Observation device

Abstract

To provide an observation device capable of observing an observation object between a distant observation object and the observation device.SOLUTION: An observation device 10 includes: a transmission section 20 that has a transmission light visual field Ss, and transmits pulse light with a wavelength that belongs to an ultraviolet region of a solar blind band into the transmission light visual field; a reception section 30 that has a reception light visual field Sr, and receives reflection light within the reception light visual field from among reflection light of the pulse light reflected by an observation object; and an observation data generation section. A light axis AXs of the transmission section and a light axis AXr of the reception section are parallel mutually, a transmission light visual field θs for prescribing the transmission light visual field is larger than a reception light visual field angle θr for prescribing the reception light visual field, the transmission light visual field and the reception light visual field overlap mutually at least partially, and the observation data generation section generates LiDAR data that are observation data on the basis of a signal outputted by a light receiving element.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an observation device, and more particularly to an observation device capable of observing an object to be observed near the ground surface and at a short distance from the observation device.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Document 1, although it is possible to observe an object to be observed existing relatively far away (for example, several kilometers away) by using laser light, there is a problem that it is impossible to observe an object to be observed between the far object to be observed and the observation device, for example, an object to be observed near the ground surface and at a short distance from the observation device.

[0005] The present disclosure has been made to solve such problems, and an object thereof is to provide an observation device capable of observing an object to be observed near the ground surface and at a short distance from the observation device.

Means for Solving the Problems

[0006] The observation device according to the present disclosure has a transmission light field of view, and includes a transmission unit that transmits pulsed light having a wavelength belonging to the ultraviolet region of the solar blind band within the transmission light field of view, a reception unit that has a reception light field of view and receives the reflected light within the reception light field of view among the reflected light of the pulsed light reflected by the observation object, and an observation data generation unit. The transmission unit includes 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 reception unit includes a reception optical system that condenses the reflected light within the reception light field of view, and a light receiving element that receives the condensed reflected light and outputs a signal corresponding to the received reflected light. The optical axis of the transmission unit and the optical axis of the reception unit are parallel to each other. The transmission light field of view angle that defines the transmission light field of view is larger than the reception light field of view angle that defines the reception light field of view. The transmission light field of view and the reception light field of view at least partially overlap each other. The observation data generation unit generates lidar data, which is observation data, based on the signal output by the light receiving element.

[0007] With such a configuration, it is possible to observe an observation object in the vicinity of the ground surface and at a short distance from the observation device.

[0008] This is because it is larger than the reception light field of view angle that defines the reception light field of view, and at least a part of the transmission light field of view and the reception light field of view overlap each other.

[0009] In the above observation device, the transmission light field of view may be a conical region centered on the optical axis of the transmission unit and having a diameter that increases as it moves away from the transmission unit along the optical axis of the transmission unit. The reception light field of view may be a conical region centered on the optical axis of the reception unit and having a diameter that increases as it moves away from the reception unit along the optical axis of the reception unit.

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

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

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

[0013] In addition, in the above observation device, the pulse width of the pulsed light may be 1 to 10 ns. The observation device according to claim 5.

[0014] In addition, in the above observation device, the signal output by the light receiving element may be a pulsed electrical signal corresponding to photons.

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

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

[0017] In addition, in the above observation device, the off-axis paraboloidal mirror and the folding mirror may each have an antireflection member that absorbs light other than the reflected light in the lower layer of each dielectric multilayer film or on the back surface of each mirror.

Advantages of the Invention

[0018] According to the present disclosure, it is possible to provide an observation device capable of observing an observation object near the ground surface and at a short distance from the observation device.

Brief Description of the Drawings

[0019]

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Mode for Carrying Out the Invention

[0020] Hereinafter, the observation device 10 of the embodiment of the present disclosure will be described with reference to the accompanying drawings. The same reference numerals are assigned to the corresponding components in each figure, and redundant descriptions are omitted.

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

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

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

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

[0025] FIG. 2 is a longitudinal sectional view (schematic view) of the observation device 10 shown in FIG. 1.

[0026] As shown in FIG. 2, the transmission unit 20 has a transmission light field of view Ss, and transmits pulsed light (hereinafter also referred to as transmission light) having a wavelength (for example, 265 nm) belonging to the ultraviolet region of the solar blind band within the transmission light field of view Ss. On the other hand, the reception unit 30 has a reception light field of view Sr, receives the reflected light (reflected pulsed light) that is reflected by the observation object Ob among the transmission light (pulsed light) and returns into the reception light field of view Sr, and outputs a pulsed electrical signal (electrical signal of a pulsed wave) corresponding to the received reflected light. The pulsed light may be natural emission light (incoherent light).

[0027] The optical axis AXs of the transmission unit 20 and the optical axis AXr of the reception unit 30 are arranged in a state of being separated from each other and parallel to each other. The distance L1 between the optical axis AXs of the transmission unit 20 and the optical axis AXr of the reception unit 30 is, for example, 85 mm.

[0028] The transmission light field of view Ss is a conical region centered on the optical axis AXs of the transmission unit 20 and having a diameter that increases as it moves away from the transmission unit 20 along the optical axis AXs of the transmission unit 20. The minimum diameter of the transmission light field of view Ss (the diameter at the left end in FIG. 2) is, for example, 60 mm. The transmission light field of view angle θs that defines the transmission light field of view Ss is, for example, 10 mrad (0.57°).

[0029] On the other hand, the received light field of view Sr is a conical region centered on the optical axis AXr of the receiving unit 30 and having a diameter that increases as it moves away from the receiving unit 30 along the optical axis AXr of the receiving unit 30. The minimum diameter of the received light field of view Sr (the diameter at the left end in FIG. 2) is, for example, 100 mm. The received light field of view angle θr that defines the received light field of view Sr is, for example, 3 mrad (0.17°) or 5 mrad (0.29°).

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

[0031] Next, the overlap (superposition) of the transmitted light field of view Ss and the received light field of view 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 in a state of being separated 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 a conical region, and the transmitted light field of view angle θs is set to be larger than the received light field of view angle θr.

