Tunable and switchable polarization rotation with non-reciprocal plasmonic thin films at designated wavelengths

We experimentally demonstrate an ultra-thin plasmonic optical rotator in the visible regime that induces a polarization rotation that is continuously tunable and switchable by an external magnetic field.The rotator is a magneto-plasmonic hybrid structure consisting of a magneto-optical EuSe slab and a one-dimensional plasmonic gold grating.At low temperatures,EuSe possesses a large Verdet constant and exhibits Faraday rotation,which does not saturate over a regime of several Tesla.By combining these properties with plasmonic Faraday rotation enhancement,a large tuning range of the polarization rotation of up to 8.4° for a film thickness of 220 nm is achieved.Furthermore,through experiments and simulations,we demonstrate that the unique dispersion properties of the structure enable us to tailor the wavelengths of the tunable polarization rotation to arbitrary spectral positions within the transparency window of the magneto-optical slab.The demonstrated concept might lead to important,highly integrated,non-reciprocal,photonic devices for light modulation,optical isolation,and magnetic field optical sensing.The simple fabrication of EuSe nanostructures by physical vapor deposition opens the way for many potentially interesting magneto-plasmonic systems and three-dimensional magneto-optical metamaterials.

Ultrathin monolithic 3D printed optical coherence tomography endoscopy for preclinical and clinical use

Preclinical and clinical diagnostics increasingly rely on techniques to visualize internal organs at high resolution via endoscopes.Miniaturized endoscopic probes are necessary for imaging small luminal or delicate organs without causing trauma to tissue.However,current fabrication methods limit the imaging performance of highly miniaturized probes,restricting their widespread application.To overcome this limitation,we developed a novel ultrathin probe fabrication technique that utilizes 3D microprinting to reliably create side-facing freeform micro-optics(<130μm diameter)on single-mode fibers.Using this technique,we built a fully functional ultrathin aberration-corrected optical coherence tomography probe.This is the smallest freeform 3D imaging probe yet reported,with a diameter of 0.457 mm,including the catheter sheath.We demonstrated image quality and mechanical flexibility by imaging atherosclerotic human and mouse arteries.The ability to provide microstructural information with the smallest optical coherence tomography catheter opens a gateway for novel minimally invasive applications in disease.

Robust and rapidly tunable light source for SRS/CARS microscopy with low-intensity noise

We present a fully automated laser system with low-intensity noise for coherent Raman scattering microscopy.The robust two-color system is pumped by a solid-state oscillator,which provides Stokes pulses fixed at 1043 nm.The tunable pump pulses of 750 to 950 nm are generated by a frequency-doubled fiberfeedback femtosecond optical parametric oscillator.The resulting pulse duration of 1.2 ps provides a viable compromise between optimal coherent Raman scattering signal and the necessary spectral resolution.Thus a spectral range of 1015 to 3695 cm−1 with spectral resolution of<13 cm−1 can be addressed.

Beam switching and bifocal zoom lensing using active plasmonic metasurfaces

Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators.While the larger counterparts typically rely on mechanical actuation,this can be undesirable in some cases on a microscopic scale due to inherent space restrictions.Here,we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge3Sb2Te6.In particular,we demonstrate beam switching and bifocal lensing,thus,paving the way for a plethora of active optical elements employing plasmonic metasurfaces,which follow the same design principles.

Multichannel vectorial holographic display and encryption

Since its invention,holography has emerged as a powerful tool to fully reconstruct the wavefronts of light including all the fundamental properties(amplitude,phase,polarization,wave vector,and frequency).For exploring the full capability for information storage/display and enhancing the encryption security of metasurface holograms,smart multiplexing techniques together with suitable metasurface designs are highly demanded.Here,we integrate multiple polarization manipulation channels for various spatial phase profiles into a single birefringent vectorial hologram by completely avoiding unwanted cross-talk.Multiple independent target phase profiles with quantified phase relations that can process significantly different information in different polarization states are realized within a single metasurface.For our metasurface holograms,we demonstrate high fidelity,large efficiency,broadband operation,and a total of twelve polarization channels.Such multichannel polarization multiplexing can be used for dynamic vectorial holographic display and can provide triple protection for optical security.The concept is appealing for applications of arbitrary spin to angular momentum conversion and various phase modulation/beam shaping elements.

