Tellurium spectrometer for 1S0-1P1 transitions in strontium and other alkaline-earth atoms.

We measure the spectrum of tellurium-130 in the vicinity of the 461 nm S01-P11 cycling transition in neutral strontium, a popular element for atomic clocks, quantum information, and quantum-degenerate gases. The lack of hyperfine structure in tellurium results in a spectral density of transitions nearly 50 times lower than that available in iodine, making use of tellurium as a laser-frequency reference challenging. By frequency-offset locking two lasers, we generate the large frequency shifts required to span the difference between a tellurium line and the S01-P11 resonance in strontium or other alkaline-earth atoms. The resulting laser architecture is long-term frequency stable, widely tunable, and optimizes the available laser power. The versatility of the system is demonstrated by using it to quickly switch between any strontium isotope in a magneto-optical trap and by adapting it to spectroscopy on a thermal beam with a different alkaline-earth atom.

Competition between Factors Determining Bright versus Dark Atomic States within a Laser Mode.

We observe bimodal fluorescence patterns from atoms in a fast atomic beam when the laser excitation occurs in the presence of a magnetic field and the atoms sample only a portion of the laser profile. The behavior is well explained by competition between the local intensity of the laser, which tends to generate a coherent-population-trapping (CPT) dark state in the J = 1 to J' = 0 system, and the strength of an applied magnetic field that can frustrate the CPT process. This work is relevant for understanding and optimizing the detection process for clocks or other coherent systems utilizing these transitions and could be applicable to in situ calibration of the laser-atom interaction, such as the strength of the magnetic field or laser intensity at a specific location.

Regulation of endothelial MAPK/ERK signalling and capillary morphogenesis by low-amplitude electric field.

Low-amplitude electric field (EF) is an important component of wound-healing response and can promote vascular tissue repair; however, the mechanisms of action on endothelium remain unclear. We hypothesized that physiological amplitude EF regulates angiogenic response of microvascular endothelial cells via activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway. A custom set-up allowed non-thermal application of EF of high (7.5 GHz) and low (60 Hz) frequency. Cell responses following up to 24 h of EF exposure, including proliferation and apoptosis, capillary morphogenesis, vascular endothelial growth factor (VEGF) expression and MAPK pathways activation were quantified. A db/db mouse model of diabetic wound healing was used for in vivo validation. High-frequency EF enhanced capillary morphogenesis, VEGF release, MEK-cRaf complex formation, MEK and ERK phosphorylation, whereas no MAPK/JNK and MAPK/p38 pathways activation was observed. The endothelial response to EF did not require VEGF binding to VEGFR2 receptor. EF-induced MEK phosphorylation was reversed in the presence of MEK and Ca(2+) inhibitors, reduced by endothelial nitric oxide synthase inhibition, and did not depend on PI3K pathway activation. The results provide evidence for a novel intracellular mechanism for EF regulation of endothelial angiogenic response via frequency-sensitive MAPK/ERK pathway activation, with important implications for EF-based therapies for vascular tissue regeneration.

Magnetic-field-induced crossover to a nonuniversal regime in a Kondo dot.

We have measured the magnetic splitting Delta K of a Kondo peak in the differential conductance of a single-electron transistor while tuning the Kondo temperature T K along two different paths in parameter space: varying the dot-lead coupling at a constant dot energy and vice versa. At a high magnetic field B, the changes of DeltaK with TK along the two paths have opposite signs, indicating that Delta K is not a universal function of TK. At low B, we observe a decrease in DeltaK with TK along both paths, in agreement with theoretical predictions. Furthermore, we find Delta K/Delta<1 at low B and Delta K/Delta>1 at high B, where Delta is the Zeeman energy of the bare spin, in the same system.