JP2009162629A - Interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a refractive index of air in a stable condition with high accuracy, by suppressing any effects even when distortion or expansion brings about in each element constituting an interferometer. <P>SOLUTION: An interferometer includes: a trapezoid-shaped polarization beam splitter 14 splitting a laser beam 100 from a light source 12 into a measurement beam 102 and a reference beam 104 to irradiate a synthesized beam 106; a reflective mirror 18 arranged to be opposing to the trapezoid-shaped polarization beam splitter 14; a vacuum container 16 connecting the trapezoid-shaped polarization beam splitter 14 and the reflective mirror 18 and forming an optical path of the reference beam 104; and a measuring apparatus 20 carrying out measurement associated with interference of the measurement beam 102 and the reference beam 104. Among the optical path connecting a first semi-transparent section 26a and a second semi-transparent section 26b, the optical paths of the measurement beam 102 and the reference beam 104 are set as having the same optical path length. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an interferometer capable of measuring a refractive index of a gas using a laser beam.

  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).

JP-A-6-27020

  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.

  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.

  In order to achieve the above object, an interferometer according to claim 1 divides a laser beam from a light source that generates a laser beam into a measurement beam and a reference beam, and emits the laser beam toward a recursive mirror. A trapezoidal polarization beam splitter that combines the measurement beam reflected by the recursive mirror and a reference beam to emit a combined beam; and the measurement beam and the reference beam that are disposed opposite to the trapezoidal polarization beam splitter. A recursive mirror that reflects toward the trapezoidal polarizing beam splitter through a path different from the incident path, a vacuum container that connects the trapezoidal polarizing beam splitter and the recursive mirror, and forms an optical path of the reference beam And receiving the combined beam emitted from the trapezoidal polarizing beam splitter, and based on the received combined beam A measuring instrument that performs measurement associated with interference between the constant beam and the reference beam, a branch point (26a) where the laser beam branches into the measurement beam and the reference beam, and the measurement beam and the reference beam reflected by the recursive mirror The optical path of the measurement beam and the optical path of the reference beam among the optical paths connecting the synthesis point (26b) where the beam is synthesized with the synthesized beam are set to the same optical path length.

  (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.

  An interferometer according to a second aspect is the interferometer according to the first aspect, wherein the trapezoidal polarizing beam splitter includes a right triangle portion and a parallelogram portion whose one side is joined to the hypotenuse of the right triangle portion. The four sides of the trapezoidal shape (14) are formed in the periphery thereof, and a part of the joint surface formed by joining the right-angled triangle part and the parallelogram part is obtained by transmitting the laser beam from the light source as transmitted light. A first semi-transmission portion for branching into a measurement beam and a reference beam as reflected light is configured, and a first side inclined by 45 degrees with respect to the joint surface is branched at the first semi-transmission portion. An emission surface that emits a beam and a reference beam toward the recursive mirror is configured, and a second side that is one side of the triangular portion and orthogonal to the first side transmits the laser beam from the light source. The incident surface that forms the four sides And a third side parallel to the joint surface reflects a measurement beam transmitted through the joint surface from the first side toward the incident / exit surface of the recursive mirror and the vacuum A reflection surface configured to reflect the reference beam incident from the container through the first side to the bonding surface side; and another portion of the bonding surface that reflects the reference beam reflected by the third side A measurement beam that is reflected on the side of the fourth side and is incident on the first side from the recursive mirror is transmitted to the fourth side, and a combined beam is generated by synthesizing the reference beam and the measurement beam. The fourth side that is one side of the quadrangular part and parallel to the first side emits a combined beam from the second transmission part toward the measuring instrument. Constituting the exit surface, the recursive mirror is formed in a right triangle shape; Is arranged in parallel with the first side of the trapezoidal polarizing beam splitter, and the central portion of the hypotenuse of the recursive mirror opposite to the vacuum vessel constitutes the incident / exit surface of the reference beam Of the oblique sides of the recursive mirror, a portion deviating from the central portion constitutes the incident / exit surface of the measurement beam, and one of the remaining two sides of the recursive mirror is reflected from the incident / exit surface. A first mirror reflecting surface configured to reflect the incident measurement beam to the other reflecting surface and reflect the reference beam incident from the incident / exiting surface and reflected by the other reflecting surface toward the vacuum chamber; The other reflecting surface of the recursive 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. Reference beam The second mirror reflecting surface is configured to reflect the light beam toward the first mirror reflecting surface side.

