JP5180594B2

JP5180594B2 - Interferometer

Info

Publication number: JP5180594B2
Application number: JP2008000925A
Authority: JP
Inventors: 亮寺本
Original assignee: 新東エスプレシジョン株式会社
Priority date: 2008-01-08
Filing date: 2008-01-08
Publication date: 2013-04-10
Anticipated expiration: 2028-01-08
Also published as: JP2009162629A

Description

本発明は、レーザビームを用いて気体の屈折率等を測定することができる干渉計に関する。 The present invention relates to an interferometer capable of measuring a refractive index of a gas using a laser beam.

従来、空気の屈折率を測定する干渉計として、光ビームを発生する光源と、光源からの光ビームをビームスプリッタで参照ビームと測定ビームに分割し、分割された測定ビームを再帰ミラーに向けて照射するとともに、分割された参照ビームを、ビームスプリッタに固定された逆反射体に照射し、再帰ミラーで反射した測定ビームと可動逆反射体で反射した参照ビームをビームスプリッタで合成ビームとして合成し、この合成ビームを検出器に入射し、検出器で可動逆反射体とビームスプリッタとの間の距離の変化を表わす縞の数を、気体の屈折率の変化に伴う測定ビームと参照ビームの光路長の差の変化として検出するために、参照ビームと測定ビームの差の最大変化が、使用する光ビームの１波長よりも短くなるように、ビームスプリッタと再帰ミラーの位置を調整するようにしたものが提案されている（特許文献１参照）。 Conventionally, as an interferometer that measures the refractive index of air, a light source that generates a light beam, and the light beam from the light source is divided into a reference beam and a measurement beam by a beam splitter, and the divided measurement beam is directed to a recursive mirror Irradiate and irradiate the divided reference beam to the retroreflector fixed to the beam splitter, and combine the measurement beam reflected by the retroreflector and the reference beam reflected by the movable retroreflector as a combined beam by the beam splitter. The combined beam is incident on the detector, and the number of fringes representing the change in the distance between the movable retroreflector and the beam splitter is detected by the detector, and the optical path of the measurement beam and the reference beam according to the change in the refractive index of the gas. In order to detect the change in the difference in length, the beam split is performed so that the maximum change in the difference between the reference beam and the measurement beam is shorter than one wavelength of the light beam used. That to adjust the position of recursive mirror has been proposed (see Patent Document 1).

特開平６−２７０２０号公報JP-A-6-27020

従来技術においては、ビームスプリッタと再帰ミラーとの間の大気が熱膨張すると、熱膨張に伴って大気の屈折率が変化し、大気の屈折率を高精度に計測することができない。 In the prior art, when the atmosphere between the beam splitter and the recursive mirror is thermally expanded, the refractive index of the atmosphere changes with the thermal expansion, and the refractive index of the atmosphere cannot be measured with high accuracy.

本発明は、前記従来技術の課題に鑑みて為されたものであり、その目的は、気体の屈折率を高精度に計測することができる干渉計を提供することにある。 The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide an interferometer capable of measuring the refractive index of gas with high accuracy.

