CN116840184A - Terahertz lens-free line scanning imaging device - Google Patents
Terahertz lens-free line scanning imaging device Download PDFInfo
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- G—PHYSICS
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- 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
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- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
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Abstract
The invention discloses a terahertz lens-free line scanning imaging device, and relates to the field of terahertz active imaging; the terahertz lens-less line scanning imaging device includes: the device comprises a double-device, an adjusting device and a detecting device; the dual device apparatus includes: negative roof pyramids and column pyramids; the dual-device is used for generating terahertz wave sheet-shaped diffraction-free beams; the adjusting device is used for adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured object; the detection device is used for collecting transmission signals of the detected target and obtaining terahertz transmission images of the detected target based on the transmission signals. The terahertz wave sheet-shaped diffraction-free beam is adopted for lens-free line scanning imaging, so that the imaging time is greatly saved, and the device is simplified to a certain extent. Meanwhile, the device has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, and can be matched with a detection device for use, so that the detection speed and the detection efficiency are effectively improved.
Description
Technical Field
The invention relates to the field of terahertz active imaging, in particular to a terahertz lens-free line scanning imaging device.
Background
Terahertz waves are between infrared and microwave, and have strong penetrability to many nonpolar materials. Shorter wavelengths of terahertz waves provide higher imaging spatial resolution relative to microwaves. Compared with the X-ray with strong penetrating power, the terahertz wave has low photon energy, so ionization is not easy to occur when a substance is penetrated, and the terahertz wave has important application potential and value in the fields of nondestructive detection and the like. When the penetrability of terahertz waves is utilized to perform nondestructive detection or human body security inspection on the inside of a material, terahertz imaging technology becomes an important foundation for the applications.
Terahertz imaging systems are classified into passive imaging and active imaging. Passive imaging relies on weak terahertz waves generated by the object to be tested to image, and an external terahertz radiation source is not required to irradiate, so that the imaging resolution is relatively low due to the fact that the signal is too weak. The active imaging is that terahertz radiation emitted by an imaging system irradiates a target, and terahertz wave signals containing the amplitude and phase information of the target are returned to the imaging system and converted into electric signals to form a terahertz image of the target, and feature information of the target is extracted according to the shape and gray values of the image. The existing active terahertz imaging system mainly adopts modes of point-by-point scanning imaging, area array imaging and the like, the point-by-point scanning adopts various motor structures to carry out two-dimensional scanning, the time consumption is long, the efficiency is low, and the area array imaging has the defects of relatively complex system, expensive equipment and the like.
The Bessel beam has diffraction-free characteristics, is widely used for expanding the depth of field of an imaging system, and is suitable for acquiring internal structural information of materials or detecting samples with larger thickness. The axicon is the device most commonly used for generating terahertz zero-order Bessel beams due to the simple structure, convenient manufacturing and high energy utilization rate. However, when the beam waist radius of the incident gaussian beam and the device material are fixed, different diffraction-free distances and spot sizes can be obtained only by changing the base angle of the axicon, and the degree of freedom of adjustment is lacking.
Disclosure of Invention
The invention aims to provide a terahertz lens-free line scanning imaging device, which adopts terahertz wave sheet-shaped diffraction-free beams to carry out lens-free line scanning imaging, and the device is simplified to a certain extent. Meanwhile, the device has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, and can be matched with a detection device for use, so that the detection speed and the detection efficiency are effectively improved.
In order to achieve the above object, the present invention provides the following solutions:
a terahertz lensless line scan imaging device, the terahertz lensless line scan imaging device comprising: the device comprises a double-device, an adjusting device and a detecting device;
the dual device apparatus includes: negative roof pyramids and column pyramids;
the dual-device is used for generating terahertz wave sheet-shaped diffraction-free beams;
the adjusting device is used for adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured target;
the detection device is used for collecting transmission signals of the detected target and obtaining terahertz transmission images of the detected target based on the transmission signals.
