Faster and More Accurate Geometrical-Optics Optical Force Calculation Using Neural Networks.

Optical forces are often calculated by discretizing the trapping light beam into a set of rays and using geometrical optics to compute the exchange of momentum. However, the number of rays sets a trade-off between calculation speed and accuracy. Here, we show that using neural networks permits overcoming this limitation, obtaining not only faster but also more accurate simulations. We demonstrate this using an optically trapped spherical particle for which we obtain an analytical solution to use as ground truth. Then, we take advantage of the acceleration provided by neural networks to study the dynamics of ellipsoidal particles in a double trap, which would be computationally impossible otherwise.

Experimental optical trapping with frozen waves.

We report, to the best of our knowledge, the first optical trapping experimental demonstration of microparticles with frozen waves. Frozen waves are an efficient method to model longitudinally the intensity of nondiffracting beams obtained by superposing copropagating Bessel beams with the same frequency and order. Based on this, we investigate the optical force distribution acting on microparticles of two types of frozen waves. The experimental setup of holographic optical tweezers using a spatial light modulator has been assembled and optimized. The results show that it is possible to obtain greater stability for optical trapping using frozen waves. The significant enhancement in trapping geometry from this approach shows promising applications for optical tweezers micromanipulations over a broad range.

Focus issue introduction: optical cooling and trapping.

The year 2015 is an auspicious year for optical science, as it is being celebrated as the International Year of Light and Light-Based Technologies. This Focus Issue of the journals Optics Express and Journal of the Optical Society of America B has been organized by the OSA Technical Group on Optical Cooling and Trapping to mark this occasion, and to highlight the most recent and exciting developments in the topics covered by the group. Together this joint Focus Issue features 32 papers, including both experimental and theoretical works, which span this wide range of activities.

Two-photon continuous flow lithography.

A new approach for microfluidics-based production of polymeric particles, namely two-photon continuous flow lithography, is reported. This technique takes advantage of two-photon lithography to create objects with sub-micrometer and 3D features, and overcomes the traditional process limitations of two-photon lithography by using multiple beam production under continuous flow. Polymeric fibers, helical and bow-tie particles with sub-diffraction resolution and surface roughness as low as 10 nm are demonstrated.

Electromagnetic forces for an arbitrary optical trapping of a spherical dielectric.

A double tweezers setup was employed to perform ultra sensitive force measurements and to obtain the full optical force curve as a function of radial position and wavelength. The light polarization was used to select either the transverse electric (TE), or transverse magnetic (TM), or both, modes excitation. Analytical solution for optical trapping force on a spherical dielectric particle for an arbitrary positioned focused beam is presented in a generalized Lorenz-Mie diffraction theory. The theoretical prediction of the theory agrees well with the experimental results. The algorithm presented here can be easily extended to other beam geometries and scattering particles.