| Nd-doped vanadate crystals, such as Nd:YVO4, Nd:GdV04 and Nd:LuVO4, have been proved to be ideal materials for continuous-wave lasers, because of their excellent characteristics, including broad absorption bandwidth, large emission cross section, low laser threshold as well as polarized output. Nevertheless, their limited energy storage ability has prevented them from generating large pulse energy and high peak power in the pulse laser operation. As a typical material for pulse lasers, Nd:YAG also has some disadvantages, including relatively lower efficiency, unpolarized output, thermal-induced birefringence and so on. Therefore, it is necessary to explore some new materials that are more competent for the pulse laser operation.In recent years, Nd-doped vanadate mixed crystals have been developed, such as Nd:GdxY1-xVO4 and Nd:LuxGd1-xVO4. Compared with Nd-doped vanadate single crystals, the mixed crystals are found to possess better performances in the pulse laser operation, due to the inhomogeneous broadening effect of their spectra. We speculate that the Nd:LuxY1-xVO4 mixed crystals should also possess the similar properties as Nd:GdxY1-xVO4 and Nd:LuxGd1-xVO4 that are beneficial to their applications in the pulse laser operation. During the past two years, Nd:Lu0.15Y0.85VO4, Nd:Lu0.2Y0.8VO4 and Nd:Lu0.5Y0.5VO4 have been investigated successively. In those papers, the three mixed crystals were reported independently and the main contents were concentrated on their spectra and laser performance. When it comes to our study, a series of Nd:LuxY1-xVO4 mixed crystals with multiple components are grown and researched systematically. We believe such a systematic work will be a good reference to the further development and application of Nd:LuxY1-xVO4 mixed crystals.Six kinds of Nd:LuxY1-xVO4 mixed crystals with different Lu/Y ratios were grown by the Czochralski method. The compositions of Nd:LuxY1-xVO4 mixed crystals were measured by X-ray fluorescence analysis. Experimental results show that the Nd concentrations in all crystals are about 0.1 at.% and the Lu compositions are 10%,26%,41%,61%,67%,80%, respectively. The structures of the as-grown mixed crystals were measured by X-ray powder diffraction (XRPD). Experimental results show that all the Nd:LuxY1-xVO4 mixed crystals possess the ZrSiO4 structure, with a tetragonal space group of I41/amd. Apart from the XRPD, the high resolution X-ray diffraction (HRXRD) of Nd:LuxY1-xVO4 were also measured, through which we find the as-grown mixed crystals possess good integrity of crystal lattice.We measured the density, specific heat, thermal expansion, thermal conductivity and calculated the material constant of Nd:LuxY1-xVO4. The room-temperature densities of the mixed crystals are nearly linear with the parameter x and increase gradually when x tends to 1.00. The first three mixed crystals possess relatively higher specific heat, which are very close to that of Nd:YVO4 single crystal, the other mixed crystals are more close to Nd:LuVO4 single crystal, possessing the lower specific heat. The thermal expansion anisotropy is on the rise when the parameter x tends to 1, but they are all lower than that of Nd:LuVO4. This can effectively protect the mixed crystal from cracking caused by thermal expansion during crystal growth, processing and applications. The thermal conductivity as well as the material constant of Nd:LuxY1-xVO4 mixed crystals are larger than that of Nd:YVO4 single crystal. Therefore, it can be predicted that the Nd:LuxY1-xVO4 mixed crystals can endure more thermal stress than Nd:YVO4 single crystal, which will be helpful for their applications in middle or high power lasers.In the spectral experiments, we mainly measured the absorption spectra and emission spectra of Nd:LuxY1-xVO4. Based on the J-O theory, we calculated the radiative lifetimes and emission cross sections of Nd:LuxY1-xVO4 crystals as well. The full width at half-maximum (FWHM) of 809 nm absorption peak (π-polarized) for Nd:LuxY1-xVO4 mixed crystals are much wider than those of Nd:YVO4 and Nd:LuVO4 single crystals, owing to the over-lapped inhomogeneous broadening effect in the Nd:LuxY1-xVO4 mixed crystals. The fluorescence lifetimes of Nd:Lu0.10Y0.90VO4, Nd:Lu0.26Yo.74VO4 and Nd:Luo.41Y0.59VO4 are longer than Nd:YVO4 single crystal. The fluorescence lifetimes of Nd:Lu0.61Y0.39VO4, Nd:Luo.67Y0.33VO4 and Nd:Lu0.80Y0.20VO4 are similar with Nd:YVO4 single crystal, but still longer than Nd:LuVO4 single crystal. The stimulated emission cross sections at 1064 nm of Nd:LuxY1-xVO4 mixed crystals take on an opposite tendency with the fluorescence lifetimes, showing a descending trend compared with the relevant vanadate single crystals.Based on the rate equations of four-level system, we theoretically deduced the output parameters used for continuous-wave laser and passively Q-switched laser. We measured the continuous-wave and passively Q-switched laser performances of Nd:LuxY1-xVO4.In the passively Q-switched laser experiment, we obtain a maximum pulse energy of 169μJ and a highest peak power of 26.4kW with Nd:Lu0.10Y0.90VO4, which are much better than that of Nd:YVO4 (36μJ,3 kW) and Nd:LuVO4 (71μJ,4.4 kW), exhibiting obvious enhancement of pulse energy. |
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