JP5494667B2 - Interference optical system and spectroscope equipped with the same - Google Patents

Description

  The present invention relates to an interference optical system constituting a Michelson interferometer, and a spectroscope equipped with the interference optical system.

  FIG. 9 shows a schematic configuration of an interferometer portion of a conventional spectroscope. In this optical system, light from the light source 101 is reflected by the reflecting surface of the collimating optical system 102 and converted into parallel light, and then enters a BS (beam splitter) 103 where it is separated into two light beams. The separated light beams are respectively reflected by the movable mirror 104 and the fixed mirror 105, and then enter the BS 103 again to be combined and emitted as interference light. The interference light is reflected by a plurality of reflecting surfaces of the condensing optical system 106 and guided to the detector 107 while condensing.

  Here, the optical path of the light transmitted from the collimating optical system 102 to the movable mirror 104 through the BS 103 is defined as a first optical path L1, and the condensing optical system 106 (particularly the first reflecting surface) is transmitted from the fixed mirror 105 through the BS 103. In the optical system of Patent Document 1, the light source 101 is positioned on the fixed mirror 105 side with respect to the first optical path L1, and the detector 107 is the second optical path L2. It is located on the movable mirror 104 side with respect to the optical path L2. The spectroscope of Patent Document 1 has a slightly different configuration from that of FIG. 9 in that the BS is arranged so that the fixed mirror and the movable mirror are located on the same side with respect to the light separation surface of the BS. The general operation is the same as the configuration of FIG.

  On the other hand, in the optical system of Patent Document 2, the light source 101 is positioned on the side opposite to the fixed mirror 105 with respect to the first optical path L1, and the detector 107 is on the movable mirror 104 side with respect to the second optical path L2. It is an optical system that can be regarded as equivalent to the optical system located in The optical system of Patent Document 2 is slightly different from FIG. 9 and Patent Document 1 in the arrangement of optical members, but the basic operation is the same as FIG. 9 and Patent Document 1. For convenience of explanation below, even in the case of explaining the optical system of Patent Document 2, members having the same functions as those in FIG.

JP-A-5-72128 JP 2000-171302 A

  By the way, if incident light is separated into P-polarized light and S-polarized light when transmitted or reflected through the BS, the two lights interfere when reflected by the fixed mirror and the movable mirror and return to the BS again. Disappear. In particular, when infrared light is used, it is known that the above-described polarization separation occurs unless the infrared light is incident on the BS at an angle as small as possible with respect to the normal line of the light separation surface. Such a problem of polarization separation is difficult to solve in principle even if the film design of the light separation film of the BS is devised. Therefore, in order to suppress the polarization separation without using a BS having a complicated film design and realize high coherence, the light from the light source is more than 45 ° with respect to the normal of the light separation surface of the BS. It is desirable to adopt a configuration that allows incidence at a small angle.

  In this regard, in the optical system of FIG. 9, the light source 101 is positioned on the fixed mirror 105 side with respect to the first optical path L1, and the detector 107 is positioned on the movable mirror 104 side with respect to the second optical path L2. Therefore, even if the second optical path L2 is inclined with respect to the first optical path L1 so that the incident angle is smaller than 45 ° with respect to the BS 103, the first optical path L1 and the second optical path Depending on the optical path length of L2, the light source 101 and the detector 107 interfere with the fixed mirror 105 and the movable mirror 104, respectively, or the light fluxes of the first optical path L1 and the second optical path L2 are measured by the detector 107 and the light source 101, respectively. There is a risk of being. For this reason, it becomes difficult to realize an incident angle smaller than 45 ° with respect to the BS 103.

  In the Michelson interferometer, for example, it is necessary to provide a drive mechanism for a movable mirror and a position adjustment mechanism for the BS. However, in the optical system of FIG. 9, since it is difficult for the above reasons to incline the second optical path L2 with respect to the first optical path L1, a wide space for providing the drive mechanism and the like is ensured. For this purpose, the length of the arm, that is, the distance between the BS 103 and the movable mirror 104 and between the BS 103 and the fixed mirror 105 must be long. As a result, the optical system becomes large.

