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惰性气体的基本技术。将热量输送到较小的物理区域而不附带加热周围环境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。几十年来，激光加热一直是一项成熟的技术，但新类型的激光和将激光功率耦合到样品上的新方法继续使其应用多样化。在过去的几年里，这一领域最重要的发展是半导体激光器的迅速发展，它提供了高功率强度和极高的效率。这笔赠款将提供资金，用于购买新的75W半导体激光系统，用于加州理工大学的惰性气体实验室。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项目。一个重要的用途将是用于(U-Th)/He地质年代学的磷灰石、钛铁矿、锆石和氧化铁样品的传统激光放气。这种类型的地质年代学提供了关于岩石冷却历史的信息，在某些情况下还提供了关于其形成年龄的信息。第二个应用将是使用激光系统进行高温阶梯加热，具有出色的温度精度和精确度。这种能力对于确定稀有气体在矿物中的扩散很重要，而这反过来又对确定稀有气体年龄的意义很重要。例如，氦扩散测量表明，在磷灰石上确定的年龄提供了样品冷却到~65oC的时间信息。新系统有足够的功率，它还将被用来将大质量(100毫克)的样品放出到非常高的温度(1600摄氏度)。这一能力的一个重要应用是利用S地表最高几米岩石中宇宙射线轰击产生的~(21)Ne的累积，对地貌表面(如冰川冰川或古河道)进行测年。

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.