Optical generation of nonequilibrium terahertz resonant vibrational excitations

2019-05-14 14:20:01

The aluminum 20 generated phonons

责任者: Feofilov, S.P.;Kaplyanskii, A.A.;Zakharchenya, R.I. 单位: A.F. Ioffe Physical-Technical Inst, St. Petersburg, Russia 来源出处: Journal of Luminescence,1995,66-67(1-6):349-357 摘要: The dynamics of terahertz phonons generated at liquid helium temperature by laser excitation in sol-gel technology grown transparent highly porous crystalline γ-Al2O3 samples, was studied through the phonon-induced anti-Stokes FLN spectra of Cr3+ impurity ions (2E-4A2 lines). The generated phonon spectrum contains essentially a nonequilibrium narrow peak around ω approximately equals 0.6 THz (20 cm-1) with high occupation numbers n over-bar ω and decay time approximately 1 ms besides and a slowly cooling (approximately tens of ms) thermalized Planckian distribution. The frequency (20 cm-1) of these long-living nonthermalized vibrations is consistent with the lowest acoustic, size-resonant surface mode of γ-Al2O3 spherical nanoparticles with 80 angstroms diameter, which form the network of the sample. Discussed are the nature of the long lifetime and the possible role of these surface modes in the spectral dynamics of optically generated phonons. 关键词: Porous materials;Alumina;Phonons;Sol-gels;Liquefied gases;Crystalline materials;Lattice vibrations;Thermal effects;Fluorescence;Ions;Porous aluminum oxide;Resonant vibrational excitations;Terahertz phonons;Liquid helium