JP2004258503A - Polarizing element, optical system, and optical measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a polarizing element capable of obtaining a favorable extinction ratio and a sufficient light quantity in an ultraviolet domain. <P>SOLUTION: A substrate is provided with a multi-layer anti-reflection film consisting of alternate layers in which each high refractive index layer has the same optical film thickness and each low refractive index layer has the same optical film thickness, and the layers have an anti-reflection effect in the range of an incident angle θ of 70°≤θ≤80° to p-polarized light in the wavelength range of 150nm≤λ≤250nm, and thus the substrate is made into the polarizing element. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２２】
本実施例における反射防止膜はフッ化マグネシウムおよびフッ化ランタンの交互層からなり、層数は全１０層である。各層の光学膜厚はいずれも同一で、高屈折率層と低屈折率層の光学膜厚の和である光学的周期長は０．６４λである。また高屈折率層の光学膜厚の光学周期長に対する比率Γ＝０．５となる。
【００２３】
本発明による偏光素子は、基板と該基板上に設けられた反射防止膜とからなり、該反射防止膜は斜入射光線のｐ偏光成分に対して反射防止特性が得られるように設計される。また大きな消光比を得るために、ｐ偏光成分とｓ偏光成分のそれぞれに対する反射率の差が大きいことが要求される。これらの目的のためには入射角θが７０°以上である必要がある。さらにθが８０°以上では透過光と反射光の分離が困難となるため、入射角は７０°以上８０°以下の範囲で設計されることが好ましい。また反射防止膜の設計製造の容易性という観点からは、各層の膜厚が異なる、いわゆる任意膜厚構造ではなく、高屈折率層と低屈折率層がそれぞれ同一の光学膜厚を有する周期構造とすることが望ましい。以上の条件を全て満たす反射防止膜を設計するためには、前記光学的周期長は０．６λ以上０．６５λ以下であることが好ましく、前記比率Γは０．３８以上０．７３以下であることが好ましく、また前記層数Ｎは７層以上１７層以下であることが好ましい。
【００２４】
図２は、表１に示した反射防止膜の入射角−透過率曲線である。波長λ＝１９３ｎｍとした。入射角θ＝７５°においてｐ偏光成分に対する透過率Ｔｐ＝０．９９９８、ｓ偏光成分に対する透過率Ｔｓ＝０．０４４である。ｐ偏光成分に対しては優れた反射防止特性を有し、一方ｓ偏光成分に対しては反射膜として機能し９５％以上が反射される。
【００２５】
本実施例の偏光素子では入射光線が反射防止膜を２面透過するため、各偏光成分の透過率は１面あたりの透過率の２乗となり、消光比は（０．９９９８）^２：（０．０４４）^２≒５００：１が得られる。またｐ偏光について見れば偏光素子の透過率は（０．９９９８）^２＝９９．９６％に達し、大きな出射光量を得ることができる。また平行平板基板を使用しているため、入射光線は出射光線と平行となる。
〔実施例２〕
図３は、第２の実施例による光学系を示す。図３（ａ）は斜視図、図３（ｂ）は紙面を光線入射面とする側面図である。図３に示す光学系は、実施例１で示したものと同一の偏光素子３を２枚用い、光軸に垂直な面１３に対して対称となるように配置したものである。実施例１で示した偏光素子を単独で用いる場合には、入射光が斜入射であるため屈折による入射光軸と出射光軸のずれが避けられない。本実施例では２枚の偏光素子が中心に対して対称に配置されているため、発生した光軸のずれを相殺することになり、入射光線１１と出射光線１２の光軸を一致させることができる。さらに本実施例による光学系では入射光が反射防止膜を４面通過するため、その消光比は実施例１で示した値の２乗、すなわち２．５×１０^５：１という高い値が得られる。本実施例は、図１３に示したブリュースター角を利用する従来の偏光光学系と同一の配置を持つが、従来の消光比はわずか１．３８：１に過ぎず、本発明が消光比の向上に極めて有効であることが立証された。
〔実施例３〕
図４は、第３の実施例による光学系を示す。図４（ａ）は斜視図、図４（ｂ）は紙面を光線入射面とする側面図である。
【００２６】
【表２】

【００２７】
フッ化カルシウムからなる平行平板基板２１の両面には、表２に示す構成の反射防止膜２２が形成されている。本実施例における反射防止膜はフッ化アルミニウムおよびフッ化ランタンの交互層からなり、層数は全６層である。高屈折率層の光学膜厚は０．３２λ、低屈折率層の光学膜厚は０．２９λで、高屈折率層と低屈折率層の光学膜厚の和である光学的周期長は０．６１λである。また高屈折率層の光学膜厚の光学周期長に対する比率Γ＝０．５２となる。
【００２８】
本実施例は、４枚の同一の偏光素子を、光軸に垂直な面１３に対して対称となるように配置したものである。本実施例によれば、それぞれの偏光素子による光軸のずれが相殺され、入射光軸と出射光軸を一致させることができる。光軸を一致させることにより周辺光学系の設計が容易になる他、既存の光学系に挿入することも可能で、また本光学系全体を光軸の周りに回転させれば任意の偏光面が得られるという利点がある。
【００２９】
図５は、表２に示した反射防止膜の入射角−透過率曲線である。λ＝１５７ｎｍとした。入射角θ＝７０°において、ｐ偏光成分に対する透過率Ｔｐ＝０．９９９８、ｓ偏光成分に対する透過率Ｔｓ＝０．２４４である。この場合、入射光は反射防止膜を８面通過するため、各偏光成分の透過率は図５に示す透過率の８乗となり、透過光における消光比は（０．９９９８）^８：（０．２４４）^８＝８×１０^４：１という極めて高い値が得られる。さらにｐ偏光に対する光学系の透過率は（０．９９９８）^８＝９９．８４％と十分な光量が確保できる。
