Using far-infrared two-photon excitation to measure the resonant-polaron effect in the Reststrahlen band of GaAs:Si

We demonstrate that we can use far-infrared two-photon excitation with picosecond pulses to measure the resonant polaron effect of the 1s-3d(+2) silicon impurity transition in the middle of the Reststrahlen band of GaAs:Si. Contrary to single-photon measurements, our two-photon measurements do not suffer from the problems of strong reflection and small penetration depth of light in the Reststrahlen band of the GaAs host lattice. As a result, we are able to measure a significant fraction of the magnetic field dependent anticrossing of the 1s-3d(+2) transition with the LO-phonon.