Method for measuring beam divergence angle

Abstract

An optical material (3) having a parallel flat with a thickness L and a refractive index n is inserted between a light source (1) and a camera (2) at a distance d apart, and the radius w of a light beam from the light source (1) that is irradiated to the camera (2) via the optical material (3) is found. The light beam divergence angle is found by the following relation.

Description

Technical Field

[0001] This disclosure relates to a method for measuring the beam divergence angle. Background Technology

[0002] A beam divergence angle is measured by capturing a beam emitted from a light source such as a laser diode using an imaging device. However, the beam size increases with the divergence angle, thus requiring a larger imaging area for the imaging device. Therefore, a lens is used to converge the beam and illuminate the imaging device (see, for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 07-066472

[0004] However, the beam divergence angle changes due to the lens, so the distance between the light source and the lens, the focal length of the lens, and other factors need to be considered. Therefore, calculating the beam divergence angle becomes more difficult. Summary of the Invention

[0005] This disclosure is made to solve the aforementioned problems, and its purpose is to provide a method for measuring the beam divergence angle that can be calculated simply.

[0006] The method for measuring the beam divergence angle disclosed herein is characterized by comprising the following steps:

[0007] The process of inserting an optical material of thickness L and refractive index n, a parallel plate, between a light source and an imaging device at a distance d, and determining the radius w of the light beam illuminating the imaging device from the light source through the optical material; and

[0008] The beam divergence angle can be calculated using the following formula. The process,

[0009] .

[0010] In this disclosure, the beam divergence angle is determined by inserting a parallel plate of optical material between the light source and the imaging device. Even when the beam passes through the parallel plate of optical material, the beam divergence angle remains unchanged before and after passing through. Furthermore, it is independent of the position of the optical material placed between the light source and the imaging device. Therefore, compared to the case where a lens is used, the beam divergence angle can be determined through simple calculation. Attached Figure Description

[0011] Figure 1 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 1.

[0012] Figure 2 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 1.

[0013] Figure 3This is a diagram illustrating the beam divergence angle measurement method of Embodiment 1.

[0014] Figure 4 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 2.

[0015] Figure 5 This is a diagram comparing the calculation formula and its approximation for Implementation Method 2.

[0016] Figure 6 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 3.

[0017] Figure 7 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 4.

[0018] Figure 8 This is a diagram comparing the calculation formula and its approximation in Implementation Method 4.

[0019] Figure 9 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 5.

[0020] Figure 10 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 6. Detailed Implementation

[0021] The method for measuring the beam divergence angle of the embodiment will be described with reference to the accompanying drawings. The same or corresponding components are labeled with the same reference numerals, and sometimes repeated descriptions are omitted.

[0022] Implementation method 1.

[0023] Figures 1-3 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 1.

[0024] First, such as Figure 1 As shown, a CCD camera or similar imaging device 2 is placed at a distance d from a light source 1, such as a laser diode. The shape of the light beam illuminating the imaging device 2 from the light source 1 is measured when no object is placed between the light source 1 and the imaging device 2. If the optical axis of the light beam from the light source 1 is not perpendicular to the imaging surface of the imaging device 2 but is tilted, the intensity distribution of the light beam is biased to the left or right, and therefore the beam shape becomes asymmetrical. Therefore, the tilt of the optical axis of the light source 1 relative to the imaging device 2 is adjusted by rotating the light source 1 to make the beam shape symmetrical. As a result, the light beam is incident perpendicularly onto the imaging surface of the imaging device 2.

[0025] Next, determine the center P of the light beam captured when no object is placed between light source 1 and imaging device 2. Then, as... Figure 2As shown, an optical material 3 is inserted between the light source 1 and the imaging device 2. The optical material 3 is a parallel plate, with an anti-reflective film 4 coated on both the incident and emitting surfaces. The thickness of the optical material 3 is L, and its refractive index is n.

[0026] The tilt of the optical material 3 is adjusted so that the center P' of the light beam that shines from the light source 1 through the optical material 3 onto the imaging device 2 is consistent with the center P of the light beam captured when no object is placed between the light source 1 and the imaging device 2. This causes the light beam to be incident perpendicularly onto the incident surface of the optical material 3.

[0027] Next, as Figure 3 As shown, calculate the radius w of the light beam that travels from light source 1 through optical material 3 to imaging device 2. The diameter of the light beam is 1 / e of the beam intensity at the beam center. 2 Position definition.

[0028] With the insertion of optical material 3, the tandem distance from light source 1 to imaging device 2 and the beam size... -1 Beam divergence angle Since it is 1 / 2, the following relationship holds. Therefore, the beam divergence angle can be calculated using the following relationship. .

