JPS5912981B2 - Repeated reflection optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a repeating reflection optical photonic device built into a light absorption cell, and particularly relates to an incoherent light beam with a large luminous flux (for example, a tungsten lamp (hereinafter referred to as a W lamp), a deuterium lamp (hereinafter referred to as a D2 lamp), etc. The light from a lamp) is repeatedly reflected in a light absorption cell with a small volume so that the optical axis of the light beam that is repeatedly reflected is distributed three-dimensionally, so that a long optical path length is obtained. This invention relates to a repeating reflection optical device.

In order to perform quantitative analysis with high sensitivity and accuracy from the absorption spectrum of gas, it is necessary to lengthen the optical path length in the gas.

In other words, since the 30-Lambert-Beer law holds true for light absorption by gas, the light intensity P absorbed by gas molecules is P=P0e-n0σ01 where Po is the initial light intensity, n is the molecular density, σ is the 35 absorption cross section, l is the absorption optical path length, and P is the light intensity after absorption.

It can be expressed as

Therefore, the longer the absorption optical path length l, the greater the 11-light absorption.

As an optical device for repeatedly reflecting a light beam to obtain a long optical path length, two spherical mirrors 1 are arranged facing each other so that their centers of curvature 3 are at one point, as shown in Fig. 1, and the light beam 2 is repeatedly reflected. As shown in Figure 2, two plane mirrors 4 are placed opposite each other to repeatedly reflect the light beam, and if both are plane mirrors, the light beam diverges as it is reflected. As shown in Figure 3, one side is made of two spherical mirrors 5 to adjust the angle of reflection and suppress divergence at the same time.
etc. were hot.

When a light beam is repeatedly reflected by these repeating reflection optical devices, the centers of the spots 7 of the light beam are aligned on a straight line on the mirror surface, as shown in FIG. They are all lined up on the same plane, so if you try to reflect a thick beam of light repeatedly with the same device,
As shown in FIG. (for example, 10) can only be narrowed to about the thickness of the light beam 8, so as long as mirrors of the same size are used, the number of repeated reflections will be small and only a short optical path length can be obtained. Furthermore, if an attempt is made to increase the optical path length, the area of the mirror must naturally be increased, and therefore the volume of the light absorption cell that can house the repeating reflection optical device constituted by such a large mirror also becomes large. Making the cell volume as small as possible, that is, reducing the amount of gas sampled, is necessary to speed up the measurement response time from when gas starts being sampled into the cell until the gas is completely replaced with new gas. That's a thing.

In addition, a lens is used to narrow down the parallel light beam,
Even if the light beam is incident on a conventional repeating reflection optical device, the narrower the light beam, the greater the divergence as it goes forward, resulting in greater loss due to divergence.To avoid this, it is necessary to use a large mirror. As a result, the cell volume increases. In other words, in devices such as conventional repeating reflection optical devices, where the optical axes resulting from repeated reflections are all aligned on the same plane, repeating reflection optical devices that have a large number of repeated reflections, little light loss, and a small cell volume cannot be used. The drawback was that it was not possible to create devices. The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to transmit a relatively parallel and thick beam of light using a W lamp, a D2 lamp, etc. as a light source, by attaching a plurality of independently movable mirrors to a mirror mounting board. Planar (
By using a repeating reflection optical device configured by a reflecting mirror device consisting of a group of mirrors distributed two-dimensionally and another reflecting mirror device consisting of a similar group of mirrors facing each other,
A repeating reflection optical device that can be built into a small-volume light absorption cell, which repeatedly reflects the optical axis of the repeatedly reflected light beam so that it is distributed three-dimensionally to obtain a long optical path length with little light loss in a narrow space. The goal is to provide the following.

This will be explained below with reference to the drawings.

