High-performance laser facet optical coatings fabricated by next generation microwave ion beam deposition

高功率半导体激光器（激光二极管棒）在医疗，军事，商业和工业应用的大量系统中构成和组成部分，此外还有先进的制造技术，包括表面处理，切割和焊接。通常，这些半导体激光器是通过在阵列中连接几个发射器（宽度~100um）来构建的，在末端应用光学涂层，以在激光二极管棒的激光腔内提供所需的光学反馈。许多商业和工业设备可以产生数百瓦的输出功率，这对光学涂层的性能和坚固性提出了具有挑战性的要求。离子束沉积已经成为大多数激光应用中性能最高的光学涂层的首选方法。高能溅射材料产生致密/致密的薄膜，与其他工艺相比，具有更好的环境稳定性，此外还产生具有低光学散射（rms表面粗糙度< 1nm）的超光滑薄膜。更广泛地说，许多精密测量和成像系统需要极窄的线宽激光器和超低光学损耗涂层——通常被归类为高反射（HR）、抗反射（AR）和光学滤光片（用于光谱修剪）。应用通常在生物医学和再生医学领域。例如，拉曼光谱需要极窄带滤光片，只有使用离子束沉积才能实现最高性能。斯特拉斯克莱德大学是英国唯一一所开发离子束沉积光学涂层的大学（在生物医学工程系，与物理学，IoP和Fraunhoffer CAP合作）。窄带光学涂层也可用于增强荧光成像，这是细胞水平成像的标准技术。此外，通过监测呼出的气体来检查患者的安全也可以通过使用光学滤光片来加强。最后，许多用于监测污染的气体传感器将响应光学腔（两个具有高反射涂层的镜子），以回收光并增强与镜面吸收相关的信号。该项目包含的工业赞助证明了其商业相关性。斯特拉斯克莱德大学除了从Veeco（美国）采购行业标准RF（射频）离子沉积技术外，还建立了新的ECR（电子回旋共振）离子束沉积技术。苏格兰拥有各种世界领先的激光工程公司和相关技术，这些公司可以从斯特拉斯克莱德的能力中受益。Helia Photonics是世界领先的先进，高性能光学涂层技术，特别是固体激光涂层（激光二极管棒）。该项目将是与Helia Photonics建立长期战略合作伙伴关系的理想机会，以开发ECR离子束沉积技术。将研究用于光学涂层的各种光学材料，包括二氧化硅、硅、五氧化二钽、二氧化锆、氧化钪、二氧化铪和锗。这些材料的合金也将被研究，因为这通常可以帮助制造更稳定的非晶结构，这反过来又可以提高激光损伤阈值性能。与Helia Photonics合作，我们的目标是确定这些涂料的商业应用，目的是利用斯特拉斯克莱德的设施建立咨询和合同工作。

BackgroundHigh power semiconductor lasers (laser diode bars) form and integral component within a vast array of systems for medical, military, commercial and industrial applications, in addition to advanced manufacturing techniques including surface treatment, cutting and welding. Often these semiconductor lasers are constructed by joining several emitters (width ~100um) in an array, with optical coatings applied at the ends to provide required optical feedback within the laser cavities of the laser diode bar. Many commercial and industrial devices can generate hundreds of Watts of output power, setting challenging requirements for the performance and robustness of the optical coatings.Ion beam deposition has been the method of choice for the highest performance optical coatings for the majority of laser applications. The energetic sputtered material results in a compact/dense film, with improved environmental stability compared to other processes, in addition to yielding ultra-smooth films with low optical scatter (rms surface roughness < 1nm).More broadly, many precision measurement and imaging systems, require extremely narrow linewidth lasers and the use of ultra-low optical loss coatings - typically classed as highly reflecting (HR), antireflection (AR), and optical filters (for spectral trimming). Applications often lie within the biomedical and regenerative medicine area. For example, Raman spectroscopy requires extremely narrowband optical filters, with the highest performance only being achieved using ion beam deposition. The University of Strathclyde is the only university in the UK that develops ion beam deposited optical coatings (in the Department of Biomedical Engineering, in collaboration with Physics, IoP and Fraunhoffer CAP). Narrowband optical coatings can also be used to enhance fluorescence imaging, a standard technique for imaging at the cellular level. Additionally, checking patient safety by monitoring the exhaled breath (capnography) can also be enhanced through the use of optical filters. Finally, many gas sensors designed for monitoring pollution will reply on optical cavities (two mirrors with highly-reflective coatings) for recycling the light and enhancing the signal associated with specular absorption.The industrial sponsorship included with this project demonstrates the commercial relevance.AimsThe University of Strathclyde has established novel ECR (electron cyclotron resonance) ion beam deposition, in addition to procuring the industry standard RF (radio frequency) ion deposition technology from Veeco (US). Scotland hosts a variety of world-leading laser engineering companies, and associated technologies, which could benefit from the capabilities at Strathclyde. Helia Photonics is a world-leader in advanced, high performance optical coating technologies, particularly for solid state laser coatings (laser diode bars). This project would be an ideal opportunity to explore a long-term, strategic partnership with Helia Photonics, in order to exploit the ECR ion beam deposition technology.Various optical materials will be investigated for optical coatings, including silica, silicon, tantalum pentoxide, zirconium dioxide, scandium oxide, hafnium dioxide and germanium. Alloys of these materials will also be investigated, as this can often help fabricated more stable amorphous structures, which in turn could improve the laser damage threshold performances.Working in partnership with Helia Photonics, we will aim to identify commercial applications for these coatings, with the aim to establish consultancy and contract work using the facilities at Strathclyde.