Nonlinear emission in sodium vapour upon pulsed-laser excitation of the 42 P levels

Parametric four-wave mixing, stimulated electronic Raman scattering and amplified spontaneous emission cascades have been studied experimentally by single-photon resonant and near-resonant excitation of the 4² P levels of dense sodium vapour. The dependence of emission intensities on laser detuning and exciting laser power is discussed.     

Far infrared cw raman lasing in NH3

We report evidence that two FIR laser lines generated by cw optical pumping of ¹⁴NH₃ with CO₂ laser lines are due to stimulated Raman emission instead of the usual resonant absorption-emission process.     

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)     

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.     

Single line high efficiency tunable fir generation by resonant four-wave mixing in CH3 pumped by a multiatmosphere tunable CO2 laser

By pumping CH₃F with a high pressure tunable TE-CO₂ laser, the resonant four-wave mixing process (RFWM) generates a very efficient tunable single line FIR emission at the Raman frequency. This result is strictly related to the spectroscopic structure of the CH₃F molecule. By means of this process, a tunable FIR emission on a 0.1 cm^–1 bandwidth 150 kW (8 mJ) single line, is obtained which can be used for many FIR multiphoton applications.     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

Resonant Raman studies of bound excitons in CdS

A new electronic resonant Raman effect in CdS is reported. Resonance enhancement at the I₁ and I₂ bound excitons is observed in differently doped (Cl, J, Li) samples. The energy, intensity dependency and Zeeman splitting suggest an electronic Raman effect associated with excited states of acceptor and donor bound excitons.     

Luminescent properties of Yb-doped monoclinic yttrium polyphosphates

Yb³⁺-doped monoclinic yttrium polyphosphate Y(PO₃)₃ powder compounds were synthesized and were characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy.An attempt to use Yb³⁺ ion as structural probe is carried out to investigate the site occupation. Yb³⁺ emission and fluorescence decay studies were carried out both at low and room temperatures. The interpretation of electronic energy level positions has been done by using the comparison of emission spectra with those of vibronic sideband energy positions from Raman scattering spectroscopy.The spectroscopic results are discussed and correlated with the data of the already known monoclinic structure of Y(PO₃)₃ where four slightly different octahedral sites are available for the trivalent rare earth ion.     

Modified cascade model of resonant Raman scattering: a case study of UV Raman scattering in Zn1−xMnxO thin films

The cascade model of inelastic resonant Raman scattering considers real electronic states in the conduction band (CB) as intermediaries to explain multiple longitudinal optical (LO) Stokes‐shifted lines in the emission spectra. In this study, we report modification in the cascade model under conditions where the scattered photons after multiple transitions have energy lower than the bandgap (E_g) and give rise to higher order n‐LO lines. The higher order n‐LO lines involve electron transition between the trap levels, which are created by impurities or defects in the forbidden energy gap, and are analogous to the real electronic states in CB, depending on the density of defects or impurities in the lattice. The presence of traps in the forbidden gap (1) acts as virtual intermediate states giving rise to higher order n‐LO modes and (2) tends to decrease the radiative recombination probability leading to quenching of the luminescence emission and line width (full‐width at half‐maximum) broadening. Ultraviolet Raman scattering in Mn‐doped ZnO (Zn_1−xMn_xO) thin films were investigated and the experimental observations analyzed in the domain of the modified cascade model. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiphonon resonant Raman scattering in N‐doped ZnO

Multiphonon resonant Raman scattering in N‐doped ZnO films was studied, and an enhancement of the resonant Raman scattering process as well as longitudinal optical (LO) phonon overtones up to the sixth order were observed at room temperature. The resonant Raman scattering intensity of the 1LO phonon in N‐doped ZnO appears three times as strong as that of undoped ZnO, which mainly arises from the defect‐induced Raman scattering caused by N‐doping. The nature of the 1LO phonon at 578 cm⁻¹ is interpreted as a quasimode with mixed A₁ and E₁ symmetry because of the defects formed in the ZnO lattice. In addition, the previously neglected impurity‐induced two‐LO‐phonon scattering process was clearly observed in N‐doped ZnO. Copyright © 2009 John Wiley & Sons, Ltd.     

