180 1 year, he read a paper on film color at the royal society. This paper further expands and develops Huygens' wave theory, clearly puts forward that light has frequency and wavelength, and perfects the concept of light wave. He satisfactorily explained the interference phenomenon of Newton's ring, and thought that "when two vibration movements of different origins are either the same or very close in direction, then their * * * interaction is equal to the sum of the effects of each vibration acting alone." This actually puts forward the coherent condition and interference principle of light.
This year, in his paper published in the Journal of Philosophy, he comprehensively expounded the principle of interference: "Two different parts of the same beam of light enter the eyes in different paths, either in the same direction or in very close directions. Where the path difference of light is an integer multiple of a certain length, the light will be strengthened, and in the middle of the interference area, the light is the strongest; This length is different for beams of different colors. "
1802, when Thomas Young gave a speech at the Royal Society, he quoted his own double-hole (double-slit) interference experiment. He said: "In order to superimpose the effects caused by these two parts of light on the screen, it is necessary to make the light from the same light source and passing through different paths reach the same area without making them discrete. If there is dispersion, light can be superimposed from one side or both sides according to refraction, reflection or refraction, and their effects can be superimposed. However, the simplest method is to let parallel light pass through two closely spaced pinholes. Pinhole, as a new light source, emits spherical light waves from it and irradiates the screen, and the shadow of light spreads symmetrically to both sides. However, the farther the screen is from the aperture, the more light from the aperture extends and spreads at the same angle. At the same time, the closer the distance between holes is, the more light emitted from holes will be expanded proportionally. After the two parts of light are superimposed, the center of the connecting line between the two holes is the brightest on the screen. On both sides, the light has a certain distance difference from the two small holes to each point. If the distance difference is 1 times, 2 times and 3 times of the wavelength of light waves, and the distance difference is 1/2, 3/2 and 5/2 times of the wavelength of light waves, these places on the screen are bright areas, and the distances between adjacent bright areas are equal. On the other side. " This is the famous Young's double hole (double slit) experiment.
Thomas Young irradiated the double holes with red light and observed the light band formed on the screen when the light passed through the double holes. When he covers a pinhole, there is only one red spot with uniform light intensity on the screen; When two holes are not covered, alternating bands of red and black will appear in the overlapping area of two light spots on the screen. The red band is quite bright, and its width is equal. At the same time, the width of each black belt is equal to that of the red belt.
According to the comparison of various experiments, the wavelength of extreme red light in the air should be L/36,000 inches, and that of extreme violet light should be1/60,000 inches, which is the accurately measured wavelength of visible light. It is of epoch-making significance in the history of optical development.
Thomas Young also applied the interference principle to explain the diffraction phenomenon. 1803165438+1October 24th, he mentioned the experimental verification of the general laws of optical interference in his speech. After several experiments on the color edge that appears with the shadow, it is found that the color edge is formed according to the interference of two parts of light.
In the first experiment, a hole was made in a wooden window, a thick paper was stuck on it, and a hole was drilled in the thick paper with a needle tip. In order to facilitate observation, a small mirror was placed in an appropriate position outside the wooden window. The sunlight reflected from the mirror hit the opposite wall horizontally, and a 1/30 inch long paper was inserted into the sunlight for observation. Other shadows reflected by thick paper on the wall or placed at various distances are also divided by parallel edges, and their edges are very thin, and their values change with the distance of observing the shadow, and the central part of the shadow is always white. These edges are the result of the combination of two parts of light on each side of the tissue paper, which is not so much refraction as diffraction.
The second experiment is that when an object with a right-angled knot forms a shadow, two or three colors can be seen on the usual outer edge. These start from the bisector of the corner, are arranged on both sides, and bend into a convex shape toward the bisector of the corner. And the farther away from the angular bisector, the thinner it is. These edges are also the result of light bending and superposition directly in the shadow direction on both sides of the object.
Thomas Young's first experiment was thin rod diffraction, and the second experiment was angular diffraction. 1883, when the light is tilted at a large angle, Guy and Wayne directly observed the boundary wave. Thomas Young's concept of boundary wave in diffraction has been confirmed.