PACS: 32.30.-r, 32.60.+i, 32.70

Abstract: We have measured light shifts, also known as AC Stark shifts, as a function of laser intensity in cold Rubidium atoms by observing sub-natural linewidth gain and loss features in the transmission spectrum of a weak probe beam passing through the atomic sample. The observed energy-level shifts for atoms in a magneto-optical trap (MOT) are found to be consistently higher than that obtained in optical molasses (i.e., when the magnetic field gradient in the MOT is turned off). Using a simple model of a multilevel Rubidium atom interacting with pump and probe beams, we have calculated the theoretical light shift as a function of intensity. A comparison of these calculated values with the light shift data obtained for molasses reveals good agreement between experiment and theory. Further, our model elucidates the role of the Zeeman shifts arising from the magnetic field gradient in the observed probe transmission spectrum for the MOT. A qualitative plot of the transmission spectrum of a probe beam through a fictitious sample of cold J = 1 → J = 2 atoms showing probe absorption at the sum of the pump frequency ω pump and δ , where δ is the difference of the light shifts between the |J = 1,mJ = 0 and the |J = 1,mJ = ± 1 ground state Zeeman sublevels. Probe gain is depicted at ω pump -δ . Se

LASER PHYSICS LETTERS

Abstract: Raman spectroscopy offers a powerful alternative analytical method for the detection and identification of lipids/oil in biological samples, such as algae and fish. Recent research in the authors' groups, and experimental data only very recently published by us and a few other groups suggest that Raman spectroscopy can be exploited in instances where fast and accurate determination of the iodine value (associated with the degree of lipid unsaturation) is required. Here the current status of Raman spectroscopy applications on algae is reviewed, and particular attention is given to the efforts of identifying and selecting oil-rich algal strains for the potential mass production of commercial biofuels and for utilization in the food industry. Normalized intensity, a.u

Ultrafast quenching of ring closure in molecular switches, self-assembled on gold nanoparticles

We report the ultrafast quenching of the ring-closure reaction in BTE-based photochromic switches self-assembled on gold nanoparticles. The photoinduced population dynamics of the switches reveals that the electronic states of the switch molecules are strongly mixed with the states of the gold particles

Heterogeneous Dynamics of Coupled Vibrations

Frequency-dependent dynamics of coupled stretch vibrations of a water molecule are revealed by 2D IR correlation spectroscopy. These are caused by non-Gaussian fluctuations of the environment around the individual OH stretch vibrations

Frozen Dynamics and Insulation of Water at the Lipid Interface

2D IR correlation spectroscopy reveals extremely slow dynamics and splitting of the OH-stretching mode of water in anionic micelles. Water at the lipid interface behaves as if the molecules were isolated in a "frozen" environment

Ultrafast Charge Photogeneration in MEH-PPV Charge-Transfer Complexes

Visible-pump - IR-probe spectroscopy is used to study the ultrafast charge dynamics in MEH-PPV based charge-transfer complexes and donor-acceptor blends. Transient anisotropy of the polymer polaron band provides invaluable insights into excitation localisation and charge-transfer pathways

Ultrafast exciton transport in organic nanotubes

The dynamics of exciton transport between the inner and outer walls of double-layer cylindrical aggregates is measured. Downhill transport is fast (275 A) and excitation intensity independent. Uphill transport is much slower (3.5 ps), but this rate increases when the excitation density is raised. This suggests that exciton-exciton annihilation is involved

Ultrafast energy and electron transfer in donor-acceptor molecules for photovoltaics

The rapid advancement in fullerene chemistry allows the covalent functionalization of C60 with electron donors. Various C60-based donor-acceptor dyads have been synthesized and studied to gain insight in the intramolecular photophysical processes, like energy and electron transfer. Although these dyads can serve as a model compounds for the conjugated photovoltaic cells, only a few examples have been reported with these C60-based dyads. Apart from being well-defined model systems for photophysical characterization, the covalent linkage between donor, and acceptor in these molecular arrays provides a simple method to achieve control over the phase segregation in donor-acceptor networks. We investigate an oligo(phenylene vinylene)fullerene dyad with 4 phenyl groups (C60-OPV4) in solvents of different polarity using femtosecond pump-probe spectroscopy. We find that photoexcitation of the oligomer leads first to an intramolecular energy transfer to the fullerene, while an electron transfer is a secondary process, only allowed in polar solvents.