Observation device

Abstract

Provided is an observation device with which it is possible to observe an object of interest between a distant object of interest and an observation device. An observation device (10) comprises: a transmission unit (20) that has a transmission light field of view (Ss) and transmits, to the transmission light field of view, pulsed light of a wavelength belonging to the solar-blind ultraviolet region; a reception unit (30) that has a reception light field of view (Sr) and receives reflected light within the reception light field of view, among reflected light due to reflection of the pulsed light by an object of interest; and an observation data generation unit. An optical axis (AXs) of the transmission unit and an optical axis (AXr) of the reception unit are parallel to each other. A transmission light field of view angle (θs) that defines the transmission light field of view is greater than a reception light field of view angle (θr) that defines the reception light field of view. The transmission light field of view and the reception light field of view overlap at least partially. The observation data generation unit generates LIDAR data, which is observation data, on the basis of a signal output by a light reception element.

Description

Observation equipment

[0001] The present disclosure relates to an observation device, and more particularly to an observation device that can observe an observation target near the earth's surface and at a short distance from the observation device.

[0002] Patent Document 1 describes an observation device that performs lidar observation based on observation light from a laser beam emitted toward an object to be observed.

[0003] International Publication No. 2003 / 073127

[0004] However, in Patent Document 1, because observation is performed using laser light, it is possible to observe objects that are located relatively far away (for example, several kilometers away), but there is a problem in that it is not possible to observe objects that are located between the distant object and the observation device, such as objects that are near the earth's surface and close to the observation device.

[0005] The present disclosure has been made to solve such problems, and aims to provide an observation device that can observe an object near the Earth's surface and at a short distance from the observation device.

[0006] The observation device according to the present disclosure comprises a transmitter having a transmission light field of view and transmitting pulsed light of a wavelength belonging to the ultraviolet region of the solar blind band within the transmission light field of view, a receiver having a reception light field of view and receiving reflected light of the pulsed light reflected by an observation object within the reception light field of view, and an observation data generator, wherein the transmitter comprises a semiconductor light-emitting element that emits the pulsed light, and a transmission optical system that controls the pulsed light emitted by the semiconductor light-emitting element so that the pulsed light emitted by the semiconductor light-emitting element is transmitted within the transmission light field of view, The receiving unit includes a receiving optical system that collects reflected light within the received light field of view, and a light receiving element that receives the collected reflected light and outputs a signal corresponding to the received reflected light, wherein the optical axis of the transmitting unit and the optical axis of the receiving unit are parallel to each other, the transmitted light field of view angle that defines the transmitted light field of view is larger than the received light field of view angle that defines the received light field of view, and the transmitted light field of view and the received light field of view at least partially overlap each other, and the observation data generating unit generates LIDAR data, which is observation data, based on the signal output by the light receiving element.

[0007] With this configuration, it is possible to observe objects near the earth's surface and at a short distance from the observation device.

[0008] This is because the angle is larger than the receiving light field angle that defines the receiving light field, and the transmitting light field and the receiving light field at least partially overlap each other.

[0009] In the above observation device, the transmitted light field of view may be a cone-shaped region centered on the optical axis of the transmitting unit and having a diameter that increases with increasing distance from the transmitting unit along the optical axis of the transmitting unit, and the received light field of view may be a cone-shaped region centered on the optical axis of the receiving unit and having a diameter that increases with increasing distance from the receiving unit along the optical axis of the receiving unit.

[0010] In the observation device, the wavelength in the ultraviolet range may be selected from a wavelength range of 240 nm to 300 nm.

[0011] In the observation device, the pulsed light may be incoherent light.

[0012] In the observation device, the frequency of the pulsed light may be 1 to 10 MHz.

[0013] In the observation device, the pulsed light may have a pulse width of 1 to 10 ns.

[0014] In the observation device, the signal output from the light receiving element may be a pulsed electrical signal corresponding to a photon.

[0015] In the observation device, the receiving optical system may be an off-axis parabolic mirror and a folding mirror.

[0016] In the above observation device, the off-axis parabolic mirror and the folding mirror may each have a dielectric multilayer film on a mirror surface that reflects the reflected light.

[0017] In the above observation device, the off-axis parabolic mirror and the folding mirror may have an anti-reflection member that absorbs light other than the reflected light, either below the dielectric multilayer film or on the back surface of each mirror.

[0018] The present disclosure makes it possible to provide an observation device that can observe an object near the earth's surface and at a short distance from the observation device.

[0019] 5 is a schematic diagram of the observation device 10. FIG. 6 is a longitudinal cross-sectional view (schematic diagram) of the observation device 10 shown in FIG. 1. FIG. 7 is a graph showing the change pattern of the field of view combination ratio Crs when the transmitted light field of view angle θs = 10 mrad and the received light field of view angle θr = 3 mrad. FIG. 8 is an enlarged view of the portion of FIG. 3 at distances of 0 to 30 m. FIG. 9 is a graph showing the change pattern of the field of view combination ratio Crs when the transmitted light field of view angle = 10 mrad and the received light field of view angle θr = 5 mrad. FIG. 10 is an enlarged view of the portion of FIG. 5 at distances of 0 to 30 m. FIG. 11 is a conceptual diagram of the observation data (lidar data) generation process. FIG. 12 is a schematic diagram of the observation device 10A. FIG. 13 is a graph showing the emission spectrum of the deep-ultraviolet LED 21. FIG. 14 is a diagram showing how light PL1 and PL2 (pulsed light) emitted from the deep-ultraviolet LED 21 (light-emitting surface) are also transmitted in a direction inclined with respect to the optical axis AXs of the transmitter 20. FIG. 15 is an example of a drive circuit 24. FIG. 16 is an example of the transmission characteristics of pulsed light. FIG. 17 is an example of the transmission characteristics of pulsed light. 9 is a graph showing the relationship between supply voltage (V) and frequency (MHz). FIG. 10 is a schematic diagram of the receiving unit 30 extracted from FIG. 8. FIG. 11 is a schematic configuration diagram of the observation device 10B. FIG. 12 is a cross-sectional view of the first receiving mirror 37. FIG. 13 is a cross-sectional view of the second receiving mirror 38. FIG. 14 shows the reflection spectrum of light reflected by each receiving mirror.

[0020] Hereinafter, an observation device 10 according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Corresponding components in each drawing are designated by the same reference numerals, and duplicated explanations will be omitted.

[0021] <Outline of Observation Device 10> First, an outline of the observation device 10 of this embodiment will be described.

[0022] FIG. 1 is a schematic diagram of an observation device 10.

[0023] The observation device 10 of this embodiment is a device (LiDAR device) that remotely and non-contactly observes an observation object Ob (e.g., airborne particles such as aerosols and dust) located at a short distance (e.g., 10 to 150 m).

[0024] As shown in FIG. 1, the observation device 10 includes a transmitting unit 20, a receiving unit 30, and a control and analysis unit 40.

[0025] FIG. 2 is a longitudinal cross-sectional view (schematic diagram) of the observation device 10 shown in FIG.

[0026] As shown in Fig. 2, the transmitter 20 has a transmission light field of view Ss and transmits pulsed light (hereinafter also referred to as transmitted light) having a wavelength (e.g., 265 nm) belonging to the ultraviolet region of the solar blind band within the transmission light field of view Ss. Meanwhile, the receiver 30 has a reception light field of view Sr and receives reflected light (reflected pulsed light) of the transmitted light (pulsed light) that is reflected by an observation target Ob and returns to the reception light field of view Sr, and outputs a pulsed electrical signal (electrical signal of a pulse wave) corresponding to the received reflected light. The pulsed light may be spontaneous emission light (incoherent light).

[0027] The optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver 30 are arranged parallel to each other and spaced apart from each other. The distance L1 between the optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver 30 is, for example, 85 mm.

[0028] The transmitted light field Ss is a cone-shaped region whose center is on the optical axis AXs of the transmitter 20 and whose diameter increases with increasing distance from the transmitter 20 along the optical axis AXs of the transmitter 20. The minimum diameter of the transmitted light field Ss (the diameter at the left end in FIG. 2 ) is, for example, 60 mm. The transmitted light field angle θs defining the transmitted light field Ss is, for example, 10 mrad (0.57°).

