Multi-reflection instrument and multi-reflection cell

Abstract

To provide a multi-reflection apparatus and a multi-reflection cell suitable for a laser beam having a high output and excellent directivity.SOLUTION: A multi-reflection apparatus 1 and a multi-reflection cell include: a pair of parallel plane mirrors 2 and 3 for multi-reflecting a laser beam at a predetermined incident angle φ in zigzags; a right-angle double mirror 4 having two right-angle reflection surfaces 41 and 42 to turn back a multi-reflection beam advancing to one end between the parallel plane mirrors 2 and 3; and a right-angle double mirror 5 having two right-angle reflection surfaces 51 and 52 to re-turn back the multi-reflection beam advancing from the right-angle double mirror 4 at one end side to the other end between the parallel plane mirrors 2 and 3. When two parallel mirror surfaces 21 and 31 constituting the parallel plane mirrors 2 and 3 are arranged in parallel with a z-x surface of an x-y-z axis coordinate system, the two reflection surfaces 41, 42, 51 and 52 constituting the right-angle double mirrors 4 and 5 are vertical to an x-y surface, and the laser beam at the incident angle φ crosses the x-y surface at a predetermined angle φz.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-reflection instrument used for optically analyzing a measurement target substance such as a gas between a pair of mirror surfaces by multiple reflection of laser light between the mirror surfaces, and in particular to a multi-reflection cell in which the instrument is incorporated within a cell. [Background technology]

[0002] One example of gas analysis is measuring the concentration of impurity gases of less than a few ppm contained in high-purity gas based on their absorbance. For this type of gas analysis, a multi-reflection (multi-pass) cell is suitable because it can ensure a longer optical path even with a cell of the same volume. A typical example is the Herriot type, which has a pair of concave spherical mirrors arranged inside the cell.

[0003] On the other hand, recent gas analysis using infrared absorption spectroscopy has seen the use of quantum cascade lasers as light sources, which have extremely high output and excellent directionality (small divergence angle) compared to conventional high-brightness ceramic light sources and halogen lamps (for example, paragraph 0044 of Patent Document 1, and paragraphs 0002 and 0021 of Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2001-509595 [Patent Document 2] WO2015 / 033582 publication Summary of the Invention [Problem to be solved by the invention]

[0005] However, the gas cell in Patent Document 1 (paragraph 0016, Figure 1) is a conventional Herriott type, and Patent Document 2 (paragraph 0022, Figure 3) also uses a conventional Herriott type, so it cannot be said that the gas cell structure fully utilizes the advantages of the quantum cascade laser.

[0006] The present invention has been made in consideration of the problems with the conventional technology described above, and an object of the present invention is to provide a multi-reflection device and a multi-reflection cell that are suitable for high-output, highly directional laser light. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention For gas measurement The multi-reflection device is a pair of parallel plane mirrors that reflect laser light with a specified incident angle (φ) in a zigzag pattern. a right-angled two-sided mirror on one end side having two right-angled reflecting surfaces for reflecting back the multiple-reflected light that has traveled to one end between the parallel plane mirrors; a right-angled two-sided mirror at the other end having two right-angled reflecting surfaces for reflecting back the multiple-reflected light that has traveled from the right-angled two-sided mirror at one end to the other end between the parallel plane mirrors; Equipped with A multi-reflection instrument for measuring a target gas present between the parallel plane mirrors. It is characterized by the above. Here, if the two parallel mirror surfaces that make up the parallel plane mirror are arranged parallel to the zx plane of the xyz axis coordinate system, The one end is one end in the x-axis direction, and the other end is the other end in the x-axis direction, The two reflecting surfaces that make up the rectangular dihedral mirror are perpendicular to the xy plane, and the laser light with an incident angle (φ) intersects with the xy plane at a specified angle (φz).

[0008] In this specification, a configuration containing the word "mirror," such as a plane mirror, refers to an optical component having a flat mirror surface formed on at least a portion thereof, and includes, for example, a prism having a reflective coating on its surface.

[0009] The configuration of the above multiple reflection device will be explained using a diagram viewed from the z-axis direction (for example, FIG. 1(A)). The laser light travels toward one end of the parallel plane mirrors while being multiple-reflected between the parallel plane mirrors at a predetermined angle of incidence φx. "φx" indicates the angle of incidence φ of the laser light projected onto the xy plane. Reflection spots are formed on the mirror surface at a constant pitch Px. The multiple-reflected light that travels to one end of the parallel plane mirrors is reflected by the first reflecting surface of the right-angled double-sided mirror on the one end side, and the reflected light is then reflected by the second reflecting surface perpendicular to the first reflecting surface. Then, the incident light on the first reflecting surface and the reflected light from the second reflecting surface become parallel in the diagram viewed from the z-axis direction. The multiple-reflected light that is turned back by the right-angled double-sided mirror on the one end side is multiple-reflected between the parallel plane mirrors again and travels toward the other end. Since the incident angle φx of the laser light on the mirror surface of the parallel plane mirror does not change before and after turning back, the pitch Px of the reflection spots formed on the mirror surface by the multiple-reflected light traveling toward the other end does not change either. However, when viewed from the z-axis direction, the light incident on the first reflecting surface and the light reflected from the second reflecting surface are shifted in parallel by an interval dx (there are cases where the light is shifted in the positive direction of the x-axis and cases where it is shifted in the negative direction of the x-axis. In Figure 1(A) it is shifted in the positive direction), and the position of the reflection spot on the mirror surface differs by the amount of this shift before and after being reflected by the right-angled double mirror on one end. Note that when the multiple-reflected light is reflected by the right-angled double mirror on the other end, it is the same as on the one end.

