Abstract

We investigate, both theoretically and experimentally, the spectroscopic and lasing properties of a Cr⁴⁺:YAG gain medium, which is of interest for near-infrared (NIR) tunable laser applications. In the theoretical part, the crystal-field energy levels for the Cr⁴⁺ ions in the D_2d site symmetry in the YAG lattice are investigated by diagonalizing the Hamiltonian matrices including the electrostatic term, the Trees correction and the crystal- field interaction. It is shown that the strong NIR absorption around 1000 nm is due to transitions from the ground state to the ³A₁(³T₁) state. The excited-state absorption transitions at the pump and lasing wavelengths are investigated. The zero-field splitting for the ground state is also considered taking into account the spin-orbit coupling. In the experimental part, we constructed a cw tunable Cr⁴⁺:YAG laser system pumped with a Nd:YAG laser in cw mode. The laser is broadly tunable from 1345 to 1557 nm using a birefringent filter and a 1% transmission output coupler. The tuning range of more than 200 nm is the broadest reported so far with one set of mirrors. The emission excited-state absorption cross sections for free-running modes are estimated from the laser efficiency data taking into account the pump and cavity parameters.

© 1998 Optical Society of America