CN113466171A - High resolution inspection device using Bessel beam - Google Patents

High resolution inspection device using Bessel beam Download PDF

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Publication number
CN113466171A
CN113466171A CN202110686748.1A CN202110686748A CN113466171A CN 113466171 A CN113466171 A CN 113466171A CN 202110686748 A CN202110686748 A CN 202110686748A CN 113466171 A CN113466171 A CN 113466171A
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China
Prior art keywords
lens
terahertz wave
terahertz
bessel beam
bessel
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玉景植
崔成旭
张玄珠
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Korea Food Research Institute KFRI
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Korea Food Research Institute KFRI
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Priority claimed from KR1020160144573A external-priority patent/KR101738395B1/en
Priority claimed from KR1020160144582A external-priority patent/KR20180047827A/en
Application filed by Korea Food Research Institute KFRI filed Critical Korea Food Research Institute KFRI
Publication of CN113466171A publication Critical patent/CN113466171A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0927—Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/095—Refractive optical elements
    • G02B27/0955—Lenses
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B2003/0093—Simple or compound lenses characterised by the shape

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The terahertz wave condensing module according to an embodiment of the present invention may include: a first lens that reduces an angle of a terahertz wave that is diffused while the terahertz wave passes through an inspection target object; and a second lens that condenses the terahertz wave that has passed through the first lens to a detector.

Description

High resolution inspection device using Bessel beam
The application is a divisional application of Chinese patent application with the patent application number of 201680090562.7 and the invention names of a high-resolution terahertz wave condensing module, a scattered light detection module and a high-resolution inspection device adopting terahertz Bessel beams, and the patent application with the entering Chinese national stage date of 2019, 04 and 30.
Technical Field
The present invention relates to a technique for inspecting an inspection target object by a nondestructive method using terahertz waves, and more particularly to a high-resolution terahertz wave condensing module having a wavelength of not more than a diffraction limit and a high resolution.
The present invention also relates to a scattered light detection module that forms an annular beam by a bessel beam, detects scattered light reflected or transmitted from an object to be inspected when the object to be inspected is inspected by the formed annular beam, and can improve contrast.
The present invention also relates to a high-resolution inspection apparatus using a terahertz wave bessel beam, wherein the shape of an object is grasped by a scanner, and an optical head and a light-converging head are synchronized according to the grasped object shape.
(Korea research and development work supporting the invention)
(topic identification number) ER160200-01
(department name) creation of the scientific department in the future
(professional institute of research and management) Korean institute of food
(research project name) Korean food institute Main project
(research subject name) development of terahertz high-resolution imaging technology for detecting food foreign matter
(contribution rate) 1/1
(director organization) Korean institute for food
(duration of study) 2016.04.01-2017.12.31
Background
In order to inspect an object or a substance by a nondestructive method, an imaging method is mainly used, and mainly two methods, specifically, an image detection method using a continuous output light source and a spectroscopic method are used. These methods have advantages and disadvantages, respectively, but an image detection method using a continuous output light source is more widely used in a field requiring relatively high power such as a transmission image.
Terahertz waves are widely used in the field of qualitatively identifying hidden objects or substances by a nondestructive method because of various excellent characteristics such as excellent permeability to substances, possibility of qualitative identification, and safety to living bodies.
Therefore, in recent years, terahertz waves have been attempted to be used in various fields, specifically, search equipment for airports or security facilities, quality inspection equipment for food or pharmaceutical companies, semiconductor inspection equipment, engineering plastic inspection equipment, and the like.
Examples of the application of terahertz waves to production sites are gradually increasing, and have shown great improvements in main performance indexes such as detection resolution, detection speed, and detection area through continuous research.
Currently, only one lens is used to condense the terahertz waves that are diffused after passing through an object, so as to obtain a terahertz transmission image. In this case, if the apex angle of the conical lens forming the bessel beam is made small so that the beam size of the terahertz wave focused on the object to be inspected is smaller than the wavelength, there arises a problem that the terahertz bessel beam is emitted at a large angle after passing through the object to be inspected and cannot be entirely condensed at the detection portion. Therefore, the light-condensing property is significantly reduced, and the SNR (signal to noise ratio) of the inspection apparatus is significantly reduced, thereby causing a problem that a normal image cannot be obtained.
In addition, if the inspection object is transparent, it is difficult to obtain a clear image. Therefore, it is now necessary to research and develop a method capable of improving contrast (contrast) for a transparent inspection object while almost preventing loss of terahertz waves.
Further, there is a problem that a high-resolution image cannot be obtained because the focal depth of the bessel beam cannot reach the end portion of the inspection target object.
In addition, if the inspection target object contains a large amount of moisture, the terahertz wave has a property of being easily absorbed by the moisture, and therefore the rate of the terahertz wave transmitting through the inspection target object is significantly reduced. Accordingly, the terahertz wave detection unit detects a weak terahertz wave signal, and thus the object to be inspected cannot be accurately inspected.
The prior art related to the present invention is described in korean registered patent No. 10-1392311.
Disclosure of Invention
(problem to be solved)
The present invention has been made to solve the above-mentioned problems, and provides a high-resolution terahertz wave module capable of improving the light condensing efficiency of a terahertz wave bessel beam transmitted through an inspection target object, and further improving the resolution.
Further, the present invention provides a scattered light detection module that forms an annular beam without losing a terahertz wave and improves contrast (contrast) with respect to a transparent inspection target object.
Further, the present invention provides a high-resolution inspection apparatus using a terahertz wave bessel beam, in which an optical head is moved along the outer shape of an inspection target object as much as possible in accordance with the shape of the inspection target object, and the focal depth of the bessel beam can be made to reach the end portion of the inspection target object.
Further, the present invention provides a high-resolution inspection apparatus using a terahertz wave bessel beam, which can rapidly cool an inspection object and perform an inspection using a terahertz wave, and can allow the terahertz wave to well transmit the inspection object containing moisture.
Other objects and advantages of the present invention will be explained in the following description, and will be more clearly understood from the embodiments of the present invention. In addition, it can be easily understood that the objects and advantages of the present invention can be realized by the means embodied in the scope of the claims and the combination thereof.
(means for solving the problems)
A high resolution inspection apparatus using a bessel beam according to another embodiment of the present invention may include: a scanner that scans a shape of an inspection target object; a terahertz wave optical head that generates a terahertz wave and irradiates the object to be inspected with the generated terahertz wave; a terahertz wave condensing head that detects a terahertz wave transmitted through the inspection target object; a first transport unit that moves the terahertz optical head in accordance with a shape of an inspection target object scanned by the scanner; and a second transport unit that moves the terahertz wave condensing head in synchronization with the first transport unit in the same manner as the optical head.
In order to place the inspection target object within the depth of focus of the generated terahertz waves, the first transport portion may move the terahertz wave optical head to keep the inspection target object and the terahertz wave optical head at a predetermined distance based on the thickness of the scanned inspection target object.
The high resolution inspection apparatus using a terahertz wave bessel beam further includes: a rapid cooling device for keeping the object to be inspected at a low temperature; the terahertz wave optical head and the terahertz wave light-gathering head can be arranged on two side faces of the rapid cooling device at intervals.
The rapid cooling device may be constituted by a housing comprising a window which is transparent to the generated terahertz waves.
The high resolution inspection apparatus using a terahertz wave bessel beam may include: and a thawing device which is arranged at the rear end of the rapid cooling device and thaws the inspection object.
A high resolution inspection apparatus using a bessel beam according to another embodiment of the present invention includes: a terahertz wave generating unit that generates terahertz waves; a bessel beam forming unit that forms a terahertz wave bessel beam on the inspection target object by using the terahertz wave incident from the terahertz wave generating unit; a first lens that reduces an angle of a terahertz wave that diverges while passing the terahertz wave bessel beam through the inspection target object; a second lens for condensing the terahertz wave passing through the first lens to a detector; and a terahertz wave detection unit that detects the terahertz wave condensed by the second lens.
The bessel beam forming portion may be a first cone lens having an apex angle formed by a diameter of the terahertz-wave bessel beam being smaller than a wavelength of the terahertz wave generated by the terahertz-wave generating portion.
The first lens may be a second tapered lens which is arranged symmetrically with respect to the first tapered lens with respect to the inspection target object.
The second tapered lens may have an apex angle of the same size as the first tapered lens.
The high-resolution inspection apparatus using bessel beams may further include an angle changing portion that reduces an angle of the terahertz waves incident from the terahertz wave generating portion to be incident to the bessel beam forming portion.
The angle changing unit may be a first convex lens that reduces the angle of the terahertz wave incident from the terahertz wave generating unit, and the second lens may be a second convex lens that is arranged symmetrically with respect to the second convex lens with respect to the inspection target object.
