Achieving high numerical aperture near-infrared imaging based on an ultrathin cylinder dielectric metalens.

An artificial subwavelength dielectric metalens (ML), the realization of being ultrathin and light-weight, provides a potential candidate with replacing a traditional bulky curved lens with a high image quality. A ML with 1.5 mm in diameter having numerical aperture (NA) $\sim{0.

Capabilities of time-resolved X-ray excited optical luminescence of the Taiwan Photon Source 23A X-ray nanoprobe beamline.

Time-resolved X-ray excited optical luminescence (TR-XEOL) was developed successfully for the 23A X-ray nanoprobe beamline located at the Taiwan Photon Source (TPS). The advantages of the TR-XEOL facility include (i) a nano-focused X-ray beam (<60 nm) with excellent spatial resolution and (ii) a streak camera that can simultaneously record the XEOL spectrum and decay time. Three time spans, including normal (30 ps to 2 ns), hybrid (30 ps to 310 ns) and single (30 ps to 1.

Defect induced ferromagnetic ordering in epitaxial ZnMnO films on sapphire (0 0 0 1).

We report the influence of Mn dopant on magnetic properties of ZnMnO (ZMO)/AlO(0 0 0 1) hetero-epitaxial systems grown by using pulsed-laser deposition. The room temperature (RT) intrinsic ferromagnetic (FM) ordering verified by superconducting quantum interference device magnetometer and x-ray magnetic circular dichroism spectrum of Mn L edges is ascribed to the substitutional Mn atoms in the Zn site of ZnO. Mn in ZMO has a tetrahedral local symmetry instead of the octahedral symmetry of MnO, after verifying the absence of the Mn-related impurities or clusters in ZMO epitaxial film by Mn K-edge and Zn K-edge x-ray absorption spectroscopy spectrum, as well as the analysis of long-range structural ordering on Renninger scan of forbidden (0 0 0 5) reflection in x-ray diffraction, transmission electron microscopy and Raman spectrum.

Investigation of Cavity Enhanced XEOL of a Single ZnO Microrod by Using Multifunctional Hard X-ray Nanoprobe.

The multifunctional hard X-ray nanoprobe at Taiwan Photon Source (TPS) exhibits the excellent ability to simultaneously characterize the X-ray absorption, X-ray excited optical luminescence (XEOL) as well as the dynamics of XEOL of materials. Combining the scanning electron microscope (SEM) into the TPS 23A end-station, we can easily and quickly measure the optical properties to map out the morphology of a ZnO microrod. A special phenomenon has been observed that the oscillations in the XEOL associated with the confinement of the optical photons in the single ZnO microrod shows dramatical increase while the X-ray excitation energy is set across the Zn K-edge.

Saturation and beating of acoustic phonon oscillations excited near the exciton resonance of strained polar ZnO/ZnMgO multiple quantum wells.

Saturation and beating of coherent acoustic phonon (CAP) oscillations were observed and attributed to the screening of a built-in electric field with increasing pump power using degenerate pump-probe measurements near the exciton resonance of polar ZnO/ZnMgO multiple quantum wells (MQWs). After purifying the CAP signals by using an empirical mode decomposition, we found not only that the CAP amplitude follows the trend of the band gap renormalization (BGR) and shows saturation at high pump power, but also that the CAP oscillation period coincides with that of the MQWs, consistent with the XRD and TEM results. An additional low-frequency oscillation modifying the CAP signal is revealed due to the negative change in refractive index caused by BGR as the pump power increases.

Peculiar near-band-edge emission of polarization-dependent XEOL from a non-polar a-plane ZnO wafer.

Polarization-dependent hard X-ray excited optical luminescence (XEOL) was used to study not only the optical properties but also the crystallographic orientations of a non-polar a-plane ZnO wafer. In addition to a positive-edge jump and extra oscillations in the near-band-edge (NBE) XEOL yield, we observed a blue shift of the NBE emission peak that follows the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Zn K-edge. This NBE blue shift is caused by the larger X-ray absorption, generating higher free carriers to reduce the exciton-LO phonon coupling, which causes a decrease in the exciton activation energy.

Non-interferometric phase retrieval using refractive index manipulation.