前記目的を達成するために、本発明にあっては、
レーザビームを発生する光源と、
前記光源からのレーザビームを測定ビームと参照ビームに分岐させて、再帰ミラーに向けて出射するとともに、前記再帰ミラーで反射した測定ビームと参照ビームを合成して、合成ビームを出射する台形型偏光ビームスプリッタと、
前記台形型偏光ビームスプリッタに相対向して配置され、入射した測定ビームと参照ビームをそれぞれ入射した経路とは異なる経路で前記台形型偏光ビームスプリッタに向けて反射させる再帰ミラーと、
前記台形型偏光ビームスプリッタと再帰ミラーとを連結するとともに、前記参照ビームの光路を形成する真空容器と、
前記台形型偏光ビームスプリッタから出射した合成ビームを受光し、受光した合成ビームを基に前記測定ビームと参照ビームの干渉に伴う測定を行う計測器とを備え、
前記レーザビームが前記測定ビームと前記参照ビームに分岐する分岐点と、前記再帰ミラーで反射した測定ビームと参照ビームが合成ビームに合成される合成点とを結ぶ光路のうち、前記測定ビームの光路と前記参照ビームの光路は、同一の光路長に設定されてなる、干渉計であって、
前記台形型偏光ビームスプリッタは、直角三角形部と、当該直角三角形部の斜辺にその一辺が接合された平行四辺形部との結合により、その周囲に台形形状の四辺が形成され、
前記直角三角形部と前記平行四辺形部との接合による接合面の一部は、前記光源からのレーザビームを透過光としての測定ビームと反射光としての参照ビームに分岐させる第１の半透過部を構成し、
前記接合面に対して４５度傾斜した第１の辺は、前記第１の半透過部で分岐された測定ビームと参照ビームを前記再帰ミラーに向けて出射する出射面を構成し、
前記直角三角形部の一辺であって、前記第１の辺と直交する第２の辺は、前記光源からのレーザビームを透過する入射面を構成し、
前記平行四辺形部の一辺であって、前記接合面と平行な第３の辺は、前記接合面を透過した測定ビームを前記第１の辺から前記再帰ミラーの入出射面に向けて反射させるとともに、前記真空容器から前記第１の辺を介して入射した参照ビームを前記接合面側に反射させる反射面を構成し、
前記接合面の他の部位は、前記第３の辺で反射した参照ビームを前記第１の辺と平行な第４の辺側に反射させ、前記再帰ミラーから前記第１の辺に入射した測定ビームを前記第４の辺側に透過し、前記参照ビームと測定ビームを合成して合成ビームを生成する第２の半透過部を構成し、
前記平行四辺形部の一辺であって、前記第４の辺は、前記第２の透過部から合成ビームを前記計測器に向けて出射する出射面を構成し、
前記再帰ミラーは、直角三角形形状に形成されて、その斜辺が、前記台形型偏光ビームスプリッタの第１の辺と平行になって配置され、
前記再帰ミラーの斜辺のうち前記真空容器と相対向する中心部は、前記参照ビームの入出射面を構成し、前記再帰ミラーの斜辺のうち前記中心部から外れた部位は、前記測定ビームの入出射面を構成し、
前記再帰ミラーの残りの二辺のうち一方の反射面は、前記入出射面から入射した測定ビームを他方の反射面に反射させるとともに、前記入出射面から入射して他方の反射面で反射した参照ビームを前記真空容器側へ反射させる第１のミラー反射面を構成し、
前記再帰ミラーの他方の反射面は、前記第１のミラー反射面で反射した測定ビームを前記真空容器から外れた領域を介して前記第１の辺側へ反射させるとともに、前記入出射面から入射した参照ビームを前記第１のミラー反射面側に反射させる第２のミラー反射面を構成してなる構成とした。 In order to achieve the above object, in the present invention,
A light source for generating a laser beam;
A trapezoidal polarization that splits the laser beam from the light source into a measurement beam and a reference beam and emits it toward the recursive mirror, and combines the measurement beam reflected by the recursive mirror and the reference beam to emit a combined beam. A beam splitter,
A recursive mirror disposed opposite to the trapezoidal polarizing beam splitter and reflecting the incident measurement beam and the reference beam toward the trapezoidal polarizing beam splitter through paths different from the incident paths,
A vacuum vessel that connects the trapezoidal polarizing beam splitter and the recursive mirror, and forms an optical path of the reference beam;
A measuring instrument that receives the combined beam emitted from the trapezoidal polarization beam splitter and performs measurement associated with interference between the measurement beam and the reference beam based on the received combined beam;
Of the optical path connecting the branch point where the laser beam branches into the measurement beam and the reference beam, and the synthesis point where the measurement beam reflected by the recursive mirror and the reference beam are combined into the combined beam, the optical path of the measurement beam And the optical path of the reference beam is an interferometer set to the same optical path length,
The trapezoidal polarization beam splitter has a trapezoidal shape formed around a right triangle portion and a parallelogram portion whose one side is joined to the hypotenuse of the right triangle portion.
A part of the joint surface formed by joining the right triangle part and the parallelogram part is a first semi-transmission part that branches the laser beam from the light source into a measurement beam as transmitted light and a reference beam as reflected light Configure
The first side inclined by 45 degrees with respect to the joint surface constitutes an emission surface that emits the measurement beam and the reference beam branched by the first semi-transmissive portion toward the recursive mirror,
A second side that is one side of the right triangle portion and is orthogonal to the first side constitutes an incident surface that transmits a laser beam from the light source,
Wherein a one side of a parallelogram-shaped part, the third side parallel to the bonding surface is to reflect toward the input-output face of the recursive mirror measurement beam transmitted through the bonding surface from said first side And a reflecting surface for reflecting the reference beam incident from the vacuum vessel through the first side to the bonding surface side,
The other part of the joint surface is a measurement in which the reference beam reflected by the third side is reflected to the fourth side parallel to the first side and is incident on the first side from the recursive mirror. A second translucent part configured to transmit a beam to the fourth side and combine the reference beam and the measurement beam to generate a combined beam;
Wherein a one side of a parallelogram shape portion, the fourth side constitutes the emitting surface for emitting the combined beam from the second transmitting portion toward the instrument,
The recursive mirror is formed in a right triangle shape, and its hypotenuse is arranged parallel to the first side of the trapezoidal polarizing beam splitter,
Of the hypotenuse of the retroreflective mirror, the central part opposite to the vacuum vessel constitutes the entrance / exit surface of the reference beam, and the part of the hypotenuse of the retroreflective mirror that is off the central part is the entrance of the measurement beam Configure the exit surface,
One reflecting surface of the remaining two sides of the recursive mirror reflects the measurement beam incident from the incident / exiting surface to the other reflecting surface and is incident from the incident / exiting surface and reflected by the other reflecting surface. Forming a first mirror reflecting surface for reflecting the reference beam toward the vacuum container;
The other reflecting surface of the retroreflecting mirror reflects the measurement beam reflected by the first mirror reflecting surface to the first side through a region outside the vacuum vessel and is incident from the incident / exiting surface. The second mirror reflection surface is configured to reflect the reference beam reflected to the first mirror reflection surface side.

（作用）台形型ビームスプリッタ１４と再帰ミラー１８を真空容器１６を介して連結するとともに、レーザビームが測定ビームと参照ビームに分岐する分岐点（２６ａ）と、再帰ミラーで反射した測定ビームと参照ビームが合成ビームに合成される合成点（２６ｂ）とを結ぶ光路のうち測定ビームの光路と参照ビームの光路を同一の光路長に設定したので、干渉計を構成する各要素に歪みや膨張が生じても、これらの影響を抑制して、空気の屈折率を安定した状態で高精度に測定することができる。 (Operation) The trapezoidal beam splitter 14 and the recursive mirror 18 are connected via the vacuum vessel 16, the branch point (26a) where the laser beam branches into the measurement beam and the reference beam, the measurement beam reflected by the recursive mirror and the reference Since the optical path of the measurement beam and the optical path of the reference beam are set to the same optical path length among the optical paths connecting the combined point (26b) where the beam is combined with the combined beam, distortion and expansion are caused in each element constituting the interferometer. Even if they occur, these effects can be suppressed and the refractive index of air can be measured with high accuracy in a stable state.

