JP6070274B2 - Diffusion element, illumination optical system and measuring device - Google Patents

Description

  The present invention relates to a diffusing element, an illumination optical system using the diffusing element, and a measuring apparatus.

  Diffusing elements are used in various optical fields. One of them is a diffractive optical element, and an apparatus that performs three-dimensional measurement by irradiating a measurement object with predetermined light emitted from a diffusion element and detecting light scattered by the measurement object is known. ing.

  For example, in Patent Document 1, a predetermined spot pattern is generated by a diffractive optical element, is projected onto a measurement object, and positional information of the measurement object is obtained by a change in reflected light or scattered light projected onto the measurement object thereafter. An obtained three-dimensional measuring device is described.

  On the other hand, as another form of the three-dimensional measuring apparatus, an apparatus using a time-of-flight method is known. The time-of-flight method is a method for obtaining distance information by measuring the time of flight of light until the light reflected from the subject is received by a light receiving unit after the illumination light is irradiated on the subject. In order to improve the S / N ratio of distance detection by the time-of-flight method, it is important to irradiate light efficiently and uniformly over a predetermined projection range.

  For example, in Patent Document 2, the accuracy of depth information is improved by increasing the amount of reflected light from a subject by using a beam shaping element such as an integrator rod in a measuring device using a time-of-flight method. An illumination optical system is described.

Special table 2009-530604 gazette JP 2012-128425 A

  Since the diffractive optical element can limit the projection range of the emitted light by controlling the wavefront of the light, if the diffractive optical element is used, the projection surface can be efficiently irradiated with light. However, when the diffractive optical element has periodicity, a spot-like pattern is formed on the projection surface as in Patent Document 1, and uniform illumination may not be obtained. If uniform illumination cannot be obtained, there is a problem that it cannot be used for a time-of-flight method or an optical system that requires uniform illumination.

  Such a spot pattern generated by the periodicity of the diffractive optical element is particularly noticeable when using a light source such as a laser light source or an LED light source in which the amount of light used is concentrated in a narrow wavelength band of 100 nm or less. Become. Further, such a spot pattern is similarly generated even in an element having periodicity such as a microlens array.

  In addition, when using an integrator rod like the illumination optical system described in Patent Document 2, it is necessary to reflect the light beam introduced into the integrator rod a plurality of times, which generally increases the illumination optical system. There is. If the illumination optical system is large, the entire three-dimensional measurement apparatus also becomes large, which causes problems such as being unable to be mounted on a device with a limited size and being unable to be attached to a device that is not preferred, such as a security device.

  Therefore, an object of the present invention is to provide a diffusing element, an illumination optical system, and a measurement device that can irradiate light efficiently and uniformly to a predetermined projection range without increasing the size of the illumination optical system.

A diffusing element according to the present invention includes a concavo-convex pattern layer that is a diffusing element that emits light within an emission angle range determined according to a predetermined projection plane and includes a structure that imparts a phase difference to incident light. The concavo-convex pattern layer divides a region within the effective diameter of light incident on the diffusion element into two or more regions and emits different diffused light when light is incident on each region. The emission angle measured from the diffusing element with respect to the position on the projection surface is β, and the light emitted from the diffusing element is normalized by the amount of light at the center when projected onto the projection surface When the light quantity distribution is I (β), at least a part of the projection plane has the following formula:
cos ⁴ β <I (β) <1 / cos ⁴ β
It is characterized by satisfying .

  Further, when the diffusing element divides the projection surface into 200 or more regions in the horizontal direction and the vertical direction, the intensity of light emitted from the diffusing element measured in each region is on the projection surface. It may be 0.25 times or more the average value of the intensity.

  The concavo-convex pattern layer is formed by arranging basic units that emit diffused light within the emission angle range when light is incident, and the arrangement has at least different unit sizes or phase distributions within the units. A configuration in which two or more basic units are included may be used.

  Moreover, the said uneven | corrugated pattern layer may contain the uneven structure which has two or more surfaces from which height differs. Here, one height surface may be a substrate surface on which a concavo-convex structure is formed.

  Moreover, the said uneven | corrugated pattern layer may contain the structure which has a curved surface.

  The diffusing element is a diffusing element that emits light within the emission angle range when diverging light is incident thereon, and the concavo-convex pattern layer has a region within the effective diameter of incident light to the diffusing element. When parallel light is incident on each region after being divided into two or more regions, the diffusion angle from the optical axis of the light emitted from each region to the outside decreases as it goes outward from the optical axis of the incident light. The phase distribution which emits the diffused light which becomes may be sufficient.

  Further, the diffusion element may have an emission angle of a luminous flux composed of a diffused light group emitted from the diffusion element of 7.5 ° or more.

  The illumination optical system according to the present invention is an illumination optical system for irradiating light onto a predetermined projection surface. When light is incident, the illumination optical system falls within a predetermined emission angle range determined according to the projection surface. A diffusion element that emits light is provided, and the diffusion element is any one of the above-described diffusion elements.

  In addition, the measuring apparatus according to the present invention includes an illumination optical system that emits inspection light toward a predetermined projection surface, and scattered light that is generated when the inspection light emitted from the illumination optical system is irradiated onto the measurement object. The illumination optical system includes a light source that emits light, and a light emitted from the light source within a predetermined emission angle range determined according to the projection plane when incident. A diffusing element that emits light, and the diffusing element is any one of the diffusing elements described above, and the detection unit uses the light emitted from the diffusing element as inspection light, and the inspection light is a measurement target. Scattered light generated by irradiating an object is detected.

  According to the present invention, light can be efficiently and uniformly irradiated to a predetermined projection range without increasing the size of the illumination optical system.

It is a block diagram which shows the structural example of the measuring device of 1st Embodiment. It is a plane schematic diagram which shows the structural example of a diffusion element. It is explanatory drawing which shows the example of the phase distribution which one basic unit has. It is a cross-sectional schematic diagram which shows the structural example of a diffusion element. It is a schematic cross section which shows the other structural example of a diffusion element. It is explanatory drawing which shows typically the relationship between the diffused light group radiate | emitted from a diffusion element, and a projection surface. It is explanatory drawing which shows the example of the projection pattern which is distribution on the projection surface of the light radiate | emitted from a diffusion element, and the relationship between the position in the projection surface and the number of each light ray which makes the projection pattern. It is explanatory drawing for demonstrating the ratio of area ratio and intensity distribution according to the outgoing angle of the light beam of diverging light. It is explanatory drawing which shows the example of the projection pattern by the basic unit of a diffraction element. It is explanatory drawing which shows the example of a projection pattern when light injects into the diffusion element which has periodicity. It is a block diagram which shows the structural example of the measuring device of 2nd Embodiment. It is a plane schematic diagram which shows the structural example of the diffusion element of 2nd Embodiment. It is explanatory drawing which compares and shows the example of the emitted light from a spreading | diffusion element, and its intensity distribution. It is explanatory drawing which shows the example of the emitted light at the time of displacing the optical axis of a lens for every area | region. It is explanatory drawing which shows the example of a phase function, and the example of phase distribution of each basic unit. It is explanatory drawing which shows the other example of a diffusion element. It is explanatory drawing which shows the projection pattern of each basic unit in a 1st example. It is explanatory drawing which shows arrangement | positioning of the basic unit in a 1st example. It is explanatory drawing which shows distribution (projection pattern) on the projection surface of the diffused light group radiate | emitted from the diffusion element of a 1st example. It is explanatory drawing which shows the light intensity distribution of a certain cross section on the projection surface by the diffused light group radiate | emitted from the diffusion element of the 1st example. It is explanatory drawing which shows the incident angle of the incident light with respect to the in-plane position of the spreading | diffusion element of a 2nd example. It is explanatory drawing which shows the projection pattern of each basic unit in a 2nd example. It is explanatory drawing which shows distribution (projection pattern) on the projection surface of the diffused light group radiate | emitted from the diffusion element of the 2nd example. It is explanatory drawing which shows the light intensity distribution of a certain cross section on the projection surface by the diffused light group radiate | emitted from the diffusion element of the 2nd example. It is explanatory drawing which shows distribution (projection pattern) on the projection surface of the diffused light group radiate | emitted from the diffusion element of the 3rd example. It is explanatory drawing which shows the light intensity distribution of a certain cross section on the projection surface by the diffused light group radiate | emitted from the diffusion element of the 3rd example.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, about the same member etc., the same code | symbol is attached | subjected and description is abbreviate | omitted.

Embodiment 1. FIG.
FIG. 1 is a configuration diagram illustrating a configuration example of the measurement apparatus according to the first embodiment of the present invention. A measuring apparatus 100 illustrated in FIG. 1 includes a light source 20, a diffusion element 130, and a detection element 50.

  The diffuser element 130 generates the diffused light group 12 as the inspection light when the incident light 11 emitted from the light source 20 is incident. In addition, the detection element 50 detects the scattered light 13 that is generated when the inspection light composed of the diffused light group 12 emitted from the diffusion element 130 is applied to the measurement objects 40a and 40b. The detection element 50 may be an imaging element for imaging the measurement objects 40a and 40b irradiated with the diffused light group 12 emitted from the diffusion element 130.

  The diffusing element 130 includes a portion having a diffusing action for generating a plurality of diffused lights. In the measurement apparatus 100 shown in FIG. 1, incident light 11 that is parallel light, divergent light, or convergent light is incident on a diffusing element 130 including such a portion having a diffusing action, and the diffused light group 12 is emitted from the diffusing element 130. Thus, effective and uniform illumination within a predetermined illumination range is realized.

