Acquisition of a Diode Laser for Noble Gas Geochemistry at Caltech

激光加热是从岩石和矿物样品中提取稀有气体的一项重要技术。在不附带加热周围环境的情况下将热量传递到小物理区域的能力允许真空系统的小型化，更高的最高可达到温度，最重要的是，大大减少了分析空白。激光加热是一项已有几十年历史的技术，但新型激光器和将激光功率与样品耦合的新方法继续使其应用多样化。在过去几年中，该领域最重要的发展是二极管激光器的迅速普及，它提供了极高的功率强度和效率。这笔资金将用于购买一个新的75w二极管激光系统，用于加州理工学院的惰性气体实验室。新的激光系统将用于目前由国家科学基金会支持的许多不同的项目。一个重要的应用将是传统的激光除气磷灰石、钛矿、锆石和氧化铁样品，用于(U-Th)/He地质年代学。这种类型的地质年代学提供了岩石冷却历史的信息，在某些情况下还提供了岩石形成年龄的信息。第二个应用将是使用激光系统的高温步进加热具有优异的温度精度和精度。这种能力对于确定稀有气体在矿物中的扩散率是很重要的，而这又对确定稀有气体年龄的意义是很重要的。例如，氦扩散测量表明，在磷灰石上测定的He年龄提供了样品冷却至~65℃的时间信息。新系统有足够的功率，它也将用于将大质量（100毫克以上）样品排出到非常高的温度（1600摄氏度）。这种能力的一个重要应用是利用宇宙射线轰击地球上最上面几米岩石中21Ne的积累来确定地貌表面（例如，冰川冰碛或化石河道）的年代。年代的表面。

Laser heating is an essential technique for the extraction of noble gases from rock and mineral samples. The ability to deliver heat to a small physical region without incidental heating of the surroundings allows for miniaturization of vacuum systems, higher maximum achievable temperatures, and, most importantly, substantial reduction in analytical blanks. Laser heating has been an established technique for several decades, but new types of lasers and new ways to couple the laser power to the sample continue to diversify its application. The most important development in this field in the last several years has been the rapid proliferation of diode lasers which provide high power intensity with extremely high efficiency. This grant will provide funds to acquire a new 75 W diode laser system for use in the noble gas laboratory at Caltech.The new laser system will be used for many different projects currently supported by the National Science Foundation. One important use will be traditional laser outgassing of apatite, titanite, zircon, and iron oxide samples for (U-Th)/He geochronology. This type of geochronology provides information on the cooling history of rocks and in certain cases on their formation age. A second application will be the use of the laser system for high temperature step-heating with excellent temperature accuracy and precision. This capability is important for determining the diffusivites of noble gases in minerals, which in turn is important in establishing the meaning of noble gas ages. For example, helium diffusion measurements indicate that He ages determined on apatite provide information on the time at which the sample cooled through ~65oC. The new system has sufficient power that it will also be used to outgas large masses (100 mg+) of sample to very high temperatures (1600 oC). An important application of this capability is to the dating of geomorphic surfaces (e.g., glacial moraines or fossil river channels) using the accumulation of 21Ne from bombardment of cosmic rays in the uppermost few meters of rock at the Earth?s surface.