Algorithms for shaping coherent light beams with pre-determined phase and intensity profiles along three-dimensional (3D) paths are important for numerous applications in imaging, laser materials processing, and particle trapping. However, such beams in 3D have only been generated with prescribed intensity values in simple geometries; high intensity and phase gradients are also needed, for example, to manipulate and induce complex particle movements in optical traps. A new noniterative holographic beam-shaping technique developed by researchers at Universidad Complutense de Madrid (Madrid, Spain) and the Samara branch of PN Lebedev Physical Institute (Samara, Russia) generates high-intensity gradient (HIG) beams with both phase and intensity prescribed along arbitrary 3D curves.
This technique uses a spatial light modulator to encode—as a computer-generated hologram—the desired beam. The hologram is illuminated by a collimated laser beam and then focused by a lens, yielding the target 3D light curve with both HIG and phase gradients. This approach allows accurate generation of 3D beams, from simple circles and spirals to complex knots and star-shaped patterns. Its performance is experimentally proven for trapping of colloidal micron-sized particles. Contact José A. Rodrigo at [email protected].