Coherent phonon generation and the two stimulated Raman tensors

Stevens, T.E.; Kühl, J.; Merlín, R.

doi:10.1103/physrevb.65.144304

Cited by 302 publications

(364 citation statements)

References 10 publications

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“…This perturbs the lattice potential and produces a force on the ions. The response of ions to the force is determined by the normal modes of the potential, which are expressible as a superposition of phonon modes 10 . If the force generated is fast compared with the period of the phonon, then coherent motions of the lattice, or coherent phonons, are induced.…”

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confidence: 99%

Ultrafast changes in lattice symmetry probed by coherent phonons

et al. 2012

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The electronic and structural properties of a material are strongly determined by its symmetry. Changing the symmetry via a photoinduced phase transition offers new ways to manipulate material properties on ultrafast timescales. However, to identify when and how fast these phase transitions occur, methods that can probe the symmetry change in the time domain are required. Here we show that a time-dependent change in the coherent phonon spectrum can probe a change in symmetry of the lattice potential, thus providing an all-optical probe of structural transitions. We examine the photoinduced structural phase transition in Vo 2 and show that, above the phase transition threshold, photoexcitation completely changes the lattice potential on an ultrafast timescale. The loss of the equilibrium-phase phonon modes occurs promptly, indicating a non-thermal pathway for the photoinduced phase transition, where a strong perturbation to the lattice potential changes its symmetry before ionic rearrangement has occurred.

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Ultrafast changes in lattice symmetry probed by coherent phonons

et al. 2012

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“…In the group V semimetals, the photoexcitation of modest plasma density leads to large amplitude atomic motion corresponding to a coherent zone-center fully symmetric (A 1g ) optical phonon 19,20 . The initial photoexcited electronic distribution is determined by the intensity, photon energy and polarization of the incident light.…”

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Free-carrier relaxation and lattice heating in photoexcited bismuth

et al. 2013

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We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole (e − h) recombination time is 12-26 ps and ambipolar diffusivity is 18-40 cm 2 /s for carrier excitation up to ∼ 10 19 cm −3 . By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the e − h plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation > ∼ 10 20 cm −3 .

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“…The coherent optical phonons have been observed as a periodic modulation in the THz frequency range, most conveniently by linear and non-linear optical techniques 1,2 . The generation mechanisms of the coherent phonons have been studied extensively in a variety of crystals and attributed, depending on the nature of the electron-phonon interaction, to impulsive stimulated Raman scattering (ISRS) 3,4 , displacive excitation of coherent phonons (DECP) 5 , and transient depletion field screening (TDFS) [6][7][8] . The time evolution of coherent phonons is in general determined by the phonon anharmonicity (phonon-phonon scattering) 9 and scattering by defects 10 .…”

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Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

2011

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Detection mechanisms of coherent phonons in variously doped GaAs are investigated by transient reflectivity method with photoexcitation near the E0 gap and probe near either the E0 or E1 gaps. By varying the probe light polarization angle, the coherent amplitudes of both the LO phonon and the LO phonon-plasmon coupled (LOPC) modes show evidence for an interference between their anisotropic and isotropic dielectric response components. We attribute the anisotropic and isotropic components to the reflectivity modulation by lattice and electronic polarizations via dipole-allowed and dipole-forbidden Raman scattering processes. The forbidden processes are resonantly enhanced at the E0 and E1 critical points due to the relaxation of momentum conservation and the strong built-in electric field near the surface. The relative contribution of the anisotropic and isotropic components depends on the modes (LO or LOPC) as well as the probe wavelength (E0 or E1), because of the different Raman scattering mechanisms involved. Reflectivity measurements with the near ultraviolet light, which is used to probe the E1 gap, also enable highly surface sensitive detection of ultrafast LO phonon-plasmon dynamics, which is strongly depth-dependent in the depletion layer of n-doped GaAs.

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Coherent phonon generation and the two stimulated Raman tensors

Cited by 302 publications

References 10 publications

Ultrafast changes in lattice symmetry probed by coherent phonons

Ultrafast changes in lattice symmetry probed by coherent phonons

Free-carrier relaxation and lattice heating in photoexcited bismuth

Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

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