また、直角三角形部と平行四辺形部との接合による接合面の一部を、光源からのレーザビームを透過光としての測定ビームと反射光としての参照ビームに分岐させる第１の半透過部として構成し、接合面に対して４５度傾斜した第１の辺を、第１の半透過部で分岐された測定ビームと参照ビームを再帰ミラーに向けて出射する出射面として構成し、第１の辺と直交する第２の辺は、光源からのレーザビームを透過する入射面を構成し、接合面と平行な第３の辺は、接合面を透過した測定ビームを第１の辺から再帰ミラーの斜辺に向けて反射させるとともに、真空容器から第１の辺を介して入射した参照ビームを接合面側に反射させる反射面を構成し、接合面の他の部位は、第３の辺で反射した参照ビームを第４の辺側に反射させ、再帰ミラーから入射した測定ビームを第４の辺側に透過し、参照ビームと測定ビームを合成して合成ビームを生成する第２の半透過部を構成し、第１の辺と平行な第４の辺は、第２の透過部からの合成ビームを計測器に向けて出射する出射面を構成し、再帰ミラーは、６０°の三角形形状に形成されて、その入射面が、台形型偏光ビームスプリッタの第１の辺と平行になって配置され、再帰ミラーの入出射面の中心部附近は、参照ビームの入出射面（入射面または出射面）を構成し、再帰ミラーの入出射面のうち中心部附近から外れた部位は、測定ビームの入出射面（入射面または出射面）を構成し、再帰ミラーの残りの二辺のうち一方の反射面は、入出射面から入射した測定ビームを他方の反射面に反射させるとともに、入出射面から入射して他方の反射面で反射した参照ビームを真空容器側へ反射させる第１のミラー反射面を構成し、再帰ミラーの他方の反射面は、第１のミラー反射面で反射した測定ビームを真空容器から外れた領域を介して第１の辺側へ反射させるとともに、入出射面から入射した参照ビームを第１のミラー反射面側に反射させる第２のミラー反射面を構成するので、第１の半透過部と第２の半透過部とを結ぶ光路のうち測定ビームの光路と参照ビームの光路を同一の光路長にすることができる。 Further, as a first semi-transmission part that branches a part of the joint surface formed by joining the right triangle part and the parallelogram part into a measurement beam as a transmitted light and a reference beam as a reflected light from a light source. The first side inclined 45 degrees with respect to the joint surface is configured as an exit surface that emits the measurement beam and the reference beam branched by the first semi-transmissive portion toward the recursive mirror, The second side orthogonal to the side constitutes an incident surface that transmits the laser beam from the light source, and the third side parallel to the junction surface reflects the measurement beam transmitted through the junction surface from the first side to the recursive mirror. And a reflection surface that reflects the reference beam incident from the vacuum vessel through the first side to the bonding surface side, and the other part of the bonding surface is reflected by the third side. The reflected reference beam is reflected to the fourth side, and the recursive mirror A second semi-transmission unit that transmits the measurement beam incident on the fourth side and generates a combined beam by combining the reference beam and the measurement beam, and a fourth side parallel to the first side. Constitutes an emission surface for emitting the combined beam from the second transmission part toward the measuring instrument, and the recursive mirror is formed in a triangular shape of 60 °, and its incident surface is the trapezoidal polarization beam splitter. Arranged parallel to the first side, the vicinity of the center of the entrance / exit surface of the recursive mirror constitutes the entrance / exit surface (incident surface or exit surface) of the reference beam, and is the center of the entrance / exit surface of the recursive mirror The part deviated from the vicinity of the part constitutes the incident / exit surface of the measurement beam (incident surface or exit surface), and one of the remaining two sides of the recursive mirror reflects the other of the measurement beam incident from the incident / exit surface. The light is reflected on the reflective surface of The first mirror reflecting surface that reflects the reference beam reflected by the emitting surface to the vacuum vessel side is configured, and the other reflecting surface of the recursive mirror is separated from the vacuum vessel by the measurement beam reflected by the first mirror reflecting surface. Since the second mirror reflecting surface that reflects the reference beam incident from the incident / exiting surface to the first mirror reflecting surface side while reflecting the first side through the region is configured, the first semi-transmissive portion The optical path of the measurement beam and the optical path of the reference beam can be set to the same optical path length.

本発明によれば、干渉計を構成する各要素に歪みや膨張が生じても、これらの影響を抑制して、空気の屈折率を安定した状態で高精度に測定することができる。 According to the present invention, even if distortion or expansion occurs in each element constituting the interferometer, these effects can be suppressed, and the refractive index of air can be measured with high accuracy.

また、第１の半透過部と第２の半透過部とを結ぶ光路のうち測定ビームの光路と参照ビームの光路を同一の光路長にすることができる。 Further, the optical path of the measurement beam and the optical path of the reference beam can be set to the same optical path length among the optical paths connecting the first semi-transmissive portion and the second semi-transmissive portion.

以下、本発明に係る波長測定用干渉計の一実施形態を図面に基づいて説明する。図１は、本発明に係る干渉計の一実施例を示すブロック構成図、図２は、測定ビームと参照ビームの光路を説明するための構成図である。 Hereinafter, an embodiment of an interferometer for wavelength measurement according to the present invention will be described with reference to the drawings. FIG. 1 is a block configuration diagram showing an embodiment of an interferometer according to the present invention, and FIG. 2 is a configuration diagram for explaining optical paths of a measurement beam and a reference beam.

図１において、波長測定用干渉計１０は、光源１２と、台形型偏光ビームスプリッタ１４と、真空容器１６と、再帰ミラー１８と、計測器２０とを備えて構成されている。 In FIG. 1, the wavelength measuring interferometer 10 includes a light source 12, a trapezoidal polarizing beam splitter 14, a vacuum container 16, a recursive mirror 18, and a measuring instrument 20.

