  When an intense THz field at frequency f_THz is applied to excitons
resonantly created in bulk GaAs by a near IR laser at frequency f_NIR,
sidebands are observed at frequencies f_sideband = f_NIR + 2nf_THz, where n is
an integer. At temperature T=10 K, sidebands of order -4 {greater than or equal
to} 2n {greater than or equal to} 16 are observed. Sidebands up to 10th order
persist at 170 K.