Optionally, the negative roof pyramid comprises two mirror-symmetrical first right-angle straight triangular prisms; the target edges of the two first right-angle triangular prisms are connected; the target right-angle side surfaces of the two first right-angle triangular prisms are positioned on the same horizontal plane; the target edge is any one side edge of the bevel side face; the target right-angle side surface is a right-angle side surface comprising a target edge;
the column ridge pyramid comprises a column lens and a roof ridge pyramid; the ridge pyramid comprises two second right-angle triangular prisms which are mirror symmetry; the selected right-angle side surfaces of the two second right-angle triangular prisms are connected.
Optionally, the adjusting device includes: a first two-dimensional translation stage;
the first two-dimensional translation stage is used for moving the horizontal position and/or the vertical position of the measured target and adjusting the positions of different rows of the measured target, which are transmitted by the terahertz wave sheet-like diffraction-free beam.
Optionally, the adjusting device includes: the device comprises a second two-dimensional translation stage, a rotating device and a rotating polygon mirror device;
the rotating polygon mirror device is positioned between the measured object and the double-device and is used for adjusting the deflection angle of the terahertz wave sheet-shaped diffraction-free beam;
the rotating device is used for rotating the double-device and adjusting the long axis direction of the terahertz wave sheet-shaped diffraction-free beam;
the second two-dimensional translation stage is used for adjusting the horizontal position and/or the vertical position of the detection device.
Optionally, the rotating polygon mirror apparatus includes: a motor and a rotating polygonal plate;
the motor is used for rotating the rotary polygon mirror plate to adjust the deflection angle of the terahertz wave sheet diffraction-free beam.
Optionally, the rotary polygonal plate includes a disc substrate and N third right angle right triangular prisms;
the method for fixing the N third right-angle triangular prisms on one surface of the disc substrate at equal angular radial intervals in sequence specifically comprises the following steps:
fixing the first right-angle side surface of the third right-angle triangular prism on one surface of the disc substrate;
wherein the next of the N-1 th third right angle triangular prism is the N-th third right angle triangular prism, n=2, 3. The first right angle side of the n-1 th third right angle triangular prism is shorter than the first right angle side of the n-th third right angle triangular prism; the second right-angle side and the hypotenuse of the n-1 third right-angle triangular prism are equal to the second right-angle side and the hypotenuse of the n third right-angle triangular prism; two vertexes of the bottom edges of the third right-angle triangular prisms, which are far away from the circle center of the disc substrate, are overlapped with the edge of the disc substrate; the first right-angle side is a right-angle side including a first right-angle side.
Optionally, the first right angle side of the third right angle triangular prism of the rotary polygonal plate is,
h 3_i ＝w 3 tanγ 3_i ＝w 3 sinθ i /(n 3 -cosθ i )；
wherein h is 3_i A first right angle side representing an ith third right angle right triangular prism; w (w) 3 A second right angle side representing a third right angle triangular prism; gamma ray 3_i Representing an angle formed by a first right-angle side and a hypotenuse of an ith third right-angle right triangular prism; n is n 3 Representing the refractive index of the third right triangular prism; θ i The deflection angle of the terahertz wave sheet-shaped diffraction-free beam passing through the ith third right-angle straight triangular prism is shown.