[0029] On the other hand, the receiving light field Sr is a cone-shaped region whose center is on the optical axis AXr of the receiving unit 30 and whose diameter increases with increasing distance from the receiving unit 30 along the optical axis AXr of the receiving unit 30. The minimum diameter of the receiving light field Sr (the diameter at the left end in FIG. 2 ) is, for example, 100 mm. The receiving light field angle θr that defines the receiving light field Sr is, for example, 3 mrad (0.17°) or 5 mrad (0.29°).

[0030] As described above, the transmitted light viewing angle θs is set to be larger than the received light viewing angle θr.

[0031] Next, the overlapping (superimposition) of the transmission light field Ss and the reception light field Sr will be described.

[0032] As described above, the optical axis AXs of the transmitting unit 20 and the optical axis AXr of the receiving unit 30 are arranged spaced apart from each other and parallel to each other, the transmitted light field of view Ss and the received light field of view Sr are each conical areas, and the transmitted light field of view θs is set larger than the received light field of view θr.

[0033] As a result, the transmitting light field Ss and the receiving light field Sr overlap each other to form a superimposed light field Sc, as shown in Fig. 2 (see the hatched area HT in Fig. 2 and the superimposed light field Sc in each cross-sectional view). Next, the superimposed light field Sc, which is the overlap of the transmitting light field Ss and the receiving light field Sr, will be described in detail.

[0034] The ratio of the superimposed light field Sc to the transmitted light field Ss can be expressed as a field combination ratio Crs, which is calculated by the following formula 1.

[0035] Field combination ratio Crs = overlapping light field of view Sc / transmitting light field of view Ss (Equation 1) where the overlapping light field of view Sc is the area of ​​the region where the transmitting light field of view Ss and the receiving light field of view Sr overlap in each cross section (see each cross section in Figure 2), and the transmitting light field of view Ss is the area of ​​the transmitting light field of view Ss in each cross section.

[0036] A large field of view combination ratio Crs indicates that there is a large amount of reflected light (reflected pulse light) that is reflected by the observation object Ob and returns to the field of view Sr of the received light.

[0037] As shown in FIG. 2, at a first position P1, which is a first distance r1 away from the lens barrel tip position P0, the outer edge of the transmitted light field Ss circumscribes the outer edge of the received light field Sr (see the B-B cross section in FIG. 2). At a second position P2, which is a second distance r2 away from the lens barrel tip position P0, the outer edge of the transmitted light field Ss tangent to the optical axis AXr of the receiver 30 (see the C-C cross section in FIG. 2). At a third position P3, which is a third distance r3 away from the lens barrel tip position P0, the outer edge of the received light field Sr is inscribed in the outer edge of the transmitted light field Ss (see the D-D cross section in FIG. 2). At positions further away from the third position P3, the outer edge of the received light field Sr is included in the outer edge of the transmitted light field Ss without tangent to it (see the E-E cross section in FIG. 2).

[0038] Next, the change pattern of the visual field coupling ratio Crs will be described.

[0039] First, a change pattern of the visual field coupling ratio Crs when the transmitted light viewing angle θs=10 mrad and the received light viewing angle θr=3 mrad will be described.

[0040] 3 is a graph showing the pattern of change in the visual field coupling ratio Crs when the transmitted light visual field angle θs=10 mrad and the received light visual field angle θr=3 mrad. FIG. 4 is an enlarged view of the portion of FIG. 3 covering a distance of 0 to 30 m.

[0041] As shown in FIG. 4 , when the transmitted light field angle θs is 10 mrad and the received light field angle θr is 3 mrad, the first position P1 is a position that is a first distance r1 (0.44 m) away from the transmitter 20 (the lens barrel tip position P0) along the optical axis AXs of the transmitter 20. The second position P2 is a position that is a second distance r2 (5.5 m) away from the transmitter 20 (the lens barrel tip position P0) along the optical axis AXs of the transmitter 20. The third position P3 is a position that is a third distance r3 (15 m) away from the transmitter 20 (the lens barrel tip position P0) along the optical axis AXs of the transmitter 20. The fourth position P4 is a position where the field of view combination ratio Crs is maximum, and is a position that is 11 m away from the transmitter 20 (the lens barrel tip position P0) along the optical axis AXs of the transmitter 20.

[0042] The distance region from the lens barrel tip position P0 to the first position P1 is a distance region where the outer periphery of the transmitted light field Ss and the outer periphery of the received light field Sr are separated. Therefore, the superimposed light field Sc is not formed, and the field combination ratio Crs is zero. Next, the distance region from the first position P1 to the second position P2 is a distance region from where the outer periphery of the transmitted light field Ss contacts the outer periphery of the received light field Sr to the optical axis AXr of the received light field Sr. During this period, the field combination ratio Crs increases sharply as the superimposed light field Sc expands. Next, the distance region from the second position P2 to the third position P3 is a distance region where the outer periphery of the transmitted light field Ss crosses the optical axis AXr of the received light field Sr and reaches the far-side outer periphery of the received light field Sr. During this period, the superimposed light field Sc expands while the transmitted light field Ss also expands, so the field combination ratio Crs gradually increases, reaches a maximum value, and then decreases. Finally, in the distance region beyond the third position P3, the transmitted light field Ss encompasses the received light field Sr. During this distance, the superimposed light field Sc and the received light field Sr are equal, but since the magnification ratio of the transmitted light field Ss is large, the field combination ratio Crs gradually decreases.

[0043] Next, a change pattern of the visual field coupling ratio Crs when the transmitted light visual field angle is 10 mrad and the received light visual field angle θr is 5 mrad will be described.

[0044] 5 is a graph showing the pattern of change in the visual field coupling ratio Crs when the transmitted light visual field angle is 10 mrad and the received light visual field angle θr is 5 mrad. FIG. 6 is an enlarged view of the portion of FIG. 5 covering a distance of 0 to 30 m.

[0045] As shown in FIG. 6 , when the transmitted light field angle θs is 10 mrad and the received light field angle θr is 5 mrad, the first position P1 is a position that is a first distance r1 (0.38 m) away from the transmitter 20 (the tip position P0 of the lens barrel) along the optical axis AXs of the transmitter 20. The second position P2 is a position that is a second distance r2 (5.5 m) away from the transmitter 20 (the tip position P0 of the lens barrel) along the optical axis AXs of the transmitter 20. The third position P3 is a position that is a third distance r3 (21 m) away from the transmitter 20 (the tip position P0 of the lens barrel) along the optical axis AXs of the transmitter 20. The fourth position P4 is a position where the field of view combination ratio Crs is maximum, and is a position that is 16 m away from the transmitter 20 (the tip position P0 of the lens barrel) along the optical axis AXs of the transmitter 20.

[0046] The change in the field of view combination ratio Crs in each distance region from the lens barrel tip position P0 to the first position P1, from the first position P1 to the second position P2, from the second position P2 to the third position P3, and beyond the third position P3 is the same as when the received light field of view angle θr is 3 mrad. However, because the received light field of view angle θr of the received light field Sr is large at 5 mrad, the field of view combination ratio Crs at the same observation distance becomes larger.

[0047] As described above, observation is possible from a distance beyond the first position P1 (circumscribed overlap distance) where the superimposed light field Sc is formed. Furthermore, observation is preferably performed from a distance beyond the second position P2 (centerline tangent overlap distance) where the superimposed light field Sc is approximately half or more of the received light field Sr. Furthermore, considering the loss of the superimposed light field Sc and the field combination ratio Crs, observation is preferably performed from a distance beyond the third position P3 (inscribed overlap distance) where the superimposed light field Sc coincides with the received light field Sr. Since the transmitter 20 and receiver 30 are separated in the observation device 10, there is no influence of light blocking by the transmitter 20 in distance regions beyond the first position P1. Furthermore, since the observation device 10 has the optical axis AXs of the transmitted light field Ss and the optical axis AXr of the received light field Sr arranged parallel to each other at a distance from each other, the superimposed light field Sc is not lost in distance regions beyond the third position P3.

