Optical vortex pulses

Optical vortex pulses. In addition to having spin angular momentum, light beams can also have orbital angular momentum (see the article by Miles Padgett, Johannes Courtial, and Les Allen in Physics Today, May 2004, page 35). Often called vortex beams, they have a helical wavefront and a doughnut-shaped profile with vanishing intensity along the beam axis, and they are being increasingly used in applications such as rotating particles in optical tweezers. Though most investigations with optical vortex beams have focused on continuous-wave (CW) operation, pulsed vortex beams could open up several additional applications in materials processing or nonlinear frequency conversion. Now Haohai Yu (Shandong University) and colleagues have demonstrated a new approach for directly and controllably generating pulsed vortex beams. To drive their pulsed laser, the researchers use a CW commercial laser diode that also has a doughnut-shaped profile. As the pump power increases, thermal effects in the...