Glucose concentration measured by the hybrid coherent anti-Stokes Raman-scattering technique

Journals published by the American Physical Society can be found at http://publish.aps.org/We investigate the possibility of using a hybrid coherent anti-Stokes Raman scattering technique for noninvasive monitoring of blood glucose levels. Our technique combines instantaneous coherent excitation of several characteristic molecular vibrations with subsequent probing of these vibrations by an optimally shaped, time-delayed, narrowband laser pulse. This pulse configuration mitigates the nonresonant four-wave mixing background while maximizing the Raman-resonant signal and allows rapid and highly specific detection even in the presence of multiple scattering. Under certain conditions we find that the measured signal is linearly proportional to the glucose concentration due to optical interference with the residual background light, which allows reliable detection of spectral signatures down to medically relevant glucose levels

Dual-tip-enhanced ultrafast CARS nanoscopy

Coherent anti-Stokes Raman scattering (CARS) and, in particular, femtosecond adaptive spectroscopic techniques (FAST CARS) have been successfully used for molecular spectroscopy and microscopic imaging. Recent progress in ultrafast nanooptics provides flexibility in generation and control of optical near fields, and holds promise to extend CARS techniques to the nanoscale. In this theoretical study, we demonstrate ultrafast subwavelentgh control of coherent Raman spectra of molecules in the vicinity of a plasmonic nanostructure excited by ultrashort laser pulses. The simulated nanostructure design provides localized excitation sources for CARS by focusing incident laser pulses into subwavelength hot spots via two self-similar nanolens antennas connected by a waveguide. Hot-spot-selective dual-tip-enhanced CARS (2TECARS) nanospectra of DNA nucleobases are obtained by simulating optimized pump, Stokes and probe near fields using tips, laser polarization- and pulse-shaping. This technique may be used to explore ultrafast energy and electron transfer dynamics in real space with nanometre resolution and to develop novel approaches to DNA sequencing.Comment: 11 pages, 6 figure

Tracking molecular wave packets in cesium dimers by coherent Raman scattering

We explore wave-packet dynamics in the ground X 1Σ+g and excited B 1Πu states of cesium dimers (Cs2). In particular, we study the dependence of the wave- packet dynamics on the relative timing between femtosecond pump, Stokes, and probe pulses in a nondegenerate BOXCARS beam geometry, which are commonly used for coherent anti-Stokes Raman scattering (CARS) spectroscopy. The experimental results are elucidated by theoretical calculations, which are based on the Liouville equations for the density matrix for the molecular states. We observe oscillations in CARS signals as functions of both Stokes and probe pulse delays with respect to the pump pulse. The oscillation period relates to the wave-packet motion cycle in either the ground or excited state of Cs2 molecules, depending on the sequence of the input laser pulses in time. The performed analysis can be applied to study and/or manipulate wave-packet dynamics in a variety of molecules. It also provides an excellent test platform for theoretical models of molecular systems