Déformation photoinduite dans les films minces contenant des ...

Chapter 2. Experimental setup and sample preparation 2520081113_8430 nm(a)(b)Figure 2.3: Tip apex diameter. (a-b) Higher and lower magnified SEM images of theapex of an optical fiber tip fabricated by heat-pulling.pastel-00527388, version 1 - 19 Oct 201020090617125 !m(a)(c)8˚15˚15˚15˚(b)(d)Figure 2.4: Tip anistropy. Optical microscope 5x (left) and 10x (right) images of anoptical fiber tip fabricated by heat-pulling: (a-b) side view; (c-d) top view.The apex geometry is approximately that of a truncated cone. We can obtain an apexdiameter of typically 400 nm (Figure 2.3), with a repeatability that mainly depends onthe detection of the critical diameter. As we can see in Figure 2.2 and Figure 2.4(ab),due to the laser assisted fabrication process, the tip has an asymmetric shape, whichcan lead to several problems (poor intensity contrast, polarization anisotropy, etc.) inthe imaging of the light field spatial distribution. This is taken into account in a calibrationprocedure that we employ systematically (see 2.1.4.2), in order to maximize thehomogeneous collection of the light field.We further decrease the tip apex diameter by chemical etching in HF. The concentrationof the HF solution, the temperature and the etching time allow to control the final