[0029]

[0030] Here, at the divergence angle In the case of small values, it can be approximated as sin ≒ tan ≒ In this situation (e.g.) In the case of <30°, the beam divergence angle can be obtained by the following approximation. .

[0031]

[0032] As explained above, in this embodiment, an optical material 3 with a refractive index n is inserted between the light source 1 and the imaging device 2, thereby determining the beam divergence angle. The refractive index n of optical material 3 is greater than 1, thus reducing the beam size by inserting optical material 3. Therefore, it is not necessary to increase the imaging area of ​​imaging device 2 based on beam divergence. Furthermore, even when the beam passes through the parallel plate optical material 3, the beam divergence angle remains unchanged before and after passing through. Moreover, the beam size on the illumination surface of imaging device 2 is independent of the position of optical material 3 placed between light source 1 and imaging device 2. Therefore, compared to the case where a lens is used, the beam divergence angle can be calculated simply.

[0033] Implementation method 2.

[0034] Figure 4 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 2. First, as in Embodiment 1... Figure 1 As shown, the tilt of the optical axis of the light beam from light source 1 is adjusted so that the light beam is incident perpendicularly on the imaging surface of imaging device 2. Next, the radius w1 of the light beam from light source 1 to imaging device 2 is calculated when no object is placed between light source 1 and imaging device 2.

[0035] Next, an optical material 3 with a thickness of L and a refractive index of n is inserted between the light source 1 and the imaging device 2, such as... Figure 2 As shown, the tilt of optical material 3 is adjusted so that the light beam is incident perpendicularly onto the incident surface of optical material 3. Then, as... Figure 4 As shown, calculate the radius w2 of the light beam that travels from the light source 1 through the optical material 3 to the imaging device 2.

[0036] The beam divergence angle changes as the beam travels through optical material 3 of length L, and returns to its original angle upon exiting optical material 3. Therefore, the following relationship holds depending on the presence or absence of optical material 3. Thus, the beam divergence angle can be calculated using the following relationship. .

[0037]

[0038] Here, at the divergence angle In the case of small values, it can be approximated as sin ≒ tan ≒ In this case, the beam divergence angle is obtained using the following approximation. . Figure 5 This is a diagram comparing the calculation formula and its approximation for Implementation Method 2. At the beam divergence angle... When the angle is less than 30°, the calculation results of the above formula are roughly consistent with the calculation results of the approximation formula.

[0039]

[0040] Therefore, in this embodiment, an optical material 3 with a refractive index n is inserted between the light source 1 and the imaging device 2, and the beam divergence angle is calculated based on the difference in beam radius before and after insertion. Therefore, the beam divergence angle can be calculated without relying on the distance between the light source 1 and the imaging device 2 while keeping the imaging device 2 fixed. The accuracy of the distance between the light source 1 and the imaging device 2 is relatively poor; therefore, this embodiment enables the high-precision calculation of the beam divergence angle. The other structures and effects are the same as in Implementation Method 1.

[0041] Implementation method 3.

[0042] Figure 6 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 3. The optical material 3 has a uniform refractive index n and is a stepped structure formed by connecting parallel plates of thicknesses L1, L2, and L3. However, L1 < L2 < L3.

[0043] First, as in implementation method 1 Figure 1 As shown, the tilt of the optical axis of the light beam from light source 1 is adjusted so that the light beam is incident perpendicularly onto the imaging surface of imaging device 2. Figure 2 As shown, the tilt of the optical material 3 is adjusted so that the light beam is incident perpendicularly onto the incident surface of the optical material 3. Next, a portion of the optical material 3 with a thickness of L1 is inserted between the light source 1 and the imaging device 2, and the radius w1 of the light beam irradiated from the light source 1 through this portion onto the imaging device 2 is calculated.

[0044] Next, as Figure 6 As shown, a portion of optical material 3 with a thickness of L2 is inserted between the light source 1 and the imaging device 2. The radius w2 of the light beam irradiated from the light source 1 to the imaging device 2 through this portion is calculated.

[0045] Based on the difference in thickness of optical material 3, the following relationship holds. Therefore, the beam divergence angle can be calculated using the following relationship. .

[0046]

[0047] Here, at the divergence angle In the case of small values, it can be approximated as sin ≒ tan ≒ In this situation (e.g.) In the case of <40°, the beam divergence angle can be obtained by the following approximation. .

[0048]

[0049] Therefore, in this embodiment, the beam divergence angle is determined based on the difference in beam radius when light passes through portions of different thicknesses. Therefore, the beam divergence angle can be calculated without depending on the distance between the light source 1 and the imaging device 2 while keeping the imaging device 2 fixed. .

[0050] Furthermore, a portion of optical material 3 with a thickness of L3 is inserted between the light source 1 and the imaging device 2, and the radius w3 of the light beam illuminating the light source 1 through this portion onto the imaging device 2 is calculated. The following formulas hold true for the thicknesses L2 and L3.

