A catheter for use in a medical procedure comprising a flexible elongate body defining a central axis and adapted to be introduced into a patient during said medical procedure and including a strain sensing assembly (140a; 140b) proximate a deformable portion of said elongate body , said strain sensing assembly including a proximal portion and a distal portion (162; 188) separated by at least one standoff member (178; 190) to define a separation between said proximal portion and said distal portion, a plurality of transmitting elements affixed to and extending from said proximal portion of said strain sensing assembly and partially spanning said separation, each of said plurality of transmitting elements including a free end to define a plurality of free ends located between said proximal portion and said distal portion, and at least one reflecting surface (164; 266) operatively coupled with at least one of said plurality of free ends to define a plurality of gaps for interferometery, one of said plurality of gaps being presented between each of said plurality of free ends and said at least one reflecting surface, each of said plurality of gaps having an operative length between the respective free end and the at least one reflecting surface, said operative length being variable and responsive to deformation of said deformable portion of said elongate body, wherein said at least one standoff portion and said transmitting element having substantially similar coefficients of thermal expansion in a direction parallel to said operative lengths of said plurality of gaps so that each of said operative lengths remains within a predetermined range when said deformable portion of said elongate body is subject to a predetermined range of bulk temperature change, wherein a difference of said substantially similar coefficients of thermal expansion of said standoff portion and said transmitting element is within 2 μ/K, one or more sources of electromagnetic radiation operatively coupled to each of said plurality of transmitting elements and transmitting electromagnetic radiation to each of said plurality of gaps to form a plurality of interferometers, each of said interferometers outputting modulated waveforms characteristic of the corresponding of said operative lengths, one or more receivers operatively coupled to said plurality of transmitting elements to detect said modulated waveforms, an end effector including a radio-frequency ablation head positioned proximate a distal portion of said elongate body and supported by said distal portion of said strain assembly, an irrigation tube (146; 230) positioned with the flexible elongate body, extending along the central axis, and in fluid communication with the radio-frequency ablation head, a means for thermally isolating said irrigation tube from said deformable portion of said elongate body, and a microprocessor configured to analyze said modulated waveforms to infer a plurality of strains on said deformable portion of said elongate body and to resolve a force vector from said plurality of strains corresponding to a contact force generated between the end effector and an object, said force vector including an axial component and a transverse component relative to said central axis. <EOS>