光源１２は、例えば、半導体レーザを備え、半導体レーザの発振によるレーザビーム１００を台形型偏光ビームスプリッタ１４に向けて出射する。 The light source 12 includes, for example, a semiconductor laser, and emits a laser beam 100 generated by the oscillation of the semiconductor laser toward the trapezoidal polarization beam splitter 14.

台形型偏光ビームスプリッタ１４は、直角三角形形状のプリズムで構成された直角プリズム２２と、平行四辺形形状のプリズムで構成された平行四辺形プリズム２４を備え、直角プリズム２２の斜辺２２ａが、平行四辺形プリズム２４の一辺２４ａに接合されて、接合面２６として形成されている。この台形型偏光ビームスプリッタ１４は、光源１２からのレーザビーム１００が接合面２６に入射したときに、接合面２６により、レーザビーム１００を透過光としての測定ビーム１０２と反射光としての参照ビーム１０４とに分岐させ、測定ビーム１０２と参照ビーム１０４を再帰ミラー１８に向けて出射する。 The trapezoidal polarization beam splitter 14 includes a right-angle prism 22 formed of a right-angled triangular prism and a parallelogram prism 24 formed of a parallelogram-shaped prism. It is joined to one side 24 a of the shaped prism 24 and formed as a joining surface 26. When the laser beam 100 from the light source 12 is incident on the joint surface 26, the trapezoidal polarization beam splitter 14 causes the joint surface 26 to cause the laser beam 100 to pass through the measurement beam 102 as transmitted light and the reference beam 104 as reflected light. The measurement beam 102 and the reference beam 104 are emitted toward the recursive mirror 18.

この際、台形を構成する四辺１４ａ、１４ｂ、１４ｃ、１４ｄのうち辺１４ａ（上底）と辺１４ｂ（下底）は互いに平行な一組の対辺として構成され、辺１４ｃと辺１４ｄは他の一組の対辺として構成されているとともに、辺１４ｃは辺１４ａ、１４ｂに直交する辺として、辺１４ｄは接合面２６に平行な辺として構成されている。 At this time, of the four sides 14a, 14b, 14c, and 14d constituting the trapezoid, the side 14a (upper base) and the side 14b (lower base) are configured as a pair of opposite sides parallel to each other, and the side 14c and the side 14d The side 14 c is configured as a side orthogonal to the sides 14 a and 14 b, and the side 14 d is configured as a side parallel to the bonding surface 26.

辺１４ｃは、三角形部２２の一辺であって、辺１４ｂ（第１の辺）に直交し、接合面２６に対して４５度傾斜した第２の辺を構成するとともに、光源１２からのレーザビーム１００を透過する入射面を構成する。 The side 14 c is one side of the triangular portion 22 and forms a second side orthogonal to the side 14 b (first side) and inclined by 45 degrees with respect to the joint surface 26, and the laser beam from the light source 12. An incident surface that transmits 100 is formed.

辺１４ｄは、接合面２６と平行な第３の辺であって、接合面２６を透過した測定ビーム１０２を辺１４ｂから再帰ミラー１８の反射面１８ｂに向けて反射させる反射面を構成する。 The side 14 d is a third side parallel to the bonding surface 26 and constitutes a reflection surface that reflects the measurement beam 102 transmitted through the bonding surface 26 from the side 14 b toward the reflection surface 18 b of the recursive mirror 18.

接合面２６は、その一部が、辺１４ｃ（第２の辺）を透過したレーザビーム１００を測定ビーム１０２と参照ビーム１０４とに分岐させる分岐点として機能し、レーザビーム１００を測定ビーム１０２として透過するとともに、参照ビーム１０４を反射光として、辺１４ｂ側に反射させる第１の半透過部２６ａを構成する。 A part of the bonding surface 26 functions as a branching point for branching the laser beam 100 transmitted through the side 14 c (second side) into the measurement beam 102 and the reference beam 104, and the laser beam 100 is used as the measurement beam 102. A first semi-transmissive portion 26a that transmits and reflects the reference beam 104 to the side 14b as reflected light is configured.

一方、真空容器１６は、円筒状に形成されて、その両端側に、円盤状に形成された光透過性のカバー２８、３０が窓として固定され、内部が真空に保たれている。カバー２８は、辺１４ｂの中心部（辺１４ｂと接合面２６との交点を中心とする領域）に固定され、カバー３０は、再帰ミラー１８の入出射面１８ａの中心部に固定されている。すなわち、真空容器１６は、カバー２８、３０を介して、台形型偏光ビームスプリッタ１４と再帰ミラー１８とを連結するとともに、台形型偏光ビームスプリッタ１４と再帰ミラー１８とを結ぶ、参照ビーム１０４の光路として構成されている。 On the other hand, the vacuum container 16 is formed in a cylindrical shape, and light-transmitting covers 28 and 30 formed in a disk shape are fixed as windows on both ends thereof, and the inside is kept in a vacuum. The cover 28 is fixed to the center of the side 14b (a region centering on the intersection of the side 14b and the joint surface 26), and the cover 30 is fixed to the center of the incident / exit surface 18a of the recursive mirror 18. That is, the vacuum vessel 16 connects the trapezoidal polarization beam splitter 14 and the recursive mirror 18 via the covers 28 and 30 and connects the trapezoidal polarization beam splitter 14 and the recursive mirror 18 to the optical path of the reference beam 104. It is configured as.

