Roadmap for Optical Tweezers 2023

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration

Simultaneous optical trapping and magnetic micromanipulation of ferromagnetic iron-doped upconversion microparticles in six degrees of freedom

Optical trapping of magnetic Fe-oxide particles is notoriously difficult due to their high refractive indices, not to mention high absorptivity at the trapping infra-red wavelengths. We synthesize Fe co-doped NaYF4:Yb,Er ferromagnetic upconversion particles that not only have refractive indices conducive for optical trapping, but also heat less than Haematite particles at off-resonant wavelengths. These particles are hexagonal shaped with dimensions of the order of 3 micrometer and also bear high coercivity of 20 mT and saturation magnetisation of 1 Am^2/kg. This enables simultaneous use of optical trapping and magnetic forces to generate micro-manipulation in all the six degrees of freedom of a rigid body. We also show that these particles heat significantly when illuminated on absorption resonance at 975 nm while emitting visible light with possible implications for fluorescence microscopy and photothermal therapy of cancer cells

Flexing Muscles in Virtual Reality: Effects of Avatars' Muscular Appearance on Physical Performance

Virtual reality (VR) allows users to embody any possible avatar. Previous work found that the appearance of avatars can change our perception and behavior. Such behavioral changes based on stereotypical assessments are known as the Proteus effect. Exergames involve physical activities of players, however, it is currently unknown if behavioral changes caused by an avatar's appearance can affect players' performance in physically engaging tasks. Therefore, we conducted a study with 30 participants to determine the effect of avatars' muscularity on physical performance and perception of effort. We found that participants in muscular avatars had a lower perceived exertion during an isometric force task. Furthermore, male participants embodying a muscular avatar had a higher grip strength. Results suggest that embodying avatars associated with power and strength can decrease the perception of effort and enhance physical performance. We discuss how body ownership, user identification, and gender moderate avatars' effects