FIG. 6, FIG. 7, and FIG. 8 are diagrams showing how to arrange a plurality of mirrors distributed two-dimensionally on a mirror mounting board. Each mirror 11 is movable independently, and two mirror mounting substrates 31 on which a plurality of mirrors are distributed in a plane are opposed to form a repeating reflection optical device. A plurality of mirrors distributed two-dimensionally on the mirror mounting board 31 can be arranged not only as shown in FIGS. 6, 7, and 8, but also as a mirror in which the mirrors are arranged along concentric circles. A plurality of mirrors can be densely arranged as a group or a mirror group in which mirrors are arranged radially. The number of mirrors arranged on each mirror mounting board 31 is determined by the distance between the mirror groups determined by the length of the light absorption cell containing the repeating reflection optical device and the desired absorption optical path length. The number of sheets is not limited. Here, a mirror group consisting of a plurality of mirrors constitutes a reflecting mirror device by being attached to a mirror mounting board via a mirror holder.

Figure 9 shows how a thick beam of light is repeatedly reflected between a pair of mirror groups made up of multiple mirrors.For easier understanding, each independent mirror in the figure is arranged on a straight line. However, in reality, they are two-dimensionally distributed as shown in FIGS. 6, 7, and 8.

In FIG. 9, the light from the light source 20 is made into a thick parallel light beam 22 by the lens 21, and is incident on the mirror 11 on the opposite side.
The mirror group 25 on the opposite side uses a spherical mirror with a radius of curvature of 2d, where the distance between the mirror groups on the incident side and the opposite side is d, and the beam is focused back to the mirror 1' on the incident side.

The mirror group 24 on the incident side uses a plane mirror (or a spherical mirror with a large radius of curvature may be used to reduce loss due to spread of the light beam). The light beam reflected by the plane mirror 1'' enters the next spherical mirror 11'' as a light beam radiated from the focal point, and is returned as a parallel light beam. By finely adjusting the angles of the mirrors one after another, The light was reflected many times as shown in FIG. 9 and extracted as a parallel light beam 23.
As explained above, when distributing multiple mirrors two-dimensionally on a mirror mounting board, a mirror holder that can be finely adjusted is used, where the area of the mirror mounting surface of the conventional mirror holder is larger than the area of the mirror. If you try to use it in the repeated reflection optical device of the present invention, you will have to prepare a space for a mirror holder that is completely unnecessary optically, and as a result, the volume of the light absorption cell that houses such a repeated reflection optical device will also be large. I get used to it and don't like it.

Therefore, in the present invention, the area of the mirror mounting surface of the mirror holder is substantially the area of the mirror or less, and the angle of incidence and exit of the mirror is finely adjusted by finely adjusting the fixing angle of the mirror from the back side of the mirror mounting board. I made it.

FIG. 10 shows how the mirror is mounted on such a mirror mounting board. In the figure, a mirror holder 12 is fastened to a screw hole 17 of a mirror mounting board 31 by a fine adjustment screw 13. A coil spring 16 is sandwiched between the mirror holder 12 and the mirror mounting board 31, and the coil spring 16 is given a force to increase the distance between the mirror holder 12 and the mirror mounting board 31. Therefore, by applying a screwdriver to the blade groove 18 provided in the fine adjustment screw 13 and turning the fine adjustment screw 13, the distance between the mirror holder 12 and the mirror mounting board 31 can be freely changed. At this time, if the fine adjustment screw 13' is not rotated, the mounting angle of the mirror holder 12 can be finely adjusted. Actually, three fine adjustment screws are provided for one mirror holder 12, and the mounting angle of the mirror holder 12 can be freely changed by so-called three-point adjustment. The mirror 11 is attached to the mirror holder 12, and by finely adjusting the mounting angle of the mirror holder 12 as described above, the incident and exit angles of the mirror 11 are finely adjusted. A counterbore hole 14 is provided in the mirror holder 12, and the counterbore hole 14 has a depth such that the head 15 of the fine adjustment screw 13 is buried therein. By fitting the mirror 11 into the counterbore hole 14, the mirror holder 12 can be made smaller than the mirror 11. The mirror 11 is attached to the mirror holder 12 with an adhesive, but it is preferable to attach it using a metal fitting such as a belt, since this allows the mirror to be removed.
Also, use a mirror holder whose area for attaching the mirror is slightly larger than the area of the mirror, make a counterbore hole in the mirror attachment surface of this mirror holder, and insert the mirror into the counterbore hole. Alternatively, the mirror may be attached using an adhesive between the outer circumference of the mirror and the inner circumference of the counterbore.

