2. 外语
  3. The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from th

The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from th

admin2011-02-28  27
问题    The word laser was coined as an acronym for Light Amplification by the Stimulated Emission of Radiation. Ordinary light, from the sun or a light bulb, is emitted spontaneously, when atoms or molecules get rid of excess energy by them selves, without any outside intervention. Stimulated emission is different because it occurs when an atom or molecule holding onto excess energy has been stimulated to emit it as light.
   Albert Einstein was the first to suggest the existence of stimulated emission in a paper published in 1917. However, for many years physicists thought that atoms and molecules always were much more likely to emit light spontaneously and that stimulated emission thus al- ways would be much weaker. It was not until after the Second World War that physicists began trying to make stimulated emission dominate. They sought ways by which one atom or molecule could stimulate many others to emit light, amplifying it to much higher powers.
   The first to succeed was Charles H. Townes, then at Columbia University in New York. Instead of working with light, however, he worked with microwaves, which have a much longer wavelength, and built a device he called a "maser" for Microwave Amplification by the Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first maser was not completed until a couple of years. Before long, many other physicists were building masers and trying to discover how to produce stimulated emission at even shorter wavelengths.
   The key concepts emerged about 1957. Townes and Artyur Schawlow, then at Bell Telephone Laboratories, wrote a long paper outlining the conditions needed to amplify stimulated emission of visible light waves. At about the same time, similar ideas crystallized in the mind of Gordon Gould, then a 37-year-old graduate student at Columbia, who wrote them down in a series of notebooks. Townes and Schawlow published their ideas in a scientific journal, Physical Review Letter, but Gould filed a patent application. Three decades later, people still argue about who deserves the credit For the concept of the laser.
A laser can be best described by______.
选项 A、a device for stimulating atoms and molecules to emit light
B、an atom in a high energy state
C、a technique for destroying atom or molecules
D、an instrument for measuring light waves
答案A
解析 这是一道细节题，也是知识题。laser 不是原子，更不是检测光波的仪器。[C]不对，因为 laser 不是“毁坏”(destroy)原子或分子，而是刺激原子或分子释放光。而且在第三段中已提到，laser 的前身maser 是一种device。
转载请注明原文地址:https://kaotiyun.com/show/Onkd777K
本试题收录于： 公共英语三级笔试题库公共英语（PETS）分类
0

公共英语三级笔试

公共英语（PETS）

相关试题推荐
随机试题
最新回复(0)