Measurement of the absolute Raman scattering cross section of the 1584‐cm−1 band of benzenethiol and the surface‐enhanced Raman scattering cross section enhancement factor for femtosecond laser‐nanostructured substrates

The absolute Raman scattering cross section (σ_RS) for the 1584‐cm⁻¹ band of benzenethiol at 897 nm (1.383 eV) has been measured to be 8.9 ± 1.8 × 10⁻³⁰ cm² using a 785‐nm pump laser. A temperature‐controlled, small‐cavity blackbody source was used to calibrate the signal output of the Raman spectrometer. We also measured the absolute surface‐enhanced Raman scattering cross section (σ_SERS) of benzenethiol adsorbed onto a silver‐coated, femtosecond laser‐nanostructured substrate. Using the measured values of 8.9 ± 1.8 × 10⁻³⁰ and 6.6 ± 1.3 × 10⁻²⁴ cm² for σ_RS and σ_SERS respectively, we calculate an average cross‐section enhancement factor (EF) of 0.8 ± 0.3 × 10⁶. Copyright © 2009 John Wiley & Sons, Ltd.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

Spontaneous Raman scattering in atomic thallium vapor

Using a cw argon-ion laser, we have measured the spontaneous Raman scattering cross section, σ_R, and linewidth in atomic thallium vapor. For 4880-Å excitation, σ_R = 1.6 × 10^?27 cm². We observe no pressure broadening of the Raman line at vapor pressures to 100 torr.     

Raman scattering cross section and density measurements of UF6

We have applied laser Raman scattering to the measurement of the density of UF₆ vapor. A linear relation between scattering intensity and density is shown. We have also measured the absolute Raman scattering cross section of the 665 cm^?1 line of UF₆ by the substitution technique and obtained a value of 1.02±0.09×10^?29 cm²/sterad at 488 nm. Measurements of the line position and the depolarization ratio of this line are also reported.     

Chemical aerosol detection and identification using Raman scattering

Early warning of the presence of chemical agent aerosols is an important component in the defense against such agents. A Raman spectrometer has been constructed for the purpose of detecting and identifying chemical aerosols. We report the detection and identification of a low‐concentration chemical aerosol in atmospheric air using 532‐nm continuous wave laser Raman scattering. We have demonstrated the Raman scattering detection and identification of an aerosol of isovanillin of mass concentration of 1.8 ng/cm³ with a signal‐to‐noise ratio of about 19 in 30 s for the 1116‐cm⁻¹ mode with a Raman cross section of 3.3 × 10⁻²⁸ cm² using 8‐W double‐pass laser power. Copyright © 2014 John Wiley & Sons, Ltd.     

Micro‐Raman depth profiling of silicon amorphization induced by high‐energy ion channeling implantation

In this work, we study the silicon amorphization dependence on the crystal depth induced by 6‐MeV Al²⁺ ions implanted in the <110> and randomly oriented silicon crystal channels, which was not directly experimentally accessible in the previous similar high‐energy ion–crystal implantation cases. Accordingly, the micro‐Raman spectroscopy scanning measurements along the crystal transversal cross section of the ion implanted region were performed. The ion fluence was 10¹⁷ particles/cm². The scanning steps were 0.2 and 0.3 µm, for the channeling and random ion implantations, respectively. The obtained results are compared with the corresponding Rutherford backscattering spectra of 1.2‐MeV protons in the random and channeling orientations measured during the channeling implantation. Additionally, scanning electron microscope picture was taken on the transversal cross section of the implanted region in the channeling implantation case. We show here that the obtained silicon amorphization maxima are in excellent agreement with the corresponding estimated maxima of the aluminum concentration in silicon. This clearly indicates that the used specific micro‐Raman spectroscopy scanning technique can be successfully applied for the depth profiling of the crystal amorphization induced by high‐energy ion implantation. Copyright © 2013 John Wiley & Sons, Ltd.     

Exploring the possible interlinked structures in single‐wall carbon nanotubes under pressure by Raman spectroscopy

High‐pressure Raman measurements on single‐wall carbon nanotubes (SWNTs) have been carried out in a diamond anvil cell by using two wavelength lasers: 830 and 514.5 nm. Irrespective of using a pressure transmitting medium (PTM) or not, we found that nanotubes undergo similar transformations under pressure. The pressure‐induced changes in Raman signals at around 2 and 5 GPa are attributed to the nanotube cross‐section transitions from circle to ellipse and then to a flattened shape, respectively. Especially with pressure increasing up to 15–17 GPa, we observed that the third transition takes place in both the Raman wavenumber and the linewidth of G‐band. We propose explanations that the interlinked configuration with sp³ bonds forms in the bundles of SWNTs under pressure, which was the cause for the occurrence of those Raman anomalies, similar to the structural‐phase transition of graphite above 14 GPa. Our TEM observations and Raman measurements on the decompressed samples support this transition picture. Copyright © 2012 John Wiley & Sons, Ltd.     

