不同波长激光激发下C6H12受激拉曼散射模式竞争

发现不同波长激光激发下C₆H₁₂的受激拉曼散射模式竞争现象. 在不同波长的激光激发下，不同拉曼模式的Stokes光占优势. 短波长(404，532nm)激光激发时小频移模式ω₁(802cm^-1)为弱增益模式，大频移模式ω₂(2852—3038cm^-1)为强增益模， 主要产生ω₂模式的Stokes光. 长波长(80 关键词： 模式竞争 6H₁₂')" href="#">C₆H₁₂ 受激拉曼散射     

Magneto-Raman scattering inp-type indium antimonide

We report for the first time stimulated magneto-Raman scattering inp-type InSb. Two different Raman scattering processes were observed. The first one has a Raman shift of about 2cm⁻¹/kG and is observed at magnetic fields up to 30kG. The other one is observable only at high magnetic fields above 30kG and shows Raman shifts between 1.2cm⁻¹ and 3.0cm⁻¹ with a tuning rate of about 0.2cm⁻¹/kG. The first process can be interpreted either as spin-flip Raman scattering by photo-excited electrons in the conduction band or as Raman scattering by holes in the valence band involving transitions from heavy to light hole states. The other Raman shift observed seems to occur on account of transitions between the heavy hole ladders.     

Variation in the fluorescent background in Raman spectra of distilled water purified by different methods

The contribution of impurity fluorescence was determined in the water Raman spectra excited by the second harmonic (λ = 532 nm) of a pulsed Nd:YAG laser. Water samples prepared by different techniques (tap water (undistilled), distilled water, Milli-Q water, water for injections, and water subjected to cavitation treatment) were investigated. The Raman (bands at ν ₂ ∼ 1550 cm⁻¹ and ν ₃ ∼ 3400 cm⁻¹) and fluorescence (Stokes shift 2500 cm⁻¹) signals were separated spectrally and according to the differences in the emission kinetics. It was established that all investigated samples, including distilled and specially purified water for injections, exhibit afterglow. The highest sensitivity to the presence of impurities was revealed near ∼ 2500 cm⁻¹. The least contribution to the fluorescence signal was found in the water for injections.     

Photoluminescence and multiphonon resonant Raman scattering in Ni-and Co-doped Zn1−x MnxTe crystals

Low-temperature photoluminescence, exciton reflection, and multiphonon resonant Raman scattering spectra of Ni-and Co-doped Zn_1−x Mn_xTe crystals were investigated. Intense emission occurs in a broad spectral region (1100–17 000 cm⁻¹) in the crystals containing Ni atoms. It is caused by intracenter transitions involving Mn²⁺ ions and transitions between the conduction band and a level of the doubly charged acceptor. The features of the exciton photoluminescence and multiphonon resonant Raman scattering involving longitudinal-optical (LO) phonons at various temperatures are investigated. The insignificant efficiency of the localization of excitons on potential fluctuations in the Zn_1−x Mn_xTe:Co crystals is established. A temperature-induced increase in the intensity of the 5LO multiphonon resonant Raman scattering line due to the approach of the conditions for resonance between this line and the ground exciton state is observed in these crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 616–621 (April 1998)     

Continuous wave stimulated Raman scattering of benzene by fluorescence enhancement in hollow fused silica fiber

We present continuous wave stimulated Raman scattering (SRS) of benzene (C₆H₆) influenced by the fluorescent dye m‐cresol purple in a hollow fused silica fiber (HFSF). Because of the transmission loss of the HFSF filled with C₆H₆, the SRS occurs when the Stokes gain equals the transmission loss, with the loss taken at the Stokes wavelength. The 992 cm⁻¹ stimulated Stokes line has been obtained at the pump wavelength 658 nm, which cannot be obtained at 532 nm because the Stokes wavelength (562 nm) does not locate in the transmission loss. Also, the pump power is 35 mW with m‐cresol purple which is much lower than 800 mW without the dye. The profile of the 992 cm⁻¹ stimulated Stokes is changed, and the weak shoulders of the profile are amplified by fluorescence. These results are expected to be of relevance in applications on the tunable Raman laser at new wavelengths. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of sub-band gap photon illumination on the properties of GaN layers grown on Si(111) by MBE