〔実施例４〕
図６は、第４の実施例による光学系を示す。図６（ａ）は斜視図、図６（ｂ）は紙面を入射面とする側面図である。
【００３０】
【表３】

【００３１】
フッ化カルシウムからなる基板３１の片面には、表３に示す構成の反射防止膜３２が形成されている。本実施例における反射防止膜はフッ化アルミニウムおよびフッ化ランタンの交互層からなり、層数は全７層である。高屈折率層の光学膜厚は０．３１λ、低屈折率層の光学膜厚は０．３３λで、高屈折率層と低屈折率層の光学膜厚の和である光学的周期長は０．６４λである。また高屈折率層の光学膜厚の光学周期長に対する比率Γ＝０．４８となる。
【００３２】
本実施例では反射防止膜３２で反射されるｓ偏光成分側を利用する。また本実施例では入射光軸と出射光軸を一致させるために反射素子を配置する。反射素子に要求される特性としては、使用波長で十分な反射率を有すること、また偏光素子の性能を減失させるような独自の偏光特性を有しないことが挙げられるが、その他の構造・材料等に特段の制限はない。本実施例では、消光比を大きく変えない反射素子の一例として、石英ガラス基板３３上に表４に示す多層膜３４を形成したものを用いた。多層膜３４はフッ化マグネシウムとフッ化ランタンの交互層からなる誘電体多層膜ミラーで、層数は全５１層である。
【００３３】
【表４】

【００３４】
図７は、表３に示した反射防止膜の入射角−反射率曲線、図８は表４に示した誘電体多層膜ミラーの入射角−反射率曲線である。λはいずれもλ＝１９３ｎｍとした。入射角θ_１＝７２°において、反射防止膜３２のｐ偏光成分に対する反射率Ｒｐ＝０．０００２、ｓ偏光成分に対する反射率Ｒｓ＝０．８９０である。また入射角θ_２＝５４°において、誘電体多層膜ミラー３４のｐ偏光成分に対する反射率Ｒ’ｐ＝０．９９９、ｓ偏光成分に対する反射率Ｒ’ｓ＝０．９８５であり、該ミラーによって消光比は影響を受けない。本実施例では、入射光は反射防止膜で２回、誘電体多層膜ミラーで１回反射するため、消光比は（０．８９０）^２×０．９８５：（０．０００２）^２×０．９９９≒２×１０^７：１という極めて高い値が得られる。また従来のブリュースター角を利用する方法では偏光素子１枚あたりのｓ偏光反射率が１５％程度であるのに対し、本実施例では９８．５％の反射率が得られる。これを光学系全体の透過率に換算すると、約４０倍の差となり、従来法に比べて大きな出射光量を得ることができる。
〔実施例５〕
図９は、第５の実施例による光学系を示す。図９（ａ）は斜視図、図９（ｂ）は紙面を入射面とする側面図である。本実施例は実施例４に示した偏光素子３５を４枚使用し、反射防止膜３２で反射されたｓ偏光成分側を利用するものである。
【００３５】
本実施例によれば、二組の偏光分離機能を有する光学系が、光軸に垂直な面１３に対して対称に配置されているため、発生した光軸のずれを相殺することによって入射光軸と出射光軸を一致させることができる。その効果は実施例３と同様である。
【００３６】
本実施例では、入射光は反射防止膜で４回反射するため、消光比は（０．８９０）^４：（０．０００２）^４≒４×１０^１４：１が得られる。
〔実施例６〕
図１４は、本発明による偏光素子を備えた、紫外光を光源とする透過率測定機の例である。
【００３７】
本透過率測定機は、光源部２０１、偏光光学系２０２、試料室２０３、透過光検出器２０４、ビームスプリッタ２０５、参照光検出器２０６から構成される。披検サンプル２０７は試料室内に置かれるが、光軸のまわりに回転できるほか、光軸に対して任意の傾斜角に固定することができる。
【００３８】
本実施例における偏光光学系２０２は、実施例５に記載した４枚の偏光素子からなる光学系をハウジング２０８に固定して一体となしたものであり、全体を光軸のまわりに任意の角度で回転することができる。
【００３９】
光源部はＫｒＦ、ＡｒＦ等のエキシマレーザーや、水銀ランプに適当なフィルタを付加して単色化したものなど、使用波長に応じて選択すればよい。
【００４０】
光源部より出た無偏光の光線２０９を、偏光光学系２０２により直線偏光光となし、被検サンプル２０７に照射する。このとき光線の一部はビームスプリッタにより分割され、参照光検出器に入射する。参照光検出器の出力を監視すれば光源の強度揺らぎを補正することができる。透過光線は透過光用検出器２０４により検出される。被検サンプルを外した状態で透過光量を同様に検出し、これらの比率を取ることで、披検サンプルの透過率が測定される。被検サンプルおよび偏光光学系のいずれか又は両方を光軸のまわりに回転させることにより、被検サンプルに対する入射光の偏光成分を任意に変更することができる。また被検サンプルの入射光軸に対する傾斜角を変えながら測定すれば、透過率の入射角度依存性を測定することも可能である。
【００４１】
【発明の効果】
本発明による偏光素子または光学系は、接合構造を持たないため、光吸収や剥離など従来の偏光素子に見られた接合面に起因する問題を解決することができ、紫外光領域で安定な性能を発揮することができる。また基板上に形成された多層膜に偏光分離機能を持たせるため、複屈折を持つ高価な単結晶材料を使用する必要がなく、石英ガラスやフッ化カルシウムなどの一般的な光学基板を用いることができ、格段に安価に製造することができる。さらに本発明による複数の光学素子を備える光学系は、入射光軸と出射光軸が一致しているため、周辺光学系の設計が容易になるという効果を有する。加えて光軸を一致させるために用いる手段自体が偏光分離機能を備えているため、別個の手段で光軸を調整する場合と比較して、より高い消光比を得ることができる。本発明による偏光素子または光学系を光学測定装置の一部として用いれば、非常に高精度な測定が可能となる。また本発明による光学系は、同一の消光比を有する他の光学系と比較して全長を短く抑えることが可能であり、既存の光学分析機器の試料室等に挿入することにより偏光測定を容易に行うことができる。
【図面の簡単な説明】
【図１】実施例１にかかる偏光素子の斜視図（ａ）および側面図（ｂ）である。
【図２】実施例１にかかる偏光素子を構成する反射防止膜の入射角−透過率曲線である。
【図３】実施例２にかかる光学系の斜視図（ａ）および側面図（ｂ）である。
【図４】実施例３にかかる光学系の斜視図（ａ）および側面図（ｂ）である。
【図５】実施例３にかかる偏光素子を構成する反射防止膜の入射角−透過率曲線である。
