Performance and wavelength tuning of green emitting terbium lasers.

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.

Spectroscopy and laser operation of Sm(3+)-doped lithium lutetium tetrafluoride (LiLuF(4)) and strontium hexaaluminate (SrAl(12)O(19)).

We report on laser operation in the orange and red spectral range in samarium (Sm(3+))-doped fluoride and oxide crystals at 300 K. Sm(3+)-doped LiLuF(4) (LLF) and SrAl(12)O(19) (SRA) crystals were grown by the Czochralski-technique and utilized for spectroscopic investigations and laser experiments. The spin-forbidden transitions of Sm(3+)exhibit low cross sections the order of 10(-21) cm(2), but high radiative upper state lifetimes of several ms in both crystal systems. Under 2ω-OPSL-pumping at 480 nm, orange laser operation was achieved with Sm:LLF and Sm,Mg:SRA at lasing wavelengths of 606 nm and 593 nm, respectively. Furthermore laser oscillation was demonstrated at 648 nm in the red and 703 nm in the deep red spectral range with Sm:LLF and Sm,Mg:SRA, respectively. Output power levels of several 10 mW were obtained at slope efficiencies of up to 15 %. Most of the realized lasers were operating in a strongly modulated or even self-pulsing regime.

SESAM mode-locked red praseodymium laser.

We present the first semiconductor saturable absorber mirror (SESAM) mode-locked praseodymium solid-state laser. The laser is based on a Pr(3+):LiYF(4) crystal as gain medium and a GaInP-quantum well-based SESAM. Self-starting continuous-wave mode-locked laser operation with an average output power of 16 mW is achieved at a center wavelength of 639.5 nm. The laser operates at a repetition rate of ∼85.55 MHz and emits pulses with a duration of ∼18 ps.

Yellow laser performance of Dy³âº in co-doped Dy,Tb:LiLuF4.

We present laser results obtained from a Dy³âº-Tb³âº co-doped LiLuF4 crystal, pumped by a blue emitting InGaN laser diode, aiming for generation of a compact 578 nm source. We exploit the yellow Dy³âº transition 4F(9/2)⇒6H(13/2) to generate yellow laser emission. The lifetime of the lower laser level is quenched, via energy transfer, to co-doped Tb³âº ions in the fluoride crystal. We report the growth technique, spectroscopic study, and room temperature continuous wave laser results in a hemispherical cavity at 574 nm, and with a highly reflective output coupler at 578 nm. A yellow laser at 578 nm is very relevant for metrological applications, in particular for pumping of the forbidden ¹S0-³P0 ytterbium clock transition, which is recommended as a secondary representation of the second in the international system of units.

High-power red, orange, and green Pr³âº:LiYF4 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.

Thin-disk laser operation of Pr³âº,Mg²âº:SrAl12O19.

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%.