[0033] As a result, as shown in FIG. 2, the transmitted light field of view Ss and the received light field of view Sr form an overlapping light field of view Sc that overlaps each other (see the overlapping light field of view Sc in the hatched region HT in FIG. 2 and each cross-sectional view). Next, the overlapping light field of view Sc, which is the overlap of the transmitted light field of view Ss and the received light field of view Sr, will be specifically described.

[0034] The ratio of the overlapping light field of view Sc to the transmitted light field of view Ss can be represented by the field of view coupling ratio Crs. The field of view coupling ratio Crs is calculated by the following formula 1.

[0035] Field of view coupling ratio Crs = overlapping light field of view Sc / transmitted light field of view Ss ··· (Formula 1) However, the overlapping light field of view Sc is the area of the overlapping region between the transmitted light field of view Ss and the received light field of view Sr in each cross-section (see each cross-sectional view in FIG. 2). The transmitted light field of view Ss is the area of the transmitted light field of view Ss in each cross-section.

[0036] A large visual field combination ratio Crs indicates that there is a large amount of reflected light (reflected pulsed light) that is reflected by the object to be observed Ob and returns into the received light visual field Sr.

[0037] As shown in Fig. 2, at the first position P1 which is at a first distance r1 from the tip position P0 of the lens barrel, the outer edge of the transmitted light visual field Ss is circumscribed by the outer edge of the received light visual field Sr (see the cross-sectional view B-B in Fig. 2). Also, at the second position P2 which is at a second distance r2 from the tip position P0 of the lens barrel, the outer edge of the transmitted light visual field Ss is tangent to the optical axis AXr of the receiving unit 30 (see the cross-sectional view C-C in Fig. 2). Further, at the third position P3 which is at a third distance r3 from the tip position P0 of the lens barrel, the outer edge of the received light visual field Sr is inscribed by the outer edge of the transmitted light visual field Ss (see the cross-sectional view D-D in Fig. 2). Furthermore, at each position beyond the third position P3, the outer edge of the received light visual field Sr is included within the outer edge of the transmitted light visual field Ss without being tangent to the outer edge of the transmitted light visual field Ss (see the cross-sectional view E-E in Fig. 2).

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

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

[0040] Fig. 3 is a graph showing the change pattern of the visual field combination 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 from distance 0 to 30 m in Fig. 3.

[0041] As shown in Fig. 4, when the transmission optical field angle θs = 10 mrad and the reception optical field angle θr = 3 mrad, the first position P1 is a position at a first distance r1 (0.44 m) from the transmission unit 20 (the position of the tip of the lens barrel P0) along the optical axis AXs of the transmission unit 20. Also, the second position P2 is a position at a second distance r2 (5.5 m) from the transmission unit 20 (the position of the tip of the lens barrel P0) along the optical axis AXs of the transmission unit 20. Further, the third position P3 is a position at a third distance r3 (15 m) from the transmission unit 20 (the position of the tip of the lens barrel P0) along the optical axis AXs of the transmission unit 20. Also, the fourth position P4 is a position where the field combination ratio Crs is maximum, and is a position 11 m from the transmission unit 20 (the position of the tip of the lens barrel P0) along the optical axis AXs of the transmission unit 20.

[0042] The distance region from the position of the tip of the lens barrel P0 to the first position P1 is a distance region where the outer periphery of the transmission optical field Ss and the outer periphery of the reception optical field Sr are separated. Therefore, the overlapping optical 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 transmission optical field Ss contacts the outer periphery of the reception optical field Sr to the optical axis AXr of the reception optical field Sr. During this period, the field combination ratio Crs increases steeply as the overlapping optical 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 transmission optical field Ss crosses the optical axis AXr of the reception optical field Sr and reaches the outer periphery on the far side of the reception optical field Sr. During this period, since the overlapping optical field Sc expands while the transmission optical field Ss also expands, the field combination ratio Crs increases gently, reaches a maximum value, and then decreases. Finally, the distance region beyond the third position P3 is a distance region where the transmission optical field Ss includes the reception optical field Sr. During this period, the overlapping optical field Sc and the reception optical field Sr are equal, but since the expansion rate of the transmission optical field Ss is large, the field combination ratio Crs decreases gently.

[0043] Next, the change pattern of the field combination ratio Crs when the transmission optical field angle = 10 mrad and the reception optical field angle θr = 5 mrad will be described.

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

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

[0046] The change in the field-of-view coupling ratio Crs in each distance region from the 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 in the case where the received light field-of-view angle θr is 3 mrad. However, since the received light field-of-view angle θr of the received light field Sr is as large as 5 mrad, the field-of-view coupling ratio Crs at the same observation distance becomes larger.

[0047] As described above, the observation can be made from a distance beyond the first position P1 (the distance at which the superimposed light fields are circumscribed) where the superimposed light field Sc is formed. Also, the observation is preferably made from a distance beyond the second position P2 (the distance at which the center lines are tangentially superimposed) where the superimposed light field Sc is at least about half of the received light field Sr. Further, considering the lack of the superimposed light field Sc and the field coupling ratio Crs, the observation is preferably made from a distance beyond the third position P3 (the distance at which the superimposed light fields are inscribed) where the superimposed light field Sc coincides with the received light field Sr. Since the transmitting unit 20 and the receiving unit 30 of the observation device 10 are separated, the observation is not affected by the light shielding by the transmitting unit 20 in the distance region beyond the first position P1. Also, since the optical axis AXs of the transmitted light field Ss and the optical axis AXr of the received light field Sr of the observation device 10 are arranged parallel to each other with a separation, the superimposed light field Sc does not lack in the distance region 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. At this time, to shorten the distance r1 from the lens barrel tip position P0 to the first position P1, it is possible by increasing the received light field angle θr, and to shorten the distance r3 from the lens barrel tip position P0 to the third position P3, it is possible by decreasing the received light field angle θr.

[0049] Hereinafter, the section between the lens barrel tip position P0 and the first position P1 is referred to as the first section. Also, the section between the first position P1 and the second position P2 is referred to as the second section. Also, the section between the second position P2 and the third position P3 is referred to as the third section. The geometric correction factors for 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 by the following formula.