Even with this method, the mirror mounting surface of the mirror holder can be made much smaller than that of conventional mirror holders.

The point is that by providing the fine adjustment screws 13 on the back side of the mirror mounting surface, the area of the mirror mounting surface of the mirror holder can be reduced.

FIG. 11 is a diagram showing an embodiment of a light absorption cell incorporating a repeating reflection optical device according to the present invention.

In FIG. 11, 20 is a light source, 21 is a lens for obtaining a parallel light beam, 22 is an incident parallel light beam, 23 is a light beam that has been repeatedly reflected and exited the light absorption cell, 24 and 25 are on the incident side and the opposite side, respectively. Mirror group, 30, 30' are outer lids for sealing the light absorption cell, 31, 3' are mirror mounting boards, 32, 32f
33 is a transparent glass window attached to the outer lid for sealing the light absorption cell.
, 335 are the entrance and exit ports for the light flux, 34 and 35 are the inlet and exhaust ports for the sample gas, and 36 is a cylindrical tube. In the example, the thickness of the parallel light beam 22 is 20φ, and the mirror 1
The size of 1 and 1' is 20φ, and the interval between the mirror groups 24 and 25 is 1 m. The mirror 11 of the mirror group 24 on the human shooting side is a spherical mirror with a radius of curvature of 3 m, and the mirror 1' on the opposite side has a radius of curvature of 2 m. This is a repeating reflection optical device with a spherical mirror and an optical path length of 12 m within the light absorption cell. The distribution arrangement of the mirrors at this time is shown in FIG. Note that FIG. 12 shows the mirror group 2 on the opposite side from the B-plane and the C-C plane in FIG.
5 is a diagram showing the arrangement of mirrors in the mirror group 24 on the incident side and the mirror group 24 on the incident side. In the figure, numerals 37 and 38 are peepholes for adjusting the mirror. Further, FIG. 13 is a diagram showing the distribution arrangement of mirrors when obtaining an optical path length of 20 m.

Since the distance of 1 m between the opposing mirror groups remains unchanged, the number of mirrors arranged to increase the number of repeated reflections is naturally increased. Next, consider the case where multiple components are measured simultaneously.

The wavelength to be measured depends on the gas components. By the way, the reflectance of a mirror has wavelength characteristics; for example, the absorption of NO is around 2300, and the absorption of NO2 is around 4500. The reflectance of the mirror is around 2300λ and 4500λ
There is a difference of a few percent between the light intensity near a person, so if the light beam is reflected many times by a mirror and measured with the same optical path length, the difference in the light intensity between the two will be large.
Both become impossible to measure accurately. Generally, when attempting to quantify gas by spectroscopic means, the sensitivity is the square root of the amount of light P incident on the receiver! Proportional to P. That is, if the sensitivity is G, then GO-c! It becomes P.

By the way, the amount of light P that enters the light receiver depends on the reflectance of the mirror, and the amount of light Pn reflected by the mirror n times is Pn or PO
-An.

Furthermore, the sensitivity G depends on the optical path length, and if the distance between the mirrors is 1 meter as in the embodiment, the optical path length is (n+1) meters, so it is expressed by the relational expression GO<:(n+1).

Therefore, putting these formulas together, we get Gc((n+1)VTn is obtained.

From this, the maximum sensitivity G is n-(-2/1na
)-1.

That is, since the absorption wavelength differs depending on the component and the wavelength to be measured differs, there is an appropriate number of reflections depending on each component. In the repeating reflection optical device of the present invention, since each mirror is independently movable, any mirror can be removed, a half mirror can be installed in its place, and a new entrance opening can be provided to allow light to be reflected from different positions. can be made to enter from the middle of repeated reflections.

