Abstract

We have investigated the cw laser properties of the lanthanide aluminate La_0.9Nd_0.1MgAl₁₁O₁₉ (LNA) at room temperature. The pump source is an Ar⁺ laser (5145 Å) or a Kr⁺ laser (7512 Å) focused onto an LNA crystal. The rod is 1 cm long and cut parallel to the c axis of its hexagonal structure.¹ Continuous wave laser emission is observed at 1.054 μm with a 10% efficiency for Ar⁺ pumping and 26% for Kr⁺ pumping.² By inserting a one-plate Lyot filter in the cavity, one can force oscillation on a secondary peak at 1.082 μm and achieve some tuning of the laser emission (35 Å on the 1.054-μm band and 75 Å on the 1.082-μm band). This tuning range is related to the relatively broad width of the fluorescence lines of Nd³⁺ in LNA. Such a laser is a convenient light source for optical pumping of helium metastable atoms making use of the 2³S–2³P atomic transition at 1.083 μm. Laser cavities have been designed delivering powers exceeding 100 mW with an appropriate mode structure³ when pumped with 1.5 W from a Kr⁺ laser (see Fig. 1). Nuclear polarization up to 50% can be achieved in a cell filled with ³He to a pressure of 0.3 Torr. Compared with color center lasers, LNA lasers have several advantages for optical pumping of metastable helium: they operate continuously at room temperature without degradation in time. It may become possible to pump LNA lasers by lamps² as soon as long enough LNA rods can be grown. Such compact, reliable, and possibly powerful laser sources at 1.083 μm could be useful for the applications of polarized helium to nuclear beam and target experiments⁴ as well as for the field of spin-polarized quantum fluids at low temperature. LNA lasers, pumped by either lamps or laser diodes, could also favorably replace conventional light sources in optically pumped ⁴He and ³He magnetometers.

© 1986 Optical Society of America