Nanostructured GaN layers are fabricated by laser-induced etching processes based on heterostructure of n-type GaN/AlN/Si grown on n-type Si(111) substrate. The effect of varying laser power density on the morphology of GaN nanostructure layer is observed. The formation of pores over the structure varies in size and shape. The etched samples exhibit dramatic increase in photoluminescence intensity compared to the as-grown samples. The Raman spectra also display strong band at 522 cm⁻¹ for the Si(111) substrate and a small band at 301 cm⁻¹ because of the acoustic phonons of Si. Two Raman active optical phonons are assigned h-GaN at 139 and 568 cm⁻¹ due to E2 (low) and E2 (high), respectively. Surface morphology and structural properties of nanostructures are characterized using scanning electron microscopy and X-ray diffraction. Photoluminance measurement is also taken at room temperature by using He–Cd laser (λ = 325 nm). Raman scattering is investigated using Ar⁺ Laser (λ = 514 nm).     

Enhanced stimulated Raman scattering by intermolecular Fermi resonance

We demonstrate the stimulated Raman scattering (SRS) of a binary solution of toluene and m-xylene at different volume concentrations in liquid-core optical fiber (LCOF). The results show that SRS of three vibration modes of 1002 cm⁻¹,2920 cm⁻¹ and 3058 cm⁻¹ bands are simultaneously generated at some volume concentrations. The 2920 cm⁻¹ band and the 3058 cm⁻¹ band are generated at one time, the SRS thresholds of the first-order Stokes of the 2920 cm⁻¹ and 3058 cm⁻¹ bands are lower compared with the second-order Stokes threshold of the 1002 cm⁻¹ band and the main peak of the 2920 cm⁻¹ and 3058 cm⁻¹ bands changes from the 2920 cm⁻¹ band to the 3058 cm⁻¹ band as the volume concentrations are changed. We assume that these phenomena are attributed to the intermolecular Fermi resonance. Raman scattering cross section (RSCS) theory is used to explain this assumption.     

Rapid and sensitive trace gas detection with continuous wave Optical Parametric Oscillator-based Wavelength Modulation Spectroscopy

A fiber-amplified Distributed Bragg Reflector diode laser is used to pump a continuous wave, singly resonant Optical Parametric Oscillator (OPO). The output radiation covers the 3–4 μm with ability of rapid (100 THz/s) and broad mode-hop-free tuning (5 cm⁻¹). Wavelength Modulation Spectroscopy is combined with the OPO to take optimal advantage of the spectral scan speed. The sensitivity of the system was determined as 0.8 ppbv (parts-per-billion by volume) for ethane (C₂H₆) for the absorption peak at 2996.9 cm⁻¹ recorded in 1.3 seconds, corresponding to a noise equivalent absorption sensitivity (NEAS) of 1.2×10⁻⁹ cm⁻¹/Hz^1/2. A comparison between results using the 1^st, 2^nd and 4^th harmonic derivative signal from wavelength modulation was performed. The broad continuous tunability was demonstrated by covering 35 cm⁻¹ while recording absorption features of ethane, methane and water.     

Raman scattering of light and IR absorption in carbon nanotubes

Raman light scattering and IR absorption spectra of samples containing multilayer carbon nanotubes in different stages of purification by the selective oxidation technique have been investigated. It was found that the Raman spectra of carbon nanotubes exhibit softening of the mode at 1582 cm⁻¹ corresponding to E _2g vibrations of graphite hexagons and a line at 120 cm⁻¹ due to the radial vibrations of nanotubes. In IR absorption spectra measured in the region of 0.07–0.3 eV, several sets of lines with a spacing of 15 meV (120 cm⁻¹) between lines of each group have been detected. We suggest that each group corresponds to electron transitions generating electron-hole pairs in semiconducting nanotubes and contains a phononless 00-line and its phonon replicas with spacing between them equal to the “breathing” mode energy of 120 cm⁻¹. Measurements of electric conductivity at a frequency of 9300 MHz indicate that, in addition to semiconducting nanotubes, the samples contain nanotubes with properties of a highly disordered semimetal. Zh. éksp. Teor. Fiz. 113, 1883–1891 (May 1998)     

Polarized Raman spectroscopy study of NiSi film grown on Si(001) substrate

We report on the growth of NiSi film on Si(001) substrate with an orientation of NiSi[200]//Si[001]. Polarized Raman spectroscopy was used to assign the symmetry of the NiSi Raman peaks. Raman peaks at 213 cm⁻¹, 295 cm⁻¹, and 367 cm⁻¹ are assigned to be A _g symmetry and peaks at 196 cm⁻¹, and 254 cm⁻¹ are B _3g symmetry.     

