31. A tungsten lamp's colour is typically controlled by inserting one or more gels ( filters ) into its optical path . 32. As this calculation demonstrates, Snell's law is equivalent to vanishing of the first variation of the optical path length. 33. This corresponds to the parabola-shaped optical path difference between two spherical wavefronts that are tangent at their radii of curvature. 34. Increasing the thickness of KBr in the beam increases the optical path because the refractive index is higher than that of air. 35. The TriDAR combines a high precision, short range triangulation sensor with a long range LIDAR sensor into the same optical path . 36. With the aid of the flow of the cells, there is a resultant force that is directed along that preferred optical path . 37. The basic concept is to introduce a split element into a telescope's optical path so as to produce a double image. 38. "Optical path difference " corresponds to the phase shift which happens between two previously coherent sources when passed through different mediums. 39. By shifting the arrangement of the optical lattice point, there is a preferred optical path where the optical forces are dominant and biased. 40. Schlieren optics show changes in the condition of a test area of space in the optical path , even when it remains fully transparent.
