Microwave phonon attenuation in yttrium aluminum garnet and gadolinium gallium garnet

Abstract

Measurements of the attenuation of longitudinal acoustic waves in pure and Nd-doped YAG and GGG between 0.3 and 3 GHz and from 4 to 300 K are presented. At low temperatures, these results are successfully interpreted in terms of scattering of microwave phonons by quasicollinear longitudinal thermal phonons. The total attenuation at 300 K and 1 GHz is 0.15 dB/μsec in YAG and 0.25 dB/μsec in GGG and varies as the square of frequency. The attenuation due to thermal phonons is within a factor of 2 of the value predicted for Akhiezer loss. The differences between pure and Nd-doped samples are smaller than experimental uncertainties.