WO2020250651A1 - Aerosol measurement device and aerosol measurement method - Google Patents

Abstract

An aerosol measurement device according to an aspect of the present disclosure is an aerosol measurement device for measuring aerosol contained in the air, the aerosol measurement device including: a light source; and an etalon that includes a first surface and a second surface and through which first light emitted from the light source and second light scattered by the aerosol pass. The first light is incident on the first surface along a first direction oblique to the first surface.

Description

Aerosol measuring device and aerosol measuring method

The present disclosure relates to an aerosol measuring device and an aerosol measuring method.

Conventionally, a technique for measuring aerosols in the atmosphere using a lidar (LIDAR: Light Detection and Ringing) is known. The lidar is a technique for observing aerosols floating in the air such as yellow sand, pollen, dust, or minute water droplets by measuring and analyzing the scattered light of pulsed light emitted into the atmosphere.

The scattered light usually includes Mie scattered light and Rayleigh scattered light. The Mie scattered light is scattered light generated by Mie scattering, which is a scattering phenomenon caused by fine particles having a particle size equal to or larger than the wavelength of the emitted light. The Mie scattered light is, for example, scattered light from an aerosol which is an object to be measured. Rayleigh scattering is a scattering phenomenon caused by fine particles and atmospheric molecules smaller than the wavelength of emitted light. By excluding Rayleigh scattered light from scattered light, Mie scattered light can be obtained.

For example, Patent Document 1 discloses a technique for spectroscopically separating scattered light from a single laser beam into Mie scattered light and Rayleigh scattered light using a filter. Further, for example, Patent Document 2 describes an interferometer that selectively transmits light having the same spectral interval as the emitted laser light by utilizing the fact that the mode interval of the spectrum of the laser beam in the multi-longitudinal mode is constant. A technique for dispersing scattered light using a laser is disclosed.

International Publication No. 2003/073127 Japanese Patent No. 6243088

However, in the above-mentioned conventional technique, when the peak wavelength of the laser beam changes due to a temperature change or the like, it is necessary to synchronize the optical path difference while sweeping one wavelength of the laser beam. Therefore, there is a problem that a structure for making the optical path difference variable is required, the device becomes large, and the measurement method becomes complicated.

Therefore, the present disclosure provides a small aerosol measuring device capable of easily measuring an aerosol, and an aerosol measuring method capable of easily measuring an aerosol.

The aerosol measuring device according to one aspect of the present disclosure is an aerosol measuring device for measuring an aerosol contained in the atmosphere, has a light source, a first surface and a second surface, and is emitted from the light source. It comprises a first light and an etalon through which the second light scattered by the aerosol passes. The first light is incident on the first surface along a first direction oblique to the first surface.

Further, the aerosol measurement method according to one aspect of the present disclosure is to irradiate the aerosol contained in the atmosphere with the first light emitted from the light source and passing through the etalon, and the second method scattered by the aerosol. Including light incident on the aerosol. The first light enters the etalon along an oblique direction with respect to the surface of the etalon.

Further, one aspect of the present disclosure can be realized as a program for causing a computer to execute the above aerosol measurement method. Alternatively, it can be realized as a computer-readable non-temporary recording medium in which the program is stored.

According to the present disclosure, it is possible to provide a small aerosol measuring device or the like capable of easily measuring an aerosol.

FIG. 1 is a diagram showing a configuration of an aerosol measuring device according to the first embodiment. FIG. 2 is a flowchart showing the operation of the aerosol measuring device according to the first embodiment. FIG. 3 is a diagram showing an example of the spectrum of the multi-laser light emitted by the aerosol measuring device according to the first embodiment. FIG. 4 is a diagram for explaining the 0th transmitted light and the 1st transmitted light passing through the optical element of the aerosol measuring device according to the first embodiment. FIG. 5 is a diagram for explaining the 0th transmitted light and the 2nd transmitted light passing through the optical element of the aerosol measuring device according to the first embodiment. FIG. 6 is a diagram showing an example of a spectrum of scattered light generated by scattering the multi-laser light emitted by the aerosol measuring device according to the first embodiment. FIG. 7 is a diagram showing a calculation result of an interferogram when scattered light including Mie scattered light and Rayleigh scattered light is interfered with by a Michelson interferometer. FIG. 8 is an enlarged view of a part of FIG. 7. FIG. 9 is a diagram for explaining the dependence of the frequency interval of the interference fringe by the Michelson interferometer when there is no scattering by the aerosol and only the atmospheric scattering is considered. FIG. 10 is a diagram schematically showing the spread angle of the emitted light emitted from the light source according to the first embodiment. FIG. 11 is a diagram schematically showing a path of light when the emitted light emitted from the light source according to the first embodiment is incident on the optical element from the front. FIG. 12 is a diagram schematically showing a path of light when the emitted light emitted from the light source according to the first embodiment is obliquely incident on the optical element. FIG. 13 is a diagram for explaining the refraction of the emitted light incident on the optical element according to the first embodiment. FIG. 14A is a diagram showing a frequency difference characteristic of the product of the transmittance T1 of the emitted light and the transmittance T2 of the scattered light when the incident angle of the emitted light is 1 °. FIG. 14B is a diagram showing a frequency difference characteristic of the product of the transmittance T1 of the emitted light and the transmittance T2 of the scattered light when the incident angle of the emitted light is 1.1 °. FIG. 14C is a diagram showing a frequency difference characteristic of the product of the transmittance T1 of the emitted light and the transmittance T2 of the scattered light when the incident angle of the emitted light is 2 °. FIG. 14D is a diagram showing a frequency difference characteristic of the product of the transmittance T1 of the emitted light and the transmittance T2 of the scattered light when the incident angle of the emitted light is 5 °. FIG. 14E is a diagram showing a frequency difference characteristic of the product of the transmittance T1 of the emitted light and the transmittance T2 of the scattered light when the incident angle of the emitted light is 21 °. FIG. 15 is a diagram showing a configuration of an aerosol measuring device according to a second embodiment. FIG. 16 is a diagram schematically showing a path of light when scattered light is obliquely incident on an optical element. FIG. 17 is a diagram showing a configuration of an aerosol measuring device according to a third embodiment. FIG. 18 is a diagram for explaining the operation of the light-shielding portion of the aerosol measuring device according to the third embodiment.

(Summary of this disclosure)
The aerosol measuring device according to one aspect of the present disclosure is an aerosol measuring device for measuring an aerosol contained in the atmosphere, has a light source, a first surface and a second surface, and is emitted from the light source. It comprises a first light and an etalon through which the second light scattered by the aerosol passes. The first light is incident on the first surface along a first direction oblique to the first surface.

As a result, by making the light incident on the incident surface of the etalon, which is an optical element, at an angle, it is possible to suppress the influence of stray light caused by the emitted light emitted by the light source on the scattered light. For example, it is possible to suppress stray light from interfering with scattered light. As a result, the measurement accuracy of the aerosol can be improved.

Moreover, since a configuration in which the optical path length is variable is not required, it is possible to suppress an increase in the size of the aerosol measuring device. Moreover, since Rayleigh scattered light can be removed by etalon, the aerosol can be easily measured without requiring complicated signal processing. As described above, according to this aspect, it is possible to realize a small aerosol measuring device capable of measuring aerosol easily and accurately.

Moreover, since etalon is used as an optical element, it is possible to suppress an increase in the size of the aerosol measuring device. For example, an optical element such as an etalon changes its optical characteristics when it expands under the influence of heat. According to this aspect, even if the optical characteristics of the optical element change, since the first light and the scattered light pass through the same single optical element, the influence of the change in the characteristics of the optical element can be sufficiently suppressed. Can be done. Therefore, the measurement accuracy of the aerosol can be improved.

Further, for example, the first light incident on the etalon may be emitted from the second surface of the etalon, and the second light may be incident on the etalon from the second surface.

This makes it possible to reduce the number of times the light path is bent in the aerosol measuring device. Therefore, the number of components such as mirrors and the arrangement space can be reduced, and a lightweight and compact aerosol measuring device can be realized.

Further, for example, the second light may be incident on the second surface along a second direction oblique to the second surface.

As a result, the optical path length can be changed by adjusting the incident angle of the scattered light.

Further, for example, the second light may be incident on the etalon from the first surface.

