Suguru Horinouchi

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.

Nonlinear optical materials derived from biopolymer (DNA)-surfactant azo dye complex

This paper reports on optical and optoelectronic properties of DNA-surfactant complex films which were intercalated with a NLO dye, Disperse Red 13(DR-13). Circular dichroism (CD) analysis indicated that the orientation of the azo dye, DR-13 doped in DNA-surfactant complex film was achieved by inserting the dye molecules into the nano-size space between base pairs of DNA. The Disperse Red 13-doped DNA thin film displayed higher THG than that of CS2 about two orders. On the other hand, SHG signal could not be observed even in the presence of anisotropic ordering of the molecular chromospheres on template of the double helix of DNA, perhaps because of absorption of the dye for SHG light.

Finite-element modal analysis of large-core multimode optical fibers.

Plastic optical fibers that are a typical large-core multimode optical fiber support a great number of modes compared with conventional silica-glass multimode optical fibers. So far the WKB method hasbeen used for most of the modal analyses of these fibers because of a great number of guided modes. We describe the accurate eigenmodal analysis of large-core multimode optical fibers with the finite-element method (FEM) and compute the propagation constants of all LP modes. In addition, the FEM has a strong advantage for arbitrary core profiles whereas the WKB method is not suitable fornonmonotonic profiles. To demonstrate the advantage, we apply the FEM to the fiber having sinusoidal fluctuations.

Strongly luminescent rare-earth-ion-doped DNA-CTMA complex film and fiber materials

A rare-earth chelate, Europium 6,6.7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5,-octanedionate, (Eu3+-FOD) doped DNACTMA complex as fiber and film materials was prepared by casting solution method and gel-spinning method. The Eu-FOD-DNA-CTMA complex was luminescent and has 750 μs of fluorescence lifetime, sharply-spiked emission spectra, excellent film and fiber formability, moderate absorption (40000M-1cm-1) at 327 nm and high quantum yield forlanthanide emission. By comparison of fluorescence lifetime of Eu-FOD doped DNA-CTMA solid matrix with that of Eu-FOD doped in PMMA, it was clear that energy transfer from DNA to FOD leads to enhancement of fluorescence emission at 613 nm. Analysis results for fluorescence spectra and fluorescence relaxation time of Eu3+ doped in the materials indicated that Eu3+-FOD is chemically bond within the DNA-CTMA matrix. Amplified spontaneous emission (ASE) at 612 nm by pumping with UV laser (355 nm) was observed in the materials. Fluorescence lifetime of the Eu-FOD doped in the DNA-CTMA solid matrix was evaluated to be 750 μs, which is ca. 230μs longer than that of Eu-FOD doped in PMMA solid matrix. Efficient Energy transfer from base of DNA to FOD, then to Eu, occurred when irradiated by UV light or 355 laser beams.

All propagation modes of large-core multimode optical fibers with an arbitrary core profile

Plastic optical fibers are typical large-core multimode optical fibers. High-bandwidth graded-index plastic optical fibers, which support a great number of propagation modes compared with conventional silica-glass multimode optical fibers, were developed in the 1990s. However, because they support a great number of propagation modes, their modal analyses have been limited to the WKB analysis. We obtain all the propagation modes of a convex-index large-core multimode optical fiber by use of the finite-element method, which has a strong advantage for arbitrary core profiles.

Finite-element modal analysis of large-core multimode optical fibers: erratum

In a previous paper [Appl. Opt.43, 2163 (2004)], there was a mistake regarding Eq. (2). That mistake is corrected here.

Fabrication and characterization of rare-earth metal-chelate-doped plastic film and fiber materials: Eu(3+)-chelate-doped PMMA

High concentration rare-earth metal ion chelates, Europium 6,6.7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5,- octanedionate, (Eu-FOD) doped PMMA fiber and film were successfully prepared for the first time by casting solution method and gel spinning method. The optical and photoelectric characteristics of Eu(3+)-FOD doped PMMA film and fiber were investigated. Amplified spontaneous emission (ASE) from the Eu-FOD doped PMMA film and fiber was observed. The high concentration Eu-FOD-doped PMMA fiber and film sample exhibited lasing threshold as low as o. 15 mJ/ cm2 when pumped with a 355 nm pulsed laser beam.

Fabrication of Novel Biocompatible Surfaces by Two-Photon Absorption Technique Using Femtosecond Laser

This study describes the preparation of biocompatible patterned surfaces by a two-photon absorption technique. We have synthesized poly(2-methoxyethyl acrylate) copolymers, which exhibit biocompatibility and photocrosslinking moiety. Fabrication resolution can be controlled in the sub-micrometer range by changing the laser power, photoinitiator concentration, and scanning speed. The patterned surfaces showed excellent human platelet compatibility. Biocompatible patterned surfaces can be used in various medical devices, implants, biosensor chips, and tissue engineering scaffolds.

Function of plastic optical fiber composed of DNA compound

DNA fibers were prepared by melt spinning method from DNA-CTMA powder. A hemicyanine dye, trans-4-{4-(dibutylamino)-styryl}-1-methylpyridinium iodide (DBASMPI) doped DNA-CTMA fiber with core diameter of 1 mm and dye concentration of 3.6 wt% was obtained by soaking it in an aqueous dye solution. Laser (532 nm) pumped amplified spontaneous emission (ASE) at 610 nm was observed in the dye-doped DNA-CTMA fiber. The ASE occurred at energy density 50 mW. The amplification of optical signals at 607 nm wavelength was confirmed. The results from ASE emphasize that DBASMPI doped DNA-CTMA fiber is appealing as a good candidate for optical amplifiers and superfluorescence sources in a variety of communication and sensor applications.

Fabrication of functional material by using DNA-lipid complex and its optical property

We observed optical properties of organic fluorescence materials doped DNA-CTMA and PMMA. The quantum yield in DNA-CTMA was higher than in PMMA. Amplified spontaneous emission properties of dye-doped DNA-CTMA film at ambient temperature were investigated. The narrowing of line shape and amplified spontaneous emission dependence occur at the same intensity indicates that both effects are the results of light amplification. We discussed the lasing capability by interacting DNA-CTMA.