Raman scattering from confined LO phonons and dispersion relation in GaAs/AlAs superlattices

The Raman scattering from both GaAs and AlAs confined LO phonons for several GaAs/AlAs superlattices is presented. The GaAs confined LO phonons were observed for two narrow GaAs layer samples at room temperature. The frequencies of observed phonons fit fairly well with the theoretical dispersion curves.     

Resonance Raman scattering of excitonic polaritons by LO and acoustic phonons in ZnTe

We have observed dispersive two-phonon Raman scattering of polaritons by LO and acoustic phonons near the lowest exciton state of ZnTe. From the Stokes shifts of these Raman lines, it has been found that the scattering process switches from an acoustic phonon followed by one LO phonon to the reversed one: a LO phonon followed by an acoustic one.     

Some features of the Resonant Raman Scattering by LO phonons

Resonant Raman Scattering by LO phonons is analysed to obtain a relationship between allowed and forbidden cross sections. The complete expression for the forbidden Raman amplitude induced by the Fröhlich interaction is then used to obtain its dependence on the phonon wave vector with CdS parameters. Comparison with a previous experimental and theoretical work is performed.     

Coherent anti-Stokes Raman scattering and normal anti-Stokes Raman scattering due to LO phonons in GaP using cw diode lasers

Coherent anti-Stokes Raman scattering (CARS) and normal anti-Stokes Raman scattering (NARS) have been measured in (001) GaP at room temperature due to the 403 cm⁻¹ LO phonons using a continuous wave (CW) 785.0 nm fixed-wavelength pump laser and a CW Stokes laser tunable in the 800-830 nm wavelength range. CARS measurements are normally made using pulsed lasers. The use of CW diode lasers allows a more accurate comparison between the measured and calculated values of the CARS signal. The pump and Stokes laser beams were linearly polarized perpendicular to each other, same as the pump and normal Stokes/anti-Stokes scattered light for the GaP sample used in this work. The pump and Stokes laser powers incident upon the GaP sample, located in the focal plane of a 20 mm effective focal length lens, were <20 and 50 mW, respectively. The diameter of the laser beams in the focal plane of the focusing lens was determined to 40±5 μm. The pump and Stokes laser beam intensities incident upon the 0.3 mm thick GaP sample were <2 and 5 kW cm², respectively. The powers of the CARS and NARS signals were measured using a Raman spectrometer. The signal output of the Raman spectrometer was calibrated using the pump laser and several neutral density filters. The Raman linewidth (full-width at half-maximum) of the LO phonons was determined to be 0.95±0.05 cm⁻¹, using the variation of the CARS signal with the wavelength of the Stokes laser. The measured powers of the CARS and NARS signals are about a factor of 5 and 1.5, respectively, smaller than those calculated from the corresponding theoretical expressions.     

Raman spectra of a coupled LO phonon-damped plasmon mode in n-GaAs

It is shown that recently observed spectra of Raman scattering from a coupled longitudinal optical (LO) phonon-damped plasmon mode in n-GaAs can be reproduced theoretically by taking into account the Landau damping of the mode itself as well as a distribution of wave number of laser light due to the attenuation of light near the surface.     

Raman scattering from confined phonons in GaAs/AlGaAs quantum wires

We report on photoluminescence and Raman scattering performed at low temperature (T =  10 K) on GaAs/Al_0.3Ga_0.7As quantum-well wires with effective wire widths ofL =  100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at ο_L10 =  285.6 cm⁻¹forL =  11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderleinas applied to the GaAs/Al_0.3Ga_0.7As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques.     

Theory of multipole-dipole resonance Raman scattering by phonons

The theory of multipole-dipole resonance Ramon scattering by phonons is given. Under conditions of resonance of the incident or scattered photon with a multipole exciton, entirely new selection rules, and polarization properties govern the process of inelastic scattering. For example, in a cubic crystal, the ‘rule of mutual exclusion’ is broken. Some illustrations are given with particular attention to the experimental results for Cu₂O recently observed by Compaan and Cummins.     

Mechanism of strong resonant 1LO Raman scattering

The interaction of electrons with impurities and the quasi-elastic scattering of electrons by acoustic phonons highly enhances the efficiency of resonant 1 LO Raman scattering. As a result, for a wide range of parameter values the efficiency of resonant scattering becomes rather strong and does not depend on the strength of interaction of electrons with the impurities and acoustic phonons, and on the impurity concentration.     

Raman scattering by optical phonons and polaritons in CuCl

We present data on forward and backward scattering in CuCl at liquid N₂ temperature. Peaks at 146 and 172 cm^-1 which appear in both forward and backward scattering spectra are attributed to other than first order scattering by optical phonons. The data on polarition scattering indicate that the atomic displacement contribution to the scattering by TO phonons is rather small. From the experimentally determined polarition dispersion curve we obtain a value of 174 ±2.5 cm^-1 for ω_T and a value of 5.3 for ?_S.     

Raman scattering by LO-phonon-plasmon coupled modes in p-type GaAs: Wave vector non conservation

Raman scattering from nearly unscreened LO-phonons in heavily doped p-GaAs has been detected in forbidden configuration resonant near the E₁ energy gap. The observed scattering is explained in terms of coupled LO-phonon-plasmon modes with large wave vectors. The required breakdown of the wave vector conservation is attributed to scattering by the ionized acceptor-impurities (Zn).