拉曼散射在共振及近共振时的条件：广义短时间近似

研究了频率失谐时共振拉曼散射的动力学过程．当入射光子能量远离共振吸收能量时,时域内的失相使散射过程变快．这使得频率失谐如同照相机的快门功能,具有规律的散射持续时间,为普通的稳态测量提供了控制散射时间的有效工具．基于这个理论对两个多模式模型系统以及反式-1,3,5-己三烯和鸟嘌呤-胞嘧啶Watson-Crick碱基对分子的共振拉曼光谱进行了研究．除了这些特殊的物理效应,快散射机制可以简化光谱,同时使散射理论得到简化．当入射光子频率在共振区域时,拉曼光谱中会出现较强的多倍频成分;当入射光子频率与第一共振吸收频率之间的失谐量为振动能量时,在快散射过程中,这些多倍频成分逐渐消失．因此,利用入射光子与共振频域的失谐可以明显地简化拉曼光谱,从复杂光谱中去除多倍频和软模的影响,并且可以避免共振态的解离和荧光衰减引起的干扰．     

Two-magnon Raman scattering in a spin density wave antiferromagnet

We present the results for a model calculation of resonant two-magnon Raman scattering in a spin density wave (SDW) antiferromagnet. The resonant enhancement of the two-magnon intensity is obtained from a microscopic analysis of the photon-magnon coupling vertex. By combining magnon-magnon interactions with ‘triple resonance’ phenomena in the vertex function the resulting intensity line shape is found to closely resemble the measured two-magnon Raman signal in antiferromagnetic cuprates. Both, resonant and non-resonant Raman scattering are discussed for the SDW antiferromagnet and a comparison is made to the conventional Loudon-Fleury theory of two-magnon light scattering.     

Excitation profiles of resonant coherent Raman scattering by impurity molecules

The amplitudes and the excitation profiles of coherent resonant Raman scattering (coherent anti‐Stokes and Stokes Raman scattering (CARS and CSRS)) by impurity centers in crystals and/or molecules in solutions are studied, taking into account the coherence of the excited mode and the inhomogeneity of the environment. The CARS and CSRS excitation profiles can directly be related to one‐photon absorption when using the transform theory known from spontaneous resonant Raman scattering. The enlargement of the amplitude of the active mode reveals itself in an enhancement of the vibrational overtones. At large amplitudes, a splitting in the profiles caused by the contribution of two turning points of a strong coherent vibration is observed. The inhomogeneous broadening is different in the excitation profiles of CARS and CSRS. The overlapping contributions to spectrally narrow and broad transitions lead to Fano peculiarities. The effects are illustrated by model calculations. Copyright © 2011 John Wiley & Sons, Ltd.     

Green's function approach in the theory of interaction of exciton-polaritons in semiconductors with direct band gaps

The renormalization procedure of perturbation theory is applied to study polariton effects in the optical processes involving photons with energies near that of an exciton: resonant Raman scattering, resonant electronic Raman scattering, and resonant high — order optical harmonic generation. To demonstrate the general method and the computation technique we consider in this work a simple model with the following properties: (a) The semiconductor has a direct band gap with allowed electrical dipole transition and with nondegenerate valence and conduction bands. (b) We consider only the photons in a definite polarization state; they are in resonance with one bound state of an electron-hole pair, and we take into account only the transition between this exciton state and the photon in the given polarization state. We work in the framework of the Green's function approach and we shall see that this approach provides for the inclusion of damping effects in a relatively rigorous manner.     

Pump polarization effect in a superradiant NH3 and CH3F FIR Raman laser

The pump polarization has an evident effect on a superradiant FIR Raman laser both in NH₃ and CH₃F gases when the pump detuning from the resonant line is larger than the Raby frequency. In particular for R resonant lines the circular polarization shows a spontaneous gain about 1.5 times greater than the linear polarization as expected from the theory.     

Light scattering as a form of modulation spectroscopy

In the conventional modulation spectroscopy the optical constants of a solid are modulated by means of an external parameter (stress, electric field, etc). As a result of the presence of elemental excitations in the solid (usually phonons) a spontaneous modulation of the optical constants takes place at the frequency of the excitations. This modulation can be observed in light scattering experiments (Raman and Brillouin). Such measurements yield information about the frequency and density of states of the excitations (conventional Raman and Brillouin measurements), about their interaction with electronic states, and about the electronic transitions themselves (resonant scattering experiments). The theory of resonant Raman and Brillouin scattering in semiconductors will be discussed in connection with that of other modulation experiments (piezoreflectance, stress induced birefringence). Another closely related phenomenon, that of spatial-dispersion-induced birefringence will also be presented.     

Multiphonon resonant Raman scattering in GaSe

Multiphonon resonant Raman scattering up to 4 phonons in GaSe has been measured. The results are interpreted by a simple cascade theory. It is shown that the dispersion of RRS here is dominated by resonances with the exciton states.     

Dynamics of F2 centers in LiF: One phonon sideband and Raman scattering

The vibrational structure of the F₂⁺ emission in LiF was investigated, together with the resonant Raman scattering from the first excited electronic state. The one phonon sideband of the emission and the resonant Raman spectrum were found to be very similar, as expected for transitions involving non degenerate electronic states.     

