We report, for the first time in a biaxial laser material, on the distribution of fluorescence cross sections in the index ellipsoid. The largest effective fluorescence cross section of pure NdP5O14 at room temperature (2.0±0.1) ×10−19 cm2 for light at 1.0512 μ wavelength polarized parallel to the 2 axis which coincides with the crystallographic b axis. We predict from the cross sections the cw thresholds and polarizations of the four highest‐gain laser transitions and verify the results quantitatively by operating one crystal in all major polarizations. We measured the major phase and group refractive indices and the thermal expansion coefficient of the optical lengths near 1.05 μ wavelength. We also discuss the twin domains which have different orientations of the crystallographic and optic axes. In imperfect crystals they can easily be created by thermal stresses which can drastically increase the laser threshold.

Anisotropy in the laser performance of NdP5O14

An x-ray diffraction and 31P MAS NMR study of rare-earth phosphate glasses of composition, (R2O3)xP2O5)1-x, where x = 0.175-0.263 and R = La-Er (except for Pm), is presented. The structures of these materials were investigated as a function of (a) rare-earth atomic number and (b) glass composition. The results show an increase in rare-earth coordination number from six to seven as the rare-earth ion increases in size. This effect is most evident for the rare earths, Ce, Pr and Nd, and appears to be independent of composition variation. The implications of sevenfold coordination in these glasses with respect to the possibilities of rare-earth clustering are discussed, as is the role of the incorporation of aluminium impurities in this regard. The increase in levels of cross-linking within the phosphate network, as a consequence of these small amounts of aluminium, is illustrated, as is the changing nature of the phosphate groups as a function of composition. The first reliable and quantitative parametrization of the second and third neighbour R-(O)-P and R-(OP)-O correlations is also given and the stability of the structures to strain when the glasses are drawn as fibres or exposed to different thermal conditions is described.

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An x-ray diffraction and 31P MAS NMR study of rare-earth phosphate glasses, (R2O3)x(P2O5)1-x, x = 0.175-0.263, R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er

Fluorescence of Pr3+-ions in La1−xPrxP5O14

Subsolidus phase equilibria in the system La2O3-P2O5 were established. The system contains six intermediate compounds having molar La2O3:P2O5 ratios of 3:1,7:3,1:1,1:2,1:3, and 1:5. It was found that the 3:1 compound has a phase transformation at 935°C. The 1:2 compound decomposes to a mixture of 1:1 and 1:3 at 755°C. The 1:3 compound melts incongruently to 1:1 and liquid at 1235°C and the 1:5 compound melts congruently at 1095°C. None of the lanthanum phosphates have lower temperature limits of stability.

J.P. Jeser

Papers

The growth of laser quality NdP5O14 crystals