JP5419770B2 - Laser oscillator - Google Patents
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- 230000003287 optical effect Effects 0.000 claims description 58
- 230000010287 polarization Effects 0.000 claims description 55
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 5
- 229910052737 gold Inorganic materials 0.000 description 5
- 239000010931 gold Substances 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 238000010586 diagram Methods 0.000 description 4
- 238000000926 separation method Methods 0.000 description 4
- 230000008033 biological extinction Effects 0.000 description 3
- 238000002310 reflectometry Methods 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
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Description
本発明は、軸対称偏光ビームを発生するレーザ発振器に関する。 The present invention relates to a laser oscillator that generates an axially symmetric polarized beam.
図３は、従来のレーザ発振器の一例を示す構成図である。このレーザ発振器は、下記の非特許文献１で提案されたものであり、部分反射鏡からなる出力ミラー５１と、折り返しミラー５２，５３と、リアミラー５４とを備え、リアミラー５４は、ラジアル偏光を発生させるための反射型回折光学素子で構成される。レーザ光は、折り返しミラー５２，５３を介してリアミラー５４と出力ミラー５１の間を往復することにより発振し、その一部が出力ミラー５１を通過し、レーザ光ＬＢとして共振器外部に取り出される。 FIG. 3 is a block diagram showing an example of a conventional laser oscillator. This laser oscillator is proposed in the following Non-Patent Document 1, and includes an output mirror 51 including a partial reflection mirror, folding mirrors 52 and 53, and a rear mirror 54. The rear mirror 54 generates radial polarization. The reflection type diffractive optical element is used. The laser light oscillates by reciprocating between the rear mirror 54 and the output mirror 51 via the folding mirrors 52 and 53, and a part of the laser light passes through the output mirror 51 and is extracted outside the resonator as laser light LB.
リアミラー５４を構成する反射型回折光学素子は、ラジアル偏光の反射率Ｒｒとアジマス偏光の反射率Ｒａが互いに異なっており、例えば、ラジアル偏光のレーザ光ＬＢを発生する場合は、Ｒｒ＞Ｒａとなるように設計される。 The reflection type diffractive optical element constituting the rear mirror 54 has a radial polarization reflectivity Rr and an azimuth polarization reflectivity Ra different from each other. For example, when the radially polarized laser beam LB is generated, Rr> Ra. Designed as such.
図３に示したレーザ発振器では、ラジアル偏光を発生するための反射型回折光学素子を共振器終端のリアミラーとして採用している。光が共振器内を往復する際、１往復あたり１回だけ反射型回折光学素子で反射する。このためラジアル偏光の反射率Ｒｒとアジマス偏光の反射率Ｒａの差ΔＲが小さいと、ラジアル偏光が十分に選択されず、所望のラジアル偏光が得られないことがある。また、ΔＲを大きくしてラジアル偏光の選択性を高めるためには、反射型回折光学素子の設計、製作が困難になり、製作コストが増加することがある。 In the laser oscillator shown in FIG. 3, a reflection type diffractive optical element for generating radial polarization is employed as a rear mirror at the end of the resonator. When light reciprocates in the resonator, it is reflected by the reflective diffractive optical element only once per reciprocation. For this reason, if the difference ΔR between the reflectance Rr of the radial polarization and the reflectance Ra of the azimuth polarization is small, the radial polarization may not be sufficiently selected, and the desired radial polarization may not be obtained. Further, in order to increase ΔR and increase the selectivity of the radial polarization, it is difficult to design and manufacture the reflective diffractive optical element, which may increase the manufacturing cost.
さらに、一般のＣＯ２レーザ発振器において、リアミラーは平面ミラーではなく、ある程度曲率が付いたものを使用する場合が多い。この場合、曲率ミラー表面に、偏光選択性を有する回折光学素子を形成する必要があり、製作が極めて困難になる。 Further, in a general CO 2 laser oscillator, a rear mirror is not a plane mirror but a mirror with a certain degree of curvature is often used. In this case, it is necessary to form a diffractive optical element having polarization selectivity on the surface of the curvature mirror, which makes it extremely difficult to manufacture.
