Monte-Carlo Simulations and the Dynamics of Highly Excited Phonons

Abstract

We have investigated the dynamics of 29cm⁻¹ phonons in ruby by direct optical excitation of the 2A(²E) (R2) level. A dye laser (t_p = 6ns) generates a column (r = 25 µm) of excited ions and the phonons are detected by a superconducting bolometer, identifying the resonant phonons by their scattering in an additional volume created by an argon laser (inset in fig. (1) or by the luminescence from the E(²E) (R1) level. We find no strong laser-like nonlinearities as reported by Hu[1], but observe that phonon bottleneck is suppressed for the first 50 ns after the excitation, so that about 70% of the phonons escape from the excited region before strong bottleneck (b >=100) sets in [2]. This has been explained qualitatively by “incoherent bleaching” of the acoustically thick medium due to the high phonon occupation numbers (p up to 100) following the excitation.