Study on the effective elastic performance of composites containing decagonal symmetric two-dimensional quasicrystal coatings

On account of the Mori-Tanaka approach,the effective elastic performance of composites containing decagonal symmetric two-dimensional(2D)quasicrystal(QC)coatings is studied.Explicit expressions for the effective elastic constants of rare-earth QC reinforced magnesium-based composites are provided.Detailed discussion is presented on the effects of the volume fraction of the inclusions,the aspect ratio of the inclusions,the coating thickness,and the coating material parameters on the effective elastic constants of the composites.The results indicate that considering the coating increases the effective elastic constants of the composites to some extent.

Interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional hexagonal quasicrystal with piezoelectric effect

The interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional(1 D) hexagonal quasicrystal with piezoelectric effect is considered. A general formula of the generalized stress field, the field intensity factor, and the image force is derived, and the special cases are discussed. Several numerical examples are given to show the effects of the material properties and the dislocation position on the field intensity factors and the image forces.

Study on a straight dislocation in an icosahedral quasicrystal with piezoelectric effects

An electro-elastic analysis is performed on an icosahedral quasicrystal with piezoelectric effects containing a straight dislocation. The closed-form expressions for the elastic and electric fields are obtained using the extended Stroh formalism. The effects of piezoelectric constant on the phonon displacement, phason displacement, and electric potential are discussed in detail.

Effective elastic properties of one-dimensional hexagonal quasicrystal composites

The explicit expression of Eshelby tensors for one-dimensional(1D) hexagonal quasicrystal composites is presented by using Green’s function method. The closed forms of Eshelby tensors in the special cases of spheroid, elliptic cylinder, ribbon-like,penny-shaped, and rod-shaped inclusions embedded in 1 D hexagonal quasicrystal matrices are given. As an application of Eshelby tensors, the analytical expressions for the effective properties of the 1 D hexagonal quasicrystal composites are derived based on the Mori-Tanaka method. The effects of the volume fraction of the inclusion on the elastic properties of the composite materials are discussed.

Terahertz emission from localized modes in one-dimensional disordered systems [Invited]

We demonstrate terahertz(THz) frequency laser emission around 3.2 THz from localized modes in one-dimensional disordered grating systems. The disordered structures are patterned on top of the double-metal waveguide of a THz quantum cascade laser. Multiple emission peaks are observed within a frequency range corresponding to the bandgap of a periodic counterpart with no disorder, indicating the presence of mode localization aided by Bragg scattering. Simulations and experimental measurements provide strong evidence for the spatial localization of the THz laser modes.

Ultra-subwavelength phase-sensitive Fano-imaging of localized photonic modes

Photonic and plasmonic devices rely on nanoscale control of the local density of optical states(LDOS)in dielectric and metallic environments.The tremendous progress in designing and tailoring the electric LDOS of nano-resonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deep-subwavelength spatial resolution.This scenario has motivated the development of different nanoscale imaging techniques.Here,we prove that a technique involving the combination of scanning near-field optical microscopy with resonant scattering spectroscopy enables imaging the electric LDOS in nano-resonators with outstanding spatial resolution(λ/19)by means of a pure optical method based on light scattering.Using this technique,we investigate the properties of photonic crystal nanocavities,demonstrating that the resonant modes appear as characteristic Fano line shapes,which arise from interference.Therefore,by monitoring the spatial variation of the Fano line shape,we locally measure the phase modulation of the resonant modes without the need of external heterodyne detection.This novel,deep-subwavelength imaging method allows us to access both the intensity and the phase modulation of localized electric fields.Finally,this technique could be implemented on any type of platform,being particularly appealing for those based on non-optically active material,such as silicon,glass,polymers,or metals.

Highly efficient surface-emitting semiconductor lasers exploiting quasi-crystalline distributed feedback photonic patterns

Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation.Once implemented on the top surface of a semiconductor laser,a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature.Therefore,this methodology offers the possibility to achieve efficient emission,combined with tailored spectra and controlled beam divergence.Here,we apply this concept to a onedimensional quantum cascade wire laser.By lithographically patterning a series of air slits with different widths,following the Octonacci sequence,on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies,we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth,achieving a maximum peak optical power of 240mW(190 mW)in multimode(single-frequency-mode)lasers,with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η≈1%.

Electrically-pumped compact topological bulk lasers driven by band-inverted bound states in the continuum

One of the most exciting breakthroughs in physics is the concept of topology that was recently introduced to photonics,achieving robust functionalities,as manifested in the recently demonstrated topological lasers.However,so far almost all attention was focused on lasing from topological edge states.Bulk bands that reflect the topological bulk-edge correspondence have been largely missed.Here,we demonstrate an electrically pumped topological bulk quantum cascade laser(QCL)operating in the terahertz(THz)frequency range.In addition to the band-inversion induced in-plane reflection due to topological nontrivial cavity surrounded by a trivial domain,we further illustrate the band edges of such topological bulk lasers are recognized as the bound states in the continuum(BiCs)due to their nonradiative characteristics and robust topological polarization charges in the momentum space.Therefore,the lasing modes show both in-plane and out-of-plane tight confinements in a compact laser cavity(lateral size~3λ_(laser)).Experimentally,we realize a miniaturized THz QCL that shows single-mode lasing with a side-mode suppression ratio(SMSR)around 20 dB.We also observe a cylindrical vector beam for the far-field emission,which is evidence for topological bulk BIC lasers.Our demonstration on miniaturization of single-mode beam-engineered THz lasers is promising for many applications including imaging,sensing,and communications.

Frequency-tunable continuous-wave random lasers at terahertz frequencies

Random lasers are a class of devices in which feedback arises from multiple elastic scattering in a highly disordered structure,providing an almost ideal light source for artefact-free imaging due to achievable low spatial coherence.However,for many applications ranging from sensing and spectroscopy to speckle-free imaging,it is essential to have high-radiance sources operating in continuous-wave(CW).In this paper,we demonstrate CW operation of a random laser using an electrically pumped quantum-cascade laser gain medium in which a bi-dimensional(2D)random distribution of air holes is patterned into the top metal waveguide.We obtain a highly collimated vertical emission at ~3 THz,with a 430 GHz bandwidth,device operation up to 110 K,peak(pulsed)power of 21 mW,and CW emission of 1.7 mW.Furthermore,we show that an external cavity formed with a movable mirror can be used to tune a random laser,obtaining continuous frequency tuning over 11 GHz.