  As the diffusing action, for example, a diffractive action by a stepped uneven surface or an uneven surface having continuity at least partially, or a refracting action by an uneven surface having continuity at least partially can be used. Here, the concavo-convex surface having continuity at least in part is, for example, a continuous change in the height of the concavo-convex surface such as an inclined surface of a blazed diffraction grating or a curved surface of a microlens array or a Fresnel lens array. Refers to the site. In addition, the scattering effect by an irregular discontinuous surface is not considered here.

  In the uniform illumination state, the light intensity at each position on the projection surface corresponding to each pixel of the image sensor 50 has a light intensity of 25% or more with respect to the average value of the light intensity on the projection surface. It is preferably 50% or more. By doing so, the difference between the high light amount region and the low light amount region can be reduced, and measurement with small measurement variations in the entire projection range can be performed. Each position when calculating the light intensity does not necessarily have a one-to-one relationship with the pixel of the image sensor 50. For example, the number of divisions of the projection plane to which the light intensity condition is applied may be greater than or equal to the number of pixels of the image sensor 50.

The number of divisions of the projection plane is preferably 200 or more in the horizontal direction and the vertical direction, for example, 320 or more in the horizontal direction and 240 or more in the vertical direction, because measurement with higher resolution is possible. Even when the diffusing element 130 is used for an application that does not require an image sensor, the degree of uniform illumination can be determined by dividing the projection plane by 200 or more in the horizontal and vertical directions. When an image sensor is used, the intensity of light observed by the image sensor is cos ⁴ β with respect to the intensity of light on the projection plane with respect to the intensity on the projection plane according to the cosine fourth law of the imaging system. There is. In such a case, instead of the light intensity on the projection surface, an average value of the light intensity observed by the image sensor may be obtained, and the intensity at each pixel may be 25% or more. Here, β is an emission angle of light from the diffusing element.

  In the example shown in FIG. 1, the measuring object 40b plays the role of a projection plane that defines a projection range. The projection range is preferably within ± 50%, more preferably within ± 10% with respect to the range of the angle of view seen by the detection element 50, that is, the detection range, and more preferably a range that substantially matches.

  The light emitted from the light source 20 is subjected to predetermined modulation. For example, the intensity of light emitted from the light source 20 may be modulated with a sine wave or a rectangular wave. By measuring the time lag between the phase of the predetermined modulation and the phase of the scattered light reflected by the measurement objects 40a and 40b detected by the detection element 50, the distance between the measurement objects 40a and 40b, Information such as a three-dimensional shape can be acquired.

  When the diffused light group 12 emitted from the diffusing element 130 is regarded as one light beam, the emission angle α of the light beam is preferably 7.5 ° or more, more preferably 15 ° or more, and further preferably 30 ° or more. This enables measurement over a wide range.

  Next, the diffusion element 130 will be described more specifically. FIGS. 2A and 2B are schematic plan views illustrating a configuration example of the diffusing element 130 of the present embodiment. As already described, the diffusing element 130 of this embodiment includes two or more parts having different diffusing actions in the element surface. As shown in FIGS. 2 (a) and 2 (b), the part includes two or more basic units with different unit sizes or different phase distributions within the units (for example, when there are three types of basic units, 31a, 31b, 31c, etc.) can be realized by two-dimensionally arranging the basic units 31. In FIG. 2, reference numerals 31a, 31b, and 31c denote basic units that express different diffusion effects.

FIG. 2A is a schematic plan view illustrating an example of the diffusing element 130 including two or more basic units having different unit sizes. 2A has a plurality of basic units 31 (31a, 31b, 31c, etc.) two-dimensionally with an average pitch P _xavg in the X-axis direction and an average pitch P _{yavg in} the Y-axis direction. Are arranged in a shape.

Here, the average pitch P _xavg in the X-axis direction is expressed by P _xavg = ΣP _xi / N where P _xi (i = 1 to N) is the size of each basic unit in the X-axis direction. The same applies to the Y-axis direction. That is, the average pitch P _yavg in the Y-axis direction is represented by P _yavg = ΣP _yi / M, where P _yi (i = 1 to M) is the size of each basic unit in the Y-axis direction. As in the example shown in FIG. 2A, the periodicity of the diffusing element 130 is reduced by two-dimensionally arranging a plurality of basic units 31 including two or more basic units having different sizes.

On the other hand, FIG. 2B is a schematic plan view showing an example of the diffusing element 130 including two or more basic units having different phase distributions within the unit. Diffusing element 130 shown in FIG. 2 (b), a plurality of basic units 31 (31a, 31b, 31c, etc.) are arranged at the same pitch _{P y} in the same pitch _{P x} and the Y-axis direction in the X-axis direction, The periodicity of the diffusing element 130 is reduced because at least two of the basic units 31 have different phase distributions.

  FIG. 3 is an explanatory diagram showing an example of the phase distribution of one basic unit 31. FIG. 3A shows an example of the basic unit 31 having a binary phase distribution. For example, when the diffusing element 130 wants to generate the phase distribution shown in FIG. 3A in a certain area in the plane, the area blacked out in FIG. A concavo-convex pattern having a hollow area as a concave portion may be formed on the surface of the member 32 that transmits light, such as glass or a resin material. Further, instead of transmitting the incident light 11, the diffused light group 12 having a desired phase distribution may be generated by reflecting the incident light 11 in the diffusion element 130.

  By varying the phase distribution or unit size of such basic units between the basic units 31a, 31b, and 31c, a diffusing element 130 as shown in FIG. 2A or 2B can be obtained.

  As a method for changing the phase distribution of the basic unit, for example, the two-dimensional shape of the concavo-convex pattern in the basic unit may be changed, or the height or sectional shape of the concavo-convex pattern may be changed.

  The diffusing element 130 is not limited to a structure that forms a concavo-convex pattern on the surface of a transparent member as long as the target phase distribution can be generated in the element emission light. For example, the diffusing element 130 is a transparent member on which a concavo-convex pattern is formed. In addition, a member having a refractive index different from that of the member may be bonded to make the surface flat, or a transparent member may be used to change the refractive index. That is, here, the concavo-convex pattern does not mean only a structure having a concavo-convex surface shape, but includes all structures that can give a phase difference to incident light.

  Further, the number of the basic units 31 in the diffusing element 130 does not need to be an integer, and it is sufficient that one or more basic units are included in the uneven pattern of the diffusing element 130. For example, the boundary between a region such as a peripheral portion that does not have a concavo-convex pattern and a region that has a concavo-convex pattern may not coincide with the boundary of the basic unit.

  3 (b) and 3 (c) show another example of the phase distribution of the basic unit. In FIG. 3 (b), the concave / convex pattern of the basic unit is composed of a plurality of annular zones. FIG. 3C shows an example in which the concave / convex pattern of the basic unit is a diffraction grating. In the case of the basic unit as shown in FIG. 3B, the phase distribution in the basic unit can be changed by changing the focal length of the Fresnel lens and the center position of the Fresnel lens in the basic unit. Further, by changing the unit size, the phase distribution of each basic unit can have a different diffusing action even between the same units.

  In the case of the basic unit as shown in FIG. 3C, the phase distribution in the basic unit can be changed by changing the diffraction angle or azimuth angle of the diffracted light of the diffraction grating in the basic unit. In addition, by changing the unit size, the phase distribution of each basic unit can have a different diffusing action even between the same units.

  The basic unit may be a refractive lens. Even when such a lens is made into a lens array, discrete diffracted light is generated, which may interfere to form a spot-like pattern, but the center of the lens in the basic unit, the aspherical shape of the lens, By changing the size of the basic unit, the periodicity at the time of arraying can be reduced.

  When a diffraction element having a two-dimensional uneven pattern shown in FIG. 3A or a diffraction grating as shown in FIG. 3C is used as a basic unit, the light intensity distribution on the projection plane is determined for each position on the projection plane. It is preferable because it can be finely controlled. Further, it is preferable to use the Fresnel lens structure shown in FIG. 3B for the basic unit because a uniform intensity distribution can be easily obtained and an intensity distribution that is difficult to realize with a refractive lens can be obtained.

  Next, the physical structure of the diffusing element 130 will be described. FIG. 4 is a schematic cross-sectional view illustrating a configuration example of the diffusion element 130. FIG. 4A shows an example of the diffusing element 130 in which the periodicity is reduced by changing the phase distribution of the basic unit. FIG. 4B shows an example of the diffusing element 130 in which the periodicity is reduced by changing the size of the basic unit. 4A and 4B show a diffusing element 130 having a structure having a concavo-convex pattern by forming convex portions 33 on the surface of a transparent substrate 32 made of glass or the like. In this diffusing element 130, a region where the convex portion 33 is not formed becomes a concave portion 34 on the surface of the transparent substrate 32. Hereinafter, for convenience, the layer constituting the concavo-convex pattern on the transparent substrate 32 is referred to as the concavo-convex pattern layer 35.

  The transparent substrate 32 only needs to be transparent to incident light, and various materials such as a resin substrate and a resin film can be used in addition to a glass substrate. However, optically isotropic materials such as glass and quartz are used for transmitting light. It is preferable because there is no influence of birefringence. The transparent substrate 32 can reduce light reflection due to Fresnel reflection, for example, by forming an antireflection film or the like by a multilayer film at the interface with air. In FIG. 4, the concavo-convex pattern formed on one surface of the transparent substrate 32 is shown, but the diffusing element 130 may form the concavo-convex pattern on both surfaces of the transparent substrate 32.