As a result, the emitted light and the scattered light can be incident on the optical element Etalon from the same surface, so that the light reflected by the optical element among the emitted light emitted from the light source is less likely to be incident on the receiver. can do. Therefore, it is possible to suppress erroneous detection of aerosol due to reflected light and failure of the receiver.

Further, for example, the second light may be incident on the first surface along a third direction oblique to the first surface.

As a result, the optical path length can be changed by adjusting the incident angle of the scattered light.

Further, for example, the etalon has a first portion including a path through which the first light passes, and a second portion including a path through which the second light passes and different from the first portion. You may.

As a result, the path of the emitted light and the path of the scattered light can be easily separated, so that the stray light caused by the emitted light can be suppressed from entering the path of the scattered light. Therefore, it is possible to suppress the stray light from interfering with the scattered light.

Further, since the path of the emitted light and the path of the scattered light can be easily separated, for example, the receiver and the light source can be arranged separately. By arranging the receiver and the light source apart from each other, it is possible to prevent the receiver from receiving the reflected light of the emitted light emitted from the light source by the optical element. The reflected light causes false detection of aerosol. Further, since the reflected light has a higher intensity than the scattered light, the intensity exceeds the limit intensity that can be detected by the receiver and may cause a failure of the receiver. According to this aspect, since it is possible to suppress the reflected light from being received by the receiver, it is possible to suppress erroneous detection of aerosol and failure of the receiver.

Further, for example, the first direction may be a direction away from the second portion.

Further, for example, the path of the first light in the first portion is inclined in a direction away from the second portion with respect to a direction orthogonal to the first surface, and the first light is , May be reflected multiple times in the etalon.

As a result, the path of the first light in the etalon is separated from the scattered light, so that the stray light caused by the first light can be further suppressed from affecting the scattered light. Therefore, the measurement accuracy of the aerosol can be further improved.

Further, for example, the path of the second light in the second portion is inclined in a direction away from the first portion with respect to a direction orthogonal to the first surface or the second surface. The second light may be reflected multiple times within the etalon.

As a result, the path of the scattered light in the etalon is separated from the first light, so that the stray light caused by the first light can be further suppressed from affecting the scattered light. Therefore, the measurement accuracy of the aerosol can be further improved.

Further, for example, in the first light, the direction in which the intensity of the first light becomes 10 to ³ times the maximum intensity coincides with the direction orthogonal to the first surface, or the first. It may be inclined from the direction orthogonal to the surface to the direction away from the second portion.

As a result, it is possible to suppress the influence of stray light caused by the first light on the scattered light, so that the measurement accuracy of the aerosol can be improved.

Further, for example, the etalon may interfere with the first light internally and emit as interference light having a plurality of peaks separated from each other at equal frequency intervals.

Further, for example, the frequency interval may be 3.9 GHz or less.

As a result, the transmission of Rayleigh scattered light can be suppressed by the optical element Etalon, so that the receiver can receive Mie scattered light based on the aerosol. Therefore, the presence / absence and concentration of aerosol can be easily measured based on the intensity of light received by the light receiver.

Further, for example, each of the first light and the second light has a plurality of peaks separated from each other at equal frequency intervals, and the frequency of each of the plurality of peaks and the frequency of the plurality of peaks When the difference from the average center frequency is defined as the frequency difference, each of the first light and the second light has the transmission rate of the first light with respect to the etalon and the second light with respect to the etalon. It may have a frequency difference in which the product of the light transmission rate is 0.3 or more.

As a result, the higher the product of the first light transmittance and the scattered light transmittance, the more the amount of Mie scattered light incident on the receiver can be increased.

Further, for example, the aerosol measuring device according to one aspect of the present disclosure may further include a receiver that receives the second light that has passed through the etalon.

Further, for example, the receiver may output a signal corresponding to the intensity of Mie scattered light among the second light.

Further, for example, the first light is pulsed light, and the receiver receives the etalon from the time when the pulsed light is emitted from the light source until the end of a predetermined period longer than the time width of the pulsed light. You may stop receiving the second light that has passed through and receive the second light that has passed through the etalon after the predetermined period ends.

As a result, it is possible to suppress false detection of aerosol due to reflected light and failure due to saturation of the receiver.

Further, for example, the aerosol measuring device according to one aspect of the present disclosure may further include an analysis unit that analyzes the aerosol based on the signal output from the receiver.

Further, for example, the light source may be a laser element or a light emitting diode (LED: Light Emitting Diode) element.

As a result, even if the intensity is attenuated by the optical element, the emitted light having a sufficient intensity can be emitted toward the aerosol.

Further, for example, the aerosol measuring device according to one aspect of the present disclosure may further include a condensing unit that condenses the second light and causes it to enter the etalon.

This makes it possible to increase the interference efficiency within the etalon. Further, since the light receiving sensitivity can be increased, the measurement accuracy of the aerosol particles can be improved.

Further, the aerosol measurement method according to one aspect of the present disclosure is to irradiate the aerosol contained in the atmosphere with the first light emitted from the light source and passing through the etalon, and the second method scattered by the aerosol. Including light incident on the aerosol. The first light enters the etalon along an oblique direction with respect to the surface of the etalon.

As a result, Rayleigh scattered light can be removed by the optical element Etalon, so that the aerosol can be easily measured based on the light receiving intensity by the light receiver without requiring complicated signal processing.

In the present disclosure, all or part of a circuit, unit, device, member or part, or all or part of a functional block in a block diagram, is a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (Large Scale Integration). It may be executed by one or more electronic circuits including. The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, it is called an LSI or an IC, but the name changes depending on the degree of integration, and it may be called a system LSI, a VLSI (Very Large Scale Integration), or a ULSI (Ultra Large Scale Integration). Field Programmable Gate Array (FPGA), which is programmed after the manufacture of the LSI, or reconfigurable logistic device, which can reconfigure the connection relationship inside the LSI or set up the circuit partition inside the LSI, can also be used for the same purpose.

Furthermore, all or part of the functions or operations of circuits, units, devices, members or parts can be executed by software processing. In this case, the software is recorded on one or more ROMs, optical disks, non-temporary recording media such as hard disk drives, and when the software is executed by a processor, the functions identified by the software are It is executed by a processor and peripheral devices. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and the required hardware device, such as an interface.

Hereinafter, the embodiment will be specifically described with reference to the drawings.

It should be noted that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, etc. shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims will be described as arbitrary components.

In addition, each figure is a schematic view and is not necessarily exactly illustrated. Therefore, for example, the scales and the like do not always match in each figure. Further, in each figure, substantially the same configuration is designated by the same reference numerals, and duplicate description will be omitted or simplified.

Further, in the present specification, terms indicating relationships between elements such as parallel, terms indicating the shape of elements such as cylinders or prisms, and numerical ranges are not expressions that express only strict meanings, but are substantial. It is an expression meaning that the same range, for example, a difference of about several percent is included.

(Embodiment 1)
[1. Constitution]
First, an outline of the aerosol measuring device according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of an aerosol measuring device 1 according to the present embodiment.

As shown in FIG. 1, the aerosol measuring device 1 according to the present embodiment emits the irradiation light L2 into the atmosphere, and the scattering body 90 existing in the atmosphere scatters the emitted light L2 to generate scattering. By acquiring the light L3 and processing the acquired scattered light L3, the presence / absence and concentration of the aerosol contained in the scatterer 90 are measured. The scatterer 90 exists in the target space for measurement by the aerosol measuring device 1. The scattered light L3 corresponds to the second light.

The target space is, for example, a room in a building such as a residence, office, long-term care facility, or hospital. The target space is, for example, a space partitioned by walls, windows, doors, floors, ceilings, etc., and is a closed space, but is not limited to this. The target space may be an outdoor open space. Further, the target space may be the internal space of a moving body such as a bus or an airplane.

The scatterer 90 includes an aerosol to be measured, machined dust, coarse particles, and molecules constituting air. Specifically, the aerosol is dust floating in the target space, suspended particulate matter such as PM2.5, biological particles, or minute water droplets. Biological particles also include molds or mites floating in the air, pollen, and the like. In addition, minute water droplets include substances dynamically generated from the human body such as coughing or sneezing.

