The construction and characterization of optical traps for manipulating microscopic particles

Optical traps use tightly focused laser light to manipulate microscopic particles and have applications in nanofabrication, characterizing DNA, and \textit{in vitro} fertilization [1]. We will describe the design, construction, and characterization of an optical trap that is capable of trapping and imaging 3 $\mu $m polystyrene spheres using a 12 mW HeNe laser. The design was based on previous work [2,3] describing how to build affordable optical traps. We will discuss trapping forces and their calibration. \\[4pt] [1] D.G. Grier, ``A Revolution in Optical Manipulation,'' Nature \textbf{424}, 810-816 (2003). \\[0pt] [2] S.P. Smith et al., ``Inexpensive optical tweezers for undergraduate laboratories,'' Am. J. Phys. \textbf{67} (1), 26-35 (1999).\\[0pt] [3] J. Bechhoefer \textit{et al.}, ``Faster, cheaper, safer optical tweezers for the undergraduate laboratory,'' Am. J. Phys. \textbf{70} (4), 393-400 (2001).