In this paper, the effect of two kinds of thermal shocks on the quality of Nd:YAG single crystal grown by Czochralski method have been investigated. The shocks induced by unexpected change in water flow of cooling system, have a drastic influence on the stability of growth process. This is the intensity and duration of the shocks that affect on the crystal quality as it is evaluated by parallel plane polariscope and Fizeau interferometer. The experimental findings indicate that the time duration of the shocks has more undesirable influence on the crystal quality than the intensity of shocks. Duration of the shocks could make the crystal not suited for laser applications. (C) 2012 Elsevier B.V. All rights reserved.