  On the other hand, the optical system of Patent Document 2 is common to the optical system of FIG. 9 and Patent Document 1 in that the detector 107 is positioned on the movable mirror 104 side with respect to the second optical path L2. 101 is positioned on the opposite side of the first optical path L1 from the fixed mirror 105, and the optical path from the BS 103 to the detector 107 is bent by a plurality of reflecting surfaces to ensure a long optical path. An incident angle smaller than 45 ° with respect to the BS 103 is realized while avoiding being scraped by a member. However, since it is necessary to ensure a long optical path from the BS 103 to the detector 107, an increase in the size of the optical system itself cannot be avoided. Furthermore, since the light source 101 and the detector 107 are arranged in four separate spaces around the BS 103, which are formed by crossing the first optical path L1 and the second optical path L2, The arrangement space cannot be used effectively, and the optical system cannot be configured compactly.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to achieve a high coherence by reducing the incident angle with respect to the BS with a small configuration, as well as a movable mirror driving mechanism and a BS. An interference optical system that can easily secure an arrangement space for the position adjustment mechanism of the optical system and that can be made compact by effectively using the arrangement space around the BS, and a spectrometer equipped with the interference optical system It is in.

  The interference optical system of the present invention separates the light emitted from the light source and the light source and guides it to the movable mirror and the fixed mirror, and combines and emits each light reflected by the movable mirror and the fixed mirror. An interference optical system comprising: a beam splitter that detects the light emitted from the beam splitter, and converts the light from the light source into parallel light that is guided to the beam splitter. A collimating optical system; and a condensing optical system that condenses the light emitted by combining with the beam splitter and guides it to the detector, and the collimating optical system and the condensing optical system are eccentric. Each of the reflection optical systems, and is disposed substantially symmetrically with respect to a plane passing through the center of the beam splitter and passing between the movable mirror and the fixed mirror, When one of the moving mirror and the fixed mirror is a first mirror and the other is a second mirror, both the light source and the detector pass through the beam splitter from the collimating optical system and pass through the first beam splitter. The light path to the mirror is opposite to the second mirror, and the light path from the second mirror through the beam splitter to the condensing optical system is the light path. It is characterized by being arranged on the opposite side to the first mirror.

  In the interference optical system of the present invention, it is desirable that an incident angle of light incident on the beam splitter from the collimating optical system is smaller than 45 ° with respect to a normal line of the light separation surface of the beam splitter.

  In the interference optical system according to the aspect of the invention, it is preferable that the incident angle is greater than 20 ° with respect to the normal line of the light separation surface of the beam splitter.

  In the interference optical system of the present invention, the incident light beam and the reflected light beam on the respective reflecting surfaces of the collimating optical system and the condensing optical system are formed on the axis along which the central light beam of the light beam traveling from the light source toward the detector travels. When the angle is an eccentric angle, the eccentric angle in the collimating optical system and the condensing optical system is preferably 20 ° or more and 45 ° or less.

  In the interference optical system according to the aspect of the invention, it is preferable that the first mirror and the second mirror are disposed on opposite sides of the light separation surface of the beam splitter.

  In the interference optical system according to the aspect of the invention, it is preferable that the collimating optical system and the condensing optical system are arranged on opposite sides with respect to the light separation surface of the beam splitter.

  The spectroscope of the present invention includes the above-described interference optical system of the present invention, a calculation unit that calculates a spectrum based on a signal output from the interference optical system, and an output unit that outputs the calculated spectrum. It is desirable that

  According to the present invention, both the light source and the detector are compared with the optical path (first optical path) of the light transmitted from the collimating optical system through the beam splitter (BS) to the first mirror (for example, movable mirror). What is the first mirror relative to the optical path (second optical path) of light that is opposite to the second mirror (for example, a fixed mirror) and that passes through the BS from the second mirror and travels toward the condensing optical system? Located on the opposite side.

