Fig. 4.

Probability density to find the Janus sphere pointing at an angle $\gamma$ to the heat source. The panels show data (symbols) measured for various distances r between particle and heat source: (a) $1.1\mathrm{\mu }\text{m}$, (b) $1.7\mathrm{\mu }\text{m}$, (c) $2.3\mathrm{\mu }\text{m}$, (d) $2.8\mathrm{\mu }\text{m}$. The solid lines are best fits by Eq. (10), with free fit parameters ${\Omega }_{1,2}/D_{\mathrm{r}}$. The dashed lines are fits by $f\propto \exp [({\Omega }_0/D_{\mathrm{r}})cos\gamma ]$ [30] for an angular speed profile ${\Omega }_z={\Omega }_{0}sin\gamma$ with ${\Omega }_0/D_{\mathrm{r}}$ as a free fit parameter. These fits yield for ${\Omega }_0/D_{\mathrm{r}}$, ${\Omega }_1/D_{\mathrm{r}}$, ${\Omega }_2/D_{\mathrm{r}}$ the values (a) 0.596, 0.722, $-0.284$, (b) 0.493, 0.526, $-0.091$, (c) 0.355, 0.377, $-0.0855$, (d) 0.224, 0.228, $-0.0248$, respectively