[0048] Here, the distance r2 from the lens barrel tip position P0 to the second position P2 depends only on the transmitted light field angle θs, regardless of the received light field angle θr. In this case, the distance r1 from the lens barrel tip position P0 to the first position P1 can be shortened by increasing the received light field angle θr, and the distance r3 from the lens barrel tip position P0 to the third position P3 can be shortened by decreasing the received light field angle θr.

[0049] Hereinafter, the section between the lens barrel tip position P0 and the first position P1 will be referred to as section 1. The section between the first position P1 and the second position P2 will be referred to as section 2. The section between the second position P2 and the third position P3 will be referred to as section 3. The geometric correction factors that affect the received light in these three sections are included in the geometric efficiency factor Y(R) of the LIDAR equation.

[0050] The lidar equation is generally expressed as:

[0051] where R is the distance, P is the received light intensity, Po is the transmitted light output, Y is the geometric efficiency factor, C is the device constant, β is the backscattering coefficient, and α is the extinction coefficient (absorption + diffusion). Furthermore, P(R), Y(R), β(R), and α(R) represent the respective intensities, factors, and coefficients at distance R. Furthermore, r is the distance traveled to distance R. Each coefficient depends on the substance (particles suspended in the air) that constitutes the observed object Ob. Furthermore, in describing the three sections, it is assumed that the observed object Ob is uniformly distributed throughout the entire space in the depth direction from the telescope tube tip position P0 to the observation limit distance (maximum observation distance, described below), and in the planar direction of the transmitted light field of view Ss and the received light field of view Sr. In other words, the three sections are the internal space of the observed object Ob.

[0052] In the first section, the transmitted light field of view Ss and the received light field of view Sr do not overlap with each other. Therefore, in the first section, there is almost no reflected light (reflected pulse light) that is reflected by the observed object Ob and returns to the received light field of view Sr. In other words, the first section is an observation blind section.

[0053] In the second section, the field of view combination ratio Crs increases or decreases, and so does the reflected light (reflected pulse light) reflected by the observed object Ob and returning to the received light field of view Sr. Specifically, the change in the field of view combination ratio Crs is due to a correlation between an increase in the overlap ratio of the transmitted light field of view Ss with the received light field of view Sr and a relative decrease in the overlapped light field of view Sc according to the magnification ratio (field of view angles θs, θr) of the transmitted light field of view Ss and the received light field of view Sr. Therefore, the reflected light (reflected pulse light) in the second section increases as the distance R increases, reaches a maximum value, and then decreases. In other words, the second section is an observation transition section.

[0054] In the third section, the field of view combination ratio Crs decreases according to the magnification ratio (field of view angles θs, θr) of the transmitted light field of view Ss and the received light field of view Sr, so the amount of reflected light (reflected pulse light) that is reflected by the observed object Ob and returns to the received light field of view Sr also decreases. In other words, the third section is a stable observation section.

[0055] By overlapping the transmission light field of view Ss and the reception light field of view Sr as described above, it is possible to receive reflected light (reflected pulse light) that is reflected by the observation object Ob and returns to the reception light field of view Sr. In other words, the received light intensity P(R) in the second and third sections where the reflected light (reflected pulse light) is obtained is corrected by the geometric efficiency factor Y(R) in Equation 1 based on the field of view combination ratio Crs. Therefore, close-range measurement can be performed without being affected by changes in the overlapping light field of view Sc. This allows the observation object Ob located at a close distance (farther than the first position P1). In other words, it is possible to accurately generate observation data (lidar data) of the observation object Ob located at a close distance (farther than the first position P1).

[0056] In particular, the transmitted light field angle θs is set larger than the received light field angle θr (see FIG. 2). This shortens the distance (first section) from the lens barrel tip position P0 to the first position P1, and also shortens the distance (second section) from the second position P2 to the third position P3. This also lengthens the section distance from the third position P3 (third section) to the maximum observation distance (the distance defined by the pulse interval of the transmitted light). Furthermore, in the observable second and third sections, if the received light field angle θr is large, the field combination ratio Crs can be increased, thereby increasing the received light intensity P(R).

[0057] On the other hand, if the viewing angle θr of the received light is small, the resolution in the plane perpendicular to the optical axis is improved, and if the viewing angle θr of the received light is large, the resolution in the plane perpendicular to the optical axis is reduced. Also, if the viewing angle θr of the received light is small, the third distance r3 (see FIG. 2) is short, and if the viewing angle θr of the received light is large, the third distance r3 is long.

[0058] From the above, when observing a short distance with high resolution, it is preferable that the viewing angle θr of the received light is small (for example, 3 mrad), whereas when observing the received light intensity P(R) from a long distance, it is preferable that the viewing angle θr of the received light is large (for example, 5 mrad).

[0059] Furthermore, if the observation object Ob is a non-shading object such as aerosol, dust, fog, rainfall, or snowfall that is screen-shaped (thin in the distance direction), other observation objects located in front of or behind the observation object Ob can also be observed in the second and third sections.

[0060] Because the received light field of view Sr is included in the transmitted light field of view Ss beyond the third position P3 (third section), it is possible to observe (measure) multiple observation targets Ob that are partially present within the received light field of view Sr. If the transmitted light is a linear beam (e.g., laser light), LIDAR data cannot be obtained for observation targets Ob other than those at the position where the transmitted light is transmitted.

[0061] Next, the observation data (lidar data) generation process will be described.

[0062] FIG. 7 is a conceptual diagram of the observation data (lidar data) generation process.

[0063] The observation data (lidar data) generation process is executed by the control and analysis unit 40. The control and analysis unit 40 can be a dedicated device that houses the equipment described below that generates and processes the observation data for the observation device 10, or it can be a composite device that includes other observation equipment such as an observation camera.

[0064] As shown in FIG. 1, the control analysis unit 40 includes an observation data generation unit 41, a coefficient analysis processing unit 42, a characteristic evaluation processing unit 43, and an observation data storage unit 44.

[0065] The observation data generation unit 41 divides the pulse electrical signal output by the receiving unit 30 in response to reflected light (reflected light (reflected pulse light; specifically, photons) that is reflected by the observation target Ob and returns to the received light field of view Sr) for each reception cycle using a photon counting circuit (a circuit that performs photon counting), and accumulates this N times to generate observation data (lidar data). The bottom graph in Figure 7 is an example of observation data (lidar data). This generated observation data (lidar data) is stored (accumulated) in the observation data storage unit 44.

[0066] In Fig. 7, the first received electrical signal to the Nth received electrical signal represent pulse electrical signals divided for each reception cycle. In Fig. 7, each pulse shown in the graph to the right of the first received electrical signal represents a pulse electrical signal output in response to reflected light (reflected light (reflected pulsed light; specifically, photons) reflected by the observation object Ob and returning to the received light field of view Sr) received by the receiving unit 30 during the reception cycle when the first pulsed light (transmitted light) is transmitted. The same applies to each pulse shown in the graph to the right of the Nth received electrical signal.

[0067] The time of flight (t) of the first received electrical signal represents the time of flight (round-trip flight time) of a photon corresponding to each pulse to the object of observation Ob. The time of flight (t) is omitted from the graph of the Nth received electrical signal.

[0068] The present invention is not limited to a photon counting circuit, and any device that can perform photon counting may be used. For example, a digital oscilloscope and a PC (information processing device such as a personal computer) may be combined.

[0069] The coefficient analysis processing unit 42 calculates the spatial distribution (distance direction) of the observed object Ob from the increase or decrease in the observation data (lidar data), and also performs processing to evaluate the observation data (lidar data) using the lidar equation to calculate the extinction coefficient α and backscattering coefficient β specific to the observed object Ob.

[0070] For example, if the observation object Ob is in a uniform atmosphere in the space from the telescope tip position P0 to the maximum observation distance (Rmax), the received light intensity P(R) will increase in accordance with the distance (R) and the geometric efficiency factor Y(R), and will attenuate after reaching a maximum value. Also, if the observation object Ob is spatially uniform, the extinction coefficient α(R) and backscattering coefficient β(R) do not change with distance, so they can be expressed as α and β. Therefore, the lidar equation is Ln((P(R)R 2 ) / Y(R))=-2αR + ln(P0Cβ), so the extinction coefficient α can be found from the slope term -2αR, and the backscattering coefficient β can be found from the intercept term ln(P0Cβ).