Optionally, calculating the delivery distance d of the terahertz wave sheet-like diffraction-free beam by solving the following equation 2 And non-diffracting distance Z max ；
n 1 sinγ 1 ＝sin(α 1 +γ 1 )；
w 0 +(d 1 -tanγ 1 )tanα 1 ＝R；
sinα 2 ＝d 1 tanα 1 /r 2 ；
sinβ 1 ＝R/r 2 ；
sin(α 1 +α 2 )＝n 2 sinα 3 ；
n 2 sin(γ 2 +α 3 -α 2 )＝sinα 4 ；
tan(α 4 -γ 2 )＝(d 1 tanα 1 )/d 2 ；
sin(α 1 +β 1 )＝n 2 sinβ 2 ；
n 2 sin(γ 2 +β 2 -β 1 )＝sinβ 3 ；
tan(β 3 -γ 2 )＝R/(d 2 +Z max )；
Wherein n represents the refractive index of the two-device apparatus; gamma ray 1 Representing the apex angle of the first right-angle straight triangular prism; alpha 1 Representing the bias of terahertz wave after passing through negative ridge pyramidA corner; w (w) 0 Representing the radius of the terahertz beam entering the negative roof pyramid; d, d 1 Representing the distance between the negative roof pyramid and the column pyramid; r represents the distance between the outermost light ray incident on the prism face of the prism-ridge pyramid and the optical axis; r is (r) 2 Representing the radius of curvature of the cylindrical lens in the cylindrical ridge pyramid; d, d 2 Representing the delivery distance of the terahertz wave sheet-like diffraction-free beam; z is Z max Indicating the non-diffraction distance; alpha 2 An angle between the normal line of the incident surface of the innermost ray incident on the cylindrical lens surface and the optical axis is represented; alpha 3 Representing the angle between the normal of the incident surface of the innermost ray passing through the cylindrical lens surface and the refracted ray thereof; alpha 4 Representing the included angle between the normal line of the incident surface of the innermost ray passing through the ridge pyramid surface and the refracted ray thereof; gamma ray 2 Representing the apex angle of the second right-angle straight triangular prism; beta 1 An angle between the normal line of the incident surface of the outermost light ray incident on the cylindrical lens surface and the optical axis is represented; beta 2 Representing the angle between the normal of the incident surface of the outermost light passing through the cylindrical lens surface and the refracted light thereof; beta 3 Representing the included angle between the normal line of the incident surface of the outermost light passing through the ridge pyramid surface and the refracted light thereof; n is n 1 Representing the refractive index of the first right triangular prism; n is n 2 The refractive index of the second right triangular prism is indicated.
Optionally, the terahertz lens-less line scanning imaging device further includes: a collimating lens;
the collimating lens is arranged between the terahertz radiation source and the double-device; the collimating lens is used for collimating terahertz waves emitted by the terahertz radiation source. .
Optionally, the collimating lens is a spherical or free-form convex lens.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the terahertz lens-less line scanning imaging device includes: the device comprises a double-device, an adjusting device and a detecting device; the dual device apparatus includes: negative roof pyramids and column pyramids; the dual-device is used for generating terahertz wave sheet-shaped diffraction-free beams; the terahertz wave sheet diffraction-free beam is adopted for lens-free imaging, so that the device is simplified to a certain extent. The adjusting device is used for adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured object; the detection device is used for collecting transmission signals of the measured object device and obtaining terahertz transmission images of the measured object based on the transmission signals. Meanwhile, the device has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, and can be matched with a detection device for use, so that the detection speed and the detection efficiency are effectively improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a terahertz lensless line scan imaging device in an embodiment of the invention;
fig. 2 is a block diagram of a terahertz lensless line scanning imaging device in an embodiment of the invention;
FIG. 3 is a schematic diagram of a negative roof pyramid of a terahertz lensless line scan imaging device in an embodiment of the invention;
FIG. 4 is a schematic diagram of a cylindrical ridge pyramid of a terahertz lensless line scan imaging device in an embodiment of the invention;
FIG. 5 is a schematic diagram of a rotating polygonal plate of a terahertz lensless line scanning imaging device in an embodiment of the invention;
FIG. 6 is a geometric optical schematic of the dual device operation of a terahertz lensless line scan imaging device in an embodiment of the invention;
FIG. 7 is a geometric optical schematic of a third rectangular prism of a terahertz lensless line scanning imaging device in an embodiment of the invention;
FIG. 8 is a schematic diagram of the design of a rotating polygonal plate of a terahertz lensless line scanning imaging device in an embodiment of the invention;
FIG. 9 is a simulation result of the light intensity distribution of the sheet-like non-diffracted beam in the xz plane and the yz plane generated by the two-device composed of the negative roof pyramid and the column-ridge pyramid of the terahertz non-lens line-scan imaging device in the embodiment of the invention;
fig. 10 is an experimental measurement result of light intensity distribution of a sheet-shaped non-diffracted beam in an xz plane and a yz plane generated by a two-device composed of a negative roof pyramid and a column pyramid of a terahertz non-lens line-scan imaging device in an embodiment of the invention.
