Solid-state reactive sintering of polycrystalline Nd:YAG ceramic laser host materials using an 83 GHZ millimeter wave system

We are investigating the solid-state reactive sintering of polycrystalline Nd:YAG ceramic laser host materials using a high power millimeter-wave beam as the heat source. The starting powder is a mixture of commercially available alumina, yttria, and neodymia powders. The laser-quality results obtained using the solid-state reactive sintering approach and the same materials in a conventional vacuum furnace¹ provide a benchmark for our experiments, which are being carried out using the Naval Research Laboratory (NRL) 83 GHz Gyrotron Beam Material Processing Facility. One objective of our work is to determine the effect of millimeter-wave heating on processing variables such as temperature and hold time and on the microstructural properties impacting the laser host application. Another objective is to optimize the heating uniformity and efficiency of the process for future use in a manufacturing process. Initial experiments with 1-hour hold times have produced translucent samples whose microstructure is currently being evaluated. Longer processing times (up to 16 hours) were needed to achieve full transparency in a conventional furnace. Hold times longer than 1 hour were also investigated and will be reported.