Fig. 1. Schematic illustrations of (a) the probe with a decreasing metal thickness profile and (b) apertured probe, respectively. Here, r1 shows the radius of curvature, _ and _ are the full cone angles of the tapered fiber and metal coating, respectively, and d1 is distal diameter of the metallized flat end of the apertured probe. In (a), the metal coating of the probe body has a constant metal thickness which is fairly thick in comparison to the skin depth. In a distal portion, the thickness gradually decreases toward the tip.