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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.

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.

Single crystals of Dy(3+)-doped YPO(4) have been grown from Pb(2)P(2)O(7) flux and investigated by optical spectroscopy techniques. The energy level scheme of the active ion has been deduced from the low temperature spectra and reproduced by means of a crystal-field calculation. The room temperature absorption spectra have been analysed in the framework of the Judd-Ofelt approach, and the results of this analysis have been applied in a discussion concerning the spectral composition of the visible luminescence.

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%.

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