Yutaka Kawabe

Thin-film lasers based on dye-deoxyribonucleic acid-lipid complexes

Amplified spontaneous emission (laser action without cavities) from deoxyribonucleic acid (DNA) derivative films was achieved by doping with a hemicyanine dye which is well known as a nonlinear optical molecule. The amplification confirmed by spectral narrowing and superlinear dependence of the emission intensity on the pumping was observed from the complex films when the film samples were irradiated with a nanosecond laser at the intensity above a threshold value (∼20 μJ). The durability and low threshold values suggest the possibility of DNA complexes as a practical candidate for thin-film dye lasers.

Real-time three-dimensional holographic display using a monolithic organic compound dispersed film

Organic holographic materials such as photorefractive polymers are one of the promising candidates for the next generation three dimensional (3D) real-time display. Recently, we found that polymer composite of monolithic organic compound of 3-[(4-nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzE) (30 wt%) doped transparent polymethylmethacrylate (PMMA) had capability of recording and displaying new images within a few seconds and fixed at ten seconds and viewing for a longer time without applying electric field. Here, we present 3D holographic display using monolithic organic compound NACzE dispersed transparent PMMA film sandwiched between two glass plates with size of 7.5 × 5 cm2. The thickness of film is ca. 50 μm. Images are easily and completely erased by over recording and it is accelerated by slight heating.

Electron mobility measurement using exciplex-type organic light-emitting diodes

A method to measure the electron mobility in organics is demonstrated. Bilayer organic light-emitting diodes composed of donor-type and acceptor-type materials often show exciplex emission. We employed a triphenyldiamine derivative and an oxadiazole derivative (PBD) as hole and electron transporters, respectively, and confirmed that the emission is from exciplex. From the transient response of the device after application of pulsed voltage, the electron mobility of neat PBD film was evaluated to be 2.0×10−5 cm2/V s under the electric field of 1 MV/cm.

Fully updatable three-dimensional holographic stereogram display device based on organic monolithic compound

Holographic technique is a unique method to reproduce object on a device in three dimensions (3D). It allows us real 3D images with full parallax without special eye glasses or any special optical devices. we present fully updatable holographic 3D display system using a holographic stereographic technique with a transparent optical device of poly(methylmethacrylate) doped organic compound of 3-[(4-nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzE). 100 elemental holograms which are a series of pictures of object took from different angles can completely reproduce updatable entire hologram of object. Former hologram of object can be over-recorded and immediately replaced by new hologram of object without erasing process. Typical recording time for an elemental hologram is 200 ms, and total recording time including translational stage movement for 100 elemental holograms is 28 s. The present system with preferred memory is a good candidate for 3D signage application.

Light amplification in dye-doped DNA-surfactant complex films

We observed amplified spontaneous emission (laser action without cavities) from several kinds of dyes doped in films of salmon DNA (deoxyribonucleic acid) derivatives. We employed laser dye Rhodamine-6G, Pyrromethene 556, and nonlinear optical dye DMASDPB for dopants. Most of sample films with several micrometers thickness were prepared as follows: 1) DNA aqueous solution was mixed with hexadecyltrimethylammonium chloride aqueous solution. 2) precipitated DNA-lipid complex and dyes were dissolved in ethanol or chloroform. 3) Films were formed on substrates by casting from the solution. The amplified spontaneous emission was observed when the films were pumped with a nanosecond laser of 532 nm at the intensity above a threshold value. Spectral narrowing occurred at the threshold energy, and it was accompanied with superlinear dependence of the emission intensity on the pumping intensity. Dye molecules in DNA films can be intercalated in the double helix structure. Because molecules are separated form one another, it is possible to increase chromophore concentration without fluorescence quenching due to aggregation. Furthermore, it is known that DNA shows a good conducting property. We will discuss the possibility of optical and electronic devices utilizing these characteristics.