Aerosol, which is the object to be measured, is sufficiently large compared to the molecules that make up air. In the present embodiment, since the particle size of the aerosol is equal to or larger than the wavelength of the irradiation light L2, the aerosol scatters the irradiation light L2 to generate Mie scattered light. Since the molecules constituting air are sufficiently smaller than the wavelength of the irradiation light L2, Rayleigh scattered light is generated by scattering the irradiation light L2. Therefore, the scattered light L3 acquired by the aerosol measuring device 1 includes Mie scattered light and Rayleigh scattered light. The Mie scattered light here is backscattered light due to Mie scattering. The aerosol measuring device 1 according to the present embodiment extracts Mie scattered light from the scattered light L3 and measures the presence / absence and concentration of the aerosol based on the extracted Mie scattered light.

The aerosol measuring device 1 according to the present embodiment emits irradiation light L2 for irradiating the scatterer 90 in different directions in the target space. The emission direction of the irradiation light L2 is changed by, for example, a MEMS (Micro-Electro-Mechanical Systems) mirror (not shown). Alternatively, the emission direction of the irradiation light L2 may be changed by changing the direction of the entire aerosol measuring device 1. The aerosol measuring device 1 can create an aerosol distribution in the target space by scanning the target space.

As shown in FIG. 1, the aerosol measuring device 1 includes an optical element 10, a light source 20, a mirror 22, a condensing unit 30, a condensing lens 40, a receiver 50, and an analysis unit 60. .. An example of the condensing unit 30 is a condensing lens 30a. Hereinafter, each component included in the aerosol measuring device 1 will be described.

The optical element 10 internally interferes with the incident light and emits it as light having a plurality of peaks separated from each other at equal frequency intervals. Light having a plurality of peaks is also called multi-light. In the present embodiment, the optical element 10 is a single optical element. That is, the optical element 10 is one member integrally configured. The shape of the optical element 10 is, for example, a cylinder or a prism. Specifically, the optical element 10 is an etalon.

As shown in FIG. 1, the optical element 10 has a light transmitting portion 11 and two multilayer films 12 and 13. The translucent portion 11 is formed by using a transparent material such as quartz or quartz. The translucent portion 11 is sandwiched between the two multilayer films 12 and 13, and is in contact with each of the two multilayer films 12 and 13. The two multilayer films 12 and 13 are dielectric multilayer films having a laminated structure of a plurality of dielectric films, respectively. For example, the two multilayer films 12 and 13 are each formed by alternately laminating a dielectric film having a low refractive index and a dielectric film having a high refractive index. As the dielectric film, for example, a titanium oxide film, a hafnium oxide film, a silicon oxide film, or the like is used. The light transmitting portion 11 may be an air layer, and the two multilayer films 12 and 13 may be fixed by a frame or the like so as to maintain a constant distance.

The optical element 10 is incident with the emitted light L1 emitted from the light source 20, causes the emitted light L1 to interfere internally, and emits as irradiation light L2 which is light having a plurality of peaks separated from each other at equal frequency intervals. To do. The irradiation light L2 is a multi-laser light. The emitted light L1 corresponds to the first light.

Although the irradiation light L2 is light having a plurality of peaks separated from each other at equal frequency intervals, the irradiation light L2 may be light having one peak.

In the present embodiment, the emitted light L1 is incident on the multilayer film 12 of the optical element 10 and emitted from the multilayer film 13. The first surface 12a of the multilayer film 12 opposite to the translucent portion 11 is an incident surface on which the emitted light L1 is incident. The second surface 13a of the multilayer film 13 opposite to the translucent portion 11 is an exit surface from which the irradiation light L2 is emitted. The second surface 13a, which is the exit surface, is a surface opposite to the first surface 12a, which is the incident surface. The first surface 12a and the second surface 13a are parallel to each other. The direction orthogonal to the first surface 12a and the second surface 13a is parallel to the central axis of the optical element 10.

Further, the scattered light L3 condensed by the condenser lens 30a is incident on the optical element 10. In the present embodiment, the scattered light L3 is incident from the multilayer film 13 of the optical element 10, and the Mie scattered light L4, which is a part of the scattered light L3, is emitted from the multilayer film 12. The second surface 13a of the multilayer film 13 opposite to the light transmitting portion 11 is an incident surface on which scattered light L3 is incident. The first surface 12a of the multilayer film 12 opposite to the light transmitting portion 11 is an exit surface from which the Mie scattered light L4 is emitted. That is, the incident surface of the emitted light L1 and the incident surface of the scattered light L3 are different.

Further, as shown in FIG. 1, the optical element 10 has a first portion 10a including a path through which the emitted light L1 passes and a second portion 10b including a path through which the scattered light L3 passes. In FIG. 1, the boundary between the first portion 10a and the second portion 10b is schematically represented by a broken line. The first portion 10a and the second portion 10b are different portions from each other. For example, when the optical element 10 is a columnar etalon, the first portion 10a and the second portion 10b correspond to a semi-cylindrical portion when the etalon is virtually divided on a surface including the central axis. The circular upper and lower surfaces of the cylindrical etalon correspond to the entrance surface and the emission surface of light.

Since the scattered light L3 includes light having a plurality of peaks separated from each other at equal frequency intervals, each light causes interference when passing through the optical element 10. In the present embodiment, the thickness of the optical element 10 is adjusted so that the Mie scattered light L4 included in the scattered light L3 is passed and the Rayleigh scattered light is suppressed from passing. As a result, the Rayleigh scattered light can be appropriately removed from the scattered light L3, so that the Mie scattered light L4 caused by the aerosol can be received by the receiver 50.

In the present embodiment, the optical element 10 is located on the optical path of the emitted light L1 emitted from the light source 20. Specifically, the optical element 10 is located between the mirror 22 and the opening provided in the outer housing of the aerosol measuring device 1. The opening is provided for the irradiation light L2 emitted from the optical element 10 to pass through. Further, the optical element 10 is located on the optical path of the scattered light L3 generated from the scattering body 90. Specifically, the optical element 10 is located between the condenser lens 30a and the condenser lens 40.

The light source 20 emits the irradiation light L2 into the atmosphere via the optical element 10. Specifically, the light source 20 emits the emitted light L1. The emitted light L1 is, for example, pulsed light, but may be continuous light. The emitted light L1 may be monochromatic light having a peak in a specific wavelength band, or light including a broad wavelength band. The emitted light L1 contains, for example, a wavelength component in the range from a wavelength 10 pm to 10 nm shorter than the peak wavelength to a wavelength 10 pm to 10 nm longer than the peak wavelength. The emitted light L1 is, for example, ultraviolet light, blue light, infrared light, or the like. Emission light L1 From a short wavelength, after being reflected by the mirror 22, it is emitted into the atmosphere as irradiation light L2, which is light having a plurality of peaks separated from each other at equal frequency intervals due to interference inside the optical element 10. To.

The light source 20 is, for example, a semiconductor laser element that emits pulsed laser light as emitted light L1. The beam mode of the emitted light L1 is, for example, a multi-mode, but may be a single mode. As an example, the light source 20 emits a laser beam having a peak in the vicinity of 405 nm as the emitted light L1. Alternatively, the light source 20 may be a light emitting diode (LED: Light Emitting Diode). Further, the light source 20 may be a discharge lamp such as a halogen lamp.

The mirror 22 reflects the emitted light L1. By arranging the mirror 22 at an appropriate angle with respect to the emitted light L1, the course of the emitted light L1 can be bent in a desired direction. In the present embodiment, the mirror 22 reflects the emitted light L1 and causes it to enter the optical element 10. The aerosol measuring device 1 does not have to include the mirror 22.

In the present embodiment, the emitted light L1 emitted from the light source 20 is incident on the optical element 10 along an oblique direction with respect to the first surface 12a of the optical element 10. Further, the emitted light L1 is light that spreads at a spreading angle α. Specific examples of the emitted light L1 and its incident angle θ will be described later.

The light collecting unit 30 collects the scattered light L3 generated by the scattering body 90 contained in the atmosphere scattering the irradiation light L2. As an example of the condensing unit 30, there is, for example, a convex condensing lens 30a, or at least one reflecting mirror. For example, the light collected by the condenser lens 30a is converted into parallel light and emitted by a lens group including a collimating lens. Therefore, the scattered light L3 collected by the condenser lens 30a is incident on the optical element 10. When the signal intensity of the scattered light L3 is strong, the condensing unit 30 may not be arranged.