  Further, the diffusing element 130 may have a plurality of surfaces having a diffusing action. In this case, it may be composed of two elements, or one element may have a plurality of surfaces having a diffusing action. When there are two or more surfaces having a diffusing action, the direction of diffusion produced by each surface may be different. This can reduce interference between diffused light caused by the two surfaces.

  FIG. 5 is a schematic cross-sectional view showing another configuration example of the diffusing element 130. As shown in FIG. 5, the diffusing element 130 may have a lens portion 36 having a refractive action on one side. By doing so, the lens element for collimating the light beam from the light source can be eliminated, and the optical system can be miniaturized.

FIG. 6 is an explanatory diagram schematically showing the relationship between the diffused light group 12 emitted from the diffusing element 130 and the projection plane. The diffusing element 130 is formed with a portion having a diffusing action so that the projection pattern of the generated diffused light group 12 has a two-dimensional distribution on the projection surface. In FIG. 6, the optical axis direction of the light beam (incident light) incident on the diffusing element 130 is defined as the Z axis, and the axes having an intersection with the Z axis and perpendicular to the Z axis are defined as the X axis and the Y axis. Assuming that the diffusion angle of each diffused light included in the diffused light group 12 generated when the light 11 is incident, that is, the angle formed by each diffused light and the Z axis, is θ, each θ is predetermined in the X-axis direction and the Y-axis direction. It is distributed within the angle range. Further, the diffusion angle θ of the diffused light emitted to the maximum position in the X-axis direction is the maximum angle θx _max , and the diffusion angle θ of the diffused light emitted to the minimum (maximum in the − direction) position in the X-axis direction. Is the minimum angle θx _min , and the diffusion angle θ of the diffused light emitted at the maximum position in the Y-axis direction is the maximum angle θy _max , and the diffused light emitted at the minimum position in the Y-axis direction (maximum in the − direction) Is the minimum angle θy _min , and the irradiation of the diffused light group 12 formed from the minimum angle θx _min to the maximum angle θx _{max in} the X-axis direction and from the minimum angle θy _min to the maximum angle θy _max in the Y-axis direction. The range is a desired projection range, in this example, a range substantially coincident with the detection range of the detection element 50, that is, a projection range onto the measurement object 40b.

In the example shown in FIG. 6, in the projection pattern of the diffusing element 130, a straight line parallel to the Y axis passing through diffused light whose angle in the X axis direction is θx _max with respect to the Z axis is the short side, and the Y axis is relative to the Z axis. A rectangular area having a long side as a straight line parallel to the X axis passing through the diffused light whose direction angle is θy _max is the irradiation range of the diffused light group 12. Hereinafter, a straight line and the Z axis and the angle connecting the intersection with the diffusion elements of the short sides and the long sides and theta _d, the angle theta _d is referred to as the diffusion angle in the diagonal direction.

Here, the above-described emission angle α may be replaced with an angle range in the X-axis direction = | θx _max −θx _min | ÷ 2 or an angle range in the Y-axis direction = | θy _max −θy _min | ÷ 2. In that case, either of these angle ranges is preferably 7.5 ° or more, more preferably 15 ° or more, and further preferably 30 ° or more.

Next, a method for designing the diffusing element 130 of this embodiment will be described. Design steps include designing one or more basic units that emit outgoing light that falls within the range of θx _min to θx _{max in} the X-axis direction and within the ranges of θy _min and θy _max in the Y-axis direction. In the following, each of the basic units will be described.

First, the basic unit design method will be described. Here, each of the one or more basic units is designed to emit outgoing light that falls within the range of θx _min to θx _{max in} the X-axis direction and within the ranges of θy _min and θy _max in the Y-axis direction. The number of basic units to be designed may be one when the periodicity is reduced by changing the size of the basic units, but the periodicity is reduced by changing the phase distribution of the basic units. There are two or more.

First, a case where a plane wave is incident on a certain basic unit 31 is considered, and an electric field provided by the basic unit 31 is U (x, y). The electric field U (x, y) to the development plane wave, the wave number of the X-axis direction is _k x, Y-axis direction of the wave number of the component of the angular spectrum as a _{k y A (k x, k} y) When an electric field U (X, y) can be described as the following formula (1). At this time, the electric field distribution of the light after passing through the basic unit 31 is obtained by Fourier transform of the electric field U (x, y) by the following equation (1).

When the angle of the X component with respect to the optical axis in the emission direction of the angular spectrum component A (k _x , k _y ) in Equation (1) is θ _x and the angle of the Y component is θ _y , k _x = 2π / λ × sin θ _x , k _y = 2π / λ × sin θ _y . Therefore, the light intensity | U (x, y) | ² has a value within the range of θx _min to θx _{max in} the X-axis direction and within the range of θy _min and θy _max in the Y-axis direction. What is necessary is just to design A (k _x , k _y ) by the equation (1).

  For example, when a diffractive element as shown in FIG. 3A is used as a basic unit, a specific phase distribution of the basic unit may be obtained using a technique such as an iterative Fourier transform method. More specifically, since the phase distribution of the basic unit 31 in the diffusing element 130 and the electric field distribution of the diffracted light generated by the diffusing element 130 are in a Fourier transform relationship, by the inverse Fourier transform of the phase distribution of the diffracted light, A phase distribution in the basic unit 31 can be obtained.

  Further, when the diffusing element 130 is manufactured, only the intensity distribution of the diffracted light is a limiting condition, and the phase condition is not included. Therefore, the phase distribution of the basic unit 31 is arbitrary. In the iterative Fourier transform method, information on the phase distribution of the basic unit 31 is extracted from the inverse Fourier transform of the light intensity distribution of the desired diffracted light, and the obtained phase distribution is used as the phase distribution of the basic unit 31. I do. By repeating the above calculation using the difference between the Fourier transform result and the distribution of the light intensity of the desired diffracted light as the evaluation value, the phase distribution of the basic unit that minimizes the evaluation value can be obtained as the optimum design value. That's fine.

  In addition to the above, the design algorithm of the diffractive element is described in documents such as “Bernard Kress, Patrick Meyrueis, Kyoko Ogura, Other Translations,“ Digital Diffractive Optics ”, Maruzen Publishing, March 2005”. There are various types. Further, as a Fourier transform method, a fast Fourier transform algorithm or the like may be used.

Next, the light quantity distribution of diffracted light will be described. For example, when the angular spectrum A (k _x , k _y ) in the above equation (1) is constant in a certain wavenumber range, the density distribution of the diffracted light on the projection plane is cos with respect to the angle β measured from the optical axis. ⁴ Proportional to β. This is because, when the angular spectrum is constant, when the diffracted light is projected onto a plane, the diffracted light farther from the optical axis increases the flight distance and forms a pincushion type distortion. Further, when diverging light is incident on the diffusing element 130 that generates such diffused light and uniform illumination is performed, the intensity distribution on the projection surface of the diffused light group 12 is relative to the angle β measured from the optical axis. It is proportional to cos ⁴ β. Hereinafter, an example in which the basic units 31 are periodically arranged will be described with respect to such a phenomenon of intensity distribution.

FIG. 7 shows an example of a projection pattern that is a distribution on a projection surface of light emitted from a diffusing element in which angles formed by adjacent orders of diffracted light are approximately uniform, and in the projection plane of each light beam that forms the projection pattern. It is explanatory drawing which shows the relationship between a position and number. In FIG. 7 (a), the pitch _{P x} is 50.7μm in the X-axis direction of the base unit, the pitch _{P y} in the Y-axis direction is 47.6Myuemu, order of the diffracted light _(m x, m _y) is Incident light 11 of parallel light having a wavelength of 830 nm is incident on a diffusing element that generates 65 × 49-point diffracted light having −32 to 32nd order in the X-axis direction and −24th to 24th order in the Y-axis direction. In this case, the distribution (projection pattern) of light appearing on the projection surface 40c at the position of z = 2000 mm is shown. 7B, the projection plane 40c is divided into a plurality of areas each having a rectangular area of 153.8 mm × 115.4 mm as a unit, and is included in each rectangular area with respect to the angle β measured from the optical axis. The figure shows a value obtained by normalizing the number of light beams, that is, the number of projected diffracted light beams, with the number of light beams included in a rectangular region near the optical axis, that is, the projected diffracted light beam. In FIG. 7B, cos ⁴ β at β = 0 °, 5 °, 10 °, 15 °, 20 °, 25 °, and 30 ° is shown at the same time.

As shown in FIG. 7A, it can be seen that a pincushion type distortion occurs in the light distribution by the diffused light group due to diffraction on the projection surface 40c. In addition, as shown in FIG. 7B, it can be seen that the distribution of the number of diffracted light, that is, the density distribution, substantially matches the value of cos ⁴ β.

As one method of correcting such an intensity distribution, C _s (β), which is the ratio of the number of diffracted lights at an angle β to the number of diffracted lights at the central portion of the projection surface 40c, is at least one of the projection surfaces. In some cases, C _s (β)> cos ⁴ β may be satisfied. As another method, C _p (β), which is the ratio of the intensity of the diffracted light at the angle β to the intensity of the diffracted light at the center, is expressed as C _p (β)> cos ⁴ β at least in a part of the projection plane. It is good. Moreover, you may combine these methods. The number and intensity of diffracted light may satisfy the above-mentioned formula as an average value. In such a case, the projection range is divided into several areas, and the average value of the number and intensity of diffracted light in this area. You may think.