【図６】実施例４にかかる光学系の斜視図（ａ）および側面図（ｂ）である。
【図７】実施例４にかかる偏光素子を構成する反射防止膜の入射角−反射率曲線である。
【図８】実施例４にかかる反射素子を構成する誘電体多層膜ミラーの入射角−反射率曲線である。
【図９】実施例５にかかる光学系の斜視図（ａ）および側面図（ｂ）である。
【図１０】合成石英ガラスの入射角−反射率曲線である。
【図１１】グラン−テーラープリズムの例である。
【図１２】ロションプリズムの例である。
【図１３】合成石英ガラスを用いた従来の偏光素子の例である。
【図１４】実施例６にかかる測定機の概略図である。
【符号の説明】
１：基板、２：反射防止膜、３：偏光素子、１１：入射光線、１２：出射光線、１３：光軸に垂直な対称面、３４：誘電体多層膜ミラー、１００：光学素子面の法線、２０１：光源、２０２：偏光光学系、２０８：ハウジング、２０７：被検サンプル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a structure of a polarizing element having a good extinction ratio in an ultraviolet region.
[0002]
[Prior art]
Normally, when an optical component is used for oblique incident light, the characteristics of the optical component differ depending on the polarization direction of the incident light. FIG. 10 shows the relationship between the reflectance of synthetic quartz glass (refractive index n = 1.55) and the incident angle. As the incident angle increases, the reflectivity Rs for s-polarized light increases, whereas the reflectivity Rp for p-polarized light decreases to an incident angle θ ≒ 57 ° and then increases. The angle at which the reflectance for p-polarized light is minimum is called the Brewster angle. The polarization characteristics at oblique incidence are also important factors for optical thin films such as antireflection films. Patent Document 1 discloses an optical thin film having an antireflection effect on obliquely incident light.
[0003]
It is necessary to measure the characteristics of the optical component at the time of such oblique incidence for each polarization component. When measuring the polarization characteristics of optical components, the purpose is to make the irradiated light to the measured component have a specific polarization component, or to separate the measurement light containing the information of the measured component into polarization components for measurement And a linear polarizing element is used.
[0004]
A birefringent crystal polarizing element using calcite (CaCO ₃ ) or the like is generally used as a linear polarizing element. In the visible light region, a Nicol prism or a Gran-Thompson (Calm) combining calcite and Canadian balsam is used. There are known a Glan-Thompson prism, a Glan-Taylor prism combining a calcite and an air layer, and a Glan-Foucault prism. Since the calcite used in these polarizing elements has a large light absorption at a wavelength of 220 nm or less, a Rochon prism in which a magnesium fluoride (MgF ₂ ) single crystal is joined by an optical contact in an ultraviolet light region of a shorter wavelength is used. Applied. FIG. 11 shows an example of a Gran-Taylor prism, and FIG. 12 shows an example of a Lochon prism. The incident light beam 101 is split by these polarizing elements into an s-polarized light beam 102 and a p-polarized light beam 103.
