Linear and Nonlinear Spectroscopy by a Common-Path Birefringent Interferometer

© 1995-2012 IEEE. We introduce a passive common-path interferometer to replace Michelson interferometers in the Fourier-Transform spectroscopy. Our device exploits birefringence to introduce a highly accurate delay between two orthogonal polarization components by continuously varying the material thickness. Due to its inherent delay stability and reproducibility, it can be used even for short wavelengths (down to ∼200 nm) without the need for any active control or position tracking. We first demonstrate its performances in linear spectroscopy, by implementing a spectrometer and a spectrophotometer. We then extend its use to nonlinear spectroscopy and, in combination with lock-in detection at MHz modulation frequencies, illustrate its application to pump-probe spectroscopy with high sensitivity (ΔT/T 500 nm) and to broadband stimulated Raman scattering microscopy in the CH stretching region

A Study of the Formation of Single- and Double-Walled Carbon Nanotubes by a CVD Method

The reduction in H2/CH4 atmosphere of aluminum-iron oxides produces metal particles small enough to catalyze the formation of single-walled carbon nanotubes. Several experiments have been made using the same temperature profile and changing only the maximum temperature (800-1070 °C). Characterizations of the catalyst materials are performed using notably 57Fe Mo¨ssbauer spectroscopy. Electron microscopy and a macroscopical method are used to characterize the nanotubes. The nature of the iron species (Fe3+, R-Fe, ç-Fe-C, Fe3C) is correlated to their location in the material. The nature of the particles responsible for the high-temperature formation of the nanotubes is probably an Fe-C alloy which is, however, found as Fe3C by postreaction analysis. Increasing the reduction temperature increases the reduction yield and thus favors the formation of surface-metal particles, thus producing more nanotubes. The obtained carbon nanotubes are mostly single-walled and double-walled with an average diameter close to 2.5 nm. Several formation mechanisms are thought to be active. In particular, it is shown that the second wall can grow inside the first one but that subsequent ones are formed outside. It is also possible that under given experimental conditions, the smallest (<2 nm) catalyst particles preferentially produce double-walled rather than single-walled carbon nanotubes

Opto-mechanical measurement of micro-trap via nonlinear cavity enhanced Raman scattering spectrum

High-gain resonant nonlinear Raman scattering on trapped cold atoms within a high-fineness ring optical cavity is simply explained under a nonlinear opto-mechanical mechanism, and a proposal using it to detect frequency of micro-trap on atom chip is presented. The enhancement of scattering spectrum is due to a coherent Raman conversion between two different cavity modes mediated by collective vibrations of atoms through nonlinear opto-mechanical couplings. The physical conditions of this technique are roughly estimated on Rubidium atoms, and a simple quantum analysis as well as a multi-body semiclassical simulation on this nonlinear Raman process is conducted.Comment: 7 pages, 2 figure

Photoproduction of phi(1020) mesons on the proton at large momentum transfer

The cross section for $\phi$ meson photoproduction on the proton has been measured for the first time up to a four-momentum transfer -t = 4 GeV^2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. At low four-momentum transfer, the differential cross section is well described by Pomeron exchange. At large four-momentum transfer, above -t = 1.8 GeV^2, the data support a model where the Pomeron is resolved into its simplest component, two gluons, which may couple to any quark in the proton and in the $\phi$.Comment: 5 pages; 7 figure

Q^2 Dependence of the S_{11}(1535) Photocoupling and Evidence for a P-wave resonance in eta electroproduction

New cross sections for the reaction $ep \to e'\eta p$ are reported for total center of mass energy $W$=1.5--2.3 GeV and invariant squared momentum transfer $Q^2$=0.13--3.3 GeV$^2$. This large kinematic range allows extraction of new information about response functions, photocouplings, and $\eta N$ coupling strengths of baryon resonances. A sharp structure is seen at $W\sim$ 1.7 GeV. The shape of the differential cross section is indicative of the presence of a $P$-wave resonance that persists to high $Q^2$. Improved values are derived for the photon coupling amplitude for the $S_{11}$(1535) resonance. The new data greatly expands the $Q^2$ range covered and an interpretation of all data with a consistent parameterization is provided.Comment: 31 pages, 9 figure

Adubação verde com leguminosas.

Efeitos da adubação verde nos agroecosistemas; Disponibilidade de nutrientes para as culturas; Cobertura do solo; Organismos edáficos benéficos; Fitopatógenos; Plantas invasoras; Decomposição dos resíduos de adubos verdes; Escolha de leguminosas para uso da adubação verde; Formas de utilização dos adubos verdes.bitstream/item/11957/2/00076310.pdfProjeto Minibibliotecas

The e p -> e' p eta reaction at and above the S11(1535) baryon resonance

New cross sections for the reaction e p -> ep eta are reported for total center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q^2 = 0.25--1.5 GeV^2. This large kinematic range allows extraction of important new information about response functions, photocouplings, and eta N coupling strengths of baryon resonances. Expanded W coverage shows sharp structure at W \~ 1.7 GeV; this is shown to come from interference between S and P waves and can be interpreted in terms of known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance.Comment: 11 pages, RevTeX, 5 figures, submitted to Phys. Rev. Let

Deeply virtual and exclusive electroproduction of omega mesons

The exclusive omega electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q2) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross sections were measured up to large values of the four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the interference terms sigma_TT and sigma_TL to the cross sections, as well as an analysis of the omega spin density matrix, indicate that helicity is not conserved in this process. The t-channel pi0 exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction gamma* p -> omega p, even for Q2 as large as 5 GeV2. Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross sections is nearly Q2-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.Comment: 15 pages,19 figure

Measurement of Inclusive Spin Structure Functions of the Deuteron

We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer ($Q^2$ = 0.27 -- 1.3 (GeV/c)$^2$) and final hadronic state mass in the nucleon resonance region ($W$ = 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target ($^{15}$ND$_3$) and detected the scattered electrons with the CEBAF Large Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal double spin asymmetry $A_{||}$ and the spin structure function $g_1^d$. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function $g_1^d$ and study its approach to both the deep inelastic limit at large $Q^2$ and to the Gerasimov-Drell-Hearn sum rule at the real photon limit ($Q^2 \to 0$). We find that the first moment varies rapidly in the $Q^2$ range of our experiment and crosses zero at $Q^2$ between 0.5 and 0.8 (GeV/c)$^2$, indicating the importance of the $\Delta$ resonance at these momentum transfers.Comment: 13 pages, 8 figures, ReVTeX 4, final version as accepted by Phys. Rev.

Measurement of the Polarized Structure Function σLT′\sigma_{LT^\prime} for p(e⃗,e′π+)np(\vec{e},e'\pi^+)n in the Δ(1232)\Delta(1232) Resonance Region

The polarized longitudinal-transverse structure function $\sigma_{LT^\prime}$ has been measured using the $p(\vec e,e'\pi^+)n$ reaction in the $\Delta(1232)$ resonance region at $Q^2=0.40$ and 0.65 GeV$^2$. No previous $\sigma_{LT^\prime}$ data exist for this reaction channel. The kinematically complete experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. A partial wave analysis of the data shows generally better agreement with recent phenomenological models of pion electroproduction compared to the previously measured $\pi^0 p$ channel. A fit to both $\pi^0 p$ and $\pi^+ n$ channels using a unitary isobar model suggests the unitarized Born terms provide a consistent description of the non-resonant background. The $t$-channel pion pole term is important in the $\pi^0 p$ channel through a rescattering correction, which could be model-dependent.Comment: 6 pages, LaTex, 5 eps figures: Submitted to PRC/Brief Reports v2: Updated referenc