Hot-Band-Absorption-Induced Anti-Stokes Fluorescence of Aggregation-Induced Emission Dots and the Influence on the Nonlinear Optical Effect

Hot-band absorption (HBA)-induced anti-Stokes fluorescence (ASF) with longer-wavelength excitation is one effective pathway to deep penetration and low autofluorescence in intravital fluorescence imaging, raising demands for fluorophores with broad spectra, high absorption, and strong emission. However, typical fluorescent dyes display some emission quenching when their concentration is increased in order to obtain brighter fluorescence. In this work, the HBA-induced ASF of aggregation-induced emission (AIE) dots is reported. BPN-BBTD dots were synthesized and confirmed with a fluorescence enhancement and a considerable ASF intensity. In addition, the mechanism of ASF and the HBA process of BPN-BBTD dots were carefully validated and discussed. To obtain the full advantages of the long-wavelength excitation and the short fluorescence lifetime in deep-tissue bioimaging, a large-depth ASF confocal microscopic imaging of in vivo cerebral vasculature was conducted under the excitation of a 980 nm continuous wave laser after intravenous injection of BPN-BBTD dots. Meanwhile, the 3D structure of the cerebrovascular network was successfully reconstructed.

Enhanced terahertz emission from mushroom-shaped InAs nanowire network induced by linear and nonlinear optical effects

The development of powerful terahertz (THz) emitters is the cornerstone for future THz applications, such as communication, medical biology, non-destructive inspection, and scientific research. Here, we report the THz emission properties and mechanisms of mushroom-shaped InAs nanowire (NW) network using linearly polarized laser excitation. By investigating the dependence of THz signal to the incidence pump light properties (e.g., incident angle, direction, fluence, and polarization angle), we conclude that the THz wave emission from the InAs NW network is induced by the combination of linear and nonlinear optical effects. The former is a transient photocurrent accelerated by the photo-Dember field, while the latter is related to the resonant optical rectification effect. Moreover, the p-polarized THz wave emission component is governed by the linear optical effect with a proportion of ~85% and the nonlinear optical effect of ~15%. In comparison, the s-polarized THz wave emission component is mainly decided by the nonlinear optical effect. The THz emission is speculated to be enhanced by the localized surface plasmon resonance absorption of the In droplets on top of the NWs. This work verifies the nonlinear optical mechanism in the THz generation of semiconductor NWs and provides an enlightening reference for the structural design of powerful and flexible THz surface and interface emitters in transmission geometry.

Aluminium nitride integrated photonics: a review

Integrated photonics based on silicon has drawn a lot of interests, since it is able to provide compact solution for functional devices, and its fabrication process is compatible with the mature complementary metal-oxide-semiconductor (CMOS) fabrication technology. In the meanwhile, silicon material itself has a few limitations, including an indirect bandgap of 1.1 eV, transparency wavelength of >1.1 μm, and insignificant second-order nonlinear optical property. Aluminum nitride (AlN), as a CMOS-compatible material, can overcome these limitations. It has a wide bandgap of 6.2 eV, a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect. Furthermore, it also exhibits piezoelectric and pyroelectric effects, which enable it to be utilized for optomechanical devices and pyroelectric photodetectors, respectively. In this review, the recent research works on integrated AlN photonics in the past decade have been reviewed and summarized. The related material properties of AlN have been summarized and presented. After that, the demonstrated functional devices, including linear optical devices, optomechanical devices, emitters, photodetectors, metasurfaces, and nonlinear optical devices, are reviewed and presented. Last but not the least, the summary and future outlook for the AlN-based integrated photonics are provided.

Nonlinearity-induced nanoparticle circumgyration at sub-diffraction scale

The ability of light beams to rotate nano-objects has important applications in optical micromachines and biotechnology. However, due to the diffraction limit, it is challenging to rotate nanoparticles at subwavelength scale. Here, we propose a method to obtain controlled fast orbital rotation (i.e., circumgyration) at deep subwavelength scale, based on the nonlinear optical effect rather than sub-diffraction focusing. We experimentally demonstrate rotation of metallic nanoparticles with orbital radius of 71 nm, to our knowledge, the smallest orbital radius obtained by optical trapping thus far. The circumgyration frequency of particles in water can be more than 1 kHz. In addition, we use a femtosecond pulsed Gaussian beam rather than vortex beams in the experiment. Our study provides paradigms for nanoparticle manipulation beyond the diffraction limit, which will not only push toward possible applications in optically driven nanomachines, but also spur more fascinating research in nano-rheology, micro-fluid mechanics and biological applications at the nanoscale.

A Novel Structure to Enhance Second Harmonic Generation in Plasmonic Waveguide using Optimized Plasmon Polariton Nanoparticles

In this paper, we propose a new structure for the plasmonic waveguide to optimize the nonlinear optical effect of the second harmonic generation (SHG). For this purpose, we use a layer of graphene grating and spherical and elliptical plasmon polariton nanoparticles made of gold and silver. The number, location and material of nanoparticles as well as the number of graphene layer gratings are optimized to achieve the highest possible nonlinear effect. The simulation results showed that the optical power of SHF wave and peak optical power of SHF is increased noticeably using grating layer of graphene along with optimized plasmon polariton nanoparticles.

From thiophosphate to chalcohalide: mixed-anion AgSxCly ligands concurrently enhancing nonlinear optical effect and laser-damage threshold

In this work, we propose a new design strategy that introducing unique mixed-anion AgSxCly ligands into thiophosphate affords a successful synthesis of promising Ag5PS4Cl2 IR NLO chalcohalide. Compared with chlorine-free...

Terahertz generation from surface of the bulk and monolayer tungsten diselenide

The study of ultrafast laser interaction with graphene-like materials based on transition metal dichalcogenides attracts most scientific groups. It is connected with potential use of these materials in flexible optoelectronic devices of visible and THz range. In this paper the parameters of generation of terahertz field from the surface of bulk layered crystal and monolayer film of tungsten diselenide are analyzed. Generation of terahertz radiation from the surface of experimental samples was studied by the terahertz time-domain spectroscopy in reflection geometry. Bulk layered crystals of tungsten diselenide were grown by gas transport reactions. Monolayers of tungsten diselenide crystals were grown by chemical vapor deposition on a silicon substrate. The bandwidth of the generated terahertz radiation from the surface of the bulk layered tungsten diselenide crystal was ~ 3.5 THz. For tungsten diselenide monolayer the spectrum bandwidth of the generated THz radiation was ~ 2.5 THz. The peak amplitude of the generated terahertz field for both samples was at a frequency of ~ 1 THz. Research of the influence of the angle of rotation of a polarization plane of optical femtosecond pump on peak-to-peak amplitude of the generated terahertz field from the surface of investigated samples was carried out. Symmetry analysis of the azimuthal dependence of THz radiation made it possible to separate the mechanisms of THz radiation and evaluate their contribution. The analysis results confirm that the only possible contribution to the generation of terahertz radiation in a tungsten diselenide monolayer crystal is the second order nonlinear optical effect – optical rectification. One of the contributions to the generation of tungsten diselenide is a nonlinear-optical effect of the third order – surface optical rectification.