Modulational instability of a laser beam in a longitudinal magnetized piezoelectric semiconductor

Using the hydrodynamic model of a homogeneous infinite plasma, the modulational instability of a laser beam with an acoustic and a helicon wave has been investigated in a piezoelectric semiconductor. 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 ≈10⁵ s^-1 when the crystal is irradiated with a 337 μm HCN laser.