The second lens may be a third tapered lens having the same shape as the second tapered lens and symmetrically arranged with respect to the second tapered lens with an axis perpendicular to the optical axis as a reference.
The first lens may be a third convex lens that reduces an angle of the terahertz waves diverged while passing the terahertz-wave bessel beam through the inspection target object.
The second lens may be a fourth convex lens arranged symmetrically with respect to the third convex lens with respect to an axis perpendicular to the optical axis.
The high-resolution terahertz wave condensing module according to another embodiment of the present invention may include: a first lens that reduces an angle of a terahertz wave that is diffused while the terahertz wave passes through an inspection target object; and a second lens that condenses the terahertz wave that has passed through the first lens to a detection section.
The first lens may be a second conical lens that forms the terahertz wave bessel beam with reference to the inspection target object and is arranged symmetrically with respect to a first cone having an apex angle formed such that a diameter of the terahertz wave incident on the detection portion is smaller than a wavelength of the terahertz wave generated by the terahertz wave generation portion.
The second tapered lens may have an apex angle of the same size as the first tapered lens.
The second lens may be a second convex lens that is disposed symmetrically with respect to the object to be inspected and that reduces the angle of the terahertz wave incident from the terahertz wave generating unit.
The second lens may have the same shape as the second pyramid lens and be arranged symmetrically with respect to the second pyramid lens with an axis perpendicular to the optical axis as a reference.
The first lens may be a third convex lens that reduces a terahertz wave angle at which the terahertz wave bessel beam diverges while passing through the inspection target object.
The second lens may be a fourth convex lens disposed symmetrically with respect to the third convex lens with respect to an axis perpendicular to the optical axis.
A high-resolution inspection apparatus using a terahertz wave bessel beam according to another embodiment of the present invention includes: a terahertz wave generating unit that generates terahertz waves; a bessel beam forming unit that generates a terahertz wave bessel beam using the terahertz wave incident from the terahertz wave generating unit; an annular beam forming unit that forms an annular (ring) beam from the terahertz wave bessel beam and condenses the formed annular (ring) beam on an inspection target object; a scattered light detection unit that detects scattered light generated from the inspection target object; and an annular beam detector for detecting the annular beam transmitted through the inspection target object.
The ring-shaped light beam forming unit includes a third lens, forms a ring-shaped (ring) light beam, and condenses the formed ring-shaped (ring) light beam on the inspection target object.
The scattered light detection unit includes a reflected scattered light detection unit that is provided inside the third lens and detects scattered light reflected from the inspection target object.
The reflected scattered light detection unit may be provided inside the annular light flux emitted from the third lens.
The scattered light detection section may include a transmission scattered light detection section that detects scattered light transmitted from the inspection target object.
The transmission scattered light detection unit may be disposed inside the annular light beam incident from the third lens.
The third lens includes an optical path changing unit that changes an optical path of scattered light reflected from the inspection target object, and the reflected scattered light detecting unit can detect scattered light incident from the optical path changing unit.
The ring-shaped beam forming part may include a fourth lens that reduces an angle of the terahertz wave bessel beam incident from the bessel beam forming part to be incident on the third lens.
The bessel beam forming portion may be a fourth conic lens having an apex angle formed by a diameter of the terahertz-wave bessel beam being smaller than a wavelength of the terahertz wave generated by the terahertz-wave generating portion.
The fourth lens may be a fifth cone lens arranged symmetrically with respect to the fourth cone with respect to the inspection target object.
The fifth conic lens may have a vertex angle of the same size as the fourth conic lens.
The high-resolution inspection apparatus using the terahertz-wave bessel beam may further include an angle changing portion that reduces an angle of the terahertz wave incident from the terahertz-wave generating portion to be incident to the bessel beam forming portion.
The angle changing unit may be a fifth convex lens that reduces the angle of the terahertz wave incident from the terahertz wave generating unit; the third lens may be a sixth convex lens arranged symmetrically with respect to the object to be inspected.
The third lens may be a sixth conic lens having the same shape as the fifth conic lens and symmetrically arranged with respect to an axis perpendicular to the optical axis.
The fourth lens may be a seventh convex lens that reduces an angle of the terahertz waves diverged while passing the terahertz-wave bessel beam through the inspection target object.
The fourth lens may be an eighth convex lens disposed symmetrically with respect to the seventh convex lens with respect to an axis perpendicular to the optical axis.
The scattered light detection module according to an embodiment of the present invention includes: an annular beam forming unit that forms an annular (ring) beam from a terahertz wave bessel beam and condenses the formed annular (ring) beam on an inspection target object; and a scattered light detection unit that detects scattered light generated from the inspection target object.
The ring-shaped light beam forming unit includes a third lens that forms a ring-shaped (ring) light beam and condenses the ring-shaped (ring) light beam on the inspection target object.
The scattered light detection unit includes a reflected scattered light detection unit that is provided inside the annular light beam emitted from the third lens and detects scattered light reflected from the inspection target object.
The scattered light detection unit includes a transmission scattered light detection unit that is disposed inside the annular light flux incident from the third lens and detects scattered light transmitted through the inspection target object.
The third lens includes an optical path changing unit that changes an optical path of scattered light reflected from the inspection target object, and the reflected scattered light detecting unit detects the scattered light incident from the optical path changing unit.
(Effect of the invention)
According to the disclosed invention, the terahertz waves transmitted through the inspection object can be condensed with almost no loss, and therefore the condensing efficiency can be improved.
In addition, the diameter of the terahertz wave beam focused on the inspection object is made smaller than the wavelength of the terahertz wave, so that the resolution is improved, and a clear image can be acquired.
Further, by forming the ring beam without losing the terahertz wave, the contrast (contrast) to the transparent inspection object can be improved.
In addition, by detecting scattered light generated from the inspection target object, the contrast (contrast) with respect to a transparent inspection target object can be improved.
Further, since the scattered light detection unit is disposed inside the generated annular light beam, it is not necessary to provide a separate space for adding the scattered light detection unit, and thus downsizing can be achieved.
In addition, even if the apex angle of the cone of the bessel beam forming portion is made small in order to achieve high resolution, the lenses of the two ring beam forming portions are used, so that the diameter of the generated ring beam is made small, and a high-resolution image can be obtained.
In addition, the optical head is moved along the outer shape of the inspection target object as much as possible according to the shape of the inspection target object, and the inspection target object is positioned in the focal depth of the bessel beam, so that a clear transmission image can be acquired.
Further, the object to be inspected is rapidly cooled and inspected by terahertz wave inspection, and further, terahertz wave can transmit the object to be inspected containing moisture well.
Drawings
Fig. 1 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam related to an embodiment of the present invention.
Fig. 2 is a diagram for specifically explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 1.
Fig. 3 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam related to another embodiment of the present invention.
Fig. 4 is a diagram for explaining a high-resolution inspection apparatus using a bessel beam according to another embodiment of the present invention.
Fig. 5 is a diagram for explaining the bessel beam forming section according to the embodiment of the present invention.
Fig. 6 is a graph for calculating the diameters of terahertz wave beams concentrated at mutually different apex angles using mathematical expression 4.
Fig. 7 and 8 are views for explaining an inspection apparatus that condenses light by a single lens.
Fig. 9 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 4 according to the first embodiment.
Fig. 10 is a diagram for explaining the high-resolution inspection apparatus of fig. 4 according to the second embodiment.
Fig. 11 is a diagram for explaining the high-resolution inspection apparatus of fig. 4 according to the third embodiment.
Fig. 12 and 13 are transmission images of the inspection target object measured by the apparatus shown in fig. 8 to 11.
Fig. 14 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to another embodiment of the present invention.
Fig. 15 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the first embodiment.
Fig. 16 is a diagram showing an embodiment of the annular beam forming portion 1540 in fig. 15.
Fig. 17 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the second embodiment.
Fig. 18 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the third embodiment.
Fig. 19 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to the fourth embodiment fig. 14.
Fig. 20 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to the fifth embodiment fig. 14.
Fig. 21 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the sixth embodiment.
Fig. 22 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the seventh embodiment.
Fig. 23 is a diagram for explaining the high resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the eighth embodiment.
Detailed Description
Hereinafter, specific contents for carrying out the present invention will be described in detail with reference to the drawings.
Fig. 1 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam related to an embodiment of the present invention.
Referring to fig. 1, a high resolution inspection apparatus 100 using a bessel beam includes a scanner 110, a terahertz wave optical head 120, an inspection target object 130, a terahertz wave condensing head 140, a first transport portion 150, and a second transport portion 160.
The scanner 110 can scan the shape of the inspection target object.
