Very low threshold lasing in Er 3+ dopedZBLAN microsphere

Abstract
A green room temperature up-conversion laser has been demonstrated in a 120 µm diameter microsphere of Er3+ doped ZBLAN. Lasing occurs around 540 nm with a 801 nm diode laser pump. The lasing threshold of only 30 µW of absorbed power is over two orders of magnitude lower than the lowest previously observed.