Designed for attachment to microscopes, the E3500 optical tweezer system from Elliot Scientific (Harpenden, UK) is a fully functional, computer-controlled unit for multiple spot trapping and manipulation of micron-sized particles in such applications as cell sorting, microrheology, colloid research and particle spectroscopy. The system uses a high-power, fiber-coupled laser for trapping and a low-power, fiber-coupled laser as the probe beam. The optical module attaches to the microscope with an epifluorescence attachment or a camera port. High-speed, acousto-optic beam deflectors provide beam control. A high-speed, GigE interface camera allows visualization of the trapped particles through the computer interface. The 1070 nm fiber laser gives a stable, high-quality TEM00 beam with an M2 of 1.05.