[0051]

Equation

[0052] In the first interval, 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 interval, there is almost no reflected light (reflected pulse light) that is reflected by the observation object Ob and returns into the received light field of view Sr. That is, the first interval is an observation insensitive interval.

[0053] In the second interval, since the field of view coupling ratio Crs increases and decreases, the reflected light (reflected pulse light) that is reflected by the observation object Ob and returns into the received light field of view Sr also increases and decreases. Specifically, the change in the field of view coupling ratio Crs is due to the correlation between an increase in the overlapping ratio of the transmitted light field of view Ss to the received light field of view Sr and a relative decrease in the superimposed light field of view Sc according to the magnification rates (field 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 interval increases as the distance R increases, reaches a maximum value, and then decreases. That is, the second interval is an observation transition interval.

[0054] In the third interval, since the field of view coupling ratio Crs decreases according to the magnification rates (field angles θs, θr) of the transmitted light field of view Ss and the received light field of view Sr, the reflected light (reflected pulse light) that is reflected by the observation object Ob and returns into the received light field of view Sr also decreases. That is, the third interval is an observation stable interval.

[0055] By overlapping the transmission light field of view Ss and the reception light field of view Sr with each other as described above, it is possible to receive the reflected light (reflected pulsed light) that is reflected by the object to be observed Ob and returns into the reception light field of view Sr. That is, the received light intensities P(R) in the second and third intervals where the reflected light (reflected pulsed light) is obtained are corrected by the geometric efficiency factor Y(R) in Equation 1 based on the field of view coupling ratio Crs. Therefore, short-distance measurement can be performed without being affected by changes in the overlapping light field of view Sc. As a result, it is possible to observe the object to be observed Ob existing at a short distance (beyond the first position P1). That is, it is possible to accurately generate the observation data (lidar data) of the object to be observed Ob existing at a short distance (beyond the first position P1).

[0056] In particular, the transmission light field of view angle θs is set to be larger than the reception light field of view angle θr (see FIG. 2). As a result, the distance from the lens barrel tip position P0 to the first position P1 (the first interval) can be shortened, and the distance from the second position P2 to the third position P3 (the second interval) can also be shortened. And the interval distance from beyond the third position P3 (the third interval) to the maximum observation distance (the distance defined by the pulse light interval of the transmission light) can be lengthened. Also, in the observable second and third intervals, if the reception light field of view angle θr is large, the field of view coupling ratio Crs can be increased, so the received light intensity P(R) can be increased.

[0057] On the other hand, if the reception light field of view angle θr is small, the resolution in the plane orthogonal to the optical axis is improved, and if the reception light field of view angle θr is large, the resolution in the plane orthogonal to the optical axis decreases. Also, if the reception light field of view angle θr is small, the third distance r3 (see FIG. 2) becomes short, and if the reception light field of view angle θr is large, the third distance r3 becomes long.

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

[0059] In addition, when the object to be observed Ob is a non-light-shielding object such as aerosol, dust, fog, rainfall, or snowfall and is in a screen shape (thin in the distance direction), in the second and third intervals, another object to be observed in front of or behind the object to be observed Ob can also be observed.

[0060] In the area beyond the third position P3 (the third interval), since the received light field of view Sr is included in the transmitted light field of view Ss, a plurality of objects to be observed Ob that are partially present within the received light field of view Sr can be observed (measured). If the transmitted light is a linear beam (for example, laser light), lidar data of objects to be observed Ob other than the object to be observed Ob at the position where the transmitted light is transmitted cannot be obtained.

[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 analysis unit 40. The control analysis unit 40 can be a dedicated device that houses the devices described later for generating observation data for the observation device 10 in the housing, or can be a composite device that includes other observation devices 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 in response to the reflected light (the reflected light (reflected pulsed light. Specifically, photons) reflected by the object to be observed Ob and returned into the received light field of view Sr) received by the receiving unit 30 by a photon counting circuit (a circuit that performs photon counting) for each reception cycle, and integrates it N times to generate observation data (lidar data). In FIG. 7, the lowermost graph is an example of the observation data (lidar data). The 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 pulsed electrical signals divided for each reception period. In FIG. 7, each pulse described in the graph shown on the right side of the first received electrical signal represents a pulsed electrical signal output according to the reflected light (the reflected pulsed light that is reflected by the observation object Ob and returns into the reception light field Sr. Specifically, photons) received by the receiving unit 30 during the reception period when the first pulsed light (transmitted light) is transmitted. The same applies to each pulse described in the graph shown on the right side of the Nth received electrical signal.

[0067] Also, the flight time (t) of the first received electrical signal represents the flight time (round-trip flight time) of the photons corresponding to each pulse to the observation object Ob. In the graph of the Nth received electrical signal, the flight time (t) is omitted.

[0068] Note that, not limited to the photon counting circuit, anything that performs photon counting may be used. For example, a digital oscilloscope and a PC (an information processing device such as a personal computer) may be used in combination.

[0069] The coefficient analysis processing unit 42 calculates the spatial distribution (distance direction) of the observation object Ob from the increase and decrease changes of the observation data (lidar data), and also executes a process of evaluating the observation data (lidar data) with the lidar equation to calculate the extinction coefficient α and the backscattering coefficient β specific to the observation object Ob.

[0070] For example, if the observation object Ob is a uniform atmosphere in the space from the mirror barrel tip position P0 to the maximum observation distance (Rmax), the received light intensity P(R) shows a change that increases according to the distance (R) and the geometric efficiency factor Y(R), reaches a maximum value, and then decays. Also, if the observation object Ob is spatially uniform, the extinction coefficient α(R) and the backscattering coefficient β(R) do not change with distance, so they can be α and β. Therefore, the lidar equation is Ln((P(R)R 2 ) / Y(R))=-2αR + ln(P 0Since it becomes Cβ), the extinction coefficient α can be obtained from the slope term -2αR, and the backscattering coefficient β can be obtained from the intercept term ln(P 0 Cβ).

[0071] The characteristic evaluation processing unit 43 executes, for example, fixed-point atmosphere evaluation, evaluation of smoke, dust, etc.