The terahertz-wave optical head 120 generates a terahertz wave, and can irradiate the generated terahertz wave to the inspection target object 130.
The terahertz-wave condensing head 140 can detect the terahertz waves transmitted through the inspection target object 130.
The first transport portion 150 can move the terahertz-wave optical head 120 along the shape of the inspection target object scanned by the scanner 110. The first transport portion 150 can move the terahertz-wave optical head 120 in a two-dimensional plane and in a direction perpendicular to the two-dimensional plane.
For example, in order to place the inspection target object 130 in the depth of focus of the terahertz waves generated by the terahertz wave optical head 120, the first transport section 150 may move the terahertz wave optical head 120 to keep the terahertz wave optical head 120 and the inspection target object 130 at a certain distance based on the thickness of the scanned inspection target object 130.
Specifically, if the thickness of the object to be inspected has a thickness portion a and a thickness portion B, the optical head 120 can be moved in the vertical direction X when the first transport unit 150 scans the thickness portion a. In addition, in the case of scanning the B thickness portion, the first conveying part 150 may move the optical head 120 in the vertical direction Y.
Accordingly, the first transport unit 150 moves the optical head 120 along the outer shape of the inspection target object 130 as much as possible, and further, the inspection target object is located in the focal depth of the bessel beam, so that a clear transmission image can be obtained.
The second transport portion 160 can move the terahertz wave condensing head 140 in synchronization with the first transport portion 150 in the same manner as the terahertz wave optical head 120. Accordingly, the first and second transport portions 150 and 160 can arrange the terahertz wave optical head 120 and the terahertz wave condensing head 140 on a straight line.
Fig. 2 is a diagram for specifically explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 1.
Referring to fig. 2, the high resolution inspection apparatus 100 using a bessel beam includes: a scanner 110, a terahertz wave optical head 120, an inspection target object 130, a terahertz wave condensing head 140, a first conveying portion 150, and a second conveying portion 160.
The scanner 110 can scan the shape of the inspection target object. The scanner 110 may be disposed in a separate frame, or may be integrally disposed on the front side of the terahertz wave optical head 120.
The terahertz-wave optical head 120 generates a terahertz wave, and can irradiate the generated terahertz wave to the inspection target object 130.
The first carrying portion 150 may be mechanically coupled to the terahertz-wave optical head 120. The first transport portion 150 can move the terahertz-wave optical head 120 along the shape of the inspection target object scanned by the scanner 110. The first transport portion 150 can move the terahertz-wave optical head 120 in a two-dimensional plane and in a direction perpendicular to the two-dimensional plane.
The inspection object 130 may be placed on a conveyor belt and may be moved from the direction of the scanner 110 and the ehz wave optical head 120. The inspection target object 130 may be moved by a conveyor or the like as in the embodiment of the present invention, but may be fixedly disposed at a specific position.
The terahertz-wave condensing head 140 can detect the terahertz waves transmitted through the inspection target object 130.
The second transport portion 160 can move the terahertz wave condensing head 140 in synchronization with the first transport portion 150 in the same manner as the terahertz wave optical head 120.
Accordingly, the first and second transport portions 150 and 160 can arrange the terahertz wave optical head 120 and the terahertz wave condensing head 140 on a straight line.
In the present embodiment, the structure is merely used to help understand the shape of the high-resolution inspection apparatus using the terahertz wave bessel beam, and in addition, the high-resolution inspection apparatus using the terahertz wave bessel beam can be realized by structures of various shapes.
Fig. 3 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam related to another embodiment of the present invention.
Referring to fig. 3, the high resolution inspection apparatus 100 using a bessel beam includes: a terahertz wave optical head 120, an inspection object 130, a terahertz wave condensing head 140, a first conveying part 150, a second conveying part 160, a rapid cooling device 300, and a thawing device 320.
The configurations of the terahertz wave optical head 120, the inspection target object 130, the terahertz wave condensing head 140, the first conveying portion 150, and the second conveying portion 160 are the same as those of fig. 1, and therefore, the descriptions thereof are omitted.
The terahertz-wave optical head 120 and the terahertz-wave condensing head 140 may be disposed at intervals on both side surfaces of the rapid cooling apparatus 300.
The rapid cooling device 300 may maintain the inspection target object 130 in a low temperature state. For example, the rapid cooling device 300 may cool the inspection target object 120 to a fixed state. The inspection object 130 maintains a low-temperature state or a solid state, and thus the proportion of the terahertz wave absorbed by the inspection object 130 can be reduced.
The rapid cooling device 300 may be constituted by a housing including a window 310, the window 310 transmitting the generated terahertz waves. The inspection object 130 may pass through the inside of the housing of the rapid cooling apparatus 300. For example, the window 310 may be formed of a heat insulating material foam having a high heat insulating effect while allowing terahertz waves to pass through well.
The thawing device 320 is disposed at the rear end of the rapid cooling device 300 and can thaw the rapidly cooled inspection object 130.
The structure of the rapid cooling device 300 in the present embodiment is merely an example shown for illustration, and the rapid cooling device 300 may be implemented by structures of various shapes.
The object 130 to be inspected is rapidly cooled so as to allow the terahertz wave to be transmitted therethrough, and a high-resolution inspection apparatus using a terahertz wave bessel beam can inspect the object to be inspected containing moisture with high resolution.
Fig. 4 is a diagram for explaining a high-resolution inspection apparatus using a bessel beam according to another embodiment of the present invention.
Referring to fig. 4, the high resolution inspection apparatus 400 using a bessel beam may include: a terahertz-wave optical head 410, an inspection target object 420, and a terahertz-wave condensing head 430. Although not shown in fig. 4, the scanner 110, the first conveying unit 150, and the second conveying unit 160 of fig. 1 may be additionally included in the present embodiment.
The terahertz-wave optical head 410 may include a terahertz-wave generating section 411, an angle changing section 412, and a bessel beam forming section 413. In the present embodiment, the description has been made with reference to the case where the terahertz-wave optical head 410 includes all of the terahertz-wave generating section 411, the angle changing section 412, and the bessel beam forming section 413, but the terahertz-wave optical head 410 may be implemented by including a part of the terahertz-wave generating section 411, the angle changing section 412, and the bessel beam forming section 413.
A bessel beam refers to an electromagnetic wave described by a bessel function of the 0th order class with a solution set of maxwell's equations to free space, and is called a non-diffractive beam. Bessel beams were first proposed by Durnin in 1987 to have axial symmetry while concentrating the energy like a needle about an axis for a certain length. Realized by an optical system with a finite aperture, rather than an infinite aperture (aperture), and therefore there is no Bessel Beam traveling indefinitely, and is therefore commonly referred to as Quasi-Bessel-Beam (QBB, Quasi-Bessel Beam). Such QBBs can be made of a combination of a circular mask formed with a hologram, rings or a finite opening (aperture) and a lens of funnel shape called axicon.
The terahertz-wave generating section 110 can generate terahertz waves. Terahertz waves refer to electromagnetic waves of the terahertz (terahertz) region, and may preferably have a frequency of 0.1THz to 10 THz. However, even if the amount is outside the range, it is needless to say that the terahertz wave in the present invention can be regarded as a terahertz wave in the present invention as long as the range can be easily conceived by a person skilled in the art to which the present invention pertains.
The angle changing unit 120 can reduce the angle of the terahertz wave incident from the terahertz wave generating unit 411 and can enter the bessel beam forming unit 413. For example, the angle changing part 412 may change the angle of the incident terahertz wave with respect to the optical axis to be smaller than a predetermined angle or parallel. The angle changing unit 412 may be a convex lens that refracts incident terahertz waves in parallel, a parabolic mirror that reflects incident terahertz waves in parallel, or the like.
The bessel beam forming unit 413 can form a terahertz wave bessel beam on at least a part of the inspection target object by the terahertz wave incident from the angle changing unit 412.
Without the angle changing unit 412, the bessel beam forming unit 413 can form a terahertz wave bessel beam on at least a part of the inspection target object by the terahertz wave incident from the terahertz wave generating unit 411.
In practice, it is difficult for the Bessel Beam forming part 413 to form an ideal Bessel Beam, and therefore the Bessel Beam formed by the Bessel Beam forming part 413 may be referred to as Quasi-Bessel Beam (QBB). A structure of forming the bessel beam by such a bessel beam forming part 413 will be described in more detail with reference to fig. 2.
The bessel beam forming unit 413 can make the terahertz waves whose angle is changed by the angle changing unit 412 enter perpendicularly to the light incident surface of the bessel beam forming unit 413.
The bessel beam forming unit 413 may be formed in various shapes such as a diffractive optical element in which a plurality of circular grooves or circular holes are formed, a lens having a positive refractive index, a conical lens, a hologram optical element, or the like.
