A system for opto-pyrometric tissue temperature monitoring in real time. The system is adapted for cardiac ablation and tissue temperature measurement, having a catheter having a tip electrode adapted for RF ablation of cardiac tissue and an optical collector whose distal end is received in an opening formed in the tip electrode to detect black body radiation from the cardiac tissue. The system includes an optical detection system in communication with the optical collector, the optical processing system processing signals representative of a wavelength of at least a portion of the black body radiation to determine a tissue temperature. The incorporation of an optical collector within a catheter tip permits real time monitoring of tissue temperature during ablation and lesion formation to prevent critical thresholds in temperature associated with events that can damage tissue, including steam pop, thrombus, char, etc.