Patent ID: 6932864

Claim:
A method of growing a crystal from a melt, said method comprising the steps of: a) providing a crystal growth container for containing the melt and the crystal grown from the melt; b) growing the crystal from the melt in the container by means of a vertical gradient freezing method; c) mounting a tube with an optical window at one end thereof in the crystal growth container so that the optical window is immersed in the melt; d) propagating an incident optical signal through the optical window immersed in the melt toward a phase interface between the melt and the crystal; e) measuring a reflected optical signal produced by reflection of the incident optical signal from the phase interface in order to determine an actual position or height of said phase interface in relation to said tube with said optical window during said growing of said crystal; and f) controlling said growing of said crystal according to said actual position or said height of said phase interface.