また、ラジアル偏光を選択する回折光学素子を透過型の媒質で製作することも考えられる。しかしながら、この場合は、レーザ光が媒質内を通過することによって熱分布が発生し、ビーム径が出力により変動するという別の影響が現れる。こうした熱レンズの影響は、レーザ光の出力が高くなるほど増大する。 It is also conceivable to manufacture a diffractive optical element that selects radial polarization with a transmissive medium. However, in this case, another influence appears that the heat distribution is generated by the laser beam passing through the medium and the beam diameter varies depending on the output. The influence of such a thermal lens increases as the output of the laser beam increases.
本発明の目的は、優れた偏光消光比を持つ軸対称偏光ビームを発生できるレーザ発振器を提供することである。 An object of the present invention is to provide a laser oscillator capable of generating an axially symmetric polarized beam having an excellent polarization extinction ratio.
上記目的を達成するために、本発明に係るレーザ発振器は、
リアミラーおよび出力ミラーを有する往復型の光共振器と、
光共振器内に設けられ、光を増幅するためのレーザ媒質と、
光共振器の光軸を折り返すための１つまたは複数の折り返しミラーとを備え、
折り返しミラーの少なくとも１つは、ラジアル偏光の反射率とアジマス偏光の反射率が互いに異なる反射型回折光学素子で構成され、
該反射型回折光学素子は、ラジアル偏光の反射率がアジマス偏光の反射率より０．８％以上大きくなるレーザ光入射角で設置されていることを特徴とする。
In order to achieve the above object, a laser oscillator according to the present invention comprises:
A reciprocating optical resonator having a rear mirror and an output mirror;
A laser medium provided in the optical resonator for amplifying the light;
One or more folding mirrors for folding the optical axis of the optical resonator,
At least one of the folding mirrors is composed of a reflective diffractive optical element having different reflectances for radial polarization and azimuth polarization ,
The reflective diffractive optical element is characterized in that it is installed at a laser beam incident angle at which the reflectance of radial polarization is 0.8% or more greater than the reflectance of azimuth polarization .
本発明によれば、軸対称偏光依存性を有する反射型回折光学素子を光共振器の折り返しミラーとして使用することによって、光が共振器内を往復する際、反射型回折光学素子で反射する回数が光共振器のリアミラーとして使用した場合と比べて２倍になり、反射型回折光学素子による偏光選択性を大幅に高めることができる。その結果、優れた偏光消光比を持つ軸対称偏光ビームを発生できる。また、反射型回折光学素子の設計、製作が容易になり、装置全体のコストを削減できる。 According to the present invention, by using a reflective diffractive optical element having axially symmetric polarization dependence as a folding mirror of an optical resonator, the number of times the light is reflected by the reflective diffractive optical element when reciprocating in the resonator. Is twice as large as when used as a rear mirror of an optical resonator, and the polarization selectivity by the reflective diffractive optical element can be greatly increased. As a result, an axially symmetric polarized beam having an excellent polarization extinction ratio can be generated. In addition, the reflective diffractive optical element can be easily designed and manufactured, and the cost of the entire apparatus can be reduced.
実施の形態１．
図１は、本発明の実施の形態１によるレーザ発振器を示す構成図である。レーザ発振器は、出力ミラー１と、折り返しミラー２，３と、リアミラー４と、一対の放電電極５などを備え、出力ミラー１とリアミラー４の間で往復型の光共振器を構成する。光共振器は、出力ミラー１およびリアミラー４の各曲率半径に応じて、平行平面型、共中心型、共焦点型、半共焦点型などに分類されるが、本発明はいずれの形式の光共振器にも適用可能である。
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a laser oscillator according to Embodiment 1 of the present invention. The laser oscillator includes an output mirror 1, folding mirrors 2 and 3, a rear mirror 4, a pair of discharge electrodes 5, and the like, and a reciprocating optical resonator is configured between the output mirror 1 and the rear mirror 4. The optical resonator is classified into a parallel plane type, a concentric type, a confocal type, a semi-confocal type, and the like according to the respective radii of curvature of the output mirror 1 and the rear mirror 4. It can also be applied to a resonator.
