（散光眼）课件

Chapter 8 Wave Optics (1) (May 11, 2005) A brief summary to the last lecture 1. The structure of the eye 2. Vision of the human eye vision of the human eye from 0.1 1.5 is the viewing angle and in unit of minute. 3. Corrective eyeglasses for visual defects (1) Myopia (nearsighted); (2) Hyperopic eye (farsighted); (3) Astigmatic eye (散光眼) 4. Optical instruments used in medicine (1) Magnifying glass (2) Compound microscope (3) Fibrescope Wave optics (part 1) 1. The corpuscular (微粒) theory of light (Until the middle of 17th century , Newton (1642-1727) supported). 2. Ray optics can explain many of the properties of light, but there exist many other interesting and beautiful effects that cannot be explained by the geometric optics. For example, Experiments show that light bends around corners. 3. The wave theory of light (Huygens (1629-95) 4. Interference effects of light were first observed by Thomas Yong in 1800. 8.1 Interference (干涉) of light Interference of wave motion, What is the phenomenon? Two coherent waves should be satisfied with the three conditions: what are they? (1) the same frequency (2) the same vibrational direction (3) the same initial phase or constant phase change. A chart of electromagnetic spectrum Visible light (very approximately): 400450 nm Violet 450500 nm Blue 500550 nm Green 550600 nm Yellow 600650 nm Orange 650700 nmRed 8.1.1 Optical length (optical length, distance, path) In Chapter 4, we learned that the phase difference of two waves are expressed as Light is also a part of electromagnetic waves. The light interference follows the rule of wave interference as you know in Yongs double-slit experiment. It is known that light travels at a different speed in different medium. The speed of light in a medium depends on the refractive index of the medium. From the definition of the refractive index, we obtain From the definition of wavelength, which is the period of the wave multiplying the speed of the wave, we have Where 0 is wavelength of light in free space. So the wavelength of light becomes shorter in medium. Light path length is not the geometrical length of the light travel and it is defined as the product of refractive index and the geometrical distance the light travels. Lets have a look at the light path length at the same period t when it travels in two different medium. We choose medium one is free space and medium two with refractive index n. in free space: opitacl length = n0 S = n0 c t = ct In medium: optical length = So it is found that though the lights traveling in different medium have different geometrical path (S and L) at the same period, they have the same light path length. So when we calculate the phase in medium n, we can use the formula directly Again 0 is wavelength of light in free space, L is the geometrical length in the medium. Also we can use the similar formula to calculate the phase difference 8.1.2 Youngs double-slit experiments 20100c