[0005]
Each of the above-mentioned polarizing elements utilizes the birefringence of a crystal, but there is also a polarizing element utilizing the Brewster angle of a material. FIG. 13 shows an example of an optical system having a polarization function in which two synthetic quartz glass plates 41 are used as polarizing elements, and these are arranged symmetrically with respect to a plane 13 perpendicular to the optical axis. In the example of FIG. 13, the incident angle θ (the angle from the normal 100 to the element surface; the same applies hereinafter) is set to the Brewster angle θ of synthetic quartz glass = 57 °, so that the reflectance of the p-polarized light component is Nearly 0, that is, the transmittance Tp ≒ 100%, whereas the transmittance Ts of the s-polarized light component ≒ 85.2%. The performance of a polarizing element is generally represented by an extinction ratio, that is, a ratio of transmittance to each polarized light component. In the case of the above polarizing element utilizing the Brewster angle of synthetic quartz glass,
Extinction ratio per element = 1: 0.852 = 1.17: 1
Extinction ratio of the entire optical system (two elements) = 1 ² : (0.852) ² = 1.38: 1
It becomes. The larger the extinction ratio, the better the polarizing element.
[0006]
[Patent Document 1]
JP-A-10-268106
[Problems to be solved by the invention]
As described above, an element utilizing a Rochon prism or a Brewster angle is used as a polarizing element in the ultraviolet region.
[0008]
However, in the former case, the separation angle of each polarized light component is as small as about 4 degrees. For example, when the light beam has a light angle width of only several degrees as in a measuring instrument using a surface light source such as a deuterium lamp, the polarized light component is However, there have been problems such as the inability to sufficiently separate the light beams, and the necessity of increasing the focal length in order to sufficiently separate the light beams. In addition, poor flatness of the optical contact surface weakens the adhesion, so a high-precision surface finish is required to ensure durability, and magnesium fluoride single crystal with good crystallinity to increase the extinction ratio Therefore, the Rochon prism tends to be expensive due to the necessity of using the light.
[0009]
On the other hand, the latter has a problem that the extinction ratio per element is insufficient. The extinction ratio required for the polarizing element varies depending on the application, but is required to be at least 100: 1, usually not less than 1000: 1. The extinction ratio can be increased by arranging a plurality of polarizing elements in series in the optical path. However, in order to achieve an extinction ratio of 1000: 1 in the above-described synthetic quartz glass, as many as 22 elements are required, There was a problem that would be very long. On the other hand, when the s-polarized component reflected on the element surface is used, the extinction ratio is very high because the reflectance of the p-polarized component is almost 0, but the reflectance for the s-polarized component is 14.8%. Therefore, there is a problem that the light amount loss increases.
[0010]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a polarizing element having a good polarization ratio and a sufficient amount of light, particularly in an ultraviolet region.
[0011]
[Means for Solving the Invention]
In order to solve the above problems, the present invention does not use the birefringence or Brewster angle of the optical member, but uses the polarization characteristics of the multilayer antireflection film. That is, the present invention, particularly in the ultraviolet region, as a polarizing element having a good extinction ratio and a sufficient amount of light,
`` A substrate, comprising an antireflection film formed on the substrate,
The antireflection film is a multilayer antireflection film in which alternating layers of a high-refractive-index layer and a low-refractive-index layer are sequentially stacked from the incident medium side, and the optical characteristics of each of the high-refractive-index layers of the alternating layers are different. The thickness is the same, and the optical thickness of each layer of the low refractive index layer is the same, the incident angle θ for p-polarized light in the wavelength range of 150 nm ≦ λ ≦ 250 nm,
70 ° ≦ θ ≦ 80 °
Polarizing element which is a multilayer antireflection film having an antireflection effect in a range of incident angles (claim 1) "
I will provide a.
[0012]
The present invention also provides a polarizing element having an antireflection film having a particularly effective polarization separation function,
"Constituting the antireflection film, the optical period length nd is the sum of the optical thickness of the high refractive index layer and the optical thickness of the low refractive index layer,
0.6λ ≦ nd ≦ 0.65λ (λ is the wavelength of the incident light)
And the ratio Γ of the optical film thickness of the high refractive index layer to the optical period length,
0.38 ≦ Γ ≦ 0.73
The polarizing element according to claim 1, wherein the polarizing element is within a range of (2).
as well as,
"The number N of the alternating layers constituting the antireflection film is:
5 ≦ N ≦ 17
The polarizing element according to claim 1 or 2, wherein the polarizing element is within the range of (3).
I will provide a.
[0013]
The present invention also provides a polarizing element having excellent transmittance in the ultraviolet region,
Material of "the high refractive index layer, lanthanum fluoride _(LaF 3), gadolinium fluoride _(GdF 3), neodymium fluoride _(NdF 3), dysprosium fluoride _(DyF 3), yttrium fluoride (YF ₃ ) And one or more components selected from the group consisting of these mixed substances or compounds, wherein the material of the low refractive index layer is aluminum fluoride (AlF ₃ ), magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), sodium fluoride (NaF), cryolite (Na ₃ AlF ₆ ), thiolite (Na ₅ Al ₃ F ₁₄ ), and at least one component selected from the group consisting of a mixture thereof and a compound. The polarizing element according to any one of claims 1 to 3, characterized in that:
as well as,
"The substrate is any one of silicon oxide (SiO ₂ ), calcium fluoride (CaF ₂ ), magnesium fluoride (MgF ₂ ), and barium fluoride (BaF ₂ ). Polarizing element or optical system according to one aspect (Claim 5) "
I will provide a.
