Monte-Carlo Simulations and the Dynamics of Highly Excited Phonons
We have investigated the dynamics of 29cm−1 phonons in ruby by direct optical excitation of the 2A(2E) (R2) level. A dye laser (tp = 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, 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 . 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.
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