Study of Ultraviolet Transmittance Measurement by Photoacoustic Method for next generation of Stepper Lens

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The purpose of this study is establishment of the high precision transmittance measurement technology (accuracy : 0.01%) of the large diameter lens(material : CaF2, diameter : Φ 200mm) for ultraviolet rays (wavelength : 193nm). Transmittance measurement method with photoacoustic spectroscopy is proposed. This technology depends on only photothermal spectroscopy at a local minute area and is independent of lens size. So this proposed method can be applied to large diameter lens. And measurement time at one point is extremely short. So the superiority of this new method is that the transmittance distribution in-plane can be easily measured. It was experimentally verified that this photoacoustic spectroscopy could be applicable to large diameter lens.In the case of transmittance measurement of CaF2 by the excimer laser(ArF) which has high photon energy, the absorption phenomenon of the light energy which is correlated with the residual stress was observed. In this report, we modeled an optical absorption as optical activity, and we verified this model experimentally, the double refraction was measured by strain testing machine (the senarmont method), and the amount of light absorption energy is formulated by dichroism model.