Symbol description:
1. a terahertz radiation source; 2. a collimating lens; 3. a negative roof pyramid; 4. a pillar ridge pyramid; 5. a measured target; 6. a first two-dimensional translation stage; 7. terahertz linear array detector; 8. a controller; 9. rotating the polygonal plate; 10. a motor; 11. a second two-dimensional translation stage.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a terahertz lens-free line scanning imaging device, which uses terahertz wave sheet-shaped diffraction-free beams to carry out lens-free imaging, and simplifies the device to a certain extent. Meanwhile, the device has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, and can be matched with a detection device for use, so that the detection speed and the detection efficiency are effectively improved.
The invention designs and makes refraction devices, namely a negative roof pyramid, a column pyramid and a rotary polygon prism plate, and builds a terahertz lens-free imaging system capable of realizing line scanning in any direction. Compared with complex scanning modes such as two-dimensional point scanning and the like, the imaging time is greatly saved by adopting a one-dimensional scanning mode; the terahertz wave sheet diffraction-free beam is adopted for lens-free imaging, so that the system structure is simplified to a certain extent. Meanwhile, the device has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, can be matched with a linear array detector for use, and effectively improves the detection speed and efficiency. The invention can realize the rapid line scanning imaging in any direction while keeping large depth of field and high resolution.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
The invention adopts a method for actively transmitting terahertz radiation by using a terahertz source and receiving the terahertz radiation by using a terahertz wave sheet-shaped diffraction-free beam one-dimensional scanning and linear array terahertz detector. The designed and manufactured rotary polygon prism plate can be used for rapidly scanning the whole target in any direction, so that the purposes of imaging and detecting hidden objects and fixed objects are achieved.
As shown in fig. 1 and 2, the present invention provides a terahertz lensless line scanning imaging device including: a two-component device, an adjusting device and a detecting device.
The dual device apparatus includes: negative roof pyramids 3 and column pyramids 4.
The dual-device is used for generating terahertz wave sheet-shaped diffraction-free beams with a certain delivery distance. The terahertz-wave sheet-like undiffracted beam can be regarded as approximately an ellipse whose eccentricity is close to 1.
The adjusting device is used for adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured object 5.
The detection device is used for collecting transmission signals of the detected target 5 and obtaining terahertz transmission images of the detected target 5 based on the transmission signals.
In a specific implementation, the terahertz radiation source 1 is used for emitting terahertz waves, and the terahertz radiation source 1 is a vacuum electronics terahertz radiation source based on a traveling wave tube, a gyrotron, a backward wave tube and the like, a solid-state electronics terahertz radiation source based on a schottky diode, a gunn oscillation diode, a silicon avalanche transit time diode and the like, or a quantum cascade laser.
As shown in fig. 3, the negative roof pyramid includes two mirror-symmetrical first right-angle straight triangular prisms; the target edges of the two first right-angle triangular prisms are connected; the target right-angle side surfaces of the two first right-angle triangular prisms are positioned on the same horizontal plane; the target edge is any one side edge of the bevel side face; the target right-angle side is a right-angle side including a target edge. The bevel side surface consists of a hypotenuse of the triangle of the bottom surface, a hypotenuse of the triangle of the bottom surface and two side edges. The height of the first right-angle straight triangular prism is h 1 . The plane width formed by the target right-angle side surfaces of the two first right-angle triangular prisms is l 1 。
The column ridge pyramid comprises a column lens and a roof ridge pyramid; the ridge pyramid comprises two second right-angle triangular prisms which are mirror symmetry; the selected right-angle side surfaces of the two second right-angle triangular prisms are connected.