We present a novel, inexpensive and non-interferometric technique to retrieve phase images by using a liquid crystal phase shifter without including any physically moving parts. First, we derive a new equation of the intensity-phase relation with respect to the change of refractive index, which is similar to the transport of the intensity equation. The equation indicates that this technique is unneeded to consider the variation of magnifications between optical images.

High-quality and Large-size Topological Insulator BiTe-Gold Saturable Absorber Mirror for Mode-Locking Fiber Laser.

A novel high-quality, large-size, reflection-type topological insulator BiTe-Gold (BG) film-based nonlinear optical modulator has been successfully fabricated as a two-dimensional saturable absorber mirror (SAM) by pulsed laser deposition (PLD). This BG-SAM possesses saturation fluence of 108.3 μJ/cm, modulation depth (ΔR) of 6.

Nonequilibrium and nonlinear defect states in microcavity-polariton condensates.

The nonequilibrium and nonlinear defect modes (NNDMs), localized by a defect in a nonequilibrium microcavity-polariton condensate (MPC), are studied. There are three analytic solutions of NNDMs in a point defect: the bright NNDM, a bound state with two dark solitons for an attractive potential, and a gray soliton bound by a defect for a repulsive potential. We find that the stable NNDMs in a nonequilibrium MPC are the bright NNDM and gray soliton bound by a defect.

Phase retrieval by using the transport-of-intensity equation with Hilbert transform.

Phase recovery by solving the transport-of-intensity equation (TIE) is a non-iterative and non-interferometric phase retrieval technique. From solving the TIE with conventional, one partial derivative and Hilbert transform methods for both the periodic and aperiodic samples, we demonstrate that the Hilbert transform method can provide the smoother phase images with edge enhancement and fine structures. Furthermore, compared with the images measured by optical and atomic force microscopy, the Hilbert transform method has the ability to quantitatively map out the phase images for both the periodic and aperiodic structures.

Finite-difference time-domain analysis for the dynamics and diffraction of exciton-polaritons.

We adopted a finite-difference time-domain (FDTD) scheme to simulate the dynamics and diffraction of exciton-polaritons, governed by the coupling of polarization waves with electromagnetic waves. The polarization wave, an approximate solution to the Schrödinger's equation at low frequencies, essentially captures the exciton behavior. Numerical stability of the scheme is analyzed and simple examples are provided to prove its validity.

Stable gray soliton pinned by a defect in a microcavity-polariton condensate.

We study the spatially localized dark state, called dark soliton, in a one-dimensional system of the non-resonantly pumped microcavity-polariton condensate (MPC). From the recent work by Xue and Matuszewski [Phys. Rev.

Tuning the functionalities of a mesocrystal via structural coupling.

In the past decades, mesocrystal, a kind of nanocrystals with specific crystallographic orientation, has drawn a lot of attention due to its intriguing functionalities. While the research community keeps searching for new mesocrystal systems, it is equally crucial to develop new approaches to tune the properties of mesocrystals. In this work, a self-organized two-dimensional mesocrystal composed of highly oriented CoFe2O4 (CFO) nano-crystals with assistance of different perovskite matrices is studied as a model system.

Single-mode selection for hard x-ray cavity resonance.

Single-mode selection is realized for hard x-ray cavity resonance using a three-mirror crystal device. The developed device consists of two coupled Si Fabry-Perot resonators (FPRs) and uses (12 4 0) backward diffraction to reflect back and forth the incident 14.4388 keV x-ray beam.

Passive mode locking of ytterbium- and erbium-doped all-fiber lasers using graphene oxide saturable absorbers.

Broadband graphene oxide/PVA films were used as saturable absorbers (SAs) for mode locking erbium-doped fiber laser (EDFL) and ytterbium-doped fiber laser (YDFL) at 1.06 μm and 1.55 μm.

12 GHz passive harmonic mode-locking in a 1.06 μm semiconductor optical amplifier-based fiber laser with figure-eight cavity configuration.

We report the generation of passively harmonic mode-locked pulses using a 1.06 μm semiconductor optical amplifier (SOA) in a figure-eight laser configuration operated in the all-normal-dispersion regime. Different orders of harmonic mode-locking can be obtained from 30 MHz to 12.