The bessel beam forming part 413 may be a first cone lens having an apex angle that makes the diameter of the terahertz bessel beam concentrated on the inspection target object smaller than the wavelength of the terahertz wave generated by the terahertz wave generating part. In the present embodiment, the apex angle of the diameter of the bessel beam forming the terahertz wave smaller than the wavelength is defined as the maximum apex angle.
In this case, the Maximum value of the apex angle τ of the first cone lens can be represented by a Full-Width Half-height (Full Width at Half Maximum) diameter ρ of the terahertz wave bessel beam concentrated on the inspection target objectFWHMWavelength lambda and refractive indices n, n0The calculation is performed by the following equation.
Mathematical formula 1
J0(kρsinα0)2＝J0(1.1264)2＝0.5
Figure BDA0003124835360000181
Here, J0(z) is a Bessel function of order 0, provided that J is satisfied0 2(z) 0.5, then J0(z) 1/√ 2, and z satisfying this value is 1.1264. From 1.1264 k ρFWHM*sinα0The above equation 1 can be derived. J. the design is a square0 2The 0.5 value of (z) ═ 0.5 can be changed.
Mathematical formula 2
Figure BDA0003124835360000182
Mathematical formula 3
Figure BDA0003124835360000183
Mathematical formula 4
Figure BDA0003124835360000184
Here, J0: bessel function of order 0
ρFWHM: full width half height of concentrated terahertz waves
λ: wavelength of terahertz wave
α0: value of half of the crossing angle of terahertz waves crossing through the conical lens
n: refractive index of first conical lens
n0: average refractive index of ambient environment
τ: vertex angle of first conical lens
Equation 4 is derived from equations 1, 2, and 3.
In contrast, the minimum value of the vertex angle of the first pyramid lens may be the vertex angle of the first pyramid lens where total reflection does not occur due to the refractive index of the first pyramid.
Accordingly, the apex angle of the first conical lens that forms the diameter of the bessel beam of the terahertz wave to be smaller than the wavelength of the terahertz wave generated by the terahertz wave generating section can be formed between the maximum value and the minimum value grasped from above.
The inspection target object 420 means a target object to be inspected, and may be disposed between the terahertz-wave optical head 410 and the terahertz-wave condensing head 430.
The terahertz-wave condensing head 430 includes: a first lens 431, a second lens 432, and a detection unit 433. In the present embodiment, the description has been made with reference to the case where all of the first lens 431, the second lens 432, and the detection section 433 are included in the terahertz-wave light condensing head 430, but the terahertz-wave light condensing head 430 may include a part of the first lens 431, the second lens 432, and the detection section 433.
The first lens 431 can be an angle of a terahertz wave that diverges while transmitting the bessel beam of the terahertz wave generated by the bessel beam forming part 413 through the inspection target object 420. For example, the first lens 431 may change an angle of the terahertz wave with respect to the optical axis to be smaller than a predetermined angle or parallel.
The second lens 432 may condense the terahertz waves passing through the first lens 431 to the detection part 433.
In the present invention, the high-resolution terahertz wave condensing module means a device including the first lens 431 and the second lens 432. For example, the terahertz wave is emitted in a circular beam shape of a ring pattern while being away from the bessel beam forming portion 413, and the terahertz wave emitted in the circular shape is condensed by the high-resolution terahertz wave condensing module (the first lens and the second lens), so that the condensed terahertz wave can be directed toward the detection portion 433.
For example, the high-resolution terahertz wave condensing module may also be implemented by structures of various shapes, such as a convex lens, a concave lens, a parabolic mirror, an ellipsoidal mirror, and the like.
The detection unit 433 can detect the terahertz wave condensed by the second lens. For example, the detection section 433 can detect the intensity of the terahertz wave. For example, the detection section 433 may have a Schottky Diode (Schottky Diode).
The image generating part (not shown) may generate an image picture using the bessel beam detected by the detecting part 433. The generated picture may be displayed on a display section (not shown).
The high-resolution inspection apparatus using the bessel beam can condense the terahertz waves transmitted through the inspection object almost without loss, and therefore can improve the condensing efficiency.
In addition, the high-resolution inspection apparatus using the bessel beam can acquire clear images by making the diameter of the terahertz wave reaching the detection portion smaller than the wavelength of the terahertz wave and further improving the resolution.
Fig. 5 is a diagram for explaining a bessel beam forming portion according to an embodiment of the present invention.
Referring to fig. 5, the bessel beam forming part may be constituted by a cone lens (axicon) 500. R is the radius of the conical lens; τ is the apex angle of the cone lens; alpha is alpha0Is formed by a coneHalf of the crossing angle of the light beams crossed by the bulk lens; w is a0Is the radius of the parallel light incident on the conical lens. In addition, the section in which the bessel beam is formed is denoted by Zmax in fig. 5, and the terahertz wave incident to the cone lens concentrates energy in the region along the center portion in the z-axis direction by constructive interference.
At this time, an axisymmetric (axial symmetry) distribution is formed by the gaussian beam incident to the cone lens and the bessel beam formed by the cone lens, and a circular field is distributed along the z-axis. That is, when viewed from the left side to the right side with reference to fig. 5, the gaussian beam on the front side of the cone lens and the bezier beam on the rear side of the cone lens are all formed in a circular shape. In particular, the bessel beam formed by the cone lens diverges as a circular beam in a ring shape while being away from the cone lens.
On the other hand, in a transmission picture obtained while moving little by little, such as raster scanning (raster scanning), the final element determining the picture resolution is the diameter of the light beam incident on the object 1.
In particular, in the case of a bessel beam formed by a conical lens, the diameter thereof is defined by the wavelength of a terahertz wave and α0Determination of alpha0The expression can be obtained by snell's law using the following equation 1.
Mathematical formula 5
Figure BDA0003124835360000211
Here, n is0Is the refractive index in air; n is the refractive index of the conical lens; τ is the apex angle of the pyramidal lens.
On the other hand, ZmaxThis focal depth corresponds to the focal depth, which can be expressed by the following equation 6.
Zmax＝w0/tanα0
Here, as shown in FIG. 5, w0Is the radius of the light beam incident on the conical lens, and by reference to this mathematical expression, it can be understood that the depth of focus can also depend on alpha0。
Accordingly, in summary, the picture resolution and the focal depth are mainly determined by α0The value of (a) is changed greatly,
based on this, for the conical lens of the structure shown in fig. 5, assume n0When n is 1.0, n is 1.54(High Density Polyethylene), τ is 150 °, and R is 25mm, α is calculated as follows0And the depth of focus.
First, α is calculated using equation 50Then alpha can be calculated0Is 8.5. In addition, the depth of focus (Z) is calculated using equation 6max) Can calculate ZmaxIs 40.2 mm.
The bessel beam forming section may have a diffractive optical element in which a plurality of circular grooves or circular holes are arranged in a concentric circle shape and a lens having a positive refractive index. In this case, the circular groove or hole formed in the diffractive optical element may be formed in a recessed shape or a penetrating shape. Then, such a lens having a positive refractive index is disposed on the side opposite to the direction in which the parallel light is incident on the diffractive optical element.
In addition to the present embodiment, the bessel beam forming part may form various shapes such as a hologram structure body.
Fig. 6 is a graph for calculating the diameters of terahertz wave beams concentrated at mutually different apex angles using mathematical expression 4.
Referring to fig. 6, it can be confirmed that the wavelength λ of the terahertz wave is 2.14mm, the refractive index n of the first conic lens is 1.54, and the average refractive index n of the surrounding environment0In the case of 1, the maximum value of the vertex angle τ of the first conical lens is about 119 degrees, and the minimum value of the vertex angle τ of the first conical mirror is about 99 degrees.
Fig. 7 and 8 are views for explaining an inspection apparatus that condenses light by a single lens.
Referring to fig. 7 and 8, the inspection apparatus 700 includes: a terahertz wave generating section 710, an angle changing section 720, a bessel beam forming section 730, a condensing section 740, and a detecting section 750.
The terahertz-wave generating section 710 can generate terahertz waves.
The angle changing unit 720 reduces the angle of the terahertz wave incident from the terahertz wave generating unit 710, and can make the terahertz wave incident on the bessel beam forming unit 730.
The bessel beam forming unit 730 can form a terahertz wave bessel beam on at least a part of the inspection target object by using the terahertz wave incident from the angle changing unit 720. For example, the bessel beam forming portion may be a cone. The inspection target object may be formed between the bessel beam forming part 730 and the light condensing part 740.
The light-condensing part 740 may be implemented by a single lens.
The detection unit 750 can detect the terahertz wave condensed by the condensing unit 740.
