Abstract: In an apparatus for sensing a distance between a sensor and a surface of a body being measured, a sensor body of the sensor is formed as a light waveguide for laser light. A light exit site for light diffracted within the sensor body is located at a surface thereof which faces away from the measured body. A detection particle is located at the surface of the sensor body, which faces the measured body. The detection particle has a substantially convex and rounded off form and a major dimension which is smaller than the wavelength of the light. The measured body is located in the optical near field of the detection particle. A detector device converts the optical energy of the diffracted light into an electrical detector signal. A continuous thin film is provided as a coating on the sensor. It substantially covers the detection particle and at least a part of the surface of the sensor body in the vicinity of the detection particle.