DUV light is of great importance in applications, including nanolithography, material science, and biology. Metasurfaces, comprising well-engineered nanoresonators, promise to improve DUV technologies due to their capability to manipulate light at the nanoscale. We present metasurfaces showing high-quality-factor resonance (high-Q) in the DUV range. We combined low-loss dielectric materials, resonance mode associated with the quasi-bound state in the continuum, and various device schemes to realize the DUV high-Q metasurfaces. We demonstrate metasurfaces with functionalities including imaging-based biosensing and high-Q optical charity. Fabrication and characterization of the high-Q metasurface will be reported. This work provides a platform to advance DUV nanophotonics in sensing, quantum optics, and nonlinear optics.
We report resonance gradient metasurfaces, which show nearly continuous tunability of the high-Q resonance over a broadband wavelength range. The spectral tuning of the high-Q resonance is realized by gradually scaling the unit cell’s geometrical parameters along one coordinate of the metasurface. By using the gradient metasurface and a tunable infrared laser, a resonantly enhanced tunable generation of optical harmonics over a broad spectral range is realized (Adv. Mater. 2024, 36, e2307494). Additionally, broadband biosensing and control of vibrational light-matter coupling by using the gradient metasurface were demonstrated. This research establishes the groundwork for innovative light-generating devices and biosensors.
We showcase plasmonic metasurfaces employing silicon (Si) nanostructures tailored for deep ultraviolet (DUV) spectroscopy. Si exhibits plasmonic resonance owing to the photon-doping effect originating from interband transitions in the DUV range. Through careful design adjustments, our metasurface achieves strong field enhancement at ~260nm. We investigate potential applications of the reported Si void metasurfaces for surface-enhanced spectroscopy by leveraging the unique properties of our Si metasurface. This study expands the range of materials employed in DUV nanophotonics, unlocking opportunities across diverse fields such as biomedical analysis and nonlinear optics.
Deep ultraviolet (DUV) light plays a critical role in many spectroscopy and imaging techniques. To advance these techniques, it is essential to develop devices that can provide substantial field enhancement within the DUV range. This presentation will introduce metasurfaces composed of various dielectric materials. Specifically, we will showcase Si metasurfaces demonstrating plasmonic modes induced by the "photon-doping effect," resulting in significant field enhancement at 266 nm. Furthermore, we will discuss DUV metasurfaces made of low-loss dielectric material HfO2, which exhibit multiple high-quality-factor quasi-bound-state-in-the-continuum resonances. Potential applications of the reported metasurfaces will be discussed.
In this talk, we report a large-scale fabrication of Mid-IR metasurfaces by using a newly developed method. The metasurfaces were produced on transparent alumina membranes. Functionalities such as quasi-bound-state-in-the-continuum (quasi-BIC) resonances, mid-IR focusing, and polarization control were realized in different dielectric metasurfaces. Metasurfaces comprising aluminum nanoantennas were also fabricated and integrated into microfluidic devices for biosensing. The reported fabrication method is CMOS compatible and able to produce metasurfaces over whole Si wafers with high precision and uniformity. This work serves as a significant step in the direction of practical applications and commercialization of Mid-IR metasurfaces [Adv. Mater. 33, 2102232 (2021)].
Optical meta-devices using metasurfaces have shown preeminent capabilities to control the optical nonlinearity and enhancing the nonlinear efficiency by arrangements of meta-atoms. With the great advantages of relaxed phase-matching requirements and CMOS compatibility for mass production, nonlinear metasurfaces can flexibly manipulate the phase, amplitude and polarization of the nonlinear waves at subwavelength scale. Various nonlinear frequency conversion processes, such as second harmonic generation (SHG), third harmonic generation (THG), have been widely realized to short wavelength such as vacuum ultraviolet (VUV) light and applied in optical communication, imaging, photochemistry and biosensing. The design, fabrication and application of the novel nonlinear optical meta-devices are reported in this talk.