再帰ミラー１８は、６０°の三角形形状に形成された全反射プリズムとして構成され、その入出射面１８ａが、台形型偏光ビームスプリッタ１４の辺１４ｂと平行になって配置されている。この再帰ミラー１８は、台形型偏光ビームスプリッタ１４からの測定ビーム１０２と参照ビーム１０４を入射するとともに、入射した測定ビーム１０２と参照ビーム１０４をそれぞれ入射した経路とは異なる経路で、台形型偏光ビームスプリッタ１４の辺１４ｂに向けて反射させるコーナーキューブプリズムとして構成されている。 The recursive mirror 18 is configured as a total reflection prism formed in a 60 ° triangular shape, and its incident / exit surface 18 a is arranged in parallel with the side 14 b of the trapezoidal polarization beam splitter 14. The recursive mirror 18 is incident on the measurement beam 102 and the reference beam 104 from the trapezoidal polarization beam splitter 14, and has a trapezoidal polarization beam on a path different from the path on which the measurement beam 102 and the reference beam 104 are incident. The corner cube prism is configured to reflect toward the side 14 b of the splitter 14.

具体的には、再帰ミラー１８の入出射面１８ａのうち真空容器１６と相対向する中心部は、参照ビーム１０４の入射面または出射面を構成し、入出射面１８ａのうち中心部から外れた部位は、測定ビーム１０２の入射面または出射面を構成するようになっている。 Specifically, the central portion of the incident / exit surface 18a of the recursive mirror 18 that is opposite to the vacuum vessel 16 constitutes the incident surface or the output surface of the reference beam 104, and deviates from the central portion of the incident / exit surface 18a. The part constitutes an incident surface or an output surface of the measurement beam 102.

また、再帰ミラー１８の頂点では反射面１８ｂ、１８ｃ、１８ｄ（図示せず）が直角をもって構成されて結合されている。再帰ミラー１８の二つの反射面１８ｂ、１８ｃの一方の反射面１８ｂは、入出射面１８ａから入射した測定ビーム１０２を他方の反射面１８ｃに反射させるとともに、入出射面１８ａから入射して他方の反射面１８ｃで反射した参照ビーム１０４を真空容器１６側へ反射させる第１のミラー反射面を構成する。 Further, reflection surfaces 18b, 18c, 18d (not shown) are formed at right angles at the apex of the recursive mirror 18 and are coupled. One reflecting surface 18b of the two reflecting surfaces 18b and 18c of the recursive mirror 18 reflects the measurement beam 102 incident from the incident / exiting surface 18a to the other reflecting surface 18c, and enters the other reflecting surface 18a from the other incident surface 18a. A first mirror reflecting surface that reflects the reference beam 104 reflected by the reflecting surface 18c toward the vacuum container 16 is configured.

さらに、再帰ミラー１８の他方の反射面１８ｃは、反射面（第１のミラー反射面）１８ｂで反射した測定ビーム１０２を真空容器１６から外れた領域（空気が存在する領域）を介して、台形型偏光ビームスプリッタ１４の反射面１４ｂ側へ反射させるとともに、入出射面１８ａから入射した参照ビーム１０４を反射面（第１のミラー反射面）１８ｂ側に反射させる第２のミラー反射面を構成する。
再帰ミラー１８で反射した測定ビーム１０２と参照ビーム１０４のうち測定ビーム１０２は、辺１４ｂから接合面２６に入射し、参照ビーム１０４は辺１４ｂから辺１４ｄに入射する。 Further, the other reflecting surface 18c of the recursive mirror 18 is trapezoidal via a region (region where air exists) where the measurement beam 102 reflected by the reflecting surface (first mirror reflecting surface) 18b is separated from the vacuum vessel 16. A second mirror reflecting surface that reflects the reference beam 104 incident from the incident / exiting surface 18a to the reflecting surface (first mirror reflecting surface) 18b side is formed while reflecting to the reflecting surface 14b side of the polarizing beam splitter 14. .
Of the measurement beam 102 and the reference beam 104 reflected by the recursive mirror 18, the measurement beam 102 is incident on the joint surface 26 from the side 14b, and the reference beam 104 is incident on the side 14d from the side 14b.

この際、辺１４ｄは、真空容器１６から辺１４ｂを介して入射した参照ビーム１０４を接合面２６側に反射させる反射面を構成する。 At this time, the side 14d constitutes a reflection surface that reflects the reference beam 104 incident from the vacuum vessel 16 through the side 14b to the bonding surface 26 side.

また、接合面２６の他の部位は、辺１４ｄで反射した参照ビーム１０４を辺１４ａ側に反射させ、再帰ミラー１８から辺１４ｂに入射した測定ビーム１０２を辺１４ａ側に透過し、参照ビーム１０４と測定ビーム１０２との合成による合成ビーム１０６を辺１４ａ側へ照射する第２の半透過部２６ｂを構成するとともに、参照ビーム１０４と測定ビーム１０２とを合成する合成点として機能する。 Further, the other part of the joint surface 26 reflects the reference beam 104 reflected by the side 14d to the side 14a side, transmits the measurement beam 102 incident on the side 14b from the recursive mirror 18 to the side 14a side, and transmits the reference beam 104. The second semi-transmissive portion 26b that irradiates the side 14a with the combined beam 106 obtained by combining the measurement beam 102 and the measurement beam 102 functions as a combination point for combining the reference beam 104 and the measurement beam 102.

さらに、辺１４ａは、辺１４ｂと平行な第４の辺であって、接合面２６からの合成ビーム１０６を透過して、計測器２０に向けて出射する出射面を構成する。 Further, the side 14 a is a fourth side parallel to the side 14 b, and constitutes an emission surface that transmits the combined beam 106 from the bonding surface 26 and emits it toward the measuring instrument 20.

