光刻中G线，I线，H线为什么叫G线，I线，H线而不是叫别的什么线？如果是我就叫A线B线C线D线，又简单又好记忆。G，I，H有什么含义吗，是什么英文单词的简写吗？
已经知道G线，I线，H线对应高压汞灯光谱中波长不同的谱线。有同学说这是光谱方面的问题。于是我查了Spectral analysis 这个关键词，在维基百科上这个词条下看到了
In nuclear and particle physics, gamma spectroscopy, and high-energy astronomy, the analysis of the output of a pulse height analyzer for characteristic features such as spectral line, edges, and various physical processes producing continuum shapes
其中的spectral line，我在此词条下的Nomenclature 部分看到了
Strong spectral lines in the visible part of the spectrum often have a unique Fraunhofer line designation, such as K for a line at 393.366 nm emerging from singly ionized Ca , though some of the Fraunhofer 'lines' are blends of multiple lines from several different species.
提到了 Fraunhofer lines ，我在此词条下看到了
In 1814, Fraunhofer independently rediscovered the lines and began a systematic study and careful measurement of the wavelength of these features. In all, he mapped over 570 lines, and designated the principal features with the letters A through K, and weaker lines with other letters.[3][4][5] Modern observations of sunlight can detect many thousands of lines.
在该词条的“See Also”栏目下有Abbe number词条，在Abbe number 维基百科词条下有这样一个表格：
其中i线，h线，g线就是光刻所对应的波长。也就是说，G线，I线，H线其实是Fraunhofer对光谱线的编号。
我又查到下面的资料。资料后面标记的是资料来源的链接。
Fraunhofer lines
Fraunhofer lines, in astronomical spectroscopy, any of the dark (absorption) lines in the spectrum of the Sun or other star, caused by selective absorption of the Sun’s or star’s radiation at specific wavelengths by the various elements existing as gases in its atmosphere. The lines were first observed in 1802 by the English physicist William Hyde Wollaston but are named for the German physicist Joseph von Fraunhofer, who from about 1814 plotted more than 500 of them and designated the brightest by the letters A through G, a system of identification still in use. About 25,000 Fraunhofer lines are now known to exist in the solar spectrum, between the wavelengths of 2,950 and 10,000 angstroms. (One angstrom equals 10-8 cm.)
来自 <https://www.britannica.com/science/Fraunhofer-lines>
JosephvonGerman physicist and optician, who investigated spectra of the sun,planets, and fixed stars, and improved telescopes and other optical instruments
来自 <http://www.dictionary.com/browse/fraunhofer>
These dark lines, sometimes called Fraunhofer lines, are also collectively referred to as an absorption spectrum. The spectra of materials that were heated in flames or placed in electric-gas discharges were studied by many scientists during the 18th and 19th centuries. These spectra were composed of numerous bright discrete lines, indicating that only certain wavelengths were present in the emitted light. They are called brightline, or emission, spectra.
来自 <https://www.britannica.com/science/spectroscopy/Basic-properties-of-atoms#ref620066>
Fraunhofer lines are dark absorption lines in the solar spectrum that can be seen when sunlight is passed through a prism to separate it into the colors of the rainbow. They occur because cooler gas, which is higher in the Sun's atmosphere, absorbs some colors of the light emitted by hotter gas lower in the Sun's atmosphere. Sir Isaac Newton (1642-1727) discovered that if white light is passed through a prism, it separates into a rainbow, which is called a spectrum. While studying the spectrum that sunlight made, Joseph Fraunhofer (1787-1826) discovered some dark lines scattered among the colors. These dark lines were segments of colors missing from the complete spectrum. Fraunhofer counted 574 of these lines, which we now call Fraunhofer lines. Today, using much more sophisticated techniques, astronomers have discovered tens of thousands of Fraunhofer lines. Why doesn't the Sun emit these missing colors? Or, if the Sun does emit these colors, what happens to the light before it reaches Earth? The answer lies at the surface of the Sun.
When we look at a picture of the Sun, the surface that we see is called the photosphere. The photosphere is a region, several hundred kilometers thick, in which the Sun changes from opaque to transparent. It is not actually the outermost surface: the Sun extends for thousands of kilometers beyond the photosphere, but it is not usually visible from Earth. The photosphere is interesting because within this thin layer of the Sun (thin compared to the whole Sun, of course) sunlight is created, and some of the colors are lost almost immediately. The lower region of the photosphere has a temperature of about 10,000o F (about 5,500o C) and glows white-hot. Any object that glows due to a high temperature gives off a complete spectrum, that is, it has all the colors of the rainbow. As this light proceeds upwards in the Sun into a higher region of the photosphere, the temperature drops several thousand degrees. Although most of the light passes right through, some of the light is absorbed by the cooler gas. Only certain colors are removed because the chemical elements in the photosphere can only absorb certain wavelengths of light, and different wavelengths correspond to different colors. For example, sodium absorbs some yellow light at a wavelength of about 5.89x10-7m. These absorbed colors cause the Fraunhofer lines. By measuring precisely the wavelengths of the missing colors, that is, the Fraunhofer lines, and how much light is actually absorbed, astronomers have learned much about the temperature inside the Sun and its chemical composition.
