a catheter is adapted to ablate tissue and provide optically - based lesion qualitative and quantitative monitoring , comprising a catheter body and a tip electrode distal the catheter body adapted for ablating tissue , the tip electrode having a shell and an alignment member defining a hollow distal portion therebetween . in accordance with the invention , the catheter further includes a plurality of optical waveguides adapted to transmit optical energy to and from the tip electrode . a distal portion of each waveguide extends through the hollow distal portion and terminates in openings formed in the shell . advantageously , the alignment member fixedly secures the distal portion of each waveguide against movement relative to the alignment member and the shell .