![]() ![]() The first vectorial HOT was demonstrated by Bhebhe et al. The radially polarized vector beam, for example, is famous for achieving the smallest spot size when tightly focused 24, 25, this property has been used to create stronger axial optical traps 26, 27. Trapping with vector beams is the most recent avenue of structured light explored in optical tweezers and has already proven beneficial to the trapping community 4, 5, 23. On the other hand, vector beams are structured in polarization as well, meaning they have a spatially varying polarization pattern. So far HOT research has focused mainly on structured beams modulated in amplitude and phase-these are called scalar beams. By employing these OAM carrying beams, optical tweezers also gain rotational control of particles 19, 20, 21, 22. The fact that light carries linear momentum is well-known and is the reason why light can trap particles, however, light can also carry orbital angular momentum (OAM), like Laguerre-Gaussian (LG) beams. Structured light beams have not only been shown to enhance the trap strength 14 but Airy beams, for example, can guide a particle along a certain trajectory enabling selective removal of particles in a sample 15, 16 with petal beams it is possible to trap particles with different refractive indices simultaneously 17 and frozen waves can increase the stability and 3D control of the trap 18. Structured beams that reconstruct themselves after being distorted by a trapped particle (Bessel beams) have allowed for trapping in multiple planes 12, whereas the far-field Bessel beam can be used as an optical shield assisting with trapping in crowded environments 13. With HOTs, an array of traps can be created to trap multiple particles simultaneously while being able to dynamically change this array pattern, allowing for highly controlled manipulation of particles 8, 9, 10, 11. These structured light traps are a well-established technique today 4, 5 and since most structured beams are created by means of a hologram, they have been dubbed holographic optical tweezers (HOTs) 6, 7. ![]() However, the employment of structured light 3 (by varying the intensity, phase and polarization of light) in optical tweezers has made it possible to not only trap but to move, rotate and direct particles. ![]() Optical tweezing was first demonstrated by Arthur Ashkin in 1970 with a Gaussian beam 1 and half a century later this beam still dominates optical trapping experiments 2. Optical trapping or tweezing describes the manipulation of nano- to micro-sized particles through momentum transfer from tightly focused light. ![]()
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