  With such an arrangement, even if the second optical path is tilted with respect to the first optical path so that the incident angle with respect to the BS becomes small, the light beam traveling in the first and second optical paths is broken by the light source and the detector. In order to avoid such inconvenience, it is not necessary to ensure a long optical path for light entering and exiting the BS. Accordingly, an optical arrangement in which the incident angle with respect to the BS is smaller than 45 ° can be easily realized with a small configuration, thereby suppressing polarization separation at the BS without using a BS having a complicated film design. High coherence can be realized. Further, both the light source and the detector can be arranged in any one of the four spaces around the BS formed by crossing the first optical path and the second optical path. It can be used effectively.

  Moreover, since an optical arrangement in which the incident angle with respect to the BS is smaller than 45 ° can be realized, a wide space can be secured on the opposite side of the BS from the arrangement space of the light source and the detector. Accordingly, both the drive mechanism of the movable mirror and the position adjustment mechanism of the BS can be arranged in the space without securing the first and second optical paths longer than necessary, and these arrangement spaces can be easily made. It can be ensured, and the arrangement space around the BS can be used effectively. Therefore, in combination with the effective use of the arrangement space for the light source and the detector, the optical system can be configured compactly.

It is explanatory drawing which shows the structure of the outline of the interference optical system applied to the spectrometer of one Embodiment of this invention. It is explanatory drawing which shows the schematic structure of the said spectrometer. It is explanatory drawing which shows the optical path in the optical system which has arrange | positioned the collimating optical system and the condensing optical system substantially point-symmetrically. It is explanatory drawing which shows the optical path in the optical system which has arrange | positioned the collimating optical system and the condensing optical system substantially line symmetrically. It is explanatory drawing which shows the optical path in an optical system when the eccentric angle (psi) in a collimating optical system and a condensing optical system is 17 degrees. It is explanatory drawing which shows the optical path in an optical system when the eccentric angle (psi) in a collimating optical system and a condensing optical system is 20 degrees. It is explanatory drawing which shows the optical path in an optical system when the eccentric angle (psi) in a collimating optical system and a condensing optical system is 30 degrees. It is explanatory drawing which shows the optical path in an optical system when the eccentric angle (psi) in a collimating optical system and a condensing optical system is 45 degrees. It is explanatory drawing which shows the schematic structure of the interferometer part of the conventional spectrometer.

  An embodiment of the present invention will be described below with reference to the drawings.

(About interference optics and spectrometers)
FIG. 2 is an explanatory diagram schematically showing a schematic configuration of the spectrometer 1 of the present embodiment. The spectrometer 1 is a Fourier transform spectrometer, and includes an interference optical system 2, a calculation unit 3, and an output unit 4.

  The interference optical system 2 is composed of a Michelson interferometer, and details thereof will be described later. The calculation unit 3 generates a spectrum indicating the intensity of light of each wavelength (wave number (= 1 / wavelength)) by performing A / D conversion and Fourier transform on the signal output from the interference optical system 2. The output unit 4 outputs (for example, displays) the spectrum generated by the calculation unit 3. Details of the interference optical system 2 will be described below.

  FIG. 1 shows the schematic configuration of the interference optical system 2 and the positional relationship between the optical members. The interference optical system 2 includes a light source 11, a collimator optical system 12, a BS (beam splitter) 13, a movable mirror 14, a fixed mirror 15, a condensing optical system 16, a detector 17, and a drive mechanism 21. It has. In FIG. 2, the collimator optical system 12 and the condensing optical system 16 are shown as a transmission type, but in actuality, as shown in FIG. 1, the collimator optical system 12 and the condensing optical system 16 are decentered. It is assumed that it is composed of a reflective optical system having a reflective surface. The positions of the movable mirror 14 and the fixed mirror 15 may be reversed.

