RIMI: Effects of Crystal Field in Quasi Four-Level Lasers

生产更小，更节能的激光器为许多应用提供了方便的光源。提高效率的关键是了解激光介质中的能量损失过程。许多有用的激光器在准四能级模式下工作，在那里它们经历了大的损耗和低效率。当激光介质为晶体时，晶体场与掺杂剂的能量流形相互作用。晶体场相互作用可使晶体中掺杂剂的能量流形调整500 cm-1，并导致相对于自由离子的较大分裂。这些歧管的位置和分裂对有效的激光性能至关重要。本研究将研究晶体场对影响稀土离子激光器性能关键指标准四能级固体截面性能的关键因素的影响，以及晶体场对能量传递、上转换和非辐射弛豫等过程的影响，从而全面了解晶体场对激光器性能的影响。下能级和上能级流形中晶体场分裂的程度决定了每个能级上的热密度，并最终决定了激光器的性能。晶体场劈裂越大，下能级居数越小，上能级居数越高。降低下激光能级，增加上激光能级族数，增大吸收和发射截面，将显著提高激光阈值和斜率效率。这些分裂对能量传递、上转换、流形间和流形内弛豫等关键过程的有利影响有助于提高激光器的性能。在三年的时间里，研究的具体目标是确定晶体场对准四能级系统阈值和斜率效率的影响，并了解场对影响激光性能的参数和过程的影响。研究了晶体场对吸收和发射截面等参数以及能量传递、上转换和非辐射弛豫等过程的影响。氟磷灰石家族，特别是Ca5(PO4)3F, Sr5(PO4)3F和Ba5(PO4)3F被选择是因为它们是高效准四能级激光器的优秀候选者，因为它们具有大的晶体场分裂和晶体场参数随碱土金属的取代而变化。利用晶体场参数从Ca到Ba的变化趋势，研究其对上述影响激光器性能的参数和工艺的影响。由于Tm3+在许多准四能级系统中表现出影响激光性能的丰富过程，因此将被用作探针。Tm3+本身也是一种重要的准四能级激光离子。在本研究中，充分了解晶体场参数对准四激光器性能的影响，同时评估潜在有用的激光系统，如Tm3+掺杂氟磷灰石。研究团队结合了高质量双电晶体生长、固态材料光谱、超快动力学和稀土离子激光开发方面的专业知识。该团队将在校园内的实验室中培育、制造和全面评估这些材料。温度依赖性吸收和发射将用于确定晶体场分裂，吸收和发射截面和能量分支比。时间分辨发射和吸收将用于检查材料中的辐射、非辐射和上转换率。将建立一个激光试验台来评估材料的激光性能。

HRD-9628321 Bonner The production of smaller, more energy efficient lasers offer the promise of a convenient light source for many applications. The key to the efficiency is an understanding of the energy loss processes in the lasing media. Many useful lasers operate in quasi-four level mode where they experience large losses and low efficiencies. When the laser media is a crystal, the crystal field interacts with the energy manifolds of the dopant. The crystal field interaction can adjust the energy manifolds of the dopant in the crystal by as much as 500 cm-1 and cause large splittings relative to the free ion. The position and splittings of these manifolds are critical for efficient laser performance. The proposed research will investigate the effect of the crystal field on the critical factors affecting the performance of quasi-four level solid state cross sections which are key metrics in rare earth ion laser performance and the effects on processes such as energy transfer, upconversion, and non-radiative relaxation will provide full understanding of effect of the crystal field on laser performance. The degree crystal field splitting in the lower laser level and the upper level manifold dictates the thermal population on each level and ultimately laser performance. The larger crystal field splitting, the smaller the lower laser level population and higher upper laser level population. The decreased lower laser level and increased upper laser level populations and larger absorption and emission cross sections will significantly improve laser thresholds and slope efficiencies. A favorable effect of these splittings on key processes such as energy transfer, upconversion, inter-manifold, and intra- manifold relaxation contributes to improved laser performance. For the proposed three years, the specific objectives of the investigation are to determine the effect of crystal field on the threshold and slope efficiency of quasi-four level systems and understanding the field effects on the parameters and processes influencing laser performance. The effect of the crystal field on parameters such as absorption and emission cross sections, and processes such as energy transfer, upconversion and non-radiative relaxation will be studied. The fluorapatite family, specifically Ca5(PO4)3F, Sr5(PO4)3F, and Ba5(PO4)3F have been chosen since they are excellent candidates for efficient quasi-four level lasers due to their large crystal field splittings and crystal field parameters are varied by substitution of the alkaline earth metal. This trend on the crystal field parameters from Ca to Ba will be utilized to study its affect on the parameters and processes influencing the laser performance above mentioned. Tm3+ will be utilized as the probe since it exhibits a wealth of processes which affects the laser performance in many quasi-four level systems. Tm3+ itself is also an important quasi-four level laser ion. In the proposed investigation, a full understanding of the effect of crystal field parameters on quasi-four laser performance will be achieved while evaluating a potentially useful laser system such as Tm3+ doped fluoroapatites. The investigative team combines the expertise of crystal growth of high quality di-electric crystals, spectroscopy in solid state materials, ultrafast kinetics, and rare earth ion laser development. This team will grow, fabricate, and fully evaluate the materials in laboratories housed on campus. Temperature dependent absorption and emission will be used to determine the crystal field splitting, absorption and emission cross sections and energy branching ratios. Time resolved emission and absorption will be used to examine the radiative, non- radiative, and upconversion rates in the materials. A laser test bed will be constructed to evaluate the laser performance of the materials.