Manipulation and imaging of particles with optical tweezers and confocal microscopy

3D micromanipulation and imaging of colloids has been achieved by combining optical tweezers and confocal microscopy using two microscope objectives. Arrays of up to several hundred time-shared traps have been created using acousto-optical deflectors. In addition, two axially separated trapping planes were addressed using a Pockels cell, making trapping and dynamic manipulation of 3D colloidal structures possible. Structures of high refractive index core-shell colloidal particles were trapped inside a concentrated dispersion of index-matched particles, thereby creating a nucleus for colloidal crystallization. Using confocal microscopy, the effects of such structures upon the non-trapped rest of the dispersion could be analysed quantitatively in 3D.