The Na+-Yb3+ (or Er3+) co-substitution of Ca2+ in Ca3Nb1.5Ga3.5O12 (CNGG) laser crystal is studied. In contrast to other garnets whose structural disorder is exclusively based on the presence of differently sized cations on the same crystal sites, Na+ incorporated in the dodecahedral site (a site also shared by Ca2+ and trivalent lanthanides) creates diverse electric charge distributions over the dodecahedral sublattice, which adds to the disorder associated with Nb5+ and Ga3+ simultaneous occupation of the octahedral and tetrahedral sites. The currently determined cationic compositions of Czochralski grown congruent CNGG and Na-modified CNGG crystals show that Na+ incorporation reduces the cationic vacancy concentration on dodecahedral and octahedral sites but does not affect that in tetrahedral sites. Physical properties of interest for laser design (optical transmission, elastic constants, hardness, specific heat, thermal conductivity, thermal expansion, refractive index dispersion, group velocity dispersion, and thermo optic coefficients) have been systematically determined at cryogenic temperatures and above room temperature. Na+ incorporation into CNGG decreases the crystal growth temperature, promotes Yb3+ doping, and importantly, increases the Yb3+ optical bandwidth, offering good prospects for the implementation of ultrashort pulses in mode-locked laser oscillators.

Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.A detailed analysis of the electrostatic interaction between an electrostatic force microscope tip and a thin film is presented. By using artificial neural networks, an equivalent semiinfinite sample has been described as an excellent approximation to characterize the whole thin film sample. A useful analytical expression has been also developed. In the case of very small thin film thicknesses (around 1 nm), the electric response of the material differs even for very high dielectric constants. This effect can be very important for thin materials where the finite size effect can be described by an ultrahigh thin filmdielectric constant.This work was supported by TIN2010-196079. G.M.S. acknowledges support from the Spanish Ramón y Cajal Program

Here, a diode‐pumped laser based on trivalent terbium (Tb3+) as the active ion is reported. Optical pumping of a Tb3+‐doped lithium‐lutetium‐fluoride (LiLuF4) crystal with up to 200 mW from a diode laser emitting at a wavelength of 488.2 nm enables continuous‐wave lasing directly in the green and in the yellow. At an emission wavelength of 542 nm, the laser reaches an output power of up to 43.8 mW with a high slope efficiency of 52% with respect to the absorbed pump power. The yellow laser at 587 nm exhibits a slope efficiency of 22% and the output power of 13.8 mW is only limited by the available pump power. Laser thresholds as low as 14 and 27 mW of absorbed pump power are observed for the green and yellow, respectively. The investigations toward further optimization of the laser performance reveal that highly Tb3+‐doped materials are suitable for compact, efficient, and affordable diode‐pumped solid‐state lasers with direct emission in the visible spectral range. These results are of high relevance, as in particular for the yellow spectral range such systems are currently not available.

In recent years, Tb3+-based solid-state lasers with emission in the green and yellow have seen a revival. This was owed to the availability of blue emitting semiconductor-based pump sources and recent findings, which reported more than 60% slope efficiency in the green and about 25% slope efficiency in the yellow. In this paper we review the state of the art of Tb3+-based solid-state lasers. We summarize the spectroscopic properties and present new insights, which enable us to provide valuable guidelines and recommendations for the choice of host materials to further improve the performance of Tb3+-based solid-state lasers.