10 - The crystal field engineered

Summary

The successful launch of the alexandrite laser by Allied Chemicals Inc. and the elucidation of essential design parameters [Walling et al. (1979), (1980)] spawned rapid growth of research into Cr³⁺-based lasers [Caird and Payne (1991)]. Possible alternative gain media to alexandrite included the Cr³⁺-doped garnets [Struve and Huber (1985)]. However, the development of Cr³⁺ : colquiriite lasers at Lawrence Livermore National Laboratory [Payne et al. (1988a), (1989a)] deflected attention away from the Cr³⁺ garnets, these mixed fluoride gain media being as efficient as alexandrite and almost as broadband as Ti-sapphire. Two distractions from the dominance of Cr³⁺ ion broadband tunable lasers were the inventions of the Ti-sapphire (Ti³⁺ : Al₂O₃) [Moulton (1982a,b)] and the Cr⁴⁺ : forsterite [Petricevic et al. (1988)] lasers. At present Ti³⁺ : Al₂O3 and Nd³⁺ : YAG are the market leaders in solid state laser production against which new developments are assessed. Their pre-eminence derives in part from the quality and quantity of laser rods that can be produced at modest cost. Both materials have excellent photothermal and thermomechanical properties, and are robust components under laser operating conditions. However, despite much spectroscopic research Ti-sapphire is still the only usable Ti³⁺-activated solid state laser. In contrast, operation of several 3d²-ion doped lasers have been reported giving broadband tunability at near-infrared wavelengths (1.0–1.7 μm) which have potential applications in optical communications, medical sciences and on remote sensing LIDAR platforms.