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Tb 3+ -based gain materials possess potential for the realization of efficient and compact continuous wave and Q-switched visible lasers [1] , [2] , [3] . When pumped in the cyan-blue at around 486 nm, slope efficiencies of about 60 % on the green and up to 25 % on the yellow laser transition of Tb 3+ are routinely obtained using fluoride host materials [4] , [5] . However, despite very high doping concentrations up to stoichiometric Tb 3+ -crystals [4] , centimeter-long laser crystals are typically required to counterbalance the low absorption cross sections on this pump transition.

We report on UV-pumping of a visible Tb:LiLuF4 laser emitting at 544 and 588 nm. Pumping with a frequency-doubled Ti:sapphire laser at 359 nm significantly improves the absorption efficiency compared to conventional in-band pumping at ~488 nm and cross relaxation from the excited level 5D3 efficiently populates the upper laser level 5D4. In this way, optical efficiencies of 29% and 12%, respectively, are obtained with respect to the incident pump power. A passively Q-switched Tb:LiLuF4 laser at 544 nm using a Co2+-doped MgAl2O4 as a saturable absorber yields 23-µJ pulses at 3.5 kHz with a pulse duration of ~200 ns.

Trivalent terbium-doped materials have been attracting the attention of the scientific community due to the capacity of Tb3+ to emit in the visible range. Efficient laser operation at green and yellow wavelengths has been demonstrated previously while laser operation in the orange and red ranges is not expected due to detrimental excited state absorption (ESA) processes [1–4]. Previous research on laser operation of Tb3+ doped materials was performed under pumping with frequency doubled optically pumped semiconductor laser (2ω-OPSL). These blue emitting pump sources exhibit an excellent beam quality at output powers up to 5 W, but they are complex, bulky, and expensive, and thus not well suited for power scaling. Diode-pumping presents a cost-efficient alternative with potential for power scaling and miniaturization. The availability of InGaN-based blue laser diodes makes it possible to match the peak absorption wavelength of the 7F 6 → 5D 4 transition of Tb3+ ions around 488 nm.

We report on continuous-wave laser operation of T b 3 + : L i L u F 4 under UV pumping. More than five times higher absorption cross sections in the UV allow for shorter gain media, which are required for future high-power diode pumping. The cross-relaxation process is found to efficiently populate the upper laser level 5 D 4 at doping concentrations typically used in T b 3 + -doped gain media. Pumping with a frequency doubled Ti:sapphire laser at 359 nm enables laser operation in the green and yellow spectral range with slope efficiencies of 41% and 20%, respectively, at optical-to-optical efficiencies a factor of two higher than under cyan-blue pumping.

We report on our current research towards efficient lasers in the visible and mid-infrared spectral range using tailored active crystals. We achieved 0.45 W of direct yellow emission with Tb:LiLuF at a slope efficiency of 23 % and 0.28 W at 2856 nm at 20 % slope efficiency in Er-doped Scandia.

Up to 15 mW of continuous wave deep red laser output at 702 nm are demonstrated using an Eu-(7.6 at.%):LiYF 4 crystal under pumping with a frequency doubled Ti:sapphire laser at 393.5 nm.

We report on yellow Tb3+:LiLuF 4 solid-state lasers. Under 2.1 W of 2ω-OPSL-pumping at 486.2 nm the laser delivers 0.45 W of cw output at a wavelength of 587.5 nm and a slope efficiency of 23 %.

A Tb3+:KYW crystal was grown by the modified Czochralski technique. Polarized ground state absorption and fluorescence spectra, as well as a fluorescence decay curve, were recorded at room temperature. Radiative properties such as emission probabilities, branching ratios, and radiative lifetime were investigated within the theory of 4f–4f transition intensity in the case of a strong configuration interaction. The limitations of visible laser operation of Tb3+-doped double tungstate crystals are discussed.

We present, to the best of our knowledge, the most efficient solid-state laser directly emitting in the yellow spectral range. Without any nonlinear conversion steps, a Tb3+:LiLuF4 laser operates at a wavelength of 587.5 nm with an output power of 0.5 W and a record-high slope efficiency of 25% with respect to the absorbed pump power at 486.2 nm. Despite the detrimental influence of 4f-excited state absorption, this efficiency is comparable to those obtained by complex nonlinear methods to generate yellow laser emission. Our approach, in combination with the progress in laser diodes at the required pump wavelength, paves the way for the development of cost-efficient, robust, and easily manageable diode-pumped yellow laser sources.

Eu3+-doped LiYF4 is reexamined as a laser material for the visible spectral region. Polarized absorption and emission cross sections as well as the fluorescence lifetime are determined. Branching ratios and radiative lifetime are calculated within the theory of 4f-4f transition intensities, which takes into account the influence of an excited configuration of the opposite parity 4fN-15d. Continuous-wave laser operation at 702 nm is demonstrated with a maximum output power of 15 mW and a slope efficiency of 4.6% under pumping with a frequency-doubled Ti:sapphire laser at 393.5 nm.

We present a detailed characterization of Cr4+ and C02+ -doped oxides as saturable absorbers for the visible spectral region. The first visibly emitting Q-switched laser utilizing a C02+: Gd 3 Gas012 saturable absorber is demonstrated.

We report the first visibly emitting Q-switched laser based on Co2+:Gd 3 Ga 5 O 12 as the saturable absorber material and present a detailed characterization of the visible saturable absorption properties of various Co2+-doped materials.

Recent developments in the field of blue emitting InGaN-based laser diodes enabled novel diode-pumped solid state lasers with direct emission in the visible based on trivalent praseodymium and terbium as active ions.