Raman spectra of various polymorphs of isotactic polypropylene

The Raman spectra of the α, γ, and smectic modifications of isotactic polypropylene (PP) are studied. The most significant spectral differences are observed in the frequency range around 2960 cm⁻¹ for the spectral doublet assigned to the asymmetric stretching vibrations of the CH₃ groups and in the frequency range around 800 cm⁻¹, which is used for analysis of the phase composition of isotactic PP. It is demonstrated that the peak positions and relative intensities of the doublet assigned to the asymmetric stretching vibrations of the CH₃ groups can be used to identify the polymorph modifications of isotactic PP.     

A comparative performance evaluation of micro-Raman spectrograph using holographic notch filter and dielectric filter

An indigenously designed and developed micro-Raman spectrograph, consisting of a diode-pumped solid-state green laser for the excitation of Raman scattering, a Raman imaging microscope, CCD as a detector and a notch filter, has been extensively studied to evaluate its performance. A dielectric edge filter (having 27 alternate layers of SiO₂ and TiO₂) and a holographic notch filter (Oriel make) have been used to block the Rayleigh scattered light from the sample to the entrance slit of the spectrograph. Holographic notch filter is found to be able to record the Raman shifts below 700 cm⁻¹ conveniently whereas dielectric edge filter (27 layers) has enabled the spectrograph to record the Raman spectra very efficiently after a wave-number shift of 700 cm⁻¹. It has also been observed that the instrument using the edge filter provides a peculiar spectrum consisting of three spectral lines having Raman shifts as 569, 1328 and 1393 cm⁻¹ in the Raman spectrum of a weakly scattering sample with large reflectivity. Similarly, a spectrum consisting of multiple lines has been observed when the instrument is being operated using a holographic notch filter. These spectral lines are not observed in the case of liquid samples such as benzene, carbon tetrachloride, ethanol, diethyl ether etc. The origin of these peculiar spectral lines has been briefly discussed in the paper. Additionally, a major motivation for this work is to utilize the results for the selection of an appropriate filter depending on the type of the sample, i.e. weakly scattered and highly reflecting sample or highly scattered and low reflecting sample.     

A new optical method for measuring the electron-phonon interaction parameter λ〈Ω2〉 using the spectral dependence of the relaxation rate

The spectral dependence of the electron-phonon relaxation rate γ_e−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γ_e−ph(ℏω) near the Fermi level E _F , using the parametrization γ_e−ph(ℏω)∝λ〈Ω²〉 (ℏω−E _F )² makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω²〉. The parameter λ〈Ω²〉 for YBa₂Cu₃O_7−δ is analyzed using this method. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999)     

Four-wave mixing spectroscopy of aqueous suspensions of single-wall carbon nanotubes in the ranges of 0.1–10 and 100–250 cm<Superscript>−1</Superscript>

Distinctive optical properties of single-wall carbon nanotubes (SWNT) are highly sensitive to variations in the environment. Here, we have studied SWNT in aqueous suspensions at a low (less than 0.1 μg ml⁻¹) concentration by four-wave mixing (FWM) spectroscopy in the spectral bands of 0.1 to 10 cm⁻¹ (≈300 GHz) and 100 to 250 cm⁻¹ (3 to 7.5 THz). We directly investigated the hydration layers around SWNT. A comparison of the FWM spectra of an SWNT aqueous suspension and Milli-Q water shows a considerable increase in the intensity of low-frequency Raman modes, which are attributed to the rotational transitions of H₂O₂ and H₂O molecules. We explain the observed phenomenon by the hydrogen peroxide production and formation of a low-density depletion layer at the water-nanotube interface. We have observed several SWNT radial breathing modes ω _RBM =118.5, 164.7, and 233.5 cm⁻¹ in an SWNT aqueous suspension and estimated the corresponding SWNT diameters as ≈2.0, 1.5, and 1 nm.     

Effect of pressure on Raman spectra of SnS2 single crystals

The 2H polytype of a SnS₂ layered crystal has been studied using Raman spectroscopy at pressures of up to 5 GPa in a diamond anvil cell. The Raman frequency of the intralayer mode increases linearly with increasing pressure at baric coefficients of 5.2 cm⁻¹/GPa for P<3 GPa and 3.4 cm⁻¹/GPa for P>3 GPa. This change in the baric coefficient for Raman scattering and the available data on X-ray measurements of the compressibility of 2H-SnS₂up to 10 GPa suggest that the crystal structure undergoes a transformation at about 3 GPa.     