[0072] For example, the fixed-point atmosphere evaluation can be performed by regularly observing every year and evaluating with the backscattering coefficient β and extinction coefficient α of fine particles such as aerosol contained in the observed atmosphere. Also, by comparing with the observed values in the reference year, the change in the atmospheric state can be evaluated. At that time, it is also possible to estimate the type of fine particles floating in space by comparing with the disclosed standard atmosphere (ex. Laser Radar Society of Japan, 4(2020), Hisayo, referring to the optical scattering measurement of aerosol and atmospheric molecules). The evaluation of fog, rain, and snow can also be performed in the same way as the fixed-point atmosphere evaluation.

[0073] The evaluation of smoke and dust, for example, the evaluation of the cleanliness of the device exhaust, the exhaust smoke from the chimney, road dust, etc. can be evaluated by comparing the characteristics of the atmosphere outside the exhaust part and the atmosphere of the exhaust part.

[0074] The observation data storage unit 44 stores the observation data (lidar data) generated by the observation data generation unit 41, and is, for example, a non-volatile storage unit such as a hard disk device or an SSD.

[0075] Since the control analysis unit 40 (observation data generation unit 41) has a function of measuring (calculating) the flight time from the received reflected light (photon) to the observation object Ob (known dToF (direct Time of Flight) method, photon counting, etc.), the flight time (round-trip flight time) from the photon corresponding to each pulse to the observation object Ob can be measured (calculated).

[0076] Observation data (lidar data) is generated by integrating the first received electrical signal to the Nth received electrical signal (N - fold integration). In the graph shown 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. This distance is obtained by converting the flight time (t) into distance.

[0077] Next, the improvement of the short - distance observability, miniaturization, and observation convenience of the observation device 10 will be described. Here, the short - distance mentioned 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 (pulse light) from the transmission unit 20 from 1 megahertz (MHz) to about 10 MHz. For example, when the observation target object Ob is locally present at a distance of about 50 m to 100 m, the maximum observation distance (Rmax) can be set to 150 m. The maximum observation distance is the distance defined by the transmission period of the transmitted light (pulse light). For example, when the transmission period of the transmitted light (pulse light) is 1 microsecond (μsec), the flight distance of the transmitted light is 300 m. That is, the maximum observation distance (Rmax) is 150 m, which is the distance at which the previously transmitted transmitted light does not interfere with the next transmitted 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 (pulse light) is 0.1 μsec, and the transmission frequency is 10 MHz.

[0079] The lidar data is generated by integrating each pulse of one unit period incident on the receiving unit 30 a plurality of times. Therefore, it becomes possible to generate lidar data in a short time by increasing the transmission frequency of the transmitted light (pulsed light). In particular, since the apparent moving speed (moving angle per unit time) of the observation object Ob at a short distance is large, short-time observation is essential for improving the spatial resolution. For example, when the distance to the observation object Ob is 100 m and the number of integrations of the lidar data is 1000 times, if the transmission frequency is 1 MHz (transmission period 1 μsec), the observation time for one time is 1 millisecond (msec). At this time, if the observation object Ob is moving at a wind speed of 3 m / s (a gentle breeze), it moves 3 millimeters (mm) from the start to the end of the observation. That is, the moving angle is 0.0017°. Therefore, the received light field angle ratio (moving angle / received light field angle θr) is 0.01 (1%) when the received light field angle θr is 3 mrad (0.17°), and 0.006 (0.6%) when it is 5 mrad (0.29°). Also, when the distance to the observation object Ob is 50 m, the moving angle is 0.0034°. Therefore, the received light field angle ratio is 0.02 (2%) when the received light field angle θr is 3 mrad, and 0.012 (1.2%) when it is 5 mrad. Thus, by increasing the transmission frequency, it becomes possible to accurately observe the observation object Ob at a short distance even when it is moving.

[0080] In addition, the observation device 10 narrows the pulse width of the transmitted light (pulsed light) transmitted from the transmission unit 20 to about 1 nanosecond (nsec). For example, when the pulse width is 10 nsec, the distance resolution is 1.5 m, and when the pulse width is 1 nsec, the distance resolution is 0.15 m. Thus, by narrowing the transmitted light, it becomes possible to accurately observe the observation object Ob in short-distance measurement.

[0081] The observation device 10 uses, as the wavelength of the transmitted light (pulsed light) transmitted from the transmission unit 20, a solar-blind wavelength in the deep ultraviolet band where there is no atmospheric absorption (absorption by oxygen and nitrogen). Here, the solar-blind wavelength in the deep ultraviolet band refers to the wavelength band of deep ultraviolet light that is significantly attenuated before reaching the earth's surface among the sunlight reaching the earth. Specifically, it is a wavelength longer than the wavelength near the absorption edge on the long wavelength side of the absorption wavelengths of oxygen and nitrogen and shorter than the absorption edge on the long wavelength side of the absorption wavelength of the ozone layer. Specifically, it is 230 nanometers (nm) or more and 300 nm or less. Preferably, it is 250 nm to 280 nm. By setting the wavelength band in this way, since it is not affected by external light and is not affected by atmospheric absorption, observation can be performed with a low-output light source.

[0082] Also, by using, as the wavelength of the transmitted light (pulsed light), a solar-blind wavelength in the deep ultraviolet band where there is no atmospheric absorption, the backscattering coefficient β and extinction coefficient α of the fine particles contained in the observation object Ob become larger than those of near ultraviolet to infrared light. As a result, even if the thickness of the observation object Ob in the distance direction is thin or the concentration of the contained particles is low, observation can be performed. Specifically, the extinction coefficient α increases in inverse proportion to the 1.25th power of the wavelength and becomes about five times when the wavelength is shortened from 900 nm to 265 nm. Since the backscattering coefficient β is generally proportional to the extinction coefficient α, it also becomes about five times. That is, highly sensitive observation is possible even at a short distance (where the passing distance of the observation object Ob is short). Also, it becomes easier to identify the characteristics of the observation object Ob (for example, aerosol, smoke, dust, fog, rain, 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, wavelength 265 nm). The deep ultraviolet LED is about □1 mm 2 in size. Also, the deep ultraviolet LED can miniaturize the transmission circuit that emits light with a high frequency and a narrow pulse width. Also, a collimating transmission system with high beam utilization efficiency can be configured with a small-diameter small lens (about φ60 mm in diameter). Therefore, the transmission unit 20 can be miniaturized.

