First results on laser-induced field emission from a CNT-based nanotip.

We present the first demonstration of ultrafast laser-induced field emission and measurement of the energy distribution of electrons from a nanotip based on a carbon nanotube (CNT). Our experimental setup extends the studies performed on conventional tungsten or gold tips by using this new innovative tip. The carbon tip consists of concentric carbon layers in the shape of a cone, and has been previously studied as a very good candidate for cold field emission. The first laser-induced field emission from a CNT-based nanotip has been observed and we measured the energy spectrum as well as the polarization dependance of the emission. We also characterize the damage threshold of the tip, when illuminated by a high repetition rate femtosecond laser. These first results are encouraging further studies of electron emission from CNT-based carbon nanotips.

Nonclassical light manipulation in a multiple-scattering medium.

We investigate the possibility of using a scattering medium as a highly multimode platform for implementing quantum walks. We demonstrate the manipulation of a single photon propagating through a strongly scattering medium using wavefront-shaping technique. Measurement of the scattering matrix allows the wavefront of the photon to be shaped to compensate the distortions induced by multiple scattering events. The photon can thus be directed coherently to a specific output mode. Using this approach, we show how entanglement of a single photon across different modes can be manipulated despite the enormous wavefront disturbance caused by the scattering medium.

Robust quantum dot exciton generation via adiabatic passage with frequency-swept optical pulses.

The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance. This observation in photoluminescence experiments is made possible by introducing a novel optical detection scheme for the resonant electron hole pair (exciton) generation.

Quantum interference in NO2.

This paper investigates the origin of a quantum interference observed when NO(2) is dissociatively ionized by short pulses of ultraviolet light. We describe time-resolved measurements of NO(+), O(+), and NO(2)(+) ions produced following the interaction of NO(2) with a approximately 70 fs duration pulse centered close to 400 nm and a subsequent time-delayed probe pulse close to 269, 205, or 400 nm. A quantum beat oscillation with a period of 524 fs and a characteristic damping time of 8 ps is observed on all transient ion signals. We investigate the effect of tuning the central wavelength of the excitation pulse over a 12 nm range, and we discuss the potential importance of three possible multiphoton pathways involving one, two, and three pump photons. We conclude that the ionization pathway responsible for the beat signal is most likely due to a process involving the absorption of two pump photons and two probe photons. This presents an interesting problem with respect to the interpretation of the mechanism responsible for the quantum interference signature since the electronic states of NO(2) reached at the two-photon level are all thought to be extremely short-lived and to dissociate on a time scale that is far shorter than the characteristic damping time of the oscillatory signals. We suggest that a possible explanation for the observed dynamics is associated with a minor dissociation channel of the (2)(2)B(2) state of NO(2) through its interaction with the longer lived (2)(2)A(1) state.

Effects of divalent cations and of a calcimimetic on adrenocorticotropic hormone release in pituitary tumor cells.

The calcium sensing receptor (CaSR), a member of the G-protein coupled receptor family, is expressed on a variety of cell types and responds to extracellular calcium. We have characterized pharmacological properties of (+/-)NPS 568, a calcimimetic, toward cloned rat brain extracellular Ca2+-sensing receptor (CaSR) expressed in Chinese hamster ovary (CHO) cells and constitutive mouse CaSR in AtT-20 cells. In the presence of 1.3 mM Ca2+, the calcimimetic displayed a potency in the micromolar range in augmenting the inositol phosphates (IP) response in both cell lines and behaved as a full agonist. (+/-)NPS 568 stimulated formation of arachidonic acid release in CHO(CaSR) with a similar potency. The IP dose response curves of (+/-)NPS 568 were shifted to the left in the presence of increasing Ca2+, indicating that the potency of the drug is dependent on extracellular Ca2+ in both cells. In AtT-20 cells, Ca2+ and Ba2+, two CaSR agonists, induced a potent stimulation of adrenocorticotropic hormone (ACTH) secretion. In the presence of 1.8 mM Ca2+, (+/-)NPS 568 led to a dose dependent secretion of ACTH with an EC50 of 0.3 microM and a maximal effect comparable to Ca2+. The similar potency of the calcimimetic on IP and ACTH responses and the sensitivity of these responses to extracellular Ca2+ indicate that the Ca2+-sensing receptor expressed in AtT-20 cells is implicated in ACTH release. These data further characterize the pharmacology of the Ca2+-sensing receptor and argue for a role for extracellular Ca2+ and CaSRs in controlling ACTH secretion, a hormone implicated in several types of stress.