Characterization of the SPP field in the vicinity of the samples with different structural parameters is accomplished by the scanning near-field optical microscope (SNOM), demonstrating the ability of the structures to enhance the peak intensity and to suppress the sidelobes. During 600 nm distance away from the sample surface, the FWHM of the central peak is below 285 nm (0.45 lambda), and the modifications of the structural parameters result in at least 1.27 times enhancement of the central peak intensity together with the sidelobe suppression of no more than 73% of the central peak intensity. Numerical simulations based on FDTD method show a good agreement with the experimental results, and give some clues to understand the physical mechanisms behind these phenomena. This type of SPP-based nano source is promising to be applied in near-field imaging, data storage, optical manipulation and localized spectrum detection.

Confined optical field based on surface plasmon polaritons and the interactions with nanospheres

A type of surface-plasmon-polariton bandgap structure for generating a confined nanometric optical field with high intensity and very small sidelobes is simulated by using the finite-difference time-domain method. The numerical results show that the intensity enhancement of the confined field can reach 2 orders of magnitude, with a resolution (FWHM of the zero-order mode) of 0.33λ and the high-order modes (sidelobes) being effectively suppressed to no more than 15%. These properties ensure the confined field to be used as a near-field source. Detailed and systematic investigations of the enhancement and the localization versus the structure parameters are performed, and the physical mechanisms behind these phenomena are explained. Potential applications of the confined field in near-field detection and imaging are discussed through interactions with different types of nanospheres. The simulated results reveal that details with feature sizes down to 0.13λ can be resolved.

Confined optical fields based on surface plasmon polaritons

A nonradiating, spatially confined optical field based on surface plasmon polaritons (SPPs) on a corrugated surface of metal film is proposed. With the help of the surface plasmon band-gap nano-structure, SPP can be collected in a spatial region beyond the diffraction limit and form a confined optical field, which can be used as a nano-source in near-field. Compared with other types of near-field sources, such confined optical field provides higher intensity, and the spot size of the nano-source can keep constant within certain distance. By using the method of Finite-Difference Time-Domain (FDTD) is used to simulate the distributions of the confined optical field, two types of confined optical fields based on SPPs excited by prism and by grating, respectively, are demonstrated in 2D- and 3D-space. Such confined optical field as a nano-source, is promising to be applied to near-field imaging and optical manipulation, and has potential applications in nano-photonics devices based on SPP.

Experimental research on laser tracking system with galvanometer scanner for measuring spatial coordinates of moving target

The spatial position of industrial object, such as robot end- effector, is an important geometric parameter whose accuracy determines whether robot can perform accurately. Therefore, we have established a laser tracking and coordinate measuring system with galvanometer scanner for high accuracy, large range, non- contact, and spatial dynamic measurement. In this paper, the laser tracking system and its setup are illuminated at first. Then, the formulae for calculating coordinates are deduced, and the calibration method of the initial distance from tracking mirror to target is presented. After that, two preliminary experiments in different distances are described. One is on CMM; the other is with grating ruler as reference. In the former, the maximum measurement error of coordinates is 70micrometers and the maximum error of length is 35micrometers in the 85x100x100mm3 measurement volume, and in the 1m initial distance. In the later, the maximum error of length is 140micrometers in the range of 480mm, and in the 5m initial distance. At the end of the paper, the error sources are analyzed and simulated.

Numerical Simulation Analysis of an Optical Virtual Probe Based on Surface Plasmon Polaritonic Band-gap Structures

A 2D optical virtual probe based on surface plasmon polaritons (SPP) in a band- gap structure with a rectangular proflle is proposed and investigated numerically by means of flnite difierence time domain (FDTD) method. The dependence of the distributions of the con- flned optical flelds on difierent structure parameters is numerically analyzed. The results indicate that with the proper structure design, the full width at half maximal (FWHM) of the conflned beam can keep constant in a certain distance range, and the fleld intensity of the conflned vir- tual probe can be enhanced greatly by SPP. Compared with the optical virtual probe based on interference of evanescent waves, this type of virtual probe has merits of high intensity and high sensitivity, and is likely to promise for the applications in nano-photonics devices based on SPP. DOI: 10.2529/PIERS060903234639

Position and attitude measurement of moving target using laser tracking system with multiple measuring stations

Dynamic geometric parameter measurement plays an important role in most industries. Research and development on this technology have attracted great attention. We proposed a laser tracking system for measuring development of laser tracking technology, a laser tracking system consisting of three tracking and measuring stations is described in detail. The three stations track respectively three retro reflectors on the moving target, and measure the position and attitude. We built the mathematical model of measurement and developed the algorithm for processing data. According to the homogeneous coordinate transformation, we deduced the formulae for computing coordinates and attitude under different coordinate systems. Some key techniques of the measuring system are discussed at the end of the paper.

Experimental measurement of the trapping force acting on a yeast cell with a lensed optical fiber probe

In conventional optical tweezers system a high numerical aperture (NA) objective is employed both to image and to generate a gradient force toward the focus on sample particles, so the system is complex and expensive especially for the multi-optical-tweezers system. We built a novel simple optical trapping system based on a lensed optical fiber probe. This new method offers several other advantages over the conventional optical tweezers. The trapping system we built includes a laser coupling unit, a multi-dimensional probe manipulating unit, a sample nano-positioning unit, and a microscopy imaging unit. Based on the system, a yeast cell is trapped and manipulated on the chamber bottom by the lensed fiber probe, and the optical trapping forces acting on the yeast cell as a function of the offset are measured and discussed in different directions by the static method and the dynamic one respectively with various powers. The results by the two measurement methods coincide with each other, and the detail experimental procedure and the data processing of the two methods are introduced in this paper.