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Trivalent praseodymium doped materials are the most established gain media for solid-state lasers with direct visible emission. The progress in blue InGaN laser diodes (LD) and frequency doubled optically pumped semiconductor lasers (2ω-OPSL) enables efficient pumping of Pr3+-doped materials and efficient laser operation was realized in the cyan, green, orange, red and deep red parts of the optical spectrum [1]. The high gain and corresponding short upper state lifetime of several of these transitions should allow for comparably high pulse energies at high repetition rates e.g. in microchip configuration. This motivates a thorough investigation of the Q-switched operation of Pr:LiYF4 (Pr:YLF) and suitable modulators for this purpose. Previously, passively Q-switched diode-pumped Pr:YLF lasers were realized by using semiconductor saturable absorber mirrors [2] and Cr4+:YAG crystals [3]. Co2+: MALO crystals are well-known saturable absorbers for Q-switched eye-safe 1.5–1.6 μm lasers [4]. Here we report for the first time to our knowledge on a passively Q-switched Pr:YLF laser with Co2+:MgAl 2 O 4 (Co:MALO) as a saturable absorber.

Wavelength tuning experiments in the green spectral range applying Tbsup3+/sup-doped LiLuFsub4/suband Tbsup3+/sup/Nasup+/sup-codoped CaFsub2/subsingle 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 Tbsup3+/supin the CaFsub2/sub-matrix allowed for a continuous tuning range exceeding 10 nm. For initial characterization, free running continuous wave laser experiments using Tbsup3+/sup-doped LiLuFsub4/sub, Nasup+/sup:CaFsub2/sub, and stoichiometric TbFsub3/subcrystals were carried out resulting in efficient continuous wave laser operation in the green spectral region. The density of active centers in TbFsub3/subis 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 Tbsup3+/sup-densities are essential to compensate for the adherent low absorption cross sections at useful pump-wavelengths.

We report on diode-pumped laser operation of Pr3+,Mg2+:SrAl12O19 at lasing wavelengths of λ L = 724.4 nm, λ L = 643.5 nm, and λ L = 622.8 nm. Furthermore, the laser threshold could be reached in the green spectral range. By pumping the crystal longitudinally from each side with two polarization beam combined InGaN laser diodes, a total pump power of ≈4 W was available. In the deep red spectral range, a maximum output power of 564 mW was achieved with a maximum slope efficiency of 50 % with respect to the absorbed pump power. The maximum possible internal losses were estimated to ≈1 %. Beam quality factors M 2 were in the range of 1.2–1.5.

We report on the crystal growth, spectroscopic properties and visible laser performances of Pr3+-doped Sr0.7La0.3Mg0.3Al11.7O19 (ASL). ASL crystals doped with 2 at.% and 4 at.% Pr3+ were grown by Czochralski method. The laser experiments were carried out in a plane-concave resonator under excitation at 486 nm, provided from a 2ω-OPSL. Efficient laser emission was obtained with an 8 mm long sample of Pr(2at.%):ASL. The maximum output power amounted to 267 mW, 52 mW, and 318 mW at an absorbed power of 1.2W for red, orange, and deep red emission, respectively.

We report on blue semiconductor laser pumped solid-state lasers doped with different rare earth ions with emission wavelengths in the visible spectral range. Highly efficient, tunable and pulsed lasers are presented.

We report on the Czochralski growth of monoclinic β- BaLu 2 F 8 single crystals. The solid-state phase transition was quenched by substituting 20% of the Lu3+-ions with Tb3+. An efficient green emitting Tb3+:BaLu 2 F 8 -laser could be demonstrated as well.

By proper selection of pump light wavelength, polarization, and crystal orientation, linearly polarized laser output, independent dual wavelength operation, and intracavity frequency doubling can be obtained in the cubic crystal Pr3+:KY3F10.

We obtained up to 0.9 W of cw green output at 544 nm with highly Tb3+-doped LiLuF4 under pumping with a 2ω-OPSL at 486 nm and investigated the laser performance at different doping concentrations.

We report on a 2ω-OPSL-pumped passively Q-switched Pr3+:LiYF4 laser operating at the wavelengths of 523, 607, and 640 nm. For this, we utilized a Co2+-doped MgAl2O4 (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.

We realized the first visible Sm3+-doped oxide laser. In Sm(6.7at.\%):SrAl12O19 28mW of self-pulsed average output power at 703.0nm were achieved with 8% slope efficiency under 2o-OPSL-pumping at 479.6nm. Furthermore, detailed spectroscopic investigations were performed.

