Temperature distribution across the growth zone of sapphire (Al2O3) and yttrium–aluminum garnet (YAG) single crystal fibers

•Experimental measurements of the temperature in molten zone.•Spectral pyrometry application.•Local temperature minimum in the area of source rod melting.•Wavy shape of temperature profile along the molten zone.

Temperature distribution along a single crystal fiber molten zone in the laser heated pedestal growth (LHPG) process of pure sapphire (Al2O3) and yttrium–aluminum garnet (Y3Al5O12) fiber was measured for the first time. The temperature was determined from thermal radiation spectra measurements in the visible spectral range. Our measurements indicate the existence of local temperature minimum in the region of source rod melting.