  The light source 11 emits infrared light, for example. The collimator optical system 12 converts the light from the light source 11 into parallel light and guides it to the BS 13. The BS 13 separates the light emitted from the light source 11 into two lights, guides them to the movable mirror 14 and the fixed mirror 15, and combines each light reflected by the movable mirror 14 and the fixed mirror 15. For example, it is composed of a half mirror. In order to realize highly accurate interference between the two separated lights, the mounting angle and position of the BS 13 are adjusted by an adjusting mechanism (not shown) when the optical system is assembled. The movable mirror 14 and the fixed mirror 15 described above are disposed on opposite sides of the light separation surface of the BS 13. The condensing optical system 16 condenses the light synthesized and emitted by the BS 13 and guides it to the detector 17. The detector 17 detects the light incident from the BS 13 via the condensing optical system 16 and outputs the detected light to the calculation unit 3.

  The drive mechanism 21 is a moving mechanism that translates the movable mirror 14 so that the optical path length between the BS 13 and the movable mirror 14 changes. For example, a parallel leaf spring that supports the movable mirror 14 is vibrated (resonated) by a piezoelectric element. ) To move the movable mirror 14 in parallel. The movable mirror 14 may be driven using a VCM (voice coil motor) instead of the piezoelectric element. Further, for example, the drive mechanism 21 may be configured using an electrostatic actuator.

  In the above configuration, the light emitted from the light source 11 is converted into parallel light by reflection at the collimator optical system 12 and then separated into two light beams by transmission and reflection at the BS 13. One of the separated light beams is reflected by the movable mirror 14, and the other light beam is reflected by the fixed mirror 15. Each of the separated light beams returns to the original optical path and is superposed on the BS 13, and is reflected on the sample S (see FIG. 2) as interference light. Irradiated. At this time, while the movable mirror 14 is continuously moved by the drive mechanism 21, the sample S is irradiated with light. The difference in optical path length from the BS 13 to each mirror (movable mirror 14, fixed mirror 15) is an integer of the wavelength. When it is doubled, the intensity of the superimposed light becomes maximum. On the other hand, when there is a difference between the two optical path lengths due to the movement of the movable mirror 14, the intensity of the superimposed light changes. The light transmitted through the sample S is reflected by the reflecting surface of the condensing optical system 16 and enters the detector 17 while condensing, where it is detected as a temporal interferogram.

  The signal output from the detector 17 of the interference optical system 2 is A / D-converted and Fourier-transformed by the calculation unit 3 and output as a spectrum by the output unit 4. Therefore, the characteristics (material, structure, component amount, etc.) of the sample S can be known based on this spectrum.

  In the present embodiment, as described above, the collimating optical system 12 and the condensing optical system 16 are configured by reflecting optical systems, so that they are compared with a case where these are configured by transmissive optical systems (for example, lenses). The optical performance independent of the wavelength can be secured. Further, since the collimating optical system 12 and the condensing optical system 16 are eccentrically arranged, a light source is used so as not to block a light beam incident on the BS 13 from the collimating optical system 12 and a light beam incident on the condensing optical system 16 from the BS 13. 11 and detector 17 can be arranged.

  Further, as shown in FIG. 1, the collimating optical system 12 and the condensing optical system 16 are arranged on the opposite sides with respect to the light separation surface of the BS 13, and pass through the center of the BS 13, passing through the movable mirror 14 and the fixed mirror. 15 are arranged almost line-symmetrically with respect to the plane P passing between the two. Thereby, the aberration (for example, axial coma aberration) generated by decentration can be canceled by the mutual optical system, and good optical performance can be realized as the entire optical system. This will be more apparent with reference to the following drawings.