Power resonances in a Raman gas laser

The observation of a new type of resonance due to double-quantum transitions in the standing-wave field of a Raman gas laser is reported. A resonance dip with a width equal to that of the optically forbidden transition was experimentally detected in the output-vs-timing curve of a Raman Ne laser (λ=1.15 m) upon pumping by radiation of a He−Ne laser at 1.52 m. The theory presented shows that the resonance arises in the third order of perturbation theory when in resonant SRS the line is inhomogeneously broadened. The resonance can be considered as resulting from the overlap of dips in the velocity distribution of the nonlinear polarization induced by the standing laser wave.     

Acoustical phonon assisted two-photon excitation of excitonic molecules and resonant raman scattering in evaporated CuCl films

In evaporated CuCl films, Chase et al. have concluded the Bose-Einstein condensation of excitonic molecules for the origin of a sharp emission line which has been ascribed so far to the resonant Raman line in single crystals. A trace of the similar works on evaporated samples confirms that the sharp line shifts its energy with the change of the excitation photon energy; indicating the Raman character. When the excitation photon energy exceeds the resonant energy the Raman line shows broadening, and a new emission band appears which can be ascribed to the radiative annihilation of excitonic molecules generated by the two-photon absorption and one acoustical phonon emission.     

Polaron effects in resonant Raman scattering

Loudon's resonant Raman scattering theory is reconsidered by including polaron effects in the intermediate electron states. The Fröhlich Hamiltonian is used to derive the polaron propagators. Numerical calculations were carried out for CdS which show that polaron effects produce a large enhancement of the scattered intensity, improving the agreement between theoretical and experimental results.     

Generation of undamped stokes radiation under resonant pumping of the dipole-forbidden transition in a Ξ-atom

We have developed a theory of the nonlinear ring interaction of three intense fields in the scheme of resonant Raman scattering on the dipole-allowed transition from the ground state to the first excited state of a cascade three-level quantum system. We show that the backward Stokes radiation generated by a pump resonant to the dipole-forbidden transition can be used in remote laser sensing of metal vapors.     

Resonant raman scattering at the E1 energy gap of semiconductor crystals

We present a discussion of resonant Raman scattering by optical phonons at the E₁ energy gap of group IV and groups III–V compound semiconductor crystals (e.g., Ge and InSb). For allowed scattering by TO and LO phonons, the q-dependent “double resonant” two-band calculation of the Raman tensor may display destructive interference effects when the intermediate electron-hole pairs are uncorrelated. We also discuss the Franz-Keldysh mechanism of resonant electric field induced Raman scattering by LO phonons. The double resonance terms due to this mechanism will, for large electric fields, broaden and have its largest resonance enhancement at the energy gap.     

Hg1—xCdxTe的共振拉曼散射

当入射光的光子能量接近Hg1-xCdxTe的Eo △o时,发现了Hg1-xCdxTe的共振拉曼散射,观察到了“禁戒”共振增强拉曼散射,同时也观察到了二级共振拉曼散射。分析了非共振条件下能在样品的（100）面观察到微弱的“禁戒”TO2模拟及在共振条件下“禁戒”TO2模大大增强的原因。通过分析,发现由双LO声子引起的二级共振拉曼散射主要由带内的Froehlich相互作用造成的。     

New features in the anti‐Stokes and Stokes Raman spectra of single‐walled carbon nanotubes that are highly separated into their semiconducting and metallic nanotube components

Surface‐enhanced Raman scattering studies were performed using nonresonant (514.5 nm) and resonant (676.4 nm) optical excitations on single‐walled carbon nanotubes thoroughly separated into semiconducting (pure 99%) and metallic (pure 98%) components. Regardless of the support (Au or Ag), the metallic nanotubes do not present an anomalous anti‐Stokes Raman emission. Regardless of whether an on‐resonant or off‐resonant optical excitation is used, only the semiconducting nanotubes produce an abnormal anti‐Stokes Raman emission that grows when increasing the excitation light intensity or temperature. The Raman studies under light polarized relative to the main nanotube axis demonstrate that only semiconducting nanotubes are sensitive toward changes in the polarization of the excitation light. Copyright © 2014 John Wiley & Sons, Ltd.     

Two-photon resonant Raman and luminescence of excitonic molecules in CuCl

Two-photon resonant Raman scattering via excitonic molecule in CuCl is studied with using dye laser excitation of different band widths. The yield of the Raman scattering is found to drop remarkably at resonant excitation and luminescence line of 0.3 meV half-width comes out. The predominance of the Raman or luminescence or their coexistence depends on the intensity and energy band width of excitation light.     

KLL Auger resonant Raman transition in metallic Cu and Ni

High energy resolution KL₂₃L₂₃ Auger spectra of polycrystalline Cu and Ni were measured using photon energies up to about 50 eV above the K-absorption edge and down to 5 eV (Cu KLL) and 4 eV (Ni KLL) below threshold. The spectra show strong satellite structures varying considerably as a function of the photon energy. In the sub-threshold region the linear dispersion of the diagram line energy positions and a distortion of the line shape as a function of photon energy, attributable to the Auger resonant Raman process, is clearly observed, indicating the one-step nature of the Auger emission. These changes in the resonant spectra are interpreted using a simple model based on resonant scattering theory in combination with partial density of states obtained from cluster molecular orbital (DV-Xα) calculations.     

Resonant Raman scattering in mixed GaSxSe1−x crystals

One- and two-phonon resonant Raman scattering around the absorption edge in mixed GaS_xSe_1?x crystals with 0 ? x < 0.23 has been measured. The results can be explained by a simple theory in which the dispersion of RRS is dominate by exciton resonances.     

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.