[0010] In addition, in the above multiple reflection device, the laser light with an incident angle of φ is not parallel to the xy plane, but intersects with the xy plane at an angle φz (for example, the three-dimensional diagram in Figure 2). Therefore, in a view of the multiple reflection device from the y-axis direction (for example, Figure 1(B)), the arrangement of reflection spots on the mirror surface of the parallel plane mirror is not parallel to the x-axis, but is in an inclined direction that forms an angle θ (upward or downward angle) with the x-axis. The arrangement of reflection spots after being reflected by the right-angled two-sided mirror on one end also forms an inclined direction that forms an angle θ with the x-axis.

[0011] Regarding laser beam interference, when reflection spots on the mirror surface overlap, beam interference (beams strengthening or canceling each other out) occurs, so when measuring an object between the mirror surfaces of a multiple reflection instrument, it is preferable to avoid such beam interference as much as possible.

[0012] From the above, by using the multiple reflection device of the present invention equipped with a pair of parallel plane mirrors and right-angled two-sided mirrors at both ends, it is possible to form a large number of reflection spots on the mirror surface by the laser light incident at a specific incidence angle φ without overlapping each other and to make them dense. Therefore, it is possible to efficiently form a long optical path in the limited volume between the mirror surfaces, and also to minimize the effect of beam interference on the measurement light.

[0013] In addition, in the multiple reflection device of the present invention, the right-angle double-sided mirror has first and second reflecting surfaces that are perpendicular to each other, and when the optical path of the multiple reflected light between the parallel plane mirrors is projected onto the xy plane, it is preferable that the distance (dx) between the optical path of the laser light incident on the first reflecting surface and the optical path of the laser light that reflects off the first reflecting surface and is then reflected back by the second reflecting surface is half the length of the pitch of the multiple reflected light between the parallel plane mirrors.

[0014] The term "one pitch" here refers to the distance traveled by the laser light in the direction of travel of the multiple reflected light when the laser light makes one round trip between parallel plane mirrors. In other words, it is equal to the interval between the reflection spots formed on one of the mirror surfaces due to multiple reflection between parallel plane mirrors. In the present invention, by setting the interval (dx) of the optical path of the laser light to the length of half the pitch of the multiple reflected laser light, it is possible to most effectively make the reflection spots on the mirror surface dense and prevent the reflection spots from overlapping each other.

[0015] The multiple reflection device of the present invention preferably includes an incident optical element that guides the laser beam to the mirror surface, and an incident drive device that changes the position and orientation of the optical element to change the angle of incidence (φ). Alternatively, the multiple reflection device of the present invention preferably includes an incident optical element that guides the laser beam to the mirror surface, and a parallel plane mirror drive device that changes the position and orientation of the parallel plane mirror and the right-angle dihedral mirror together with respect to the incident optical element to change the angle of incidence (φ).

[0016] With this configuration, the pitch of the multiple reflections of the laser light increases or decreases when the incident angle φ of the laser light on the parallel plane mirror is changed, making it possible to adjust the optical path length of the laser light that is multiple-reflected between the plane mirror surfaces.

[0017] It is preferable that the driving device changes the incident angle (φ) so that the angle (φx) obtained by projecting the incident angle (φ) onto the xy plane varies within a range of 0 to 25°.

[0018] In this book, the angle φx obtained by projecting the incident angle φ onto the xy plane is also called the "azimuth angle." For example, the reference is a case in which a parallel plane mirror and a right-angle double mirror are integrally constructed, and the laser light perpendicularly incident (φx=0°) on the parallel plane mirror is incident at 45° on the first reflecting surface of the right-angle double mirror. If the incident angle (φx) of the laser light is increased from 0° to "0°+x" (x>0°), the incident angle on the first reflecting surface (or the reflection angle from the second reflecting surface) becomes "45°+x", and the opening of the first reflecting surface (or the second reflecting surface) relative to the traveling direction of the laser light becomes smaller. If the opening of the reflecting surface becomes smaller, some of the laser light will not be reflected, and the reflection performance of the right-angle double mirror may become insufficient.

[0019] Therefore, in the configuration of the present invention, the upper limit of the incident angle φx is set to about 25° so that the size of the opening of the first reflecting surface (or the second reflecting surface) at normal incidence (φx=0°) is secured to be 50% or more, assuming that the size of the opening is 100%. As a result, even if the incident angle φ is changed by the driving device, the reflection performance of the right-angle dihedral mirror is sufficiently maintained.

