查看更多>>摘要：? 2021 Elsevier B.V.In deep space optical communications, pointing, acquisition and tracking (PAT) system need to locate the position of the beacon, precisely. The way of employing the natural celestial body as the beacon come to draw attention, in contrast to regarding the laser as the beacon which has a series of problems of limited power, serious attenuation, high cost and difficult design realization. In this paper, the primary goal is to study the problem of precise positioning for the beacon by taking the natural celestial body as the beacon. Given the long distance, with small target and large uncertain region in deep space optical communications, the location of the beacon can be realized by the combination of rough and precise positioning based on the image feature of the beacon. Firstly, it performs the rough positioning according to the image characteristic information of the beacon's edge, then in the uncertain region, the processing scope has been narrowed according the results of the rough positioning, finally the beacon is precisely located based on its minutiae feature by the way of feature point matching to achieve the position of the beacon. The impact due to the autorotation of celestial body on the image transform has been also discussed and analyzed with the mapping relationship of coordinate and geometric transform. The feasibility of the algorithm is verified by a long distance far-field Earth–Moon experiment. The design of system implementation on embedded hardware system can provide a reference for the real-time positioning system in deep space optical communications.
查看更多>>摘要：? 2021 Elsevier B.V.Considering germanium (Ge) material with one of the highest refractive index and semi-metal properties, the light scattering properties of Ge trimer and its metasurface structures are studied theoretically in this paper. In contrast to other dielectric materials, for which the magnetic-type resonance is commonly dominant, Ge has a strong electric-type resonance due to its semi-metal properties, which can be seen in the visible and near-infrared spectral range. The influence of the unique feature on the Fano line shapes can be reflected in the scattering spectra. Simultaneously, taking into account the substrate effects, we show that the behavior of the light scattering anisotropy exhibits a big difference in the presence of the different substrates, which can be manipulated to some extent. The results can provide a feasible way to control the “hot spots” in the local light field. Our work in this paper shows that Ge trimers as an excellent candidate can be applied to enhanced spectroscopy, directional sources, and other nanometer photonic devices, as well as on metasurface structures.
查看更多>>摘要：? 2021Photovoltaic effect of neutral atoms using inhomogeneous light in a double-trap opened system is studied theoretically. Using asymmetric external driving field to replacing original asymmetric chemical potential of atoms, we create polarization of atom population in the double-trap system. The polarization of atom number distribution induces net current of atoms and works as collected carriers in the cell. The cell can work even under partially coherent light. The whole configuration is described by quantum master equation considering weak tunneling between the system and its reservoirs at finite temperature. The model of neutral atoms could be extended to more general quantum particles in principle.
查看更多>>摘要：? 2021 Elsevier B.V.We demonstrated a high-power laser diode (LD) side-pumped two-rod Er:YSGG mid-infrared laser by optimizing the location of the two laser heads in resonator based on the matrix formalism. A maximum output power of 61.02 W was achieved at repetition rate of 100 Hz and pulse width of 750μs, corresponding to optical–optical efficiency of 12.6%. The experimental results illustrated that the technology of double rods in series can effectively improve the output power of the LD side-pumped Er:YSGG laser.
查看更多>>摘要：? 2021 Elsevier B.V.The experimental findings regarding laser wavelength effects on the proton emission from a palladium plasma are reported. A palladium target is irradiated with fundamental, second, and third harmonics of a nanosecond pulsed laser in a broad laser fluence range (1.3–39.7 J/cm2). Time-of-flight traces of the proton pulses, measured with a planar ion collector, are used to estimate protons yield and kinetic energy. These are important parameters to consider when injecting a proton pulse into a high-energy accelerator. It was found that below the fluence of ～10 J/cm2, the proton yield is higher for shorter wavelengths, but it does not depend on the wavelength at higher laser intensities and is ～2 × 109 proton/pulse. For all three wavelengths, proton yield initially grows at a considerably quicker rate but slows down as fluence increases. For 355 nm and 532 nm wavelengths, the proton kinetic energies are comparable and are in the range of 280–800 eV. But the protons are 2 to 4 times less energetic in the case of 1064 nm wavelength. The disparities in proton yield and kinetic energy are attributed to the wavelength-dependent laser energy absorption in the target and plasma. The persistence of proton yield, for the successive laser pulses fired at the same target location, implies that the palladium can serve as a proton source for extended operation if ablated in suitable vacuum pressure.
