Realization of pitch-rotational torque wrench in two-beam optical tweezers

3D Pitch (out-of-plane) rotational motion has been generated in spherical particles by maneuvering the laser spots of holographic optical tweezers. However, since the spherical particles, which are required to minimise drag are perfectly isotropic, a controllable torque cannot be applied with it. It remains free to spin about any axis even after moving the tweezers beams. It is here that we trap birefringent particles of about 3 mu m diameter in two tweezers beams and then change the depth of one of the beam foci controllably to generate a pitch rotational torque-wrench and avoid the free spinning of the particle. We also detect the rotation with newly developed pitch motion detection technique and apply controlled torques on the particle.

Automated summary

Rotational motion in spherical particles has been achieved by manipulating laser spots in holographic optical tweezers. By trapping birefringent particles in two beams and adjusting the depth of one beam's focus, a controllable pitch rotational torque-wrench is generated to prevent free spinning of the particle. The rotation is detected using a new pitch motion detection technique and controlled torques are applied.