An optical vortex is an inhomogeneous light beam having a phase singularity at its axis, where the intensity of the electric and/or magnetic field may vanish. Already well studied are the paraxial beams, which may carry well-defined values of spin (polarization $\sigma$) and orbital angular momenta; the orbital angular momentum per photon is given by the topological charge $\ell$ times the Planck constant. Here we study the light hole–to–conduction band transitions in a semiconductor quantum dot induced by a highly focused beam originating from a $\ell =1$ paraxial optical vortex. We find that at normal incidence the pulse will produce two distinct types of electron-hole pairs, depending on the relative signs of $\sigma$ and $\ell$. When sgn($\sigma$) $=$ sgn($\ell$), the pulse will create electron-hole pairs with band+spin and envelope angular momenta both equal to 1. In contrast, for sgn($\sigma$) $\ne$ sgn($\ell$), the electron-hole pairs will have neither band+spin nor envelope angular momenta. A tightly focused optical-vortex beam thus makes possible the creation of pairs that cannot be produced with plane waves at normal incidence. With the addition of co-propagating plane waves or switching techniques to change the charge $\ell$ both the band+spin and the envelope angular momenta of the pair wave function can be precisely controlled. We discuss possible applications in the field of spintronics that open up.

• Received 14 March 2014
• Revised 19 August 2014

DOI:https://doi.org/10.1103/PhysRevB.90.115401