Calculations of theA1Phonon Frequency in Photoexcited Tellurium

Abstract

Calculations of the A 1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of photoexcited carriers on a sub-picosecond time-scale.

Dynamics of coherent phonons in CsPbCl3 nanocrystals studied by femtosecond laser spectroscopy

“…One can see a slight decrease in phonon frequency when tuning the wavelength from transparency region into the exciton absorption for modes 2, 3 and 4. This can be interpreted in terms of the phonon softening by changing the real carrier population (due to variable absorption) which leads to the screening of the ion charges and consequently to the altering the force constants [14]. However, the frequency of the mode f 1 has an opposite spectral dependence.…”

Laser‐Induced Softening of Lattice Vibrations

“…The assumption that electrons acquire a well-defined temperature during the first stages of the laser-induced lattice dynamics was used for some molecular dynamics simulations [28,29] and by us for the construction of excited PESs [30,31]. Fahy and coworker use for semiconductors and semimetals a constraint model in which it is assumed that electrons and holes thermalize separately and acquire two different chemical potentials [32]. We discussed in Refs [33] and [16] the drawbacks of this assumption for semimetals in general and also for semiconductors excited by very intense laser pulses.…”

“…The main changes that excitation of electron-hole pairs can produce on the PES are (i) a shift of the minimum with respect to the ground-state PES U 0 in clusters and solids with more than one atom per unit cell [32,33,38,39] and (ii) a deformation of the shape near the minimum due to the presence of anharmonicities [24-26, 31, 34]. In most nanostructures, and particularly in covalent systems, the minimum is shifted to larger interatomic distances.…”

Precursor Phenomenon of Laser Ablation in Bismuth

“…Up to date, dynamics of the coherent phonons generated by femtosecond pulses with low-density excitation ( several mJ/cm 2 ) have actively reported in various materials (Cheng et al, 1990;Zeiger et al, 1992;Hase et al, 1996;Garret et al, 1996;Dekorsy et al, 2000). Recently, the coherent phonon under high-density excitation have been studied by several workers (Cheng et al, 1993;Hunsche et al, 1995;Brennan and Nelson, 1997;Tangney and Fahy, 1999;DeCamp et al, 2001). However, there is little report that reveals the dynamical properties of the coherent phonon under high-density excitation from the viewpoint of the femtosecond laser ablation.…”