Metasurfaces comprising 3D chiral structures have shown great potential in chiroptical applications such as chiral
optical components and sensing. So far, the main challenges lie in the nanofabrication and the limited operational
bandwidth. Here, we present an effective nanofabrication method to create a 3D chiral metasurface with far- and nearfield
broadband chiroptical properties. A focused ion beam is used to cut and stretch nanowires into 3D Archimedean
spirals from stacked films. The spiral exhibits far- and near-field broadband chiroptical responses from 2 to 8 μm. With
circularly polarized light (CPL), the spiral shows superior far-field transmission dissymmetry and handedness-dependent
near-field localization. The reported method and chiral metasurface may find applications in broadband chiral optics and
chiral sensing.
We propose a Light-sheet fluorescent microscopy (LSFM) system with a flat metalens, which is used to replace the bulky illuminating components. The metalens is a diffractive optics elements (DOEs) composed of various gallium nitride (GaN) nanopillar for light-sheet generation, and it can be readily integrated in existing LSFM systems. In contrast to the traditional LSFM system, the metalens-based system is more compact and flexible, and its sectioning capability is comparable to the conventional illumination arm in LSFMs. The live fluorescent-labeled transgenic Caenorhabditis elegans (C. elegans) are exploited to verify the performance of this system. The intensity profile of oocytes in C. elegans with cellular resolution level was obtained.
Vacuum ultraviolet (VUV) light is electromagnetic radiation in the wavelength regime between 100nm and 200nm. Due to its high photon energy, VUV light is very important in many advanced applications, such as photochemistry, nanolithography, and novel spectroscopy. While several methods to generate coherent VUV light have been developed, a multifunctional nanophotonic device for efficient VUV light generation and control still remains an outstanding challenge. In this work, we demonstrate an all-dielectric metasurface device (metadevice) which can be used for nonlinearly generating coherent VUV light. Metasurfaces are artificial nanostructures with resonance properties that can be designed by carefully tailoring their geometric parameters. The metadevice demonstrated in this work consists of an array ZnO nano-resonators. To fabricate the metadevice, a 150-nm multicrystalline ZnO was nanopatterned using a focus ion beam system. In the linear transmission measurement, the metadevice shows a resonance dip at around 400nm. This resonance was found to be associated to a magnetic dipole resonance of the nano-resonators. When a visible femtosecond laser beam (wavelength: 394nm) as an excitation source was loosely focused on the metadevice, VUV light originating from second harmonic generation of the metadevice was produced. The dependence of the VUV signal on the excitation power as well as on the incident angle were carefully measured and analyzed. Furthermore, manipulation of the output VUV wavefront was realized by carefully controlling the nano-resonator arrangement. This work paves a novel route toward high-efficiency multifunctional nanophotonic devices for VUV applications [Nano Lett. 18, 5738 (2018)].
Upconversion fluorescence from Lanthanide-doped nanocrystals has attracted widespread interests because of its greatly potential applications in various fields, such as photonic crystal lasers, material science, biological therapy, and so on. However, the relatively low quantum yield (typically < 5%) is the major limitation for upconversion nanocrystals. Meanwhile, in addition to the chemical methods, plasmonic structures have been adopted as another strategy to improve the radiation efficiency and control the relaxation process of the upcovnersion nanocrystals. We designed the anti-symmetric split ring resonators with various periods and the fishnet structures. The surface plasmon resonance peaks of the structure shift as the periods varies. For example, in a multi-layered plamsonic metasurface with the period of 250nm, both the electric and magnetic modes could be generated simultaneously when excited by the incident light with proper polarization. This plasmonic structure provides two different channels for the enhancement of upconversion fluorescence. The resonance peak of 650nm is magnetic resonance mode, while the peak of 980nm is electric resonance mode. The resonance peak of 980nm coincides with the absorption band of the Lanthanide-dopoed nanocrystal, and the peak of 650nm matches with its emission band. We found that the upconversion fluorescence intensity could be enhanced more than 10 times when the electric resonance frequency of the metasurface matches with the absorption band of the upconversion nanocrystals, while the magnetic mode overlaps with its emission band. This is due to the local density of optical states was significantly enhanced by the plasmonic metasurface. The detailed results and mechanism will be discussed.
