80 research outputs found
Optical and RF Metrology for 5G
Specification standards will soon be available for 5G mobile RF
communications. What optical and electrical metrology is needed or available to
support the development of the supporting optical communication systems? Device
measurement, digital oscilloscope impairments and improving system resolution
are discussed.Comment: 2017 IEEE Photonics Society Summer Topical Meeting Series (SUM
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Sub-picosecond temporal resolution of anomalous Hall currents in GaAs
Peroxidase-mimicking DNAzyme was applied as a catalyst of silver deposition on gold nanoparticles. This DNAzyme is formed when hemin binds to the G-quadruplex-forming DNA sequence. Such a system is able to catalyze a redox reaction with a one- or two-electron transfer. The process of silver deposition was monitored via a localized surface plasmon resonance technique (LSPR), which allows one to record scattering spectrum of a single nanoparticle. Our study showed that DNAzyme is able to catalyze silver deposition. The AFM experiments proved that DNAzyme induced the deposition of silver shells of approximately 20 nm thickness on Au nanoparticles (AuNPs). Such an effect is not observed when hemin is absent in the system. However, we noticed non-specific binding of hemin to the capture oligonucleotides on a gold NP probe that also induced some silver deposition, even though the capture probe was unable to form G-quadruplex. Analysis of SEM images indicated that the surface morphology of the silver layer deposited by DNAzyme is different from that obtained for hemin alone. The proposed strategy of silver layer synthesis on gold nanoparticles catalyzed by DNAzyme is an innovative approach and can be applied in bioanalysis (LSPR, electrochemistry) as well as in material sciences
Characterization of high-speed balanced photodetectors
We report the characterization of a balanced ultrafast photodetector. For this purpose, we use a recently developed time-domain laser-based vector network analyzer (VNA) to determine the common-mode rejection ratio (CMRR) of the device under test. This includes the frequency-domain response above the single-mode frequency of the coaxial connector. Although the balanced photodetector has a nominal bandwidth of 43 GHz, it generates voltage pulses with frequency components up to 180 GHz. We obtain a CMRR of better than 30 dB up to 70 GHz and better than 20 dB up to 110 GHz. The laser-based measurements are compared with the measurements using a digital sampling oscilloscope and with the frequency-domain measurements using a conventional VNA. We obtain good agreement between the three techniques with the laser-based method providing the largest measurement bandwidth, although it also constitutes the most complicated characterization setup
All-optically induced ultrafast photocurrents: Beyond the instantaneous coherent response
It is demonstrated that the non-instantaneous response of the optically
induced coherent polarization tremendously influences the real-space shift of
electronic charges in semiconductors. The possibility to coherently control
this real-space shift with temporally non-overlapping excitation pulses allows
for the observation of a new type of shift current, which only exists for
certain polarization-shaped excitation pulses and vanishes in the
continuous-wave limit. In contrast to previously studied shift currents, the
new current requires a phase mismatch between two orthogonal transition dipole
moments and leads, within a nonlinear second-order description, to a tensor
which is antisymmetric with respect to the order of the two exciting electric
field amplitudes. These observations, which can even be made at room
temperature and are expected to occur in a variety of semiconductor crystal
classes, contribute to a better understanding of light-matter interaction
involving degenerate bands. Thus, they are expected to prove important for
future studies of coherent and nonlinear optical effects in semiconductors
Optical creation and annihilation of skyrmion patches in a bulk chiral magnet
A key challenge for the realization of future skyrmion devices comprises the
controlled creation, annihilation and detection of these topologically
non-trivial magnetic spin textures. In this study, we report an all-optical
approach for writing, deleting, and reading skyrmions in the cubic chiral
magnet FeCoSi based on thermal quenching. Using focused
femtosecond laser pulses, patches of a skyrmion state are created and
annihilated locally, demonstrating unprecedented control of thermally
metastable skyrmions in a bulk compound. The skyrmion state is read-out by
analyzing the microwave spin excitations in time-resolved magneto-optical Kerr
effect measurements. Extracting the magnetic field and laser fluence
dependence, we find well-separated magnetic field regimes and different laser
fluence thresholds for the laser-induced creation and annihilation of
metastable skyrmions. The all-optical skyrmion control, as established in this
study for a model system, represents a promising and energy-efficient approach
for the realization of skyrmions as magnetic bits in future storage devices,
reminiscent of magneto-optical storage devices in the past
Structure and stability of DNA containing an aristolactam II-dA lesion: implications for the NER recognition of bulky adducts
Aristolochic acids I and II are prevalent plant toxicants found in the Aristolochiaceae plant family. Metabolic activation of the aristolochic acids leads to the formation of a cyclic N-hydroxylactam product that can react with the peripheral amino group of purine bases generating bulky DNA adducts. These lesions are mutagenic and established human carcinogens. Interestingly, although AL-dG adducts progressively disappear from the DNA of laboratory animals, AL-dA lesions has lasting persistence in the genome. We describe here NMR structural studies of an undecameric duplex damaged at its center by the presence of an ALII-dA adduct. Our data establish a locally perturbed double helical structure that accommodates the bulky adduct by displacing the counter residue into the major groove and stacking the ALII moiety between flanking bases. The presence of the ALII-dA perturbs the conformation of the 5ā²-side flanking base pair, but all other pairs of the duplex adopt standard conformations. Thermodynamic studies reveal that the lesion slightly decreases the energy of duplex formation in a sequence-dependent manner. We discuss our results in terms of its implications for the repair of ALII-dA adducts in mammalian cells
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