Optical Tweezers

This multi-touch interface displays microscope video images in real-time and allows the users to intuitively trap and control objects within the microscope using optical traps

Optical tweezers are a micromanipulation technology in which the gradient forces associated with tightly focussed laser light are exploited to exert forces on dielectric particles. By using a high numerical aperture objective lens, a laser beam is brought to a focus in a liquid sample chamber, forming a trap for micron-sized particles (see image below). These traps make an ideal environment for the investigation of systems such as dielectric colloidal particles and single cells.

Multiple optical traps can be generated and controlled by imposing a diffractive optical element (DOE) in a plane optically conjugate with the back-aperture of the objective lens. We use liquid crystal spatial light modulators (LCSLMs) for this purpose, with a 'gratings and lenses' algorithm running on a graphics card generating the necessary patterns to produce arbitrary arrays of laser focii in the microscope's image plane.

Further details are available on the Nanophysics and Soft Matter research group pages.

Cells in suspension

Optical tweezers can be exploited to study the behaviour of single cells in suspension, as well as the behaviour of small populations of cells as they are brought into close proximity with one another. The 'light touch' of optical tweezers are ideal for investigations in physiologically relavent in vitro conditions.

A haptic force-feedback controller enabling control of multiple optical traps in three dimensions within a sample. The positions of the optical traps are determined by the position of the user's finger tips, and the forces experienced by any trapped objects are fed back to the user.

Who to contact

For information relating to optical tweezers, please contact Professor Mervyn Miles or Dr Dave Phillips.

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