Fig. and show the temperature distributions in the x-y and y-z planes, respectively. In the x-y plane shown in Fig. , the temperature decreases radially from the heat source, which is the laser spot, following a 1/r distance dependence. On the other hand, in the x-y plane shown in Fig. , despite adding a constant amount of heat to the heat source within the cylinder, the temperature decreases within the heat source near the interface between the glass and water in the z-direction. This temperature drop is due to the cooling effect of the glass substrate. Figs. ande show the magnitude of temperature gradients calculated by differentiating the temperature distributions in Figs. and. As the temperature distribution is almost uniform around the center of the heat source, the temperature gradients are quite small within the heat source. In contrast, near the interface of a cylindrical heat source, the temperature gradient is on the order of 10 6 to 10 7 K m -1 . And within a distance of about 20 m from the interface of the heat source, the temperature gradient is on the order of 10 5 K m -1 . These values are sufficient to drive thermophoresis. shows the magnitude of temperature gradient in the x-y plane, and (e) shows the magnitude of temperature gradient in the y-z plane.