OPTICAL PROPERTIES OF TRANSITION-METAL DOPED SPINELS

Strong blue emission is observed from Ti-doped MgAl2O4, yellow emission from a Mn-doped one and white light emission from a V-doped one. The optimum condition to obtain the strongest emission was studied by changing the doping density and growing atmosphere. The microscopic models for these emission processes are proposed from observation of other optical responses and electron spin resonance spectra both in the electronic ground and excited states.

Electroluminescence as a probe for electrical and optical properties of deoxyribonucleic acid

Several class of dyes doped in deoxyribonucleic acid (DNA) derived from salmon show enhancement of fluorescence due to suppression of molecular aggregation. Also, some recent studies support electric conduction in DNA strands. Combination of these properties suggests the possibility to develop organic LED devices (OLED) based on biopolymer systems. Furthermore, the electroluminescence (EL) effect can be employed as a probe for electrical and optical properties of DNA. We fabricated OLED devices based on DNA- lipid complex and dopant dyes (ethidium bromide and fluorescein). Devices are composed of hole injection layer, dye-doped DNA-lipid layer and electrodues. OLED with ethidium bromide doped DNA showed LED emission under DC bias, but the origin of the emission was tris-(8- hydroxyquinolinato)aluminum(III)(Alq3) which was employed as an electron transporter. The current-voltage characteristics of the devices show apparent rectification behavior. From these experimental results, it is confirmed that DNA transports hole current under external DC bias. When employing fluorescein as a dopant in DNA and fabricating the devices without Alq3 layer, we observed emission from the dyes incorporated in DNA. Although the origins of the emission centers in spectra are not clear, it shows that the DNA-lipid complex will be basically applicable to OLED if additional improvements are made.

Light amplification in DNA-surfactant complex films stained by hemicyanine dye with immersion method

Organic dye-doped deoxyribonucleic acid (DNA)-surfactant complex films for dye lasers were fabricated by immersing non-doped complex films into a solution of hemicyanine dye. The threshold pumping intensity for amplified spontaneous emission was found to be 0.3 mJ/cm2, the value was one order smaller than those obtained for the samples made by conventional methods. Durability under pumping was also significantly improved and laser oscillation under optical excitation was observed. Dye concentration of the final products was estimated to be 10 wt% and there were no deformation of the samples, suggesting that dye molecules in the complex did not necessarily intercalate in DNA strand but replace with surfactant molecules.

Transition from laminar to turbulent flow of water in a pipe measured by a pulsed NMR method

The transition from the laminar flow to the turbulent flow of water in a long circular pipe has been studied by observing the spin echo amplitudes in a pulsed NMR method. The spin echo signal is characteristic to the flow condition, i.e., its amplitude is large when the flow is laminar, while it is small when the flow is turbulent. In the transition region spin echo signals with large amplitudes and those with small amplitudes appear intermittently. The intermittency factor of the flow has been measured in the transition region. This experiment shows That the pulsed NMR method might be useful to study dynamical characters of the transition region.

Photoinduced grating formation in a polymer containing azo-carbazole dyes.

Although some azo-carbazole derivatives attached on or doped into inert polymers are known to show photorefractive effect without external electric field, the origin of their asymmetric energy transfer in two-beam coupling experiments were unknown. We made the two-beam coupling experiment followed by sample translation and one-beam diffraction at 633 nm for thick films composed of 3-[(4-nitrophenyl)]azo-9H-carbazole-9-ethanol (NACzEtOH) and poly(methylmethacrylate), finding that photoinduced gratings grew in several minutes accompanied with phase displacement of the gratings, but the phase shift was not always synchronized with the refractive index modulation. We reformulated the Kogelniks coupled-wave theory with strict energy conservation law for analysis. Comparison of the grating growth and erasure at 532 nm to Disperse Red 1 (DR1), the most well-known azo dye showed that the photoisomerization was dominant at this wavelength and that the azo-carbazole dyes were faster in response time and more resistive to erasure than DR1.