A high-performance and simplified quasi-elastic laser scattering method using homodyne detection in beam divergence

We devise the new principle of the quasi-elastic laser scattering (QELS) method using a homodyne detection technique in a beam divergence and successfully facilitate the equipment The QELS method is a unique technique for the noncontact and time-resolved study of surface tension at liquid surfaces and liquid/liquid interfaces. The conventional QELS method requires a precise optical alignment using a local oscillator such as a diffraction grating, and the determination of the surface tension accompanies much difficulty because of the low S/N ratio of the power spectra. Our new principle allows high-performance QELS measurements by only a simple alignment of a downsized experimental setup. The power spectra are obtained with 50-100 times higher S/N ratios than the conventional ones. The power spectra are analyzed by a new theory, and the calculated surface tensions agree with the literature values. The accuracy of the surface tension measurements using the QELS method is substantially improved.