Raman spectroscopy was used to characterize TiN films deposited by using an off-plane double bend filtered cathodic vacuum arc technique. The influence of substrate bias on the Raman spectra was systematically studied. Four peaks at 235, 320, 440, and 570 cm−1, related to transverse acoustic (TA), longitudinal acoustic (LA), second-order acoustic (2A), and transverse optical (TO) modes of TiN, respectively, were observed in the Raman spectra of TiN films. The intensity of all four peaks and the area fraction as well as the full width at half maximum (FWHM) of the TO peak increase drastically with increasing substrate bias, reaching a maximum at −100 V, and then decrease greatly. However, the area fraction of TA, LA, and 2A peaks, the FWHM of TA and 2A peaks, as well as the frequency of all four peaks decrease rapidly with increasing substrate bias to −100 V, and then increase greatly. At a bias above −200 V, only a slight change in the Raman spectra of TiN films were observed. The change in the N/Ti ratio is the main reason for the evolution in the Raman spectra of TiN films with increasing substrate bias. The internal stress and the crystal size play only a minor role in the Raman spectra of TiN films in the present study.
Mid-infrared ultrafast fiber lasers are valuable for various applications, including chemical and biomedical sensing, material processing and military applications. Here, we report all-fiber high-power graphene mode-locked Tm/Ho co-doped fiber laser at long wavelength with evanescent field interaction. Ultrafast pulses up to 7.8 MHz are generated at a center wavelength of 1879.4 nm, with a pulse width of 4.7 ps. A graphene absorber integrated with a side-polished fiber can increase the damage threshold significantly. Harmonics mode-locking can be obtained till to the 21th harmonics at a pump power of above 500 mW. By using one stage amplifier in the anomalous dispersion regime, the laser can be amplified up to 450 mW and the narrowest pulse duration of 1.4 ps can be obtained simultaneously. Our work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies.
Substrate bias dependence of the structure and internal stress of TiN films deposited by the filtered cathodic vacuum arc Influence of deposition temperature on the structure and internal stress of TiN films deposited by filtered cathodic vacuum arc High quality TiN films were deposited by an off-plane double bend filtered cathodic vacuum arc technique. The influence of deposition pressure, substrate bias, and deposition temperature on the structure and electrical resistivity of TiN films were systematically studied. As the deposition pressure is increased, the film structure evolves from hexagonal ␣-TiN 0.30 to cubic TiN, and the electrical resistivity decreases drastically at the pressure below 2ϫ10 Ϫ4 Torr, then increases slightly with the further increase of deposition pressure. With the increase of substrate bias, the electrical resistivity decreases drastically, reaching the minimum of 45 ⍀ cm at a substrate bias of Ϫ100 V, then increases greatly, which results from the variation of N content in TiN films with increasing substrate bias. The increase in the deposition temperature results in a significant decrease in the defect density and a slight increase in the grain size, which accounts for a linear decrease in the electrical resistivity. Our results indicate that the main factors that affect the electrical resistivity of TiN films are the N content, phase structure, and defect density in the films. The grain size plays only a minor role in the electrical resistivity of TiN films.
Topological photonics has been introduced as a powerful platform for integrated optics, since it can deal with robust light transport, and be further extended to the quantum world. Strikingly, valley-contrasting physics in topological photonic structures contributes to valley-related edge states, their unidirectional coupling, and even valley-dependent wave-division in topological junctions. Here, we design and fabricate nanophotonic topological harpoon-shaped beam splitters (HSBSs) based on 120-deg-bending interfaces and demonstrate the first on-chip valley-dependent quantum information process. Two-photon quantum interference, namely, Hong-Ou-Mandel (HOM) interference with a high visibility of 0.956 ± 0.006, is realized with our 50/50 HSBS, which is constructed by two topologically distinct domain walls. Cascading this kind of HSBS together, we also demonstrate a simple quantum photonic circuit and generation of a path-entangled state. Our work shows that the photonic valley state can be used in quantum information processing, and it is possible to realize more complex quantum circuits with valley-dependent photonic topological insulators, which provides a novel method for on-chip quantum information processing.
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