The scattered light L3 collected by the condenser lens 30a is incident on the optical element 10. In the present embodiment, the scattered light L3 is incident on the optical element 10 from the front with respect to the second surface 13a of the optical element 10, that is, at an incident angle of 0 °.

The condenser lens 40 collects the Mie scattered light L4 that has passed through the optical element 10 among the scattered light L3 condensed by the condenser lens 30a. The condenser lens 40 is, for example, a convex lens. The condenser lens 40 concentrates the Mie scattered light L4 on the light receiving surface of the receiver 50.

The light receiver 50 receives the Mie scattered light L4 that has passed through the optical element 10 among the scattered light L3 collected by the condenser lens 30a, and outputs a signal corresponding to the light receiving intensity. The light receiving intensity is the intensity of the Mie scattered light L4, and is represented by, for example, the signal level of the signal output by the light receiver 50.

The light receiver 50 is an element that performs photoelectric conversion, for example, a PMT (Photomultiplier Tube). Alternatively, the receiver 50 may have a PMT and a photon counter. Further, the receiver 50 may be an avalanche photodiode.

The analysis unit 60 analyzes the aerosol contained in the scatterer 90 by analyzing the signal output from the receiver 50. For example, the analysis unit 60 determines the presence / absence and concentration of aerosol based on the signal level of the signal. Specifically, the analysis unit 60 determines the concentration of the aerosol corresponding to the signal level by referring to the correspondence information in which the signal level and the concentration of the aerosol are associated with each other. Correspondence information is stored in advance in, for example, a memory (not shown) included in the analysis unit 60.

Further, the analysis unit 60 calculates the distance to the aerosol by the TOF (Time Of Flight) method based on the time required from the emission of the irradiation light L2 to the reception of the Mie scattered light L4. The analysis unit 60 identifies the position of the aerosol in the target space based on the calculated distance and the direction in which the irradiation light L2 is emitted. By repeating the identification of the position of the aerosol while changing the emission direction of the irradiation light L2, the analysis unit 60 creates the distribution of the aerosol in the target space.

The analysis unit 60 is composed of one or a plurality of electronic circuits including a plurality of circuit components. Each of the one or more electronic circuits may be a general-purpose circuit or a dedicated circuit. That is, the function executed by the analysis unit 60 is realized by hardware such as an electronic circuit. Alternatively, the analysis unit 60 may be realized by a non-volatile memory in which the program is stored, a volatile memory which is a temporary storage area for executing the program, an input / output port, a processor in which the program is executed, or the like. The function executed by the analysis unit 60 may be realized by software executed by the processor.

Each component included in the aerosol measuring device 1 is housed inside a housing (not shown), for example. The housing is an outer housing of the aerosol measuring device 1 and has a light-shielding property. The housing is provided with an opening for passing the irradiation light L2 and the scattered light L3. One aperture may be provided corresponding to each of the irradiation light L2 and the scattered light L3. The condenser lens 30a may be provided in the aperture.

[2. motion]
Next, the operation of the aerosol measuring device 1 will be described with reference to FIG. FIG. 2 is a flowchart showing the operation of the aerosol measuring device 1 according to the present embodiment.

As shown in FIG. 2, first, the light source 20 emits the emitted light L1 (S10). The emitted light L1 is reflected by the mirror 22 and its traveling direction is bent, and is incident on the optical element 10 along a direction oblique to the first surface 12a of the optical element 10. The emitted light L1 is converted into multi-light, which is light having a plurality of peaks separated from each other at equal frequency intervals by passing through the optical element 10 at an angle. That is, the optical element 10 internally interferes with the incident light and emits it as light having a plurality of peaks separated from each other at equal frequency intervals (S12). The irradiation light L2, which is multi-light, is emitted into the atmosphere and scattered by the scatterer 90.

Next, the condenser lens 30a collects the scattered light L3 generated from the scatterer 90 (S14). The scattered light L3 collected by the condenser lens 30a is incident on the second surface 13a of the optical element 10 from the front. By passing through the optical element 10, the Mie scattered light L4 is extracted. That is, the scattered light L3 collected by the condensing unit 30 interferes with each other inside the optical element 10 and passes through the Mie scattered light L4 (S16). In other words, the optical element 10 substantially removes the Rayleigh scattered light among the scattered light L3 and allows only the Mie scattered light L4 to pass through.

Next, the light receiver 50 receives the Mie scattered light L4 and outputs a signal according to the light receiving intensity (S18).

The analysis unit 60 analyzes the aerosol contained in the scatterer 90 by processing the signal output from the receiver 50 (S20).

The aerosol measuring device 1 repeats the above processes from step S10 to step S20 while changing the emission direction of the irradiation light L2. For example, when the irradiation light L2 is emitted in a predetermined direction in the target space and the scattered light L3 can be acquired, the position and concentration of the aerosol contained in the scattering body 90 that is the source of the scattered light L3 can be determined. Identify. As a result, the aerosol measuring device 1 can generate, for example, a distribution map showing the position and concentration of the aerosol in the target space. The aerosol measuring device 1 may generate a distribution map showing only the position of the aerosol.

[3. Function of optical element]
Subsequently, a specific function of the optical element 10 will be described.

As described above, the optical element 10 is a multi-laser light composed of light having a plurality of peaks separated from each other at equal frequency intervals by internally interfering with the emitted light L1 which is the laser light emitted from the light source 20. It is emitted as a certain irradiation light L2. In the following, first, the multi-laser light will be described with reference to FIG.

FIG. 3 is a diagram showing an example of the spectrum of the multi-laser light emitted by the aerosol measuring device 1 according to the present embodiment. In each of the parts (a) and (b) of FIG. 3, the horizontal axis represents the frequency and the vertical axis represents the signal strength.

Part (a) of FIG. 3 shows the spectrum of the irradiation light L2, which is the multi-laser light after passing through the optical element 10. Each of the plurality of peaks included in the spectrum corresponds to the plurality of peaks included in the irradiation light L2. The frequency intervals LW2 of the plurality of peaks are equal to each other, for example, 3 GHz. Here, an example in which the signal intensities of a plurality of peaks are equal to each other is shown, but they may be different from each other. The center wavelength λ of the irradiation light L2 is, for example, 405 nm.

Part (b) of FIG. 3 is an enlarged view of part (a) of FIG. 3, and shows one peak of the spectrum, that is, only one light included in the irradiation light L2 in an enlarged manner. The full width at half maximum LW1 of one light is, for example, 360 MHz. LW1 is 1/20 or more and 1/5 or less of LW2, but may be 1/10 or more and 1/8 or less.

In the present embodiment, when the emitted light L1 passes through the optical element 10, it interferes with the inside of the optical element 10 and is emitted as the irradiation light L2. The etalon, which is the optical element 10, utilizes the interference between the incident light and the light that is repeatedly reflected in the etalon. When the phase of the incident light and the phase of the light repeatedly reflected in the etalon match, interference that strengthens the light occurs, and the light is enhanced and transmitted in the etalon. The multilayer films 12 and 13 of Etalon can transmit or reflect light. The transmittance of each of the multilayer films 12 and 13 is, for example, 75%, but is not limited to this.

Here, FIGS. 4 and 5 are diagrams for explaining light passing through the optical element 10 of the aerosol measuring device 1 according to the present embodiment, respectively. Specifically, FIG. 4 schematically shows the 0th transmitted light and the 1st transmitted light. FIG. 5 schematically represents the 0th transmitted light and the 2nd transmitted light.

The optical element 10 transmits a part of the incident light as it is. As shown in FIGS. 4 and 5, the light transmitted as it is without being reflected by the multilayer films 12 and 13 of the optical element 10 is the 0th transmitted light.

As shown in FIG. 4, the first transmitted light is light that is reflected once by the multilayer film 12 after the incident light is reflected once by the multilayer film 13. Interference occurs when the phases of the 0th transmitted light and the 1st transmitted light match, and the light corresponding to the first interference fringe is emitted. Interfering fringes will be described later with reference to FIGS. 7 and 8.

As shown in FIG. 5, the second transmitted light is light in which the incident light is reflected twice by the multilayer film 13 and the multilayer film 12, respectively. Interference occurs when the phases of the 0th transmitted light and the 2nd transmitted light match, and the light corresponding to the second interference fringe is emitted.

