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用于微型光刻技术中的多数紫外线(UV)或深紫外线激光器,无论是基于气体的准分子或二极管泵浦固态(DPSS)激光器,其输出频谱均较宽。与此同时,能传送紫外或深紫外光的多数光学材料均具有较高度频散性(即它们的折射率,n(λ) ,随波长λ变化) 。在这种情况下构建一台紫外干涉仪比那拥有狭窄光谱的激光和几乎恒定折射率的光学材料的情况要复杂得多。本文描述一项激光干涉技术,据此可以补偿光学材料的高频散性,从而构建传统意义上所定义的相干长度之外的激光干涉仪。给出理论上的陈述,并提供初步实验结果。本文最后讨论了此情况下干涉条纹的对比度、激光相干长度,以及如何控制光源的时域不稳定性和空间不均匀性的方法。
Most UV or UV lasers used in microlithography are gas-based excimer or diode-pumped solid-state (DPSS) lasers with wide output spectrum. In the meantime, most optical materials that transmit ultraviolet or deep ultraviolet light have a higher degree of dispersion (ie, their refractive index, n (λ), which varies with wavelength λ). It is far more complicated to build a UV interferometer in this case than an optical material that has a narrow spectrum of laser light and a nearly constant refractive index. This article describes a laser interferometry technique that compensates for the high frequency dispersion of optical materials and thereby creates a laser interferometer beyond the coherence length conventionally defined. Give a theoretical statement and provide preliminary experimental results. Finally, we discuss the contrast of interference fringes, the coherence length of laser and how to control the time-domain instability and spatial inhomogeneity of the light source.