Fig. 7: Simulations with a reduced gold cap.
From: Evanescent field trapping and propulsion of Janus particles along optical nanofibers
a–c Distributions of the temperature increase, ΔT = T − T0 (with respect to the room temperature of T0 = 20∘C = 273.15 K), around a Janus particle (Rp = 1.5 μm, d = 20 nm, α0 = 28. 5∘) near an ONF (Rf = 0.35 μm, P = 100 mW) in water. The gold cap has a variable base radius, Rcap; (a) same as in Fig. 2a (Rcap = Rp), (b) slightly reduced (Rcap = 0.866 Rp), (c) reduced to zero (no coating). d Maximum temperature increase (for P = 100 mW), (e) longitudinal and (f) radial optical forces (reduced by P), (g) propulsion enhancement simulated for a Janus particle with a reduced gold cap, \(\tilde{R}={R}_{{{{{{{{\rm{cap}}}}}}}}}/{R}_{{{{{{{{\rm{p}}}}}}}}}\le 1\), the two different coating thicknesses (10 and 20 nm with α0 = 27. 5∘ and 28. 5∘, respectively), and a fixed ONF radius (Rf = 0.35 μm). Markers indicate the simulated points, solid and dashed lines refer to spline interpolations, shaded bands mark the standard deviation ranges for the experimental data. Inset in (g) shows the measured (markers with error bars, same data as in Fig. 5e) and the simulated (lines) propulsion enhancement as a function of the ONF radius, Rf. The gold cap is simulated with \(\tilde{R}=0.934\) and the experimentally found values of the balance orientation angle, α0.