[0071] The characteristic evaluation processing unit 43 performs, for example, fixed-point atmospheric evaluation, evaluation of smoke, dust, and the like.

[0072] For example, atmospheric assessment at fixed points can be performed annually using the backscattering coefficient β and extinction coefficient α of aerosols and other particles contained in the observed atmosphere. Furthermore, by comparing the observed values ​​with those from a base year, changes in atmospheric conditions can be assessed. In this case, comparison with a disclosed standard atmosphere can also be used to estimate the types of particles floating in space (e.g., see Laser Radar Society of Japan, 4 (2020), Kuze, Light Scattering Measurement of Aerosols and Atmospheric Molecules). Fog, rain, and snow can also be assessed in the same way as fixed-point atmospheric assessment.

[0073] Smoke and dust, for example, the cleanliness of equipment exhaust, exhaust smoke from chimneys, dust on the road, etc., can be evaluated by comparing the characteristics of the air outside the exhaust section with the characteristics of the air at the exhaust section.

[0074] The observation data storage unit 44 is a non-volatile storage unit such as a hard disk drive or SSD that stores the observation data (lidar data) generated by the observation data generation unit 41.

[0075] The control analysis unit 40 (observation data generation unit 41) has a function (using the well-known dToF (direct Time of Flight) method, photon counting, etc.) to measure (calculate) the flight time of the reflected light (photons) received by the receiving unit 30 to the observation object Ob, and is therefore able to measure (calculate) the flight time (round-trip flight time) of the photons corresponding to each pulse to the observation object Ob.

[0076] Observation data (lidar data) is generated by integrating the first to Nth received electrical signals (integration N times). In the graph at the bottom of Figure 7, the vertical axis represents the received light intensity, which corresponds to the number of photons. The horizontal axis represents the distance, which is calculated by converting the time of flight (t) into distance.

[0077] Next, we will explain the improvement of short-distance observation capability, miniaturization, and observation convenience using the observation device 10. Note that the short distance mentioned here refers to a distance of about several meters to several hundred meters.

[0078] (Short-Distance Observability) The observation device 10 can increase the transmission frequency of the transmitted light (pulsed light) transmitted from the transmitter 20 from 1 megahertz (MHz) to approximately 10 MHz. For example, if the observation target Ob is locally located at a distance of approximately 50 m to 100 m, the maximum observation distance (Rmax) can be set to 150 m. The maximum observation distance is the distance determined by the transmission period of the transmitted light (pulsed light). For example, if the transmission period of the transmitted light (pulsed light) is 1 microsecond (μsec), the flight distance of the transmitted light is 300 m. In other words, the maximum observation distance (Rmax) is 150 m, the distance at which the previously transmitted light does not interfere with the next transmitted light. The transmission frequency at this time is 1 MHz. Similarly, if the maximum observation distance (Rmax) is 15 m, the transmission period of the transmitted light (pulsed light) is 0.1 μsec, and the transmission frequency is 10 MHz.

[0079] Lidar data is generated by integrating each pulse of one unit period incident on the receiver 30 multiple times. Therefore, increasing the transmission frequency of the transmitted light (pulsed light) enables Lidar data to be generated in a short time. In particular, the apparent movement speed (movement angle per unit time) of a short-distance observation object Ob is large, making short-time observations essential for improving spatial resolution. For example, if the distance to the observation object Ob is 100 m and the Lidar data is integrated 1,000 times, a transmission frequency of 1 MHz (transmission period of 1 μsec) will result in a single observation time of 1 millisecond (msec). In this case, if the observation object Ob is moving at a wind speed of 3 msec (similar to a gentle breeze), it will move 3 millimeters (mm) from the start to the end of observation. In other words, the movement angle is 0.0017°. Therefore, the received light field of view angle ratio (movement angle / received light field of view angle θr) is 0.01 (1%) if the received light field of view angle θr is 3 mrad (0.17°), and 0.006 (0.6%) if it is 5 mrad (0.29°). Furthermore, when the distance to the observation target Ob is 50 m, the movement angle is 0.0034°. Therefore, the received light field of view angle ratio is 0.02 (2%) if the received light field of view angle θr is 3 mrad, and 0.012 (1.2%) if it is 5 mrad. In this way, by increasing the transmission frequency, accurate observation becomes possible even when the observation target Ob is moving at a close distance.

[0080] Furthermore, the observation device 10 narrows the pulse width of the transmitted light (pulsed light) sent from the transmitter 20 to about 1 nanosecond (nsec). For example, a pulse width of 10 nsec provides a distance resolution of 1.5 m, while a pulse width of 1 nsec provides a distance resolution of 0.15 m. By narrowing the transmitted light in this way, it becomes possible to observe the observation target Ob with high accuracy in close-range measurements.

[0081] The observation device 10 transmits light (pulsed light) from the transmitter 20 at a solar-blind wavelength in the deep-ultraviolet light band, which is free from atmospheric absorption (absorption by oxygen and nitrogen). Here, the solar-blind wavelength in the deep-ultraviolet light band refers to a deep-ultraviolet wavelength band of sunlight that reaches the Earth and is significantly attenuated before reaching the Earth's surface. Specifically, the solar-blind wavelength refers to a wavelength longer than the wavelength near the long-wavelength absorption edge of oxygen and nitrogen, and shorter than the long-wavelength absorption edge of the ozone layer. Specifically, the wavelength is between 230 nanometers (nm) and 300 nm, preferably between 250 nm and 280 nm. By using such a wavelength band, observations are not affected by external light or atmospheric absorption, enabling observations with a low-power light source.

[0082] Furthermore, by setting the wavelength of the transmitted light (pulsed light) to a solar-blind wavelength in the deep ultraviolet light band, where atmospheric absorption is not present, the backscattering coefficient β and extinction coefficient α of the particles contained in the observation object Ob become larger than those for near-ultraviolet to infrared light. This enables observation even when the observation object Ob is thin in the distance direction or contains low concentrations of particles. Specifically, the extinction coefficient α increases inversely proportional to the wavelength to the 1.25th power, and shortening the wavelength from 900 nm to 265 nm increases it by approximately five times. The backscattering coefficient β is roughly proportional to the extinction coefficient α, so it also increases by approximately five times. In other words, highly sensitive observation is possible even at close distances (where the observation object Ob travels a short distance). It also makes it easier to identify the characteristics of the observation object Ob (e.g., aerosols, smoke, dust, fog, rain, and snow).

[0083] (Miniaturization) The observation device 10 uses a deep ultraviolet LED (Light Emission Diode), which is a semiconductor light emitting element that emits deep ultraviolet light (for example, a wavelength of 265 nm). ２ The size is about the same as the transmitter 20. Furthermore, the deep-ultraviolet LED allows the oscillator circuit that emits high-frequency, narrow-pulse-width light to be miniaturized. Furthermore, a collimated transmission system with high luminous flux utilization can be configured using a small lens with a small aperture (diameter of about 60 mm). Therefore, the transmitter 20 can be miniaturized.

[0084] The observation device 10 uses a photon-counting-compatible ultraviolet photomultiplier tube (PMT) as the light-receiving element. This allows the PMT to be compact. Furthermore, because the light transmitted by the transmitter 20 is in the solar-blind wavelength range of the deep ultraviolet light band, which is not subject to atmospheric absorption, the primary collector of the receiver 30 can be a small lens or reflector (diameter φ100 mm or so). This allows the receiver 30 to be compact.

[0085] (Convenience of Observation) The observation device 10 uses a semiconductor light-emitting element (e.g., an LED with a wavelength of 265 nm) that emits ultraviolet light in the solar blind band that is not absorbed by the atmosphere as the light source of the transmitter 20, making it possible to observe both day and night. For example, observation is possible during the day under clear skies, and at night under illumination such as fluorescent lamps or halogen lamps. This makes it possible to observe at regular intervals throughout the day and night. Furthermore, since illumination can be projected onto the observation target Ob even at night, aiming at the observation target Ob becomes easier.