高速沉积微晶硅薄膜光发射谱的研究

采用PR650光谱光度计对高速沉积微晶硅薄膜的生长过程进行了在线监测研究,并对所对应的材料进行了Raman谱和红外吸收谱(FTIR)的测试.结果表明：能反映材料晶化程度的I_［SiH^*］/I_［Hβ^*］比值在沉积时间为100 s之内有下降的趋势,且反应气体总流量T_fl越小下降趋势越明显,这与拉曼散射光谱对材料的结构测试结果一致;沉积5 min时I 关键词： 高速沉积 微晶硅薄膜 电子温度     

Dispersion of Exciton Polaritons in Terbium Nitrate Hexahydrate

The dispersion relations of exciton polariton waves in terbium nitrate hexahydrate are determined based on the model of the interaction of electromagnetic waves with resonant electronic states of Tb³⁺ ions at the ⁵D₄–⁷F₆ transition. Frequencies of unitary polaritons characterized by refractive indices equal to unity are determined. It is shown that the group velocity of electromagnetic waves in the region of unitary polaritons is lower than the speed of light in vacuum by several orders of magnitude. A sharp increase in the efficiency of photoluminescence and Raman scattering is predicted in the case where the excitation radiation frequency approaches the unitary polaritons frequency.     

A‐band structural dynamics of thioanisole by resonance Raman spectroscopy

The structural dynamics of thioanisole in the S₂(ππ*) electronic state that has large oscillator strength was studied by using the resonance Raman spectroscopy. The vibrational assignments were done for thioanisole on the basis of the FT‐Raman and FT‐IR measurements, the density‐functional theory computations and the normal mode analysis. The A‐ and B‐band resonance Raman spectra were obtained in cyclohexane, methanol and acetonitrile, in which ten modes in A’ irreducible representations were observed. The structural dynamics were obtained according to the resonance Raman intensity pattern. The vibroinc‐coupling between the S₃(πσ*) electronic state that has no oscillator strength and the S₂(ππ*) electronic state were revealed. We discuss the correlation between our present structural dynamics and the previous S₂(ππ*)/S₃(πσ*) conical intersectional dynamics revealed by resonant‐enhanced two‐photon ionization and the photofragment excitation spectroscopic study. Copyright © 2012 John Wiley & Sons, Ltd.     

Observation of resonance electronic and non‐resonance‐enhanced vibrational natural Raman optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low‐lying electronic transition is reported. These new phenomena were measured using the rare‐earth complex Eu(tfc)₃ (+)‐tris[3‐trifluoroacetyl‐D ‐camphorato]europium(III), where electronic resonance occurs between the 532‐nm laser excitation and the ⁷F₁ → ⁵D₁ transition of the Eu³⁺ metal center. Electronic Raman spectra involve the Raman transitions terminating on the low‐lying electronic states of Eu(tfc)₃. The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)₃ to its low‐lying electronic states with significant magnetic‐dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance‐enhanced since the 532‐nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064‐nm laser excitation. Copyright © 2010 John Wiley & Sons, Ltd.     

Infrared laser magnetic resonance detection of SD at 1885·76 cm-1

The visible and near infrared luminescence spectra of MoCl₆ ^3- in Cs₂NaMCl₆ (M=Sc, Y, In) and MoBr₆ ^3- in Cs₂NaYBr₆ have been measured between 15 000 cm^-1 and 3000 cm^-1 at liquid helium temperatures. Comparison with new electronic absorption, infrared and Raman spectra have enabled five luminescence transitions between the states derived from the t _2g ³ configuration to be assigned unambiguously. Each electronic transition shows extensive vibronic structure which can be analysed to yield the vibrational frequencies of the MoX ₆ ^3- ion in each state. The spectra are strongly influenced by resonant interactions between the MoX ₆ ^3- ion and the internal and lattice modes of the host lattices and there is an enormous variation in the intensities of the vibronic origins.     

