Superslow Self-Organized Motions in a Multimode Microwave Phonon Laser   (Phaser) under Resonant Destabilization of Stationary Acoustic Stimulated   Emission
  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 
D. N. Makovetskii