Compact optical trapping microscope using a diode laser

Single beam gradient force optical trapping (laser tweezers) is increasing in importance as a technique for microparticle and cell manipulation and for the measurement of piconewton forces in aqueous media. An optical trap constructed using an optical microscope and a diode laser is described here. The system incorporates novel beam steering optics allowing the positioning of the trapping spot within the field of view of the microscope. Despite its full functionality the system is compact, portable, relatively inexpensive, and easy to construct and operate. A new scheme for trapping force calibration is also reported and measurements compared to theoretical results. The trapping efficiency is found to be similar to that obtained when using other trapping systems.