Complex oxide-noble metal conjugated nanoparticles.

Hybrid nanoparticles (NPs) composed of multiple components offer new opportunities for next-generation materials. In this study, a paradigm for the noble metal/ternary complex oxide hybrid NPs is reported by adopting pulsed laser ablation in liquids. As model hybrids, gold-spinel heterodimer (Au-CoFe2O4) and gold-pervoskite heterodimer (Au-SrTiO3) NPs are investigated.

Lasing action in gallium nitride quasicrystal nanorod arrays.

We report the observation of lasing action from an optically pumped gallium nitride quasicrystal nanorod arrays. The nanorods were fabricated from a GaN substrate by patterned etching, followed by epitaxial regrowth. The nanorods were arranged in a 12-fold symmetric quasicrystal pattern.

Room temperature polariton lasing vs. photon lasing in a ZnO-based hybrid microcavity.

We report on the room temperature polariton lasing and photon lasing in a ZnO-based hybrid microcavity under optical pumping. A series of experimental studies of the polariton lasing (exciton-photon detunings of δ = -119 meV) in the strong-coupling regime are discussed and compared to a photon lasing (δ = -45 meV) in the weak-coupling regime obtained in the same structure. The measured threshold power density (31.

Single frequency 1070 nm Nd:GdVO4 laser using a volume Bragg grating.

We demonstrate a single frequency diode-pumped Nd:GdVO(4) laser at 1070 nm using a volume Bragg grating as the output coupler of a short plano-concave cavity. The TEM(00) output had a maximum power of 300 mW and a linewidth less than 23 MHz. The beam propagation parameter M2 and the divergence angle at 200 mW were 1.

A highly efficient graphene oxide absorber for Q-switched Nd:GdVO4 lasers.

We demonstrated that graphene oxide material could be used as a highly efficient saturable absorber for the Q-switched Nd:GdVO4 laser. A novel and low-cost graphene oxide (GO) absorber was fabricated by a vertical evaporation technique and high viscosity of polyvinyl alcohol (PVA) aqueous solution. A piece of GO/PVA absorber, a piece of round quartz, and an output coupler mirror were combined to be a sandwich structure passive component.

Spontaneous emission dynamics in an omnidirectional waveguide made of photonic crystals.

The spontaneous emission dynamics of atoms embedded in an omnidirectional waveguide (ODWG), a novel optical waveguide, is studied on the basis of the complete reflection of one-dimensional photonic crystals. With the dispersion curve of the single waveguide mode within the photonic band gap and various extents of background dissipation, we characterize the photon-atom interaction in the ODWG. The photon emitter of the system is a two-level atom embedded in the low-index medium of the multilayer-film ODWG or the atom-ODWG system.

High-power, passively mode-locked Nd:GdVO₄ laser using single-walled carbon nanotubes as saturable absorber.

We use a new (to our knowledge) fabrication method of a single-walled carbon nanotube (SWCNT) absorber without polymer to sustain high-power illumination. Using a series of saturable absorbers (SAs) incorporating different amounts of SWCNTs, we demonstrate mode-locking for a Nd:GdVO₄ laser in the 1 μm spectral range. Continuous-wave mode-locking (CWML) pulses with a maximum output power of 3.

Characteristics of exciton-polaritons in ZnO-based hybrid microcavities.

Wide bandgap semiconductors are promising materials for the development of polariton-based optoelectronic devices operating at room temperature (RT). We report the characteristics of ZnO-based microcavities (MCs) in the strong coupling regime at RT with a vacuum Rabi splitting of 72 meV. The impact of scattering states of excitons on polariton dispersion is investigated.

Electron transfer properties of organic dye-sensitized solar cells based on indoline sensitizers with ZnO nanoparticles.

Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO dye-sensitized solar cells (DSCs) with optimal energy conversion efficiencies of more than 5%, under AM 1.5 full sunlight illumination (100 mW cm( - 2)). Higher interfacial charge transfer rate and retardant fluorescence decay confirmed from transient fluorescence illustrated that D205-sensitized ZnO DSCs could possess better electron transport than D149-sensitized ZnO DSCs.