Abstract

It is well known that the light carries linear and angular momentum that can be transferred to the irradiated objects. Angular momentum of the beam is comprised of spin angular momentum (SAM) and orbital angular momentum (OAM). SAM is associated to the beam’s polarization and is always intrinsic. OAM comes from the azimuthal phase variations of the beam and can be both extrinsic and intrinsic. The beam with helical phase φ = lϕ, where φ is phase, ϕ is polar angle and l is positive or negative integer number, possesses well-defined OAM with lℏ [1]. Such beams are often refered to as optical vortices and are exploited in optical tweezer experiments enabling the rotation of trapped particles. Changing the wavefront’s helicity, also the geometry of the beam is changed. The higher is |l|, the larger is the diameter of the beam. In order to change the total angular momentum of the beam, either the shape of the beam or the photon density has to be changed. As a result, the experiments which require fixed beam size and intensity are limited to fixed OAM. Recently, we implemented optical tweezers with tunable angular momentum, there OAM could be changed from -1 to 1 by controlling ellipticity of the incident laser beam. Here we extend this technology and demonstrate the generation of optical vortices of high topological charge up to 100 (Fig. 1(a)–(i)) using femtosecond laser written polarization converters (the S-waveplate) [2].

© 2015 IEEE