計測器２０は、例えば、合成ビーム１０６を構成する参照ビーム１０４と測定ビーム１０２との干渉に伴う干渉信号を電気信号に変換する光検出器と、電気信号を位相信号に変換し、位相信号を基に空気の屈折率の絶対値を演算する演算器で構成されている。なお、演算器としては、位相信号を基にビームの波長を演算するもので構成することもできる。 The measuring instrument 20 includes, for example, a photodetector that converts an interference signal associated with interference between the reference beam 104 and the measurement beam 102 constituting the combined beam 106 into an electrical signal, and converts the electrical signal into a phase signal. Based on an arithmetic unit that calculates the absolute value of the refractive index of air. Note that the calculator can be configured to calculate the wavelength of the beam based on the phase signal.

上記構成において、光源１２から辺１４ｃに向けてレーザビーム１００が出射されると、このレーザビーム１００は、辺１４を透過して接合面２６の第１の半透過部２６ａで測定ビーム１０２と参照ビーム１０４に分岐される。測定ビーム１０２は、辺１４ｄで反射した後、空気中を伝播して再帰ミラー１８に入射し、再帰ミラー１８の反射面１８ｂ、１８ｃでそれぞれ反射した後、空気中を伝播して辺１４ｂから接合面２６の第２の半透過部２６ｂに入射する。 In the above configuration, when the laser beam 100 is emitted from the light source 12 toward the side 14c, the laser beam 100 passes through the side 14 and is referred to the measurement beam 102 at the first semi-transmissive portion 26a of the bonding surface 26. The beam 104 is branched. The measurement beam 102 is reflected by the side 14d, propagates in the air, enters the recursive mirror 18, is reflected by the reflecting surfaces 18b and 18c of the recursive mirror 18, and then propagates in the air and joins from the side 14b. The light enters the second semi-transmissive portion 26 b of the surface 26.

一方、第１の半透過部２６ａで分岐された参照ビーム１０４は、カバー２８、真空容器１６、カバー３０を伝播して再帰ミラー１８に入射し、再帰ミラー１８の反射面１８ｃ、１８ｂでそれぞれ反射した後、カバー３０、真空容器１６、カバー２８を伝播して辺１４ｄに入射し、辺１４ｄで反射した後、接合面２６の第２の半透過部２６ｂに入射する。 On the other hand, the reference beam 104 branched by the first semi-transmissive portion 26a propagates through the cover 28, the vacuum vessel 16, and the cover 30, enters the recursive mirror 18, and is reflected by the reflecting surfaces 18c and 18b of the recursive mirror 18, respectively. After that, the light propagates through the cover 30, the vacuum container 16, and the cover 28, enters the side 14 d, is reflected by the side 14 d, and then enters the second semi-transmissive portion 26 b of the joint surface 26.

接合面２６の第２の半透過部２６ｂに入射した参照ビーム１０４は、接合面２６の第２の半透過部２６ｂで測定ビーム１０２と合成される。参照ビーム１０４と測定ビーム１０２の合成による合成ビーム１０６は、辺１４ａから計測器２０に向けて出射される。 The reference beam 104 incident on the second semi-transmissive portion 26b of the joint surface 26 is combined with the measurement beam 102 by the second semi-transmissive portion 26b of the joint surface 26. A combined beam 106 obtained by combining the reference beam 104 and the measurement beam 102 is emitted from the side 14 a toward the measuring instrument 20.

この際、第１の半透過部２６ａ（分岐点）と第２の半透過部２６ｂ（合成点）とを結ぶ、測定ビーム１０２の光路と、第１の半透過部２６ａ（分岐点）と第２の半透過部２６ｂ（合成点）とを結ぶ、参照ビーム１０４の光路は、同一の光路長に設定されている。 At this time, the optical path of the measurement beam 102 connecting the first semi-transmissive part 26a (branch point) and the second semi-transmissive part 26b (synthesis point), the first semi-transmissive part 26a (branch point) and the second The optical path of the reference beam 104 connecting the two semi-transmissive portions 26b (combining points) is set to the same optical path length.

具体的には、図２に示すように、第１の半透過部２６ａと辺１４ｄにおける測定ビーム１０２の反射点Ｐ１との距離をＬ１とし、第２の半透過部２６ｂと辺１４ｄにおける参照ビーム１０４の反射点Ｐ２との距離をＬ２とすると、Ｌ１、Ｌ２は、平行四辺形部２４の各辺に等しいので、Ｌ１＝Ｌ２となる。 Specifically, as shown in FIG. 2, the distance between the first semi-transmissive portion 26a and the reflection point P1 of the measurement beam 102 at the side 14d is L1, and the reference beam at the second semi-transmissive portion 26b and the side 14d. Assuming that the distance from the reflection point P2 of 104 is L2, L1 and L2 are equal to the respective sides of the parallelogram portion 24, so L1 = L2.

反射点Ｐ１と測定ビーム１０２の反射面１８ｂにおける反射点Ｐ３との距離をＬ３とし、第１の半透過部２６ａと、再帰ミラー１８の反射面１８ｃに入射する参照ビーム１０４と測定ビーム１０２との交点Ｐ４との距離をＬ４とすると、台形の辺１４ｂと再帰ミラー１８の入出射面１８ａが互いに平行であるので、Ｌ３＝Ｌ４となる。 The distance between the reflection point P1 and the reflection point P3 on the reflection surface 18b of the measurement beam 102 is L3, and the reference beam 104 and the measurement beam 102 incident on the first semi-transmissive portion 26a and the reflection surface 18c of the recursive mirror 18 are set. When the distance from the intersection P4 is L4, the trapezoidal side 14b and the incident / exit surface 18a of the recursive mirror 18 are parallel to each other, and therefore L3 = L4.

