A combined experimental and theoretical study is carried out to probe the rotational behavior of red blood cells (RBCs) in a single beam optical trap. We induce shape changes in RBCs by altering the properties of the suspension medium in which live cells float. We find that certain shape anisotropies result in the rotation of optically trapped cells. Indeed, even normal (healthy) RBCs can be made to rotate using linearly polarized trapping light by altering the osmotic stress the cells are subjected to. Hyperosmotic stress is found to induce shape anisotropies. We also probe the effect of the medium's viscosity on cell rotation. The observed rotations are modeled using a Langevin-type equation of motion that takes into account frictional forces that are generated as RBCs rotate in the medium. We observe good correlation between our measured data and calculated results.
We theoretically investigated the stability of highly charged fullerene cations produced with an ultrashort intense nearinfrared
(IR) laser pulse (light intensity I~ 5 × 10<sup>14</sup> W/cm<sup>2</sup> and wavelength λ ~ 1800 nm). The effects of nonlinear
interactions with near-IR pulses are taken into account by combining an ab initio molecular dynamics method with an
time-dependent adiabatic state approach. The results indicate that large-amplitude vibration with energy of > 10 eV is
induced by impulsive Raman excitation in the delocalized <i>h</i><sub>g</sub>(1)-like mode of C<sub>60</sub>
<sup>z+</sup>. The field-induced large-amplitude
vibration of the <i>h</i><sub>g</sub>(1) mode persists for a rather long period. In conclusion, C<sub>60</sub> and its cations created upon ionization are
extremely robust against field-induced structural deformation. We found that the acquired vibrational energy is
maximized at T<sub>p</sub> ~
<sub>vib</sub>/2, where <i>T</i><sub>p</sub> is the pulse length and T<sub>vib</sub> is the vibrational period of the <i>h</i><sub>g</sub>(1) mode. We confirmed
that the vibrational energy deposited in C<sub>60</sub> can be controlled by a pulse train, i.e., by changing the intervals between
pulses. Vibrational mode selectivity is also achieved by adjusting the pulse intervals.