Parametric excitation of acoustohelicon waves in a piezoelectric semiconductor

The parametric excitation of acoustohelicon waves has been studied in a piezoelectric semiconductor in the presence of a strong high frequency oscillatory electric field. The threshold electric field amplitude and the growth rate of the unstable mode have been obtained analytically and for n-InSb at 77 K the unstable mode is found to be propagating with a growth rate ～10³ s^?1 when the crystal is irradiated with a 10.6 μm CO₂ laser.