Characterisation of near-field optical trapping and biological applications

Optical tweezers are powerful and versatile tools for optical micromanipulation, and have emerged as a discipline in itself, providing a great range of exibility and accuracy for all optical micromanipulation of diverse microscopic samples. The forces associated with far-field optical tweezers are of piconewton range and hence tweezers are used to pull on bead-handles for measuring forces in the sub-piconewton range. The highly concerned imaging and optical manipulation which is required in the nanometric range could be achieved in an efficient manner, by using optical near-fields. Optical near-fields or evanescent fields enable non-diffractive interaction of light with matter, and provide imaging and manipulation with nanometric resolution. Evanescent fields have also been used for particle guiding, where the characteristic feature of evanescent wave guiding is the ability to confine the particles along a surface.