[0020] It is preferable that the driving device changes the angle (φz) between the incident direction of the laser light and the xy plane so that the number of times the light makes multiple round trips between the right-angled dihedral mirrors on one end and the other end increases or decreases by N times (N is an integer greater than or equal to 1).

[0021] In this document, the angle φz that the incident direction of the laser light makes with the xy plane is also called the "elevation angle." According to the configuration of the present invention, this elevation angle φz is changed so as to increase or decrease the number of times the light makes round trips between the right-angle double mirrors, so that the optical path length between the parallel plane mirrors can be finely adjusted for each round trip of the optical path.

[0022] In addition, it is preferable that the driving device changes the angle (φx) obtained by projecting the incident angle (φ) onto the xy plane so that the number of times the laser light makes a round trip between the parallel plane mirrors from the right-angled double mirror at one end to the right-angled double mirror at the other end increases or decreases by M times (M is an integer greater than or equal to 1).

[0023] According to the configuration of the present invention, the angle φx (azimuth angle) obtained by projecting the incident angle φ onto the xy plane is changed so as to increase or decrease the number of times the laser light makes a round trip between the parallel plane mirrors, thereby making it possible to finely adjust the optical path length between the parallel plane mirrors for each round trip of the optical path.

[0024] According to the present invention For gas measurement The multi-reflection cell is a multi-reflection instrument and a measurement object. gas and a cell body configured to allow the insertion and removal of A configuration in which the cell body incorporates multiple reflecting devices; A configuration in which the cell body is disposed between parallel plane mirrors of a multi-reflection instrument; and A part of the cell body is formed by a multiple reflector. The gas to be measured is placed between the parallel plane mirrors. It is characterized by the above. Effect of the Invention

[0025] With the above configuration, it is possible to provide a multiple reflection device and a multiple reflection cell that are suitable for high-output, highly directional laser light. [Brief description of the drawings]

[0026] [Figure 1] 1A is a diagram showing the optical paths of multiple reflected light occurring between the mirror surfaces of a multiple reflection device of one embodiment, as viewed from the z-axis direction, and FIG. 1B is a diagram showing the multiple reflection device as viewed from the y-axis direction. [Diagram 2] 4 is a stereoscopic view for explaining the incident angle φ of the laser light on the mirror surface. FIG. [Diagram 3] 4 is a diagram for explaining how multiple reflected light generated in the multiple reflection device travels. FIG. [Figure 4] FIG. 4 is a diagram for explaining the range of processing precision required for the right-angled two-sided mirror of the multiple reflection device. [Diagram 5] FIG. 13 is a diagram of a mechanism for adjusting the angle of incidence of a gas cell incorporating the multi-reflection device. [Figure 6] FIG. 11 is a diagram of another mechanism for adjusting the angle of incidence. [Figure 7] 10 is a diagram for explaining how the size of the aperture of the rectangular dihedral mirror changes depending on the magnitude of the incident angle. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a multiple reflection device and a multiple reflection cell including the same according to the present invention will be described with reference to the drawings.

[0028] 1(A) and (B) show a multiple reflection device 1 of this embodiment. The multiple reflection device 1 includes a pair of parallel plane mirrors 2 and 3, a right-angled two-sided mirror 4 provided at one end of the parallel plane mirror 2, and a right-angled two-sided mirror 5 provided at the other end of the parallel plane mirror 3. The mirror surfaces 21 and 31 of the parallel plane mirrors 2 and 3 are, for example, square and arranged parallel to each other. For the sake of explanation, the mirror surfaces 21 and 31 are parallel to the zx plane of the xyz-axis coordinate system. FIG. 1(A) is a view of the multiple reflection device 1 seen from the z-axis direction, and FIG. 1(B) is a view of the multiple reflection device 1 seen from the y-axis direction. Here, for the space sandwiched between the pair of parallel plane mirrors 2 and 3, the end in the positive direction of the x-axis is called the "one end" and the end in the negative direction of the x-axis is called the "other end."

[0029] The right-angled double-sided mirror 4 has a first reflecting surface 41 arranged along an edge of the mirror surface 21, and a second reflecting surface 42 of the same shape and perpendicular to the first reflecting surface 41. The intersection line of the two reflecting surfaces 41, 42 that form a right angle is parallel to the z-axis. In other words, the reflecting surfaces 41, 42 are perpendicular to the xy plane.

[0030] Similarly, the right-angled double-sided mirror 5 also has a first reflecting surface 51 arranged along an edge of the mirror surface 31, and a second reflecting surface 52 of the same shape and perpendicular to the first reflecting surface 51. The intersection line of the two reflecting surfaces 51 and 52 that form a right angle is parallel to the z-axis. In other words, the reflecting surfaces 51 and 52 are perpendicular to the xy plane.

[0031] Commercially available optical elements such as a rooftop mirror, a roof prism mirror, or a right-angle prism mirror (with reflective coating on the right-angled surfaces) can be used for the right-angle double mirrors 4 and 5. The parallel plane mirrors 2 and 3 and the right-angle double mirrors 4 and 5 may be formed integrally.