Referring to fig. 7, when the apex angle of the cone as the bessel beam forming portion 730 is 140 degrees, the radius of the terahertz wave transmitted through the inspection object and incident on the detection portion 750 is about 5.1mm, and therefore the diameter of the terahertz wave in the detection portion 750 is about 10.2 mm.
In this case, most of the terahertz waves incident from the condensing portion 740 using a single lens have a diameter of about 9mm, and can be condensed to the detection portion 750 having an angle (Horn).
Referring to fig. 8, in order to form a diameter of a terahertz wave bessel beam that is smaller than a wavelength of a terahertz wave and is concentrated on an inspection object, an apex angle of a cone should be made small. That is, the apex angle of the taper is reduced to realize high resolution. Accordingly, a vertex angle of 110 degrees smaller than that of the taper in fig. 7 is formed.
When the apex angle of the cone as the bessel beam forming portion 730 is 110 degrees, the radius of the terahertz wave transmitted through the inspection object and incident on the detection portion 750 is about 17mm, and therefore the diameter of the terahertz wave in the detection portion 750 is about 34 mm.
As such, as the diameter of the terahertz wave incident to the detection portion 750 becomes larger, only a part of the terahertz wave incident from the condensing portion 740 using a single lens is condensed to the detection portion 750. That is, most of the terahertz waves incident from the condensing portion 740 are not incident on the detection portion 750, and thus the detection performance of the detection portion 750 is significantly reduced.
Fig. 9 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 4 according to the first embodiment.
Referring to fig. 9, the high resolution inspection apparatus 900 includes: a terahertz wave generating unit 910, an angle changing unit 920, a bessel beam forming unit 930, a first lens 940, a second lens 950, and a detecting unit 960.
The terahertz-wave generating section 910 can generate terahertz waves.
The angle changing unit 920 reduces the angle of the terahertz wave incident from the terahertz wave generating unit 910, and the terahertz wave can be incident on the bessel beam forming unit 930.
The bessel beam forming unit 930 can form a terahertz wave bessel beam on at least a part of the inspection target object by using the terahertz wave incident from the angle changing unit 920. For example, the bessel beam may be a cone.
The inspection target object may be formed between the bessel beam forming part 930 and the first lens 940.
The bessel beam forming part 930 may be a first conical lens having an apex angle formed by a diameter of the terahertz wave being smaller than a wavelength of the terahertz wave generated by the terahertz wave generating part.
The maximum value of the vertex angle of the first pyramid lens can be calculated based on math figures 1 to 3. For example, when the wavelength λ of the terahertz wave is 2.14mm, the refractive index n of the first conical lens is 1.54, and the average refractive index n of the surrounding environment is0In the case of 1, the vertex angle τ of the first tapered lens has a value of about 119 degrees. Accordingly, the maximum value of the vertex angle of the first conic lens is about 119 degrees.
In contrast, the minimum value of the first pyramid lens may be the vertex angle of the first pyramid lens at which total reflection does not occur due to the refractive index of the first pyramid. For the refractive index in this embodiment, since the critical angle for total reflection is 99 degrees. Accordingly, the minimum value of the vertex angle of the first conical lens is about 99 degrees.
Finally, the apex angle of the first conical lens is formed only between 119 degrees of the maximum value and 99 degrees of the minimum value, and the diameter of the terahertz wave bessel beam is smaller than the wavelength of the terahertz wave generated by the terahertz wave generating portion.
The first lens 940 can reduce the angle of the terahertz waves that diverge while transmitting the terahertz-wave bessel beam formed by the bessel beam forming part 930 through the inspection target object.
The first lens 940 may be a second tapered lens disposed symmetrically with respect to the first tapered lens 930 with respect to the inspection target object.
Second conical lens 950 may have an apex angle that is the same size as first conical lens 930. In this case, the size of the second conic lens may be smaller, equal to, or larger than the first conic lens 930. When the apex angle of the second conical lens is the same as that of the first conical lens 930, the efficiency of condensing the terahertz wave to the detection unit 950 is optimal.
If the angle changer 920 is a first convex lens, the second lens 950 may be a second convex lens symmetrically arranged with respect to the first convex lens with respect to the inspection target object.
In the case where the wavelength λ of the terahertz wave is 2.14mm and the first cone lens of the bessel beam forming part 930 is 110 degrees, the radius of the terahertz wave in the detection part 960 is 0.006mm, and thus the diameter of the terahertz wave is 0.012 mm.
Since the terahertz waves are condensed by the first lens 940 and the second lens 950, the diameter of the terahertz waves condensed to the detection unit 960 is significantly smaller than the diameter of the terahertz waves condensed to the detection unit 950 in fig. 8, and thus the condensing efficiency can be improved.
Therefore, when the terahertz waves are condensed using the first lens 940 and the second lens 950, the terahertz waves have high condensing efficiency even when the apex angle of the first conical lens is small, and the resolution can be significantly improved, so that a high-resolution inspection image can be acquired.
Fig. 10 is a diagram for explaining the high-resolution inspection apparatus of fig. 4 according to the second embodiment.
Referring to fig. 10, the high resolution inspection apparatus 1000 includes: a terahertz wave generating unit 1010, an angle changing unit 1020, a bessel beam forming unit 1030, an object to be inspected 1040, a first lens 1050, a second lens 1060, and a detecting unit 1070.
The terahertz-wave generating section 1010 can generate terahertz waves.
The angle changing unit 1020 may reduce the angle of the terahertz wave incident from the terahertz wave generating unit 1010 and may cause the terahertz wave to enter the bessel beam forming unit 1030.
The bessel beam forming unit 1030 can form a terahertz wave bessel beam on at least a part of the inspection target object by using the terahertz wave incident from the angle changing unit 1020. For example, the bessel beam forming portion may be a cone.
The inspection target object may be formed between the bessel beam forming section 1030 and the condensing section 1040.
The bessel beam forming part 1030 may be a first conical lens having an apex angle formed by a diameter of the terahertz wave being smaller than a wavelength of the terahertz wave generated by the terahertz wave generating part.
The first lens 1040 may be a third convex lens that reduces the angle of the terahertz wave that diverges while passing the terahertz wave bessel beam through the inspection target object.
The second lens 1050 may be a fourth convex lens arranged symmetrically with respect to the third convex lens with respect to an axis perpendicular to the optical axis.
In the case where the wavelength λ of the terahertz wave is 2.14mm, the radius of the terahertz wave that is incident on the detection portion 1060 through the inspection object is approximately 2.5mm, and therefore the diameter of the terahertz wave in the detection portion is approximately 5 mm.
Since the terahertz waves are condensed by the first lens 1040 and the second lens 1050, the diameter of the terahertz waves condensed to the detection portion 950 in fig. 8 is significantly smaller, and the condensing efficiency can be improved. Accordingly, the high-resolution inspection apparatus according to the present embodiment has high light collection efficiency even when the vertex angle of the first conical lens is small, and can significantly improve resolution, so that a high-resolution inspection image can be acquired.
Fig. 11 is a diagram for explaining the high-resolution inspection apparatus of fig. 4 according to the third embodiment.
Referring to fig. 11, the high resolution inspection apparatus 1100 includes: a terahertz wave generating unit 1110, an angle changing unit 1120, a bessel beam forming unit 1130, an object to be inspected 1140, a first lens 1150, a second lens 1160, and a detecting unit 1170.
The terahertz-wave generating section 1110 can generate terahertz waves.
The angle changing unit 1120 can reduce the angle of the terahertz wave incident from the terahertz wave generating unit 1110 and make the terahertz wave incident on the bessel beam forming unit 1130.
The bessel beam forming unit 1130 can form a terahertz wave bessel beam on at least a part of the inspection target object by using the terahertz wave incident from the angle changing unit 1220. For example, the bessel beam forming portion may be a cone.
The inspection target object may be formed between the bessel beam forming part 1130 and the light condensing part 1140.
The bessel beam forming part 1130 may be a first conic lens that forms an apex angle at which the diameter of the terahertz wave is smaller than the wavelength of the terahertz wave generated by the terahertz wave generating part.
The first lens 1140 may be a second tapered lens disposed symmetrically to the first tapered lens 1130 with respect to the object to be inspected.
The second tapered lens may have an apex angle that is the same size as the first tapered lens 1130.
The second lens 1150 may have the same shape as the second taper lens 1140 and may be symmetrically disposed with respect to the second taper lens 1140 with reference to light perpendicular to the optical axis.
In the case where the wavelength λ of the terahertz wave is 2.14mm, the radius of the terahertz wave that is incident on the detection portion 1160 through the inspection object is about 1.7mm, and therefore the diameter of the terahertz wave in the detection portion 1160 is about 3.4 mm.