  The number of divisions when dividing the projection range into several regions is preferably 3 × 3 or more. In addition, since 11x11 or more can grasp | ascertain the tendency of light quantity more, it is more preferable. In addition, it is preferable to set the number of divisions to 1/10 or less in the horizontal direction and the vertical direction with respect to the number of pixels of the image sensor because the influence of local light amount fluctuations can be reduced.

Further, when the detection element 50 includes an optical element such as a lens, there arises a problem that the amount of light detected by the detection element 50 from a position with a large angle of view is reduced by the cosine fourth law. In such a case, if the light quantity distribution on the projection surface satisfies 1 / cos ⁴ β, the intensity distribution of the light detected on the detection element 50 becomes uniform. Therefore, it is more preferable that at least one of cos ⁴ β <C _s (β) <1 / cos ⁴ β and cos ⁴ β <C _p (β) <1 / cos ⁴ β is satisfied. As a result, light is incident on the diffusing element 130, and the light quantity distribution I () normalized by the light quantity at the center when the diffused light group 12 which is a group of divergent light beams generated by the diffusing element 130 is projected onto the projection surface 40c. β) can satisfy cos ⁴ β <I (β) <1 / cos ⁴ β in at least part of the projection plane.

FIG. 8 is an explanatory diagram for explaining the area ratio and the intensity distribution ratio according to the emission angle of the divergent light beam. As shown in FIG. 8, for example, it is assumed that a divergent light beam A is emitted from the diffusing element 130 toward the flat projection surface 40c at a distance z at an emission angle β. Similarly, it is assumed that a divergent light beam B is emitted from the diffusion element 130 toward the projection surface 40c at an emission angle of 0 °. The light beams A and B are both light beams having a divergence angle φ _o . Further, the distance to the projection plane 40c of the light beam A and _{z A.} For the light beams A and B, only the exit angle and the divergence angle are defined, and it does not matter whether the actual light beam is a light beam group of a plurality of diffracted lights or one diffracted light.

At this time, (1) the area ratio (S0 / S2) of the surfaces perpendicular to the traveling phrases of the light beams A and B irradiated to the projection surface 40c is proportional to (z / z _A ) ² = (cos β) ² . (2) For the light flux A, the area ratio (S2 / S1) of the surface perpendicular to the traveling direction and the surface projected onto the projection surface is proportional to cos β. (3) When the diffusing element 130 generates the diffusing light group 12 in which the angles formed by the adjacent orders of diffracted light are approximately uniform, sin θ = mλ / P is established from the grating equation. The angle interval Δθ with the next order in 12 can be obtained from sin (θ + Δθ) = (m + 1) λ / P. If the second and higher order terms of Δθ are ignored, the above equation can be approximated by sin θ + Δθ cos θ = (m + 1) λ / P. Therefore, Δθ = λ / P / cos θ holds when the difference from the original equation is taken. Therefore, it can be seen that the diffraction angle near the angle β is 1 / cos β times larger than the angle interval Δθ = λ / P of the diffracted light near the center, and the density decreases in proportion to cos β.

It can be seen that due to the above (1) to (3), the number distribution of the diffused light group due to diffraction having an evenly distributed order distribution is proportional to cos ⁴ β with respect to the angle β measured from the optical axis. Therefore, the order distribution of the diffracted light included in the generated diffused light group 12 is set to the number of diffused light groups by diffraction applied to other portions of the same size with respect to the number of diffused light groups irradiated by diffraction near the center. If the ratio is adjusted so as to approach 1 regardless of the angle β, uniform illumination can be performed on the entire surface.

As shown in FIG. 7, since when the number distribution of the diffused light group by the diffraction when the incident parallel light is proportional to cos ⁴ beta, the number of the diffracted light in proportion to the cos ⁴ beta changes, For example, even if the incident light is expanded by making it divergent, the intensity distribution is proportional to cos ⁴ β.

The above description also holds for the diffusing element 130 having no periodicity. In this case, the intensity of the diffracted light in the range of wave number _{k x ~k x + 2π / P} x and the wave number _{k y ~k y + 2π / P} y, in the same manner as described above by replacing the eta _mn in equation (3) below Can think.

  Next, a method for arranging the designed basic unit will be described. Below, the case where a diffraction element as shown to Fig.3 (a) is used as a basic unit is demonstrated to an example.

  As the arrangement of the basic units, it is preferable to arrange two or more basic units that emit light beam groups having different projection patterns within the effective diameter of the incident light. Here, as described above, there are two methods for changing the projection pattern of the light beam group emitted from the basic unit. These two methods are expressed in the basic unit arrangement method as follows. That is, one is a method of arranging basic units having different uneven patterns within the effective diameter of incident light, and one is a similar uneven pattern when viewed in units, but the pitch at which each basic unit is arranged is This is a method of arranging at least within the effective diameter of incident light.

  Hereinafter, each arrangement method will be described. First, a method for arranging basic units having different concavo-convex patterns will be described.

  FIG. 9 is an explanatory diagram showing an example of a projection pattern by the basic unit of the diffraction element. Since the projection pattern by the basic unit of the diffractive element is a bright and dark pattern as shown in FIG. 9B, there are cases where light cannot be irradiated to all within the projection range. In such a case, it is possible to uniformly illuminate the projection plane by using a plurality of basic units that project different bright and dark patterns. For example, the basic unit having the projection pattern shown in FIG. 9B and the basic unit having the projection pattern shown in FIG. 9C are arranged within the effective diameter of the incident light as shown in FIG. 2B. As a result, the projection pattern on the projection plane is obtained by superimposing the projection pattern of FIG. 9B and the projection pattern of FIG. 9C as shown in FIG. In this case, the pitch of the uneven pattern in the surface, that is, the size of the basic unit may be the same or different. In addition, when changing a pitch, it becomes arrangement | positioning, for example to Fig.2 (a).

  When the pitch is varied as shown in FIG. 2A, the size of each basic unit can take an arbitrary value as long as the projection pattern is different. The processing width of the unevenness becomes small and processing becomes difficult. On the other hand, as the size of the basic unit increases, the ratio of the area occupied by one basic unit to the effective diameter increases, and therefore the effect of reducing variation in the light amount distribution of incident light decreases. Accordingly, the pitch of the uneven pattern, that is, the size of the basic unit is preferably 10 μm or more and 5 mm or less, and more preferably 100 μm or more and 2.5 mm or less.

Next, a description will be given of a method of arranging the concave and convex patterns that are similar when viewed in units, so that the pitch of the concave and convex patterns changes within at least the effective diameter of incident light. When parallel light is incident on the basic unit of the diffractive element, the electric field distribution of the emitted light by the basic unit can be calculated by the above formula (1). Since the integration range of Expression (1) is 0 to P _{xi in the} X-axis direction and 0 to P _{yi in the} Y-axis direction, the light rays emitted in the θ _x direction and θ _y direction are expressed by the following Expression (2 ) Can be rewritten. In equation (2), m ′ _x and m ′ _y are variables, and λ is the wavelength of incident light.

Here, m ′ _x and m ′ _y take integer values particularly when the Fourier transform is calculated by the fast Fourier transform. When m ′ _x and m ′ _y are integer values, the minimum angular interval of the diffracted light in the X-axis direction and the Y-axis direction is expressed as arcsin (λ, where m ′ _x and m ′ _y are 1, / P _xi ), arcsin (λ / P _yi ), and when the pitch is sufficiently larger than the wavelength λ, λ / P _xi and λ / P _yi are obtained.

In the above equation (1), U (x, y) represents the electric field after passing through the basic unit and reflects the uneven pattern of the basic unit. In the case of a concavo-convex pattern extended to ' _xi / P _xi times and P' _yi / P _yi times, the light rays emitted in the θ _x direction and θ _y direction due to the change in the pitch of the basic unit are expressed by the following formula (2b -2) and (as shown in 2b-2) θ _{'x-direction, theta'} to be emitted in the _y-direction. At this time, the minimum angular interval between the X-axis direction and the Y-axis direction of the diffracted light is arcsin (λ / P ′ _xi ) and arcsin (λ / P ′ _yi ), and the pitch is sufficiently larger than the wavelength λ. , Λ / P ′ _xi , λ / P ′ _yi .

  Therefore, the angular interval of the emitted light can be modulated by changing the size of the basic unit. FIG. 9 (d) schematically shows the effect of such modulation. By performing such modulation, each light beam can be projected at different positions between basic units of different sizes, and the projection surface can be illuminated uniformly by superimposing them.

By the way, if θ ′ _x = θ _x + Δθ _x and P ′ _xi = P _xi + ΔP _xi in the above equation (2b-1), then equation (2b-1) takes the first-order quantities of Δθ _x and ΔP _xi. Thus, Δθ _x ≈−m ′ _x λΔP _xi / (cos θ ′ _x P _xi ² ) = − tan θ ′ _x ΔP _xi / P _xi can be approximated. If the absolute value of this value is about half the value of λ / P _xi that is the angle interval, the light beam can be projected onto the median value of the angle interval, and uniformization on the projection surface is possible. Δθ _x depends on θ _x , and in the vicinity of θ _x = 0, Δθ _x = (− λ / P _xi ) × (ΔP _xi / P _xi ), which is the maximum Δθ _x . Therefore, the range of _{ΔP xi / P xi, ΔP xi} / P xi <0.5 is preferred. When there are a plurality of basic units, P _xi may be replaced with P _xavg . The average pitch of the basic units is preferably 10 μm or more and 5 mm or less, more preferably 100 μm or more and 2.5 mm or less, as described above. The above explanation can be applied to the pitch in the Y-axis direction based on the equation (2b-2).

