Abstract

Recently we achieved tunable laser operation of Yb³⁺ in the uniaxial crystal NaY(WO₄)₂ or NaYW [1]. This compound belongs to a more general class of tetragonal double tungstates and double molybdates with nominal formula MT(XO₄)₂, where M and T are monovalent and trivalent cations respectively, and X=W or Mo. These compounds are locally disordered crystals due to the random distribution of M and T cations on the same lattice sites. Yb³⁺ dopant ions replacing T cations of the host experience a crystal field distribution, and the optical absorption and photoluminescence bands are broadened in comparison to ordered crystals, such as the monoclinic KT(WO₄)₂, T=Y, Gd, Lu. Continuous wave lasing of Yb³⁺ and tuning has been demonstrated already in NaGd(WO₄)₂, NaLa(W0₄)₂, NaLa(MoO₄)₂, and LiGd(MoO₄)₂ [2] but mode-locking has been reported only with 8 at. % Yb-doped NaGd(WO₄)₂ [3], achieving a pulse duration of 75 fs with a time-bandwidth product exceeding roughly 3 times the Fourier limit.

© 2007 IEEE