9321052 Meltzer The optical dephasing time of dopant ions will be used as a tool to investigate two-level systems (TLS) in disordered crystalline materials such as mixed solid solutions and polycrystalline films, where the disorder is generally experimentally variable. These types of experiments will be extended to ordered arrangements of atoms in a restricted geometry, such as MBE grown undoped as well as rare earth ion doped superlattices. In a second set of experiments phonon dynamics will be studied with a number of innovative approaches. These include use of a very short duration (100 ps) pulses to study phonon-phonon interactions in RE doped fluoride crystals, and use of two FIR pulse sources to study the interaction between two narrow band phonon populations. A third study will apply coherent and transient holeburning techniques to study the dynamics of the photoionization process of transition metal ion sites in ferrolectric materials. %%% Unique optical techniques will be applied to study the nature of disorder in doped crystals, mixed solid solutions, and ultrathin semiconductor layers. The unique techniques include two ultrashort pulsed lasers which emit radiation at very long infrared wavelengths used for directly generating sound waves in solids, and a special laser which emits visible light which is extremely close to a single frequency. The latter light source will allow to study changes in absorption induced by a laser very accurately as a function of light wavelength. A key aspect of this work is that the degreee of disorder can be experimentally varied when preparing a particular sample material. This study is expected to provide new sensitive tools for characterizing disorder with applications to more controlled growth of a variety of optoelectronic materials. ***
