Shigeki Miyanaga

Excited-state absorption and pump propagation effects on optical phase conjugation in a saturable absorber

Phase conjugation by degenerate four-wave mixing in a saturable absorbing medium with a relatively long-lived excited state is analyzed; the analytical results are compared with experimental results. We propose a four-level model and take into account the effects of both excited-state absorption and pump propagation to explain the experimental results, which could not be explained by the models proposed previously. The numerical result predicts that the value of the phase-conjugate reflectivity as a function of the pump intensity is maximum at a certain absorbance (as absorbance increases) that is dependent on the cross section of the excited-state absorption. The present analysis explains most observations in the experiment, which was performed with a saturable-dye-doped polymer film as the saturable absorbing medium.

Power transfer by nearly degenerate two-wave mixing in a saturable dye-doped film

We analyze power transfer by nearly degenerate two-wave mixing (TWM) in a saturable absorbing medium by assuming a three-level model for the saturable absorbing medium. The theoretical results are compared with the experimental ones by using an erythrosin-B-doped polymer film as the saturable absorbing medium. Pump-intensity-dependent behavior of the TWM gain that is predicted by the theory was experimentally verified with this dye-doped film. The saturation intensity Is and the detuning parameter δ of erythrosin B were estimated by the comparison of the theory and the experiment: Is ≈ 1.6 W/cm2, δ ≈ 1.1. The theoretical curves calculated from these values are in good agreement with the experimental curves near resonance, whereas they disagree with the experimental results as the laser frequency shifts off resonance.

Measurements of dispersion properties of refractive indices and absorption coefficients in organic-dye-doped thin films by a prism-coupling method

Refractive indices and thicknesses of organic-dye-doped thin films are measured by a prism-coupling method. Anomalous dispersion of refractive indices which is caused by absorption of dyes, can be observed. The measured film thicknesses are used to determine the absorption coefficients of those films together with transmission measurements. In a highly absorptive wavelength region, the accuracy of measurements is decreased as a consequence of the broadening of m line corresponding to each guided mode. From the measurements in eosin-Y-doped polymer films, it is found that this method is not available when transmission is less than about 80%.

Generation of a phase-conjugate wave by degenerate four-wave mixing in an erythrosin-B-doped planar waveguide

A phase-conjugate wave (PCW) generated by degenerate four-wave mixing (DFWM) in a nonlinear-optical waveguide excited by a cw Ar-ion laser was observed. The planar waveguide consisted of a transparent polyvinyl alcohol layer partly doped with erythrosin-B. The DFWM excitation was performed as follows: Two pump waves impinged in the interaction region of the waveguide from the outside, and a probe wave was introduced into the guiding layer by a prism coupler. A PCW reflectivity of 6.3 x 10(-5) outside the prism coupler was obtained at a pump intensity of 1.2 W/cm(2).

Polarization-dependent phase-conjugate reflectivity in randomly oriented saturable absorbers

Polarization dependence of phase-conjugate reflectivity by degenerate four-wave mixing is clarified theoretically and experimentally in a saturable-dye-doped polymer film. 1. _INTRODUCTLON A dyedoped film in which optically anisotropic saturable dye molecules are rigidly fixed and are randomly oriented has been used as a nonlinear material which can generate a phase-conjugate (PC) wave by degenerate four-wave mixing13 (DFWM). Such a film can generate a PC wave which has the same polarization state as the probe wave even for a probe wave orthogonally polarized to two pump waves. Tompkin et. al. 4 showed that in such a phase conjugator the nearly perfect vectorial phase conjugation can be obtained at the pump intensity near the saturation intensity of the phase conjugator. In this work following the analysis of Tompkin et. al. 4 closed-form solutions for the PC reflectivities in the dye-doped film are derived for two states of the polarization: the probe wave is polarized parallel and perpendicular to the pump waves. Some experimental results are also demonstrated in an eosin-Y-doped poly-vinyl alcohol (PVA) film and are compared with the theoretical results. 2. POLARIZATION DEPENDENT PC REFLECTIVITIES Dye molecules are modeled as dipoles which are randomly and uniformly oriented and are rigidly fixed in a solid matrix. We assume that each dye molecule has only one component of transition dipole moments at a wavelength considered5. An induced dipole moment of each dye molecule by

Self-Diffraction by Two-Wave Mixing in Organic-Dye-Doped Film

Self-diffraction by nondegenerate two-wave mixing (TWM) in a saturable-dye-doped film is analyzed by means of a model of a three-level system for dyes. The rate equation approximation of a density matrix method leads to the electric polarization for nondegenerate TWM. Under the approximation of a strong pump limit and no pump absorption and depletion, the solution for the self-diffracted probe beam can be analytically obtained. The theoretical predictions are found to be in fair agreement with the experimental results.