[0032] As shown in FIG. 1B, an entrance hole 53 for external laser light is formed at the end of the second reflecting surface 52 of the right-angled double-sided mirror 5 in the negative direction of the z-axis, and the laser light entering through this entrance hole 53 travels toward one end while being multiple-reflected in a zigzag pattern between the parallel plane mirrors 2 and 3. hole The position of 53 will be described as the origin O of the xyz-axis coordinate system.

[0033] The laser light entering through the entrance hole 53 is alternately reflected by the mirror surfaces 21, 31 at the incident angle φ. By using a highly directional laser light with parallel mirror surfaces 21, 31, the incident angle φ is kept constant, and the shape of the reflected spot on the mirror surfaces 21, 31 is also kept constant. The angle φx in Fig. 1(A) is the angle obtained by projecting the incident angle φ onto the xy plane, and corresponds to the "azimuth angle" when the xy plane is regarded as a horizontal plane.

[0034] Circular reflection spots according to the beam diameter are formed at the points where the laser light is reflected by the mirror surfaces 21 and 31. Because the incident angle φ of the laser light on the mirror surfaces 21 and 31 has an azimuth angle component (angle φx), these reflection spots are formed at a constant pitch Px.

[0035] In the example of Fig. 1(A), after making seven round trips between mirror surfaces 21 and 31, the laser light advances to first reflecting surface 41 of right-angled double-sided mirror 4. The numerous small circles arranged at pitch Px on mirror surface 3 in Fig. 1(B) indicate reflection spots. The small black circles are seven reflection spots that are formed when the multiple-reflected light travels from entrance hole 53 to first reflecting surface 41. Note that pitch Px is the x-axis component of pitch P of the reflection spots.

[0036] In addition, since the incidence angle φ of the laser light has an elevation angle component (angle φz), the arrangement direction of the small black circles in Fig. 1(B) is the direction of the elevation angle θ with respect to the x-axis. The relationship between the incidence angle φ and the elevation angle θ is shown in the stereoscopic view of Fig. 2. The angle φx is the angle obtained by projecting the incidence angle φ onto the xy plane, while the angle φz is equal to the angle that the incident light entering from the entrance hole 53 (origin O) makes with the xy plane.

[0037] 1(A), the laser light incident on the first reflecting surface 41 on one end side is reflected by the first reflecting surface 41 and the second reflecting surface 42 in that order. Since the first reflecting surface 41 and the second reflecting surface 42 are perpendicular to each other, in a diagram in which the optical path of the laser light is projected onto the xy plane, the incident light on the first reflecting surface 41 and the reflected light from the second reflecting surface 42 are parallel to each other regardless of the angle of incidence on the first reflecting surface 41. However, since the incident angle φ of the laser light has an elevation angle component (φz), in a diagram in which the optical path of the laser light is projected onto the yz plane, the incident light on the first reflecting surface 41 and the reflected light from the second reflecting surface 42 form an angle (2φz) that is twice the elevation angle component.

[0038] In this way, the right-angled two-sided mirror 4 bends the multiple-reflected light that has traveled to one end back toward the other end, and the bent multiple-reflected light similarly travels in the direction of the upward angle θ with respect to the x-axis.

[0039] The reflection spots of the multiple reflected light reflected by the right-angled double mirror 4 are formed at positions shifted exactly by half the pitch Px from the reflection spots indicated by small black circles, as shown in Fig. 1(B). In Fig. 1(A), the distance between the light incident on the first reflecting surface 41 and the light reflected from the second reflecting surface 42 is indicated as d. As shown in Fig. 1(B), the component dx in the x-axis direction of the distance between the reflection spot SP1 on the mirror surface 31 for the light incident on the first reflecting surface 41 and the reflection spot SP2 on the mirror surface 31 for the light reflected from the second reflecting surface 42 is equal to half the pitch (Px / 2) of the multiple reflected light.

[0040] The multiple-reflected light that travels toward the other end while being shifted by half a pitch in the x-axis direction by right-angled double-faced mirror 4 makes seven round trips between mirror surfaces 21 and 31, and is then reflected again by right-angled double-faced mirror 5 at the other end. Right-angled double-faced mirrors 4 and 5 are arranged rotationally symmetrical to each other, and the multiple-reflected light is reflected at the other end in the same manner as at the one end.

[0041] That is, the component in the x-axis direction of the distance between the reflection spot on mirror surface 21 for the light incident on first reflection surface 51 and the reflection spot on mirror surface 21 for the light reflected from second reflection surface 52 is the same as dx, which is equal to half the pitch (Px / 2) of the multiple reflected light. The multiple reflected light turned back at the other end proceeds to the one end while forming a similar optical path from a position shifted by one pitch (Pz) in the z-axis direction with respect to the optical path of the multiple reflections of the laser light that entered from entrance hole 53.