[0014]
Further, the present invention provides a higher extinction ratio, and a polarizing element having an incident optical axis and an output optical axis parallel to each other.
6. The polarizing element according to claim 1, wherein the substrate includes two planes parallel to each other, and the antireflection film is provided on each of the two planes. 7. (Claim 6) "
I will provide a.
[0015]
Further, the present invention is an optical system including a plurality of the polarizing element, having a polarization separation function as a whole, a higher extinction ratio is obtained, or as an optical system that coincides the incident optical axis and the output optical axis,
An optical system comprising a plurality of polarizing elements according to claim 6, wherein the plurality of polarizing elements are arranged symmetrically with respect to a plane perpendicular to the optical axis, and the incident optical axis and the output optical axis are on the same straight line. Optical system characterized in that there is (claim 7) "
I will provide a.
[0016]
In addition, the present invention particularly as an optical system that can use the s-polarized component,
“An optical system in which optical elements are arranged in the order of a first polarizing element, a reflecting element, and a second polarizing element from the light incident side,
The first polarizing element and the second polarizing element are the polarizing elements according to any one of claims 1 to 5,
An optical system wherein the input optical axis and the output optical axis are on the same straight line (claim 8). "
I will provide a.
[0017]
Further, the present invention includes an optical system having the polarizing element or the polarization separating function described above, as an apparatus capable of measuring the polarization characteristics of the optical element with high accuracy,
"An optical measuring device provided with a polarizing element or an optical system according to any one of claims 1 to 8 (claim 9)"
I will provide a.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples. The thin film of each layer constituting the antireflection film according to the present invention is not particularly limited in a film forming method such as vacuum deposition, sputtering, and ion plating, and any film formed by any method can be used. Further, the materials used in the examples are merely examples, and as a substrate constituting the polarizing element in the present invention, silicon oxide (SiO ₂ ), calcium fluoride, magnesium fluoride, or barium fluoride (BaF ₂ ) In addition, as the material of the high refractive index layer, lanthanum fluoride (LaF ₃ ), gadolinium fluoride (GdF ₃ ), neodymium fluoride (NdF ₃ ), dysprosium fluoride (DyF ₃ ), yttrium fluoride (YF) ₃ ) and one or more components selected from the group consisting of a mixed substance or a compound thereof; aluminum fluoride (AlF ₃ ), magnesium fluoride (MgF ₂ ), calcium fluoride (CaF ₂ ), sodium fluoride (NaF), cryolite (Na ₃ AlF ₆ ), thiolite (Na ₅ Al ₃₎ One or more components selected from the group consisting of F ₁₄ ) and mixtures or compounds thereof can be used.
[0019]
【Example】
[Example 1]
FIG. 1 shows a polarizing element according to the first embodiment. FIG. 1A is a perspective view, and FIG. 1B is a side view in which the paper surface is a light incident surface. In order to avoid complicating the drawing, thin films such as an anti-reflection film are omitted in the perspective view (the same applies hereinafter). The incident light 11 enters from the left side of the figure at an incident angle θ, and the outgoing light exiting to the right becomes p-polarized light. In FIG. 1A, the arrows on the light beams indicate the polarization plane of each light beam.
[0020]
The polarizing element 3 of the present embodiment is obtained by forming an antireflection film 2 having the configuration shown in Table 1 on both surfaces of a parallel plate substrate 1 made of quartz glass (SiO ₂ ).
[0021]
[Table 1]

[0022]
The antireflection film in this embodiment is composed of alternating layers of magnesium fluoride and lanthanum fluoride, and the total number of layers is ten. The optical thickness of each layer is the same, and the optical period length, which is the sum of the optical thicknesses of the high refractive index layer and the low refractive index layer, is 0.64λ. Further, the ratio of the optical film thickness of the high refractive index layer to the optical cycle length is Γ = 0.5.
[0023]
The polarizing element according to the present invention comprises a substrate and an antireflection film provided on the substrate, and the antireflection film is designed so as to obtain antireflection characteristics for a p-polarized component of obliquely incident light. Further, in order to obtain a large extinction ratio, it is required that the difference in reflectance between the p-polarized component and the s-polarized component is large. For these purposes, the incident angle θ needs to be 70 ° or more. Further, when θ is 80 ° or more, it becomes difficult to separate transmitted light and reflected light, and therefore, it is preferable that the incident angle is designed in the range of 70 ° to 80 °. In addition, from the viewpoint of the easiness of designing and manufacturing the antireflection film, it is not a so-called arbitrary thickness structure in which the thickness of each layer is different, but a periodic structure in which the high refractive index layer and the low refractive index layer each have the same optical thickness. It is desirable that In order to design an antireflection film that satisfies all of the above conditions, the optical period length is preferably 0.6λ or more and 0.65λ or less, and the ratio Γ is 0.38 or more and 0.73 or less. It is preferable that the number N of layers is 7 or more and 17 or less.
