Fig. 5. Analysis of the results from trapping silica beads using the UNM-enhanced fibre.

a Power-spectral-density (PSD) analysis of a representative dataset (shown in Fig. 4d), including the corresponding fits (thick lines) for the axial (blue) and transverse (green) directions. b Corresponding mean-square-displacement (MSD) analysis for the same dataset including fits. c Resulting trap stiffness at different power levels for both samples (sample 1: NA = 0.84, sample 2: NA = 0.88, for details, see Fig. 2b) determined using the MSD method (Fig. 5b). As expected, a higher NA yields stronger trapping, while the transverse stiffness is approximately one order of magnitude higher than that in the axial direction (compare ref. ¹³)