[0086] <Configuration Example 1 of Observation Apparatus 10> Next, a specific configuration example 1 of the observation apparatus 10 will be described. Hereinafter, the observation apparatus 10 of configuration example 1 will be referred to as observation apparatus 10A.

[0087] FIG. 8 is a schematic diagram of the observation device 10A.

[0088] The observation device 10A is an observation device (LiDAR device) equipped with a transmitter 20 and a receiver 30 of a refractive optical system.

[0089] As shown in Fig. 8, the observation device 10A includes a transmitter 20, a receiver 30, and a control and analysis unit 40 (omitted from Fig. 8). The optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver 30 are arranged parallel to and spaced apart from each other.

[0090] <Transmitter 20> The transmitter 20 includes a semiconductor light-emitting element 21 and a transmitter lens 22 (an example of the transmission optical system of the present disclosure). In Fig. 8, reference numeral 23 denotes a transmitter lens barrel, and reference numeral 24 denotes a drive circuit for the semiconductor light-emitting element 21.

[0091] The semiconductor light-emitting element 21 is a semiconductor light-emitting element having an excellent response speed (for example, capable of emitting high-frequency, short-pulse light) and emitting light (pulse light) with a wavelength belonging to the ultraviolet region of the solar blind band, such as a deep-ultraviolet LED. Hereinafter, this will also be referred to as a deep-ultraviolet LED 21.

[0092] Hereinafter, an example will be described in which a deep-ultraviolet LED having a peak wavelength (center wavelength) of 265 nm and a Lambertian light distribution (distribution) with a half-value angle of approximately 120° is used as the semiconductor light-emitting element 21. Hereinafter, this will also be referred to as a deep-ultraviolet LED 21.

[0093] The specifications of the deep ultraviolet LED 21 are as shown in the following table.

[0094] The spectrum of the deep-ultraviolet LED used, which has no atmospheric absorption, has a peak wavelength (λp) of 265 nm and a full width at half maximum (FWHM) of 12 nm. The directivity is Lambertian with a half-maximum angle of 120°. The optical output is 50 mW at an input power of 3 W under continuous output (cw) conditions, and 1 mW to 500 mW at pulse output. The response is 1 ns or more.

[0095] The deep-ultraviolet LED 21 used in the transmitter 20 of the observation device 10A is sealed in a CAN package. The CAN package is mounted on a heat sink provided in the drive circuit 24. The portion of the CAN package other than the light exit port is covered with a partition plate made of a material that absorbs stray light emitted from the deep-ultraviolet LED. In addition to the CAN package, the deep-ultraviolet LED may be mounted on a ceramic substrate such as aluminum oxide, silicon nitride, or aluminum nitride that has high thermal conductivity (e.g., 30 to 200 W / m·K) and absorbs stray light. Alternatively, the deep-ultraviolet LED may be mounted on a ceramic-inlay-type glass-epoxy substrate with ceramic embedded in the portion where the deep-ultraviolet LED is mounted. It is preferable to provide a heat sink on the back side (the side opposite the side on which the deep-ultraviolet LED is mounted) of the ceramic substrate or ceramic-inlay-type glass-epoxy substrate.

[0096] The deep-ultraviolet LED 21 has a light-emitting surface of 1.04 mm square. The light (pulsed light) emitted by the deep-ultraviolet LED is incoherent light or incoherence light (random phase, wide half-width, divergent light). The light (pulsed light) emitted by the deep-ultraviolet LED 21 is isotropic light (light without polarization).

[0097] The transmitting lens 22 is, for example, a condenser lens that is rotationally symmetric with respect to the optical axis AXs of the transmitter 20. The transmitting lens 22 is made of quartz glass that transmits the light emitted from the deep-ultraviolet LED 21. The transmitting lens 22 may also be made of borosilicate glass, silicate glass, amorphous fluororesin, or the like that transmits deep-ultraviolet light.

[0098] The specifications of the transmitting lens 22 are as shown in the following table.

[0099] When the acceptance angle θi (see FIG. 10) of the transmitting lens 22 is 30° and the diameter φs (see FIG. 10) of the transmitting lens 22 is 60 mm, the focal length f (see FIG. 10) is 52 mm. This can be calculated from the formula tan(θi) = (φs / 2) / f. On the other hand, when the size Es of the deep-ultraviolet LED 21 (light-emitting surface) is 1.04 mm square, the transmitted light viewing angle θs is approximately 10 mrad. This can be calculated from the formula tan θs = (Es / 2) / f.

[0100] The optical axis of the transmitting lens 22 and the optical axis of the far-ultraviolet LED 21 (light-emitting surface) coincide (substantially coincide) with the optical axis AXs of the transmitter 20. The optical axis of the far-ultraviolet LED 21 (light-emitting surface) passes through the center of the light-emitting surface and extends in a direction perpendicular to the light-emitting surface.

[0101] The focal point of the transmitting lens 22 is located near the center of the far-ultraviolet LED 21 (light-emitting surface). Therefore, the light (pulsed light) emitted by the far-ultraviolet LED 21 is collimated by the transmitting lens 22. This allows the transmitted light to be suitable for observation at short distances (for example, 15 m to 150 m).

[0102] The beam diameter (aperture) of the transmitted light is sufficiently larger than the observation object Ob (e.g., fine particles (aerosols) in the atmosphere) in order to stably observe (measure) the observation object Ob. For example, the beam diameter (aperture) of the transmitted light is 60 mm in diameter.

[0103] As described above, by using a condenser lens (collimator lens) as the transmitting lens 22, the light (pulsed light) emitted from the deep-ultraviolet LED 21 can be shaped into collimated light having a diameter equal to the lens diameter (60 mm) of the transmitting lens 22.

[0104] On the other hand, the far-ultraviolet LED 21 (light-emitting surface) is not a point light source but has a certain size. Therefore, the light (pulsed light) emitted from the far-ultraviolet LED 21 (light-emitting surface) is also transmitted in a direction inclined with respect to the optical axis AXs of the transmitter 20.

[0105] FIG. 10 is a diagram showing how the light PL1, PL2 (pulsed light) emitted from the deep-ultraviolet LED 21 (light-emitting surface) is also transmitted in a direction inclined with respect to the optical axis AXs of the transmitter 20.

[0106] 10 , light PL1 emitted from the center Pa of the deep-ultraviolet LED 21 (light-emitting surface) is refracted (collimated) by the transmitting lens 22 and transmitted in the direction of the optical axis AXs of the transmitter 20. On the other hand, light PL2 emitted from a position Pb shifted downward from the center of the deep-ultraviolet LED 21 (light-emitting surface) is refracted by the transmitting lens 22 and transmitted in a direction tilted upward at a predetermined angle with respect to the optical axis AXs of the transmitter 20. Similarly, although not shown, light emitted from a position shifted upward from the center of the deep-ultraviolet LED 21 (light-emitting surface) is refracted by the transmitting lens 22 and transmitted in a direction tilted downward at a predetermined angle with respect to the optical axis AXs of the transmitter 20. The same applies to light emitted from other positions of the deep-ultraviolet LED 21 (light-emitting surface).

[0107] As a result, the transmitted light field of view Ss is a conical area centered on the optical axis AXs of the transmitter 20 and whose diameter increases as it moves away from the transmitter 20 (tip position P0 of the telescope tube) along the optical axis AXs of the transmitter 20 (see Figure 2).

[0108] The transmitted light field of view Ss (transmitted light field of view θs) can be adjusted by changing the focal length f. For example, when the acceptance angle θi is constant, shortening the focal length f can widen the transmitted light field of view θs compared to before shortening the focal length f. In this case, the lens diameter φs of the transmitting lens 22 becomes smaller. Conversely, lengthening the focal length f can narrow the transmitted light field of view θs compared to before lengthening the focal length f. In this case, the lens diameter φs of the transmitting lens 22 becomes larger. In this way, the transmitted light field of view θs can be easily adjusted by using a deep-ultraviolet LED 21 and a transmitting lens 22 with Lambertian directivity characteristics. In other words, the transmitted light field of view Ss can be easily made larger than the received light field of view Sr.