  As the number of basic units having different projection patterns increases, the effect of superposition increases, and more uniform outgoing light can be obtained. Therefore, the number of basic units that project different projection patterns included within the effective diameter of incident light is preferably two or more, more preferably four or more, and even more preferably nine or more. In addition, when the incident light has an intensity distribution such as a Gaussian distribution, the degree to which the intensity distribution of the incident light affects the emitted light can be reduced by causing a plurality of basic units to act on the incident light. Therefore, regardless of whether the projection patterns are the same, the number of basic units included in the effective diameter of incident light is preferably two or more, more preferably four or more, and even more preferably nine or more.

  When a diffraction element as shown in FIG. 3A is used as a basic unit, the surface irregularities are generally complicated, and it may be difficult to determine the boundary of the basic unit. However, the above design is a design in which the effective diameter of incident light is divided into two or more regions, and a different projection pattern is obtained in each region. Therefore, in other words, the conditions relating to the number of the basic units can be said that the diffusing element 130 of the present embodiment is an element having regions where different projection patterns can be obtained within the effective diameter of incident light. At this time, it is only necessary to divide at least the effective diameter of the incident light into two or more regions and obtain different projection patterns in each region, and different projections when divided into four or more regions within the effective diameter. It is more preferable that a pattern is obtained, and it is more preferable that different projection patterns are obtained when the pattern is divided into nine or more regions within the effective diameter.

Although the case where the diffraction element is used as the basic unit has been described as an example, when the Fresnel lens structure as shown in FIG. 3B is used as the basic unit, the phase represented by Φ = Σa _i r ²ⁱ By performing ray tracing by geometric optics using the function Φ, the light emitted from the Fresnel lens can be kept in a range of θx _min and θx _{max in} the X-axis direction and θy _min and θy _max in the Y-axis direction. Here, r is the distance from the center of the Fresnel lens. The pitch Fp of each annular zone of the Fresnel lens can be obtained by Fp = 2π / (∂Φ / ∂r). When there is such an unevenness with the pitch Fp, the diffraction angle θ _out of the first-order diffracted light of the light incident at the incident angle θ _in can be obtained by sin θ _out = sin θ _in + λ / p. Therefore, each pitch _{Fp ymin} annular in pitch _{Fp xmin} and Y-axis direction of the ring-shaped zone in the X-axis direction at the edge of the basic _{unit, sin | θ xmax | = sinθ} in + λ / Fp xmin, sin | θ ymax | = It is only necessary to satisfy sin θ _in + λ / Fpy _ymin .

As described above, the design is such that the light emitted from the basic unit falls within the range of θx _min and θx _{max in} the X-axis direction and θy _min and θy _max in the Y-axis direction. .

By the way, when the single basic unit 31 is two-dimensionally arranged with a pitch P _{x in} the X-axis direction and a pitch P _{y in} the Y-axis direction, the emitted light flux becomes discrete, and such diffusion is performed. In the element, (m _x , m _y ) -order discrete diffracted light is generated. At this time, the diffraction efficiency η _mn of the (m _x , m _y ) _-order diffracted light is expressed by the following formula (3). _{Incidentally, m x,} m _y are integers.

At this time, the exit angle of the (m _x , m _y ) _-th order diffracted light can be expressed as the following formula (4). In equation (4), θ _xi is the incident angle to the diffusing element in the X-axis direction, θ _yi is the incident angle to the diffusing element in the Y-axis direction, θ _xo is the exit angle from the diffusing element in the X-axis direction, θ _yo is an exit angle from the diffusing element in the Y-axis direction. Further, in the equation _{(4), m x, m} y are integers.

  FIG. 10 is an explanatory diagram showing an example of a projection pattern when light is incident on a diffusing element in which basic units having the same Fresnel lens structure are periodically arranged. In FIG. 10, the size of each basic unit is 40 μm × 30 μm, and the projection when light is incident on a diffusing element in which Fresnel lenses with an emission angle of 30 ° in the horizontal direction and 24 ° in the vertical direction are periodically arranged. The pattern is shown. A discrete Fresnel lens does not result in a discrete projection pattern, but the periodicity causes interference on the projection surface, resulting in a discrete projection pattern as shown in FIG.

  When the basic units having the same projection pattern are periodically arranged as described above, the projection pattern of the entire element becomes discrete. Therefore, when the Fresnel lens structure as shown in FIG. 3B is arranged as a basic unit, the basic unit is changed by changing the focal length of the Fresnel lens, the center position of the Fresnel lens with respect to the center of the basic unit, and the like. Changes the projection pattern of the image to reduce the periodicity. In this case, the basic unit may be arranged as shown in FIG. Moreover, it is good also as arrangement | positioning as shown to Fig.2 (a) by changing the magnitude | size of a basic unit.

When changing the focal length of the Fresnel lens, the center position of the Fresnel lens with respect to the center of the basic unit, etc., the greater the amount of change, the more the periodicity can be reduced, but the amount of light emitted outside the projection range increases. Therefore, the amount of change is preferably within ± 50% and more preferably within ± 20% of the average value of all basic units for each parameter. In addition, it is preferable that the amount of change in the size of the basic unit is ΔP _xi / P _xi <0.5. Further, the average pitch of the basic units is preferably 10 μm or more and 5 mm or less, and more preferably 100 μm or more and 2.5 mm or less, as described above.

Further, when the basic unit is constituted by a diffraction grating as shown in FIG. The diffraction angle θ _out of the first-order diffracted light of the light incident at the incident angle θ _in is determined by sin θ _out = sin θ _in + λ / p, where p is the pitch of the unevenness of the diffraction grating. Therefore, the light ray calculated by the above equation may be set within the projection range. Note that in the case of a diffraction grating as shown in FIG. 3C, light cannot be projected onto the entire projection surface with only one type of basic unit, and therefore, multiple types of diffraction having different diffraction angles and diffraction directions. Arrange the grid as a basic unit. The arrangement may be an arrangement in which the pitch is changed as shown in FIG. 2 (a) or an arrangement in which the pitch is not changed as shown in FIG. 2 (b).

Even when the refractive lens is used as the basic unit, the projection pattern of the basic unit can be changed by changing the focal length of the refractive lens, the center position of the refractive lens with respect to the center of the basic unit, and the like. In this case as well, the greater the amount of change, the more the periodicity can be reduced.However, the amount of light emitted outside the projection range may increase, so these amounts of change are the same for all basic units for each parameter. The average value is preferably within ± 50%, and more preferably within ± 20%. Further, the projection pattern of the basic unit may be changed by changing the size of the basic unit. In this case, it is preferable that the amount of change in size is ΔP _xi / P _xi <0.5. In addition, the average pitch of the basic units is preferably 10 μm or more and 5 mm or less, and more preferably 100 μm or more and 2.5 mm or less, as described above.

As another guideline when designing the basic unit, when the detection element 50 is an image sensor, the projection plane irradiated by each basic unit in each area on the projection plane divided by the image sensor When the number of divided areas is N _i and the number of divided areas of the entire projection surface is N, the entire projection surface can be illuminated if ΣN _i > N. It is more preferable to satisfy ΣN _i > 1.2N because higher uniformity can be obtained when the output patterns of the basic unit overlap. Further, when the effective diameter of the light beam incident on the element is divided, and the number of the divided areas irradiated onto the projection plane by the projection pattern emitted from each divided area is M _i , ΣM _i > N. And it is more preferable that ΣM _i > 1.2N is satisfied. It can be considered in the same way using divided areas for applications that do not use an image sensor.

  As described above, if light emitted from each basic unit can be emitted substantially within the projection range, a diffusing element with high light utilization efficiency can be obtained. When the ratio of the amount of light incident on the diffusing element 130 and the total amount of light emitted from the diffusing element 130 is used efficiency, the utilization efficiency is preferably 60% or more, more preferably 70% or more, and 80%. The above is more preferable. Further, by including two or more basic units having different projection patterns within the effective diameter of the incident light, the influence of the periodicity of the basic units can be reduced, and the emission light can be prevented from being discretized. Furthermore, a highly uniform diffusion element can be obtained by superimposing different projection patterns. In addition, by providing such a diffusion element, it is possible to realize a small-sized measuring apparatus that can obtain accurate distance information.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a configuration diagram illustrating a configuration example of the measurement apparatus according to the present embodiment. In the following description, the same members and the like as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. A measuring apparatus 200 illustrated in FIG. 11 includes a light source 20, a diffusion element 230, and a detection element 50.

  Compared with the measurement apparatus 100 shown in FIG. 1, the difference is that a diffusion element 230 is provided instead of the diffusion element 130 and that the incident light 11 to the diffusion element is the incident light 11 '.

  When the incident light 11 ′ emitted from the light source 20 is incident, the diffusing element 230 generates the diffused light group 12 as inspection light. In addition, the detection element 50 detects the scattered light 13 that is generated when the inspection light composed of the diffused light group 12 emitted from the diffusion element 230 is irradiated onto the measurement objects 40a and 40b. The detection element 50 may be an imaging element for imaging the measurement objects 40a and 40b irradiated with the diffused light group 12 emitted from the diffusion element 230.

  The diffusing element 230 includes a portion having a diffusing action for generating a plurality of diffused lights, similarly to the diffusing element 130 of the first embodiment. However, in the present embodiment, incident light 11 ′ that is diverging light or convergent light is incident on the diffusing element 230 including the portion having such a diffusing action, and the diffused light group 12 is emitted from the diffusing element 230. A uniform illumination within a predetermined illumination range is realized. The projection range and the modulation of light from the light source are the same as in the first embodiment.