  3 and 4 show the optical path from the light source 11 to the detector 17 without considering the bending of the optical path at the BS 13, the movable mirror 14, and the fixed mirror 15. FIG. 3 shows the collimating optics. FIG. 4 shows the optical path in the optical system in which the system 12 and the condensing optical system 16 are arranged substantially symmetrically. FIG. 4 shows the optical path in the optical system in which the collimating optical system 12 and the condensing optical system 16 are arranged almost symmetrically. Show.

  In the point-symmetric optical system shown in FIG. 3, the axial coma is not canceled by the collimating optical system 12 and the condensing optical system 16, and the aberration is deteriorated as shown in the enlarged view of the broken line. On the other hand, in the line-symmetric optical system shown in FIG. 4, since the axial coma is canceled out by the collimating optical system 12 and the condensing optical system 16, as shown in the enlarged view of the broken line, good optical performance is obtained. Performance can be realized. As described above, when the decentered collimating optical system 12 and the condensing optical system 16 are used in one optical system, the line-symmetric arrangement has better optical performance than the point-symmetric arrangement.

(About the location of the light source and detector)
Next, the arrangement positions of the light source 11 and the detector 17 will be described. For convenience of explanation below, as shown in FIG. 1, the optical path of light that passes through the BS 13 from the collimating optical system 12 and travels toward the movable mirror 14 (first mirror) is defined as a first optical path L1, and a fixed mirror. An optical path of light that passes through the BS 13 from 15 (second mirror) and travels toward the condensing optical system 16 is defined as a second optical path L2. When the positional relationship between the movable mirror 14 and the fixed mirror 15 is reversed, the fixed mirror 15 constitutes a first mirror and the movable mirror 14 constitutes a second mirror.

  In the present embodiment, as described above, in the configuration in which the movable mirror 14 and the fixed mirror 15 are arranged on opposite sides with respect to the light separation surface of the BS 13, both the light source 11 and the detector 17 have the first optical path. It is disposed on the opposite side of the fixed mirror 15 as the second mirror with respect to L1 and on the opposite side of the movable mirror 14 as the first mirror with respect to the second optical path L2. As a result, the light source 11 and the detector 17 are divided and formed by the intersection of the first optical path L1 and the second optical path L2, in the same space among the four spaces S1 to S4 around the BS 13. Will be located. In FIG. 1, the spaces S1 to S4 are assumed to be positioned in this order counterclockwise around the BS 13, and the same space where the light source 11 and the detector 17 are arranged is S1. With the arrangement of the light source 11 and the detector 17 as described above, the following effects can be obtained.

  First, the light source 11 is not located between the collimating optical system 12 and the fixed mirror 15 (space S2 in FIG. 1), and the detector 17 is located between the condensing optical system 16 and the movable mirror 14 (FIG. 1 is not located in the space S4), the first optical path L1 is the second in the direction in which the collimating optical system 12 and the fixed mirror 15 approach each other (the direction in which the condensing optical system 16 and the movable mirror 14 approach each other). It is possible to easily realize an optical arrangement for inclining the second optical path L2. In addition, since the light source 11 and the detector 17 are not located in the spaces S2 and S4 at this time, when the second light path L2 is inclined with respect to the first light path L1, the light source 11 and the detector 17 are There is no obstacle. That is, even if the second optical path L2 is tilted with respect to the first optical path L1, the light beams on the first optical path L1 and the second optical path L2 are not scattered by the light source 11 and the detector 17. Accordingly, it is not necessary to ensure a long optical path for light entering and exiting the BS 13 in order to avoid the light flux being scattered.

  Therefore, an optical arrangement in which the incident angle θ of light incident on the BS 13 from the collimating optical system 12 is smaller than 45 ° can be easily realized with a small configuration without using the BS 13 having a complicated film design. High coherence can be achieved by suppressing polarization separation at the BS 13.