[0109] The transmitting lens barrel 23 is made of aluminum (Al), and the inner cylindrical surface is treated with an anti-reflection coating of black anodized aluminum to prevent reflection (absorption) of the light (stray light) emitted from the deep-ultraviolet LED 21. The transmitting lens barrel 23 can also be made of corrosion-resistant metal materials such as stainless steel and invar, resin materials such as polycarbonate, acrylic, polypropylene, polyethylene, and epoxy, or low-thermal expansion ceramic materials such as alumina and silica. The anti-reflection treatment may be matte black chrome plating or nickel plating. Alternatively, a black alumina or carbon ceramic coating may be used. By treating the inner cylindrical surface of the transmitting lens barrel 23 in this way, excess light (stray light) other than the light directly entering the transmitting lens 22 from the deep-ultraviolet LED 21 can be prevented from being reflected by the inner cylindrical surface and exiting the transmitting lens 22. In other words, the transmitted light can be transmitted at a predetermined transmitted light field of view θs (transmitted light field of view Ss), preventing distance errors in LIDAR data during dToF observation. That is, it becomes possible to observe the received light intensity P(R) with high accuracy.

[0110] The transmitting lens barrel 23 may also be provided with a hood in front of the transmitting lens 22. The inner cylindrical surface of the hood is also subjected to the same anti-reflection treatment as above.

[0111] <Drive Circuit 24> Next, the drive circuit 24 will be described.

[0112] Fig. 11 shows an example of the driver circuit 24, and Figs. 12A and 12B show examples of pulsed light transmission characteristics. Fig. 13 is a graph showing the relationship between supply voltage (V) and frequency (MHz). The driver circuit 24 shown in Fig. 11 is a driver circuit that utilizes avalanche breakdown of a transistor. The horizontal axis in Figs. 12A and 12B represents time (ns), and the vertical axis represents the relative value of light emission intensity (AU).

[0113] The drive circuit 24 is a drive circuit for realizing pulsed light having a frequency of 1 MHz to 10 MHz and a pulse width of 1 ns to 10 ns as the transmitted light. The control and analysis unit 40 controls the deep-ultraviolet LED 21 via the drive circuit 24 so as to emit transmitted light (pulsed light) having a frequency of 1 MHz and a pulse width of 9.6 ns.

[0114] The pulse width of the transmitted light is adjusted by selecting the capacitance of the capacitor C1 of the drive circuit 24. For example, by setting the capacitance of the capacitor C1 to a small or large value, the emitted pulse width (half width) can be adjusted to 1.58 ns (see FIG. 12A) or 3.2 ns (see FIG. 12B).

[0115] The frequency of the transmitted light (emission light period) can be adjusted (controlled) by fixing the value of resistor R1 of the driver circuit and selecting the voltage applied between Vcc and ground. For example, as shown in FIG. 13, by setting the applied voltage to 72 V to 92 V, the recharge time can be adjusted and the emission light period can be controlled to 1 MHz to 2.1 MHz. The optical intensity of the pulsed light at this time can be kept approximately constant because the avalanche breakdown voltage of the transistor is constant. Alternatively, the frequency of the transmitted light can be selected by selecting the value of resistor R1 while keeping the voltage between Vcc and ground constant.

[0116] The distance resolution (spatial resolution) is determined by the pulse width of the transmitted light (pulsed light). For example, if the pulse width is 1 ns, the distance resolution (spatial resolution) is 0.15 m (speed of light c (m / s) × pulse width τ (s) / 2). This makes it possible to observe the detailed distribution of the object to be observed Ob (for example, particles in space). Furthermore, if the pulse width is 10 ns, the distance resolution (spatial resolution) is 1.5 m. This makes it possible to observe the distribution of the object to be observed Ob (for example, particles in space).

[0117] The observation distance (measurement distance) is determined by the frequency of the transmitted light (pulsed light). For example, when the frequency is 1 MHz (period 1 μs = 1 / 1,000,000 ( / s)), the maximum observation distance is 150 m (speed of light c (m / s) × period f (s) / 2). When the frequency is 10 MHz, the maximum observation distance is 15 m. In other words, the observation distance (measurement distance) can be set within a range where the return light (received light) of the previously transmitted light does not overlap with the emission time of the next transmitted light.

[0118] In this way, the pulse width and frequency of the transmitted light can be easily adjusted by selecting the capacitor C1 and resistor R1 of the drive circuit 24 and the voltage between Vcc and ground. Specifically, by preparing and selecting capacitors C1a, C1b, C1c, ... with different capacitances as the capacitor C1 and resistors R1a, R1b, R1c, ... with different resistance values ​​as the resistor R1, the pulse width or frequency of the transmitted light can be adjusted over a wide range.

[0119] <Receiving unit 30> As shown in Figures 8 and 14, the receiving unit 30 includes a first receiving lens 31 (an example of the receiving optical system of the present disclosure), a field stop 32, a second receiving lens 33, a receiving filter 34, and a light receiving element 35. In Figure 8, reference numeral 36 indicates a receiving lens barrel. Figure 14 is a schematic diagram of the receiving unit 30 extracted from Figure 8.

[0120] The first receiving lens 31 is, for example, a focusing lens that is rotationally symmetric with respect to the optical axis AXr of the receiving unit 30. The first receiving lens 31 (and the second receiving lens 33) are made of quartz glass, similar to the transmitting lens 22. The first receiving lens 31 focuses reflected light PL3, PL4 (reflected pulsed light) that is reflected by the observation target Ob and returns to the receiving light field of view Sr, out of the transmitted light (pulsed light).

[0121] In order to improve the amount of captured reflected light PL3, PL4 (reflected pulsed light) that is reflected by the observation target Ob and returns to the receiving light field of view Sr, the first receiving lens diameter φr (aperture of the receiving lens barrel 36) is larger than the diameter φs of the transmitting lens 22 (aperture of the transmitting lens barrel 23). This makes it possible to receive reflected light PL3, PL4 (reflected pulsed light) that is reflected by the observation target Ob that is present in the intended area and returns to the receiving light field of view Sr.

[0122] The specifications of the first receiving lens 31 are as shown in the following table.

[0123] The viewing angle θr of the received light is set narrow (3 mrad (0.173°) to 5 mrad (0.286°)) so that the intended area (plane perpendicular to the optical axis) can be observed.

[0124] When the lens diameter φr of the first receiving lens 31 is 100 mm and the focal length f is 200 mm, the convergence angle θj (see FIG. 14) of the first receiving lens 31 is approximately 14 degrees. This can be calculated using the formula tan(θj) = (φr / 2) / f. On the other hand, when the received light field of view angle θr (see FIG. 14) is 3 mrad (0.173°) and the focal length f is 200 mm, the field of view image size Er is approximately 0.3 mm square. This can be calculated using the formula tan(θr) = (Er / 2) / f.

[0125] The receiving lens barrel 36 is made of aluminum, just like the transmitting lens barrel 23, and has an anti-reflection treatment applied to the inner cylindrical surface. This absorbs light that enters the receiving lens 31 outside the predetermined receiving light viewing angle θr, preventing it from reaching the light receiving element 35.

[0126] The field stop 32 is a light blocking stop that controls (narrows or widens) the received light field Sr.

[0127] The observation range (received light field Sr) can be defined by providing a field diaphragm 32 at the focal point (focal plane) of the first receiving lens 31. For example, when observing a wide received light field Sr, the field diaphragm 32 is opened, and conversely, when observing only a narrow received light field Sr, the field diaphragm 32 is closed. This allows the received light field Sr to be adjusted.

[0128] Furthermore, when the received light viewing angle θr is constant, the field of view image on the focal plane can be made smaller by shortening the focal length f of the first receiving lens 31. Conversely, the field of view image on the focal plane can be made larger by lengthening the focal length f of the first receiving lens 31.