Temperature dependence of the Raman cross section and light absorption in cubic BaTiO3

The temperature dependence of the Raman spectrum in the cubic phase of BaTiO₃ is described. The cross section decreases when the temperature increases, which is contrary to a normal second order effect behaviour. The associated measurements of the optical absorption definitely prove that this variation is intrinsic. The anomalous Raman spectrum is related to the existence in the crystal of anisotropic fluctuation domains.     

Experimental study of the enhanced Raman scattering in the Sarid-type 4-layered attenuated total reflection configurations

We experimentally explored the enhanced Raman scattering in pyridine (C₅H₅N) due to the excitation of long range surface plasmons (LRSP's) guided by a symmetrically bounded silver slab in the Sarid-type ATR (attenuated total reflection) configuration. We have observed that, with decreasing the metallic thickness, the absolute enhancement of the Raman cross section increases while the width of the polar angular distribution of the signal decreases. This observed dependence of the enhanced Raman intensity on the thickness of the thin Ag slab and the collecting solid angle is well explained by assuming that the Raman scattering is mediated by LRSP's. The observed maximum enhancement factor is 4 × 10⁶ for the 140 Å silver slab which agrees well with the theoretically predicted value of 6 × 10⁶.     

The rovibrational Raman spectrum of water vapour v 1 and v 3

The OH stretching region in the Raman spectrum of water vapour has been observed and reproduced by computer simulation using rovibrational wave functions derived from the analysis of high-resolution absorption spectra. Relative intensity measurements allow the determination of the depolarization ratio and the ratio of the two non-vanishing second-order irreducible tensor components for v ₁. These quantities have been combined with the literature value for the cross section of this band to calculate the principal cartesian components of the v ₁ derived polarizability tensor. The cross section for the v ₃ vibration was also determined, and these results are considered in terms of the bond polarizability theory.     

Raman scattering cross section and density measurements of UF6

We have applied laser Raman scattering to the measurement of the density of UF₆ vapor. A linear relation between scattering intensity and density is shown. We have also measured the absolute Raman scattering cross section of the 665 cm⁻¹ line of UF₆ by the substitution technique and obtained a value of 1.02±0.09×10⁻²⁹ cm²/sterad at 488 nm. Measurements of the line position and the depolarization ratio of this line are also reported. Work supported by the U. S. Energy Research and Development Administration.     

Raman susceptibility measurements and stimulated Raman effect in KDP

The propagation constant of the stimulated Raman process and Raman susceptibility measurements in KDP are reported. The stimulated Raman scattering due to 915 cm^-1 and 93 cm^-1 vibration in KDP has been experimentally observed.     

Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6‐mm‐thick sulfur specimen at 1500 m

The absolute Raman scattering cross sections (σ_RS) for the 471, 217, and 153 cm⁻¹ modes of sulfur were measured as 6.0 ± 1.2 × 10⁻²⁷, 7.7 ± 1.6 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁶ cm² at 815, 799, and 794 nm, respectively, using a 785‐nm pump laser. The corresponding values of σ_RS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10⁻²⁷, 1.2 ± 0.24 × 10⁻²⁷, and 1.2 ± 0.24 × 10⁻²⁷ cm² using a 1064‐nm laser. A temperature‐controlled, small‐cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6‐mm‐thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4‐W, CW, 785‐nm pump laser. Copyright © 2010 John Wiley & Sons, Ltd.     

分子间费米共振增强二元溶液体系的受激拉曼散射研究

研究了液芯光纤内不同体积比的甲苯和间二甲苯二元混合溶液的受激拉曼散射.实验结果表明:在不同的体积比之下二元溶液的环呼吸振动模式1002 cm^-1,甲基的CH伸缩振动模式2920 cm^-1 以及芳香环CH对称伸缩振动模式3058 cm^-1的拉曼带同时产生受激拉曼辐射,并且2920 cm^-1 和 3058 cm^-1 拉曼带的一阶受激拉曼散射阈值要低于1002 cm^-1拉曼带的二阶 关键词： 分子间费米共振 二元溶液 受激拉曼散射 拉曼散射截面     

Antiresonance of Raman Scattering in CdSxSe1-x Mixed Crystals

Abstract

Resonant enhancement of the Raman scattering cross section in II - IV semiconductors has recently received much attention both theoretically and experimentally. All existing theories anticipate a monotonic increase in the scattering intensities when the scattering radiation energy approaches the direct-energy gap. Contrary to them in an early Raman study of CdS¹ a cancellation of scattering efficiencies for the two TO modes prior to the onset of the resonance was pointed out. In a latter work on pure CdS Damen et al.² found even a more pronounced “antiresonance” behavior of the nonpolar E₂ phonon at 41 cm^?1. Thus, this striking feature seems to be rather common for the Raman active modes in CdS for which no electrooptic contribution to the scattering amplitude exists. The experimental data were qualitatively explained by assuming a destructive addition between nonresonant and the weaker resonant terms in LoudoN′s expression for the first-order Raman tensor³. Consequently the cancellation energy difference /E_G - hw_L/ depends on the ratio of the resonant term to the nonresonant terms.     

