Short vertical tube furnace for the fabrication of doped glass microsphere lasers

We report on the design of an electric tube furnace that can be used for the fabrication of doped glass microsphere lasers. The tube furnace has a short hot zone of length 133 mm and is based on a quartz tube design. Doped laser glass particles, specifically Er:Yb phosphate glass (IOG-2), of ∼1 μm diameter are blown into the furnace using a 60 ml syringe and microspheres ranging in size from 10 to 400 μm are collected at the output of the tube furnace in a Petri dish. The furnace operates at a wall temperature of ∼900 °C and is capable of making microspheres from glasses with glass transition temperatures of at least 375 °C. High quality (Q∼ ¹⁰⁵) whispering gallery modes have been excited within the microspheres by optically pumping at 978 nm via a tapered optical fiber.