If the phase of the incident light and the phase of the repeatedly reflected light do not match, the light is reflected toward the incident surface and the intensity of the light passing through the etalon is weakened. As a result, the transmitted light has a periodic spectrum. That is, when the emitted light L1 is incident, the optical element 10 can emit the irradiation light L2 having a plurality of peaks separated by the same frequency interval LW2.

The length Δx of the etalon for realizing the frequency interval LW2 is determined based on the following equation (1). The length Δx of the etalon is the distance between the multilayer film 12 and the multilayer film 13, that is, the thickness of the translucent portion 11, as shown in FIGS. 4 and 5.

In the formula (1), n ₀ is the refractive index in vacuum, for example 1.0. n is the refractive index of the translucent portion 11 of etalon, which is 1.47 in the case of quartz. c is the speed of light, which is 3 × 10 ⁸ m / s. When LW2 = 3 GHz, the length Δx of the etalon is 34 mm from the above formula (1). Further, the length Δx of the etalon is limited to about 80 mm in manufacturing. Therefore, the lower limit of LW2 is about 1.3 GHz.

The optical path difference dx when Fabry-Perot interference is caused by Etalon is expressed by the following equation (2).

For example, when Δx = 34 mm, the optical path difference dx is 100 mm.

Next, the scattered light L3 generated by the scattering body 90 scattering the irradiation light L2 shown in FIG. 3 will be described with reference to FIG.

FIG. 6 is a diagram showing an example of the spectrum of scattered light L3 generated by scattering the multi-laser light emitted by the aerosol measuring device 1 according to the present embodiment. In each of the parts (a) and (b) of FIG. 6, the horizontal axis represents the frequency and the vertical axis represents the signal strength.

Part (a) of FIG. 6 shows the spectrum of scattered light L3. The scattered light L3, like the irradiation light L2, is composed of light having a plurality of peaks separated from each other at a frequency interval MW2 equal to each other. Each of the plurality of peaks included in the spectrum corresponds to the plurality of peaks included in the irradiation light L2. The frequency interval MW2 of the scattered light L3 is equal to the frequency interval LW2 of the irradiation light L2. Here, an example in which the signal intensities of a plurality of peaks are equal to each other is shown, but they may be different from each other.

Part (b) of FIG. 6 is an enlarged view of part (a) of FIG. 6, and shows one peak of the spectrum, that is, only one light included in the scattered light L3 in an enlarged manner.

As described above, the scattered light L3 includes Mie scattered light and Rayleigh scattered light. The spectrum of Mie scattered light is substantially the same as the spectrum of irradiation light L2 before scattering. On the other hand, the frequency width of Rayleigh scattered light is widened by the thermal motion of the molecules that make up the atmosphere. Also, the intensity of Rayleigh scattered light is usually lower than the intensity of Mie scattered light.

Therefore, as shown in the part (b) of FIG. 6, the spectrum of the scattered light L3 has a shape in which the base of the peak is widened as compared with the spectrum of the irradiation light L2 shown in FIG. The high peak at the center corresponds to Mie scattered light, and the base part corresponds to Rayleigh scattered light. In the part (b) of FIG. 6, the signal intensity of Rayleigh scattered light by the molecules constituting the atmosphere and the signal intensity of Mie scattered light by the aerosol are set to 3: 1. The signal strength here is represented by the area of the peak. Further, the full width at half maximum MW1 of the peak representing the Mie scattered light is equal to the full width at half maximum LW1 of the irradiation light L2.

It is known that the full width at half maximum RW of the foot portion representing the Rayleigh scattered light is about 3.4 GHz to 3.9 GHz according to a general actual measurement. As an example, the full width at half maximum RW of Rayleigh scattered light can be 3.6 GHz (Δλ = 1.9 pm).

Note that Δλ is calculated based on the following equation (3).

In the formula (3), Δf = RW. c is the speed of light, which is 3 × 10 ⁸ m / s. λ is the central wavelength, which is 405 nm here.

In the present embodiment, by passing the scattered light L3 through the optical element 10, light having a plurality of peaks appearing at a frequency interval of 3 GHz, that is, Me scattered light is transmitted, and light of another frequency component, that is, , Rayleigh scattered light can be removed.

FIG. 7 is a diagram showing the calculation result of the interferogram when the scattered light including the Mie scattered light by the aerosol and the Rayleigh scattered light by the molecules constituting the atmosphere are interfered with by the Michelson interferometer. In FIG. 7, the horizontal axis represents the optical path difference dx that causes interference, and the vertical axis represents the intensity of the interference light. FIG. 8 is an enlarged view of the region VIII surrounded by the broken line in FIG. 7.

As shown in FIGS. 7 and 8, an interference fringe appears every time the optical path difference dx becomes an integral multiple of Δx. The interference fringe of dx = 0 is defined as the 0th interference fringe, and the interference fringe of dx = n × Δx is defined as the nth interference fringe. n is a natural number. FIG. 8 shows the 0th interference fringe, the 1st interference fringe, and the 2nd interference fringe. The first interference fringe is the light generated by the interference between the 0th transmitted light and the 1st transmitted light shown in FIG. The second interference fringe is the light generated by the interference between the 0th transmitted light and the second transmitted light shown in FIG.

In the receiver 50, the interference light including the 0th interference fringe to the nth interference fringe is received as Mie scattered light L4. In the present embodiment, by adjusting the length Δx of the etalon which is the optical element 10, the interference fringe due to the Rayleigh scattered light caused by atmospheric scattering can be removed. A method for determining a length Δx suitable for removing Rayleigh scattered light will be described.

FIG. 9 is a diagram for explaining the dependence of the frequency interval of the interference fringe by the Michelson interferometer when only atmospheric scattering is considered without scattering by aerosol. In the parts (a) to (l) of FIG. 9, the horizontal axis represents dx and the vertical axis represents the signal strength. In the parts (a) to (l) of FIG. 9, the frequency intervals LW2 of the irradiation light L2 are 2.4 GHz, 3.0 GHz, 3.6 GHz, 3.7 GHz, 3.8 GHz, 3.9 GHz, 4 GHz, 5 GHz, respectively. It shows the calculation result of the interferogram in the case of 6 GHz, 10 GHz, 15 GHz, and 30 GHz.

As shown in FIG. 9, as the frequency interval LW2 increases, the number of appearing interference fringes increases, and the signal strength of the appearing interference fringes increases. For example, when the frequency interval LW2 is 2.4 GHz, substantially only the 0th interference fringe appears, and the first or more interference fringes do not appear. In the frequency interval LW2 in the range of 3.0 GHz to 4 GHz, the 0th interference fringe and the 1st interference fringe appear, and the second and higher interference fringes do not appear. When the frequency interval LW2 is 5 GHz, a second interference fringe appears in addition to the 0th interference fringe and the first interference fringe. In FIG. 9, the range in which the first interference fringe and above appear is represented by a broken line frame.

The appearance of the second or higher interference fringes when only atmospheric scattering is taken into consideration means that interference is occurring only by Rayleigh scattered light. That is, it means that the Rayleigh scattered light is transmitted when the Rayleigh scattered light is incident on the optical element 10. Therefore, if the frequency interval LW2 is 3.9 GHz or less, the first interference fringe becomes small, and the transmission of Rayleigh scattered light is suppressed.

That is, the magnitude of the first interference fringe when the frequency interval LW2 is 3.9 GHz is 50% or less of the magnitude of the 0th interference fringe. Therefore, since the first interference fringe is small, it is possible to suppress the Rayleigh scattered light from passing through the optical element 10.

From the above, when the frequency interval LW2 is 3.9 GHz or less, Rayleigh scattered light can be efficiently removed from the scattered light L3. When the frequency interval LW2 is 3.9 GHz, the length Δx of the etalon made of quartz is about 26 mm according to the formula (1). That is, by using an etalon having a length Δx of 26 mm or more as the optical element 10, Rayleigh scattered light can be efficiently removed, and the measurement accuracy of the aerosol can be improved.

