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 i n a quantum well of polar material under an intense laser field is pre sented by taking into account the discontinuity of the electronic effe ctive mass crossing the interface of the quantum-well materials. We ha ve found that for the confined-polar-optical phonons, the number of ph onons 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(parall el-to). For the interfacial-polar-optical (IPO) phonons, the condition s 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(paral lel-to), k2l + k2l') in the barrier regions. We have also found that t he amplification of the IPO-phonon population is easier in material i than in material j if the electronic effective mass m(i) < m(j)*. Und er 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 am plified under an intense laser field and the amplification of the (alp ha + q) IPO-phonon population is mainly determined by the amplificatio n of the (alpha + q) IPO-phonon population inside the well region. The change regulation of the rates of the phonon excitations with the qua ntum-well width are studied.