Since the terahertz waves are condensed by the first lens 1140 and the second lens 1150, the diameter of the terahertz waves condensed to the detection portion 350 in fig. 8 is significantly smaller, and the condensing efficiency can be improved. Accordingly, the high-resolution inspection apparatus according to the present embodiment can obtain a high-resolution inspection image because the high light-collecting efficiency is high and the resolution can be significantly improved even when the vertex angle of the first conical lens is small.
Fig. 12 and 13 are transmission images of the inspection target object measured by the apparatus shown in fig. 8 to 11.
Specifically, fig. 12 is a view for measuring an inspection object by the apparatus illustrated in fig. 8; fig. 12 is a view for measuring an inspection target object by the apparatus described in fig. 8 to 11.
Referring to fig. 12, it was confirmed that the inspection target object was not recognized at all in the transmission image obtained by condensing light with only a single lens.
In contrast, referring to fig. 13, it was confirmed that the inspection target object can be clearly recognized by the transmission image obtained by condensing light with the lens structure corresponding to fig. 8 to 11.
As described above, a high-resolution image can be acquired using the high-resolution inspection apparatus using a bessel beam according to the present invention.
Fig. 14 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to another embodiment of the present invention.
Referring to fig. 14, a high resolution inspection apparatus 1400 using a bessel beam may include: a terahertz wave optical head 1410, an inspection target object 1420, and a terahertz wave condensing head 1430. Although not shown in fig. 14, the scanner 110, the first conveying unit 150, and the second conveying unit 160 of fig. 1 may be further included in the present embodiment.
The terahertz wave optical head 1410 may include: a terahertz wave generating unit 1411, an angle changing unit 1412, a bessel beam forming unit 1413, and a ring beam forming unit 1414. In the present embodiment, the description has been made with reference to the case where the terahertz-wave optical head 1410 includes all of the angle changing section 1412, the bessel beam forming section 1413, and the ring beam forming section 1414, but the terahertz-wave optical head 1410 may be implemented by including a part of the angle changing section 1412, the bessel beam forming section 1413, and the ring beam forming section 1414.
The terahertz-wave generating portion 1411 can generate terahertz waves.
The angle changing unit 1412 may make the angle of the terahertz wave incident from the terahertz wave generating unit 1411 smaller and then the terahertz wave may be incident on the bessel beam forming unit 1413. For example, the angle changing unit 1412 may change the angle of the incident terahertz wave with respect to the optical axis to be smaller than a predetermined angle or parallel. The angle changing unit 1412 may be a convex lens that refracts incident terahertz waves in parallel, a parabolic mirror that reflects incident terahertz waves in parallel, or the like.
The bessel beam forming unit 1413 can generate a terahertz wave bessel beam by using the terahertz wave incident from the angle changing unit 1412.
Without the angle changing portion 1412, the bessel beam forming portion 1413 can generate a terahertz wave bessel beam using the terahertz wave incident from the terahertz wave generating portion 1411.
In practice, it is difficult for the Bessel Beam forming portion 1413 to form an ideal Bessel Beam, and therefore the Bessel Beam formed by the Bessel Beam forming portion 1413 may be referred to as Quasi-Bessel Beam (QBB). The structure of the bessel beam formed by the bessel beam forming unit 1413 is described in detail with reference to fig. 5.
The bessel beam forming unit 1413 may be arranged such that the terahertz waves whose angle is changed by the angle changing unit 1412 enter perpendicularly to the light incident surface of the bessel beam forming unit 1413.
The bessel beam forming portion 1413 may be a fourth conical lens having an apex angle formed so that the diameter of the terahertz bessel beam concentrated on the inspection target object is smaller than the wavelength of the terahertz wave generated by the terahertz wave generating portion. In the present embodiment, the apex angle of the diameter of the bessel beam forming the terahertz wave smaller than the wavelength is defined as the maximum apex angle.
In this case, the Maximum value of the vertex angle τ of the fourth conical lens can be represented by a Full-Width Half-height (Full Width at Half Maximum) diameter ρ of the terahertz wave bessel beam concentrated on the inspection target objectFWHMWavelength lambda and foldRefractive index n, n0The calculation is performed by the following equation. Since the detailed description of this is already given in fig. 4, the description thereof will be omitted below.
The ring beam forming unit 1414 forms a ring beam (ring) using the terahertz wave bessel beam, and can condense the formed ring beam (ring) on the inspection target object 1420.
For example, the ring beam forming unit 1420 may condense the terahertz wave bessel beam, which is concentrated and then diverged by the bessel beam forming unit 1413, on the inspection target object again in a circular beam shape of a ring shape.
For example, the ring beam forming unit 1420 may be a third lens that forms a ring beam (ring) and condenses the formed ring beam (ring) on the inspection object.
The description of the annular beam forming portion 1420 will be described in detail with reference to fig. 15 to 23.
The inspection target object 1420 means a target object to be inspected, and may be disposed between the terahertz-wave optical head 1410 and the terahertz-wave condensing head 1430.
The terahertz-wave condensing head 1430 may include an annular beam detection part 1431 and a scattered light detection part 1432. In the present embodiment, although not shown, a first lens and a second lens (condensing portion) described in fig. 4 to 11 may be further included between the target object 1420 and the terahertz wave condensing head 1430. Accordingly, the first lens and the second lens condense the ring beam transmitted through the inspection target object 1420 to the ring beam detection part 1431, and the resolution of the inspection apparatus can be improved.
The annular beam detector 1431 can detect the annular beam transmitted through the inspection target object 1420.
The scattered light detection unit 1432 can detect scattered light generated from the detection target object 1420. For example, the scattered light detection part 1432 may include: reflected scattered light detection that can detect scattered light reflected from the inspection target object 1420; or a transmission scattered light detection unit for detecting scattered light transmitted through the inspection target object 1420.
The image generating part (not shown) may generate an image using the bessel beams detected by the annular beam detecting part 1431 and the scattered light detecting part 1432. The generated image may be displayed on a display unit (not shown).
The high-resolution inspection apparatus using the bessel beam forms terahertz waves without loss, and can improve contrast (contrast) to a transparent inspection object.
Further, the high-resolution inspection apparatus using the bessel beam detects scattered light generated from the inspection target object, and can improve the contrast (contrast) with respect to the transparent inspection target object.
In addition, since the high-resolution inspection apparatus using the bessel beam has the scattered light detection unit disposed inside the generated annular beam, it is not necessary to provide a separate space for adding the scattered light detection unit, and thus downsizing can be achieved.
In addition, since the high-resolution inspection apparatus using the bessel beam uses the lenses of the two ring beam forming portions even when the apex angle of the cone of the bessel beam forming portion is made small in order to achieve high resolution, the diameter of the generated ring beam is made small, and a high-resolution image can be obtained.
Fig. 15 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the first embodiment.
Referring to fig. 15, the high resolution inspection apparatus 1500 using a bessel beam may include: a terahertz wave generating unit 1510, an angle changing unit 1520, a bessel beam forming unit 1530, an annular beam forming unit 1540, an inspection target object 1550, an annular beam detecting unit 1560, a transmitted scattered light detecting unit 1570, and a reflected scattered light detecting unit 1571.
The terahertz wave generating section 1510 can generate a terahertz wave.
The angle changing unit 1520 reduces the angle of the terahertz wave incident from the terahertz wave generating unit 1510 and makes the terahertz wave incident on the bessel beam forming unit 1530 incident thereon.
The bessel beam forming unit 1530 can form a terahertz wave bessel beam by using the terahertz wave incident from the angle changing unit 1520. For example, the bessel beam forming portion may be a cone.
The ring beam forming part 1540 may be a third lens that forms a ring beam (ring) using the terahertz wave bessel beam incident from the bessel beam forming part 1530 and may condense the formed ring beam (ring) to the inspection target object 1550.
The ring beam detector 1560 can detect the ring beam transmitted through the inspection target object 1550.
The transmitted scattered light detection unit 1570 can detect scattered light transmitted from the inspection target object 1550. For example, the transmitted scattered light detecting section 1570 may be arranged inside the ring-shaped light beam incident from the third lens. In this way, the transmitted scattered light detecting unit 1570 is disposed inside the ring beam, and there is an advantage that the size of the entire apparatus of the transmitted scattered light detecting unit 1570 is not changed even if the size is increased.
The reflected scattered light detection unit 1571 is disposed inside the annular light beam irradiated from the third lens 1540 as an annular light beam forming unit, and is disposed inside the third lens 1540.
Fig. 16 is a diagram showing an embodiment of the annular beam forming portion 1540 in fig. 15.