[0084] The observation device 10 uses a photomultiplier tube (PMT) for ultraviolet light corresponding to photon counting as a light receiving element. Therefore, the PMT is small. In addition, since the transmission light of the transmission unit 20 is in the deep ultraviolet band solar blind wavelength without atmospheric absorption, the main condenser of the reception unit 30 can be a small lens or mirror (about φ100 mm in diameter). Therefore, the reception unit 30 can be miniaturized.

[0085] (Observation convenience) The observation device 10 enables observation day and night by using a semiconductor light emitting element (for example, an LED with a wavelength of 265 nm) that emits ultraviolet band light in the solar blind band without atmospheric absorption as the light source of the transmission unit 20. For example, observation under clear sky during the day and observation under illumination such as fluorescent lamps and halogen lamps at night are possible. As a result, observation at regular intervals day and night becomes possible. In addition, since it is possible to project illumination light onto the observation object Ob even at night, aiming at the observation object Ob becomes easy.

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

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

[0088] The observation device 10A is an observation device (LiDAR device) including a transmission unit 20 and a reception unit 30 of a refractive optical system.

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

[0090] <Transmission unit 20> The transmitting unit 20 includes a semiconductor light-emitting element 21 and a transmitting lens 22 (an example of the transmitting optical system of the present disclosure). In FIG. 8, reference numeral 23 indicates the transmitting barrel, and reference numeral 24 indicates the drive circuit of the semiconductor light-emitting element 21.

[0091] The semiconductor light-emitting element 21 is a semiconductor light-emitting element that has an excellent response speed (for example, can emit high-frequency and short-pulse light) and emits light (pulse light) having a wavelength belonging to the ultraviolet region of the solar blind band, and is, for example, a deep ultraviolet LED. Hereinafter, it is also referred to as the deep ultraviolet LED 21.

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

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

[0094]

Table 1

[0095] The deep ultraviolet LED 21 used in the transmitter 20 of the observation device 10A is encapsulated in a CAN package. The CAN package is mounted on a heat sink provided in the drive circuit 24. And, portions other than the light emission port of the CAN package are 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 having high thermal conductivity (for example, 30 to 200 W / m·K) and capable of absorbing stray light. Further, it may be mounted on a ceramic inlay type glass epoxy substrate in which a ceramic is fitted into the portion where the deep ultraviolet LED is mounted. Note that it is preferable to provide a heat sink on the back side (the surface opposite to the surface on which the deep ultraviolet LED is mounted) of the ceramic substrate and the ceramic inlay type glass epoxy substrate.

[0096] The deep ultraviolet LED 21 has a light emitting surface with a size of 1.04 mm square. The light (pulsed light) emitted by the deep ultraviolet LED is incoherent light or incoherent light (random phase, wide half-value width, divergent light). Also, the light (pulsed light) emitted by the deep ultraviolet LED 21 is isotropic light (light having no 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. Also, the transmitting lens 22 is made of quartz glass that transmits the light emitted from the deep ultraviolet LED 21. As the transmitting lens 22, borosilicate glass, silicate glass, amorphous fluororesin, etc. that transmit deep ultraviolet light may also be used.

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

[0099]

Table 2

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

[0101] The focal point of the transmission lens 22 is arranged near the center of the deep ultraviolet LED 21 (light emitting surface). Therefore, the light (pulse light) emitted by the deep ultraviolet LED 21 is collimated by the transmission lens 22. As a result, it is possible to obtain transmission light suitable for observation at a short distance (for example, 15 m to 150 m).

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

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

[0104] On the other hand, the deep ultraviolet LED 21 (light emitting surface) is not a point light source but has a certain size. Therefore, the light (pulse 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 transmission unit 20.

[0105] FIG. 10 is a diagram showing that the light PL1 and PL2 (pulse light) emitted from the deep ultraviolet LED 21 (light emitting surface) are also transmitted in directions inclined with respect to the optical axis AXs of the transmitting unit 20.

[0106] As shown in FIG. 10, the 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 transmitting unit 20. On the other hand, the light PL2 emitted from the position Pb shifted downward with respect to the center of the deep ultraviolet LED 21 (light emitting surface) is refracted by the transmitting lens 22 and transmitted in a direction inclined upward by a predetermined angle with respect to the optical axis AXs of the transmitting unit 20. Similarly, although not shown, the light emitted from the position shifted upward with respect to the center of the deep ultraviolet LED 21 (light emitting surface) is refracted by the transmitting lens 22 and transmitted in a direction inclined downward by a predetermined angle with respect to the optical axis AXs of the transmitting unit 20. The same applies to the 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 region centered on the optical axis AXs of the transmitting unit 20 and having a diameter that increases as it moves away from the transmitting unit 20 (the position P0 at the tip of the lens barrel) along the optical axis AXs of the transmitting unit 20 (see FIG. 2).

[0108] The transmitted light field of view Ss (transmitted light field angle θs) can be adjusted by changing the focal length f. For example, when the capture angle θi is kept constant, by shortening the focal length f, the transmitted light field angle θs can be widened compared to before shortening the focal length f. In this case, the lens diameter φs of the transmitting lens 22 becomes smaller. Conversely, by increasing the focal length f, the transmitted light field angle θs can be narrowed compared to before increasing the focal length f. In this case, the lens diameter φs of the transmitting lens 22 becomes larger. Thus, the transmitted light field angle θs can be easily adjusted by using the deep ultraviolet LED 21 with a Lambertian directivity characteristic and the transmitting lens 22. That is, the transmitted light field of view Ss can be easily made larger than the received light field of view Sr.

