Attenuating filter for ultraviolet light

Abstract

An attenuating filter provides a prescribed attenuation of the intensity of transmitted, short-wavelength, ultraviolet light, in particular, at wavelengths below 200 nm, that is governed by a predefinable spatial distribution of its spectral transmittance. The filter has a transparent substrate ( 3 ), e.g. fabricated from crystalline calcium fluoride. A filter coating ( 5 ) fabricated from a dielectric material that absorbs over a predefined wavelength range is applied to at least one surface ( 4 ) of the substrate. In the case of operating wavelengths of about 193 nm, the filter coating consists largely of tantalum pentoxide. Filters of the type, which may be inexpensively fabricated with high yields, are noted for their high abilities to withstand laser radiation and may be effectively antireflection coated employing simply designed antireflection coatings.

What is claimed is:  
     
         1 . An attenuating filter providing a prescribed attenuation of the intensity of transmitted ultraviolet light over a predefined wavelength range according to a predefmable spatial distribution of a spectral transmittance, the attenuating filter comprising: 
 a substrate fabricated from a transparent material; and    at least one filter coating applied to a surface of the substrate;    the filter coating comprising at least one layer fabricated from a dielectric material that absorbs over a predefined wavelength range.    
     
     
         2 . An attenuating filter according to  claim 1 , wherein a thickness of the dielectric material is substantially uniform across the layer, thereby producing a uniform transmittance of the filter coating.  
     
     
         3 . An attenuating filter according to  claim 1 , wherein the dielectric material from which the filter coating is fabricated has an absorption coefficient, k, that is greater than 0.5.  
     
     
         4 . An attenuating filter according to  claim 1 , wherein the dielectric material from which the layer of the filter coating is fabricated contains at least one metal oxide.  
     
     
         5 . An attenuating filter according to  claim 1 , wherein the dielectric material contains tantalum oxide.  
     
     
         6 . An attenuating filter according to  claim 5 , wherein the dielectric material consists largely of tantalum oxide.  
     
     
         7 . An attenuating filter according to  claim 1 , wherein the thickness of the filter coating varies over the surface of the attenuating filter, whereby a spatial variation of the transmittance of the filter coating across the surface of the attenuating filter is obtained.  
     
     
         8 . An attenuating filter according to  claim 7 , wherein the thickness of the filter coating varies continuously over the surface of the attenuating filter.  
     
     
         9 . An attenuating filter according to  claim 1 , wherein the filter coating has a maximum thickness of less than 10 nm.  
     
     
         10 . An attenuating filter according to  claim 1 , wherein the filter coating has a maximum thickness of less than 2 nm.  
     
     
         11 . An attenuating filter according to  claim 1 , wherein a dielectric antireflection coating is arranged on the filter coating.  
     
     
         12 . An attenuating filter according to  claim 11 , wherein the antireflection coating has a n essentially uniform thickness over the entire surface of the filter.  
     
     
         13 . An attenuating filter according to  claim 11 , wherein the antireflection coating has several layers, each of which has an essentially uniform thickness.  
     
     
         14 . An attenuating filter according to  claim 11 , wherein the antireflection coating has a multilayer stack fabricated from alternating layers of a dielectric material with a high refractive index and layers of a dielectric material with a low refractive index.  
     
     
         15 . An attenuating filter according to  claim 14 , wherein one of the layers of the dielectric material with a high refractive index is applied directly to the filter coating.  
     
     
         16 . An attenuating filter according to  claim 15 , wherein magnesium fluoride (MgF 2 ) is employed as the dielectric material with a low refractive index.  
     
     
         17 . An attenuating filter according to  claim 15 , wherein aluminum oxide (Al 2 O 3 ) is employed as the dielectric material with a high refractive index.  
     
     
         18 . An attenuating filter according to  claim 1 , wherein an antireflection coating is applied to the surface of the substrate opposite to that surface on which the filter coating is applied.  
     
     
         19 . An attenuating filter according to  claim 1 , wherein an antireflection coating is arranged between the substrate and the filter coating.  
     
     
         20 . An attenuating filter according to  claim 1 , wherein the filter is designed for use in the ultraviolet spectral region at wavelengths of less than about 200 nm.  
     
     
         21 . An attenuating filter according to  claim 20 , wherein the filter is designed for use at wavelengths of about 193 nm.  
     
     
         22 . An attenuating filter providing a prescribed attenuation of the intensity of transmitted ultraviolet light over a predefined wavelength range according to a predefinable spatial distribution of a spectral transmittance, the attenuating filter comprising: 
 a substrate fabricated from a transparent material; and    at least one filter coating applied to a surface of the substrate;    the filter coating comprising at least one layer fabricated from a dielectric material that absorbs over a predefined wavelength range, wherein the thickness of the filter coating varies over the surface of the attenuating filter, thereby obtaining a spatial variation of the transmittance of the filter coating across the surface of the attenuating filter.    
     
     
         23 . An attenuating filter providing a prescribed attenuation of the intensity of transmitted ultraviolet light over a predefined wavelength range at wavelengths of less than about 200 nm according to a predefinable spatial distribution of a spectral transmittance, the attenuating filter comprising: 
 a substrate fabricated from a transparent material; and    at least one filter coating applied to a surface of the substrate;    the filter coating comprising at least one layer fabricated from a dielectric material that contains tantalum oxide and that absorbs over a predefined wavelength range.    
     
     
         24 . An attenuating filter according to  claim 23 , wherein a thickness of the dielectric material varies across the layer, thereby producing spatial variations in transmittance of the filter coating.  
     
     
         25 . An attenuating filter according to  claim 23 , wherein a thickness of the dielectric material is substantially uniform across the layer, thereby producing a uniform transmittance of the filter coating.