Study on Transmittance Measurement of CaF2 Lens for Ultraviolet Rays by the Photoacoustic Effect(1st Report)

The purpose of this study is the realization of the high precision measurement technology (accuracy : 0.01%) of the large diameter lens for ultraviolet rays(wavelength:193nm). Transmittance measurement method with photoacoustic spectroscopy is proposed. This technology depends on only photothermal effect at a local minute area and is independent of lens size. Therefore, this proposed method can be applied to large diameter lens. Further, measurement time at one point is extremely short. So the features of this new method is that the transmittance distribution in-plane can be easily measured in a very short time. Using the small diameter lens, we obtain the equation of the relationship between the absorption coefficient and the amplitude of the photothermal effect by the conventional calorimetric measurement. And, based on this equation, it was experimentally verified that this photoacoustic spectroscopy could be applied to large diameter lens.