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Pd nanoparticles (NPs) were prepared by focused femtosecond laser irradiation of PdCl2 dissolved in ethanol. Transmission electron microscopy (TEM) analysis revealed that Pd NPs show certain crystalline microstructure, and the average diameter is 3.4 nm with narrow size distribution from 2.0 to 6.0 nm. The nonlinear optical absorption and refraction of Pd NPs solution were investigated with nanosecond laser pulses at 532 nm. The nonlinear absorption of Pd NPs is saturable at low intensity of 3.28×1011 W/m2 but it is changed to reverse saturable with the intensity increased to 7.96×1011 W/m2, which accordingly indicates the nonlinear refraction is changed from self-defocusing to self-focusing. The transition of the nonlinear absorption with the increase in pulse intensity is analyzed by an empirical model which includes mostly saturable absorption (SA) and two-photon absorption (TPA). The intensity of saturable Is is obtained, along with TPA coefficient β. SA and TPA are both originated from the interband transition between the d band and s-p conduction band. The SA possess less occupied density of states in the ground state and less unoccupied density of states in the excited state than that of TPA, so the TPA dominates the nonlinear absorption when the pulse intensity is high, leading to as-observed transition from SA to TPA. The refraction variation with increase in pulse intensity is attributed to the interband transition of electrons from d band to s-p conduction band in the Pd NPs.

Quantum technology establishes a foundation for secure communication via quantum key distribution (QKD). In the last two decades, the rapid development of QKD makes a global quantum communication network feasible. In order to construct this network, it is economical to consider small-sized and low-cost QKD payloads, which can be assembled on satellites with different sizes, such as space stations. Here we report an experimental demonstration of space-to-ground QKD using a small-sized payload, from Tiangong-2 space lab to Nanshan ground station. The 57.9-kg payload integrates a tracking system, a QKD transmitter along with modules for synchronization, and a laser communication transmitter. In the space lab, a 50 MHz vacuum + weak decoy-state optical source is sent through a reflective telescope with an aperture of 200 mm. On the ground station, a telescope with an aperture of 1200 mm collects the signal photons. A stable and high-transmittance communication channel is set up with a high-precision bidirectional tracking system, a polarization compensation module, and a synchronization system. When the quantum link is successfully established, we obtain a key rate over 100 bps with a communication distance up to 719 km. Together with our recent development of QKD in daylight, the present demonstration paves the way towards a practical satellite-constellation-based global quantum secure network with small-sized QKD payloads.

Two Gram-negative, rod-shaped, motile, aerobic bacterial strains designated HY-14 T and HY-24 were isolated from the sludge of an anaerobic ammonium-oxidizing bioreactor. The strains could not grow with 5 % (w/v) NaCl, did not produce acid from D-glucose or utilize D-glucose, gluconate or citrate as a sole carbon source. Summed feature 3 and C 16 : 0 were the most abundant fatty acids; hydroxyl fatty acids C 12 : 0 3-OH and C 10 : 0 3-OH were also present. Fatty acid C 12 : 0 2-OH was absent. The DNA G+C contents of strains HY-14 T and HY-24 were 50.6±0.5 mol%. Phylogenetic analyses based on 16S rRNA gene sequences showed that strains HY-14 T and HY-24 formed a monophyletic clade within the genus Pseudomonas. The highest sequence similarities were to Pseudomonas pseudoalcaligenes DSM 50188 T (95.9 %). On the basis of phenotypic and phylogenetic properties, strains HY-14 T and HY-24 are proposed as a novel species of the genus Pseudomonas, for which the name Pseudomonas caeni sp. nov. is proposed. The type strain is HY-14 T (5KCTC 22292 T 5CCTCC AB208156 T ).

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