We can also learn about other stars in the sky by looking at the absorption lines in their spectra. By studying the similarities and differences that they have with the Fraunhofer lines, we can learn a lot about the similarities and differences that other stars have with our Sun.
来自 <http://science.jrank.org/pages/2851/Fraunhofer-Lines.html>
Altogether, Fraunhofer found some 700 lines in the solar spectrum. The nine most prominent he labeled with capital letters A to K, starting at the red end. The A and B bands are now known to be caused by absorption in Earth's atmosphere, while the rest are due to absorption in the Sun'sphotosphere. C and F are now better known as H-alphaand H-beta; the D lines are of sodium, the H and K lines of calcium, and the G band by neutral iron and the CH molecule. All these features occur generally in stars of spectral types F, G, and K.
| A selection of Fraunhofer lines | ||
| lines | due to | wavelengths (Å) |
| A band | O2 (molecular oxygen in Earth's atmosphere) | 7594–7621 |
| B band | O2 (molecular oxygen in Earth's atmosphere) | 6867–6884 |
| C (H-alpha) | H (hydrogen) | 6563 |
| a band | O2 (molecular oxygen in Earth's atmosphere) | 6276–6287 |
| D1 & D2 | Na (sodium) | 5896 & 5890 |
| E | Fe (iron) | 5270 |
| b1, b2, b3, b4 | Mg (magnesium) | 5184, 5173, 5169, 5167 |
| c | Fe (iron) | 4958 |
| F (H-beta) | H (hydrogen) | 4861 |
| d | Fe (iron) | 4668 |
| e | Fe (iron) | 4384 |
| f | H (hydrogen) | 4340 |
| G | Fe | 4308 |
| g | Ca | 4227 |
| h | (H-delta) H (hydrogen) | 4102 |
| H & K | Ca (calcium) | 3968 & 3934 |
来自 <http://www.daviddarling.info/encyclopedia/F/Fraunhofer_line.html>
我不知道为啥这个表格里的i线，g线和h线跟上面那个表格不一样。
总的来说，G线，I线，H线等等这些称呼隶属于对光谱的一种分类和标记体系。
下面是Fraunhofer这个人以及同样的对Fraunhofer line的解释
Fraunhofer line (plural Fraunhofer lines)
Fraunhofer Lines of the Sun
When you let sunlight pass through a prism, you can see that the light is broken up into the colors of the rainbow (a spectrum). If you observe the spectrum more carefully, you will find countless dark features. These are absorption lines caused by impurities such as calcium, sodium, magnesium, iron, and so on. The chief element of the Sun is hydrogen, and the impurities in minuscule quantities absorb the light coming from the inside at specific wavelengths, resulting in the dark features.
The Fraunhofer lines are a set of famous absorption lines named after a German physicist. Fraunhofer designated the principal features with the letters A through K from longer wavelength (redder) to shorter (bluer). For example, the D line is caused by sodium, and the H and K lines are caused by calcium. Some Fraunhofer lines were known to originate in absorption in the Earth's atmosphere.
The Fraunhofer lines are, indeed, a lifeline of solar physicists. The depths of the absorption lines provide information about temperature, and the wavelength shifts of the lines tell us the motion of gas. If the Sun consisted only of pure hydrogen, there would be no absorption line. This would mean that the researchers could not study the temperature or the motion of the Sun's atmosphere. This would be the end for them. Thanks to the impurities, we can investigate the Sun in detail.
Image 1: Solar spectra observed by 25cm Cornagraph at Norikura Solar Observatory. The Fraunhofer lines (C, D, E, F, G, H,and K lines) are indicated.
Column3-D Structure of the Sun's atmosphere
A dark feature in a spectrum results from absorption of light at a given wavelength. This means a low degree of transparency of the atmosphere at this wavelength. Therefore, we can only observe the outer region of the Sun at this wavelength. We utilize this to study the atmosphere outside the region where we usually observe. The degree of the transparency of the Sun's atmosphere depends on the absorption lines. Thus, we combine several absorption lines to observe several layers and to study the 3D structure of the Sun's atmosphere.
Image 2 shows sunspots observed in the Fraunhofer lines using Hinode's solar optical telescope. The Sun's photosphere, the surface of the Sun, appears in the G band image (panel (a)), while the outer layers called chromospheres can be observed in the H (panel (b)) and C (panel (c)) bands.
Image2a：G band image (hydrocarbon molecules)
Image2b：H line (calsium)
Image2c：C line (hydrogen)
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