出力ミラー１は、部分反射鏡で構成され、光共振器の内部で増幅されたレーザ光の一部を取り出す機能を有し、共振器外部にレーザ光ＬＢを発生する。リアミラー４は、好ましくは完全反射鏡で構成され、光共振器の内部で増幅されたレーザ光を同軸方向に反射する機能を有する。 The output mirror 1 is composed of a partial reflection mirror, has a function of extracting a part of the laser light amplified inside the optical resonator, and generates the laser light LB outside the resonator. The rear mirror 4 is preferably composed of a complete reflecting mirror, and has a function of reflecting the laser light amplified inside the optical resonator in the coaxial direction.
折り返しミラー２，３は、一般に平面ミラーで構成され、光共振器の光軸を折り返す機能を有し、これにより装置の小型化とともに大きな共振器長を確保している。ここでは、２つの折り返しミラー２，３を用いた、いわゆるＺ型共振器を例として説明するが、１つの折り返しミラーを用いたＶ型共振器やＬ型共振器、３つ以上の折り返しミラーを用いたＷ型共振器などにも本発明は適用可能である。 The folding mirrors 2 and 3 are generally constituted by plane mirrors and have a function of folding the optical axis of the optical resonator, thereby ensuring a large resonator length as well as miniaturization of the device. Here, a so-called Z-type resonator using two folding mirrors 2 and 3 will be described as an example. However, a V-type resonator or L-type resonator using one folding mirror, and three or more folding mirrors are used. The present invention is also applicable to the W-type resonator used.
放電電極５は、光共振器の内部に供給されたレーザ媒質を放電によって励起する機能を有する。ここでは、レーザ媒質の流れ方向７（紙面垂直）、放電電極５の放電方向、および光共振器の光軸が互いに直交した三軸直交型レーザ発振器を例として説明するが、３つの方向が同軸である同軸流型レーザ発振器やその他のレーザ発振器などにも本発明は適用可能である。レーザ媒質として、一般にＣＯ２、ＣＯ、エキシマなどが使用できる。 The discharge electrode 5 has a function of exciting the laser medium supplied into the optical resonator by discharge. Here, a laser medium flow direction 7 (perpendicular to the paper surface), a discharge direction of the discharge electrode 5, and a three-axis orthogonal laser oscillator in which the optical axes of the optical resonators are orthogonal to each other will be described as an example. The present invention is also applicable to a coaxial flow type laser oscillator and other laser oscillators. Generally, CO 2 , CO, excimer, etc. can be used as the laser medium.
本実施形態において、折り返しミラーの少なくとも１つ、例えば、折り返しミラー３を、ラジアル偏光の反射率Ｒｒとアジマス偏光の反射率Ｒａが互いに異なる反射型回折光学素子で構成している。 In the present embodiment, at least one of the folding mirrors, for example, the folding mirror 3 is formed of a reflective diffractive optical element having different reflectance Rr for radial polarization and reflectance Ra for azimuth polarization.