  In addition, since an optical arrangement in which the incident angle with respect to the BS 13 is smaller than 45 ° can be realized, a wide space S3 is secured on the opposite side of the BS 13 from the space S1 where the light source 11 and the detector 17 are arranged. Can do. Accordingly, the drive mechanism 21 of the movable mirror 14 and the position adjustment mechanism of the BS 13 are efficiently arranged (in the same wide space S3) without securing the first optical path L1 and the second optical path L2 longer than necessary. be able to. Therefore, in order to arrange the drive mechanism 21 of the movable mirror 14 and the position adjustment mechanism of the BS 13, it is not necessary to increase the length of the arm of the interferometer (the distance between the BS 13 and the movable mirror 14 and the distance between the BS 13 and the fixed mirror 15). .

  Further, the light source 11 and the detector 17 can be arranged in the same space S1 according to the above-described positional relationship of the light source 11 and the detector 17 with respect to the first optical path L1 and the second optical path L2, and the movable mirror as described above. Since the 14 drive mechanisms 21 and the position adjustment mechanism of the BS 13 can also be arranged in the same space S3, the arrangement space around the BS 13 can be used effectively. Therefore, a compact and compact optical arrangement can be realized as a whole, and the interference optical system 2 and thus the spectroscope 1 can be configured to be small and compact.

(About the range of incident angles with respect to BS)
Due to the arrangement of the light source 11 and the detector 17 described above, in this embodiment, as shown in FIG. 1, the incident angle θ of light incident on the BS 13 from the collimating optical system 12 is relative to the normal line of the light separation surface of the BS 13. The angle is smaller than 45 °, for example, 30 °. As described above, when the incident angle θ with respect to the BS 13 is smaller than 45 °, polarization separation at the BS 13 can be suppressed without using the BS 13 having a complicated film design.

  Here, in the Michelson interferometer, it is better in optical performance that the incident angle θ with respect to the BS 13 is smaller. However, when the incident angle θ is 20 ° or less, the movable mirror 14, the condensing optical system 16, and the fixed mirror 15 In order to arrange the collimating optical system 12 without interfering with each other, it is necessary to lengthen the arm length of the interferometer. If the arm of the interferometer is made too long, the coherence decreases even if the same light beam is separated, which is not preferable.

  From the above, it can be said that the incident angle θ of light incident on the BS 13 from the collimating optical system 12 is desirably larger than 20 ° and smaller than 45 ° with respect to the normal line of the light separation surface of the BS 13. Thereby, it is possible to reliably obtain an interference image with high contrast with a small configuration in which the length of the arm is shortened.

(About eccentric angle)
In the present embodiment, the eccentric angle ψ in the collimating optical system 12 and the condensing optical system 16 is 20 ° or more and 45 ° or less. Here, the eccentric angle ψ is an incident ray and a reflected ray on each reflecting surface of the collimating optical system 12 and the condensing optical system 16 on the axis along which the central ray of the light beam traveling from the light source 11 toward the detector 17 travels. Refers to the angle (°) between As shown in FIG. 1, when the eccentric angle in the collimating optical system 12 is ψ1 (°) and the eccentric angle in the condensing optical system 16 is ψ2 (°), 20 ° ≦ ψ1 ≦ 45 °, 20 As long as ° ≦ ψ2 ≦ 45 ° is satisfied, ψ1 = ψ2 may be satisfied, or ψ1 ≠ ψ2. In the case of ψ1 = ψ2, aberrations caused by decentration can be easily canceled, and the optical performance is further improved.

  When the eccentric angle ψ is smaller than 20 °, the light source 11 and the detector 17 have a size, and the light beam 11 travels along the first optical path L1 when a certain amount of light beam width is necessary to realize highly accurate interference. It cannot be avoided that the light beam is scattered by the light source 11 or that the light beam traveling in the second optical path L2 is scattered by the detector 17.

  Here, FIG. 5 shows the optical path from the light source 11 to the detector 17 without considering the bending of the optical path at the BS 13, the movable mirror 14, and the fixed mirror 15. The optical path in the optical system when the eccentric angle ψ in the optical optical system 16 is 17 ° is shown. In the optical system shown in the figure, it can be seen that the light beam is displaced by the light source 11 and the detector 17.

