Conformable Nanowire-in-Nanofiber Hybrids for Low-Threshold Optical Gain in the Ultraviolet

The miniaturization of diagnostic devices that exploit optical detection schemes requires the design of light sources combining small size, high performance for effective excitation of chromophores, and mechanical flexibility for easy coupling to components with complex and nonplanar shapes. Here, ZnO nanowire-in-fiber hybrids with internal architectural order are introduced, exhibiting a combination of polarized stimulated emission, low propagation losses of light modes, and structural flexibility. Ultrafast transient absorption experiments on the electrospun material show optical gain which gives rise to amplified spontaneous emission with a threshold lower than the value found in films. These systems are highly flexible and can conveniently conform to curved surfaces, which makes them appealing active elements for various device platforms, such as bendable lasers, optical networks, and sensors, as well as for application in bioimaging, photo-cross-linking, and optogenetics.

Dual wavelength lasing of InGaN/GaN axial-heterostructure nanorod lasers

Optical confinement effects are investigated in InGaN/GaN axial-heterostructure nanolasers. Cylindrical nanorods with GaN/InGaN/GaN structures are prepared using combined processes of top-down and bottom-up approaches. The lasing of InGaN is observed at a low threshold (1 μJ cm-2), which is attributed to an efficient carrier transfer process from GaN to InGaN. The lasing of GaN is also found in the threshold range of 10-20 μJ cm-2 with a superlinear increase in emission intensity and high quality factors (Q = 1000), implying that dual wavelengths of lasing are tunable as a function of excitation intensity. The non-classical Fabry-Pérot modes suggest strong light-matter interactions in nanorods by optical confinement effects. The polarization of lasing indicates that the non-classical modes are in the identical transverse mode, which supports the formation of exciton-polaritons in nanorods. Polariton lasing in a single axial-heterostructure nanorod is observed for the first time, which proposes small-sized light sources with low threshold, polarized light, and tunable wavelengths in a single nanorod.

Spatiotemporal Evolution of Coherent Polariton Modes in ZnO Microwire Cavities at Room Temperature

Tunable waveguides for propagating coherent quantum states are demanded for future applications in quantum information technology and optical data processing. We present coherent whispering gallery mode polariton states in ZnO-based hexagonal microwires at room temperature. We observed their propagation over the field of view of about 20 μm by picosecond time-resolved real space imaging using a streak camera. Spatial coherence was proven by time integrated Michelson interferometry superimposing the inverted spatial emission pattern with its original one. We furthermore show that the real and momentum space evolution of the coherent states can not only be described by the commonly used model developed for ballistically propagating Bose-Einstein condensates based on the Gross-Pitaevskii equation but equivalently by classical ray optics considering a spatially varying particle density dependent refractive index of the cavity material, not yet considered in literature so far. By changing the excitation spot size, the refractive index gradient and thus the propagation velocity is changed.

Ergonomic Synthesis Suitable for Industrial Production of Silver-Festooned Zinc Oxide Nanorods

For maximizing productivity, minimizing cost, time-boxing process and optimizing human effort, a single-step, cost-effective, ultra-fast and environmentally benign synthesis suitable for industrial production of nanocrystalline ZnO , and Ag -doped ZnO has been reported in this paper. The synthesis based on microwave-supported aqueous solution method used zinc acetate dehydrate and silver nitrate as precursors for fabrication of nanorods. The synthesized products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and UV-Vis–NIR spectroscopy. The undoped and Ag -doped ZnO nanorods crystallized in a hexagonal wurtzite structure having spindle-like morphology. The blue shift occurred at absorption edge of Ag -doped ZnO around 260 nm compared to 365 nm of bulk ZnO . The red shift occurred at Raman peak site of 434 cm-1 compared to characteristic wurtzite phase peak of ZnO (437 cm-1). The bandgap energies were found to be 3.10 eV, 3.11 eV and 3.18 eV for undoped, 1% Ag -doped, and 3% Ag -doped ZnO samples, respectively. The TEM results provided average particle sizes of 17 nm, 15 nm and 13 nm for undoped, and 1% and 3% Ag -doped ZnO samples, respectively.

Nonlinear excitation of polariton cavity modes in ZnO single nanocombs

Tunable second harmonic (SH) polaritons have been efficiently generated in ZnO nanocombs, when the material is excited close to half of the band-gap. The nonlinear signal couples to the nanocavity modes, and, as a result, Fabry-Pérot resonances with high Q factors of about 500 are detected. Due to the low effective volume of the confined modes, matter-light interaction is very much enhanced. This effect lowers the velocity of the SH polariton in the material by 50 times, and increases the SH confinement inside the nanocavity due to this higher refractive index. We also show that the SH phase-matching condition is achieved through LO-phonon mediation. Finally, birrefringence of the crystal produces a strong SH intensity dependence on the input polarization, with a high polarization contrast, which could be used as a mechanism for light switching in the nanoscale.