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 fo r the measurement of piconewton forces in aqueous media. An optical trap co nstructed 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 i ts full functionality the system is compact, portable, relatively inexpensi ve and easy to construct and operate. A new scheme for trapping force calib ration is also reported and measurements compared to theoretical results. T he trapping efficiency is found to be similar to that obtained when using o ther trapping systems.