  Also in this embodiment, when the diffused light group 12 emitted from the diffusing element 230 is regarded as one light beam, the emission angle α of the light beam is preferably 7.5 ° or more, more preferably 15 ° or more, and 30 ° or more. Is more preferable. This enables measurement over a wide range.

  Next, the diffusion element 230 will be described more specifically. FIG. 12 is a schematic plan view illustrating a configuration example of the diffusion element 230 of the present embodiment. As already described, the diffusing element 230 of the present embodiment also includes two or more parts having different diffusing actions in the element surface. As shown in FIG. 12, the part includes two or more basic units 31 including two or more basic units having different phase distributions (for example, 31a, 31b, 31c, etc. as three basic units). This is realized by arranging in a dimension.

  In the present embodiment, the basic unit 31 is arranged so that the diffusion angle becomes smaller when parallel light is incident toward the outside from the optical axis of the incident light. In the example shown in FIG. 12, the basic unit 31a is disposed near the center of the element, and is irradiated with a light beam having a small incident angle among the incident light 11 '. In addition, the basic unit 31b is disposed in a peripheral portion of the element as compared with the basic unit 31a, and is irradiated with a light beam having a larger incident angle than the basic unit 31a. In addition, the basic unit 31c is disposed in a peripheral portion of the element as compared with the basic unit 31b, and is irradiated with a light beam having a larger incident angle than the basic unit 31b. Here, when parallel light is incident on each basic unit 31, the emission angle of the emitted light emitted from the basic unit 31a is larger than the emission angle of the emitted light emitted from the basic unit 31b, and is emitted from the basic unit 31b. The outgoing angle of the outgoing light is larger than the outgoing angle of the outgoing light emitted from the basic unit 31c.

  FIG. 13 is an explanatory view showing an example of the emitted light and its intensity distribution in the entire element when the outgoing angle of the outgoing light of the basic unit is adjusted according to the in-plane position and when it is not. FIG. 13A is an explanatory diagram schematically showing an example of the emitted light and the intensity distribution of the entire element when the emission angle of the emitted light of the basic unit is adjusted by the in-plane position. FIG. 13B is an explanatory diagram schematically showing an example of the emitted light and the intensity distribution of the entire element when the emission angle of the emitted light of the basic unit is not adjusted by the in-plane position. Note that FIGS. 13A and 13B show the case where divergent light is incident on the element.

The emission angle of each light beam included in the diffused light group 12 that is the emitted light from the entire element satisfies the relationship of the above-described formula (4). Therefore, for example, in the case of projecting to the emission range of the maximum angle θ _{xmax with} respect to the X-axis direction, if the incident angle of incident light incident on each basic unit is θ _xi and the following equation (5) is satisfied, FIG. As shown to 13 (a), the emitted light from each basic unit can be contained in a predetermined projection range, and the utilization efficiency of light can be made high.

That is, the structure of each basic unit may be determined so that emitted light having a minimum angle θ _xmin and a maximum angle θ _xmax is generated when incident light with a predetermined incident angle is incident on each basic unit.

  On the other hand, FIG. 13B shows an example of the diffusion element 930 in which one type of basic unit (31a in this example) is arranged on the entire surface of the element. In this case, in order to realize uniform illumination. When divergent light is incident so as to broaden the spot area of each diffracted light emitted from each basic unit, an oblique light beam is incident on the peripheral portion of the element, and thus a diffused light group 92 that is emitted light from the element A part of the light is irradiated outside the predetermined projection range, and the light use efficiency is lowered.

  In the diffusing element 230 of the present embodiment, basic units having a large emission angle such as the basic unit 31a in FIG. 13A may be periodically arranged in part. In this case, when parallel light is incident, a spot pattern due to diffraction may be generated due to the influence of periodicity. However, as a method for suppressing the influence of such diffraction, the spread angle of incident light may be sufficiently increased. Diffracted light due to periodicity is emitted according to the following equation (6).

For this reason, the interval of the diffracted light is arcsin (λ / P _x ) in the X-axis direction and arcsin (λ / P _y ) in the Y-axis direction. Therefore, the divergence angle φ of the incident light is preferably φ> MIN (arcsin (λ / P _x ), arcsin (λ / P _y )) / 2 in order to fill the gap of the generated diffracted light, and φ> MIN (arcsin). (Λ / P _x ) and arcsin (λ / P _y )) are more preferable. MIN (,) is a function that returns the smallest value among the numerical values in ().

  As the basic unit 31, the same unit as in the first embodiment can be used. Although FIG. 12 shows a case where three types of basic units 31a, 31b, 31c having different emission angles are used, the number of divisions of the basic unit for each incident angle may be increased or decreased. In addition, the basic unit 31 having the same concave / convex pattern with respect to a certain incident angle is not limited to the case, and a plurality of basic units 31 having a concave / convex pattern having substantially the same emission angle may be used. In this way, the influence of periodicity can be reduced, and the influence of diffraction can be reduced even when the divergence angle φ of incident light is small.

Next, a method for designing the diffusing element 230 of this embodiment will be described. In the present embodiment, first, the incident angle of the diverging light 11 ′ incident on the diffusing element 230 is obtained for each position on the diffusing element 230. If the distance between the light emitting point of the diverging light and the diffusing element 230 is z _in , and the position on the diffusing element 230 is (x, y), the incident angle θ _xi in the X-axis direction and the incident angle θ _{yi in the} Y-axis direction are ^{_{sinθ xi = x / (x 2}} + y 2 + z in 2) 0.5, the ^{_{sinθ yi = y / (x 2}} + y 2 + z in 2) 0.5.

After determining the incident angle at each position in this way, it is determined what kind of emission angle the basic unit is arranged at each position of the diffusing element 230 according to the incident angle. The outgoing light emitted from each basic unit can be calculated by the above-described equation (1). Further, emission angle in the X-axis direction of the emission angle theta _xo and Y-axis direction when the light beam incident angle theta _yi incident angle theta _xi and Y-axis direction similarly X-axis direction and the above equation (2) is incident θ _yo can be described as the following equation (7). In Equation (7), m ′ _x and m ′ _y are variables, and λ is the wavelength of incident light.

Then, the basic units 31 arranged at the respective positions are set to m ′ _xmin and m ′ _ymin which are the minimum values of m ′ _x and m ′ _y obtained from the equation (7), and m ′ _xmax and m ′ _ymax which are the maximum values. On the other hand, it designs so that the above-mentioned formula (6) may be satisfied. Thereby, light can be efficiently projected within the projection range. Note that the same basic unit may be used in regions having the same incident angle as long as Expression (6) is satisfied.

  As an example of the design and arrangement of each basic unit, the surface of the element is divided into regions where the incident angle is 0 ° to 5 °, 5 ° to 10 °, 10 ° to 15 °, 15 ° or more, for example. A basic unit that satisfies the above formula (6) may be designed and arranged for the region. In this case, the emission angle of the basic unit is smaller in the region where the incident angle is large than in the region where the incident angle is small. The division of the incident angle is preferably 2 or more, and more preferably 4 or more. For example, if the number of incident angle divisions is two or more, the basic unit 31 having at least two kinds of emission angles may be designed according to the incident angle.

  As another example, there is a method of displacing the optical axis of the refractive lens or the Fresnel lens in the basic unit in the optical axis direction of incident light for each region divided according to each position or incident angle. FIG. 14 is an explanatory diagram showing an example of emitted light when the optical axis of the lens is displaced for each region, taking a refractive lens as an example. In FIG. 14A, an example of outgoing light when divergent light is incident in an example in which the optical axis of a refractive lens arranged at a position where incident light is incident obliquely is displaced to the optical axis side of incident light. Is schematically shown. FIG. 14B schematically shows an example of emitted light when parallel light is incident in the example shown in FIG.

  FIGS. 14A and 14B show an example in which the optical axis of the refractive lens disposed at a position where incident light is incident obliquely is displaced toward the optical axis side of the incident light. As indicated by the one-dot chain line in FIG. 14A, when the diverging light 11 ′ is incident on the diffusing element 230 of this example, the center of the obliquely incident light beam is emitted in a direction that coincides with the optical axis of the incident light. The In this way, it is possible to project light onto the projection range around the light beam that becomes the one-dot chain line. Note that the amount of displacement of the center position of such a refractive lens can be calculated using ray tracing.

Further, as shown in FIG. 14B, the diffusing element 230 of the present example has a diffusion angle ζ _b when parallel light is incident on the basic unit 31b arranged outside the optical axis of the incident light, Comparing with the diffusion angle ζ _a when parallel light is incident on the basic unit 31 a arranged at a position including the optical axis of the incident light, it can be seen that ζ _b <ζ _a . Similarly, the diffusion angle ζ _c when parallel light is incident on the basic unit 31c arranged outside the optical axis of the incident light, and the basic unit 31a arranged at a position including the optical axis of the incident light. Comparing the diffusion angle ζ _a when parallel light is incident, it can be seen that ζ _c <ζ _a . In the case of a basic unit having a refracting lens or a Fresnel lens structure, the diffusion angle in the direction toward the outside with respect to the optical axis of the incident light when parallel light is incident as it goes outward from the optical axis of the incident light is The diffusion angle under the condition “become smaller” refers to the angle in the direction toward the outside with respect to the optical axis of the incident light, as indicated by the arrow attached to the ζ symbol in FIG.