[0051]

[0052] By eliminating the refractive index n based on the calculation formulas for thicknesses L1 and L2, and for thicknesses L2 and L3, the beam divergence angle can be calculated independently of the refractive index n. By increasing the number of segments and calculating from multiple points, higher accuracy results can be obtained. The other structures and effects are the same as in Implementation Method 1.

[0053] Implementation method 4.

[0054] Figure 7 This is a diagram illustrating the beam divergence angle measurement method of Embodiment 4. The optical material 3 is a parallel plate made by bonding materials having a uniform thickness L and different refractive indices n1, n2, and n3 together. However, n1 < n2 < n3.

[0055] First, as in implementation method 1 Figure 1 As shown, the tilt of the optical axis of the light beam from light source 1 is adjusted so that the light beam is incident perpendicularly onto the imaging surface of imaging device 2. Figure 2 As shown, the tilt of the optical material 3 is adjusted so that the light beam is incident perpendicularly onto the incident surface of the optical material 3. Next, a portion of the optical material 3 with a refractive index n1 is inserted between the light source 1 and the imaging device 2, and the radius w1 of the light beam irradiated from the light source 1 through this portion to the imaging device 2 is determined.

[0056] Next, as Figure 7 As shown, a portion of optical material 3 with a refractive index n2 is inserted between the light source 1 and the imaging device 2, and the radius w2 of the light beam irradiated from the light source 1 to the imaging device 2 through this portion is calculated.

[0057] The beam divergence angle changes due to differences in refractive index, therefore the following relationship holds. Thus, the beam divergence angle can be calculated using the following relationship. .

[0058]

[0059] Here, at the divergence angle In the case of small values, it can be approximated as sin ≒ tan ≒ In this case, the beam divergence angle is obtained using the following approximation. . Figure 8 This is a diagram comparing the calculation formula and its approximation for implementation method 4. At the beam divergence angle... When the angle is less than 40°, the calculation results of the above formula are roughly consistent with the calculation results of the approximation formula.

[0060]

[0061] As explained above, in this embodiment, the beam divergence angle is determined based on the difference in beam radius when light passes through portions of the optical material 3 with different refractive indices. Furthermore, the refractive index can be changed from n1 to n2, but the same calculation can be performed when it is changed from n2 to n3. By performing calculations from multiple points of the optical material 3, more accurate results can be obtained. Other structures and effects are the same as in Embodiment 1.

[0062] Implementation method 5.

[0063] Figure 9 This diagram illustrates the beam divergence angle measurement method of Embodiment 5. In this embodiment, the optical material 3 is made of a material such as LiNbO3 (lithium niobate) or LiTaO3 (lithium tantalate) that exhibits an electro-optic effect (Pokels effect) where the refractive index changes upon application of a voltage. Electrodes 5 are formed on both sides of the optical material 3, and the electrodes 5 are connected to a power supply 6. The optical material 3 has an optical axis in the direction of the optical axis of the beam.

[0064] A voltage is applied to the optical material 3 from the power source 6, thereby changing the refractive index from n1 to n2 through the electro-optic effect. In the same manner as in embodiment 4, the beam radii w1 and w2 are determined to calculate the beam divergence angle. Therefore, in this embodiment, the beam divergence angle can be calculated based on the difference in beam radius before and after voltage application while the optical material 3 is fixed. The other structures and effects are the same as in implementation method 4.

[0065] Implementation method 6.

[0066] Figure 10 This diagram illustrates the beam divergence angle measurement method of Embodiment 6. The difference from Embodiment 2 is that the optical material 3 is tilted relative to the vertical direction.

[0067] First, as in implementation method 1 Figure 1 As shown, the tilt of the optical axis of the light source 1 is adjusted so that the light beam is incident perpendicularly on the imaging surface of the imaging device 2. Next, the radius w and center P of the light beam illuminating the imaging device 2 from the light source 1 are calculated when no object is placed between the light source 1 and the imaging device 2.

[0068] Next, as Figure 10 As shown, an optical material 3 with a thickness of L and a refractive index of n is inserted between the light source 1 and the imaging device 2 at an angle φ relative to the vertical direction. The distance w1 between the upper end and the center P of the light beam irradiated from the light source 1 to the imaging device 2 through the optical material 3 and the distance w2 between the lower end and the center are calculated.

[0069] Since the imaging device 2 is not parallel to the optical material 3, the angle φ of the optical material 3 is used to calculate the difference in beam size. Let the difference between w and w1 be Δw1, and the difference between w and w2 be Δw2. The following two relationships hold. Therefore, the beam divergence angle can be obtained using the following two relationships. .

