The crystal structural parameters of Nd3+-doped rare earth orthotantalate GdxLu1−xTaO4 (x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction, and its emission and excitation spectra at 77 K are analysed. The relativistic model of ab initio self-consistent DV-Xα method, which is applied to the cluster NdO8 in GdxLu1−xTaO4, and the effective Hamiltonian model are used to investigate its spin—orbit and crystal-field parameters. The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm−1. According to the crystal-field calculations, 96 levels of Nd3+ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd3+:YAlO3. The results indicate that the free-ion parameters are similar to those of the Nd3+ in GdxLu1−xTaO4 and YAlO3 hosts, and the crystal-field interaction of Nd3+ in GdxLu1−xTaO4 is stronger than that in YAlO3.

5 at%Yb3+:YNbO4 crystal is grown by Czochralski(CZ) method. Its transmission and emission spectra are measured. The absorption peaks are located at 933, 955, 974 and 1003 nm with their corresponding absorbtion cross section values 0.7310-20, 1.8510-20, 0.8610-20 and 0.4410-20 cm2; and the FWHM of 955 nm absorbtion peak is 17 nm. Its emission band centered at 1020 nm with the FWHM is 41 nm, which is over three times that of Yb3+:YAG crystal. The emission cross section values of 955, 974, 1005, 1021 and 1030 nm peaks are calculated to be 0.6910-20, 0.8610-20, 1.8110-20, 1.1110-20 and 0.5710-20 cm2, respectively, and the biggest one is comparable to that of Yb3+:YAG crystal. The laser parameters of 5 at% Yb3+:YNbO4 crystal are evaluated and the results suggest that it is a potential all-solid-state pumped laser crystal in tunable and ultrafast lasers field.

A Cassegrain optical antenna with parabolic structure is designed. By detailed analysis of Cassegrain optical antenna in partial axis situation，the expression of the area of the receiving spot and the power decline curve are obtained for different deflection angles. The relations between the received antenna gain and the wavelength and deflection angles are discussed in partial axis situation，the curves of gain for partial axis and axis alignment are simulated. The simulation result indicates that the gain of the maximal partial axis decreases by 6.564dB compared with that of axis alignment. Experiments of the optical spot test and the antenna coupling efficiency test are carried out separately for axis alignment and certain partial axis situations. The results show that the antenna coupling efficiency under partial axis situation is 26.97% lower than that of axis alignment. This study will provide a theoretical foundation for the control system to realise perfect alignment of optical axis in inter-satellite optical communications.

In this paper, the refractive index of GdTaO4 crystal is measured by the auto-collimation method. GdTaO4 crystal is processed into three rectangular prisms, their planes with longer right angle side are planes a, b and c of the crystal, respectively, and their normal directions are the directions of crystal plane axes a, b and c, respectively. with a side by angle . Plane enclosed by hypotenuse and the longer right angle side is subjected to fine polishing, while the surface plating for the latter is subjected to Al reflectance coating, so that the light is incident along the hypotenuse plane with minimum angle of deviation (), reflects on the plane with longer right angle and returns along the original path. The rectangular prisms processed by GdTaO4 crystal are placed on the platform of 32 J goniometer with an accuracy of arc seconds. The 473, 532 nm YAG double frequency laser, 633 nm He-Ne laser and 1064 nm YAG laser with stable light intensity are used as a measuring light source, light will refract into the light perpendicular to the longer right angle side when the laser of measuring light source shoots towards the bevel of a prism with a minimum angle of deviation (). The refractive indexes nx, ny, and nz of a crystallographic axis directions can be measured by , and the relationship between refractive index ellipsoid section and prism refraction of light. The constants Ai, Bi, Ci, and Di (i=x, y, z) are given in Sellmeier's equation ni2 =Ai+Bi/(2-Ci)-Di2, and the values of angle Vz included between light axis and refractive index at wavelengths of 473, 532, 632.8 and 1064 nm are calculated to be 22.5, 22.5, 21.9 and 22.0, respectively. It is proved that GdTaO4 crystal is optically positive biaxial crystal.

In this paper, the DV-X method of ab-initio calculations and the effective Hamiltonian model are introduced to calculate the crystal-field and spin-orbit parameters of rare earth ions doped in various crystals, especially for the crystal with low-symmetry. For the low-symmetry crystal, the number of parameters is more than that of energy levels, thus experimental energy levels fitting cannot determine all parameters, while ab-initio calculations can determine all crystal-field and spin-orbit parameters accurately. Firstly, the crystal-field and spin-orbit parameters of Yb3+ doped in GdTaO4 crystal are calculated by this model, and then the energy level structure of Yb3+:GdTaO4 is given and the continuous emission band of Yb3+:GdTaO4 emission spectrum is analyzed, which is conducive to the laser tunable and laser mode-locking output, so Yb3+:GdTaO4 is a potential laser medium for high efficiency laser operation and new ultrashort pulse output. Also, the crystal-field and spin-orbit parameters of Yb3+ doped in YTaO4 and ScTaO4 are calculated by this model, and the energy level structures of Yb3+:YTaO4 and Yb3+ :ScTaO4 are given, which leads to a conclusion similar to that drawn from the Yb3+:GdTaO4 crystal.