[4. Characteristics of emitted light]
FIG. 10 is a diagram schematically showing the spread angle of the emitted light L1 emitted from the light source 20 according to the present embodiment. As shown in FIG. 10, the emitted light L1 emitted from the light source 20 has a predetermined spread angle α. That is, the emitted light L1 is light whose beam diameter is not always constant and spreads outward as the distance from the light source 20 increases.

The spread angle α of the emitted light L1 is an angle formed by the optical axis direction of the emitted light L1 and the direction in which the intensity of the emitted light L1 becomes 10 to ³ times the maximum intensity. The optical axis direction is shown by the broken line in FIG. 10, and coincides with the normal direction of the exit surface of the light source 20. The spread angle α is, for example, 2 ° or less.

When the emitted light L1 spreads at the spreading angle α and is incident on the optical element 10 from the front, a part of the light affects the scattered light L3. FIG. 11 is a diagram schematically showing a path of light when the emitted light L1 is incident on the optical element 10 from the front. In the present embodiment, "incident from the front" means a case where the optical axis direction of the emitted light L1 is perpendicular to the first surface 12a which is the incident surface. That is, in FIG. 11, the incident angle θ of the emitted light L1 is 0 °. Although details will be described with reference to FIG. 13, the incident angle θ of the emitted light L1 is an angle formed by the optical axis direction of the emitted light L1 and the normal direction of the first surface 12a. In FIGS. 11 to 13, the optical axis of light is represented by a solid arrow.

In FIG. 11, for the sake of simplicity, the refraction when the emitted light L1 is incident on the optical element 10 is not shown. In addition, dots are shaded in the range of the emitted light L1 having an intensity of 10 to ³ times or more the maximum intensity. The same applies to FIGS. 12 and 16 described later.

As shown in FIG. 11, of the emitted light L1 spreading at the spreading angle α, a part of the light spreading toward the path side of the scattered light L3 is at the interface between the light transmitting portion 11 and each of the multilayer films 12 and 13. By multiple reflection, it can pass on the path of scattered light L3 as stray light L5. Therefore, since the stray light L5 and the scattered light L3 interfere with each other, the Mie scattered light L4 contains a noise component not caused by the aerosol. Therefore, the detection accuracy of the aerosol is lowered.

On the other hand, in the present embodiment, as shown in FIG. 12, the emitted light L1 is incident on the optical element 10 along a direction oblique to the first surface 12a of the optical element 10. FIG. 12 is a diagram schematically showing a path of light when the emitted light L1 is incident on the optical element 10 along an oblique direction with respect to the first surface 12a of the optical element 10.

As shown in FIG. 12, the emitted light L1 is incident on the optical element 10 along an oblique direction with respect to the first surface 12a of the optical element 10. In the present embodiment, in the emitted light L1, the direction in which the intensity of the emitted light L1 becomes 10 to ³ times the maximum intensity coincides with the normal direction D orthogonal to the first surface 12a, or is from the normal direction D. Is also inclined in a direction away from the path through which the scattered light L3 passes. In the example shown in FIG. 12, the direction in which the intensity of the emitted light L1 becomes 10 to ³ times the maximum intensity is inclined in a direction away from the path of the scattered light L3 at an angle β with respect to the normal direction D. β is 0 ° or more.

As shown in FIG. 12, of the emitted light L1 spreading at the spreading angle α, a part of the light spreading toward the path side of the scattered light L3 is at the interface between the light transmitting portion 11 and each of the multilayer films 12 and 13. Multiple reflections. At this time, the light L6 closest to the path of the scattered light L3 among the emitted light L1, that is, the light L6 corresponding to the direction in which the intensity of the emitted light L1 becomes 10 to ³ times the maximum intensity is with respect to the normal direction D. It is inclined in a direction away from the path of the scattered light L3. Therefore, since the light L6 is multiplely reflected in the direction away from the path of the scattered light L3, the interference with the scattered light L3 is sufficiently suppressed. Since the noise component caused by the stray light L6 is sufficiently suppressed, the detection accuracy of the aerosol can be improved.

[5. angle]
Subsequently, the range in which the incident angle θ of the emitted light L1 can be taken will be described.

FIG. 13 is a diagram for explaining the refraction of the emitted light L1 incident on the optical element 10. The emitted light L1 shown in FIG. 13 is incident on the first surface 12a at an incident angle θ. The emitted light L1 is refracted when it enters the optical element 10 and when it passes through the multilayer film 12, and travels in the translucent portion 11 at a refraction angle φ. When the refractive index around the optical element 10 is 1 and the refractive index of the translucent portion 11 is n, nsinφ = sinθ is established.

Further, among the emitted light L1, the incident angle of the light L6 in the direction in which the intensity of the emitted light L1 becomes 10 to ³ times the maximum intensity is θ−α because the spreading angle is α. Therefore, nsinβ = sin (θ−α) is established.

In the present embodiment, since the emitted light L1 is incident on the first surface 12a so that β is 0 ° or more, the incident angle θ of the emitted light L1 is α or more.

Further, each of the emitted light L1 and the scattered light L3 has a plurality of peaks separated from each other at equal frequency intervals, and the frequency of each of the plurality of peaks and the center frequency which is the average of the frequencies of the plurality of peaks. If the difference is defined as a frequency difference, the output light L1 has a product (T1 × T2) of the transmittance T1 of the emitted light L1 with respect to the optical element 10 and the transmittance T2 of the scattered light L3 with respect to the optical element 10 of 0.3. It is incident on the first surface 12a at an angle having the above frequency difference. That is, the incident angle θ of the scattered light L1 is an angle having a frequency difference df at which T1 × T2 is 0.3 or more. Specifically, the incident angle θ is an angle at which a frequency difference df in which the product of T1 × T2 is 0.3 or more exists within a range of a predetermined frequency difference. The range of the predetermined frequency difference is, for example, a range of −6 GHz or more and + 6 GHz or less. Further, the product of T1 × T2 may be 0.5 or more.

The transmittance T is represented by the following equations (4), (5) and (6).

In the formulas (4), (5) and (6), λ is the central wavelength of the emitted light L1 or the scattered light L3. As an example, λ is 405 nm. c is the speed of light, which is 3 × 10 ⁸ m / s. Therefore, when λ is 405 nm, the center frequency f ₀ is 7.41 × 10 ¹⁴ Hz.

R is the reflectance at the end face of the optical element 10. In the case of the emitted light L1, R is the reflectance on the first surface 12a. In the case of scattered light L3, it is the reflectance on the second surface 13a. A is the loss of the emitted light L1 or the scattered light L3 by the optical element 10.

df is the frequency difference. The frequency difference df is the difference from the center frequency f ₀ of a certain frequency f (df = ff ₀ ). Therefore, the frequency interval of the plurality of peaks of the light transmitted through the optical element 10 is the interval of the frequency difference. n is the refractive index of the optical element 10. Specifically, n is the refractive index of the translucent portion 11 of the optical element 10. Δx is the length of the optical element 10. Specifically, Δx is the length of the translucent portion 11 of the optical element 10. θ is the incident angle of the emitted light L1 or the scattered light L3. φ is the angle of incidence inside the optical element 10, that is, the angle formed by the direction of travel in the translucent portion 11. Both θ and φ correspond to θ and φ shown in FIG. As described above, sinθ = nsinφ holds.

In the following, the frequency difference characteristics of T1 × T2 when the incident angles θ are set to 1 °, 1.1 °, 2 °, 5 ° and 21 ° will be described with reference to FIGS. 14A to 14E. In FIGS. 14A to 14E, the horizontal axis is indicated by a frequency difference which is a value obtained by removing the center frequency from the frequency.

14A to 14E are diagrams showing the frequency difference characteristics of T1 × T2 when the incident angles of the emitted light L1 are 1 °, 1.1 °, 2 °, 5 ° and 21 °, respectively. The horizontal axis represents the frequency difference df, and the vertical axis represents T1 × T2. T1 and T2 can be obtained by calculating each of the emitted light L1 and the scattered light L3 using the above formulas (4) to (6). The incident angle of the scattered light L3 is set to 0 °, but the same applies even if the incident angle of the scattered light L3 is larger than 0 °.

As shown in FIG. 14A, when the incident angle θ is 1 °, T1 × T2 is about 0.03 at the maximum. Therefore, since Mie scattered light L4 having sufficient intensity cannot be obtained, it is not suitable for detecting aerosols.

