Figure 12.7 — Optical fibre traps Figure 12.7 — Optical fibre traps. (a) Dual-beam optical fibre trap showing the optical gradient (Fgrad) and scattering (Fscat,1, Fscat,2) forces that act on the trapped particle. (b) Optical stretching of an osmotically swollen red blood cell (RBC) in an optical fibre trap. As the laser power is increased (text below the images), the RBC becomes elongated along the trap axis. The top row shows the RBC trapped at 5 mW in each beam; the bottom row was obtained by increasing the power to the value indicated below the image and then reducing it again to 5 mW to demonstrate the reversibility of the process. (c) Longitudinal optical binding of an increasing number of particles in an optical fibre trap.Figures (a) and (b) are reprinted from Guck et al., Biophys. J. 81, 767–84, copyright (2001), with permission from Elsevier.Figure (c) is reprinted figure from Gordon et al., Phys. Rev. B 77, 245125. Copyright (2008) by the American Physical Society.