Kyungtae Kim

Biological characterization of angiopoietin-3 and angiopoietin-4

The angiopoietin (Ang) family of growth factors includes Ang1, Ang2, Ang3, and Ang4, all of which bind to the endothelial receptor tyrosine kinase Tie2. Ang3 (mouse) and Ang4 (human) are interspecies orthologs. In experiments with human endothelial cell lines, Ang3 was identified as an antagonist of Tie2 and Ang4 was identified as an agonist of Tie2. However, the biological roles of Ang3 and Ang4 are unknown. We examined the biological effect of recombinant Ang3 and Ang4 proteins in primary cultured endothelial cells and in vivo in mice. Recombinant Ang3 and Ang4 formed disulfide‐linked dimers. Ang4 (400 ng/mL) markedly increased Tie2 and Akt phosphorylation in primary cultured HUVECs whereas Ang3 (400 ng/mL) did not produce significant changes. Accordingly, Ang4, but not Ang3, induced survival and migration in primary cultured HUVECs. Unexpectedly, intravenously administered Ang3 (30 µg) was more potent than Ang4 (30 µg) in phosphorylating the Tie2 receptor in lung tissue from mice in vivo. Accordingly, Ang3 was more potent than Ang4 in phosphorylating Akt in primary cultured mouse lung microvascular endothelial cells. Ang3 and Ang4 both produced potent corneal angiogenesis extending from the limbus across the mouse cornea in vivo. Thus, Ang3 and Ang4 are agonists of Tie2, but mouse Ang3 has strong activity only on endothelial cells of its own species.—Lee, H. J., Cho, C.‐H., Hwang, S.‐J., Choi, H.‐H., Kim, K.‐T., Ahn, S. Y., Kim, J.‐H., Oh, J.‐L., Lee, G. M., Koh, G. Y. Biological characterization of angiopoietin‐3 and angiopoietin‐4. FASEB J. 18, 1200–1208 (2004)

Coherent control of resonant two-photon transitions by counterpropagating ultrashort pulse pairs

We describe optimized coherent control methods for two-photon transitions in atoms of a ladder-type three-state energy configuration. Our approach is based on the spatial coherent control scheme, which uses counterpropagating ultrashort laser pulses to produce complex excitation patterns in an extended space. Because coherent control requires constructive interference of constituent transition pathways, applying it to an atomic transitionwithaspecificenergyconfigurationrequiresspeciallydesignedlaserpulses.Weshowinanexperimental demonstration that two-photon transition with an intermediate resonant energy state can be coherently controlled andretrievedfromtheresonance-inducedbackground,whenphaseflippingofthelaserspectrumneartheresonant intermediate transition is used. A simple reason for this behavior is the fact that the transition amplitude function (added to give an overall two-photon transition) changes its sign at the intermediate resonant frequency and, thus, by proper spectral-phase programing, the excitation patterns (or the position-dependent interference of the transition given as a consequence of the spatial coherent control) can be well isolated in space along the focal region of the counterpropagating pulses.

Direct frequency-comb spectroscopy of 6s2S1/2–8s2S1/2 transitions of atomic cesium

Direct frequency-comb spectroscopy is used to probe the absolute frequencies of the – two-photon transitions of atomic cesium in a hot vapor environment. By utilizing the coherent control method of temporally splitting the laser spectrum above and below the two-photon resonance frequency, Doppler-free absorption is built in two spatially distinct locations and imaged for high-precision spectroscopy. Theoretical analysis finds that these transition lines are measured with uncertainty below 5 × 10−10, mainly contributed from laser-induced AC Stark shift.

Spectro-spatial coherent control of ultrafast laser interaction with atomic vapor

Spectro-spatial coherent control methods are reported demonstrating optimized resonant two-photon transitions of rubidium atomic vapor by counter-propagating ultrashort pulse pairs. By properly programming the spectral sign changes across resonance frequencies, unlike non-resonant two-photon transitions, the resonant two-photon transitions probabilities could be enhanced, experiment finds.