図２（ａ）は、反射型回折光学素子の一例を示す平面図であり、図２（ｂ）は、半径方向に沿った部分断面図である。反射型回折光学素子は、銅基板もしくはシリコン基板を旋盤で削りだしてリッジ部ＲＧを形成した後、金蒸着もしくは誘電体多層膜を積層したもの、あるいはシリコン基板の上に、平坦な表面を有するＴｉ層と、リッジ部ＲＧを形成するＣｕ層とが積層されたものである。ラジアル偏光を優勢に発振させる場合は、図２（ａ）に示すように、多数のリッジ部ＲＧが同心円状に形成されたグレーティング構造を有し、Ｒｒ＞Ｒａを満たす反射型回折光学素子を使用する。ここで、リッジ部の周期、高さなどを適当に選ぶことによってＲｒ＜Ｒａを満たす反射型回折光学素子を作ることも可能でありアジマス偏光を優勢に発振させることもできる。ここで、ｄはリッジ部の幅、ｈはリッジ部の高さ、Λはリッジ部の周期である。 FIG. 2A is a plan view showing an example of a reflective diffractive optical element, and FIG. 2B is a partial cross-sectional view along the radial direction. The reflective diffractive optical element has a flat surface on a copper substrate or a silicon substrate that is formed by lathing with a lathe to form a ridge portion RG and then deposited with gold vapor deposition or a dielectric multilayer film, or on a silicon substrate. The Ti layer and the Cu layer that forms the ridge portion RG are stacked. When oscillating radial polarization predominantly, as shown in FIG. 2A, a reflective diffractive optical element having a grating structure in which a number of ridges RG are concentrically formed and satisfying Rr> Ra is used. To do. Here, it is possible to make a reflective diffractive optical element satisfying Rr <Ra by appropriately selecting the period, height, etc. of the ridge portion, and to oscillate azimuth polarized light predominantly. Here, d is the width of the ridge, h is the height of the ridge, and Λ is the period of the ridge.
次に、動作を説明する。光共振器の内部には、レーザ媒質とバッファガスを混合したレーザガスが充填されている。レーザガスは、送風機（不図示）を用いて方向７に沿って放電電極５の間の空間に連続的に供給されながら、放電によって励起される。光は、出力ミラー１、折り返しミラー２，３、リアミラー４で反射しながら光共振器の光路を往復することにより、励起されたレーザガスによって増幅される。増幅されたレーザ光の一部は、出力ミラー１を介して外部に取り出され、レーザ光ＬＢを発生する。 Next, the operation will be described. The optical resonator is filled with a laser gas in which a laser medium and a buffer gas are mixed. The laser gas is excited by discharge while being continuously supplied to the space between the discharge electrodes 5 along the direction 7 using a blower (not shown). The light is amplified by the excited laser gas by reciprocating the optical path of the optical resonator while being reflected by the output mirror 1, the folding mirrors 2 and 3, and the rear mirror 4. A part of the amplified laser beam is taken out through the output mirror 1 and generates a laser beam LB.
このとき折り返しミラー３として、図２に示すような同心円状のグレーティングを有する反射型回折光学素子を使用した場合、ラジアル偏光の反射率Ｒｒがアジマス偏光の反射率Ｒａを上回る。詳細には、反射型回折光学素子のグレーティングのリッジ部ＲＧの幅ｄを波長程度またはそれ以下に設定すると、リッジ部上面のカットオフ電流はリッジ部に沿う方向（円周方向）には流れやすいが、リッジ部と垂直方向（径方向）には流れにくくなる。その結果、リッジ部は、リッジ部に沿った偏光を良く反射する（乱す）性質を有することになる。ここで、リッジ部の高さに応じて、基板表面からの反射とリッジ部上面からの反射には位相差が生じる。従って、リッジ部の高さを適切に選ぶことによって、リッジ部からの反射光を基板表面からの反射光と協調的に作用させたり、あるいは破壊的に作用させたりして、偏光依存の反射率を制御することができる。図２に示した反射型回折光学素子の場合は、アジマス偏光の反射光同士を破壊的に作用させて、ラジアル偏光を優勢に発振させることができる。なお、ここでは同心円状のグレーティングを例示しているが、完全な同心円ではなく各円の中心が多少偏心したものでも同様の効果が得られる。 At this time, when a reflection type diffractive optical element having a concentric grating as shown in FIG. 2 is used as the folding mirror 3, the reflectance Rr of the radial polarization exceeds the reflectance Ra of the azimuth polarization. Specifically, when the width d of the ridge portion RG of the grating of the reflective diffractive optical element is set to about the wavelength or less, the cut-off current on the upper surface of the ridge portion tends to flow in the direction along the ridge portion (circumferential direction). However, it becomes difficult to flow in the direction (radial direction) perpendicular to the ridge portion. As a result, the ridge portion has a property of reflecting (disturbing) the polarized light along the ridge portion well. Here, depending on the height of the ridge portion, a phase difference occurs between the reflection from the substrate surface and the reflection from the upper surface of the ridge portion. Therefore, by appropriately selecting the height of the ridge part, the reflected light from the ridge part can act cooperatively or destructively with the reflected light from the substrate surface, and the polarization-dependent reflectance. Can be controlled. In the case of the reflective diffractive optical element shown in FIG. 2, the azimuth-polarized reflected light can be caused to act destructively to oscillate radial polarized light predominantly. Although a concentric grating is illustrated here, the same effect can be obtained even if the center of each circle is slightly decentered rather than a complete concentric circle.