[0024]
FIG. 2 is an incident angle-transmittance curve of the antireflection film shown in Table 1. The wavelength λ was 193 nm. At the incident angle θ = 75 °, the transmittance Tp for the p-polarized component is 0.9998, and the transmittance Ts for the s-polarized component is 0.044. It has excellent anti-reflection properties for the p-polarized component, while it functions as a reflective film for the s-polarized component and reflects 95% or more.
[0025]
In the polarizing element of this embodiment, since the incident light passes through the antireflection film on two surfaces, the transmittance of each polarized light component is the square of the transmittance per surface, and the extinction ratio is (0.9998) ² : (0 .044) ² @ 500: 1. As for the p-polarized light, the transmittance of the polarizing element reaches (0.9998) ² = 99.96%, and a large amount of emitted light can be obtained. Further, since a parallel plate substrate is used, an incident light beam is parallel to an outgoing light beam.
[Example 2]
FIG. 3 shows an optical system according to the second embodiment. FIG. 3A is a perspective view, and FIG. 3B is a side view in which the paper surface is a light incident surface. The optical system shown in FIG. 3 uses two polarizing elements 3 identical to those shown in the first embodiment and is arranged so as to be symmetrical with respect to a plane 13 perpendicular to the optical axis. When the polarizing element shown in the first embodiment is used alone, since the incident light is obliquely incident, a shift between the incident optical axis and the output optical axis due to refraction cannot be avoided. In this embodiment, since the two polarizing elements are arranged symmetrically with respect to the center, the generated optical axis shift is offset, and the optical axes of the incident light beam 11 and the outgoing light beam 12 can be matched. it can. Furthermore, in the optical system according to the present embodiment, since the incident light passes through the four antireflection films, the extinction ratio is a square of the value shown in the first embodiment, that is, a high value of 2.5 × 10 ⁵ : 1 is obtained. Can be The present embodiment has the same arrangement as the conventional polarization optical system using the Brewster angle shown in FIG. 13, but the conventional extinction ratio is only 1.38: 1, and the present invention has an extinction ratio of It was proved to be extremely effective for improvement.
[Example 3]
FIG. 4 shows an optical system according to the third embodiment. FIG. 4A is a perspective view, and FIG. 4B is a side view in which the paper surface is a light incident surface.
[0026]
[Table 2]

[0027]
An antireflection film 22 having the configuration shown in Table 2 is formed on both surfaces of the parallel plate substrate 21 made of calcium fluoride. The antireflection film in this embodiment is composed of alternating layers of aluminum fluoride and lanthanum fluoride, and the total number of layers is six. The optical thickness of the high refractive index layer is 0.32λ, the optical thickness of the low refractive index layer is 0.29λ, and the optical period length which is the sum of the optical thicknesses of the high refractive index layer and the low refractive index layer is 0. .61λ. Further, the ratio of the optical film thickness of the high refractive index layer to the optical period length is Γ = 0.52.
[0028]
In this embodiment, four identical polarizing elements are arranged symmetrically with respect to a plane 13 perpendicular to the optical axis. According to the present embodiment, the shift of the optical axis due to each polarizing element is canceled, and the incident optical axis and the output optical axis can be made to coincide. By matching the optical axes, the design of the peripheral optical system becomes easy, and it is also possible to insert the optical system into an existing optical system.If the entire optical system is rotated around the optical axis, an arbitrary polarization plane can be obtained. There is an advantage that it can be obtained.
[0029]
FIG. 5 is an incident angle-transmittance curve of the antireflection film shown in Table 2. λ = 157 nm. At an incident angle θ = 70 °, the transmittance Tp for the p-polarized component is 0.9998, and the transmittance Ts for the s-polarized component is 0.244. In this case, since the incident light passes through the eight antireflection films, the transmittance of each polarized light component is the eighth power of the transmittance shown in FIG. 5, and the extinction ratio of the transmitted light is (0.9998) ⁸ : (0. An extremely high value of 244) ⁸ = 8 × 10 ⁴ : 1 is obtained. Further, the transmittance of the optical system for p-polarized light is (0.9998) ⁸ = 99.84%, and a sufficient amount of light can be secured.
[Example 4]
FIG. 6 shows an optical system according to the fourth embodiment. FIG. 6A is a perspective view, and FIG. 6B is a side view with the paper surface as an incident surface.
[0030]
[Table 3]

[0031]
On one surface of a substrate 31 made of calcium fluoride, an antireflection film 32 having a configuration shown in Table 3 is formed. The antireflection film in this embodiment is composed of alternating layers of aluminum fluoride and lanthanum fluoride, and the total number of layers is seven. The optical thickness of the high refractive index layer is 0.31λ, the optical thickness of the low refractive index layer is 0.33λ, and the optical period length, which is the sum of the optical thicknesses of the high refractive index layer and the low refractive index layer, is 0. .64λ. Further, the ratio of the optical film thickness of the high refractive index layer to the optical period length is 周期 = 0.48.