查看更多>>摘要：? 2021 Elsevier B.V.We present the characteristics of intra-mode forward stimulated Brillouin scattering (FSBS) induced by HE11 and high-order optical mode (HOM) in nanofibers, respectively. Multiple transverse acoustic modes (TAMs) would be excited in the FSBS process. However, only a few specific low-order TAMs participate in the interaction of different optical mode pairs and then contribute to Brillouin gain. Meanwhile, the changes of dominating Brillouin peaks with the nanofiber radius are shown in detail, which further clearly confirms the difference in the gain characteristics of different intra-mode Brillouin gain spectrums. Especially, several obvious maximum and minimum gain values exist at the nanofiber radius of around 0.8 μm. The HOM induced intra-mode FSBS is of great importance for understanding of the phonon–photon interaction in multi-mode waveguides.
查看更多>>摘要：? 2021A novel chirped-pulse compression scheme is proposed to pursue higher pulse peak power of chirped-pulse amplifiers based on state-of-the-art gratings. It is characterized by the spectral non-uniformity of the beam cross section as well as by the uniform size of the beam projections on the four compression gratings. The spatial distribution of spectra is well designed so that the beam can remain generally collimated in the compressor and the gratings can be employed with a full work area. The maximum possible output pulse energy can therefore be increased within the damage threshold limit. A detailed design is developed for a scheduled 50-PW optical parametric chirped-pulse amplifier. Results of the numerical simulation on the focused output show that the spot size and pulse duration in the focal plane are close to those of conventional grating compression. Further, it is a promising method for upgrading existing chirped-pulse amplifiers.
查看更多>>摘要：? 2021 The Author(s)Ion beam figuring (IBF) provides a deterministic figuring method for fabricating ultra-high precision optical components such as lithographic objective lenses. But in the previous IBF process, the convergence of surface accuracy is often uncertain. Therefore, the iterative processing methods are mostly adopted. In the iterative process, the convergence ratio (the ratio of root mean square before and after figuring) of single figuring is relatively low. With the improvement of machining accuracy, the convergence ratio continues to decrease. The study analyzes the factors that limit the convergence ratio of single processing and the influence form and degree of each element on the convergence ratio. Furthermore, we present an IBF strategy with a high convergence ratio based on an optimized removal function. Based on this strategy, we complete the figuring experiment. The convergence ratio is much higher than the previous level. Compared with the surface of iterative figuring, the surface is simple and more favorable to figuring to sub-nanometer precision. The experimental results show that we can optimize the removal function to achieve rapid optical surface fabrication with nanometer precision.
查看更多>>摘要：? 2021 Elsevier B.V.As an additional degree of freedom and emerging resource, orbital angular momentum (OAM) has been widely used in both classical and quantum information technologies. Flexible manipulation of OAM modes is fundamentally important to various OAM-based applications. In this Letter, we demonstrate OAM mode conversion in a photonic chip by properly engineering the three-dimensional laser direct writing. More specifically, we find that by increasing the direct-written power, the input OAM±1 modes first remains unchanged, and then transforms into its superpositions. When mapping OAM±2 into the waveguide, it gradually evolves from OAM±1 and its superpositions to OAM±2. This mode conversion is essentially determined by the eigenmodes supported by the waveguide. Furthermore, the input OAM±1 modes can be reversed by tuning the direct-written velocity. Our results demonstrate the more complete manipulation of twisted-light-inside a photonic chip and may further contribute to the integration of high-dimensional quantum information processing.
查看更多>>摘要：? 2021High-precision piston detection within a large capture range is a key for segmented telescopes. In this paper, we propose a simple and efficient piston detection method based on multiple neural networks coordination. By setting a mask with a sparse multi-subpupil configuration at conjugate plane of the segmented mirror, a new dataset that is extremely sensitive to the piston is created. And two kinds of neural networks are built for different stages of detection, which ensures the method is of both large-scale and high-precision. Simulation shows that the piston can be detected in the range of the coherence length of the operating light with a sub-nanometer scale precision by this method. This method is robust and does not require complex hardware. It can be widely applied in segmented and deployable primary mirror telescopes.
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