Dielectric Mie voids: confining light in air

Manipulating light on the nanoscale has become a central challenge in metadevices,resonant surfaces,nanoscale optical sensors,and many more,and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics.Here,we experimentally implement a novel strategy for dielectric nanophotonics:Resonant subwavelength localized confinement of light in air.We demonstrate that voids created in high-index dielectric host materials support localized resonant modes with exceptional optical properties.Due to the confinement in air,the modes do not suffer from the loss and dispersion of the dielectric host medium.We experimentally realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm(4.68 eV).Furthermore,we utilize the bright,intense,and naturalistic colours for nanoscale colour printing.Mie voids will thus push the operation of functional high-index metasurfaces into the blue and UV spectral range.The combination of resonant dielectric Mie voids with dielectric nanoparticles will more than double the parameter space for the future design of metasurfaces and other micro-and nanoscale optical elements.In particular,this extension will enable novel antenna and structure designs which benefit from the full access to the modal field inside the void as well as the nearly free choice of the high-index material for novel sensing and active manipulation strategies.

All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers

Dynamic control of compact chip-scale contactless manipulation of particles for bioscience applications remains a challenging endeavor,which is restrained by the balance between trapping efficiency and scalable apparatus.Metasurfaces offer the implementation of feasible optical tweezers on a planar platform for shaping the exerted optical force by a microscale-integrated device.Here we design and experimentally demonstrate a highly efficient silicon-based metalens for two-dimensional optical trapping in the near-infrared.Our metalens concept is based on the Pancharatnam–Berry phase,which enables the device for polarization-sensitive particle manipulation.Our optical trapping setup is capable of adjusting the position of both the metasurface lens and the particle chamber freely in three directions,which offers great freedom for optical trap adjustment and alignment.Two-dimensional(2D)particle manipulation is done with a relatively low-numerical-aperture metalens(NA(ML)=0.6).We experimentally demonstrate both 2D polarization-sensitive drag and drop manipulation of polystyrene particles suspended in water and transfer of angular orbital momentum to these particles with a single tailored beam.Our work may open new possibilities for lab-on-a-chip optical trapping for bioscience applications and microscale to nanoscale optical tweezers.

DNA-assembled bimetallic plasmonic nanosensors

Plasmonic hybrid nanomaterials are highly desirable in advanced sensing applications.Different components in these materials undertake distinct roles and work collectively.One material component may act as an efficient light concentrator and optical probe,whereas another provides specific chemical or biological functionality.In this work,we present DNA-assembled bimetallic plasmonic nanostructures and demonstrate their application for the all-optical detection of hydrogen.Gold(Au)nanorods are functionalized with DNA strands,which serve both as linkers and seeding sites for the growth of palladium(Pd)nanocrystals and facilitate reliable positioning of Pd satellites around an Au nanorod at an ultrashort spacing in the nanometer range.Dark-field scattering spectra of single Au–DNA–Pd nanorods were recorded during controlled cycles of hydrogen gas exposure,and an unambiguous concentration-dependent optical response was observed.Our method enables,for the first time,the all-optical detection of hydrogen-induced phase-change processes in sub-5-nm Pd nanocrystals at the single-antenna level.By substituting the Pd satellites with other functional materials,our sensor platform can be extended to plasmonic sensing of a multitude of chemical and biological reagents,both in liquid and gaseous phases.

Emission spectroscopy of NaYF_(4):Eu nanorods optically trapped by Fresnel lens fibers

NaYF_(4):Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 μm and light powers down to 10 m W. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective σ and π orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4–5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means.

Photosensitive Material Enabling Direct Fabrication of Filigree 3D Silver Microstructures via Laser-Induced Photoreduction

Dear Editor Laser-induced photoreduction(LPR)as a direct fabrication technique that promises to be one of the most versatile routes for fabricating highly conductive 3D metallic microstructures on-chip(e.g.,metamaterials,electro-mechanical systems,and high-frequency components like antennas).

Synchronization-free all-solid-state laser system for stimulated Raman scattering microscopy

We introduce an extremely simple and highly stable system for stimulated Raman scattering(SRS)microscopy.An 8-W,450-fs Yb:KGW bulk oscillator with 41 MHz repetition rate pumps an optical parametric amplifier,which is seeded by a cw tunable external cavity diode laser.The output radiation is frequency doubled in a long PPLN crystal and generates 1.5-ps long narrowband pump pulses that are tunable between 760 and 820 nm with 450 mW average power.Part of the oscillator output is sent through an etalon and creates Stokes pulses with 100 mW average power and 1.7 ps duration.We demonstrate SRS microscopy at a 30-μs pixel dwell time with high chemical contrast,signal-to-noise ratio in excess of 45 and no need for balanced detection,thanks to the favorable noise properties of the bulk solid-state system.Cw seeding intrinsically ensures low spectral drift.We discuss its application to chemical contrast microscopy of freshly prepared plant tissue sections at different vibrational bands.