Growth And Characterization Of Nd:Re_xGd_3-xGa₅O₁₂(Re=Lu³⁺, La³⁺) Laser Crystal

Diode-pumped solid-state lasers possess the merits of compactness, high efficiency, reliability and long lifetime that have enabled them become one of the most promising direction in laser development. Considerable efforts have been devoted to search for good solid-state gain media, in which Nd:Gd3Ga5O12(Nd:GGG) has been proved to be an excellent candidate for laser applications owing to its good mechanic properties, excellent thermal conductivity and high efficiency laser performance. However, some intrinsic disadvantages of Nd:GGG, like low segregation coefficient (0.4-0.52) and lattice distortion owing to the mismatching ionic radius of Nd3+and Gd-1+, limit its applications. Therefore, my master thesis aims at modifying the Nd:GGG crystal to improve its properties. On the one hand, the Nd:(LuxGd1.x)3Ga5O12(Nd:LGGG) crystal was grown by substituting a fraction of Gd3+ions with Lu3+ions in the Nd:GGG crystal to eliminate lattice distortion (volume compensation effect). On the other hand, in order to enhance the segregation coefficient of Nd3+in GGG crystal, we have grown the Nd:(LaxGd1-x)3Ga5O12(Nd: LaGGG) crystal by using bigger La3+ions to replace Gd3+ions partially. The main work includes the following sections:1. Crystal growth and characterization of Nd:LGGG crystalA Nd:LGGG crystal with dimensions of φ26mm x14mm was successfully grown by the Czochralski (Cz) method. The effective segregation coefficients of the Nd3+and Lu3+ions in the crystal were measured to be0.50and1.32, respectively. The thermal properties of the crystal, including the average linear thermal expansion coefficient, specific heat and thermal diffusion coefficient were measured, and the thermal conductivity was calculated. Its room-temperature thermal conductivity is9.66W·m-1·K-1, which is larger than that of Nd:GGG crystal and comparable to that of Nd:YAG. What’s more, the spectral properties were investigated. Among all absorption peaks, the strongest one located at805nm with a full-width at half-maximum (FWHM) of8.6ran, which is much larger than that of Nd:YAG (FWHM=0.9-2.1nm). The Judd-Ofelt theory was applied to calculate the spectral parameters. In addition, the continuous wave (CW) and passively Q-switched (PQS) laser properties of the Nd:LGGG crystal at1062nm have been demonstrated. In the CW laser operation, the maximum output power of9.73W was achieved with the optical-to-optical and slope efficiency of60.7%and61.2%, respectively. While in the Q-switched operation, the output power of1.24W, minimum pulse width9.95ns, single pulse energy148uJ and maximum peak power14.20kW were realized.2. Crystal growth and characterization of Nd:LaGGG crystalA bulk mixed Nd:LaGGG laser crystal with dimensions of φ26mm×30mm was successfully grown by the Cz method. The structure and the effective segregation coefficients of Nd3+and La3+ions in the as-grown Nd:LaGGG crystal were measured. The thermal properties were also investigated as a function of temperature, in which the room-temperature thermal conductivity of Nd:LaGGG is8.28W·m-1·K-1, which is comparable to that of Nd:GGG. In addition, the spectral properties were measured and the J-O theory was applied to calculate the spectral parameters. In the1.33μm CW and PQS laser operation, the maximum output power of5.1W and1.1W were achieved, respectively, which is much better than that of Nd:GGG crystal.3. The differences between Nd:LGGG and Nd:LaGGG crystalWe compared the Nd:LGGG and Nd:LaGGG crystal from the aspects of crystal growth and their properties. It can be found that the Nd:LGGG crystal has advantages in thermal properties, while the Nd:LaGGG crystal exhibits better laser performance.