PHONON AMPLIFICATION BY ABSORPTION OF AN INTENSE LASER FIELD IN A QUANTUM-WELL OF POLAR MATERIAL

A theory of the amplification of the polar-optical-phonon population in a quantum well of polar material under an intense laser field is presented by taking into account the discontinuity of the electronic effective mass crossing the interface of the quantum-well materials. We have found that for the confined-polar-optical phonons, the number of phonons will grow with time if the laser field strength E(d) is greater than a threshold value E(dL)c and the phonon wave vector q < 2k(parallel-to). For the interfacial-polar-optical (IPO) phonons, the conditions of the amplification of the phonon population are E(d) > E(dsi)c (i = 1,2) and q < 2k(parallel-to) in the well region and q < min(2k(parallel-to), k2l + k2l') in the barrier regions. We have also found that the amplification of the IPO-phonon population is easier in material i than in material j if the electronic effective mass m(i)* < m(j)*. Under the conditions of the small phonon wave vector q and large quantum-well potential V0, the number of the (alpha - q) IPO phonons is not amplified under an intense laser field and the amplification of the (alpha + q) IPO-phonon population is mainly determined by the amplification of the (alpha + q) IPO-phonon population inside the well region. The change regulation of the rates of the phonon excitations with the quantum-well width are studied.