Multiple optical trapping by means of diffractive optical elements

In this paper we report multiple optical trapping of microscopic dielectric particles using diffractive optical elements implemented on twisted nematic liquid crystal spatial light modulators. The particles are trapped in arrays disposed in plane or in volume and can be moved independently in x-y-z by changing the configuration of the diffractive optical element. We show also multiple trapping using Laguerre-Gaussian and Gaussian beams simultaneously. The orbital angular momentum of the Laguerre-Gaussian beam is transferred to the particle, making it to move on a circular trajectory defined by the intensity pattern specific to this beam. We use sample cells built with two microscope slides separated by 120mum with a sticky tape. The space between the two slides is filled with 2mum diameter silica spheres diluted in water (concentration 0.026% wt). We show that optical trapping is also possible in a small glass capillary with a diameter of 100mum.