In this study, we use a thermal radiometer to detect the thermal radiation of lithium niobate in a 3-5 mu m, and a 10.6 mu m spectrum for the laser heated pedestal growth (LHPG) system. A measurement technique developed according to the different radiation characteristics in each spectrum is employed to find the physical parameters during the growth of a lithium niobate crystal. The meniscus angle (phi(0)) for growing a constant diameter crystal is measured. The value of phi(0) at the facet tri-junction along the a-axis growth is - 4.3 degrees +/- 0.5 degrees, while phi(s) - 5.7 degrees +/- 0.5 degrees is found at the a-face of the c-axis growth. In addition, the temperature distribution is monitored during the growth. The maximum surface temperature gradient, which occurs at the growth interface, is extremely high, i.e. around several hundred degree per millimeter. The gradient decreases when the diameter of the grown crystal decreases.