[0109] The transmission lens barrel 23 is made of aluminum (Al), and the inner barrel surface is subjected to an antireflection treatment with a black anodized film that prevents (absorbs) the emitted light (stray light) of the deep ultraviolet LED 21. As the transmission lens barrel 23, a corrosion-resistant metal material such as stainless steel or invar, a resin material such as a polycarbonate-based, acrylic-based, polypropylene-based, polyethylene-based, or epoxy-based material, or a low thermal expansion ceramic material such as an alumina-based or silica-based material can also be used. As the antireflection treatment, a matte black chrome plating or nickel plating treatment may be used. Also, a ceramic film treatment of black alumina or carbon may be used. By performing the antireflection treatment on the inner barrel surface of the transmission lens barrel 23 in this way, it is possible to prevent surplus light (stray light) other than the light directly incident on the transmission lens 22 from the deep ultraviolet LED 21 from being reflected by the inner barrel surface and emitted from the transmission lens 22. That is, it becomes possible to transmit the transmitted light at a predetermined transmitted light viewing angle θs (transmitted light viewing field Ss), and in the observation by the dToF method, it is possible to prevent the occurrence of a distance error in the lidar data. That is, it becomes possible to observe the received light intensity P(R) with high accuracy.

[0110] The transmission lens barrel 23 can also be provided with a hood on the front side of the transmission lens 22. The inner barrel surface of the hood is also subjected to the same antireflection treatment as described above.

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

[0112] FIG. 11 is an example of the drive circuit 24, and FIGS. 12(a) and 12(b) are examples of the transmission characteristics of pulsed light. FIG. 13 is a graph showing the relationship between the supply voltage (V) and the frequency (MHz). The drive circuit 24 shown in FIG. 11 is a drive circuit that utilizes the avalanche breakdown of a transistor. In FIGS. 12(a) and 12(b), the horizontal axis represents time (ns), and the vertical axis represents the relative value of the light emission intensity (A.U.).

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

[0114] The pulse width of the transmission light is adjusted by selecting the capacitance of the capacitor C1 in the drive circuit 24. For example, by setting the capacitance of the capacitor C1 to a small value or a large value, the emission pulse width (half-value width) can be adjusted to 1.58 ns (see Fig. 12(a)) or 3.2 ns (see Fig. 12(b)).

[0115] The frequency (emission light period) of the transmission light can be adjusted (controlled) by fixing the value of the resistor R1 in the drive circuit and selecting the applied voltage between Vcc and ground. For example, as shown in Fig. 13, by setting the applied voltage to 72 V to 92 V, the charging time can be adjusted, and the emission light period can be controlled to 1 MHz to 2.1 MHz. At this time, the light intensity of the pulsed light can be made substantially constant because the avalanche breakdown voltage of the transistor is constant. As another method, the frequency of the transmission light can also be selected by keeping the voltage between Vcc and ground constant and selecting the value of the resistor R1.

[0116] The distance resolution (spatial resolution) is determined by the pulse width of the transmission light (pulsed light). For example, when 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). Thereby, the detailed distribution of the observation object Ob (for example, particles in space) can be observed. Also, when the pulse width is 10 ns, the distance resolution (spatial resolution) is 1.5 m. Thereby, the distribution of the observation object Ob (for example, rough particles in space) can be observed.

[0117] The observation distance (measurement distance) is determined by the frequency of the transmitted light (pulse light). For example, when the frequency is 1 MHz (period 1 μs = 1 / 1,000,000 ( / s)), the maximum observable distance is 150 m (speed of light c (m / s) · period f (s) / 2). Also, when the frequency is 10 MHz, the maximum observable distance is 15 m. That is, the observation distance (measurement distance) can be set within the range where the return light (received light) of the previous transmitted light overlaps with the emission time of the next transmitted light.

[0118] In this way, by selecting the capacitor C1 and resistor R1 of the drive circuit 24 and also selecting the voltage between Vcc and ground, the pulse width and frequency of the transmitted light can be easily adjusted. 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 FIGS. 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 FIG. 8, the reference numeral 36 indicates the receiving lens barrel. FIG. 14 is a schematic diagram of the receiving unit 30 extracted from FIG. 8.

[0120] The first receiving lens 31 is, for example, a condenser lens that is rotationally symmetric with respect to the optical axis AXr of the receiving unit 30. Also, the first receiving lens 31 (and the second receiving lens 33) is made of quartz glass, similar to the transmitting lens 22. The first receiving lens 31 condenses the reflected lights PL3, PL4 (reflected pulse lights) that are reflected by the observation object Ob among the transmitted lights (pulse lights) and return into the received light field Sr.

[0121] In order to improve the amount of captured light of the reflected light PL3 and PL4 (reflected pulsed light) that is reflected by the object to be observed Ob and returns into the received light field of view Sr, the diameter φr of the first receiving lens (the aperture of the receiving lens barrel 36) is larger than the diameter φs of the transmitting lens 22 (the aperture of the transmitting lens barrel 23). As a result, it is possible to receive the reflected light PL3 and PL4 (reflected pulsed light) that is reflected by the object to be observed Ob existing in the intended area and returns into the received light field of view Sr.

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

[0123]

Table 3

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

[0125] The receiving lens barrel 36 is made of aluminum, similar to the transmitting lens barrel 23, and an antireflection treatment is applied to the inner cylindrical surface. As a result, it is possible to absorb the light that enters the receiving lens 31 outside the predetermined received light field of view angle θr and prevent it from reaching the light receiving element 35.

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

[0127] By providing the field stop 32 at the focal point (focal plane) of the first receiving lens 31, the observation range (received light visual field Sr) can be defined. For example, when observing a wide received light visual field Sr, the field stop 32 is opened, and conversely, when observing while limiting to a narrow received light visual field Sr, the field stop 32 is narrowed. Thereby, the received light visual field Sr can be adjusted.

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

[0129] The second receiving lens 33 adjusts the visual field image on the focal plane to the size of the light receiving surface of the light receiving element 35. Note that the second receiving lens 33 may be omitted if not necessary.

[0130] The receiving filter 34 is a band-pass filter configured so that only the reflected light (reflected pulse light) reflected by the observation object Ob and returning into the received light visual field Sr can pass through. In Configuration Example 1, a band-pass filter of 266 nm ± 5 nm (corresponding to the half-value width of the deep ultraviolet LED 21) was used. By providing the receiving filter 34, the S / N ratio of the signal (pulse electrical signal) corresponding to the reflected light (reflected pulse light) received by the receiving unit 30 (light receiving element 35) output by the receiving unit 30 is improved.