[0042] In this way, the multiple reflected light travels back and forth between the right-angled double mirrors 4 and 5 multiple times, zigzagging in the z-axis direction. In this embodiment, the two reflecting surfaces 41 and 42 of the right-angled double mirror 4 are long along their intersection line (z-axis direction), and the reflecting surfaces 51 and 52 of the right-angled double mirror 5 are similarly long. Therefore, when the multiple reflected light travels back and forth between the right-angled double mirrors 4 and 5 multiple times, the turning points on the right-angled double mirrors 4 and 5 move along the intersection line by a predetermined pitch (Pz). The pitch Pz in the z-axis direction is maintained constant. In the example of FIG. 1(B), after 13 round trips between the right-angled double mirrors 4 and 5, the laser light goes out through the exit hole 54 formed at the end of the first reflecting surface 51 of the right-angled double mirror 5 in the positive direction of the z-axis. It should be noted that the entrance hole 53 and the exit hole 54 need only be able to transmit laser light, and are formed from an infrared-transmitting window material such as ZnS (zinc sulfide), ZnSe (zinc selenide), Si (silicon), Ge (germanium), diamond, glass, etc., appropriately selected according to the wavenumber range of the laser mounted on the optical analysis device (for example, in the case of a QCL light source, oscillation in the mid-infrared to far-infrared band is expected).

[0043] Fig. 3 is a simplified diagram showing the configuration of the multiple reflection device 1 of this embodiment to facilitate explanation of the effects. Fig. 3(A) is a schematic diagram of the multiple reflection device 1 as viewed from the z-axis direction, and the angle of incidence φ projected onto the xy plane is indicated as φx. Fig. 3(B) is a schematic diagram of the multiple reflection device 1 as viewed from the y-axis direction, and the upward angle of the multiple reflected light between the mirror surfaces 21 and 31 is indicated as θ. The multiple reflected light traveling from the other end to one end is indicated by a solid line, and the multiple reflected light traveling from one end to the other end is indicated by a dashed line.

[0044] As is clear from Figures 3(A) and (B), the length (Lx) in the x-axis direction from the turning point (origin O) on the second reflecting surface 52 at the other end to the turning point on the second reflecting surface 42 at one end must be an integer multiple of the shift amount of the optical path in the right-angle double mirrors 4 and 5 (equal to dx), which is a condition for the laser light to efficiently exit to the outside from the emission hole 54.

[0045] Next, Fig. 3(C) is a schematic diagram of the multiple reflection device 1 as viewed from the x-axis direction. The amount of movement in the z-axis direction while the multiple reflected light travels from the right-angled double mirror 5 on the other end side to the right-angled double mirror 4 on the one end side is indicated by dz (half the pitch Pz). As is clear from this figure, the position of the entrance hole 53 of the laser light (original The length (Lz) in the z-axis direction from point O) to the position of the emission hole 54 must be an integer multiple of the movement amount (dz) in the z-axis direction, which is a condition for the laser light to efficiently exit from the emission hole 54 to the outside.

[0046] The arrangement of the right-angle double mirrors 4 and 5 is not limited to that shown in Fig. 3, and the right-angle double mirrors 4 and 5 may be arranged at both ends of the same mirror surface (2 or 3). The positions of the entrance hole 53 and exit hole 54 of the laser light are not limited to the positions shown in Fig. 3, and may be the positions of the reflection spots of either mirror surface 21 or 31, or the positions of the turning points of the right-angle double mirrors 4 and 5. The traveling direction of the laser light in Fig. 3 may be reversed.

[0047] The range in which machining accuracy of the right-angled double mirror 4 is required will be described with reference to FIG. 4. In this embodiment, the entire surfaces of the reflecting surfaces 41, 42 of the right-angled double mirror 4 are not used to reflect the laser light. Therefore, high machining accuracy is not required near the intersection line (joint) where the reflecting surfaces 41, 42 intersect at a right angle. As shown in FIG. 4, the area near the intersection line may be rounded, or grooves may remain. Since imperfections in the right-angled double mirror 4 are thus permitted, a metal mirror with a pseudo rooftop shape may also be used.

[0048] The mechanism for adjusting the incident angle φ of the laser light will be described with reference to FIGS.

[0049] First, Figures 5 and 6 show a multi-reflection type gas cell (multi-reflection cell) 10 incorporating a multi-reflection device 1. This gas cell 10 has a cell body 9 configured to allow the gas to be measured to be introduced and discharged, and the multi-reflection device 1 is housed in the cell body 9. A gas inlet pipe 91 and a gas outlet pipe 92 are connected to the cell body 9, and the structure is airtight except for these connection parts. There are no particular limitations on the material of the cell body 9, as long as at least the part through which the laser light passes is translucent.

[0050] 5 and 6, an optical element 6 for making the laser light incident on the multiple reflection device 1 is disposed outside the gas cell 10. For example, an alignment mechanism using a combination of two plane mirrors assuming 90° reflection in order to maintain polarization characteristics can be used for the optical element 6. The configuration of the optical element 6 is not limited to this, and optical elements of other configurations can also be used. Laser light from a light source 11 such as a QCL (quantum cascade laser) with high output and excellent directivity is introduced into the entrance hole 53 of the multiple reflection device 1 via this entrance optical element 6. A QCL can provide a very high output compared to conventional high-brightness ceramic light sources, halogen lamps, etc., and can provide a high output in the fingerprint region (1850 to 890 cm). -1 ) and has excellent directivity (small divergence angle). However, the light source 11 is not limited to a QCL, and various other high-output, high-directivity lasers may be used.