The intensity of the Mie scattered light L4 corresponds to the area of the graph shown in FIG. 14A, substantially the total value of the areas of each peak. Therefore, the larger the area of each peak, the more the Mie scattered light L4 having sufficient intensity can be received by the receiver 50, so that the state is suitable for aerosol detection.

As shown in FIG. 14B, when the incident angle θ is 1.1 °, there is a frequency difference df in which T1 × T2 satisfies 1. Therefore, since Mie scattered light L4 having sufficient intensity can be obtained, it is suitable for detecting aerosols.

Similarly, as shown in FIG. 14C, when the incident angle θ is 2 °, there is a frequency difference df in which T1 × T2 is about 0.5. Therefore, since Mie scattered light L4 having sufficient intensity can be obtained, it is suitable for detecting aerosols.

Further, as shown in FIG. 14D, when the incident angle is 5 °, T1 × T2 is about 0.03 at the maximum. Therefore, since Mie scattered light L4 having sufficient intensity cannot be obtained, it is not suitable for detecting aerosols.

Further, as shown in FIG. 14E, when the incident angle θ is 21 °, the value of T1 × T2 is small when the frequency difference is a negative number. On the other hand, when the frequency difference is about 0, the value of T1 × T2 exceeds 0.3. Further, when the frequency difference is a positive number, there is a frequency difference in which T1 × T2 exceeds 0.6 and 0.9, respectively. Therefore, since Mie scattered light L4 having sufficient intensity can be obtained, it is suitable for detecting aerosols.

As described above, by setting the incident angle θ in an appropriate range, it is possible to suppress the inclusion of noise in the Mie scattered light L4, and the Mie scattered light L4 is received by the receiver 50 with sufficient intensity. Can be made to. As a result, the aerosol detection accuracy can be improved.

(Embodiment 2)
Next, the second embodiment will be described.

In the first embodiment, the incident surface with respect to the optical element 10 is different between the emitted light L1 and the scattered light L3. On the other hand, in the present embodiment, the incident surfaces of the emitted light L1 and the scattered light L3 with respect to the optical element 10 are the same. In the following, the differences from the first embodiment will be mainly described, and the common points will be omitted or simplified.

FIG. 15 is a diagram showing the configuration of the aerosol measuring device 101 according to the present embodiment. As shown in FIG. 15, the aerosol measuring device 101 includes mirrors 32, 34 and 36 instead of the mirror 22 as compared with the aerosol measuring device 1 shown in FIG. Further, the arrangement of the light source 20, the condenser lens 40, the receiver 50, and the analysis unit 60 is different from that of the first embodiment.

As shown in FIG. 15, the mirrors 32 and 34 reflect the scattered light L3 condensed by the condenser lens 30a. By arranging the mirrors 32 and 34 at an appropriate angle with respect to the scattered light L3, the course of the scattered light L3 can be bent in a desired direction. In the present embodiment, the mirrors 32 and 34 reflect the scattered light L3 and cause it to enter the optical element 10.

As a result, both the emitted light L1 and the scattered light L3 are incident on the optical element 10 from the first surface 12a of the multilayer film 12. That is, the emitted light L1 and the scattered light L3 are incident on the first surface 12a of the optical element 10 and emitted from the second surface 13a on the opposite side of the first surface 12a. By making the incident surfaces of the emitted light L1 and the scattered light L3 the same, it is possible to easily separate the light paths in the optical element 10.

The mirror 36 reflects the Mie scattered light L4 that has passed through the optical element 10. By arranging the mirror 36 at an appropriate angle with respect to the Mie scattered light L4, the course of the Mie scattered light L4 can be bent in a desired direction. In the present embodiment, the Mie scattered light L4 is reflected and incident on the receiver 50 via the condenser lens 40.

As a result, as shown in FIG. 15, the light source 20 and the receiver 50 can be arranged apart from each other. Specifically, of the emitted light L1 emitted from the light source 20, the reflected light reflected by the optical element 10 can be prevented from being incident on the receiver 50. The reflected light causes false detection of aerosol. Further, since the reflected light has a higher intensity than the scattered light, the intensity exceeds the limit intensity that can be detected by the receiver 50 and may cause a failure of the receiver 50. Therefore, according to the present embodiment, it is possible to suppress erroneous detection of aerosol due to reflected light and failure of the receiver 50.

Further, in the present embodiment, the scattered light L3 reflected by the mirror 34 is incident on the optical element 10 along an oblique direction with respect to the first surface 12a of the optical element 10. The incident angle γ of the scattered light L3 is, for example, 5 ° or less. As a result, the optical path difference dx that causes Fabry-Perot interference when the scattered light L3 passes through the optical element 10 is represented by the following equation (7).

At this time, the amount of change Δdx from the case of γ = 0 is expressed by the equation (8).

By adjusting the amount of change Δdx of the optical path difference to be an integral multiple of the wavelength λ of the light emitted by the light source 20, it is possible to adjust to the bright point of interference due to the wavelength in the interference fringe.

Further, as shown in FIG. 16, the scattered light L3 is inclined in a direction away from the path through which the emitted light L1 passes, and is multiple-reflected in the optical element 10. FIG. 16 is a diagram for explaining a case where the scattered light L3 is incident on the optical element 10 along an oblique direction with respect to the first surface 12a of the optical element 10.

As shown in FIG. 16, the scattered light L3 is incident on the optical element 10 from an oblique direction with respect to the first surface 12a of the optical element 10. The scattered light L3 is multiplely reflected at the interface between the light transmitting portion 11 and each of the multilayer films 12 and 13. The multiplely reflected scattered light L3 is inclined in a direction away from the path of the emitted light L1 with respect to the normal direction D. Since the emitted light L1 and the scattered light L3 pass through the optical element 10 in a direction away from each other, the interference of the light with each other is sufficiently suppressed. Therefore, the noise component contained in the Mie scattered light L4 is sufficiently suppressed, so that the detection accuracy of the aerosol can be improved.

(Embodiment 3)
Subsequently, the third embodiment will be described.

In the third embodiment, the receiver 50 has a function of blocking light incident on the predetermined period. In the following, the differences from the first or second embodiment will be mainly described, and the common points will be omitted or simplified.

FIG. 17 is a diagram showing the configuration of the aerosol measuring device 201 according to the present embodiment. As shown in FIG. 17, the aerosol measuring device 201 is newly provided with a light-shielding portion 251 as compared with the aerosol measuring device 1 shown in FIG.

The light-shielding unit 251 blocks the emitted light L1 emitted by the light source 20. The light-shielding unit 251 is, for example, a movable light-shielding shutter. As shown by the white double-headed arrow in FIG. 17, the light-shielding portion 251 is movable between a position that covers the light-receiving surface of the receiver 50 and a position that does not cover it. The position shown by the broken line in FIG. 17 is the position that covers the light receiving surface, and the light shielding portion 251 covers the light receiving surface, so that the light incident on the light receiving device 50 can be blocked. Further, when the light-shielding portion 251 does not cover the light-receiving surface, light can be incident on the light-receiving receiver 50. The position of the light-shielding portion 251 is controlled by the receiver 50.

FIG. 18 is a diagram for explaining the operation of the light-shielding portion 251 of the aerosol measuring device 201 according to the present embodiment. In the part (a) of FIG. 18, the horizontal axis represents time and the vertical axis represents the intensity of the emitted light L1. In the part (b) of FIG. 18, the horizontal axis represents time and the vertical axis represents the light receiving intensity by the receiver 50.

As shown in the part (a) of FIG. 18, the light source 20 emits the pulse-shaped emitted light L1. The time width tp of the emitted light L1 is, for example, 10 nanoseconds. For example, the light source 20 periodically emits a pulsed emitted light L1 having a time width of tp. The emission interval of the emitted light L1, that is, the time interval of the pulse is not particularly limited, but is longer than, for example, the time required for the light to travel twice the maximum distance at which the aerosol can be detected.

When the emitted light L1 is incident on the optical element 10, as shown in FIG. 17, some light is reflected as reflected light L7 on the incident side without passing through the optical element 10. When the reflected light L7 at this time is received by the light receiver 50, a signal corresponding to the intensity of the reflected light L7 is output as shown in the portion (b) of FIG.

