Out of the blue: semiconductor laser pumped visible rare‐earth doped lasers

The rise of semiconductor‐based pump sources such as In x Ga 1‐x N‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr 3+ , Sm 3+ , Tb 3+ , Dy 3+ , Ho 3+ and Er 3+ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd 3+ ‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.