[0131] The light receiving element 35 is an ultraviolet photomultiplier tube (PMT: Photomultiplier Tube) for photon counting. The PMT which is the light receiving element 35 in Configuration Example 1 is provided with a high voltage circuit necessary for the operation of the PMT and a preamplifier circuit for amplifying the pulse 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 the PMT. The light receiving element 35 outputs a signal (pulse electrical signal) corresponding to the reflected light (reflected pulse light) received by the light receiving element 35.

[0132] The received light field of view Sr is a circle obtained by adding the aperture φr of the first receiving lens 31 to the circle drawn by the received light field 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 with a radius equal to the sum of the radius of the circle of the received light field angle θr and the radius of the aperture φr of the first receiving lens 31.

[0133] The optical axis AXs of the transmitting unit 20 and the optical axis AXr of the receiving unit 30 are arranged so as to be separated from each other and parallel to each other. The distance L1 (see FIG. 8) between the optical axis AXs of the transmitting unit 20 and the optical axis AXr of the receiving unit 30 is, for example, 85 mm. The distance L1 is preferably close to the half-value distance of the sum of the apertures of the transmitting lens 22 of the transmitting unit 20 and the aperture of the receiving lens 31 of the receiving unit 30 because the overlapping start distance r1 of the transmitted light field of view Ss and the received light field of view Sr becomes shorter. Generally, the distance L1 is preferably about 1.05 to 1.1 times the half-value distance of the sum of the apertures.

[0134] Also in Configuration Example 1, the transmitted light field of view Ss and the received light field of view Sr overlap each other (see the hatched area HT in FIG. 2 and the overlapping light field of view Sc in each cross-sectional view).

[0135] As a result, also in Configuration Example 1, the reflected light (reflected pulsed light) reflected by the observation object Ob and returning into the received light field of view Sr can be received, so that the observation object Ob existing at a short distance (beyond the first position P1) can be observed. That is, observation data (lidar data) can be generated with high accuracy.

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

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

[0138] The observation device 10B is an observation device (LiDAR device) including a refractive transmitting unit 20 and a reflective receiving unit 30.

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

[0140] <Transmission unit 20> The transmission unit 20 includes a semiconductor light-emitting element 21 and a transmission lens 22 (an example of the transmission optical system of the present disclosure).

[0141] The transmission unit 20 has different specifications for the transmission lens 22 compared to the transmission unit 20 in Configuration Example 1. The specifications of the transmission lens 22 are as described in the following table.

[0142]

Table 4

[0143] <Reception unit 30> As shown in Fig. 15, the reception unit 30 is different from the reception unit 30 in Configuration Example 1 in that it includes a first reception mirror 37 and a second reception mirror 38 (an example of the reception optical system of the present disclosure) instead of the first reception lens 31. Otherwise, the reception unit 30 is the same as the reception unit 30 in Configuration Example 1. In Fig. 15, the reference numeral 39 indicates the main reception lens barrel, and the reference numeral 40 indicates the sub-reception lens barrel.

[0144] The first reception mirror 37 is an off-axis paraboloidal mirror (the peripheral part of the parabolic mirror) and has a focus F outside the main reception lens barrel 39. 37 It has.

[0145] The second reception mirror 38 is between the first reception mirror 37 and the focus F of the first reception mirror 37.37 It is disposed between them. The second receiving mirror 38 is an example of the folding mirror of the present disclosure.

[0146] The reflected light (reflected pulsed light) that is reflected by the object to be observed Ob and returns into the received light field of view Sr is reflected by the first receiving mirror 37 so as to be condensed toward the focal point F37, and 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 transmission unit 20 and the reception unit 30. Further, the second receiving mirror 38 and the light receiving element 35 are provided outside the opening of the receiving main barrel 39 of the receiving unit 30 (the opening for taking in the received light). Thereby, in the observation distance region beyond the first position P1, the received light field of view Sr is prevented from being shielded.

[0147] In Configuration Example 2, since the optical axis AXr of the receiving unit 30 (the center line of the first receiving mirror 37) and the optical axis AX 33 (the center line of the light receiving element 35) are arranged in parallel, the second receiving mirror 38 is inclined by 1 / 2 of the angle θm formed by the reflected light (light ray) reflected at the center of the first receiving mirror 37 and the optical axis AX of the second receiving lens 33. 33 and arranged.

[0148] The received light field of view angle θr is 3 mrad or 5 mrad, the same as in Configuration Example 1.

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

[0150] The first receiving mirror 37 includes an aspherical paraboloid mirror substrate 37a having a main surface that is an aluminum-coated aspherical paraboloid, an amorphous silicon (α-Si) first antireflection film 37c (an example of the antireflection member of the present disclosure) that absorbs light in the near ultraviolet to visible light band 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 (incident at 22.5°) provided on the first antireflection film 37c. It is a mirror that reflects and condenses light incident parallel to the optical axis of the original parabolic mirror to the focal point F of the original parabolic mirror. 37 of the original shape.

[0151] In addition, the various films and arrangements of the first receiving mirror 37 may have the same configuration as the second receiving mirror 38 described later.

[0152] A non-axis parabolic mirror is a mirror obtained by cutting out the outer peripheral portion of a parabolic mirror, and the focal point (the focal point of the original mirror) is outside the mirror.

[0153] The first antireflection film 37c is formed of amorphous silicon (α-Si), titanium carbonitride (TiCN), and diamond-like carbon (DLC), and is a layer that absorbs light in the near-ultraviolet to visible light band. In Configuration Example 2, the first antireflection film 37c has a function of absorbing light in the visible light band from the near-ultraviolet light transmitted through the first dielectric multilayer film 37d.

[0154] The first dielectric multilayer film 37d is a film formed by laminating thin films of silicon oxide (SiO2) and hafnium oxide (HfO2) in multiple layers. It has a high reflectivity (90% or more) for light at a deep ultraviolet 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 base material 38a (folding mirror base material), a second dielectric multilayer film 38c that reflects light with a wavelength of 265 nm (incident at 22.5°) on the main surface 38b, and a second antireflection film 38e (an example of the antireflection member of the present disclosure) made of graphite (carbon) that absorbs light in the near-ultraviolet to visible light band on the sub-surface 38d (the back surface), and symmetrically reflects the light incident on the main surface 38b.