反射型回折光学素子のリッジ部の周期Λは、光の波長程度の長さで、リッジ部の幅ｄはそれ以下に設定することが好ましい。例えば、ＣＯ２レーザでは発振波長１０．６μｍであり、リッジ部の幅ｄはサブミクロン〜ミクロンオーダーとなる。また、ラジアル偏光とアジマス偏光の分離を良くするためには、リッジ部の高さｈはミクロンオーダーとなり、場合によってはリッジ部の幅より大きな値となる。しかしながら、幅がサブミクロン〜ミクロンオーダーのリッジ部を作るのは高精度の加工技術が要求され、製作費用も高くなる。また、リッジ部の高さｈがリッジ部の幅ｄより大きくなると、加工が難しくなるうえ、リッジ部が壊れやすい構造になり、取り扱いが容易ではない。製作あるいは取り扱いを容易にするために、リッジ部の幅ｄを大きくし、高さｈを低くすると、今度はラジアル偏光とアジマス偏光の分離が悪くなる結果となる。 The period Λ of the ridge portion of the reflective diffractive optical element is preferably about the length of the wavelength of light, and the width d of the ridge portion is preferably set smaller than that. For example, in a CO 2 laser, the oscillation wavelength is 10.6 μm, and the width d of the ridge portion is on the order of submicron to micron. Further, in order to improve separation of radial polarization and azimuth polarization, the height h of the ridge portion is on the order of microns, and in some cases is a value larger than the width of the ridge portion. However, producing a ridge having a width of sub-micron to micron order requires a high-precision processing technique and increases the manufacturing cost. Further, when the height h of the ridge portion is larger than the width d of the ridge portion, the processing becomes difficult and the ridge portion becomes fragile and the handling is not easy. If the width d of the ridge portion is increased and the height h is decreased in order to facilitate manufacture or handling, this results in poor separation of radial polarization and azimuth polarization.
例えば、図２に示した反射型回折光学素子において、リッジ部分の幅ｄを０．８μｍ、リッジ部分の高さｈを０．８μｍ、リッジ部分の周期Λを１６μｍ、ミラーコート材質を金コートとした場合、ラジアル偏光の反射率Ｒｒは９８．９％、アジマス偏光の反射率Ｒａは９６．７％となる。 For example, in the reflection type diffractive optical element shown in FIG. 2, the width d of the ridge portion is 0.8 μm, the height h of the ridge portion is 0.8 μm, the period Λ of the ridge portion is 16 μm, and the mirror coat material is gold coat. In this case, the reflectance Rr of radial polarization is 98.9%, and the reflectance Ra of azimuth polarization is 96.7%.
一方、図２に示した反射型回折光学素子において、リッジ部分の幅ｄを１．６μｍ、リッジ部分の高さｈを０．５μｍ、リッジ部分の周期Λを１６μｍ、ミラーコート材質を金コートとした場合、ラジアル偏光の反射率Ｒｒは９８．６％、アジマス偏光の反射率Ｒａは９７．８％となる。 On the other hand, in the reflection type diffractive optical element shown in FIG. 2, the width d of the ridge portion is 1.6 μm, the height h of the ridge portion is 0.5 μm, the period Λ of the ridge portion is 16 μm, and the mirror coat material is gold coat. In this case, the reflectance Rr of radial polarization is 98.6%, and the reflectance Ra of azimuth polarization is 97.8%.