Referring to fig. 16, the annular beam forming part 1540 may include a member capable of accommodating the reflected scattered light detecting part 1571. For example, the ring-shaped beam forming portion 1540 has a hole (hole)1600, and the reflected scattered light detecting portion 1571 may be disposed inside the hole 1600. For example, the reflected/scattered light detector 1571 is disposed inside the annular beam shaper 1640 and inside the annular beam irradiated from the third lens 1540. In this way, the reflected scattered light detection unit 1571 is disposed inside the annular beam forming unit 1540, and there is an advantage that the size of the entire scattered light detection unit 1571 is not changed even if the size is increased.
Further, the high-resolution inspection apparatus using the bessel beam detects scattered light generated from the inspection target object, and can improve the contrast (contrast) with respect to the transparent inspection target object.
In addition, since the high-resolution inspection apparatus using the bessel beam has the scattered light detection unit disposed inside the generated annular beam, it is not necessary to provide a separate space for adding the scattered light detection unit, and thus downsizing can be achieved.
Fig. 17 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the second embodiment.
Referring to fig. 17, a high resolution inspection apparatus 1700 using a bessel beam may include: a terahertz wave generating unit 1710, an angle changing unit 1720, a bessel beam forming unit 1730, an annular beam forming unit 1740, an inspection target object 1750, an annular beam detecting unit 1760, an optical path changing unit 1770, a transmitted scattered light detecting unit 1780, and a reflected scattered light detecting unit 1781.
The terahertz wave generating portion 1710, the angle changing portion 1720, the bessel beam forming portion 1730, the ring beam forming portion 1740, and the inspection target object 1750 have already been described, and therefore, the description will be omitted below.
The ring beam detector 1760 can detect the ring beam transmitted through the inspection target object 1750.
The optical path changing unit 1770 can change the optical path of the scattered light reflected from the inspection target object 1750. For example, the optical path changer 1770 may cause the scattered light reflected from the test object 1750 to enter the reflected scattered light detector 1781.
The optical path changing unit 1770 may be a device having various shapes capable of making the scattered light incident on the reflected scattered light detecting unit 1781.
The annular beam forming portion 1740 may include a member capable of accommodating the optical path changing portion 1770.
The transmitted scattered light detector 1780 can detect scattered light transmitted through the object 1750 to be inspected. For example, the transmitted scattered light detection unit 1780 may be disposed inside the annular light beam incident from the third lens. In this way, the transmission/scattered light detection unit 1780 is disposed inside the ring beam, and there is an advantage that the size of the entire apparatus is not changed even if the transmission/scattered light detection unit 1780 is increased.
The reflected scattered light detection unit 1781 can detect scattered light incident from the optical path changing unit 1770.
The high-resolution inspection apparatus using the bessel beam detects scattered light generated from an inspection target object, and can further improve contrast (contrast) with respect to a transparent inspection target object.
Fig. 18 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the third embodiment.
Referring to fig. 18, the high resolution inspection apparatus 1800 using a bessel beam may include: a terahertz wave generating unit 1810, an angle changing unit 1820, a bessel beam forming unit 1830, annular beam forming units 1840 and 1850, an object to be inspected 1860, an annular beam detecting unit 1870, a transmitted scattered light detecting unit 1880, and a reflected scattered light detecting unit 1881.
The terahertz wave generating unit 1810, the angle changing unit 1820, the bessel beam forming unit 1830, the inspection object 1860, the annular beam detecting unit 1870, the transmitted scattered light detecting unit 1880, and the reflected scattered light detecting unit 1881 have been described above with reference to fig. 17, and therefore, description thereof will be omitted in this embodiment.
The ring-shaped beam forming parts 1840, 1850 may include: a fourth lens 1840 that reduces the angle of the terahertz wave bessel beam incident from the bessel beam forming unit and enters the third lens 1850; and a first lens 1850 that forms a ring-shaped (ring) beam using the terahertz wave bessel beam incident from the fourth lens 1840 and condenses the formed ring-shaped (ring) beam to the inspection object 1860.
In the case where the bessel beam forming unit 1830 is a fourth conical lens, the fourth lens 1840 may be a fifth conical lens disposed symmetrically to the fourth conical lens 1830 with reference to a line perpendicular to the optical axis.
The fifth pyramidal lens 1840 may have an apex angle of the same size as the fourth pyramidal lens 1830. In this case, the size of the fifth conic lens may be smaller than or equal to, larger than the fourth conic lens 1830.
The third lens 1850 has the same shape as the fifth conic lens 1840, and may be a sixth conic lens disposed symmetrically with the fifth conic lens 1840 with respect to an axis perpendicular to the optical axis.
As described above, the ring beam forming unit is realized by the fourth lens 1840 and the third lens 1850, and when the apex angle of the fourth cone lens is made smaller in order to improve the resolution, the diameter of the ring beam incident on the inspection target object may be made smaller. Therefore, the resolution can be significantly improved, and high-resolution reflection and transmission inspection images can be acquired.
Fig. 19 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to the fourth embodiment fig. 14.
Referring to fig. 19, a high resolution inspection apparatus 1900 using a bessel beam includes: a terahertz wave generating unit 1910, an angle changing unit 1920, a bessel beam forming unit 1930, ring beam forming units 1940, 1950, an object to be inspected 1960, a ring beam detecting unit 1970, a transmitted scattered light detecting unit 1980, and a reflected scattered light detecting unit 1981.
The terahertz wave generating unit 1910, the angle changing unit 1920, the bessel beam forming unit 1930, the ring beam detecting unit 1970, the transmitted scattered light detecting unit 1980, and the reflected scattered light detecting unit 1981 are explained in detail in fig. 17, and therefore, the explanation of the present embodiment is omitted.
The angle changing part 1920 may be a fifth convex lens that can reduce the angle of the terahertz wave incident from the terahertz wave generating part 1910.
The annular beam forming portions 1940, 1950 may include: a fourth lens 1940 that reduces an angle of the terahertz wave bessel beam incident from the bessel beam forming portion to be incident on the third lens; and a third lens 1950 forming a ring-shaped (ring) beam with the terahertz wave bessel beam incident from the fourth lens 1940 and condensing the formed ring-shaped (ring) beam to the target object 1960.
The fourth lens 1940 may be a seventh convex lens that reduces an angle of the terahertz waves diverged while transmitting the terahertz-wave bessel beam through the inspection target object.
The third lens 1950 may be an eighth convex lens which is disposed symmetrically with respect to an axis perpendicular to the optical axis and a fifth convex lens as the angle changing part 1920, and is disposed opposite to a seventh convex lens as the fourth lens 1940. The seventh convex lens and the eighth convex lens may have the same shape/size.
As described above, when the annular beam forming unit is realized by using the first lens and the second lens, and the apex angle of the fourth cone lens is reduced to improve the resolution, the diameter of the annular beam incident on the inspection target object may be reduced. Therefore, the resolution can be significantly improved, and high-resolution reflection and transmission inspection images can be acquired.
Fig. 20 is a diagram for explaining a high-resolution inspection apparatus using a terahertz wave bessel beam according to the fifth embodiment fig. 14.
Referring to fig. 20, a high resolution inspection apparatus 2000 using a bessel beam includes: the terahertz wave generating section 2010, the angle changing section 2020, the bessel beam forming section 2030, the ring beam forming sections 2040, 2050, the object to be inspected 2060, the ring beam detecting section 2070, the transmitted scattered light detecting section 2080, and the reflected scattered light detecting section 2081.
The terahertz wave generating section 2010, the angle changing section 2020, the bessel beam forming section 2030, the object to be inspected 2060, the annular beam detecting section 2070, the transmitted scattered light detecting section 2080 and the reflected scattered light detecting section 2081 have already been described with reference to fig. 17, and therefore, description of the above-described structures is omitted in this embodiment.
The angle changing part 2020 may be a fifth convex lens that can reduce the angle of the terahertz wave incident from the terahertz wave generating part 2010.
The annular beam forming portions 2040, 2050 may include: a fourth lens 2040 which reduces the angle of the terahertz wave bessel beam incident from the bessel beam forming portion to be incident on the third lens 2050; and a third lens 2050 that forms a ring-shaped (ring) beam with the terahertz-wave bessel beam incident from the fourth lens 2040 and condenses the formed ring-shaped (ring) beam to the target object 2060.
In the case where the bessel beam forming section 2030 is a fourth cone lens, the fourth lens 2040 may be a fifth cone lens disposed symmetrically with respect to the fourth cone lens 2030 with reference to a line perpendicular to the optical axis.
The third lens 2050 may be a sixth convex lens arranged symmetrically with respect to the fourth convex lens as the angle changing unit 2020 with respect to an axis perpendicular to the optical axis.
