Spatial light-cone induced by a cylinder

It is found that the interference of reflected, refracted and diffracted light beams from an inclined cylinder illuminated by a collimated or convergent laser beam will form a spatial light-cone with a conic node at the incident point of the laser beam. On the plane normal to the cylinder axis, the projection of the light cone becomes a circle light-ring, the formation of which is independent of the material and the diameter of selected cylinder, so long as its surface has certain reflectivity. The experimental measurement and phenomenological analysis show that the coning angle of the spatial light-cone is double of the angle between the incident beam and the cylinder axis, and independent of wavelength and the diameter of the cylinder and the incident beam. In this paper we present the experimental observations by using light-fiber, glass and metal bar with various diameters. The origin of the spatial light-cone can be simply explained with wave-vector analysis. As a conclusion, the diffaction pattern induced by a thin bar is in practice a synthesizing result of the diffraction and surface reflection. For transparent cylinders, the refraction of the bar is also an important factor. The principle of the spatial light-cone formation may be used in beam orientation, configuration, and surface testing.