Optical Dephasing and Phonon Dynamics in Ordered Crystals, Disordered Crystals and Molecular Beam Epitaxy Films

掺杂离子的光学失相时间将被用作研究无序晶体材料（如混合固溶体和多晶薄膜）中的双能级系统（TLS）的工具，其中无序通常是实验可变的。这些类型的实验将扩展到限制几何结构中原子的有序排列，例如未掺杂的MBE生长以及稀土离子掺杂的超晶格。在第二组实验中，声子动力学将用一些创新的方法来研究。其中包括使用非常短的持续时间（100 ps）脉冲来研究稀土掺杂氟化物晶体中的声子-声子相互作用，以及使用两个FIR脉冲源来研究两个窄带声子种群之间的相互作用。第三项研究将应用相干和瞬态烧孔技术来研究铁电材料中过渡金属离子位的光离过程动力学。独特的光学技术将被应用于研究掺杂晶体、混合固溶体和超薄半导体层中的无序性质。独特的技术包括两个超短脉冲激光器，发射非常长的红外波长的辐射，用于直接在固体中产生声波，以及一个特殊的激光器，发射非常接近单一频率的可见光。后一种光源将允许非常精确地研究激光引起的吸收变化作为光波长的函数。这项工作的一个关键方面是，在制备特定样品材料时，可以通过实验改变无序程度。该研究有望为表征无序提供新的敏感工具，并应用于各种光电材料的更可控的生长。＊＊＊

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. ***