In other words, different optical path lengths can be extracted from the same optical axis. FIG. 14 is an embodiment of a light absorption cell incorporating repeating reflection optics to provide different optical path lengths. In the figure, 20 and 20' are light sources, 21 and 2' are lenses for obtaining parallel light beams, 22 and 22' are incident parallel light beams, and 3
2, 32', 321 a transparent glass window attached to the cell sealing outer lid 30; 33, 33', 331; an entrance and an exit opening for the light beam on the disk-shaped mirror mounting board 31; 39;
indicates a half mirror holder, and 40 indicates a half mirror. Note that the half mirror can obtain arbitrary reflectance and transmittance in regions such as the ultraviolet region and the visible region, and an example of the half mirror is shown in FIG. 15.

In FIG. 15, reference numeral 41 indicates a substrate transparent to light, reference numeral 42 indicates a transmitting surface, and reference numeral 43 indicates a reflective surface (reflective film adhering surface). Figure 16 shows
It is a figure showing a half mirror holder.

In FIG. 16, reference numeral 44 indicates a hole for the incidence of a light beam, and reference numeral 45 indicates a hole for a fine adjustment screw in the half mirror holder. FIG. 17 is a diagram showing an example of the distribution arrangement of mirrors and half mirrors on the incident side when two different optical path lengths are provided.

As explained above, the present invention enables a long optical path length to be obtained by repeatedly reflecting a thick beam of light using a repeating reflection optical device consisting of a pair of mirror groups facing each other and consisting of a plurality of independently movable mirrors. In addition, the volume of the light absorption cell containing the repeating reflection optical device is reduced.

The following are the applications that can be more easily considered than the present invention: (!
) Provide the entrance and exit ports at positions other than on the disc-shaped mirror mounting substrate on the entrance side and the opposite side, that is, on the side of the cylindrical tube.

(1) A spherical mirror with a radius of curvature of substantially 2d is used on the opposing side, and a plane mirror is used on the input side, or a spherical mirror with a radius of curvature of substantially d is used on both the input side and the opposite side. What I used.

(111) Instead of a coil spring, which is an elastic material used for fine adjustment of the mirror holder, rubber, plate springs, or other sponges are used.

('V) As shown in FIG. 18, the mirror 11 is attached to the mirror holder 12 by a thin cylindrical metal fitting 50.

() The half mirror is formed of a dielectric multilayer film or other metal evaporated film whose reflection and transmittance are controlled by the film thickness.

(Vl) One with one entrance port and multiple exit ports, or one with multiple injection ports and multiple exit ports.

(11) The mirror mounting board is square and the absorption cell is box-shaped.

~11) A spherical mirror or an aspherical mirror is used instead of a lens that creates a thick parallel beam of light.

There are applications such as

As explained above, according to the repeating reflection optical device according to the present invention, the following effects can be obtained.

(a) Since the fine adjustment mechanism was used to adjust the incident and output angles of the mirror from the back side of the mirror mounting board, it was possible to create a mirror holder that could be finely adjusted to a size smaller than the size of the mirror. (
(b) Since the area of the mirror mounting surface of the mirror holder was made smaller than the area of the mirror, multiple mirrors could be densely arranged on the mirror mounting board.

(・→ Because we were able to arrange multiple independently movable mirrors densely on the mirror mounting board, we were able to reduce the cell volume. (d) Since the thick beam of light was reflected repeatedly, the We were able to reduce the amount of light loss due to divergence.

(e) Since the thick light beam was repeatedly reflected three-dimensionally, it passed through the gas inside the cell evenly, making it possible to reduce errors caused by uneven concentration. (f) Since the mirrors that repeatedly reflect each other are movable independently, the optical axis can be adjusted by
This can be easily done by simply adjusting the order of reflection of the light flux.