Since the distance between the optical element 10 and the light receiver 50 is sufficiently shorter than the distance between the scatterer 90 and the light receiver 50, the reflected light L7 by the optical element 10 is the Mie scattered light L4 after the emitted light L1 is emitted. Is received by the light receiver 50 within the period until the light is received.

Therefore, in the present embodiment, the receiver 50 controls the light-shielding unit 251 to block the light-receiving light until the end of the predetermined period tm after the emitted light L1 is emitted. The period tm is a period longer than the time width tp of the pulsed emitted light L1. For example, the period tm is 10.1 nanoseconds. The start time of the period tm is, for example, the same as the emission of the emitted light L1.

As described above, according to the aerosol measuring device 201 according to the present embodiment, it is possible to suppress erroneous detection of aerosol due to reflected light and failure due to saturation of the receiver 50.

In the present embodiment, an example of physically blocking the light incident on the receiver 50 has been described, but the present invention is not limited to this. For example, among the signals output from the receiver 50, the signal corresponding to the reflected light may be ignored by the analysis unit 60, that is, it may not be used for aerosol analysis. Alternatively, the receiver 50 does not have to output a signal during the period tm. That is, the aerosol measuring device 201 may block the light incident on the receiver 50 in a signal processing manner.

(Other embodiments)
Although the aerosol measuring device and the aerosol measuring method according to one or more embodiments have been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as the gist of the present disclosure is not deviated, various modifications that can be conceived by those skilled in the art are applied to the present embodiment, and a form constructed by combining components in different embodiments is also included in the scope of the present disclosure. Is done.

For example, the optical element does not have to be etalon. The optical element may be an element that causes Fabry-Perot interference, like Etalon.

Further, in the above embodiment, another processing unit may execute the processing executed by the specific processing unit. Further, the order of the plurality of processes may be changed, or the plurality of processes may be executed in parallel. Further, the distribution of the components of the aerosol measuring device to a plurality of devices is an example. For example, the components of one device may be included in another device. Further, the aerosol measuring device may be realized as a single device.

For example, the processing described in the above embodiment may be realized by centralized processing using a single device or system, or may be realized by distributed processing using a plurality of devices. .. Further, the number of processors that execute the above program may be singular or plural. That is, centralized processing may be performed, or distributed processing may be performed.

Further, in the above embodiment, all or a part of the components such as the analysis unit may be composed of dedicated hardware, or may be realized by executing a software program suitable for each component. May be good. Each component may be realized by a program execution unit such as a CPU (Central Processing Unit) or a processor reading and executing a software program recorded on a recording medium such as an HDD (Hard Disk Drive) or a semiconductor memory. Good.

Further, a component such as an analysis unit may be composed of one or a plurality of electronic circuits. The one or more electronic circuits may be general-purpose circuits or dedicated circuits, respectively.

One or more electronic circuits may include, for example, a semiconductor device, an IC (Integrated Circuit), an LSI (Large Scale Integration), or the like. The IC or LSI may be integrated on one chip or may be integrated on a plurality of chips. Here, it is called IC or LSI, but the name changes depending on the degree of integration, and it may be called system LSI, VLSI (Very Large Scale Integration), or ULSI (Ultra Large Scale Integration). An FPGA (Field Programmable Gate Array) programmed after the LSI is manufactured can also be used for the same purpose.

Further, the general or specific aspects of the present disclosure may be realized by a system, an apparatus, a method, an integrated circuit or a computer program. Alternatively, it may be realized by a computer-readable non-temporary recording medium such as an optical disk, HDD or semiconductor memory in which the computer program is stored. Further, it may be realized by any combination of a system, an apparatus, a method, an integrated circuit, a computer program and a recording medium.

Further, in each of the above embodiments, various changes, replacements, additions, omissions, etc. can be made within the scope of claims or the equivalent scope thereof.

The present disclosure can be used as a small aerosol measuring device or the like capable of easily measuring an aerosol, and can be used, for example, for measuring harmful fine particles indoors and observing weather outdoors.

1, 101, 201 Aerosol measuring device 10 Optical element 10a 1st part 10b 2nd part 11 Translucent part 12, 13 Multilayer film 12a 1st surface 13a 2nd surface 20 Light source 22, 32, 34, 36 Mirror 30 Condensing part 30a, 40 Condensing lens 50 Receiver 60 Analytical unit 90 Scatterer 251 Shading unit L1 Emitting light L2 Irradiating light L3 Scattered light L4 Mie scattered light L5 Stray light L6 Light L7 Reflected light

Claims (20)

1. An aerosol measuring device for measuring aerosols contained in the atmosphere.
   Light source and
   It has a first surface and a second surface, and includes a first light emitted from the light source and an etalon through which a second light scattered by the aerosol passes.
   The first light is incident on the first surface along a first direction oblique to the first surface.
   Aerosol measuring device.
2. The first light incident on the etalon is emitted from the second surface of the etalon.
   The second light is incident on the etalon from the second surface.
   The aerosol measuring device according to claim 1.
3. The second light is incident on the second surface along a second direction oblique to the second surface.
   The aerosol measuring device according to claim 2.
4. The second light is incident on the etalon from the first surface.
   The aerosol measuring device according to claim 1.
5. The second light is incident on the first surface along a third direction oblique to the first surface.
   The aerosol measuring device according to claim 4.
6. The etalon is
   The first part including the path through which the first light passes, and
   It includes a path through which the second light passes and has a second portion that is different from the first portion.
   The aerosol measuring device according to any one of claims 1 to 5.
7. The first direction is a direction away from the second portion.
   The aerosol measuring device according to claim 6.
8. The path of the first light in the first portion is inclined in a direction away from the second portion with respect to a direction orthogonal to the first surface.
   The first light is reflected a plurality of times in the etalon.
   The aerosol measuring device according to claim 6 or 7.
9. The path of the second light in the second portion is inclined in a direction away from the first portion with respect to a direction orthogonal to the first surface or the second surface.
   The second light is reflected multiple times within the etalon.
   The aerosol measuring device according to any one of claims 6 to 8.
10. In the first light, the direction in which the intensity of the first light becomes 10 to ³ times the maximum intensity coincides with the direction orthogonal to the first surface, or is orthogonal to the first surface. Tilt from the direction away from the second part,
    The aerosol measuring device according to any one of claims 6 to 9.
11. The etalon internally interferes with the first light and emits it as interference light having a plurality of peaks separated from each other at equal frequency intervals.
    The aerosol measuring device according to any one of claims 1 to 10.
12. The frequency interval is 3.9 GHz or less.
    The aerosol measuring device according to claim 11.
13. Each of the first light and the second light has a plurality of peaks separated from each other at equal frequency intervals.
    The difference between the frequency of each of the plurality of peaks and the center frequency, which is the average of the frequencies of the plurality of peaks, is defined as the frequency difference.
    Each of the first light and the second light has a frequency at which the product of the transmittance of the first light with respect to the etalon and the transmittance of the second light with respect to the etalon is 0.3 or more. Have a difference,
    The aerosol measuring device according to any one of claims 1 to 12.
14. Further, it includes a receiver that receives the second light that has passed through the etalon.
    The aerosol measuring device according to any one of claims 1 to 13.
15. The receiver outputs a signal corresponding to the intensity of Mie scattered light among the second light.
    The aerosol measuring device according to claim 14.
16. The first light is pulsed light.
    The receiver is
    After the pulsed light is emitted from the light source, the reception of the second light that has passed through the etalon is stopped until a predetermined period longer than the time width of the pulsed light ends.
    After the predetermined period ends, the second light that has passed through the etalon is received.
    The aerosol measuring device according to claim 14 or 15.
17. Further, it includes an analysis unit that analyzes the aerosol based on the signal output from the receiver.
    The aerosol measuring device according to any one of claims 14 to 16.
18. The light source is a laser element or a light emitting diode.
    The aerosol measuring device according to any one of claims 1 to 17.
19. Further, a condensing unit that condenses the second light and causes it to enter the etalon is provided.
    The aerosol measuring device according to any one of claims 1 to 18.
20. Irradiating the aerosol contained in the atmosphere with the first light emitted from the light source and passing through the etalon,
    Including that the second light scattered by the aerosol is incident on the etalon.
    The first light enters the etalon along an oblique direction with respect to the surface of the etalon.
    Aerosol measurement method.

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