Encryption/decryption and microtarget capturing by pH-driven Janus microstructures fabricated by the same femtosecond laser printing parameters

Several natural organism can change shape under external stimuli. These natural phenomena have inspired a vast amount of research on exploration and implementation of reconfigurable shape transformation. The Janus structure is a promising approach to achieve shape transformation based on its heterogeneous chemical or physical properties on opposite sides.However, the heterogeneity is generally realized by multi-step processing, different materials,and/or different processing parameters. Here, we present a simple and flexible method of producing p H-sensitive Janus microactuators from a single material, using the same laser printing parameters. These microactuators exhibit reversible structural deformations with large bending angles of ~31°and fast response(~0.2 s) by changing the p H value of the aqueous environment. Benefited from the high flexibility of the laser printing technique and the spatial arrangements, pillar heights, and bending directions of microactuators are readily controlled,enabling a variety of switchable ordered patterns and complex petal-like structures on flat surfaces and inside microchannels. Finally, we explore the potential applications of this method in information encryption/decryption and microtarget capturing.

Three-dimensional chiral microstructures fabricated by structured optical vortices in isotropic material

Optical vortices,a type of structured beam with helical phase wavefronts and‘doughnut’-shaped intensity distributions,have been used to fabricate chiral structures in metals and spiral patterns in anisotropic polarization-dependent azobenzene polymers.However,in isotropic polymers,the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to the two-dimensional‘doughnut’-shaped intensity profile of the optical vortices.Here we develop a powerful strategy to realize chiral microstructures in isotropic material by coaxial interference of a vortex beam and a plane wave,which produces threedimensional(3D)spiral optical fields.These coaxial interference beams are generated by designing contrivable holograms consisting of an azimuthal phase and an equiphase loaded on a liquid-crystal spatial light modulator.In isotropic polymers,3D chiral microstructures are achieved under illumination using coaxial interference femtosecond laser beams with their chirality controlled by the topological charge.Our further investigation reveals that the spiral lobes and chirality are caused by interfering patterns and helical phase wavefronts,respectively.This technique is simple,stable and easy to perform,and it offers broad applications in optical tweezers,optical communications and fast metamaterial fabrication.

Dynamic Airy imaging through high_efficiency broadband phase microelements by femtosecond laser direct writing

Manipulating Airy beams to symmetric Airy beams(SABs)with abruptly autofocusing and self accelerating properties has attracted much attention.With such a particular propagation dynamic,SABs may provide great potential in dynamic signal imaging.On the other hand,the generation of SABs by spatial light modulators suffers from the limitations of phase gradient accuracy,low optical efficiency(<40%),and a bulky footprint.Therefore,exploring imaging applications and optimal generation methods of these Airy-type beams deserves further research.Here,based on the coordinate transformation of SAB,an asymmetric Airy beam(AAB)is realized.Symmetric/asymmetric cubic phase microplates(SCPPs/ACPPs)are designed and fabricated for generating SAB/AAB.The SCPP/ACPP demonstrates superior performance:compact construction(60μm × 60μm × 1.1μm),continuous variation of phase,high efficiency(~81%at 532 nm),and broadband operation from 405 to 780 nm.Dynamic imaging under monochromatic and polychromatic lights is realized by the SAB/AAB,indicating various results at different propagation distances with a certain initial signal.Further investigation reveals that the SCPP on a soft substrate maintains its physical dimensions and optical properties unchanged during stretching.Our work enables wide potential applications in integrated optics,beam manipulation,and imaging.