| Research Abstract |
In surveying a trend of the field related to this Project, we notice that the effectiveness of multiple light scattering and of spherical resonance (morphology-dependent resonance ; MDR) has been discussed independently each other, up to the present. This Project pursued probing the fundamental dynamics of optical properties in single microdroplets containing gain-highly scattering turbid media, combining the multiple light scattering and the MDR with high quality-factor of resonances.
Lasing action in optical gain random media has attracted recently a great deal of interest and experimental studies were performed to reveal the output, spatial, and spectral characteristics of the emission. They are divided into two categories according to the experimental methods. The first one, initiated by Lawandy's group [N.M.Lawandy et al. Nature, p.436,1994], is based on optically pumped bulk solution of dye mixed with strongly scattering solid-nanoparticles of TiO_2 scatterers. The second approach
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relies originally on dye-doped liquid spherical microdroplets (microspheres) in which transparent medium produces optical cavities with high-Q values so that laser action can be readily Observed by excitation with intense laser beams [P.W.Barber and R.K.Chang, Eds., "Optical effects associated with small particles, "World Scientific, Singapore, 1988]. The results obtained from this Project are as follows :
1) By substituting the poly (methyl methacrylate) (PMMA) solid-nanoparticles into Rhodamine 6G (RH6G) dye microdroplet, we have first reported significantly enhanced laser emission accompanying with the well-defined thresholds [H.Taniguchi et al.Opt.Lett.p.263,1996]. 2) Succeeding experiments were performed using highly scattering fat emulsion Intralipid-10% in spherical microdroplets mixed with some laser dyes [Appl.Phys.Lett.p.719,1996 ; Appl.Opt.in Press] and, 3) a new biochemical material (Ribo-Flavin) [CLEO/Pacific Rim '97, P7, p.157,1997], 4) together with pigments extracted directly from biological tissues [Electron.Lett.p.1484,1996 ; CLEO/Pacific Rim '97, P6, p.156,1997 ; Electron.Lett.p.1797,1997] as lasants. 5) We have also confirmed in these dye-highly scattering nanoparticle mixtures, the disappearance of the mode structures due to MDR's of spherical cavities depending on the substituted contents of the scatteres ; i.e., indicative of dominant role of multiple light scattering to establish lasing inside the microdroplet.
The main aim of this Project was accomplished sufficiently in advance of the world by this Project. Less
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