Nonlinear oscillation of interfacial tension was found for a liquid/liquid interface composed of di(2ethylhexyl) phosphoric acid/n-heptane/calcium chloride/water. The range of the oscillations was over several millineutons per meter, with the longest one continuing over a few hours. A wide variety of oscillation patterns was observed, but they were classified into two groups. One group showed that the power spectrum was proportional to f -2 , with f being the frequency, and the distribution function of the amplitudes followed a Gaussian distribution function. This type of oscillation, type A, became slightly weaker with decreasing temperature and looked like a random process which may be associated with thermal energy. Another type, type B, was entirely different from type A. The power spectrum approximately followed a scaling law. The scaling index was almost unity; however, the scaling law was not perfect compared to that of type A. The distribution function of the amplitudes was not a Gaussian distribution. An increase in temperature made the average amplitude smaller. This type of oscillation required a higher interfacial tension than that for type A. Further, a quasi-periodic change of interfacial tension was sometimes observed. Those changes suggested that type B oscillation was caused by an attractive interaction between surfactant molecules. It introduced an unstable region in the interfacial pressure-interfacial area isotherm which caused type B oscillation. A simple model was proposed to explain type B oscillations, which could capture some experimental trends.

A computationally efficient numerical simulation of a diode-pumped alkali laser (DPAL) has been developed. It considers the thermal lensing effect by a wave-optics optical resonator model coupled with a simplified gas-flow model. The calculation results indicate that the proposed gas-flow model correctly predicts the temperature distribution of the active medium heated by exothermic reactions. As a result, there is good agreement between the calculations and experiments, especially with the output power as a function of the gas-flow velocity. The calculations have shown that the population of the high-lying excited levels of the Cs atom is negligible within a pump power intensity of 10 kW/cm2.

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We have developed a numerical simulation method for diode-pumped alkali lasers (DPALs). We previously reported the use of a simplified gas-flow model, whose adaptability was restricted to forced gas-flow DPALs. In the present study, we have employed an incompressible, three-dimensional computational fluid dynamics (CFD) model. The natural convective flow is modeled using a modified Boussinesq approximation. The results of the simulations were found to be in good agreement with those for a compressible CFD model for a heat-induced flow problem. As a result, good agreement with the experimental results was achieved for a sealed DPAL. On the other hand, the results for the forced gas-flow DPAL were the same as those for the simplified gas-flow model, which confirms the validity of the latter model. The dependence of the beam quality on the pump power for the sealed DPAL was consistent with previously reported results.