(B) Since each of the mirrors in the mirror group in the reflecting mirror device is movable independently, if you remove any mirror, install a half mirror in its place, and create a new entrance, you can use the same repeating reflection optical device. , it was possible to simultaneously input light beams from light sources from different positions, and it was possible to obtain different optical path lengths on the same optical axis. )

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are diagrams showing a conventional repeating reflection optical device. FIG. 4 is a diagram showing the state of the light beam on one mirror surface when a narrow light beam is repeatedly reflected by a conventional repeating reflection optical device. FIG. 5 is a diagram showing the arrangement of light beams on one mirror surface when a thick light beam is repeatedly reflected by a conventional repeating reflection optical device. FIG. 6, FIG. 7, and FIG. 8 are diagrams showing how mirrors are two-dimensionally distributed on a mirror mounting board. Figure 9 shows
FIG. 2 is an explanatory diagram depicting in a plane how a light beam is repeatedly reflected by a plurality of independently movable mirrors. FIG. 10 is a diagram showing a mirror fine adjustment mechanism. FIG. 11 is a diagram showing an embodiment of a light absorption cell incorporating a repeating reflection optical device according to the present invention. Figures 12 and 13 show the arrangement of the mirrors when looking at the incident side and the opposite side from the B-plane and c-σ plane in Figure 11.
The figure shows the arrangement of mirrors. 30 Figure 14 shows an embodiment of a light absorption cell incorporating a repeating reflection optical device that provides different optical path lengths on the same optical axis.
FIG. 15 is a diagram showing an example of a half mirror that provides desired reflectance and transmittance. FIG. 16 is a diagram showing a half mirror holder. FIG. 17 is a diagram showing the arrangement of the mirror and half mirror when looking at the incident side from the D-plane in FIG. 14. FIG. 18 is a diagram showing a modification of the mirror holder. In the figure, 11 is a mirror, 1
2 is a mirror holder, 13 is a fine adjustment screw, 14 is a counterbore hole, 15 is a screw head, 16 is a coil spring, 17 is a screw hole provided on the mirror mounting board, 18 is a blade groove, 24 is on the incident side, Mirror group, 25 is the mirror group on the opposite side, 30,3
0' is the outer cover for sealing the light absorption cell, 31 is the mirror mounting board, 32, 321, 3211 is a transparent glass window attached to the outer cover for sealing the light absorption cell, and 33, 33', 335 are the entrance and exit ports for the light flux. , 34, 35 are sample gas intake and exhaust ports;
36 is a cylindrical tube, 37 and 38 are peepholes for adjusting the angle of the mirror, 39 is a half mirror holder, and 40 is a half mirror.

Claims (1)

[Claims] 1. Two mirror mounting boards, a plurality of independently movable mirror holders mounted on each mirror mounting board with fine adjustment screws, and a plurality of mirror holders mounted on each mirror holder. two reflecting mirror devices are constituted by the mirrors; each of the reflecting mirror devices has the plurality of mirrors arranged two-dimensionally on the mirror mounting substrate; 1. A repeating reflection optical device characterized in that mirrors included in the mirror device are spaced apart so that their reflecting surfaces face each other. 2. The mirror holder is such that the area of the mirror mounting surface is substantially equal to or smaller than the area of the mirror, and the multiple mirrors are two-dimensionally distributed on the mirror mounting board so as to be densely arranged. A repeating reflection optical device according to claim 1, characterized in that: 3 When the distance between the reflecting surface of the mirror of the reflecting mirror device and the reflecting surface of the opposing mirror of the reflecting mirror device is d,
The radius of curvature of all mirrors in one reflecting mirror device is 2d
3. The repeated reflection optical device according to claim 1, wherein the repeating reflection optical device is a spherical mirror. 4. When the distance between the reflecting surface of the mirror of the reflecting mirror device and the reflecting surface of the mirror of the opposing reflecting mirror device is d,
3. The repeating reflection optical device according to claim 1, wherein all the mirrors of the double reflecting mirror device are spherical mirrors with a radius of curvature of d. 5. The repeated reflection optical device according to claim 1, 2, 3, or 4, wherein the mirror mounting substrate is disk-shaped. 6. The repeating reflection optical device according to claim 1, 2, 3, 4, or 5, wherein one or more of the mirrors is a half mirror.