Discerning Weld Seam Pro les from Strong Arc Background for the Robotic Automated Welding Process via Visual Attention Features

In the robotic welding process with thick steel plates,laser vision sensors are widely used to profile the weld seam to implement automatic seam tracking.The weld seam profile extraction(WSPE)result is a crucial step for identifying the feature points of the extracted profile to guide the welding torch in real time.The visual information processing system may collapse when interference data points in the image survive during the phase of feature point identification,which results in low tracking accuracy and poor welding quality.This paper presents a visual attention featurebased method to extract the weld seam profile(WSP)from the strong arc background using clustering results.First,a binary image is obtained through the preprocessing stage.Second,all data points with a gray value 255 are clustered with the nearest neighborhood clustering algorithm.Third,a strategy is developed to discern one cluster belonging to the WSP from the appointed candidate clusters in each loop,and a scheme is proposed to extract the entire WSP using visual continuity.Compared with the previous methods the proposed method in this paper can extract more useful details of the WSP and has better stability in terms of removing the interference data.Considerable WSPE tests with butt joints and T-joints show the anti-interference ability of the proposed method,which contributes to smoothing the welding process and shows its practical value in robotic automated welding with thick steel plates.

Temperature dependent terahertz giant anisotropy and cycloidal spin wave modes in BiFeO3 single crystal

THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A giant birefringence up to around 3.6 is observed at 1 THz.The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances(SCR)ψandΦ,corresponding to the out-of-plane and in-plane modes of the spin cycloid,respectively.We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam.In addition,we observe a resonance appearing below 140 K,which might be interpreted as an electromagnon mode and related to a spin reorientation transition.Our present observations present that the temperature and polarization,as the external control parameters,can be used to modulate the THz optical properties of BFO single crystal.

Photoinduced large polaron transport and dynamics in organic-inorganic hybrid lead halide perovskite with terahertz probes

Organic-inorganic hybrid metal halide perovskites(MHPs)have attracted tremendous attention for optoelectronic applications.The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs.However,it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics.Here,we show,in a one-step spectroscopic method,that the optical-pump and terahertz-electromagnetic probe(OPTP)technique allows us to access the nature of interplay of photoexcited unbound charge carriers and optical phonons in polycrystalline CH_(3)NH_(3)PbI_(3)(MAPbI_(3))of about 10μm grain size.Firstly,we demonstrate a direct spectral evidence of the large polarons in polycrystalline MAPbI_(3).Using the Drude-Smith-Lorentz model along with the Frӧhlich-type electron-phonon(e-ph)coupling,we determine the effective mass and scattering parameters of photogenerated polaronic carriers.We discover that the resulting moderate polaronic carrier mobility is mainly influenced by the enhanced carrier scattering,rather than the polaron mass enhancement.While,the formation of large polarons in MAPbI_(3)polycrystalline grains results in a long charge carrier lifetime at room temperature.Our results provide crucial information about the photo-physics of MAPbI3 and are indispensable for optoelectronic device development with better performance.

Ultra-sensitive Dirac-point-based biosensing on terahertz metasurfaces comprising patterned graphene and perovskites

Biosensors are a focus of research on terahertz metasurfaces. However, reports of ultra-sensitive biosensors based on Dirac points are rare. Here, a new terahertz metasurface is proposed that consists of patterned graphene and perovskites. This serves as an ultra-sensitive Dirac-point-based biosensor for qualitative detection of sericin.Theoretically, sericin may make graphene n-doped and drive the Fermi level to shift from the valence band to the Dirac point, causing a dramatic decrease in conductivity. Correspondingly, the dielectric environment on the metasurface undergoes significant change, which is suited for ultra-sensitive biosensing. In addition, metal halide perovskites, which are up-to-date optoelectronic materials, have a positive effect on the phase during terahertz wave transmission. Thus, this sensor was used to successfully detect sericin with a detection limit of 780 pg/m L, achieved by changing the amplitude and phase. The detection limit of this sensor is as much as one order of magnitude lower than that of sensors in published works. These results show that the Dirac-pointbased biosensor is a promising platform for a wide range of ultra-sensitive and qualitative detection in biosensing and biological sciences.

Ultrafast photocarrier and coherent phonon dynamics in type-II Dirac semimetal PtTe2 thin films probed by optical spectroscopy

We report the ultrafast photocarrier dynamics and coherent phonon excitation in type-II Dirac semimetal platinum ditelluride(PtTe2)thin films via femtosecond(fs)pump-probe spectroscopy at room temperature.Quantitative analysis revealed that the incoherent electronic relaxation consists of two components:a subpicosecond fast relaxation process and a slow component with a time constant of hundreds of picoseconds(ps).Furthermore,the launch of a coherent acoustic phonon(CAP)in the 20 nm film but absence in the 6.8 nm film uncovers the dominant role of temperature gradient in producing a strain wave.The sound velocity and Young’s modulus in the thick PtTe_(2) are determined to be 1.736 km/s and 29.5 GPa,respectively.In addition,the coherent optical phonon(COP)with a frequency of 4.7 THz corresponding to Te atoms out-of-plane A1g vibration has been well resolved in all films,which is ascribed to displacive excitation of coherent phonon(DECP).The observation of a strong probe-wavelength dependent COP amplitude reveals the resonant feature of the optical excitation-induced atomic displacement in PtTe2.Our findings provide deep insight into the excitation and dynamics of CAP and COP as well as the photocarriers’recovery pathway and lifetimes in PtTe_(2).Our study also demonstrates that the COP spectroscopy is a powerful tool to reveal the modulation of frequency-dependent optical constants induced by atomic vibrations,which may find applications in the fields of optoelectronics and ultrafast photonics.