Figure 3.

Temperature spatial profile of the heating laser beam. Measurements were taken at five different positions within the heating beam spot (see inset). (a–d) The distances from (a) and (b), and from (c) and (d) to the center of the screen are ∼23 μm and ∼42 μm, respectively. Red dots show the measured temperature at 5.7 mW inside the fluidics chamber (full heating laser power), and orange dots show the measured temperature at 4 mW. Blue dots show the measured temperature with the heating laser off. This measured temperature (∼27°C) is taken as ambient for the 1D heat-flow model (Supporting Material), whose predictions are the red and orange continuous curves for 5.7 and 4 mW, respectively. Left graph: Stokes’ law analysis; right graph: thermal noise analysis. To see this figure in color, go online.