  Two qualitatively different kinds of resonant destabilization of phonon
stimulated emission (SE) are experimentally revealed for periodically forced
multimode ruby phaser (phonon laser) operating at SE frequencies about 9 GHz,
i.e. at microwave acoustic wavelengths of 1 micron. The inversion state of
Cromium(3+) spin-system in ruby was created by electromagnetic pump at 23 GHz.
Under deep modulation of pump power at low frequencies OMEGA_m = 70-200 Hz
deterministic chaotic reconfigurations of the acoustic microwave power spectra
(AMPS) were observed. This range of SE destabilization corresponds to the
relaxational resonance that is well known for optical class-B lasers. Outside
the relaxational resonance range, namely at ultra-low (infrasonic) frequencies
OMEGA_m about 10 Hz, the other type of resonant destabilization of stationary
phonon SE was observed by us for the first time. This new nonlinear resonance
(we call it lambda-resonance) manifests itself as very slow and periodically
repeated self-reconfigurations of AMPS. Near the vertex of lambda-resonance the
period of AMPS self-reconfigurations takes giant values of several hours (at
T=1.8 K). The second type of SE resonant destabilization is explained in terms
of antiphase energy exchange between acoustic SE modes in a modulated phaser.
The role of polarized nuclear spin-reservoir (formed by Aluminium-27 nuclei of
the ruby crystalline matrix) in these superslow self-organized motions is
discussed. PACS: 05.65.+b, 42.65.Sf, 43.35.+d
