High Light Response Uniformity in Industrial Growth of 600-mm-Long BGO Crystals for DArk Matter Particle Explorer

Hundreds of high-quality 25 mm $\times $ 25 mm $\times \,\, 600$ mm Bi4Ge3O12 single crystals were industrially grown by the Bridgman method for the DArk Matter Particle Explorer (DAMPE) project. With respect to the crystals with the best optical quality, the optical transmittance along the longitudinal and transversal directions can achieve 72% and 76% at 480 nm, respectively. Most of the grown crystals satisfied the light output uniformity requirement of the DAMPE calorimeter. For the remaining crystals, the effects of air annealing, reflector materials, and surface treatment on the improvement of light response uniformity were also studied.