A tip for a medical device includes a hollow body having a window, a sensor positioned within the hollow body and oriented such that its active surface is pointed towards the window, and a membrane positioned within a beam path of the sensor. The membrane passes energy without preventing an outer surface of the hollow body of the tip from coming in contact with tissue, thus allowing the hollow body to deliver therapy to an adjacent tissue and/or diagnose adjacent tissue. The membrane can cover the window or the sensor. The membrane is desirably permeable to an irrigant, such that a suitable level of irrigant outflow from the window is maintained, and thin enough that it minimizes attenuation of energy passing to and/or from the sensor.
