Periodic Structuring of Material Parameters in Ferroelectric Crystals with Ion Exposure

在这个项目中，将用一种新的方法来制作光波导：将铌酸锂晶体(LiNb03)和钽酸锂晶体(LiTaO_3)暴露在加速离子(如2D、3He、a粒子)中。这种曝光会产生足够大的折射率变化，从而形成导光结构。该方法特别适用于C4项目中研究的晶体。然而，制造不影响其他晶体性质的低损耗光波导的技术通常是几种具有小形状因数的高效器件的关键。在该项目中，将通过X射线吸收光谱和正电子微探针测量来揭示潜在的微观机制的详细物理理解。这些技术将允许研究富锂LiNb03：Mn和LiTaO3：Mn晶体中产生的局部缺陷以及一般缺陷化学，因为它们将在C4项目中使用。关键问题是：哪些缺陷是由辐射引起的？这些缺陷的特性是什么，例如影响铁电和光折变、扩散行为、寿命和吸收？在周期极化的LiNbO_3或LiTaO_3中利用准相位匹配进行倍频和光学参数振荡是两个很有前途的应用例子。例如，项目C4的目标是实现包含布拉格光栅作为反射镜的单片光学参量振荡器。较高的频率转换效率需要较高的光强和较长的相互作用长度。两者都可以通过利用晶体中的波导结构来提供。此外，较高的金属含量会增加电导率，从而减少所谓的“光学损伤”(空间电荷场引起的电光折射率变化)。粒子曝光产生的折射率变化以及本项目对LiNbO_3和LiTaO_3晶体缺陷化学的研究具有迷人的物理意义，可能成为这些应用的关键因素。

Within this project, waveguides will be fabricated by a novel method: lithium niobate crystals (LiNb03) and lithium tantalate crystals (LiTaO3) will be exposed to accelerated ions (e.g.,2D, 3He, a particles). This exposure generates refractive index changes that are large enough to create light-guiding structures. The method should be applied especially to crystals studied in Project C4. However, techniques to fabricate low-loss waveguides that do not impact the other crystal properties are in general the key for several efficient devices with small form factors. Within the project a detailed physical understanding of the underlying microscopic mechanisms will be revealed by X-ray absorption spectroscopy and positron microprobe measurements. These techniques will allow for a study of the generated local defects as well as the general defect chemistry in Li-enriched LiNb03:Mn and LiTaO3:Mn crystals as they will be used in Project C4. Key questions are: Which defects are induced by the radiation? What are the properties, e.g. impact an ferroelectricity and photorefractivity, diffusion behavior, life-time, and absorption, of these defects? Frequency doubling and optical parametric oscillation by using quasi-phase-matching in periodically-poled LiNbO3 or LiTaO3 are two examples of promising applications. The goal of, e.g., Project C4 is to realize monolithic optical parametric oscillators that contain Bragg gratings as mirrors. Large frequency conversion efficiencies require high light intensities and long interaction lengths. Both can be provided by utilizing waveguiding structures in the crystals. Furthermore, high metal contents will increase the electric conductivity and hence reduce the so-called "optical damage" (unwanted space-charge-field-induced electro-optic refractive-index changes). Generation of refractive-index changes by particle exposure as well as a study of the defect chemistry of LiNbO3 and LiTaO3 crystals by the present project bear fascinating physics and can become key enablers for these applications.