As another example, a phase function Φ (x, y) that makes incident light parallel light and a phase distribution Ψ _i (x−) of each basic unit that emits light within the projection range when the parallel light is incident. x _{i_center} , _{yy i_center} ) is _added . The phase function Φ (x, y) is the phase distribution of the Fresnel lens centered on the optical axis of the incident light, and is shown, for example, in FIG. In FIG. 15A, the phase is binary, but it is preferable to have a phase of 4 or more because the diffraction efficiency can be increased. Further, the phase distribution Ψ _i of the basic unit is, for example, various types such as FIG. 3A, FIG. 3B, and FIG. 3C centering on the center coordinates (x _{i_center} , y _{i_center} ) of each basic unit. Can be used. FIG. 15A is an explanatory diagram showing an example of the phase function Φ, and FIG. 15B is an explanatory diagram showing an example of the phase distribution Ψ _i of each basic unit on the element. FIG. 15B schematically shows an example in which the basic units having the phase distribution shown in FIG. 3A are two-dimensionally arranged. A broken line in FIG. 15B represents the boundary position of the basic unit. The phase distribution Ψ _i of the basic unit is not limited to one type. 15A and 15B separately show the phase distribution of the phase function Φ and the phase distribution Ψ _i of each basic unit at the time of parallel light incidence. The phase wavefront is obtained by superimposing FIG. 15 (a) and FIG. 15 (b). When incident light is incident obliquely, each basic unit has a direction that coincides with the optical axis of the incident light, as indicated by a one-dot chain line in FIG. 14A, due to the phase generated by the phase function Φ (x, y). Can emit light. _Further , light can be projected onto the projection range by the phase distribution Ψ _i (xx _{i_center} , _{yy i_center} ) of the basic unit.

  By designing each basic unit according to the design method as described above, the light beams of two or more different emission patterns can be superimposed on the projection surface, so that more uniform projection light can be obtained. In the diffusing element 230 of the present embodiment, similarly to the first embodiment, the light distribution by the diffusing light group 12 on the projection surface 40c takes into account the pincushion type distortion and the like, and the diffusing light group It is preferable to correct the intensity distribution on the 12 projection planes. The correction of the intensity distribution may be performed by calculation at the design stage of each basic unit, or the correction amount may be calculated from the result of actual projection and fed back to the design value, or a combination of these may be used. May be.

  Also in this embodiment, it may be difficult to determine the boundary of the basic unit. However, it can be said that the diffusing element 230 of the present embodiment is an element that becomes smaller as the emission angle in the positive direction becomes farther away from the element when the direction away from the optical axis of the element is a plus direction when parallel light is incident. This property is not limited to the example shown in FIG. 14, but is a property that the diffusion element 230 of the present embodiment has in common.

  Further, the incident light 11 ′ to the diffusing element 230 in the present embodiment may be convergent light as long as it has a spread with respect to the traveling direction when projected onto the measurement object. For example, the convergent light having a condensing position between the diffusing element 230 and the projection surface 40c can be the incident light 11 '. When the light incident on the concavo-convex pattern layer 35 is convergent light, the distribution of the diffusion angle of the basic unit in the plane when the parallel light is incident on the diffusion element 230 goes outward from the optical axis of the incident light. Accordingly, each basic unit 31 may be arranged so that the diffusion angle in the direction toward the inner side with respect to the optical axis of the incident light when parallel light is incident becomes smaller.

  As a method of making the incident light 11 ′ a divergent light or a convergent light, a diffractive lens such as a lens or a Fresnel lens is arranged on the incident side of the diffusing element 230, and the spread angle φ of the incident light 11 ′ to the diffusing element 230 is set. You may adjust. In addition to the diffractive lens, a diffusion plate having a predetermined diffusion angle may be used. Further, a diffractive optical element or a hologram element may be used.

  In addition to the method in which the incident light 11 ′ is diverged light or convergent light, an element that changes the spread angle of light, such as a diffusion plate, may be disposed on the incident side of the diffusing element 230. In such a case, the incident light 11 'can be parallel light. Further, even when diverging light or convergent light is incident on the diffusing element 230, these elements may be arranged on the incident side of the diffusing element 230 so that the spread angle of the incident light 11 ′ can be adjusted. .

  Further, as shown in FIGS. 16A to 16C, an element having such a diverging function or a converging function and the diffusing element 230 may be integrally formed. In the example shown in FIG. 16A, the concave lens 36a and the diffusing element 230 are integrated, and the concavo-convex pattern having different diffusing action for each region as described above on one surface (outgoing side) of the transparent substrate 32. The layer 35 is formed, and a concave lens 36a that imparts a divergence function is formed on the other surface (incident side). In the example shown in FIG. 16B, a convex lens type Fresnel lens 36b and a diffusing element 230 are integrated, and a converging function is given to the incident side surface instead of the concave lens 36a shown in FIG. A convex lens type Fresnel lens 36b is formed. In the example shown in FIG. 16C, the diffusing plate and the diffusing element 230 are integrated, and a diffusing plate 36c is formed on the incident side surface instead of the concave lens 36a shown in FIG. . When the element having the divergence function or the convergence function and the diffusing element 230 are integrated, the incident light 11 ′ to the diffusing element 230 may use parallel light. The concave lens 36a, the Fresnel lens 36b, and the diffusion plate 36c may be formed by processing the transparent substrate 32, or may be provided by processing a transparent material different from the transparent substrate 32 on the transparent substrate 32.

  In each of the above embodiments, an example is shown in which a diffusing element that realizes uniform illumination within a predetermined emission angle range is applied to a measuring apparatus, but the application destination of the diffusing element of the present invention is not limited to the measuring apparatus. For example, the present invention can be applied to a processing machine that processes a member by irradiating light within a predetermined emission angle range.

  Hereinafter, the diffusion elements 130 and 230 described above will be described using specific numerical values and the like. The diffusion elements in the following examples have a desired irradiation range of ± 30 ° in the horizontal direction and ± 23.4 ° in the vertical direction. Here, Examples 1 and 2 are examples, and Example 3 is a comparative example.

(Example 1)
Hereinafter, a first example will be described. The diffusing element 130 of this example is obtained by processing quartz into a two-step concavo-convex shape, and the basic unit 31 is two-dimensionally arranged in a 4 mm × 3 mm region. In this example, as each basic unit 31, a diffractive element having a two-dimensional concavo-convex structure as in the example shown in FIG. 3 (a) is used, and the arrangement is a pitch within the plane as shown in FIG. 2 (a). Are different.

  Each basic unit is designed such that the range of the emission angle calculated by the above equation (1) is ± 30 ° in the horizontal direction and ± 23.4 ° in the vertical direction. Specifically, each basic unit has a phase distribution that emits light that becomes one of the nine projection patterns shown in FIGS. 17A to 17I when Fourier transformed. Each of these projection patterns is composed of 10,000 dot patterns. In this example, nine different projection patterns are designed by generating random numbers with a computer. In any of the projection patterns, an inclination is given to the probability of occurrence of spots so that the number of spots is more than double around the center of each projection pattern. In this example, a method based on the iterative Fourier transform is used as a method for obtaining the phase distribution of the basic unit from the projection pattern.

  Each basic unit is arranged with its size modulated such that the pitch in the X-axis direction is 250 μm ± 4 μm and the pitch in the Y-axis direction is 250 μm ± 4 μm. FIG. 18 is an explanatory diagram showing the arrangement of basic units in the diffusing element 130 of this example. The basic units in the diffusing element 130 of this example are arranged as shown in FIG. In FIG. 18, alphabets a to i indicate the alphabets of the projection patterns shown in FIGS. 17 (a) to 17 (i). Each pattern is randomly arranged in the element. FIG. 18B shows an enlarged part of the lower right of the arrangement shown in FIG. As shown in FIG. 18B, the basic units are arranged such that the pitch in the X-axis direction is any one of 246 μm, 250 μm, and 254 μm, and the pitch in the Y-axis direction is any of 246 μm, 250 μm, and 254 μm.

  The manufacturing method of the diffusing element 130 of this example is as follows. First, the concavo-convex pattern for realizing the phase distribution of each basic unit is determined. Thereby, the in-plane uneven pattern is determined. Next, a quartz substrate is used as the transparent substrate 32, and a resist pattern corresponding to the determined uneven pattern is formed on the surface of the quartz substrate 32. Then, dry etching such as RIE (Reactive Ion Etching) is performed on the resist pattern to form the concave / convex pattern layer 35 on the surface of the quartz substrate 32.

  The black pattern shown in FIG. 19 is an image of the distribution of diffused light projected on a certain surface installed for detecting the light intensity when parallel light having a wavelength of 830 nm is incident on the diffusing element 130 of this example. It is what. The installed surface has a larger area than the desired projection surface. As shown in FIG. 19, in this example, no spot-like pattern is observed in the projection plane, and the entire projection plane can be illuminated. FIG. 20 shows the intensity distribution of the cross section in the horizontal direction in FIG. The intensity distribution shown in FIG. 20 is the intensity when the cross section is divided into 2500, and the unit of intensity is arbitrary. In FIG. 20, the average value of the intensity from the position 200 to the position 2250 corresponding to the edge of the horizontal region of the projection plane is 215, and the minimum value is 101. Thereby, it can be seen that the intensity of light in each region is 47% or more of the average value. The utilization efficiency of light within the projection range was 73%.