Selective excitation of specific multipolar resonances in matter can be of great utility in understanding the internal make-up of the underlying material and, as a result, in developing novel nanophotonic devices. Many efforts have been addressed on this topic. For example, the emission spectra related to the different multipolar transitions of trivalent europium can be modulated by changing the thickness of the dielectric spacer between the gold mirror and the fluorescent layer. In this talk, we reported the results about active control of the multipolar resonance in metadevices using the coherent control technique. In the coherent control spectroscopy system, the optical standing wave constructed from two counterpart propagation coherent beams is utilized as the excitation. By controlling the time delay between two ultrafast pulses to decide the location of metadivce as the electromagnetic field node or antinode node of standing wave, the absorption related to the specific multipolar resonance can be controlled. Using this technique, with the 30-nm-thick metadevice, the broadband controlling light with light without nonlinearity can be realized. The switching contrast ratios can be as high as 3:1 with a modulation bandwidth in excess of 2 THz. The active control of the high order and complex optical resonance related to the magnetic dipole, electric quadrupole, and toroidal dipole in the metamaterial is reported as well. This research can be applied in the all ultrafast all-optical data processing and the active control of the resonances of metadevice with high order multipolar resonance.
KEYWORDS: Optical storage, Data storage, Optical recording, Digital video discs, Optical resolution, Objectives, Atomic force microscopy, Spatial resolution, Nondestructive evaluation, Applied research
Conventional optical data storage such as digital versatile disc (DVD) and Blu-ray disc (BD), provide us inexpensive and compact media for satisfying information storage requirement for decades. As the knowledge and information increase rapidly, the requirement cannot be already satisfied by current data storage systems. As far as we know, the size of recording mark, the critical storage density indicator, depends on recording energy, writing strategies, opto-thermal threshold plane and thermal conductivity. Readout is limited by optical resolution limit, the wavelength of readout laser and numerical aperture (N.A.) of objective lens. In this talk, I will introduce several means to increase the optical storage density. A powerful tool, conductive-tip atomic force microscopy (C-AFM), with the advantages of high spatial resolution, high contrast of conductivity and non-destructive method to help us better understand the formation of recording marks is also presented. Finally, I will show our recent efforts on realizing the extreme of recording mark.
Phase change materials are used as the recording layer in optical data storage, electronic storage and nanolithography due to the enormous physical difference between crystalline and amorphous states. In recent years, they are demonstrated to exploit in various tunable plasmonic devices, such as perfect absorber, planar lenses, plasmonic antenna, Fano resonance and so on. However, in these researches, the phase change material merely plays a role as a refractive index switchable substrate. In this paper, we study the intrinsic optical properties of phase change material Ge2Sb2Te5 (GST) in the near-infrared regime. A clear insight into the dipole resonance system of GST is provided. The reflection phase retardation and intensity of each unit cells depending on the phase state and geometry are estimated. Further, we introduce the concept of reconfigurable gradient metasurface, which has different anomalous reflection angles by switching the combination of nanorods with different geometries and phase states. The research has great potential in the area of tunable metamaterial device (metadevice) in the future.
The scattering of surface plasmon polariton (SPP) waves can be manipulated by various plasmonic structures. The plasmonic structure composed of arranged subwavelength nanobumps on a gold thin film is the promising structure to manipulation SPP wave. By controlling the geometric shape of the structures, the height, position, and pattern of scattered light from SPP wave can be modulated as desired. A clear single focusing spot can be reconstructed at a specific altitude by a particular curved structure with appropriate curvature and adjacent interspacing of nanobumps. The designed light patterns reconstructed by the focusing spot from the arranged curved structures at a specific observation plane are clearly demonstrated.
Nanobump structures are fabricated on the gold thin film by femtosecond laser direct writing (fs-LDW) technique. The
height and diameter of the gold nanobump are about 30nm, and 400 nm, respectively. The scattering light of surface
plasmon wave radiated from a nanobump is observed using a total internal reflection microscopy. A quarter-circle
structure composed of nanobumps is designed and produced to manipulate scattering light into specific pattern: The
focusing and diverging of the quarter circular structure in three dimensional space are demonstrated. The polarization
properties of focusing spot are also examined.
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