Particle-Based Reconfigurable Scattering Masks for Lensless Imaging

Abstract

Light scattering is typically undesired in optical systems as it often introduces defects or otherwise negatively impacts device performance. However, rather than being a hindrance, scattering can also be exploited to achieve lensless imaging using a scattering mask instead of lenses to enable devices with low-cost, compact construction, and yet a large field of view. Lensless imaging can benefit greatly from the ability to dynamically tune the scattering pattern produced by the mask; however, this often results in increased complexity and cost. Herein, we propose and demonstrate particle-based reconfigurable scattering masks to dynamically tune light scattering for lensless imaging, enabling multishot image reconstruction. Disordered particle populations are tuned by rational application of electric fields without requiring bulky or expensive components. Several assembly motifs are explored and studied for optimal performance; in particular, gold nanowires chained between planar electrodes yield the best reconstruction quality and are the main focus in this study. The distinct gold nanowire based scattering masks achieve a complex wavelet structural similarity as low as 0.36. By leveraging the submicrometer thickness of particles and the resultant large optical memory effect, an angular field of view of ±45° is demonstrated. The reconfigurable nature of the particle arrays enables multishot reconstruction which results in enhanced image quality and improved signal-to-noise ratios by up to 10-fold. These results suggest that reconfigurable particle masks could be a broadly applicable means of achieving dynamically tunable light scattering with potential applications in lensless microscopy or high-resolution imaging.

Effect of Particle Composition on Dielectrophoretic Co-Assemblies around Topographic Features: Experiment and Theory

“…Colloidal particles can be assembled in applied electric fields to generate tunable, dynamic superstructures able to be annealed or reconfigured by changes in the applied field. − For example, colloidal crystals, − chains, − nanowire lattices, , and other structures have been generated using applied AC fields. − Such assemblies can be reconfigured in real time by changing applied field conditions, enabling a particle based, AC field-tunable optical response. For example, core–shell microparticle assembly for tunable metamaterials, switchable mid-IR broadband polarizers, reconfigurable scattering masks, field-responsive random lasers, gradient index lenses, and various surface-enhanced Raman scattering techniques − have been demonstrated based on controlling the orientation and/or local number density of various particle types. The dielectrophoretic force on particles subjected to an AC electric field is influenced by the properties of the solvent and particle and the electric field gradient, all of which can be altered and tuned with changing field conditions. − The response of particles to the applied field is determined by the difference in materials properties [i.e., permittivity (ε) and conductivity (σ)] of the suspending solvent and particle and dictates whether they will assemble in low field or high field intensity regions. ,− It is important to note that a particle’s material properties and field response are not independent of one another as the refractive index can be determined by electric permittivity and magnetic permeability, factors that are also important for a material’s response to an electric field .…”

“…15−19 Such assemblies can be reconfigured in real time by changing applied field conditions, enabling a particle based, AC field-tunable optical response. For example, core−shell microparticle assembly for tunable metamaterials, 20 switchable mid-IR broadband polarizers, 13 reconfigurable scattering masks, 1 field-responsive random lasers, 21 gradient index lenses, 22 and various surface-enhanced Raman scattering techniques 23−26 have been demonstrated based on controlling the orientation and/or local number density of various particle types. The dielectrophoretic force on particles subjected to an AC electric field is influenced by the properties of the solvent and particle and the electric field gradient, all of which can be altered and tuned with changing field conditions.…”

“…Colloidal particles can be assembled in applied electric fields to generate tunable, dynamic superstructures able to be annealed or reconfigured by changes in the applied field. − For example, colloidal crystals, − chains, − nanowire lattices, , and other structures have been generated using applied AC fields. − Such assemblies can be reconfigured in real time by changing applied field conditions, enabling a particle based, AC field-tunable optical response. For example, core–shell microparticle assembly for tunable metamaterials, switchable mid-IR broadband polarizers, reconfigurable scattering masks, field-responsive random lasers, gradient index lenses, and various surface-enhanced Raman scattering techniques − have been demonstrated based on controlling the orientation and/or local number density of various particle types.…”