[0051] In the examples of Figures 5 and 6, the gas Sending The inlet pipe 91 is configured to feed the gas to be measured to one end of the multiple reflecting device 1, and the gas exhaust pipe 92 is configured to exhaust the gas to be measured from the other end of the multiple reflecting device 1. Sending There is no particular limitation on the connection positions of the inlet pipe 91 and the gas outlet pipe 92. In addition, although the examples in Fig. 5 and Fig. 6 are configured by combining the cell body 9 and the multiple reflection device 1, the gas cell 10 may be configured by integrating the multiple reflection device 1 as a part of the cell body 9.

[0052] In FIG. 5, a driving device 7 for an optical element is provided as a first incident angle adjuster. For example, when the optical element 6 has a variable angle mirror, the angle adjustment device corresponds to this driving device 7. The driving device 7 is, for example, a rotational tilt stage, and changes the attitude of the incident optical element 6 to change the incident angle φ of the laser light. In addition to the above-mentioned rotation axis, the driving device 7 may have a driving mechanism for moving the position of the optical element 6 along at least one driving axis. Note that, when the optical element 6 is, for example, an alignment mechanism for the above-mentioned two plane mirrors, its driving part corresponds to this driving device 7.

[0053] 6, a gas cell driver 8 is provided as a second incident angle adjuster. This driver 8 is a device that changes the position and attitude of the gas cell 10 in order to change the incident angle φ of the laser light. For example, this gas cell driver 8 is useful when there is a limit to changing the attitude and position of the optical element 6.

[0054] At least one of the driving devices 7 and 8 changes the incident angle φ so that the angle φx obtained by projecting the incident angle φ onto the xy plane varies within a range of 0 to 25°. Either or both of the driving devices 7 and 8 may be used. These driving devices 7 and 8 may also be used for alignment to cause the laser light to enter the entrance hole 53.

[0055] The driving devices 7 and 8 are configured to change the incident angle φ so that the number of times the multiple reflected light makes a round trip between the right-angled double mirrors 4 and 5 on one end side and the other end side increases or decreases by N times (N is an integer equal to or greater than 1). In this embodiment, the right-angled double mirror 4 having two reflecting surfaces 41 and 42 long in the z-axis direction and the right-angled double mirror 5 having a similar configuration are used, so that the number of times the multiple reflected light makes a round trip between the right-angled double mirrors 4 and 5 can be easily increased or decreased by simply adjusting the incident angle φ.

[0056] The driving devices 7 and 8 may be configured to change the incidence angle φ so that the number of times the laser light travels back and forth between the mirror surfaces 21 and 31 from the right-angled double mirror 4 on one end side to the right-angled double mirror 5 on the other end side increases or decreases by M times (M is an integer of 1 or more). In this case, the pitch Px changes depending on the number of times the laser light travels back and forth. ,straight Positional relationship between the first and second reflecting surfaces 41, 42 of the square dihedral mirror 4 , and the positional relationship between the first and second reflecting surfaces 51, 52 of the right-angled double-sided mirror 5 of each It's good to change it.

[0057] If the multiple reflection device 1 of this embodiment is used as a cell for measuring the absorbance of a sample gas, it becomes easy to reduce the required volume of the gas to be measured. It also becomes easy to lengthen the optical path length of the light passing through the gas to be measured, which makes it easy to improve the measurement sensitivity. Or, these effects can be obtained simultaneously.

[0058] Since the same concentration of target gas can be analyzed using a cell with a smaller volume, the time it takes to feed the gas into the cell / discharge it from the cell is shortened. For example, when measuring the time change of a low concentration component contained in the target gas, it becomes possible to measure changes at short time intervals.

[0059] Compared to cells using conventional spherical mirrors, the use of plane mirrors 2 and 3 improves the degree of freedom in optical design. For example, design constraints such as the arrangement of a pair of spherical mirrors (such as designing one so that the center of the radius of curvature is on the opposite sphere) are eliminated. The optical structure is simplified, reducing manufacturing time and costs, and also making it easier to adjust the mirror orientation, etc. Furthermore, since the structure is not complicated, maintenance is also easier.

[0060] According to the multiple reflection device 1 of this embodiment, the multiple reflection spots formed on the mirror surfaces 21, 31 by the laser light incident at a predetermined incident angle φ can be made dense and not overlap each other. Therefore, a long optical path can be efficiently formed in the limited volume between the mirror surfaces 21, 31, and the effect of beam interference on the measurement light can be suppressed to a minimum.

[0061] In this embodiment, the light source QC The advantage of using L and other high-power lasers is that the output power of these lasers is large enough to cover the surface reflection losses associated with multiple reflections at the mirror surfaces (parallel plane mirrors 2 and 3 and right-angle double mirrors 4 and 5).

