Two counterpropagating laser beams were used to significantly stretch soft dielectrics such as cells.
The deforming forces act on the surface between the object and the surrounding medium and are considerably
higher than the trapping forces on the object. Radiation damage is avoided since a double-beam
trap does not require focusing for stable trapping. Ray optics was used to describe the stress profile on
the surface of the trapped object. Measuring the total forces and deformations of well-defined elastic
objects validated this approach.