Resonant Raman scattering of CdCr2Se4

The scattering cross section of the Raman-active phonons at 156 cm^?1 (Eg) and 169 cm^?1 (F2g) in the ferromagnetic semiconductor CdCr₂Se₄ (T_c=130 K) has been measured as a function of incident photon energy between 1.55 and 2.81 eV, both in the ferromagnetic and paramagnetic phases. The resonance curve peaks sharply near 2 eV and shows a broadening for temperatures below the Curie point. The relative line intensities change significantly with photon energy. The results show that the concept of spin-dependent Raman scattering in the ferromagnetic spinels has to be revised in terms of exchange-splitting-induced resonant Raman scattering.     

Differential Raman cross section of dimethyl sulfide

Biogenic sulfur compounds such as dimethyl sulfide (DMS) are important contributors to the global carbon cycle. The differential Raman cross section of DMS relative to the nitrogen fundamental, σ_DMS, has been measured at several excitation wavelengths in order to assess the applicability of Raman spectroscopy for the direct quantitative measurement of this compound. At 488 nm, σ_DMS for the ν₆ carbon–sulfur stretching mode was found to be 4.9 ± 1.6, while for the ν₂ carbon–hydrogen stretching mode it was 2.8 ± 0.9. Using, KrF laser excitation, values for σ_DMS could be measured simultaneously at two excitation wavelengths, 248.32 and 248.69 nm. The average values of σ_DMS for 248‐nm excitation based on measurements at these two excitation wavelengths were 3.5 ± 1.4 for the carbon–sulfur stretching mode and 4.6 ± 0.6 for the carbon–hydrogen stretching mode. The results indicate that no significant resonance enhancement of σ_DMS for either mode occurs, although they show some slight enhancement of the cross section for the ν₂ band (C H stretching mode). It was concluded that the measured values of σ_DMS are high enough to allow the quantitative detection of DMS at the millimolar level. Copyright © 2010 John Wiley & Sons, Ltd.     

Picosecond stimulated Raman scattering in crystals

The comparative values of the peak and integral cross sections of spontaneous Raman scattering and the optical dephasing time of molecular vibrations were determined for several oxide crystals by spontaneous Raman spectroscopy. The spectral, time, and energy parameters of stimulated Raman scattering (SRS) were measured for ten crystals using picosecond YLF: Nd laser pumping with a radiation wavelength of 1047 nm. An analysis of the experimental dependence of the threshold energy of pumping SRS on the integral and peak cross sections of spontaneous Raman scattering showed that the SRS gain increment explicitly depended on the integral cross section and was independent of the peak cross section of spontaneous Raman scattering as the ratio between the pumping pulse width (11 ps) and the time of optical dephasing of molecular vibrations changed from 0.42 to 9.3. The gain coefficients of steady-state stimulated Raman scattering under threshold stimulated Raman scattering conditions were determined for all the crystals studied on the basis of the measured threshold SRS pumping energies, the duration and width of the spectrum of pulses, the nonlinear interaction length, the intensity of pumping, and the theoretical dependences that relate the steady-state and transient SRS gain increments. The steady-state SRS gain coefficients obtained in this work fitted well a linear dependence on the peak cross sections of spontaneous Raman scattering, which substantiated the correctness of our analysis and measurements.     

Raman scattering in the spin glass system EuxSr1-xS due to spin correlation effects

Raman measurements in all magnetic phases of Eu_xSr_1-xS show a new type of q ≠ 0 magnetic scattering at low temperatures. The intensity is quantitatively described using a modified Ornstein-Zernike ansatz for the spin correlation function in the scattering cross section. Systematic variations of spin correlations as function of composition and temperature in high magnetic fields allow a consistent interpretation of the Raman data in correspondence with the magnetic phase diagram.     

Origin of the Raman mode at 379 cm−1 observed in ZnO thin films grown on sapphire

In this work, we present a detailed Raman scattering study to clarify the origin of the mode at 379 cm⁻¹ which is observed in Raman spectra of the ZnO films grown on c‐sapphire substrates and generally attributed to the A₁‐transverse optical (A₁‐TO) mode of ZnO. The studied ZnO films were deposited by metal‐organic chemical vapor deposition on c‐sapphire and (0001) ZnO substrates. In the z(−,−)z̄ backscattering configuration, the A₁‐TO mode is forbidden, while the 379 cm⁻¹ peak is still observed in the as‐deposited film grown on sapphire substrate. However, this mode is not observed in Raman spectra of the as deposited film grown on ZnO substrate. We suggest that the peak at 379 cm⁻¹ is the E_1g mode of the sapphire substrate which is allowed in z(−,−)z̄ backscattering configuration. The effects of annealing, the substrate and the collection cross‐section on Raman active modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.