Nonlinear landscaping of optical trap potentials by the trapped objects

In this paper pairs of microspheres, are collected and suspended in high-resistance, distilled water, in the beam of a linearly polarized Ar⁺ laser. The sample is illuminated from below and the upper surface of a microcell is placed in the focal plane of a microscope objective. The light transmitted is collected with the help of an optical system and the image, formed on a screen, is digitized with a CCD camera and stored in a computer. The images are then analyzed with standard techniques.