Mitsuo Tsukiji

Novel Tweezers for Biological Cells Using Piezoelectric Polylactic Acid Fibers

Abstract We fabricated poly-L-lactic acid (PLLA) fiber samples using high-speed spinning in order to improve their piezoelectricity. If an electric field is applied to the PLLA fiber in the direction perpendicular to its fiber axis, the PLLA fiber must be driven by the piezoelectric effect. We developed an effective method of applying an electric field to the PLLA fiber. As a result, we could drive the PLLA fiber by the shear piezoelectric effect under the application of ac voltage, and observed the bending motion of the entire PLLA fiber. Next, we have designed tweezers using a pair of PLLA fibers controlled by applied ac voltage, and have pursued the realization of PLLA fiber tweezers; finally, this was achived. On the basis of our experimental results, we believe that there is a high possibility of realizing the PLLA fiber tweezers for the manipulation of soft and minute samples such as biological cells.

Accurate Measurement of Light Modulation Properties of Piezoelectric Polymer

In order to study the light modulation properties due to the electrooptical effect, we prepared piezoelectric poly(L-lactic acid) (PLLA) films by drawing and annealing, and ferroelectric polyurea-5 (PU5) by vapor deposition. In all PLLA films fabricated in this study, we found that light amplitude modulation (LM) caused by applying an electric field occurs, using our experimental system based on the heterodyne interferometry principle. However, the LM was very weak. LM in the recrystallized PLLA film is stronger than those in the other PLLA films. The occurrence of LM in PU5 was confirmed using our experimental system. Such results have not been reported until now. Here, we emphasize that the occurrence of LM in PLLA fabricated by the drawing and annealing method and in PU5 film fabricated by the vapor-deposition method is clarified in this study for the first time.

Development of a visual encryption device using higher-order birefringence

We propose and demonstrate a novel visual encryption device composed of higher-order birefringent elements. When an optical material with higher-order birefringence is placed between a pair of polarizers and illuminated by white light, it appears only white. In contrast, when it is illuminated by monochromatic light, the transmitted intensity varies depending cosinusoidally on the wavelength. An array of such materials can express information (e.g., letters and/or images) by controlling the birefringence of each pixel. If birefringence phase retardation can be adjusted for a specific wavelength, the information will be clearly displayed when it is illuminated at this wavelength. We denote this wavelength a key wavelength. The encryption device was fabricated by controlling the amount of higher-order birefringence to achieve high contrast only by using polarized illumination at the key wavelength. Thus, the information stored in the encryption device can be decoded only by illuminating it at the key wavelength. To demonstrate the validity of this encryption principle, we constructed a 3 × 3 pixel device in which commercial retarder films were laminated. The device was illuminated by a monochromatic light. When a readout experiment was performed using the monochromatic light at the key wavelength, the stored letter was clearly visible. On the other hand, when pixel brightness was randomly distributed with illumination at the wavelength other than the key wavelength, the letter could not be recognized. Furthermore, the stored information can be easily distributed to multiple physical keys that display arbitrary images. In this case, the birefringence phase retardation is obtained by summing the values of retardation of each pixel of the physical keys. In the experimental device, the observed image was decoded by superimposing the two images using different physical keys.

Simultaneous measurement of linear and circular birefringence with heterodyne interferometry

We present a novel technique to measure both linear and circular birefringence, simultaneously. This technique is based on an optical heterodyne interferometry which is performed by an orthogonally polarized two frequency laser. Two orthogonal components of the optical beat signal are detected by two-phase lock-in amplifier. The two components change sinusoidally with the rotation of azimuth angle of polarization devices. The retardation and the orientation of linear birefringence and the rotation angle of circular birefringence can be calculated by applying a Fourier analysis to the two sinusoidal variations. The measurement sensitivity for this method is verified by using the combination of a Babinet Soleil compensator and a half-wave plate as a sample. It is demonstrated that the birefringence of commercially available twisted nematic liquid crystal cell where a driving voltage is applied can be measured by using the proposed technique.

Measurement of Pockels Effect in Piezoelectric Chiral Polymer Film

The possibility has been indicated that a piezoelectric polymer with helical chirality (chiral polymer) such as poly-L-lactic acid (PLLA) shows a large linear electrooptical constant (Pockels effect). However, the linear electrooptical constant of a PLLA film may be very small because such a film fabricated by the conventional method has a complex high-order structure with intermingled crystalline and amorphous regions. In order to measure the small linear electrooptical constant of a PLLA film, we developed a new measurement system, which is based on the heterodyne interferometry principle. In this system, the accuracy of retardation is 0.08 nm and the measurement time is 0.1 s. In our attempt to realize a PLLA film with a large linear electrooptical constant, we fabricated a PLLA film, which was heated to 120°C under 320 MPa. Finally, using our new measurement system, we obtained a linear electrooptical constant of 0.070 pm/V in the PLLA film, which is very small compared with those of other famous Pockels materials. However, the linear electrooptical constant of the PLLA film is clarified in this study for the first time.