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激光器之所以能作为长度计量标准是因为激光的光源具有方向性好、单色性好和光强大的特点,特别是激光辐射的光谱宽度可以小至30kHz(即0.0001m~(-1)。这样,在用干涉法测量长度时,即使光程差大至几千米的距离,仍然可以观察到对比非常清晰的干涉图象。这些特点与氪-86原子辐射的谱线相比要优越得多。就氦—氖激光而言,其辐射谱线的频率f取决于激光器腔的光学长度L(见图5),即f=KC/2L,同时由于腔内又有电激励的光学
The reason why the laser can be used as the length measurement standard is because the laser light source has the characteristics of good directivity, good monochromaticity and light intensity, especially the laser radiation can have a spectral width as small as 30 kHz (ie 0.0001 m -1) When interferometry was used to measure length, very clear contrast images were observed, even at distances as large as a few kilometers, which are far superior to those of krypton-86 atomic radiation. In the case of a helium-neon laser, the frequency f of its radiation line depends on the optical length L (see FIG. 5) of the laser cavity, ie, f = KC / 2L,