  On the other hand, FIGS. 6 to 8 show the optical path from the light source 11 to the detector 17 without considering the bending of the optical path at the BS 13, the movable mirror 14, and the fixed mirror 15, and the collimating optical system 12 and The optical paths in the optical system when the eccentric angles ψ in the condensing optical system 16 are 20 °, 30 °, and 45 °, respectively, are shown. From these drawings, it can be seen that the light source 11 and the detector 17 can avoid the luminous flux being within the range of 20 ° ≦ ψ ≦ 45 °.

  If the eccentric angle ψ is larger than 45 °, it is difficult to arrange the light source 11 and the detector 17 close to each other, and a small and compact optical system cannot be realized. In addition, optical aberrations are deteriorated. In other words, the aberration caused by the decentration cannot be completely canceled by the collimating optical system 12 and the condensing optical system 16, and good optical performance cannot be realized. If the optical performance is extremely deteriorated, the interference optical system 2 cannot be used for the spectrometer 1.

  Therefore, by setting the decentering angle in the collimating optical system 12 and the condensing optical system 16 to 20 ° or more and 45 ° or less, the interference optical system 2 is compact and has a compact configuration, while achieving high-precision interference and good. Therefore, the interference optical system 2 suitable for the spectroscope 1 can be realized.

(Examples)
Next, examples of the above-described interference optical system 2 will be described as Examples 1 to 3. Examples 1 to 3 are numerical examples corresponding to the optical systems of FIGS. 6 to 8, and the construction data is as follows.

  In the following construction data, Si (i = 0, 1, 2,...) Indicates the i-th surface counted from the object side. Specifically, S0 is a light emitting surface (OBJ; object surface) of the light source 11, S1 is a dummy surface, S2 is a reflecting surface of the collimating optical system 12, S3 is a virtual diaphragm surface (STO), and S4 is a light incident surface of the BS13. , S5 indicates the light exit surface of the BS 13, S6 indicates the reflecting surface of the condensing optical system 16, S7 indicates the light receiving surface of the detector 17, and S8 indicates the image plane (IMG) = S7 surface. 6 to 8, illustration of the S1 surface is omitted.

  RDY indicates the radius of curvature (mm) of the surface Si, and THI indicates the axial upper surface distance (mm) between the Si surface and the S (i + 1) surface. RMD indicates a surface characteristic. If it is REFL, it indicates a reflecting surface, and if there is no notation, it indicates a refracting surface. GLA indicates the glass name, and when there is no notation, it indicates air.

ここで、ｚは面のローカルなＺ軸方向の面頂点からの位置、Ｃは近軸の曲率で曲率半径の逆数（１／ｍｍ）、ｋは円錐定数、ｈはＺ軸からの高さ（ｈ²＝ｘ²＋ｙ²）、Σはｎとｍについて０次から∞次の総和、ＸｎＹｍはＸのｎ次、Ｙのｍ次の係数、である。なお、非球面データにおいて、Ｅ−ｎ＝×１０^-nを指す。SPS XYP indicates an aspheric surface represented by the following XY polynomial. In the XY polynomial, when the optical axis is the axis along which the central ray of the light beam traveling from the light source 11 toward the detector 17 travels, the optical axis direction is the Z axis, and the direction perpendicular to the Z axis in the meridional section is the Y axis. In the cross section, the direction perpendicular to the Z axis is taken as the X axis, and the distance from the surface apex is expressed as follows.

Here, z is the position from the surface vertex in the local Z-axis direction of the surface, C is the paraxial curvature and the reciprocal of the radius of curvature (1 / mm), k is the conic constant, and h is the height from the Z-axis ( h ² = x ² + y ² ), Σ is the sum of the 0th to ∞ orders for n and m, and XnYm is the nth order of X and the mth order coefficient of Y. In the aspheric data, E−n = × 10 ⁻ⁿ is indicated.

