| 摘要 |
PURPOSE:To obtain a beam attenuating element which has dependency on wavelength to a smaller extent in optional quantity of beam attenuation by providing the constitution in which at least >=2 layers of a film of the characteristic having the quantity of beam attenuation on a short wavelength side larger than the quantity of beam attenuation on a long wavelength side and the film of the characteristic having the quantity of beam attenuation on the short wavelength side smaller than the quantity of beam attenuation on the long wavelength side are alternately superposed. CONSTITUTION:The dependency on wavelength of the quantity of beam attenuation of an independent Cr film and Ni film is plotted in such a way that both attain 20dB quantity of beam attenuation at 850nm wavelength, in the figure. The quantity of beam attenuation of the Cr film is larger on the short wavelength side than on the long wavelength side. The quantity of beam attenuation of the Ni film is smaller on the short wavelength side than on the long wavelength side. The wavelength characteristics are reverse with the Cr film and the Ni film as shown and therefore the characteristics for the quantity of beam attenuation and wavelength are made uniform in an optional wavelength region if the ratio of the quantity of beam attenuation of both films is set at an adequate value and both films formed independently are superposed. |