[0129] The second receiving lens 33 adjusts the field of view image on the focal plane to the size of the light receiving surface of the light receiving element 35. If the second receiving lens 33 is not necessary, it may be omitted.

[0130] The receiving filter 34 is a bandpass filter configured to transmit only reflected light (reflected pulsed light) that is reflected by the observation target Ob and returns to the receiving light field of view Sr. In configuration example 1, a bandpass filter of 266 nm±5 nm (corresponding to the half-width of the deep-ultraviolet LED 21) is used. Providing the receiving filter 34 improves the S / N ratio of the signal (pulse electrical signal) output by the receiving unit 30 (light-receiving element 35) and corresponding to the reflected light (reflected pulsed light) received by the receiving unit 30.

[0131] The light receiving element 35 is an ultraviolet photomultiplier tube (PMT) for photon counting. The PMT, which is the light receiving element 35 in Configuration Example 1, is equipped with a high-voltage circuit necessary for the PMT's operation and a preamplifier circuit that amplifies the pulsed electrical signal photoelectrically converted by the PMT. Note that the light receiving element 35 may be a photoelectric conversion element for photon counting other than a PMT. The light receiving element 35 outputs a signal (pulsed electrical signal) corresponding to the reflected light (reflected pulsed light) received by the light receiving element 35.

[0132] The received light field of view Sr is a circle obtained by adding the diameter φr of the first receiving lens 31 to a circle drawn by the received light field of view angle θr centered on the optical axis AXr of the receiving unit 30. In other words, the received light field of view Sr is a circle whose radius is the sum of the radius of the circle of the received light field of view angle θr and the radius of the diameter φr of the first receiving lens 31.

[0133] The optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver 30 are arranged parallel to and spaced apart from each other. The distance L1 (see FIG. 8 ) between the optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver 30 is, for example, 85 mm. It is preferable that the distance L1 be closer to the combined half-aperture distance, which is half the sum of the apertures of the transmitter lens 22 of the transmitter 20 and the receiver lens 31 of the receiver 30, because this shortens the overlap start distance r1 of the transmitted light field Ss and the received light field Sr. Generally, it is preferable that the distance L1 be approximately 1.05 to 1.1 times the combined half-aperture distance.

[0134] In the first configuration example, the transmission light field Ss and the reception light field Sr also overlap each other (see the hatched area HT in FIG. 2 and the overlapping light field Sc in each cross-sectional view).

[0135] As a result, even in configuration example 1, it is possible to receive reflected light (reflected pulsed light) that is reflected by the observation object Ob and returns to the reception light field of view Sr, making it possible to observe the observation object Ob that is located at a short distance (farther than the first position P1). In other words, it is possible to generate observation data (lidar data) with high accuracy.

[0136] <Configuration Example 2 of Observation Apparatus 10> Next, a specific configuration example 2 of the observation apparatus 10 will be described. Hereinafter, the observation apparatus 10 of configuration example 2 will be referred to as observation apparatus 10B.

[0137] FIG. 15 is a schematic diagram of the observation device 10B.

[0138] The observation device 10B is an observation device (LiDAR device) equipped with a refractive transmitter 20 and a reflective receiver 30.

[0139] As shown in Fig. 15, the observation device 10B includes a transmitter 20, a receiver 30, and a control and analysis unit 40 (omitted from Fig. 15). The optical axis AXs of the transmitter 20 and the optical axis AXr of the receiver are arranged parallel to and spaced apart from each other.

[0140] <Transmitting Section 20> The transmitting section 20 includes a semiconductor light emitting element 21 and a transmitting lens 22 (an example of a transmitting optical system of the present disclosure).

[0141] The transmitting unit 20 differs from the transmitting unit 20 of Configuration Example 1 in the specifications of the transmitting lens 22. The specifications of the transmitting lens 22 are as shown in the following table.

[0142] That is, the transmitting lens 22 has a shorter focal length and a wider transmitted light field of view θs than the transmitting lens 22 of Configuration Example 1. As a result, even if the receiving light aperture is increased, the receiving light field of view Sr can overlap and encompass the transmitted light field of view Ss at close range. Because a 1.04 mm square deep-ultraviolet LED is used, the transmitted light field of view θs is 1.489° (25.99 mrad ≒ 26 mrad). Otherwise, the transmitting unit 20 is similar to the transmitting unit 20 of Configuration Example 1.

[0143] <Receiving unit 30> As shown in Fig. 15 , the receiving unit 30 differs from the receiving unit 30 of Configuration Example 1 in that it includes a first receiving mirror 37 and a second receiving mirror 38 (an example of the receiving optical system of the present disclosure) instead of the first receiving lens 31. Otherwise, the receiving unit 30 is similar to the receiving unit 30 of Configuration Example 1. In Fig. 15 , reference numeral 39 denotes a main receiving barrel, and reference numeral 40 denotes a secondary receiving barrel.

[0144] The first receiving mirror 37 is an off-axis parabolic mirror (periphery of a parabolic mirror) and has a focal point F outside the main receiving lens barrel 39. ３７ It has the following characteristics.

[0145] The second receiving mirror 38 is located at the focal point F ３７ The second receiving mirror 38 is an example of a folding mirror of the present disclosure.

[0146] The reflected light (reflected pulsed light) reflected by the observation target Ob and returning to the receiving light field of view Sr is reflected by the first receiving mirror 37 so as to be focused toward the focal point F37, and is further reflected by the second receiving mirror 38 and guided to the light receiving element 35. In this way, the observation device 10B separates the transmitter 20 and the receiver 30. In addition, the second receiving mirror 38 and the light receiving element 35 are provided outside the opening (opening that takes in received light) of the main receiving mirror 39 of the receiver 30. This prevents the receiving light field Sr from being blocked in the observation distance region beyond the first position P1.

[0147] In the second example configuration, the optical axis AXr of the receiving unit 30 (the center line of the first receiving mirror 37) and the optical axis AX of the second receiving lens 33 are ３３ Since the center lines of the first receiving mirror 37 and the second receiving lens 33 are arranged parallel to each other, the reflected light (light beam) reflected at the center of the first receiving mirror 37 and the optical axis AX of the second receiving lens 33 are aligned parallel to each other. ３３ The second receiving mirror 38 is disposed so as to be tilted by half the angle θm formed by the first receiving mirror 38 and the second receiving mirror 38 .

[0148] The received light viewing angle θr is 3 mrad or 5 mrad, similarly to the first configuration example.

[0149] FIG. 16 is a cross-sectional view of the first receiving mirror 37.

[0150] The first receiving mirror 37 includes an off-axis parabolic mirror substrate 37a having an aluminum-coated off-axis parabolic surface as its main surface, an amorphous silicon (α-Si) first anti-reflection film 37c (an example of an anti-reflection member of the present disclosure) that absorbs light in the near ultraviolet to visible light band and is provided on the aluminum-coated surface of the main surface 37b, and a first dielectric multilayer film 37d that reflects light with a wavelength of 265 nm (22.5° incidence) and is provided on the first anti-reflection film 37c. The first receiving mirror 37 reflects light that is incident parallel to the optical axis of the parabolic mirror of the original shape to a focal point F of the parabolic mirror of the original shape. ３７ It is a mirror that reflects and focuses light.

[0151] The various films and arrangement of the first receiving mirror 37 may be the same as those of the second receiving mirror 38 described later.

[0152] An off-axis parabolic mirror is a mirror in which the outer periphery of a parabolic mirror has been hollowed out, and the focal point (the focal point of the original mirror) is located outside the mirror.

[0153] The first antireflection film 37c is made of amorphous silicon (α-Si), titanium carbon nitride (TiCN), or diamond-like carbon (DLC), and is a layer that absorbs light in the near-ultraviolet to visible light ranges. In configuration example 2, the first antireflection film 37c has the function of absorbing light in the near-ultraviolet to visible light ranges that has passed through the first dielectric multilayer film 37d.

[0154] The first dielectric multilayer film 37d is a film formed by laminating multiple thin films of silicon oxide (SiO2) and hafnium oxide (HfO2), and has a high reflectance (90% or more) for deep ultraviolet light of 265 nm (incident angle 22.5°), and transmits light in the near ultraviolet to visible light band.