As shown in FIG. 4, as a specific embodiment, the roof pyramid in the present invention adopts a cylindrical lens with a curved surface of a cross section being an arc, and the height of the selected second right-angle triangular prism is h 2 . The plane of the cylindrical lens is connected with the plane formed by connecting the selected right-angle side surfaces of the two second right-angle triangular prisms. The widths of the planes formed by the connection of the planes of the cylindrical lenses and the selected right-angle side surfaces of the second right-angle triangular prism are l 2 。
As a specific embodiment, as shown in fig. 1, the adjusting device includes: a first two-dimensional translation stage 6.
The first two-dimensional translation stage 6 is used for moving the horizontal position and/or the vertical position of the measured object 5, and adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured object 5.
In a specific implementation, as shown in fig. 1, the detection device includes a terahertz linear array detector 7 and a controller 8, the terahertz linear array detector 7 collects a transmission signal of the device of the measured target 5, and transmits the transmission signal to the controller 8, the controller 8 obtains a terahertz transmission image of the measured target 5 based on the transmission signal, and the controller 8 is also used for controlling the first two-dimensional translation stage 6. The terahertz linear array detector 7 is a linear array composed of schottky diodes or a bolometer arrangement.
In specific implementation, the terahertz wave source 1 is used for generating terahertz waves, the waves propagate in free space according to Gaussian beam characteristics, the waves are collimated by the collimating lens 2 and then are incident into a double-device consisting of the negative roof pyramid 3 and the column ridge pyramid 4 in a circular light spot mode to generate terahertz wave sheet-shaped non-diffraction beams, the terahertz wave sheet-shaped non-diffraction beams are incident onto the measured target 5 on the first two-dimensional translation table 6, and finally the terahertz linear array detector 7 collects transmission signals and transmits the transmission signals to the controller 8. The controller 8 synchronously controls the first two-dimensional translation stage 6 and the terahertz linear array detector 7 to match the scanning speed and the image acquisition frame rate.
The specific scanning method comprises the following steps: the terahertz wave sheet diffraction-free beam is incident on the measured target 5, and the terahertz linear array detector 7 with a fixed position collects transmission signals of the measured target 5 to obtain information of one row of pixels of the measured target 5. The measured object 5 is moved through the first two-dimensional translation stage 6, so that terahertz wave sheet diffraction-free beams scan each row of pixels of the measured object 5 and are collected through the terahertz linear array detector 7. And finally, transmitting the signals to a controller 8 for splicing and restoring, so as to acquire the image information of the measured target 5.
As a specific embodiment, as shown in fig. 2, the adjusting device includes: a second two-dimensional translation stage 11, a rotation device and a rotating polygon device.
The rotating polygon mirror device is located between the measured object 5 and the two-device, and is used for adjusting the deflection angle of the terahertz wave sheet diffraction-free beam.
The rotating device is used for synchronously rotating a double-device consisting of the negative ridge pyramid 3 and the column ridge pyramid 4 and adjusting the long axis direction of the terahertz wave sheet diffraction-free beam.
The second two-dimensional translation stage 11 is used for adjusting the horizontal position and/or the vertical position of the detection device.
The rotary polygon mirror apparatus includes: a motor 10 and a rotating polygon mirror plate 9.
The motor 10 is used for rotating the rotary polygonal plate 9 to adjust the deflection angle of the terahertz wave sheet-shaped diffraction-free beam.
