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The equilibrium optical phonons of graphene are well characterized in terms of anharmonicity and electron–phonon interactions; however, their non-equilibrium properties in the presence of hot charge carriers are still not fully explored. Here we study the Raman spectrum of graphene under ultrafast laser excitation with 3 ps pulses, which trade off between impulsive stimulation and spectral resolution. We localize energy into hot carriers, generating non-equilibrium temperatures in the ~1700–3100 K range, far exceeding that of the phonon bath, while simultaneously detecting the Raman response. The linewidths of both G and 2D peaks show an increase as function of the electronic temperature. We explain this as a result of the Dirac cones’ broadening and electron–phonon scattering in the highly excited transient regime, important for the emerging field of graphene-based photonics and optoelectronics [ABSTRACT FROM AUTHOR]

Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular phenomena, including metal-insulator transitions, superconductivity and subpicosecond modification of magnetic order. The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, Eex, is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photo-induced dynamics of magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to Eex. By unravelling the photo-induced modification of the two-magnon line frequency from a dominating nonlinear optical effect, we find that Eex is increased by the electromagnetic stimulus. [ABSTRACT FROM AUTHOR]

Non-activated macrophages express low levels of A2ARs and lipopolysaccharides (LPS) upregulates A2AR expression in an NF-κB-dependent manner. The murine A2AR gene is encoded by three exons, m1, m2 and m3. Exons m2 and m3 are conserved, while m1 encodes the 5′ untranslated UTR. Three m1 variants have been defined, m1A, m1B and m1C, with m1C being farthest from the transcriptional start site. LPS upregulates A2ARs in primary murine peritoneal and bone-marrow-derived macrophages and RAW264.7 cells by selectively splicing m1C to m2, through a promoter located upstream of m1C. We have cloned ∼1.6 kb upstream of m1C into pGL4.16(luc2CP/Hygro) promoterless vector. This construct in RAW 264.7 cells responds to LPS, and adenosine receptor agonists augmented LPS responsiveness. The NF-κB inhibitors BAY-11 and triptolide inhibited LPS-dependent induction. Deletion of a key proximal NF-κB site (402-417) abrogated LPS responsiveness, while deletion of distal NF-κB and C/EBPβ sites did not. Site-directed mutagenesis of CREB (309-320), STAT1 (526-531) and AP2 (566-569) sites had little effect on LPS and adenosine receptor agonist responsiveness; however, mutation of a second STAT1 site (582-588) abrogated this responsiveness. Further analysis of this promoter should provide valuable insights into regulation of A2AR expression in macrophages in response to inflammatory stimuli. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate relationship between migraine and cerebral infarction in young people. Patients aging 16–44 years, referred for stroke and age- and gender-matched controls were investigated for migraine following the International Headache Society criteria. Included people were 314 strokes and 314 controls. Each group consisted of 150 men and 164 women. Of the 105 persons with migraine (16.7%), 57 had migraine with aura (9.1%). In women, migraine with aura was related to stroke [35 women among strokes (21.3%) vs. 9 among controls (5.5%), P < 0.0001], whereas migraine without aura was not. After multivariate analysis, migraine with aura remained independently associated with stroke together with hypertension, and the estro-progestinic utilization. In men, migraine was not associated with stroke. In conclusion, migraine with aura appears to be associated with ischemic stroke in young women, independently from other common risk factors. [ABSTRACT FROM AUTHOR]

Photon echo experiments on diethylthiacarbocyanine iodide (DTCI) in dibuthylphthalate (DBP) and glycerol in the glass phase with femtosecond pulses are presented. The PE signal shows nonexponential decays even at low temperatures. This behavior is attributed to the many vibronic resonances of the chromophore/ glass system which can be simultaneously excited by the spectral bandwith of the laser pulses. We are able to extract from the PE decays the contribution of the homogeneous dephasing rate of the 0-0 transition of DTCI up to 20 K in dibutylphthalate and 40 K in glycerol. A beating structure in the echo decay for the system DTCI/DBP is also observed from 8 K up to 180 K (glass transition temperature for DBP). This feature is attributed to an intereference process involving excitation of a vibronic transition of DTCI characterized by a vibrational frequency of 300 cm. [ABSTRACT FROM AUTHOR]

The issue of the relations that multiresonance CARS spectra and excitation profiles (CEP) bear to the corresponding spontaneous resonance Raman scattering (RRS) counterparts is addressed in the present paper with particular reference to the case of chromophoric molecules in room temperature solutions. On the basis of a fifth-order calculation of the CARS susceptibility, it is predicted that the properties of multiresonance CARS spectra and CEP strongly depend on the excited-state dynamics and pure dephasing rates. New experimental CARS and CEP results are reported for β-carotene and are shown to be closely related to the corresponding RRS data. This is attributed to the fact that its very fast excited-state dynamics allows one to use a simple third-order description of the data. [ABSTRACT FROM AUTHOR]

Some properties of multiresonance CARS spectra of polyatomic molecules in condensed phases are briefly discussed with reference to the possible effects of having a transfer of population under one-photon resonance conditions. Some experimental results are presented for the case of quinizarin in chloroform solution at room temperature. The observation of vibrational resonances of the first excited state as well as evidences of the participation of higher excited states to the multiresonant processes clearly indicate the need to go beyond the usual four level system description of the CARS spectra. [ABSTRACT FROM AUTHOR]

Spontaneous Raman spectroscopy is a powerful characterization tool for graphene research. Its extension to the coherent regime, despite the large nonlinear third-order susceptibility of graphene, has so far proven challenging. Due to its gapless nature, several interfering electronic and phononic transitions concur to generate its optical response, preventing to retrieve spectral profiles analogous to those of spontaneous Raman. Here we report stimulated Raman spectroscopy of the G-phonon in single and multi-layer graphene, through coherent anti-Stokes Raman Scattering. The nonlinear signal is dominated by a vibrationally non-resonant background, obscuring the Raman lineshape. We demonstrate that the vibrationally resonant coherent anti-Stokes Raman Scattering peak can be measured by reducing the temporal overlap of the laser excitation pulses, suppressing the vibrationally non-resonant background. We model the spectra, taking into account the electronically resonant nature of both. We show how coherent anti-Stokes Raman Scattering can be used for graphene imaging with vibrational sensitivity. Coherent anti-Stokes Raman Scattering (CARS) accesses the vibrational properties of a material via nonlinear four-wave mixing (FWM); CARS in graphene has not been observed to date despite its high nonlinear third-order susceptibility. Here, the authors devised a FWM scheme to perform stimulated Raman spectroscopy in single and multi-layer graphene through CARS. [ABSTRACT FROM AUTHOR]