[0155] FIG. 17 is a cross-sectional view of the second receiving mirror 38.

[0156] As shown in FIG. 17 , the second receiving mirror 38 includes a flat substrate 38 a (folding mirror substrate), a second dielectric multilayer film 38 c that reflects light with a wavelength of 265 nm (22.5° incidence) on its main surface 38 b, and a second antireflection film 38 e (an example of an antireflection member of the present disclosure) made of graphite (carbon) that absorbs light in the near-ultraviolet to visible light band on its subsurface 38 d (back surface), and symmetrically reflects light that is incident on the main surface 38 b.

[0157] The second anti-reflection film 38e is made of graphite, carbon, diamond-like carbon, or the like, and absorbs light that has passed through the second dielectric multilayer film 38c. In other words, it absorbs light that becomes noise components other than the light intended for observation (transmitted light).

[0158] The second dielectric multilayer film 38c has the same configuration as the first dielectric multilayer film 37d.

[0159] Next, the reflectance of each receiving mirror will be described.

[0160] FIG. 18 shows the reflection spectrum of the light reflected by each receiving mirror.

[0161] The reflectance of light incident at an angle of 22.5° was measured on the reflecting surfaces of the first receiving mirror 37 (off-axis parabolic mirror) and the second receiving mirror 38 (folding mirror). In Fig. 13, the horizontal axis represents wavelength and the vertical axis represents reflectance (%).

[0162] 18, "OA_Al" represents the reflection spectrum of the first receiving mirror 37, which has a first antireflection coating 37c and a first dielectric multilayer coating 37d provided on the main surface 37b of the off-axis parabolic mirror substrate 37a with an aluminum layer. The configuration of this first receiving mirror 37 is as shown in the following table.

[0163] In Figure 18, "Φ40_Black" represents the reflection spectrum of the second receiving mirror 38, which has a second dielectric multilayer film 38c on the main surface 38b of the folding mirror substrate 38a and a second anti-reflection film 38e on the secondary surface 38d (rear surface).

[0164] The configuration of the second receiving mirror 38 is as shown in the following table.

[0165] In FIG. 18, "OAxφ40" represents the product of the reflectances of the first receiving mirror 37 and the second receiving mirror 38 (total reflectance spectrum).

[0166] Next, the function, action and effect of the anti-reflection film will be described.

[0167] The reflectance in the deep ultraviolet band, particularly the reflectance product at the transmitted light wavelength of 265 nm, is high at 90% or more.

[0168] In contrast, the reflectance product of light in the near ultraviolet band of 300 nm to 400 nm is reduced to 1 / 10 or less, and the reflectance of light in the visible light band of 400 nm to 700 nm is reduced to 1 / 100 or less.

[0169] As described above, by providing an anti-reflection coating layer on the first receiving mirror 37 and the second receiving mirror 38, it is possible to remove noise light before it reaches the light receiving element 35. This makes it possible to suppress the effects of sunlight, particularly during daytime observation. The light receiving element 35 for photon counting has high reception sensitivity. Therefore, it is designed to be able to remove light other than the target wavelength for detection (265 nm wavelength) before it reaches the light receiving element 35. This makes it possible to suppress noise and enable highly accurate observation.

[0170] The numerical values ​​shown in the above embodiments are all examples, and it goes without saying that other appropriate numerical values ​​can be used.

[0171] The above-described embodiments are merely exemplary in all respects. For example, the transmitter 20 may be a reflective optical system. Furthermore, the transmitter 20 and / or the receiver 30 may each be a mixed optical system of a tropic and reflective system. Furthermore, while the observation target in each of the above-described embodiments is the air containing particulate matter, the present disclosure makes it possible to observe the distance to obstacles (trees, buildings, etc.) simultaneously with the air containing particulate matter. In other words, the present disclosure should not be construed as being limited by the description of the above-described embodiments. The present disclosure may be embodied in various other forms without departing from its spirit or essential features.

[0172] This application claims priority based on Japanese Patent Application No. 2023-197526, filed November 21, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0173] DESCRIPTION OF SYMBOLS 10, 10A, 10B... Observation device 20... Transmitter 21... Deep ultraviolet LED (semiconductor light-emitting element) 22... Transmitting lens 23... Transmitting lens barrel 24... Driver circuit 30... Receiving section 31... Receiving lens (first receiving lens) 32... Field stop 33... Second receiving lens 34... Receiving filter 35... Light-receiving element 36... Receiving lens barrel 37... First receiving mirror 37a... Off-axis parabolic mirror substrate with aluminum layer 37b... Main surface 37c... First anti-reflection coating 37d... First dielectric multilayer coating 38... Second receiving mirror 38a... Folding mirror substrate 38b... Main surface 38c... Second dielectric multilayer coating 38d... Second surface 38e... Second anti-reflection coating 39... Main receiving lens barrel 40... Control analysis unit 41... Observation data generation unit 42... Coefficient analysis processing unit 43... Characteristics evaluation processing unit 44...Observation data storage unit AX ３３ , AXr, AXs...Optical axis C1, C1a...Condenser Cr...Field of view coupling ratio F ３７ ...Focus point Ob...Object to be observed P...Received light intensity P0...Tip position of telescope tube P1...First position P2...Second position P3...Third position P4...Fourth position R1, R1a...Resistance Sc...Superimposed light field of view Sr...Received light field of view Ss...Transmitted light field of view r1...First distance r2...Second distance r3...Third distance θs...Transmitted light field of view angle θr...Received light field of view angle

Claims

1. A system comprising: a transmitting unit having a transmission light field of view and transmitting pulsed light of a wavelength belonging to the ultraviolet region of the solar blind band within the transmission light field of view; a receiving unit having a reception light field of view and receiving reflected light within the reception light field of view of the pulsed light reflected by an object to be observed; and an observation data generating unit, wherein the transmitting unit comprises: a semiconductor light-emitting element that emits the pulsed light; and a transmission optical system that controls the pulsed light emitted by the semiconductor light-emitting element so that the pulsed light emitted by the semiconductor light-emitting element is transmitted within the transmission light field of view; the receiving unit comprises: a reception optical system that collects the reflected light within the reception light field of view; and a light-receiving element that receives the collected reflected light and outputs a signal according to the received reflected light; the optical axis of the transmitting unit and the optical axis of the receiving unit are parallel to each other; a transmission light field angle that defines the transmission light field of view is larger than a reception light field angle that defines the reception light field of view; and the transmission light field and the reception light field of view at least partially overlap each other; The observation data generation unit is an observation device that generates LIDAR data, which is observation data, based on the signal output by the light receiving element.

2. The observation device described in claim 1, wherein the transmitted light field of view is a cone-shaped region centered on the optical axis of the transmitting unit and whose diameter increases with increasing distance from the transmitting unit along the optical axis of the transmitting unit, and the received light field of view is a cone-shaped region centered on the optical axis of the receiving unit and whose diameter increases with increasing distance from the receiving unit along the optical axis of the receiving unit.

3. The observation device according to claim 1, wherein the wavelength in the ultraviolet range is selected from the wavelength range of 240 nm to 300 nm.

4. An observation device according to claim 3, wherein the pulsed light is spontaneous emission light (incoherent light).

5. An observation device according to claim 4, wherein the frequency of the pulsed light is 1 to 10 MHz.

6. An observation device according to claim 5, wherein the pulse width of the pulsed light is 1 to 10 ns.

7. The observation device according to claim 1, wherein the signal output by the light receiving element is a pulse electrical signal corresponding to a photon.

8. An observation device according to claim 1, wherein the receiving optical system comprises an off-axis parabolic mirror and a folding mirror.

9. An observation device according to claim 8, wherein said off-axis parabolic mirror and said folding mirror each have a dielectric multilayer film on a mirror surface for reflecting said reflected light.

10. An observation device as described in claim 9, wherein the off-axis parabolic mirror and the folding mirror have an anti-reflection material that absorbs light other than the reflected light, either under the dielectric multilayer film of each or on the back surface of each mirror.

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