As described above, when the annular beam forming unit is realized by using the first lens and the second lens, and the apex angle of the fourth cone lens is reduced to improve the resolution, the diameter of the annular beam incident on the inspection target object may be reduced. Therefore, the resolution can be significantly improved, and high-resolution reflection and transmission inspection images can be acquired.
Fig. 21 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the sixth embodiment.
Referring to fig. 21, the high resolution inspection apparatus 2100 using a bessel beam includes: a terahertz wave generating unit 2110, an angle changing unit 2120, a bessel beam forming unit 2130, ring beam forming units 2140, 2150, an inspection object 2160, a ring beam detecting unit 2170, an optical path changing unit 2180, a transmitted scattered light detecting unit 2190, and a reflected scattered light detecting unit 2191.
The terahertz wave generating unit 2110, the angle changing unit 2120, the bessel beam forming unit 2130, the inspection object 2160, the ring beam detecting unit 2170, the optical path changing unit 2180, the transmitted scattered light detecting unit 2190, and the reflected scattered light detecting unit 2191 have been described above with reference to fig. 17, and therefore, description thereof is omitted in this embodiment.
The annular beam forming portions 2040, 2050 may include: a second lens 2140 that reduces the angle of the terahertz wave bessel beam incident from the bessel beam forming section to be incident on the third lens 2150; and a third lens 2150 that forms a ring-shaped (ring) beam with the terahertz wave bessel beam incident from the fourth lens 2140 and condenses the formed ring-shaped (ring) beam to the target object 2160.
When the bessel beam forming unit 2130 is a fourth conic lens, the fourth lens 2140 may be a fifth conic lens disposed symmetrically with respect to the fourth conic lens 2130 with respect to a line perpendicular to the optical axis.
The fifth tapered lens 2140 can have a vertex angle that is the same size as the fourth tapered lens 2130. In this case, the size of the fifth conical lens may be smaller than or equal to, larger than the fourth conical lens 2130. When the apex angle of the fifth cone lens is the same as that of the fourth cone lens 2130, the terahertz wave is condensed to the detection portion 2170 with the best efficiency.
The third lens 2150 has the same shape as the fifth conical lens 2140, and may be a fifth conical lens arranged symmetrically with respect to the fifth conical lens 2140 with an axis perpendicular to the optical axis as a reference.
Fig. 22 is a diagram for explaining the high-resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the seventh embodiment.
Referring to fig. 22, the high resolution inspection apparatus 2200 using the bessel beam includes: a terahertz wave generating section 2210, an angle changing section 2220, a bessel beam forming section 2230, ring beam forming sections 2240, 2250, an object under examination 2260, a ring beam detecting section 2270, a light path changing section 2280, a transmitted scattered light detecting section 2290, and a reflected scattered light detecting section 2291.
The terahertz wave generating unit 2210, the angle changing unit 2220, the bessel beam forming unit 2230, the inspection target object 2260, the ring beam detecting unit 2270, the optical path changing unit 2280, the transmitted scattered light detecting unit 2290, and the reflected scattered light detecting unit 2291 have already been described with reference to fig. 17, and therefore, description thereof is omitted in this embodiment.
The angle changing part 2220 may be a fifth convex lens that can reduce the angle of the terahertz wave incident from the terahertz wave generating part 2210.
The ring beam forming part 2240, 2250 may include: a fourth lens 2240 that reduces the angle of the terahertz wave bessel beam incident from the bessel beam forming unit and makes the terahertz wave bessel beam incident on the third lens 2250; and a third lens 2250 that forms a ring-shaped (ring) beam with the terahertz wave bessel beam incident from the fourth lens 2240 and condenses the formed ring-shaped (ring) beam to the target object 2260.
The third lens 2240 may be a seventh convex lens that reduces the angle of the terahertz wave that diverges while passing the terahertz wave bessel beam through the inspection target object.
The third lens 2250 may be an eighth convex lens that is disposed symmetrically with respect to the fifth convex lens as the angle changing unit 2220 with respect to an axis perpendicular to the optical axis and faces the seventh convex lens as the fourth lens 2240.
Fig. 23 is a diagram for explaining the high resolution inspection apparatus using a terahertz wave bessel beam of fig. 14 according to the eighth embodiment.
Referring to fig. 23, the high resolution inspection apparatus 2300 using a bessel beam includes: a terahertz wave generating unit 2310, an angle changing unit 2320, a bessel beam forming unit 2330, annular beam forming units 2340 and 2350, an object to be inspected 2360, an annular beam detecting unit 2370, an optical path changing unit 2380, a transmitted scattered light detecting unit 2390, and a reflected scattered light detecting unit 2391.
The terahertz wave generating section 2310, the angle changing section 2320, the bessel beam forming section 2330, the annular beam forming sections 2340 and 2350, the inspection target object 2360, the annular beam detecting section 2370, the optical path changing section 2380, the transmitted scattered light detecting section 2390, and the reflected scattered light detecting section 2391 have already been described with reference to fig. 17, and therefore, the description thereof is omitted in this embodiment.
The angle changing part 2320 may be a fourth convex lens that may reduce the angle of the terahertz wave incident from the terahertz-wave generating part 2310.
The annular beam forming portions 2340, 2350 may include: a fourth lens 2340 that reduces the angle of the terahertz wave bessel beam incident from the bessel beam forming portion to be incident on the third lens 2350; and a third lens 2250 that forms an annular (ring) beam with the terahertz wave bessel beam incident from the fourth lens 2340 and condenses the formed annular (ring) beam to the target object 2360.
When the bessel beam former 2330 is a fourth cone lens, the fourth lens 2340 may be a fifth cone lens arranged symmetrically with respect to the fourth cone lens 2330 with reference to a line perpendicular to the optical axis.
The third lens 2350 may be a sixth convex lens symmetrically arranged with respect to the fifth convex lens as the angle changing part 2320 with respect to an axis perpendicular to the optical axis
The illustrated embodiments may be combined selectively to form all or a part of each embodiment.
Additionally, it should be noted that the embodiments are illustrative and not restrictive. It should be understood by those having ordinary knowledge in the technical field of the present invention that various embodiments can be implemented within the technical idea of the present invention.

Claims (9)

1. A high resolution inspection apparatus using bessel beams, comprising:
a terahertz wave generating unit that generates terahertz waves;
a bessel beam forming unit that forms a terahertz wave bessel beam on the inspection target object by using the terahertz wave incident from the terahertz wave generating unit;
a first lens that reduces an angle of a terahertz wave that diverges while passing the terahertz wave bessel beam through the inspection target object;
a second lens that condenses the terahertz wave having passed through the first lens to a detection unit; and
a terahertz wave detection section that detects the terahertz wave condensed by the second lens,
the bessel beam forming part is a first cone lens,
the first conic lens has an apex angle formed by a diameter of the terahertz-wave bessel beam being smaller than a wavelength of the terahertz wave generated by the terahertz-wave generating portion.
2. The high resolution inspection apparatus using Bessel beams according to claim 1,
the minimum value of the vertex angle of the first conic lens is the vertex angle of the first conic lens where total reflection does not occur according to the refractive index of the first conic lens.
3. The high resolution inspection apparatus using Bessel beams according to claim 1,
the first lens is a second tapered lens,
the second conical lens is arranged symmetrically with respect to the first conical lens with the object to be inspected as a reference.
4. The high resolution inspection apparatus using Bessel beams according to claim 3,
the second conical lens has an apex angle of the same size as the first conical lens.
5. The high resolution inspection apparatus using a bessel beam according to claim 1, characterized by further comprising:
an angle changing unit that reduces an angle of the terahertz wave incident from the terahertz wave generating unit so as to be incident on the bessel beam forming unit.
6. The high resolution inspection apparatus using Bessel beams according to claim 5,
the angle changing unit is a first convex lens that reduces the angle of the terahertz wave incident from the terahertz wave generating unit, and the second lens is a second convex lens that is arranged symmetrically with respect to the first convex lens with respect to the inspection target object.
7. The high resolution inspection apparatus using Bessel beams according to claim 3,
the second lens is a third tapered lens having the same shape as the second tapered lens and arranged symmetrically with respect to the second tapered lens with an axis perpendicular to the optical axis as a reference.
8. The high resolution inspection apparatus using Bessel beams according to claim 3,
the first lens is a third convex lens,
the third convex lens reduces a terahertz wave angle at which the terahertz wave bessel beam diverges while passing through the inspection target object.
9. The high resolution inspection apparatus using Bessel beams according to claim 8,
the second lens is a fourth convex lens,
the fourth convex lens is arranged symmetrically with respect to the third convex lens with respect to an axis perpendicular to the optical axis.
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