In a specific implementation, the long axis direction of the terahertz wave sheet-shaped diffraction-free beam is changed through a double-device formed by synchronously rotating the negative roof pyramid 3 and the column ridge pyramid 4, in a specific implementation, one prism unit (right-angle straight triangular prism) and the terahertz wave sheet-shaped diffraction-free beam are matched (overlapped) through the translation of the translation frame, if one right-angle straight triangular prism of the rotation multi-prism plate 9 is matched with the terahertz wave sheet-shaped diffraction-free beam, the movement is not needed, the rotation multi-prism plate 9 is rotated by utilizing the motor 10, and the terahertz wave sheet-shaped diffraction-free beam is subjected to line scanning along the direction perpendicular to the long axis. Since the terahertz wave sheet-like undiffracted beam can be rotated 360 ° in the long axis direction, line scanning imaging in an arbitrary direction can be realized. The controller 8 controls the motor 10 to rotate the rotating polygonal plate, so that the terahertz wave sheet-shaped non-diffraction beam scans each row of pixels of the measured object 5 at different deflection angles, and synchronously collects signals by controlling the second two-dimensional translation stage 11 to move the terahertz linear array detector 7. And finally, transmitting the signals to a controller 8 for splicing, so as to acquire the terahertz transmission image of the measured target 5. The terahertz linear array detector 7, the motor 10 and the second two-dimensional translation stage 11 are synchronously controlled by the controller 8 to match the scanning speed and the image acquisition frame rate.
The specific scanning method comprises the following steps: the terahertz wave source 1 is used for generating terahertz waves, the waves propagate in free space according to Gaussian beam characteristics, the terahertz waves are collimated by the collimating lens 2 and then are incident into a double-device structure consisting of the negative roof pyramid 3 and the column pyramid 4 in a circular light spot mode to generate terahertz wave sheet-shaped diffraction-free beams, the terahertz wave sheet-shaped diffraction-free beams are incident onto a measured target 5 with a fixed position at a certain deflection angle after passing through the rotating polygonal prism plate 9, and the terahertz linear array detector 7 collects transmission signals of the measured target 5 to obtain information of one row of pixels of the measured target 5. The controller 8 controls the motor 10 to rotate the rotating prism plate, so that the terahertz wave sheet-shaped non-diffraction beam scans each row of pixels of the measured target 5 at different deflection angles, and synchronously collects signals by moving the terahertz linear array detector 7 through the second two-dimensional translation stage 11. And finally, transmitting the signals to a controller 8 for splicing, and simultaneously processing geometric correction of the image according to parameters such as scanning distance, scanning angle and the like of the optical system, so as to acquire terahertz image information of the measured target 5. The rotating polygon mirror plate 9 is controlled to rotate by a motor 10, the terahertz linear array detector 7 is located on a second two-dimensional translation stage 11, and the terahertz linear array detector 7, the motor 10 and the second two-dimensional translation stage 11 are synchronously controlled by a controller 8 to match the scanning speed and the image acquisition frame rate.
As shown in fig. 5, the rotary polygonal plate includes a disk substrate and N third right-angle right triangular prisms; the method for fixing the N third right-angle triangular prisms on one surface of the disc substrate at equal angular radial intervals in sequence specifically comprises the following steps:
and fixing the first right-angle side surface of the third right-angle triangular prism on one surface of the disc substrate.
Wherein the next of the N-1 th third right angle triangular prism is the N-th third right angle triangular prism, n=2, 3. The first right angle side of the n-1 th third right angle triangular prism is shorter than the first right angle side of the n-th third right angle triangular prism; the second right-angle side and the hypotenuse of the n-1 third right-angle triangular prism are equal to the second right-angle side and the hypotenuse of the n third right-angle triangular prism; two vertexes of the bottom edges of the third right-angle triangular prisms, which are far away from the circle center of the disc substrate, are overlapped with the edge of the disc substrate; the first right-angle side is a right-angle side including a first right-angle side.
