Photonic nanojets in optical tweezers

Abstract

Photonic nanojets have been brought into attention ten years ago for potential application in ultramicroscopy, because of its sub-wavelength resolution that can enhance detection and interaction with matter. For these novel applications under development, the optical trapping of a sphere acts as an ideal framework to employ photonic nanojets. In the present study, we generated nanojets by using a highly focused incident beam, in contrast to traditional plane waves. The method inherits the advantage of optical trapping, especially for intracellular applications, with the microsphere in equilibrium on the beam propagation axis and positioned arbitrarily in space. Moreover, owing to optical scattering forces, when the sphere is in equilibrium, its center shifts with respect to the focal point of the incident beam. However, when the system is in stable equilibrium with a configuration involving optical tweezers, photonic nanojets cannot be formed. To overcome this issue, we employed double optical tweezers in an unorthodox configuration involving two collinear and co-propagating beams, the precise positioning of which would turn on/off the photonic nanojets, thereby improving the applicability of photonic nanojets.

Optical tweezers and their applications

“…where the integration is carried out over the surface S surrounding the scattering Maxwell stress tensor simplifies as [6,18]: expansion coefficients of the scattered fields [65,87]. The precise connection between the T-matrix formulation and GLMTs can be found in [88], while a description of the use of GLMTs for calculations in optical tweezers can be found, e.g., in [89,90,91,92,93].…”

Optical Manipulation of Lanthanide-Doped Nanoparticles: How to Overcome Their Limitations

“…When it is optically trapped, the particle focuses the light and a nanosized photonic jet is generated at its shadow-side surface. Photonic nanojets can propagate over a distance corresponding to several optical wavelengths without significant divergence, and their waist size is below the diffraction limit, depending on the microlens diameter, diffraction index, and laser wavelength (Chen et al, 2004 ; Neves, 2015 ). In addition, the light backscattering and the nanoparticle luminescence can be enhanced and recorded, making fiber-coupled microspheres suitable for NPs:Ln optical manipulation.…”

Coated High-Refractive-Index Barium Titanate Glass Microspheres for Optically Trapped Microsphere Super-Resolution Microscopy: A Simulation Study

“…Meanwhile, an ultra-narrow PNJ can be gained by overstepping the upper refractive index [22], a dielectric cylinder, with a glass cuboid [23] and a nanohole-structured mesoscale dielectric sphere [24]. It is responsible for switching the PNJ on and off for a microsphere with an incident focused beam [25]. The PNJ theory is regarded as a part of the super-resolution mechanism, and there is a qualitative relation between PNJ property and imaging performance [26][27][28].…”