[0062] In conventional devices for measuring infrared absorbance (e.g., FTIR), a TGS detector is often installed as a standard detector. In addition, an MCT detector capable of detecting weaker light may be installed as an option. The TGS detector has lower sensitivity and responsiveness than the MCT detector, but has the advantages of not requiring liquid nitrogen cooling, a relatively wide measurement band, and being inexpensive, and is useful in terms of vertical axis stability of measured values ​​and long-term measurement. However, conventional infrared light sources do not have a high enough output, and the output (transmitted light amount) becomes insufficient due to multiple reflections about 100 times, so the TGS detector cannot be used and the MCT detector has to be used. In contrast, in this embodiment, by using a high-output infrared laser, such restrictions on the selection of detectors are eliminated, and measurements can be made using a standard detector such as the TGS detector. This also applies to the case where a gas cell for sample gas is placed between the parallel plane mirrors 2 and 3, and even if the infrared laser repeatedly undergoes surface reflection loss at the gas cell, there is no shortage of transmitted light amount, and a standard detector can be used.

[0063] In this embodiment, the light source QC The second advantage of using infrared lasers and other high power lasers is that the spectral width of infrared lasers is narrow, so the absorption peak of the substance to be measured is not directly related to the absorption peak of environmental gases (e.g. CO). 2 Or H 2 O), the absorption peak of the substance to be measured can be selectively extracted.

[0064] Furthermore, in this embodiment, in particular, by making the interval between the incident light and the reflected light on the right-angle double-faceted mirror 4 (the interval shown by dx in FIG. 1(B)) equal to the length of half the pitch (Px / 2) of the laser light that is multiple-reflected between the mirror surfaces 21 and 31, it is possible to most effectively make the reflection spots on the mirror surfaces 21 and 31 dense and prevent the reflection spots from overlapping each other.

[0065] In addition, by changing the azimuth angle φx in the range of 0 to 25° by the driving devices 7 and 8 of the multiple reflection device 1 of this embodiment, the optical path length of the laser light between the mirror surfaces 21 and 31 can be easily adjusted. Here, as shown in FIG. 7, when the size of the opening of the first reflection surface 41 (or the second reflection surface 42) at normal incidence (φx=0°) is 100%, the size of the opening can be secured to 50% or more by setting the upper limit of the azimuth angle φx to 25°. Therefore, even if the azimuth angle φx is changed, the reflection performance of the right-angle two-sided mirror 4 (or the right-angle two-sided mirror 5) can be sufficiently maintained.

[0066] Here, the characteristics of the right-angled two-sided mirror 4 will be described with reference to FIG. 7. As shown in FIG. 7, even if the angle of the reflecting surface 41 with respect to the incident light changes, the reflected light from the reflecting surface 42 returns along the same path (the path projected onto the xy plane is the same) as before the angle change, so long as it is within the range of the mirror aperture. However, the condition is that the length from the center line of the right-angled two-sided mirror 4 to the incident light does not change. In other words, regardless of the angle of the reflecting surface 41, the amount of translation before and after reflection is constant. In this embodiment, the right-angled two-sided mirrors 4 and 5 with such characteristics are used, which makes it easier to assemble and adjust the multiple reflection device 1.

[0067] 5 and 6, the angle φx can be adjusted to finely adjust the optical path length of the laser light traveling back and forth between the mirror surfaces 21 and 31 for each round trip. The drivers 7 and 8 can also adjust the angle φz, making it possible to finely adjust the optical path length of the multiple-reflected light traveling back and forth between the right-angled double mirrors 4 and 5 at both ends for each round trip.

[0068] For example, a case will be described in which the absorption spectrum of a specific component in a sample gas is measured using a gas cell 10 having a multi-reflection device 1 of this embodiment. When the sample gas contains components with high and low absorbance, even if the detection of the high absorbance component is saturated, the measurement of the high absorbance component can be continued under appropriate optical path length conditions by shortening the optical path using the automatic optical path length switching mechanism of this embodiment. In other words, the automatic optical path length switching mechanism eliminates the need to refill the sample gas, and data can be smoothly acquired using different measurement systems.

[0069] For example, if the shape of the mirror surfaces 21 and 31 in Figures 1(A) and (B) is a square with each side of 50 mm, and the distance between the mirror surfaces 21 and 31 is 50 mm, the laser light will make about 15 round trips between the mirror surfaces 21 and 31 while making one round trip between the right-angled double mirrors 4 and 5 at both ends. The optical path length is 100mm x 15 round trips = 1.5m Furthermore, the multiple reflected light makes 13 round trips between the right-angled two-sided mirrors 4 and 5 at both ends, so the total optical path length is 1.5m x 13 round trips = 19.5m A gas cell 10 using such a multiple reflection instrument 1 can be made in a box shape with a side length of 80 mm or less (volume of about 512 ml). This is less than 1 / 4 the volume of a conventional gas cell, making it possible to miniaturize the gas cell. A miniaturized gas cell is suitable for cases where the amount of sample that can be used is limited.

[0070] As an example of the gas cell of this embodiment, a cell chamber made of an infrared-transmitting window plate may be disposed between a pair of parallel plane mirrors 2 and 3. The sample gas is sealed in the cell chamber between the plane mirrors 2 and 3. Alternatively, as described above, a part of the surface of the cell body 9 may be formed by the pair of parallel plane mirrors 2 and 3 of the multiple reflection device 1.