  XDE is the X direction parallel eccentricity, YDE is the Y direction parallel eccentricity, ZDE is the Z direction parallel eccentricity (mm), ADE is the rotation around the X axis, and BDE is the Y axis. Rotation around, CDE refers to the angle of rotation (°) around the Z axis. GLB Gi indicates a global eccentricity based on the Si surface (local eccentricity if not indicated). The refractive index of BK7_SCHOTT at a wavelength of 900 nm is 1.508997. In Examples 1 to 3, it is assumed that the light from the light source 11 is incident on the BS 13 at an incident angle of 30 °.

<Example 1> Eccentric angle 20 °

<Example 2> Eccentric angle 30 °

<Example 3> Eccentric angle 45 °

  In addition, each reflecting surface in the collimating optical system 12 and the condensing optical system 16 is not limited to the aspherical surface indicated by the XY polynomial in the above-described embodiment. When the size of the light source 11 is small, a paraboloid of revolution and an axisymmetric aspherical surface can also be used as each of the reflecting surfaces. It is a well-known fact that the light beam emitted from the focal point of the paraboloid can be converted into parallel light without aberration.

  The interference optical system of the present invention can be used for, for example, a Fourier transform spectrometer.

DESCRIPTION OF SYMBOLS 1 Spectrometer 2 Interference optical system 11 Light source 12 Collimating optical system 13 BS (beam splitter)
14 movable mirror 15 fixed mirror 16 condensing optical system 17 detector L1 first optical path L2 second optical path

Claims (7)

A light source;
A beam splitter that separates the light emitted from the light source and guides it to a movable mirror and a fixed mirror, and combines and emits each light reflected by the movable mirror and the fixed mirror;
An interference optical system comprising a detector for detecting light synthesized and emitted by the beam splitter,
A collimating optical system that converts light from the light source into parallel light and guides it to the beam splitter;
A condensing optical system for condensing the light synthesized and emitted by the beam splitter and guiding it to the detector;
The collimating optical system and the condensing optical system are each composed of a reflection optical system that is at least inclined and decentered with respect to a central ray of received light , passes through the center of the beam splitter in the thickness direction , and , Being arranged substantially line symmetrically with respect to a plane passing between the movable mirror and the fixed mirror,
Of the movable mirror and the fixed mirror, if one is a first mirror and the other is a second mirror,
The light source and the detector are both on the side opposite to the second mirror with respect to the optical path of light that passes through the beam splitter from the collimating optical system and travels toward the first mirror, and the second An interference optical system, wherein the interference optical system is disposed on a side opposite to the first mirror with respect to an optical path of light passing through the beam splitter from the mirror toward the condensing optical system.   The interference optical system according to claim 1, wherein an incident angle of light incident on the beam splitter from the collimating optical system is smaller than 45 ° with respect to a normal line of a light separation surface of the beam splitter.   The interference optical system according to claim 2, wherein the incident angle is greater than 20 ° with respect to a normal line of a light separation surface of the beam splitter. On the axis along which the central light beam of the light beam traveling from the light source toward the detector travels, the angle formed by the incident light beam and the reflected light beam on each reflecting surface of the collimating optical system and the condensing optical system is an eccentric angle.
The eccentric angle in the collimating optical system and the light converging optical system, the interference optical system according to any one of claims 1 to 3, characterized in that at 20 ° to 45 °. Said first mirror and said second mirror, the interference optical system according to any one of claims 1 to 4, characterized in that arranged on opposite sides with respect to the light splitting surface of the beam splitter . The collimating optical system and the light converging optical system, the interference optical system according to any one of claims 1 to 5, characterized in that arranged on opposite sides with respect to the light splitting surface of the beam splitter. The interference optical system according to any one of claims 1 to 6 ,
A calculation unit for calculating a spectrum based on a signal output from the interference optical system;
A spectrometer comprising: an output unit that outputs the calculated spectrum.

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