[0032]
In this embodiment, the s-polarized light component side reflected by the antireflection film 32 is used. Further, in this embodiment, a reflection element is arranged to make the incident optical axis coincide with the output optical axis. The characteristics required for a reflective element include that it has sufficient reflectivity at the wavelength used, and that it does not have a unique polarization characteristic that would impair the performance of the polarizer, but other structures and materials There are no particular restrictions on the etc. In the present embodiment, as an example of a reflection element that does not change the extinction ratio significantly, a reflection element in which a multilayer film 34 shown in Table 4 is formed on a quartz glass substrate 33 was used. The multilayer film 34 is a dielectric multilayer mirror composed of alternating layers of magnesium fluoride and lanthanum fluoride, and has a total of 51 layers.
[0033]
[Table 4]

[0034]
FIG. 7 is an incident angle-reflectance curve of the antireflection film shown in Table 3, and FIG. 8 is an incident angle-reflectance curve of the dielectric multilayer mirror shown in Table 4. λ was 193 nm in all cases. At the incident angle θ ₁ = 72 °, the reflectance Rp of the anti-reflection film 32 for the p-polarized component is 0.0002, and the reflectance Rs for the s-polarized component is 0.890. At an incident angle θ ₂ = 54 °, the dielectric multilayer mirror 34 has a reflectance R′p = 0.999 for the p-polarized component and a reflectance R ′s = 0.885 for the s-polarized component. The extinction ratio is not affected. In this embodiment, since the incident light is reflected twice by the antireflection film and once by the dielectric multilayer mirror, the extinction ratio is (0.890) ² × 0.985: (0.0002) ² × 0. An extremely high value of 999 ≒ 2 × 10 ⁷ : 1 is obtained. In the conventional method using the Brewster angle, the s-polarized light reflectance per polarizing element is about 15%, whereas in the present embodiment, a reflectance of 98.5% is obtained. When this is converted into the transmittance of the entire optical system, the difference is about 40 times, and a larger amount of emitted light can be obtained as compared with the conventional method.
[Example 5]
FIG. 9 shows an optical system according to the fifth embodiment. FIG. 9A is a perspective view, and FIG. 9B is a side view with the paper surface as an incident surface. In this embodiment, four polarizing elements 35 shown in the fourth embodiment are used, and the s-polarized light component side reflected by the antireflection film 32 is used.
[0035]
According to the present embodiment, two sets of optical systems having a polarization splitting function are arranged symmetrically with respect to the plane 13 perpendicular to the optical axis. The axis and the output optical axis can be matched. The effect is the same as that of the third embodiment.
[0036]
In this embodiment, since the incident light is reflected four times by the antireflection film, an extinction ratio of (0.890) ⁴ : (0.0002) ⁴ ≒ 4 × 10 ¹⁴ : 1 is obtained.
[Example 6]
FIG. 14 is an example of a transmittance measuring apparatus provided with a polarizing element according to the present invention and using ultraviolet light as a light source.
[0037]
The transmittance measuring apparatus includes a light source unit 201, a polarizing optical system 202, a sample chamber 203, a transmitted light detector 204, a beam splitter 205, and a reference light detector 206. The test sample 207 is placed in the sample chamber, but can rotate around the optical axis and can be fixed at an arbitrary tilt angle with respect to the optical axis.
[0038]
The polarization optical system 202 in the present embodiment is obtained by fixing the optical system composed of the four polarizing elements described in the fifth embodiment to the housing 208 and integrally forming the optical system. Can rotate.
[0039]
The light source may be selected according to the wavelength used, such as an excimer laser such as KrF or ArF, or a monochromatic one obtained by adding an appropriate filter to a mercury lamp.
[0040]
The unpolarized light beam 209 emitted from the light source unit is converted into linearly polarized light by the polarization optical system 202 and is irradiated on the test sample 207. At this time, a part of the light beam is split by the beam splitter and enters the reference light detector. By monitoring the output of the reference light detector, it is possible to correct the intensity fluctuation of the light source. The transmitted light is detected by the transmitted light detector 204. With the test sample removed, the amount of transmitted light is similarly detected, and by taking these ratios, the transmittance of the test sample is measured. By rotating one or both of the test sample and the polarization optical system around the optical axis, the polarization component of the incident light with respect to the test sample can be arbitrarily changed. Further, if the measurement is performed while changing the inclination angle of the test sample with respect to the incident optical axis, it is possible to measure the incident angle dependence of the transmittance.
[0041]
【The invention's effect】
Since the polarizing element or the optical system according to the present invention does not have a bonding structure, it is possible to solve problems caused by the bonding surface such as light absorption and peeling, which are observed in the conventional polarizing element, and to provide stable performance in an ultraviolet light region. Can be demonstrated. In addition, it is not necessary to use an expensive single crystal material having birefringence because a multilayer film formed on the substrate has a polarization separation function, and a general optical substrate such as quartz glass or calcium fluoride is used. And can be manufactured at a significantly lower cost. Further, the optical system including a plurality of optical elements according to the present invention has an effect that the design of the peripheral optical system is facilitated because the incident optical axis and the output optical axis coincide with each other. In addition, since the means used to make the optical axes coincide with each other has a polarization splitting function, a higher extinction ratio can be obtained as compared with a case where the optical axis is adjusted by a separate means. If the polarizing element or the optical system according to the present invention is used as a part of an optical measurement device, extremely high-precision measurement can be performed. Further, the optical system according to the present invention can reduce the overall length as compared with other optical systems having the same extinction ratio, and can easily perform polarization measurement by inserting the optical system into a sample chamber of an existing optical analysis instrument. Can be done.