Crystal growth and a basic spectroscopic characterization of Pr3+-doped orthorhombic β-(Y0.5Gd0.5)F3 single crystals was performed. Laser operation on transitions in the green to the red spectral region could be demonstrated under InGaN laser diode excitation.

Recent developments in blue emitting laser sources, in particular InGaN laser diodes (InGaN-LDs) and frequency doubled optically pumped semiconductor lasers (2ω-OPSLs), opened access both to visible laser operation with unprecedented efficiencies in the well-established praseodymium doped laser systems [1, 2] as well as to the realization of new rare earth based solid state laser systems with emission wavelengths in the visible spectral range [3].

We report to the best of our knowledge on the first green laser operation of a Pr3+-doped crystalline waveguide laser. Furthermore red and deep red laser operation with output powers of > 1 W and >500 mW was achieved. The optical-to-optical efficiency was as high as 31% and 19%, respectively.

We report on laser operation in the visible spectral region of Pr,Mg:CaAl12O19. Output powers and slope efficiencies in excess of 300 mW and 25 % were achieved, respectively. In addition spectroscopic investigations will be presented.

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.

We report on the crystal growth of the orthorhombic low-temperature β-phase of (Y0.5,Gd0.5)F3 (YGF) single crystals. The crystals were activated with trivalent praseodymium (Pr3+) and characterized with respect to their ground state absorption and stimulated emission properties. Under InGaN-laser-diode pumping, laser oscillation was obtained at more than ten wavelengths in the green, orange, red, and dark red spectral regions. In these initial experiments, output powers exceeding 100 mW and slope efficiencies between 10% and 30% were obtained. To the best of our knowledge, these results represent the first application of YGF crystals as laser host material for any active ion.

In this paper we report on the suitability of Ho3+:LiLuF4 and Ho3+:LaF3 as active media for solid state lasers emitting in the green spectral region. The ground state absorption spectra were measured and employed to calculate the emission cross section spectra via the reciprocity method. These allowed to derive the gain characteristics for various inversion ratios. The decay dynamics of the 5F4,5S2 multiplet, which would act as upper laser level, were investigated to estimate the quantum efficiency. Measurements of the excited state absorption were conducted which showed that stimulated emission is the dominating effect around 550 nm. Laser operation was demonstrated in the green spectral region by employing Ho3+:LaF3 as gain medium. Laser oscillation occurred in a self-pulsed regime with a maximum average output power of 7.7 mW, a repetition rate of 5.3 kHz, and a pulse duration of 1.6 μs. To the best of our knowledge this constitutes the first green laser emission of a Ho3+-doped crystal at room temperature.

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.

We present first results in applying the thin-disk concept to lasers directly emitting in the visible spectral range. The pump light was provided by 24 InGaN laser diodes emitting 1 W each at 444 nm, which were coupled into a 200 μm fiber. A 300 μm thin Pr3+,Mg2+:SrAl12O19 crystal served as gain medium. In continuous-wave operation an output power of 0.88 W and a slope efficiency of 12% with respect to the absorbed pump power were achieved at an emission wavelength of 643.5 nm. Modulating the pump source at a duty cycle of 10% yielded an instantaneous output power of 1.67 W, corresponding to a slope efficiency of 26%.

We report on the crystal growth, spectroscopic investigations, and the demonstration of visible laser operation of Pr,Mg:CaAl12O19. Crystals with dopant concentrations of 1 and 6 at. % were grown by the Czochralski method. Polarization-dependent ground-state absorption and emission spectra as well as the excited state absorption characteristics were recorded in the visible spectral region. Furthermore, the decay dynamics of the P03 manifold and the radiative lifetime were determined. By employing a 6 at. % doped Pr,Mg:CaAl12O19 crystal as gain medium and a frequency doubled optically pumped semiconductor laser as pump source, cw laser operation was realized at 644.3 and at 725.2 nm. Maximum output powers and slope efficiencies exceeded 320 mW and 25%, respectively.

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 the fabrication and visible laser operation of Pr,Mg:SrAl12O19 waveguides. Waveguiding structures were created by focusing the radiation of a femtosecond Ti:sapphire laser into bulk material. Guiding losses were determined to be as low as 0.12 dB cm(-1) at 632.8 nm. By employing a frequency-doubled optically pumped semiconductor laser, waveguide laser operation was realized at wavelengths of 525.3, 644.0, and 724.9 nm with output powers as high as 36, 1065, and 504 mW, respectively. To the best of our knowledge this is the first demonstration of green laser operation in a Pr(3+)-doped crystalline waveguide laser.

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 our latest laser results on Pr3+, Sm3+, Tb3+, Dy3+, Ho3+, and Er3+ doped lasers in the visible spectral range pumped with blue emitting semiconductor based pump sources.