Patent Application
20120212830
This application claims the priority of German application no. 10 2011 012 155.2, filed Feb. 23, 2011, and which is incorporated herein by reference.
The invention relates to a nonpolarizing beam splitter. More particularly, the invention relates to a nonpolarizing beam splitter having at least one substrate to which a partially reflective coating having a plurality of layers is applied, and the plurality of layers includes at least a first and a second refractive layer having respective refraction indices.
These types of beam splitters are generally known, and include at least one substrate to which a partially reflective coating having a plurality of layers is applied.
Such beam splitters are used, for example, in conjunction with an optical examination of components, using radiation in the UV range, for example for the examination of wafers.
In particular for the examination of wafers, there are currently two types of applications. In the first type, wafers undergo a surface inspection using light having a low bandwidth. In the second type, the surface inspection is carried out in the broadband range, in a wavelength range between UV and near infrared (NIR).
From U.S. Pat. No. 4,367,921 a nonpolarizing beam splitter is known which has a specialized layered structure comprising a metal layer in addition to a plurality of layers having high and low indices of refraction.
Similar nonpolarizing beam splitters are also known from JP 60 113 203 A and JP 61 011 701 A.
From U.S. Pat. No. 5,179,471 a spectrally selective mirror and a method for producing same are known.
An object of the invention is to provide a nonpolarizing beam splitter which is usable in a broad wavelength range and whose function is independent of the polarization of the radiation used, and in which the absorption, which changes over the wavelength range, is at least partially compensated for.
This and other objects are achieved by the invention set forth herein.
In sum, the invention includes a nonpolarizing beam splitter including:
The invention likewise includes that a layer sequence of the coating has
The invention thus provides a coating having an at least five-layer structure in which, for example and in particular, the transmission and reflection values do not change in a wavelength range from 250 nm to 800 nm, the transmission and reflection properties being independent of the polarization of the incident radiation.
According to the invention, a material having a low index of refraction is understood to mean a material having an index of refraction nd<1.5. For a material having a medium index of refraction within the meaning of the invention, 1.5 nd<1.8. Within the meaning of the invention, a material having a high index of refraction has an index of refraction nd>1.8.
It has surprisingly been shown that particularly favorable properties may be obtained when, with regard to the material and/or the thickness of the layers, the layer sequence is symmetrical with respect to the metal layer.
One advantageous further embodiment of the invention provides that the thickness of the metal layer is about 1-30 nm.
Other advantageous further embodiments of the invention provide that the thickness of the first refractive layers in each case is about 1-200 nm, preferably about 40-70 nm, and/or that the thickness of the second refractive layers in each case is about 1-200 nm, preferably about 40-70 nm.
Another advantageous further embodiment of the invention provides that at least one of the first refractive layers and/or at least one of the second refractive layers contains fluoridic material and/or oxidic material, or is made of one or more of such materials.
According to another advantageous further embodiment of the invention, the fluoridic or oxidic material in particular of the first refractive layers is or contains LaF3 and/or GdF3 and/or Al2O3 and/or HfO2 and/or NdF3 and/or CeF3.
With regard to the second refractive layers, another advantageous further embodiment of the invention provides that the fluoridic or oxidic material in particular of the second refractive layers is or contains SiO2 and/or AlF3 and/or MgF2 and/or BaF2 and/or Na3AlF6 and/or Na5Al3F14 and/or LaF3 and/or GdF3 and/or Al2O3 and/or NdF3 and/or CeF3.
Another advantageous further embodiment of the invention provides that the beam splitter is configured for function in a wavelength range of 175 to 1300 nm, in particular 190 to 900 nm, preferably 250 to 800 nm, and that in this wavelength range the ratio of reflection to transmission is 1 or about 1.
Another advantageous further embodiment of the invention provides that the reflection and transmission is 31%±9% in the wavelength range for which the beam splitter is configured.
Another advantageous further embodiment of the invention provides that the difference between the s-polarization and the p-polarization of the incident light is <10%, in particular <8%, in the wavelength range for which the beam splitter is configured.
For a nonpolarizing beam splitter, in addition to the reflection to transmission ratio, it is important that the values of the reflection and transmission for the s- and p-polarized light components do not differ too greatly, wherein for a nonpolarizing beam splitter, the second criterion is often the primary focus and is weighted more highly than a change in the values for reflection and transmission according to wavelength. According to the invention, the difference in the respective values for the reflection and transmission of the two polarization components of the light is <10% over the entire design wavelength range. According to the invention, in this range the transmission and reflection are in a corridor of <25%, respectively. For the 250-800 nm range, the difference between the polarization components is <8%, and the reflection and transmission are in a corridor of <18%.
According to the invention, it is possible for the coating to be provided on a single substrate or accommodated between two substrates, as provided in another further embodiment of the invention. If the coating is secured between two substrates, the substrates may be configured as prisms which together form a cube. The two substrates may be made of the same material, or of two different materials. They may be joined together without an air gap, for example by cementing, optical contact bonding, or immersion contacting, the coating being accommodated between the substrates.
The material of the substrate or substrates is selectable within a wide range, depending on the particular requirements. In this regard, one advantageous further embodiment of the invention provides that the substrate or at least one substrate is made of quartz glass and/or CaF2 and/or MgF2.
The invention is explained below with reference to the accompanying drawings, in which embodiments of a beam splitter according to the invention are illustrated in a highly schematic manner. All features described, illustrated in the drawings, and claimed in the patent claims constitute the subject matter of the invention, alone or in any given combination, independently of their combination in the patent claims or their dependencies, and independently of their description or illustration in the drawings.
Identical or corresponding components are provided with the same reference numerals in the figures of the drawing.
The structure of the coating 6 is explained in greater detail below with reference to
According to the invention, the first refractive layers are made of a high or medium refractive index dielectric material, while the second refractive layers are made of a low or medium refractive index dielectric material. In the illustrated embodiment, the material and layer thicknesses of the layers 12, 14, 14′, 16, 16′ are selected as follows:
In the illustrated embodiment, the beam splitter 2 is configured for functioning in a wavelength range of 175-1200 nm, in particular 250-800 nm, and in this wavelength range the ratio of reflection to transmission being 1 or about 1. According to the invention, the phrase “configured for a wavelength range” is understood to mean that the transmission/reflection properties of the beam splitter 2 in this wavelength range do not change, or change only insignificantly. In the illustrated embodiment, the reflection and transmission are 31%±9% in the wavelength range for which the beam splitter 2 is configured. In the illustrated embodiment, in this wavelength range the difference between the s-polarization and the p-polarization of the incident light is <10%, in particular <8%.
In the embodiment according to
For the splitting of the polarization components, here as well a value less than 10% results, and for reflection and transmission a corridor of less than 25% results.
The invention provides a nonpolarizing beam splitter which is suitable for function in a broad wavelength range, and whose mode of operation is independent of the polarization of the incident light. Furthermore, according to the invention the absorption, which changes over the wavelength range, is partially or completely compensated for.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 02 155.2 | Feb 2011 | DE | national |
