Optimization of some growth process parameters of an Nd:YAG cylindrical bar grown in a vacuum by edge-defined film-fed growth method

摘要

The main purpose of this paper is to find those values of the die radius r_0, pulling rate v and melt temperature T_0 at the meniscus basis which assures the growth of an Nd:YAG cylindrical bar with a prescribed diameter 2r_f for which the nonuniformities of the surface of the bar, due to small uncontrollable oscillations of v and T_0 are minimum possible. Numerical results are given for an Nd: YAG cylindrical bar of 5 mm diameter, grown in a furnace in which the vertical temperature gradient is k = 33K/mm. For a value of v in the range υ ∈ [0.0001,0.53] mm/s and a value of T_0 in the range T_0 ∈ [2244,3000], four types of uncontrollable oscillations O_i, i=1,4, of these parameters are considered: O_1 = (Δυ = ± 0.001mm/s and ΔT = ± 1K), O_2= (Δυ = ± 0.01 mm/s and ΔT = ± 10K), O_3= (Δυ= ± 0.02mm/s and ΔT= ± 20K), O_4= (Δυ = ± 0.001 mm/s and ΔT = ± 30K). For a set of six values of r_0 in the range r_0 ∈[2.6,4.0]mm, the amplitude of the crystal radius variation due to the above four oscillations is computed. It is found that the amplitude of the crystal radius variation due to the considered oscillations is minimum for 1. r_0 = 2.6mm, υ = 0.0119mm/s, T_0 = 2305K for O_1; 2. r_0 = 2.6mm, υ = 0.0243mm/s, T_0 = 2303K for O_2; 3. r_0 = 2.6mm, υ = 0.0466mm/s, T_0 = 2299K for O3; 4. r_0 = 2.7mm, υ = 0.0011mm/s, T_0 = 2360K for O_4.