前者では、ラジアル偏光とアジマス偏光の反射率の差は２％以上あるが、リッジ部の高さｈと幅ｄが同じぐらいのオーダーとなっており、製作が容易ではない上、リッジ部が壊れやすく取り扱いが困難である。 In the former, the difference in reflectance between radial polarization and azimuth polarization is 2% or more, but the height h and width d of the ridge are on the same order, making the fabrication difficult and breaking the ridge. Easy to handle.
後者では、リッジ部の高さｈに対してその幅ｄは３倍以上あり、取り扱いが容易となるが、ラジアル偏光とアジマス偏光の反射率の差は０．８％程度である。これは、通常のＣＯ２レーザ用反射ミラーとして使用される４５°入射の金コートミラーと同程度のオーダーであり、十分な偏光選択性があるとはいいがたい。十分な偏光選択性を持たせるためには１％以上の反射率差が望ましい。このため反射型回折光学素子を共振器のリアミラーに使用してラジアル偏光を発生させるためにはリッジ部の高さｈをリッジ部の幅ｄ以上にする必要があり、上述したように製作費用の増大、取り扱いの困難さを招く原因となる。 In the latter, the width d is 3 times or more with respect to the height h of the ridge portion, and the handling becomes easy, but the difference in reflectance between the radial polarization and the azimuth polarization is about 0.8%. This is on the same order as a 45 ° incidence gold-coated mirror used as a normal CO 2 laser reflecting mirror, and it cannot be said that there is sufficient polarization selectivity. In order to have sufficient polarization selectivity, a reflectance difference of 1% or more is desirable. For this reason, in order to generate radial polarized light by using the reflection type diffractive optical element for the rear mirror of the resonator, the height h of the ridge portion needs to be equal to or greater than the width d of the ridge portion. This causes an increase and difficulty in handling.
さらに、通常のＣＯ２レーザ共振器は、リアミラーとして曲率ミラーを用いており、曲率ミラーの表面上に反射型回折光学素子を形作るのは非常に難しい。 Furthermore, a normal CO 2 laser resonator uses a curvature mirror as a rear mirror, and it is very difficult to form a reflective diffractive optical element on the surface of the curvature mirror.
本発明では、製作および取り扱いが容易なリッジ部の高さｈがリッジ部の幅ｄより小さい反射型回折光学素子を用い、さらにこれを共振器内部の折り返しミラーとして採用することにより、ラジアル偏光とアジマス偏光の分離を良くし、高品質のラジアル偏光ビームあるいはアジマス偏光ビームを得ることが可能になる。 In the present invention, by using a reflection type diffractive optical element whose height h of the ridge portion, which is easy to manufacture and handle, is smaller than the width d of the ridge portion, and further adopting this as a folding mirror inside the resonator, The separation of azimuth polarized light is improved, and a high-quality radial polarized beam or azimuth polarized beam can be obtained.
図１に示したように、共振器内部の折り返しミラー３として反射型回折光学素子を用いた場合、光は光共振器を１回往復するごとに、反射型回折光学素子で２回反射する。このため反射型回折光学素子をリアミラーとして用いた場合と比べて、ラジアル偏光の反射率Ｒｒとアジマス偏光の反射率Ｒａの差ΔＲによる偏光制御の効果は２回反射分だけ増加することが期待できる。 As shown in FIG. 1, when a reflection type diffractive optical element is used as the folding mirror 3 inside the resonator, light is reflected twice by the reflection type diffractive optical element every time the optical resonator reciprocates once. For this reason, compared with the case where the reflective diffractive optical element is used as a rear mirror, the effect of polarization control due to the difference ΔR between the reflectance Rr of the radial polarization and the reflectance Ra of the azimuth polarization can be expected to increase by the amount reflected twice. .
