SBIR PHASE I: Novel Bridgman Growth of Tungsten Bronze Crystals for Emerging Nonlinear Optical Applications

这个小企业创新研究第一阶段项目解决了新颖的垂直布里奇曼生长的铁电钨青铜材料，已知具有大的电光和光折射效应。它们包括一类非常有前途的应用，如可调全息波长滤波，全息海量数据存储，电光调制和光束转向，相位共轭，和集成光开关的光学材料。目前大多数钨青铜晶体都是通过直拉法生长的，主要问题是折射率条纹，直径不稳定，以及对有害成分挥发损失的敏感性。条纹会导致显著的光散射并降低器件性能。它们产生于虚假的生长速率波动，主要是由于在熔体-固体界面的温度变化。这些变化的主要来源是在一个非轴对称的温度分布的晶体旋转。 我们建议开发一个垂直布里奇曼系统生长SBN和PBN，因为这种方法本质上避免了晶体旋转和浮力驱动的熔体对流，从而最大限度地减少条纹。此外，晶体直径由坩埚壁决定，因此直径不稳定性不是问题，并且可以通过使用密封坩埚技术来消除挥发。 SBN、PBN和其他钨青铜晶体的垂直布里奇曼生长将提供具有更大尺寸和显著更低成本的更高光学质量的样品。这项技术将有助于进一步推进许多电光和光折射应用。

This Small Business Innovation Research Phase I project addresses novel vertical Bridgman growth of ferro-electric tungsten bronze materials which are known to have large electro-optic and photorefractive effects. They comprise a class of optical materials that are very promising for applications such as tunable holographic wavelength filtering, holographic mass data storage, electro-optic modulation and beam steering, phase conjugation, and integrated optical switching. Most tungsten bronze crystals are currently grown by the Czochralski method where the main problems are refractive index striations, diameter instability, and susceptibility to volatilization loss of hazardous constituents. Striations can cause significant light scattering and degrade device performance. They arise from spurious growth rate fluctuations, principally due to temperature variations at the melt-solid interface. The dominant source of these variations is crystal rotation in a non-axisymmetric temperature profile. We propose to develop a vertical Bridgman system for growing SBN and PBN because this method inherently avoids crystal rotation and minimizes buoyancy-driven melt convection, thereby minimizing striations. Furthermore, the crystal diameter is determined by the crucible walls so that diameter instability is not an issue, and volatilization can be eliminated by using a sealed-crucible technique. Vertical Bridgman growth of SBN, PBN, and other tungsten bronze crystals will provide higher optical quality samples with larger sizes and significantly lower cost. This technology will help to further advance numerous electro-optic and photorefractive applications.