Narrowing of the vibrational spectrum under compression of liquid carbon dioxide

The broadening and shift of the Q bands of the 1388/1285-cm⁻¹ Fermi doublet of carbon dioxide have been measured by means of the spectroscopy of coherent anti-Stokes Raman scattering in a wide density range realized at compression in dense gaseous and liquid states. The spectrum of the low-frequency Q band exhibits an essential narrowing upon the compression of the liquid in the density range of 320–400 amagat from a maximum width of about 2.2 cm⁻¹ to about 1.7 cm⁻¹ determined by elastic dephasing. The observed dependence is connected with the progressive narrowing of the spectral contribution attributed to the collapsed rotational structure.     

Non-steady-state photo-EMF in nanostructured GaN and polypyrrole within porous matrices

We report an experimental investigation of the non-steady-state photoelectromotive force in nanostructured GaN within porous glass and polypyrrole within chrysotile asbestos. The samples are illuminated by an oscillating interference pattern created by two coherent light beams and the alternating current is detected as a response of the material. Dependences of the signal amplitude versus temporal and spatial frequencies, light intensity, and temperature are studied for two wavelengths λ=442 and 532 nm. The conductivity of the GaN composite is measured: σ=(1.1–1.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=442 nm, I ₀=0.045–0.19 W/cm², T=293 K) and σ=(3.5–4.6)×10⁻¹⁰ Ω⁻¹ cm⁻¹ (λ=532 nm, I ₀=2.3 W/cm², T=249–388 K). The diffusion length of photocarriers in polypyrrole nanowires is also estimated: L _D=0.18 μm.     

Breit–Wigner Approximation and the Distribution¶of Resonances

For operators with a discrete spectrum, {λ _j ²}, the counting function of λ _j 's, N (λ), trivially satisfies N ( λ+δ ) −N ( λ−δ ) =∑ _j δ_{λ j} ((λ−δ,λ+δ]). In scattering situations the natural analogue of the discrete spectrum is given by resonances, λ _j ∈ℂ₊, and of N (λ), by the scattering phase, s(λ). The relation between the two is now non-trivial and we prove that

Kilohertz high power extracavity KGW yellow raman lasers based on pulse LD side-pumped ceramic Nd: YAG

We report an efficient operation of a kilohertz nanosecond extracavity KGd(WO₄)₂ (KGW) crystal Raman yellow laser, which is pumped by a 532 nm lasers based on pulse laser diode (LD) side-pumped ceramic Nd: YAG, BBO electro-optical Q-switched and LBO crystal extracavity frequency doubling. With the 5 W, 10 ns and 1 kHz output power pumped at 532 nm, we obtained 2.58 W, 7.4 ns, 1 kHz second Stokes Raman laser output at 579.54 nm for 768 cm⁻¹ Raman shift of KGW crystal, corresponding to a conversion efficiency of 51.4%. By changing the KGW crystal orientation, we further obtained 3.18 W, 7.8 ns, 1 kHz Raman pulses at 588.33 nm for 901 cm⁻¹ Raman shift, corresponding to a conversion efficiency of 63.3%. The beam quality factors M² of 579.54 and 588.33 nm were (M _x−579.54² = 5.829, M _y−579.54² = 6.336) and (M _x−588.33² = 6.405, M _y−588.33² = 6.895), respectively.     

Metallic/semiconducting ratio of carbon nanotubes in a bundle prepared using CVD technique

We present an investigation of the nature of single-walled carbon nanotubes (SWCNTs) in a bundle by resonant Raman spectroscopy. The calculation has been done for the three peak positions in radial breathing mode (RBM) spectra obtained by using a laser excitation wavelength (γ) of 633 nm from He-Ne laser on SWNT bundle sample prepared by chemical vapor deposition (CVD) technique using iron catalyst at 800°C. The detailed analysis in the present study is focused on peak positions 162 cm⁻¹, 186 cm⁻¹, and 216 cm⁻¹. The firs step of the analysis is to construct a list of possible (n, m) pairs from the diameters calculated from the RBM peak positions. The parameters of SWNTs studied gives in-depth understanding of many symmetry, resonance and characteristic properties of SWNT bundles. Our results indicate that the contribution of metallic SWNTs in the bundle is small at RBM peak positions 162 cm⁻¹, 186 cm⁻¹ and in agreement with pervious results at peak position 216 cm⁻¹.