  We propose a photoexcitation scheme for pure spin current generation in
graphene subject to a Rashba spinorbit coupling. Although excitation using
circularly-polarized light does not result in optical orientation of spins in
graphene unless an additional magnetic field is present, we show that
excitation with linearly-polarized light at normal incidence yields spin
current injection without magnetic field. Spins are polarized within the
graphene plane and are displaced in opposite directions, with no net charge
displacement. The direction of the spin current is determined by the linear
polarization axis of the light, and the injection rate is proportional to the
intensity. The technique is tunable via an applied bias voltage and is
accessible over a wide frequency range. We predict a spin current polarization
as high as 75% for photon frequencies comparable to the Rashba frequency. Spin
current injection via optical methods removes the need for ferromagnetic
contacts, which have been identified as a possible source of spin scattering in
electrical spin injection in graphene.