[Brief description of the drawings]
FIG. 1 is a perspective view (a) and a side view (b) of a polarizing element according to a first embodiment.
FIG. 2 is an incident angle-transmittance curve of an antireflection film constituting the polarizing element according to the first embodiment.
FIG. 3 is a perspective view (a) and a side view (b) of an optical system according to a second embodiment.
FIG. 4 is a perspective view (a) and a side view (b) of an optical system according to a third embodiment.
FIG. 5 is an incident angle-transmittance curve of an antireflection film constituting a polarizing element according to Example 3;
FIG. 6 is a perspective view (a) and a side view (b) of an optical system according to a fourth embodiment.
FIG. 7 is an incident angle-reflectance curve of an antireflection film constituting a polarizing element according to Example 4.
FIG. 8 is an incident angle-reflectance curve of a dielectric multilayer mirror constituting a reflection element according to Example 4;
FIG. 9 is a perspective view (a) and a side view (b) of an optical system according to Example 5.
FIG. 10 is an incidence angle-reflectance curve of synthetic quartz glass.
FIG. 11 is an example of a Gran-Taylor prism.
FIG. 12 is an example of a Lochon prism.
FIG. 13 is an example of a conventional polarizing element using synthetic quartz glass.
FIG. 14 is a schematic diagram of a measuring instrument according to a sixth embodiment.
[Explanation of symbols]
1: substrate, 2: antireflection film, 3: polarizing element, 11: incident light beam, 12: outgoing light beam, 13: symmetry plane perpendicular to the optical axis, 34: dielectric multilayer mirror, 100: optical element surface method Line, 201: light source, 202: polarizing optical system, 208: housing, 207: sample to be tested

Claims (9)

A substrate, comprising an antireflection film formed on the substrate,
The antireflection film is a multilayer antireflection film in which alternating layers of a high-refractive-index layer and a low-refractive-index layer are sequentially stacked from the incident medium side, and the optical characteristics of each of the high-refractive-index layers of the alternating layers. The film thickness is the same, and the optical thickness of each layer of the low refractive index layer is the same, the incident angle θ for the p-polarized light in the wavelength range of 150 nm ≤ λ ≤ 250 nm,
70 ° ≦ θ ≦ 80 °
The polarizing element is a multilayer antireflection film having an antireflection effect in the range of the incident angle. The optical period length nd, which is the sum of the optical thickness of the high refractive index layer and the optical thickness of the low refractive index layer, constituting the antireflection film,
0.6λ ≦ nd ≦ 0.65λ (λ is the wavelength of the incident light)
And the ratio Γ of the optical film thickness of the high refractive index layer to the optical period length,
0.38 ≦ Γ ≦ 0.73
The polarizing element according to claim 1, wherein: The number N of the alternating layers constituting the antireflection film is:
5 ≦ N ≦ 17
The polarizing element according to claim 1 or 2, wherein Material of the high refractive index layer, lanthanum fluoride _(LaF 3), gadolinium fluoride _(GdF 3), neodymium fluoride _(NdF 3), dysprosium fluoride _(DyF 3), yttrium fluoride _(YF 3) And one or more components selected from the group consisting of: a mixture of these substances or compounds; and the material of the low refractive index layer is aluminum fluoride (AlF ₃ ), magnesium fluoride (MgF ₂ ), calcium fluoride ( CaF ₂ ), sodium fluoride (NaF), cryolite (Na ₃ AlF ₆ ), thiolite (Na ₅ Al ₃ F ₁₄ ), and at least one component selected from the group consisting of a mixture thereof and a compound. The polarizing element according to any one of claims 1 to 3, wherein: 5. The substrate according to claim 1, wherein the substrate is any one of silicon oxide (SiO ₂ ), calcium fluoride (CaF ₂ ), magnesium fluoride (MgF ₂ ), and barium fluoride (BaF ₂ ). A polarizing element or an optical system according to the item. The polarizing element according to claim 1, wherein the substrate has two planes parallel to each other, and the antireflection film is provided on each of the two planes. 7. An optical system comprising a plurality of polarizing elements according to claim 6, wherein the plurality of polarizing elements are arranged symmetrically with respect to a plane perpendicular to the optical axis, and the incident optical axis and the output optical axis are on the same straight line. An optical system characterized in that: An optical system in which optical elements are arranged in the order of a first polarizing element, a reflecting element, and a second polarizing element from a light incident side,
The first polarizing element and the second polarizing element are the polarizing elements according to any one of claims 1 to 5,
An optical system wherein the incident optical axis and the output optical axis are on the same straight line. An optical measuring device comprising the polarizing element or the optical system according to claim 1.

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