Section 4. OPTICAL FORCES AND TORQUES ON PARTICLES
In 1986 Ashkin et al. (4.1, Paper 4.1) published their seminal paper on optical tweezers which describes the way in which a tightly focused laser beam may be used to trap and manipulate micron-sized particles in three dimensions. The paper has received over 400 scientiﬁc citations and, apart from its great importance in optical and atomic physics, has spawned a multitude of biological experiments including measurements of individual muscle forces, stretching of DNA and, when combined with other lasers, the cutting and manipulation of biological materials (4.2).