反射点Ｐ３と、反射点Ｐ３で反射した測定ビーム１０２と再帰ミラー１８の反射面１８ｂで反射した参照ビーム１０４との交点Ｐ５との距離をＬ５とし、交点Ｐ５と反射面１８ｂにおける参照ビーム１０４の反射点Ｐ６との距離をＬ６とすると、再帰ミラー１８が直角三角形であるので、Ｌ５＝Ｌ６となる。 The distance between the reflection point P3 and the intersection P5 of the measurement beam 102 reflected at the reflection point P3 and the reference beam 104 reflected by the reflection surface 18b of the recursive mirror 18 is L5, and the reference beam 104 at the intersection P5 and the reflection surface 18b When the distance from the reflection point P6 is L6, the recursive mirror 18 is a right triangle, so L5 = L6.

交点Ｐ５と交点Ｐ４との距離をＬ７とし、再帰ミラー１８の反射面１８ｃにおける参照ビーム１０４の反射点Ｐ７と反射面１８ｂにおける参照ビーム１０４の反射点Ｐ６との距離をＬ８とすると、再帰ミラー１８が直角三角形であるので、Ｌ７＝Ｌ８となる。 When the distance between the intersection point P5 and the intersection point P4 is L7 and the distance between the reflection point P7 of the reference beam 104 on the reflection surface 18c of the recursive mirror 18 and the reflection point P6 of the reference beam 104 on the reflection surface 18b is L8, the recursion mirror 18 Since L is a right triangle, L7 = L8.

交点Ｐ４と、再帰ミラー１８の反射面１８ｃにおける測定ビーム１０２の反射点Ｐ８との距離をＬ９とし、交点Ｐ４と反射点Ｐ７との距離をＬ１０とすると、再帰ミラー１８が直角三角形であるので、Ｌ９＝Ｌ１０となる。 When the distance between the intersection point P4 and the reflection point P8 of the measurement beam 102 on the reflection surface 18c of the recursive mirror 18 is L9 and the distance between the intersection point P4 and the reflection point P7 is L10, the recursive mirror 18 is a right triangle. L9 = L10.

反射点Ｐ８と第２の半透過部２６ｂとの距離をＬ１１とし、交点Ｐ５と辺１４ｄにおける反射点Ｐ２との距離をＬ１２とすると、台形の辺１４ｂと直角三角形の入出射面１８ａが互いに平行であるので、Ｌ１１＝Ｌ１２となる。 When the distance between the reflection point P8 and the second semi-transmissive portion 26b is L11, and the distance between the intersection P5 and the reflection point P2 at the side 14d is L12, the trapezoidal side 14b and the right-angled triangular entrance / exit surface 18a are parallel to each other. Therefore, L11 = L12.

距離Ｌ１、Ｌ３、Ｌ５、Ｌ７、Ｌ９、Ｌ１１の合計は、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ光路のうち測定ビーム１０２の光路長に対応し、距離Ｌ４、Ｌ１０、Ｌ８、Ｌ６、Ｌ１２、Ｌ２の合計は、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ光路のうち参照ビーム１０４の光路長に対応し、Ｌ１＋Ｌ３＋Ｌ５＋Ｌ７＋Ｌ９＋Ｌ１１＝Ｌ２＋Ｌ４＋Ｌ６＋Ｌ８＋Ｌ１０＋Ｌ１２の関係にある。 The sum of the distances L1, L3, L5, L7, L9, and L11 corresponds to the optical path length of the measurement beam 102 among the optical paths connecting the first semi-transmissive portion 26a and the second semi-transmissive portion 26b, and the distance L4, The sum of L10, L8, L6, L12, and L2 corresponds to the optical path length of the reference beam 104 among the optical paths connecting the first semi-transmissive portion 26a and the second semi-transmissive portion 26b, and has a relationship of L1 + L3 + L5 + L7 + L9 + L11 = L2 + L4 + L6 + L8 + L10 + L12. is there.

従って、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ、測定ビーム１０２の光路（Ｌ１＋Ｌ３＋Ｌ５＋Ｌ７＋Ｌ９＋Ｌ１１）と、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ、参照ビーム１０４の光路（Ｌ４＋Ｌ１０＋Ｌ８＋Ｌ６＋Ｌ１２＋Ｌ２）は、同一の光路長となる。 Accordingly, the optical path of the measurement beam 102 (L1 + L3 + L5 + L7 + L9 + L11) connecting the first semi-transmissive part 26a and the second semi-transmissive part 26b, and the first semi-transmissive part 26a and the second semi-transmissive part 26b are connected. The optical path (L4 + L10 + L8 + L6 + L12 + L2) of the reference beam 104 has the same optical path length.

本実施例によれば、台形型ビームスプリッタ１４と再帰ミラー１８を真空容器１６を介して互いに平行に配置するとともに、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ測定ビーム１０２の光路と、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ参照ビーム１０４の光路を同一の光路長に設定したので、干渉計を構成する各要素に歪みや膨張が生じても、これらの影響を抑制して、空気の屈折率を安定した状態で高精度に測定することができる。 According to this embodiment, the trapezoidal beam splitter 14 and the recursive mirror 18 are arranged in parallel to each other via the vacuum vessel 16, and the measurement beam connecting the first semi-transmissive portion 26a and the second semi-transmissive portion 26b. Since the optical path of the reference beam 104 connecting the optical path 102 and the first semi-transmissive part 26a and the second semi-transmissive part 26b is set to the same optical path length, distortion and expansion are caused in each element constituting the interferometer. Even if they occur, these effects can be suppressed and the refractive index of air can be measured with high accuracy in a stable state.

