While supercapacitors can deliver high electrical power, their low energy density limits their application. Here, we designed and fabricated a facile asymmetric supercapacitor (ASC) with excellent electrochemical performance, where MnO 2 nanoflowers (NFs) and La 2 O 3 nanospheres (NSs) were successfully electrodeposited onto carbon paper as work electrodes in an aqueous 0.5 M Na 2 SO 4 electrolyte. Such nanostructures endow the electrodes with short electrons, ion diffusion paths, and abundant charge adsorption sites. The assembled MnO 2 NF//La 2 O 3 NS asymmetric cell presents a gravimetric energy density of 80.56 Wh kg −1 , a volumetric energy density of 0.74 mWh cm −3 at 35.71 mA cm −3 , and excellent cycle performance. Moreover, a packaged device displays a superior energy density of 0.49 mWh cm −3 with a power density of 94.29 mW cm −3 . The satisfactory improvement in performance mainly stems from the homogeneous nanostructured architecture and an extended workable potential region of 0− 2.0 V. The resulting supercapacitors could have great potential for designing high energy and power density devices as effective power sources.
We present the first, to the best of our knowledge, direct generation of pulsed optical vortices in the 2.7-µ m spectral range by employing polycrystalline Fe:ZnSe as a saturable absorber (SA). A modified theoretical model taking into account the propagation features of the reshaped annular pump beam is elaborated to accurately determine the excitation conditions of the Laguerre–Gaussian (LG0,l) modes, yielding a lasing efficiency comparable to the fundamental TEM00 mode in continuous-wave (CW) regime. Nanosecond scalar optical vortices with well-defined handedness are successfully produced by taking advantages of designated mode-matching, high polarization extinction ratio (PER), and the "spatial filter" effect of the SA on other transverse modes. Such scalar vortex laser pulses in the mid-infrared region will enable new applications such as frequency down conversion to produce optical vortices at longer (far-infrared) wavelengths, structuring organic materials, novel molecular spectroscopy, etc.
In this paper, we report on a wide wavelength tuning optical vortex carrying orbital angular momentum (OAM) of ±ħ, from a thulium-doped yttrium aluminum perovskite (YAP) laser employing a birefringent filter. The OAM is experimentally found to be well maintained during the whole wavelength tuning process. The Laguerre-Gaussian (LG 0,1 ) mode with a tuning range of 58 nm from 1934.8 to 1993.0 nm and LG 0,−1 mode with a range of 76 nm from 1920.4 to 1996.6 nm, are, respectively, obtained. This is, to the best of our knowledge, the first experimental implementation of wavelength tuning for a scalar vortex laser in the 2 μm spectral range, as well as the broadest tuning range ever reported from the vortex laser cavity. Such a vortex laser with robust structure and straightforward wavelength tuning capability will be an ideal light source for potential applications in the field of optical communication with one additional degree of freedom.
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