The radius of the rotary polygon mirror plate is r 3 Is composed of a disk substrate and a series of third right-angle triangular prisms with different bottom edges, and is used for deflecting terahertz wave sheet-shaped diffraction-free beams. The bottom surface of a series of third right-angle triangular prisms, which are coincident with the substrate, are all the same in size, i.e. l of each third right-angle triangular prism 3 And w 3 Are all equal. The heights of the bottom edges of the third right-angle straight triangular prisms are designed in an equidistant scanning mode, and all the third right-angle straight triangular prisms are arranged at equal angles along the disc substrate, and the bottom edges are twoThe apex coincides with the disk base edge.
According to FIG. 5, the first right-angle side is the short side of the surface of the third right-angle triangular prism in contact with the disk base, r 3 Represents the radius, w, of the disc substrate 3 W representing the second right-angle side and N third right-angle triangular prisms 3 Are equal, l 3 Indicating the hypotenuse of the third right angle triangular prism, the N third right angle triangular prism hypotenuses being equal.
As shown in fig. 7 and 8, the relationship between the deflection angle and the base angle of the terahertz-wave sheet-like undiffracted beam is:
nsinγ 3_i ＝sin(θ i +γ 3_i )；
the deflection angle of the terahertz wave sheet-shaped diffraction-free beam of each unit of the rotary polygonal plate is designed according to the equal scanning interval, namely:
d(tanθ i -tanθ i+1 )＝Δl；
Δl represents a distance between the terahertz wave sheet-like undiffracted beam deflected by the ith third right-angle triangular prism and the terahertz wave sheet-like undiffracted beam deflected by the (i+1) th third right-angle triangular prism. d represents the distance between the rotating polygonal plate and the object to be measured.
One right-angle side of the third right-angle triangular prism of the rotary polygonal plate is,
h 3_i ＝w 3 tanγ 3_i ＝w 3 sinθ i /(n 3 -cosθ i )；
wherein h is 3_i A first right angle side representing an ith third right angle right triangular prism; w (w) 3 A second right angle side representing a third right angle triangular prism; gamma ray 3_i Representing an angle formed by a first right-angle side and a hypotenuse of an ith third right-angle right triangular prism; n is n 3 Representing the refractive index of the third right triangular prism; θ i The deflection angle of the terahertz wave sheet-shaped diffraction-free beam passing through the ith third right-angle straight triangular prism is shown.
As a specific example, as shown in fig. 8, d=100 mm, Δl=10 mm, and the beam scanning range is 180mm, 18 third right-angle straight triangular prisms are provided for the corresponding rotating polygonal plate, the terahertz-wave sheet-like diffraction-free beam scanning angle is from-42 ° to 42 °, and the bottom surface height of each third right-angle straight triangular prism is also determined therefrom.
As shown in FIG. 6, the double-device structure composed of the negative roof pyramid and the column pyramid can be manufactured by changing the spacing d between devices 1 Base angle gamma of each device 1 、γ 2 Radius of curvature r of cylindrical lens 2 Adjusting delivery distance d of terahertz wave sheet diffraction-free beam 2 And non-diffracting distance Z max Thereby adjusting the depth of field of the system and realizing imaging and detection of targets at different positions.
