Active and passive materials for miniature diode-pumped 1.5 μm erbium glass lasers

The 3-level nature of erbium ions lasing at 1.5 μm requires minimizing the volume of the active medium in order to reduce the lasing threshold. Efficient optical pumping of small volumes of bulk laser glass needs high pump extinction in the laser medium, i.e. as high Yb concentration as technologically possible. The main problem in this case is to avoid crystallization of the concentrated glasses. Our search for a stable concentrated glass composition resulted in developing a technologically producible Yb-Er glass containing 4.2×10²¹ cm^-3 of ytterbium ions about twice as usually used in commercially available laser glasses. This feature makes efficient pumping of small (2-3 mm) laser rods easily possible without bothering about the exact pump wavelength (in the range from ∼850 to 1000 nm) and without LD array thermal stabilization. A secondary goal was the development of a new Yb-Er activated laser glass that should combine good laser efficiency and sufficiently higher thermo-mechanical properties them the available ones. We have investigated another cobalt-doped material for passive Q-switching of erbium glass lasers: magnesium-aluminum spinel MgAl₂O₄ grown by a number of methods: Czochralski, flux and Verneuil.