Akihiro Tomioka

Optical properties of two‐dimensional dye aggregate

Absorption and emission spectra of a monolayer J aggregate of a cyanine dye have been studied in detail from room temperature to liquid helium temperature. Various sources of disorder that affects the degree of delocalization of the exciton have been investigated including the hitherto unnoticed effect of He gas. Simple numerical simulations were performed, which reproduce the basic features of the spectra fairly well. The spectral signatures indicate that we have a typical two‐dimensional Frenkel exciton system characterized by large red shift and large cooperation number despite strong disorder, which is in contrast to the well‐studied pseudoisocyanines (PICs) that have been analyzed as one‐dimensional even in the Langmuir–Blodgett monolayers. The disorder stems partly from the exciton–phonon coupling but is dominantly of the static character at low temperatures.

A simple and accurate method to determine the third-order nonlinear susceptibility of thin films

Abstract A method is presented to determine the phase as well as the magnitude of the third-order nonlinear susceptibilities of thin films. The method is based on the analysis of the Maker fringes produced by the interference between the third harmonic wave from a thin film sample and that from the substrate under a full 360° rotation . No reference measurement is required in which the film has to be removed in situ . This simplifies the experiment considerably.

Local‐field effects in the second‐harmonic generation from Langmuir–Blodgett monolayers

The validity of the local‐field approximation (LFA) has been tested in hemicyanine dye Langmuir–Blodgett monolayers. Resonant structures of absorption and the second‐harmonic generation revealed that LFA is adequate to describe the second‐harmonic generation in the monolayers even when the intermolecular interaction is very strong (H aggregate). A simple calculation procedure is also presented which enables one to treat monolayers as a macroscopic object in a consistent manner with the microscopic structure.

Optical detection of local field in vinylidene fluoride copolymer

Electro‐absorption spectroscopy has been used to monitor the local field in a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The local‐field factor deduced is in good agreement with the previous numerical simulation.

Excitons in Two-Dimensional Organic Dye Aggregate

Abstract Excitons in monolayer dye aggregates have been studied using linear optical spectroscopy. Through the analysis of the spectra aided by a simple numerical simulation, we found that the system is characterized by rather large static disorder.

Localized state in two-dimensional Frenkel exciton: Resonant Rayleigh scattering and numerical study

Abstract Reflection, transmission, and resonant Rayleigh scattering of a J -aggregate monolayer have been measured at the Brewsters angle of the substrate. Low-energy shift of the resonance Rayleigh scattering relative to the absorption peak corresponds to large variation of homogeneous width and observed energy dependence of homogeneous width can be attributed to the higher degree of localization of the low-energy excitons.

Langmuir–Blodgett technique without solvent

A new Langmuir–Blodgett (LB) technique has been developed in which molecules are dispersed on the water surface by evaporation. Films of materials hard to dissolve in conventional volatile solvents can thus be formed and be transferred onto solid substrates. As a demonstration, unsubstituted quinacridone LB films have been formed.

A simple method to determine the phase of the optical nonlinear susceptibility of ultrathin films

Abstract A simple method to determine the phase of the nonlinear susceptibility is described for ultrathin films. It is based on the interference between the harmonic waves from the substrate and the film which is asymmetric with respect to the 180° rotation of the sample. Some examples are shown.