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.

Laser experiments with Pr(3+):LiYF4 under excitation with a frequency doubled optically pumped semiconductor laser emitting 5 W at 479 nm were performed at seven different laser wavelengths of 523, 546, 604, 607, 640, 698, and 720 nm. At all these wavelengths the output power exceeded 1 W. The best performance at 523 nm with an output power of 2.9 W at a slope efficiency of 72% and an optical-to-optical efficiency of 67% with respect to the incident pump power represents the highest efficiency ever reported for a praseodymium-doped laser material.

In this work Tb 3+ is revisited as a laser ion for efficient visible laser operation. In detailed spectroscopic investigations of absorption and fluorescence properties we reveal, that neither the spin-forbidden transitions nor the widespread belief of excited state absorption or upconversion into 4f 7 5d 1 -states ultimately prevent efficient visible laser operation in Tb 3+ -doped fluorides. In contrast, the rise of blue semiconductor-based pump sources enabled us to achieve slope efficiencies up to 58% around 545 nm in the green spectral region in highly Tb 3+ -doped LiLuF 4 , LiYF 4 , KY 3 F 10 , β-BaLu 2 F 8 and LaF 3 crystals. In addition, we obtained laser emission from Tb 3+ in the yellow spectral region around 585 nm with slope efficiencies approaching 20%. To the best of our knowledge, these results represent the first continuous wave laser operation of Tb 3+doped crystals and demonstration of laser oscillation on the 5 D 4 → 7 F 4 -transition in this ion.

We report on wide spectral tunability of a quasi-continuous wave Pr(3+):KY(3)F(10) laser under InGaN laser diode excitation at 445 nm. The total tuning range exceeded 100 nm in the visible spectral range on several intervals between 521 nm and 737 nm. The broadest continuously tunable region of almost 50 nm extended from 688 nm to 737 nm. Furthermore we present what is to the best of our knowledge the first demonstration of continuous wave laser operation in Pr(3+):KY(3)F(10) on three transitions in the green spectral region. The highest output power of 121 mW was achieved at an emission wavelength of 554 nm with a slope efficiency of 27%.

We report on the first results of diode pumped laser operation of Pr3+:LaF3 in a quasi continuous wave (qcw) mode with average output powers of up to 80.0 mW (≈ 161.3 mW qcw) and a maximum slope efficiency of 37% at 719.8 nm. Furthermore it was possible to operate the laser at 537.1 nm and 635.4 nm and to tune the emission wavelength from 609 nm to 623 nm. The pump source was an InGaN laser diode with a maximum output power of 1 W at a central emission wavelength of 442 nm.

Wavelength tuning experiments in the green spectral range applying Tb³⁺-doped LiLuF₄ and Tb³⁺/Na⁺-codoped CaF₂ single crystals are presented. While in the former case almost 100 mW could be obtained throughout a total range of 7 nm, the inhomogeneously broadened emission features of Tb³⁺ in the CaF₂-matrix allowed for a continuous tuning range exceeding 10 nm. For initial characterization, free running continuous wave laser experiments using Tb³⁺-doped LiLuF₄, Na⁺:CaF₂, and stoichiometric TbF₃ crystals were carried out resulting in efficient continuous wave laser operation in the green spectral region. The density of active centers in TbF₃ is among the highest that can be obtained in solid state gain materials. Nevertheless, a slope efficiency as high as 32% was obtained from this crystal. High Tb³⁺-densities are essential to compensate for the adherent low absorption cross sections at useful pump-wavelengths.

In this Letter, we report on laser operation of Pr3+,Mg2+:SrAl12O19 pumped by a frequency-doubled optically pumped semiconductor laser. By employing a V-type cavity, we demonstrate cw laser operation at room temperature in the green spectral range in a doped oxide host for the first time to the best of our knowledge. Furthermore, efficient laser operation was realized in the orange, red, and deep red spectral range with output powers exceeding 1.1 W at emission wavelengths of 643.6 and 724.4 nm.

We report on a 2ω-OPSL-pumped passively Q-switched Pr:LiYF laser operating at the wavelengths of 523, 607, and 640 nm. For this, we utilized a Co-doped MgAlO (MALO) crystal as a saturable absorber in the visible range for the first time, to the best of our knowledge. In the green spectral region, the pulse duration was 210 ns with a pulse energy of 3.6 μJ and a repetition rate of 125 kHz. The minimum pulse duration of 87 ns at the highest pulse energy of 8.6 μJ was obtained at a repetition rate of 110 kHz at 607 nm. The highest Q-switched average laser power of 1.4 W was obtained at an absorbed continuous-wave pump power of 3.3 W with a slope efficiency of 47% at 640 nm. Absorption saturation measurements with Co:MALO were performed, and ground and excited state absorption cross sections in the visible spectral range were determined.