[0071] Moreover, a pair of parallel plane mirrors 2 and 3 may be used in which a reflective film is formed on the rear surface of an infrared-transmitting window plate. With these gas cell configurations, the mirror surfaces of the plane mirrors 2 and 3 are not directly contaminated by the sample gas (prevention of mirror surface contamination). Instead, the surface of the infrared-transmitting window plate will become contaminated by the sample gas, but maintenance is easy because it can be easily wiped off or replaced. [Industrial Applicability]

[0072] The method of multiple reflection of laser light according to the present invention is suitable not only for measuring the absorbance of gas in a cell but also for measuring the absorbance of gas in an open atmosphere. In addition, the method according to the present invention is suitable not only for measuring absorbance but also for exciting gas to extract Raman scattered light in Raman spectroscopy and for exciting gas to extract fluorescence in a fluorescence method, because the Raman scattered light and fluorescence of gas are very weak. [Explanation of symbols]

[0073] 1 Multiple reflective equipment 2,3 A pair of parallel plane mirrors 4 Right-angle double mirror on one end 5 Right-angle double mirror at the other end 6. Optical elements for incidence 7 Optical element driving device 8 Gas cell drive unit 9 Cell Body 10 Gas cell (multiple reflection cell) 11 Light source 21 1st mirror surface 31 Second mirror surface 41,51 1st reflective surface 42,52 2nd reflective surface 53 Entrance hole 54 Output hole 91 Gas supply pipe 92 Gas exhaust pipe

Claims

1. A pair of parallel plane mirrors that multiple-reflect laser light with a predetermined incident angle (φ) in a zigzag pattern; a right-angled two-sided mirror on one end side having two right-angled reflecting surfaces for reflecting back the multiple-reflected light that has traveled to one end between the parallel plane mirrors; a right-angled two-sided mirror on the other end side having two right-angled reflecting surfaces for reflecting back the multiple-reflected light that has traveled from the right-angled two-sided mirror on the one end side to the other end between the parallel plane mirrors; A multi-reflection instrument for measuring a measurement target gas present between the parallel plane mirrors, comprising: A multi-reflection instrument for gas measurement, characterized in that when two parallel mirror surfaces constituting the parallel plane mirror are arranged parallel to the z-x plane of an x-y-z axis coordinate system, the one end is one end in the x-axis direction and the other end is the other end in the x-axis direction, the two reflecting surfaces constituting the right-angled two-sided mirror are perpendicular to the x-y plane, and laser light of the incident angle (φ) intersects with the x-y plane at a predetermined angle (φz).

2. 2. The multiple reflection instrument for measuring gases according to claim 1, The rectangular two-sided mirror has first and second reflecting surfaces that are perpendicular to each other; When the optical path of the multiple reflected light between the parallel plane mirrors is projected onto the xy plane, a distance (dx) between the optical path of the laser light incident on the first reflecting surface and the optical path of the laser light reflected by the first reflecting surface and then reflected by the second reflecting surface is a half pitch of the multiple reflected light between the parallel plane mirrors.

3. 3. A multiple reflection instrument for measuring gases according to claim 1, an optical element for guiding the laser light to the mirror surface; and an incidence driver for changing the position and orientation of the optical element to change the angle of incidence (φ).

4. 3. A multiple reflection instrument for measuring gases according to claim 1, an optical element for guiding the laser light to the mirror surface; and a driving device for the parallel plane mirror that changes the position and orientation of the parallel plane mirror and the right-angle dihedral mirror together with respect to the optical element for incidence in order to change the angle of incidence (φ).

5. 5. A multiple reflection instrument for gas measurement according to claim 3 or 4, characterized in that the driving device changes the incident angle (φ) so that the angle (φx) projected onto the xy plane changes in the range of 0 to 25°.

6. A multiple reflection instrument for gas measurement according to any one of claims 3 to 5, The driving device changes the angle (φz) between the incident direction of the laser light and the x-y plane so that the number of times the multiple reflected light travels back and forth between the right-angled two-sided mirrors on the one end side and the other end side increases or decreases by N times (N is an integer greater than or equal to 1).

7. A multiple reflection instrument for gas measurement according to any one of claims 3 to 6, The driving device changes the angle (φx) obtained by projecting the incident angle (φ) onto the xy plane so that the number of times the laser light travels back and forth between the parallel plane mirrors from the right-angled double-sided mirror on one end to the right-angled double-sided mirror on the other end increases or decreases by M times (M is an integer greater than or equal to 1).

8. A multiple reflection instrument for gas measurement according to any one of claims 1 to 7, A cell body configured to allow the measurement target gas to be introduced and removed, A configuration in which the cell body incorporates the multiple reflector device; The cell body is disposed between the parallel plane mirrors of the multi-reflection instrument; and A multi-reflection cell for gas measurement, characterized in that a portion of the cell body has any of the configurations formed by the multi-reflection device, and is configured so that the gas to be measured is present between the parallel plane mirrors.

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