Electrochemical functionalisation of SWNTs with poly(3,4‐ethylenedioxythiophene) evidenced by anti‐Stokes/Stokes Raman spectroscopy

The capability of anti‐Stokes/Stokes Raman spectroscopy to evaluate chemical interactions at the interface of a conducting polymer/carbon nanotubes is demonstrated. Electrochemical polymerisation of the monomer 3,4‐ethylenedioxythiophene (EDOT) on a Au support covered with a single‐walled carbon nanotube (SWNT) film immersed in a LiClO₄/CH₃CN solution was carried out. At the resonant optical excitation, which occurs when the energy of the exciting light coincides with the energy of an electronic transition, poly(3,4‐ethylenedioxythiophene) (PEDOT) deposited electrochemically as a thin film of nanometric thickness on a rough Au support presents an abnormally intense anti‐Stokes Raman spectrum. The additional increase in Raman intensity in the anti‐Stokes branch observed when PEDOT is deposited on SWNTs is interpreted as resulting from the excitation of plasmons in the metallic nanotubes. A covalent functionalisation of SWNTs with PEDOT both in un‐doped and doped states takes place when the electropolymerisation of EDOT, with stopping at +1.6 V versus Ag/Ag⁺, is performed on a SWNT film deposited on a Au plate. The presence of PEDOT covalently functionalised SWNTs is rationalised by (1) a downshift by a few wavenumbers of the polymer Raman line associated with the symmetric C C stretching mode and (2) an upshift of the radial breathing modes of SWNTs, both variations revealing an interaction between SWNTs and the conjugated polymer. Raman studies performed at different excitation wavelengths indicate that the resonant optical excitation is the key condition to observe the abnormal anti‐Stokes Raman effect. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Quantized infrared-optical triple resonance on a single cold barium ion

A single trapped and cooled Ba⁺ ion is irradiated by resonant visible light (493, 650 nm) alternating with light at 1.76 µm which may excite the ion to its² D _5/2 metastable state. The (absence of) visible resonance scattering probes the excitation, tuning spectra of which show vibrational sidebands that characterize the ion's temperature. Observed values as low as 120 µK, one-eighth the Doppler limit, are ascribed to electronic Raman cooling by the visible light. Tuning spectra of the events of stimulated deexcitation indicate ion heating by the IR interaction. The results demonstrate the feasibility of vibrational spectrometry on a single particle that oscillates in a potential well, forming a quasi-molecule.     

Photoemission study of the modification of the electronic structure of transition-metal overlayers on TiO2 surfaces: I. Fe on TiO2(1 1 0)

The electronic states of the Fe overlayers on TiO₂(1 1 0) surfaces have been investigated using normal-emission and resonant photoelectron spectroscopy with synchrotron radiation. It was found that Fe grows in a Stranski-Krastanov mode. At low coverages, Fe deposition on TiO₂(1 1 0) is supposed to create surface Ti³⁺(3d¹) ions leading to the same in-gap emission as that is produced by surface oxygen vacancies of TiO₂. At high coverages, Fe-induced in-gap emission is evolved into a bulk Fe spectrum. However, at the beginning, a Fermi edge is not observed, indicating that the small Fe clusters of non-metallic nature are formed. A sharp Fermi edge is formed at higher coverages, indicating that the cluster becomes metallic as the size increases.     

Indirect exciton luminescense and Raman scattering in CdI2

Intrinsic luminescence and Raman scattering in 4HCdI₂ have been investigated at 2 K. Weak emission bands observed near the absorption edge are attributed to the phonon-assistes indirect exciton luminescence. Several new Raman lines are observed under resonant excitation in addition to known lines. The symmetry of the phonon modes associated with the indirect transitions as well as with Raman scattering is discussed.