[0070]

[0071] Here, at the beam divergence angle When the tilt angle φ of optical material 3 is close to 0° (e.g.) For cases where φ < 40° and φ < 30°, the following approximation holds.

[0072]

[0073] Therefore, assuming the above approximation holds true, the beam divergence angle can be obtained using the following approximation. .

[0074]

[0075] As explained above, in this embodiment, when the optical material 3 is tilted, the beam divergence angle can be calculated by determining the difference between the upper and lower beam diameters. The other structures and effects are the same as in Implementation Method 1.

[0076] Explanation of reference numerals in the attached figures

[0077] 1…light source; 2…shooting device; 3…optical material.

Claims

1. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of inserting an optical material of thickness L and refractive index n, a parallel plate, between a light source and an imaging device at a distance d, and determining the radius w of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 2. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of inserting an optical material of thickness L and refractive index n, a parallel plate, between a light source and an imaging device at a distance d, and determining the radius w of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 3. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of determining the radius w1 of the light beam illuminating the imaging device from the light source without placing any object between the light source and the imaging device; The process of inserting an optical material of thickness L and refractive index n, which is a parallel plate, between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 4. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of determining the radius w1 of the light beam illuminating the imaging device from the light source without placing any object between the light source and the imaging device; The process of inserting an optical material of thickness L and refractive index n, which is a parallel plate, between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 5. A method for measuring the divergence angle of a beam, characterized in that, It includes the following processes: The process of inserting an optical material with a thickness of L1 and a refractive index of n into a parallel plate between a light source and an imaging device, and determining the radius w1 of the light beam that travels from the light source through the optical material to the imaging device. The process of inserting an optical material with a thickness of L2 and a refractive index of n into the space between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 6. A method for measuring the divergence angle of a beam, characterized in that, It includes the following processes: The process of inserting an optical material with a thickness of L1 and a refractive index of n into a parallel plate between a light source and an imaging device, and determining the radius w1 of the light beam that travels from the light source through the optical material to the imaging device. The process of inserting an optical material with a thickness of L2 and a refractive index of n into the space between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 7. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of inserting a parallel plate optical material with a thickness of L and a refractive index of n1 between a light source and an imaging device, and determining the radius w1 of the light beam that shines from the light source through the optical material onto the imaging device. The process of inserting an optical material of thickness L and refractive index n2 into the space between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 8. A method for measuring the divergence angle of a beam, characterized in that, It includes the following processes: The process of inserting a parallel plate optical material with a thickness of L and a refractive index of n1 between a light source and an imaging device, and determining the radius w1 of the light beam that shines from the light source through the optical material onto the imaging device. The process of inserting an optical material of thickness L and refractive index n2 into the space between the light source and the imaging device, and determining the radius w2 of the light beam illuminating the imaging device from the light source through the optical material; and The beam divergence angle can be calculated using the following formula. The process, 。 9. The method for measuring the beam divergence angle according to claim 7 or 8, characterized in that, A voltage is applied to the optical material to change its refractive index through an electro-optic effect.

10. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of determining the radius w and center of the light beam illuminating the imaging device from the light source without placing any object between the light source and the imaging device; The process of inserting an optical material of thickness L and refractive index n, a parallel plate, between the light source and the imaging device at an angle φ relative to the vertical direction; and determining the distance w1 between the upper end and the center of the light beam illuminating the imaging device from the light source via the optical material, and the distance w2 between the lower end and the center; and Let the difference between w and w1 be Δw1, and the difference between w and w2 be Δw2. The beam divergence angle can be calculated using the following formula. The process, 。 11. A method for measuring beam divergence angle, characterized in that, It includes the following processes: The process of determining the radius w and center of the light beam illuminating the imaging device from the light source without placing any object between the light source and the imaging device; The process of inserting an optical material of thickness L and refractive index n, which is a parallel plate, between the light source and the imaging device at an angle relative to the vertical direction; and determining the distance w1 between the upper end and the center of the light beam illuminating the imaging device from the light source via the optical material, and the distance w2 between the lower end and the center; and Let the difference between w and w1 be Δw1, and the difference between w and w2 be Δw2. The beam divergence angle can be calculated using the following formula. The process, 。 12. The method for measuring the beam divergence angle according to any one of claims 1 to 11, characterized in that, The shape of the light beam illuminating the imaging device from the light source is measured without any object placed between the light source and the imaging device, and the tilt of the optical axis of the light beam is adjusted in a manner that makes the shape of the light beam symmetrical from left to right.

13. The method for measuring the beam divergence angle according to any one of claims 1 to 9, characterized in that, The tilt of the optical material is adjusted so that the center of the light beam illuminating the imaging device from the light source via the optical material is aligned with the center of the light beam captured when no object is placed between the light source and the imaging device.

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