(Example 2)
Hereinafter, a second example will be described. The diffusion element 230 of this example is obtained by processing quartz into a two-step uneven shape, and the basic unit 31 is two-dimensionally arranged in a 3 mm × 4 mm region. In this example, a diffractive element having a two-dimensional concavo-convex structure as in the example shown in FIG. 3A is used as each basic unit. In the diffusion element 230 of this example, incident light having a full width at half maximum of the emission angle in the X axis direction of 8 ° and an incident light having a full width at half maximum of the emission angle in the Y axis direction of 16 ° is incident. It is used for the measuring apparatus 200 in which the distance between the light emitting points is 4 mm. In such an arrangement, the incident angle of the light beam incident on the surface of the diffusing element 230 of this example is as shown in FIG.

  FIG. 21 is an explanatory diagram showing a distribution of incident angles of incident light in the plane of the diffusing element 30 of this example. In FIG. 21, the in-plane is divided into 12 × 16 areas, and the incident angle distribution in the element plane is represented by indicating the incident angles of the divided areas.

  Each basic unit is arranged so that the diffusion angle when parallel light is incident on the four regions divided according to the incident angle shown in FIG. 21 is different. More specifically, as surrounded by a thick line in FIG. 21, the in-plane region includes a first region having an incident angle of 5 ° or less, a second region having 5 ° or more and 10 ° or less, and 10 ° or more and 15 °. It is divided into four regions, the following third region and a fourth region of 15 ° or more, and the size relationship of the diffusion angle when the parallel light is incident on the basic unit arranged in each region is expressed as follows: First region> Second region> One of the following four types of basic units is arranged with a pitch in the X-axis direction of 250 μm and a pitch in the Y-axis direction of 250 μm so that the third region> the fourth region. .

  Specifically, each basic unit has a phase distribution of a diffractive element that emits light that becomes one of the four projection patterns shown in FIGS. 22A to 22D when Fourier transformed. . In the first area, the basic units 31 having the phase distribution shown in FIG. 22A are arranged at the above-mentioned pitch, and in the second area, the basic units 31 having the phase distribution shown in FIG. The basic units 31 having the phase distribution shown in FIG. 22 (c) are arranged in the third area at the above pitch, and the basic units having the phase distribution shown in FIG. 22 (d) are arranged in the fourth area. Units 31 are arranged at the pitch described above. 22A to 22D, the projection pattern shown in FIG. 22A has the largest emission range, and the projection pattern shown in FIG. 22D has the most emission range. Is narrower. In this example, a method based on the iterative Fourier transform is used as a method for obtaining the phase distribution of the basic unit from the projection pattern.

  When the wavelength of incident light is set to 830 nm in each region, a table in which the maximum emission angles in the X-axis direction and the Y-axis direction and the maximum value of the right side of the above equation (6) are obtained is shown below. In Table 1 below, the maximum diffraction angle corresponding to each incident angle calculated from the above equation (5) is shown as the maximum emission angle. In each region, the maximum emission angles in the X-axis direction and the Y-axis direction are 23.4 ° and 30 °, respectively, and it can be seen that light can be efficiently projected into the projection region even if the incident light is divergent light.

  The manufacturing method of the diffusing element 230 of this example is the same as that of the first example. That is, first, a concavo-convex pattern for realizing the phase distribution of each basic unit is determined. Thereby, the in-plane uneven pattern was determined. Next, a quartz substrate was used as the transparent substrate 32, and a resist pattern corresponding to the determined uneven pattern was formed on the surface of the quartz substrate 32. Then, dry etching such as RIE was performed on the resist pattern to form an uneven pattern layer 35 on the surface of the quartz substrate 32.

  The black pattern shown in FIG. 23 is an image of the distribution of diffused light projected on a certain surface installed for light intensity detection when divergent light having a wavelength of 830 nm is incident on the diffusing element 230 of this example. It is what. As shown in FIG. 23, in this example, a spot-like pattern is not observed in the projection plane, and the entire projection plane can be illuminated. FIG. 24 shows the intensity distribution of the cross section in the vertical direction in FIG. The intensity distribution shown in FIG. 24 is the intensity when the cross section is divided into 3000, and the unit of intensity is arbitrary. In FIG. 24, the average value from position 500 to position 2500 corresponding to the edge of the vertical area of the projection plane is 77, the minimum value is 42, and the intensity of light in each area is 55% of the average value. That was all.

(Example 3)
Hereinafter, a third example will be described. The diffusion element 930 of this example is a comparative example to the first example described above, in which quartz is processed into a two-step uneven shape, and the pitch in the X-axis direction is 502 μm within a 2 mm × 2.5 mm region. A single basic unit 31 having a pitch in the Y-axis direction of 477 μm is two-dimensionally and periodically arranged.

  Each basic unit 31 included in the diffusing element 930 of the present example has a range of emission angles calculated in the above-described equation (1) of ± 30 ° in the horizontal direction and ± 23.4 ° in the vertical direction as in the first embodiment. It is designed to be. Specifically, one diffractive element that projects a random pattern on the projection plane is designed and used as the basic unit 31. The phase distribution of the basic unit was obtained by iterative Fourier transform.

  The manufacturing method of the diffusing element 930 of this example is the same as that of the first example. That is, first, a concavo-convex pattern for realizing the phase distribution of each basic unit is determined. Thereby, the in-plane uneven pattern is determined. Next, a quartz substrate is used as the transparent substrate 32, and a resist pattern corresponding to the determined uneven pattern is formed on the surface of the quartz substrate 32. Then, dry etching such as RIE is performed on the resist pattern to form an uneven pattern layer 35 on the surface of the quartz substrate 32.

  The black pattern shown in FIG. 25 is an image of the distribution of diffused light projected on a certain surface installed for detecting the light intensity when parallel light having a wavelength of 830 nm is incident on the diffusing element 930 of this example. It is what. As shown in FIG. 25, in this example, a spot-like pattern is generated in the projection plane due to the periodicity of the basic unit, and an area where light is not irradiated is generated on a part of the projection plane. FIG. 26 shows the intensity distribution of the cross section in the horizontal direction in FIG. The intensity distribution shown in FIG. 26 is the intensity when the cross section is divided into 2500, and the unit of intensity is arbitrary. In FIG. 26, the average value of the intensity from the position 200 to the position 2250 corresponding to the edge of the horizontal area of the projection plane is 120, and the minimum value is 21. Thereby, it is understood that the light intensity in the region showing the minimum value is 18% with respect to the average value. The utilization efficiency of light within the projection range was 72%.

  The present invention can be applied not only to a measuring apparatus, but also to applications where it is desired to efficiently and uniformly irradiate light within a specific range.

100, 200 Measuring device 11, 11 ′ Incident light 12 Diffused light group (inspection light)
13 Scattered light 20 Light source 130, 230 Diffusing element 40a, 40b, 40c Measurement object (including projection surface)
50 Detection elements 31, 31a, 31b, 31c Basic unit 32 Transparent substrate 33 Convex part 34 Concave part 35 Concave pattern layer 36 Lens part 36a Concave lens 36b Fresnel lens 36c Diffusion plate

Claims (9)

A diffusing element that emits light within an emission angle range determined according to a predetermined projection plane,
A concavo-convex pattern layer that is a layer including a structure that imparts a phase difference to incident light,
The uneven pattern layer is
The region within the effective diameter of the incident light to the diffusion element is divided into two or more regions, and has a phase distribution that emits different diffused light when light is incident on each region ,
An emission angle measured from the diffusion element with respect to a position on the projection surface is β, and a light amount distribution normalized by the light amount at the center when the light emitted from the diffusion element is projected onto the projection surface Is I (β), at least a part of the projection surface satisfies the following expression:
cos ⁴ β <I (β) <1 / cos ⁴ β
A diffusion element characterized by that. When the projection surface is divided into 200 or more regions in the horizontal direction and the vertical direction, the intensity of light emitted from the diffusion element measured in each region is an average value of the intensity on the projection surface. The diffusion element according to claim 1, wherein the diffusion element is 0.25 times or more. The concavo-convex pattern layer is formed by arranging basic units that emit diffused light within the emission angle range when each light is incident thereon,
The diffusing element according to claim 1 or 2, wherein the array includes two or more basic units having at least different unit sizes or phase distributions within the units. The uneven pattern layer, the diffusion element as claimed in any one of claims 3, including an uneven structure having two or more different surface heights. The uneven pattern layer, the diffusion element as claimed in any one of claims 3, including a structure having a curved surface. A diffusing element that emits light within the emission angle range when diverging light enters,
The concavo-convex pattern layer is a light emitted from each region when a region within the effective diameter of incident light to the diffusion element is divided into two or more regions and parallel light is incident on each region. according to any one of claims 1 to 5 which has a phase distribution which emits smaller diffused light according diffusion angle from the optical axis toward the outside going outwardly from the optical axis of the incident light Diffusion element. The diffusing element according to any one of claims 1 to 6 , wherein an emission angle of a light beam composed of a diffused light group emitted from the diffusing element is 7.5 ° or more. An illumination optical system for irradiating a predetermined projection surface with light,
A diffusion element that emits light within a predetermined emission angle range determined according to the projection plane when light is incident;
The illumination optical system, wherein the diffusion element is the diffusion element according to any one of claims 1 to 7 . An illumination optical system that emits inspection light toward a predetermined projection surface;
A detection unit that detects scattered light generated by irradiating the measurement object with inspection light emitted from the illumination optical system;
The illumination optical system includes:
A light source that emits light;
A diffusion element that emits light within a predetermined emission angle range determined according to the projection plane when the light emitted from the light source is incident;
The diffusing element is the diffusing element according to any one of claims 1 to 7 ,
The detection unit detects scattered light generated by irradiating the measurement object with the inspection light using the light emitted from the diffusion element as the inspection light.

Images