[0157] The second antireflection film 38e is formed of graphite, carbon, diamond-like carbon, etc., and absorbs the light transmitted through the second dielectric multilayer film 38c. In other words, it absorbs the light that becomes noise components other than the observation target light (transmission light).

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

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

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

[0161] The reflectivity of the incident light at 22.5° with respect to the reflecting surfaces of the first receiving mirror 37 (off-axis parabolic mirror) and the second receiving mirror 38 (folding mirror) was measured. FIG. 13 shows that the horizontal axis represents the wavelength and the vertical axis represents the reflectivity (%).

[0162] In FIG. 18, "OA_Al" represents the reflection spectrum of the first receiving mirror 37 in which a first antireflection film 37c and a first dielectric multilayer film 37d are 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 described in the following table.

[0163] [Table 5] In FIG. 18, "Φ40_Black" represents the reflection spectrum of the second receiving mirror 38 in which a second dielectric multilayer film 38c is provided on the main surface 38b of the folding mirror substrate 38a and a second antireflection film 38e is provided on the secondary surface 38d (back surface).

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

[0165] [Table 6] In FIG. 18, "OAxφ40" represents the product of the reflectivities of the first receiving mirror 37 and the second receiving mirror 38 (total reflectivity spectrum).

[0166] Next, the functions, actions, and effects of the antireflection film will be described.

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

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

[0169] As described above, by providing the antireflection film layers on the first receiving mirror 37 and the second receiving mirror 38, it becomes possible to remove noise light before it enters the light receiving element 35. As a result, in particular, the influence of sunlight can be suppressed in daytime observation. The light receiving element 35 for photon counting has high reception sensitivity. Therefore, it is configured to be able to remove light other than the light reception target wavelength (wavelength 265 nm) before it reaches the light receiving element 35. Thereby, noise can be suppressed and highly accurate observation becomes possible.

[0170] All the numerical values shown in the above embodiments are merely examples, and it goes without saying that appropriate different numerical values can be used.

[0171] The above embodiments are merely illustrative in every respect. For example, the transmission unit 20 can also be an optical system of a reflection system. Also, each of the transmission unit 20 or / and the reception unit 30 can be a mixed optical system of a refractive system and a reflection system. Further, the observation target object in the above embodiments is the atmosphere containing fine particles, but according to the present disclosure, it is possible to observe the distance to obstacles (trees, buildings, etc.) simultaneously with the atmosphere containing fine particles. That is, the present disclosure is not to be construed in a limited sense by the description of the above embodiments. The present disclosure can be implemented in various other forms without departing from its spirit or main features.

Explanation of Reference Numerals

[0172] 10, 10A, 10B... Observation device 20... Transmission unit 21... Deep ultraviolet LED (semiconductor light emitting element) 22... Transmission lens 23... Transmission lens barrel 24... Drive circuit 30... Reception unit 31... Reception lens (first reception lens) 32... Field stop 33… Second receiving lens 34… Receiving filter 35… Light receiving element 36… Receiving lens barrel 37… First receiving mirror 37a… Non-axis parabolic mirror substrate with aluminum layer 37b… Main surface 37c… First anti-reflection film 37d… First dielectric multilayer film 38… Second receiving mirror 38a… Folding mirror substrate 38b… Main surface 38c… Second dielectric multilayer film 38d… Sub surface 38e… Second anti-reflection film 39… Main receiving lens barrel 40… Control and analysis unit 41… Observation data generation unit 42… Coefficient analysis processing unit 43… Characteristic evaluation processing unit 44… Observation data storage unit AX 33 、AXr、AXs… Optical axis C1、C1a… Capacitor Crs… Field of view combination ratio F 37 … Focus Ob… Observation object P… Received light intensity P0… Lens barrel tip position P1… First position P2… Second position P3… Third position P4… Fourth position R1、R1a… Resistor 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 transmission unit having a transmission light field of view, and transmitting pulsed light having a wavelength belonging to the ultraviolet region of the solar blind band within the transmission light field of view; A reception unit having a reception light field of view, and receiving reflected light within the reception light field of view among the reflected light of the pulsed light reflected by an object to be observed; An observation data generation unit, and comprising: The transmission unit: A semiconductor light emitting element that emits the pulsed light; 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 reception unit: A reception optical system that condenses the reflected light within the reception light field of view; A light receiving element that receives the condensed reflected light and outputs a signal corresponding to the received reflected light; An optical axis of the transmission unit and an optical axis of the reception unit are parallel to each other; A transmission light field of view angle that defines the transmission light field of view is larger than a reception light field of view angle 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 with each other; The observation data generation unit is an observation device that generates lidar data, which is observation data, based on a signal output by the light receiving element.

2. The transmission light field of view is a conical region centered on the optical axis of the transmission unit and having a diameter that increases as it moves away from the transmission unit along the optical axis of the transmission unit; The reception light field of view is a conical region centered on the optical axis of the reception unit and having a diameter that increases as it moves away from the reception unit along the optical axis of the reception unit. The observation device according to claim 1.

3. The wavelength belonging to the ultraviolet region is a wavelength selected from a wavelength range of 240 nm to 300 nm. The observation device according to claim 1.

4. The pulsed light is spontaneous emission light (incoherent light). The observation device according to claim 3.

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

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

7. The signal output by the light receiving element is a pulsed electrical signal corresponding to photons. The observation device according to claim 1.

8. The reception optical system is an off-axis paraboloid mirror and a folding mirror. The observation device according to claim 1.

9. The off-axis paraboloid mirror and the folding mirror each have a dielectric multilayer film that reflects the reflected light on each mirror surface. The observation device according to claim 8.

10. The observation apparatus according to claim 9, wherein the non-axis parabolic mirror and the folding mirror each have an antireflection member that absorbs light other than the reflected light on the lower layer of each dielectric multilayer film or on the back surface of each mirror.

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