また、本実施例によれば、計測器２０で合成ビーム１０６を基にビームの波長を測定するときには、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ、測定ビーム１０２の光路と、第１の半透過部２６ａと第２の半透過部２６ｂとを結ぶ、参照ビーム１０４の光路が同一の光路長に設定されているので、ビームの波長を高精度に測定することができる。 Further, according to the present embodiment, when measuring the wavelength of the beam based on the combined beam 106 by the measuring instrument 20, the measurement beam 102 connecting the first semi-transmissive portion 26a and the second semi-transmissive portion 26b is used. Since the optical path of the reference beam 104 connecting the optical path and the first semi-transmissive part 26a and the second semi-transmissive part 26b is set to the same optical path length, the wavelength of the beam can be measured with high accuracy. it can.

また、本実施例によれば、レーザビーム１００を合成ビーム１０６として出射するに際して、１／４波長板を用いることなく、台形型偏光ビームスプリッタ１４の入射面（辺１４ｃ）に対して９０度の方向（辺１４ａ）に合成ビーム１０６を出射することができるので、受光装置である計測器２０の設置が容易となる。 In addition, according to the present embodiment, when the laser beam 100 is emitted as the combined beam 106, it is 90 degrees with respect to the incident surface (side 14 c) of the trapezoidal polarization beam splitter 14 without using a quarter-wave plate. Since the combined beam 106 can be emitted in the direction (side 14a), the installation of the measuring instrument 20 that is a light receiving device is facilitated.

本発明に係る干渉計の一実施例を示すブロック構成図である。It is a block block diagram which shows one Example of the interferometer which concerns on this invention. 測定ビームと参照ビームの光路を説明するための構成図である。It is a block diagram for demonstrating the optical path of a measurement beam and a reference beam.

１０干渉計
１２光源
１４台形型偏光ビームスプリッタ
１６真空容器
１８再帰ミラー
２０計測器
１００レーザビーム
１０２測定ビーム
１０４参照ビーム
１０６合成ビーム DESCRIPTION OF SYMBOLS 10 Interferometer 12 Light source 14 Trapezoidal polarization beam splitter 16 Vacuum container 18 Recursive mirror 20 Measuring instrument 100 Laser beam 102 Measuring beam 104 Reference beam 106 Composite beam

Claims

A light source for generating a laser beam;
A trapezoidal polarization that splits the laser beam from the light source into a measurement beam and a reference beam and emits it toward the recursive mirror, and combines the measurement beam reflected by the recursive mirror and the reference beam to emit a combined beam. A beam splitter,
A recursive mirror disposed opposite to the trapezoidal polarizing beam splitter and reflecting the incident measurement beam and the reference beam toward the trapezoidal polarizing beam splitter through paths different from the incident paths,
A vacuum vessel that connects the trapezoidal polarizing beam splitter and the recursive mirror, and forms an optical path of the reference beam;
A measuring instrument that receives the combined beam emitted from the trapezoidal polarization beam splitter and performs measurement associated with interference between the measurement beam and the reference beam based on the received combined beam;
Of the optical path connecting the branch point where the laser beam branches into the measurement beam and the reference beam, and the synthesis point where the measurement beam reflected by the recursive mirror and the reference beam are combined into the combined beam, the optical path of the measurement beam And the optical path of the reference beam is an interferometer set to the same optical path length,
The trapezoidal polarization beam splitter has a trapezoidal shape formed around a right triangle portion and a parallelogram portion whose one side is joined to the hypotenuse of the right triangle portion.
A part of the joint surface formed by joining the right triangle part and the parallelogram part is a first semi-transmission part that branches the laser beam from the light source into a measurement beam as transmitted light and a reference beam as reflected light Configure
The first side inclined by 45 degrees with respect to the joint surface constitutes an emission surface that emits the measurement beam and the reference beam branched by the first semi-transmissive portion toward the recursive mirror,
A second side that is one side of the right triangle portion and is orthogonal to the first side constitutes an incident surface that transmits a laser beam from the light source,
Wherein a one side of a parallelogram-shaped part, the third side parallel to the bonding surface is to reflect toward the input-output face of the recursive mirror measurement beam transmitted through the bonding surface from said first side And a reflecting surface for reflecting the reference beam incident from the vacuum vessel through the first side to the bonding surface side,
The other part of the joint surface is a measurement in which the reference beam reflected by the third side is reflected to the fourth side parallel to the first side and is incident on the first side from the recursive mirror. A second translucent part configured to transmit a beam to the fourth side and combine the reference beam and the measurement beam to generate a combined beam;
Wherein a one side of a parallelogram shape portion, the fourth side constitutes the emitting surface for emitting the combined beam from the second transmitting portion toward the instrument,
The recursive mirror is formed in a right triangle shape, and its hypotenuse is arranged parallel to the first side of the trapezoidal polarizing beam splitter,
Of the hypotenuse of the retroreflective mirror, the central part opposite to the vacuum vessel constitutes the entrance / exit surface of the reference beam, and the part of the hypotenuse of the retroreflective mirror that is off the central part is the entrance of the measurement beam Configure the exit surface,
One reflecting surface of the remaining two sides of the recursive mirror reflects the measurement beam incident from the incident / exiting surface to the other reflecting surface and is incident from the incident / exiting surface and reflected by the other reflecting surface. Forming a first mirror reflecting surface for reflecting the reference beam toward the vacuum container;
The other reflecting surface of the retroreflecting mirror reflects the measurement beam reflected by the first mirror reflecting surface to the first side through a region outside the vacuum vessel and is incident from the incident / exiting surface. An interferometer comprising a second mirror reflection surface configured to reflect the reference beam reflected toward the first mirror reflection surface.