Development of Crystal Furnace to Produce Large Single Crystal Nd:YAG Slabs for High Power Industrial Laser Systems

9413860目前美国的板材(尤其是汽车)行业需要高功率和高重复频率的激光器，这些激光器可通过光纤传输，并连接到机械臂上，用于高速和高精度的钻孔、切割和焊接过程。虽然现在电源和光学传输系统都可用，但激光系统的心脏--激光介质--仍然缺失。激光介质是在相干(激光二极管)和非相干(闪光灯)泵浦下产生激光功率的大尺寸单晶NdYAG板。目前最先进的生长工艺被限制为最大25x200x10mm3的板坯，这是由于熔体拉制单晶的固有芯缺陷。基于板条结构的激光器可以以更简单的设计和更高的效率产生更多的功率。它与现有的二极管阵列泵浦设计非常吻合。我们建议建立一种新的晶体生长系统来生长这种晶体。该系统由学生和科研人员自行设计、建设和运行。它将提供巨大规模的培训经验。该系统原理上采用三个射频感应加热区的高温轮廓控制，并在超过2000℃的温度下进行精确的温度轮廓控制。系统全自动，采用自适应PID反馈控制，通过计算机监控从升温到生长的整个生长周期，并同时在所有区域冷却。该系统的原型已经具备了生产高达125×300×10 mm~3的单晶片的能力。在这种新系统中生产的晶体将不会含有传统晶团中常见的芯状或角状生长条纹。通过这种工艺生产的晶体能够提供几千瓦的功率，重复频率为几千赫兹，每个脉冲的焦耳能量接近折射限制的光束质量，因此它可以通过光纤传输。这是我国在晶体生长技术上向前迈出的一大步。拟议中的系统将是美国唯一的系统。目前，日本和中国都追求相同的目标，并取得了良好的进展。这项技术的好处是生产出所需的Nd：YAG晶片，这将为各种工业应用创造一个全新的新一代激光制造系统。我们的生长系统，一旦其运作完善，可以进一步扩大规模，为大口径激光传输系统生产更大尺寸的板材。它将开启一个研究和制造的全新时代。这种高功率板条激光器的另一个潜在用途是建立用于亚微米光刻应用的台式软X射线产生系统。这将为中小型公司(他们负担不起同步辐射设施)提供一个低成本的系统，使他们能够在任何他们选择的地点制造自己的芯片，以便在市场上竞争。***

9413860 Chai Current U.S. sheet metal (especially auto) industries have the need of high power and high repetition rate lasers which are deliverable via optical fibers and linked to robotic arms for high speed and high precision drilling, cutting and welding processes. While both the power supply and optical delivery system are available now, the heart of the laser system, the lasing medium, is still missing. The lasing medium is a large single crystal Nd:YAG slab which produces the laser power under either coherent (laser diode) or incoherent (flash lamp) pumping. Current state-of-the-art growth process is limited to a maximum of 25x200x10mm3 slab due to intrinsic core defects in melt pulled single crystals. Lasers based on slab configuration can generate more power with simpler design and better efficiency. It fits well with current diode array pumping design. We propose construct a novel crystal growth system to grow such Nd:YAG slabs. The system is designed and will be constructed and operated by the students and research staffs. It will provide training experience of enormous scale. It is based on high temperature profile control operating at principle with three RF induction heated zones and precise temperature profile control operating at temperature in excess of 2000{SYMBOL 176 \f "Symbol"}C. The system is fully automatic using adaptive PID feed-back control with a computer to monitor the entire growth cycle from heating up to growth and to cool down in all zones simultaneously. The system in its proto-form already has the capability of producing up to 125x300x10mm3 single crystal slabs. The Nd:YAG crystals produced in this new system will not contain core nor angular growth striations which are common in conventional crystal boules. The crystals produced by this process is capable to deliver multi-kilo watt power with multi-kilo hertz repetition rate and joules energy per pulse in near defraction limited beam quality so that it is deliverable via optical fibers. Our pr ocess represents a giant step forward in the Nd:YAG crystal growth technology. The proposed system will be the only one in the U.S. At present, both Japan and China have pursued the same aim with good progress. The benefit of this technology is to produce the needed Nd:YAG crystal slabs which will create a totally new generation laser manufacturing systems for a variety of industrial applications. Our growth system, once perfects its operation, can be further scaled up to produce even larger size slabs for large aperture laser beam delivery systems. It will open a total new era for both research and manufacture. Another example of potential use of this high power Nd:YAG slab laser is to build a table top soft x-ray generating system for sub-micron lithography applications. This will provide a low cost system for small to medium companies (who can not afford synchrotron radiation facilities) to be able to manufacture their own chips at any locations of their choice to compete in the market. ***