例えば、前述と同様に、ｄ＝１．６μｍ、ｈ＝０．５μｍ、Λ＝１６μｍで金コートの反射型回折光学素子を用いた場合、１回反射では、ラジアル偏光の反射率Ｒｒ＝９８．６％、アジマス偏光の反射率Ｒａ＝９７．８％で、両者の差ΔＲ＝０．８％である。一方、２回反射では、ラジアル偏光の反射率Ｒｒ＝９７．２％（＝０．９８６×０．９８６）、アジマス偏光の反射率Ｒａ＝９５．６％（＝０．９７８×０．９７８）となり、両者の差ΔＲは１．６％に増加し、偏光選択性が大幅に高くなる。 For example, when a gold-coated reflective diffractive optical element is used with d = 1.6 μm, h = 0.5 μm, and Λ = 16 μm as described above, the radial polarization reflectivity Rr = 98. The reflectance Ra of the azimuth polarization is 67.8%, and the difference ΔR = 0.8% between the two. On the other hand, in the case of two-time reflection, the reflectance Rr of radial polarization Rr = 97.2% (= 0.986 × 0.986) and the reflectance of azimuth polarization Ra = 95.6% (= 0.978 × 0.978) Thus, the difference ΔR between the two increases to 1.6%, and the polarization selectivity is significantly increased.
これによりラジアル偏光とアジマス偏光の分離、即ち、偏光消光比をより改善でき、純度の高い高品質のラジアル偏光ビームが得られる。さらに、リアミラーとして通常の曲率ミラーを採用することができるため、より安価にラジアル偏光を発生するレーザ発振器が実現できる。 Thereby, separation of radial polarization and azimuth polarization, that is, polarization extinction ratio can be further improved, and a high-quality radial polarization beam with high purity can be obtained. Furthermore, since a normal curvature mirror can be employed as a rear mirror, a laser oscillator that generates radial polarized light can be realized at a lower cost.
こうしたラジアル偏光のレーザ光を発生するレーザ発振器は、レーザ加工装置に利用できる。レーザ光を集光した場合、集光ビームの偏光が全てｐ成分となって、効率的な切断や溶接を実現できる。また、ラジアル偏光のレーザ光は、高解像度顕微鏡や光ピンセットにも応用可能である。 Such a laser oscillator that generates a radially polarized laser beam can be used in a laser processing apparatus. When the laser beam is condensed, all the polarized light of the condensed beam becomes a p component, and efficient cutting and welding can be realized. Radially polarized laser light can also be applied to high-resolution microscopes and optical tweezers.
１ 出力ミラー、 ２，３ 折り返しミラー、 ４ リアミラー、 ５ 放電電極、
７ レーザ媒質の流れ方向、 ＬＢ レーザ光、 ＲＧ リッジ部。
1 Output mirror, 2, 3 Folding mirror, 4 Rear mirror, 5 Discharge electrode,
7 Flow direction of laser medium, LB laser light, RG ridge part.
Claims (4)
光共振器内に設けられ、光を増幅するためのレーザ媒質と、
光共振器の光軸を折り返すための１つまたは複数の折り返しミラーとを備え、
折り返しミラーの少なくとも１つは、ラジアル偏光の反射率とアジマス偏光の反射率が互いに異なる反射型回折光学素子で構成され、
該反射型回折光学素子は、ラジアル偏光の反射率がアジマス偏光の反射率より０．８％以上大きくなるレーザ光入射角で設置されていることを特徴とするレーザ発振器。 A reciprocating optical resonator having a rear mirror and an output mirror;
A laser medium provided in the optical resonator for amplifying the light;
One or more folding mirrors for folding the optical axis of the optical resonator,
At least one of the folding mirrors is composed of a reflective diffractive optical element having different reflectances for radial polarization and azimuth polarization ,
The reflection type diffractive optical element is installed at a laser beam incident angle at which the reflectance of radial polarization is 0.8% or more greater than the reflectance of azimuth polarization .
リッジ部の幅は、リッジ部の高さより大きいことを特徴とする請求項２記載のレーザ発振器。 The grating structure is a structure in which ridges having a predetermined width and a predetermined height are arranged concentrically with a predetermined period,
3. The laser oscillator according to claim 2, wherein the width of the ridge portion is larger than the height of the ridge portion.
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