  (Operation) First semi-transmission part for branching a part of the joint surface formed by joining the right triangle part and the parallelogram part into a measurement beam as transmitted light and a reference beam as reflected light. The first side inclined by 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 first side constitutes an incident surface that transmits the laser beam from the light source, and the third side parallel to the bonding surface recurs the measurement beam transmitted through the bonding surface from the first side. A reflection surface is formed that reflects toward the oblique side of the mirror and reflects the reference beam incident from the vacuum vessel via the first side to the bonding surface side. The other part of the bonding surface is the third side. The reflected reference beam is reflected to the fourth side, and a recursive mirror A measurement beam incident on the fourth side is transmitted to the fourth side, and a second semi-transmission unit that combines the reference beam and the measurement beam to generate a combined beam constitutes 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 light and incident from the light incident / exit surface. A first mirror reflecting surface that reflects the reference beam reflected by the reflecting surface to the vacuum vessel side is configured, and the other reflecting surface of the recursive mirror is separated from the measurement vessel reflected by the first mirror reflecting surface from the vacuum vessel. 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.

  According to the present invention, according to the interferometer of the first aspect, even if distortion or expansion occurs in each element constituting the interferometer, these effects are suppressed and the refractive index of air is stabilized. It can be measured with high accuracy.

  According to the second aspect, the optical path of the measurement beam and the optical path of the reference beam in the optical path connecting the first semi-transmissive part and the second semi-transmissive part can be set to the same optical path length.

  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.

  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.

  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.

  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, and the hypotenuse 22a of the right-angle prism 22 is a parallelogram. 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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

  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.

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.

  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.

  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.

  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.

  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.

  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 14, propagates in the air, enters the return mirror 18, is reflected by the reflecting surfaces 18 b and 18 c of the return mirror 18, and then propagates in the air and joins from the side 14 b. The light enters the second semi-transmissive portion 26 b of the surface 26.

  On the other hand, the reference beam 104 branched by the first semi-transmissive portion 26a propagates through the cover 29, 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 return 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.

  The reference beam 104 incident on the second semi-transmissive portion 26 b of the joint surface 26 is combined with the measurement beam 102 by the second semi-transmissive portion 26 b 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.

  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.

  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.

  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.

  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.

  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.

  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.

  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 triangle input / output surface 18a are parallel to each other. Therefore, L11 = L12.

  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.

  Therefore, 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.

  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.

  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.

  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.

It is a block block diagram which shows one Example of the interferometer which concerns on this invention. It is a block diagram for demonstrating the optical path of a measurement beam and a reference beam.

Explanation of symbols

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 Measurement beam 104 Reference beam 106 Composite beam

Claims (2)

A light source that generates a laser beam, a laser beam from the light source is branched into a measurement beam and a reference beam, and emitted toward the recursive mirror, and the measurement beam reflected by the recursive mirror and the reference beam are combined, A trapezoidal polarizing beam splitter that emits a combined beam;
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;
An optical path of the measurement beam among optical paths connecting a branch point where the laser beam branches to the measurement beam and the reference beam, and a synthesis point where the measurement beam reflected by the recursive mirror and the reference beam are combined with the combined beam, The interferometer, wherein the optical path of the reference beam is set to the same optical path length. The interferometer according to claim 1, wherein
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 triangular portion and is orthogonal to the first side constitutes an incident surface that transmits a laser beam from the light source;
A third side that is one side of the quadrangular portion and is parallel to the joint surface reflects the measurement beam transmitted through the joint surface from the first side toward the incident / exit surface of the recursive mirror. A reflection surface configured to reflect the reference beam incident from the vacuum vessel through the first side to the bonding surface side;
The other part of the joint surface reflects the reference beam reflected by the third side to the fourth side, and the measurement beam incident on the first side from the recursive mirror is reflected by the fourth side. A second semi-transmissive portion that transmits to the side and combines the reference beam and the measurement beam to generate a combined beam;
A side that is one side of the quadrangular part and is parallel to the first side constitutes an emission surface that emits a combined beam from the second transmission part toward the measuring 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.

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