We realized integrated photonics multi-waveguide devices for optical trapping and Raman spectroscopy of particles in a fluid. In these devices, multiple beams directed towards the device center lead to a local field enhancement around this center and thus counteract the effect of light concentration near the facets, which is a disadvantage of dual-waveguide traps. Thus, a trapping region is created around the center, where a single particle of a size in a wide range can be trapped and studied spectroscopically, free from the influence of surfaces. We report the design (including simulations), fabrication and performance demonstration for multi-waveguide devices, using our Si₃N₄ waveguiding platform as the basis. The designed ridge waveguides, optimized for trapping and Raman spectroscopy, emit narrow beams. Multiple waveguides arranged around the central microbath result from fanning out of a single input waveguide using Y-splitters. A second waveguiding layer is implemented for detection of light scattered by the trapped particle. For reliable filling of the device with sample fluid, microfluidic considerations lead to side channels of the microbath, to exploit capillary forces. The interference of the multiple beams produces an array of hot spots around the bath center, each forming a local trap. This property is clearly confirmed in the experiments and is registered in videos. We demonstrate the performance of a 2-waveguide and a 16-waveguide device, using 1 and 3 pm polystyrene beads. Study of the confined Brownian motion of the trapped beads yields experimental values of the normalized trap stiffness for the in-plane directions. The stiffness values for the 16-waveguide device are comparable to those of tightly focused Gaussian beam traps and are confirmed by our own simulations. The Raman spectra of the beads (in this work measured via an objective) show clear peaks that are characteristic of polystyrene. In the low-wavenumber range, the spectra have a background that most likely originates from the Si₃N₄ waveguides.

Photoionization of the chiral monoterpene limonene has been investigated using polarized synchrotron radiation between the adiabatic ionization threshold, 8.505 and 23.5 eV. A rich vibrational structure is seen in the threshold photoelectron spectrum and is interpreted using a variety of computational methods. The corresponding photoelectron circular dichroism—measured in the photoelectron angular distribution as a forward–backward asymmetry with respect to the photon direction—was found to be strongly dependent on the vibronic structure appearing in the photoelectron spectra, with the observed asymmetry even switching direction in between the major vibrational peaks. This effect can be ultimately attributed to the sensitivity of this dichroism to small phase shifts between adjacent partial waves of the outgoing photoelectron. These observations have implications for potential applications of this chiroptical technique, where the enantioselective analysis of monoterpene components is of particular interest.