Optimization of the cooling profile to achieve crack-free Yb:S-FAP crystals

Abstract

To suppress cracking during cool down, a numerical simulation of the growth system was used to understand the correlation between the furnace power during cool down and the radial temperature differences within the crystal. The critical radial temperature difference, above which the crystal cracks, has been determined by benchmarking the simulation results against experimental observations. Based on this comparison, an optimal three-stage ramp-down profile was implemented and produced high quality, crack-free Yb:S-FAP crystals.

Hot zone design for controlled growth to mitigate cracking in laser crystal growth

“…[4] shows that crystals are mainly cracked into two pieces in the middle. The top part of the crystal looks better than the lower part.…”

“…The bottom portion cracking is inevitable due to the ending process of growth. During cooling the bottom of the crystal is attached to the melt in the experiments [4]. It will have thermal shock from the solidifying melt to the crystal through the attached section.…”

“…Numerical studies were conducted for Yb:S-FAP crystal growth. An optimized cooling profile was obtained and has been used in the growth process to produce high quality large diameter crystals [4]. To grow even larger diameter crystals and further reduce the growth and cooling time, it is necessary to understand the causes of crystal cracking and redesign the hot zone so that large thermal stress during growth and cooling can be reduced.…”

Advanced Material Development for Inertial Fusion Energy (IFE)

“…A model of the furnace was fi rst produced by a group at the State University of New York at Stony Brook. With this model, predictions of thermal gradients and stresses in the crystal during the growth process [26] made it possible to reduce the number of growths required for successful mitigation of defects.…”

Study and optimization of gas flow and temperature distribution in a Czochralski configuration

“…The work [1,[3][4][5][6][7][8][9][10] covers many topics, such as hot zone design, defect control, modeling technique and so on, and has greatly speeded up the pace to achieve high-quality crystals in experiments and industries. The shape of the grown crystal is usually cylindrical due to the natural characteristics of the Cz technique, which is advantageous for the growth of crystals with uniform properties.…”