Norihito Kawaguchi

Visualization of magnetic microparticles in liquid and control of their motion using dynamic magnetic field

Visualization technique of micro- or nanoparticles with sufficient spatial and temporal resolutions is required for quantitative study of motion of magnetic particles and their control using a dynamic magnetic field. Based on the particle tracking velocimetry method, a visualization system of micron-size particles has been developed. A proof-of-concept experiment of controlling magnetic particles using a dynamic magnetic field was made, and motions of magnetic particles under a dynamic magnetic field were visualized successfully using the developed system: the motions of particles synchronizing with the applied dynamic magnetic field could be observed.

Q-switched fiber laser based on carbon nano wall saturable absorber

We report a saturated absorption characteristic of carbon nanowall and Q-switched laser operation using carbon nanowall saturable absorber. Carbon nanowall is vertically aligned nanographite sheets on Si substrate synthesized by plasma-enhanced chemical vapor deposition method. A polyimide thin film, with incorporated carbon nanowall, coated by spin-coating method, is used as saturable absorber. Linear absorption spectrum of carbon nano-walls was observed without absorption peak wavelength range from 1000 to 2000nm. Modulation depth of carbon nanowall saturable absorber was measured with wavelength of about 1560nm. Q-switch laser operation with carbon nanowall saturable absorber and erbium doped optical fiber was demonstrated.

The Behavior of Nano- and Micro-Magnetic Particles Under a High Magnetic Field Using a Superconducting Magnet

Magnetic force has been used for drug delivery, magnetic separation, and other kinds of micro- and nano-particle handling. As fundamental studies of these applications, we have investigated the visualization of the motion of micro-magnetic particles under a dynamic magnetic field. We have also studied the contactless grasp of a micro-magnetic particle suspended in a fluid by using coil currents. In the study, we have developed a method for quantitatively estimating the influencing forces. However, these experiments have limitations in the magnetic field strength of normal conducting electromagnets or permanent magnets. Therefore, much higher magnetic force is needed for the application to drug delivery or cell/DNA manipulation. High magnetic field generating high magnetic force saturates the magnetization of magnetic particles during the particle control, and the magnetic saturation influences the particle behavior. However, such behavior of magnetic particles has not been sufficiently studied yet. In this paper, the behavior of the particles nearly or fully saturated under the high magnetic field of a superconducting magnet was visualized successfully, and ferrite and feeble magnetic particles were introduced in order to gain insight into their behavior.