When the radius after collimation is w 0 When the terahertz wave beam of (a) is incident on the two-device from the air, a section of delivering distance d is formed behind the column ridge pyramid 2 Length of Z max Is not diffracted (grey parts). The refractive index n=1.54 of the material, according to the refractive theorem and geometric relationship:
calculating the delivery distance d of the terahertz wave sheet diffraction-free beam by solving the following equation 2 And non-diffracting distance Z max ；
n 1 sinγ 1 ＝sin(α 1 +γ 1 )；
w 0 +(d 1 -tanγ 1 )tanα 1 ＝R；
sinα 2 ＝d 1 tanα 1 /r 2 ；
sinβ 1 ＝R/r 2 ；
sin(α 1 +α 2 )＝n 2 sinα 3 ；
n 2 sin(γ 2 +α 3 -α 2 )＝sinα 4 ；
tan(α 4 -γ 2 )＝(d 1 tanα 1 )/d 2 ；
sin(α 1 +β 1 )＝n 2 sinβ 2 ；
n 2 sin(γ 2 +β 2 -β 1 )＝sinβ 3 ；
tan(β 3 -γ 2 )＝R/(d 2 +Z max )；
Wherein n represents the refractive index of the two-device apparatus; gamma ray 1 Representing the apex angle of the first right-angle straight triangular prism; alpha 1 Representing the deflection angle of the terahertz wave after passing through the negative ridge pyramid; w (w) 0 Representing the radius of the terahertz beam entering the negative roof pyramid; d, d 1 Representing the distance between the negative roof pyramid and the column pyramid; r represents the distance between the outermost light ray incident on the prism face of the prism-ridge pyramid and the optical axis; r is (r) 2 Representing the radius of curvature of the cylindrical lens in the cylindrical ridge pyramid; d, d 2 Representing the delivery distance of the terahertz wave sheet-like diffraction-free beam; z is Z max Indicating the non-diffraction distance; alpha 2 An angle between the normal line of the incident surface of the innermost ray incident on the cylindrical lens surface and the optical axis is represented; alpha 3 Representing the angle between the normal of the incident surface of the innermost ray passing through the cylindrical lens surface and the refracted ray thereof; alpha 4 Representing the included angle between the normal line of the incident surface of the innermost ray passing through the ridge pyramid surface and the refracted ray thereof; gamma ray 2 Representing the apex angle of the second right-angle straight triangular prism; beta 1 An angle between the normal line of the incident surface of the outermost light ray incident on the cylindrical lens surface and the optical axis is represented; beta 2 Representing the angle between the normal of the incident surface of the outermost light passing through the cylindrical lens surface and the refracted light thereof; beta 3 Representing the included angle between the normal line of the incident surface of the outermost light passing through the ridge pyramid surface and the refracted light thereof; n is n 1 Representing the refractive index of the first right triangular prism; n is n 2 The refractive index of the second right triangular prism is indicated.
N in a specific application 1 、n 2 And n 3 May be equal.
As a specific example, solving the above equation is readily available d 2 ＝f 1 (γ 1 ,d 1 ,γ 2 ,r 2 )，Z max ＝f 2 (γ 1 ,d 1 ,γ 2 ,r 2 ). Thus d 2 And Z max Are all gamma 1 、d 1 、γ 2 、r 2 Can be turned onThe parameters are reasonably set to generate the required terahertz wave sheet-shaped diffraction-free beam. Alternatively, let w 0 ＝15mm，γ 1 ＝15°，γ 2 ＝10°，d 1 =100 mm. Then calculate the corresponding delivery distance d available 2 Approximately 87mm, no diffraction distance Z max ≈207mm。
As shown in fig. 9, from the distribution of the light beam in the xz plane and the yz plane in the simulation result, it can be seen that the light beam has a sheet-like non-diffraction characteristic, and the delivery distance is about 100mm, and the non-diffraction distance is about 200mm, which substantially coincides with the calculation result.
As shown in fig. 10, it can be seen from the measurement results that the terahertz wave sheet-like non-diffraction beam has a good non-diffraction effect in the range of 150mm to 350 mm. In practical application, different negative ridge pyramids and column ridge pyramids can be selected to form a double-device structure according to the requirements, and the distance d between devices is adjusted 1 The required terahertz wave sheet-like non-diffraction beam is generated.
As shown in fig. 1 and 2, the terahertz lens-less line scanning imaging apparatus further includes: a collimator lens 2.
The collimating lens 2 is arranged between the terahertz radiation source 1 and the two-device; the collimating lens 2 is used for collimating terahertz waves emitted by the terahertz radiation source. The dual-device receives the collimated terahertz waves and generates terahertz wave sheet-shaped diffraction-free beams based on the collimated terahertz waves.
The collimating lens 2 is a spherical or free-form convex lens.
The collimating lens 2, the negative roof pyramid 3, the column ridge pyramid 4 and the rotary polygonal prism plate 9 can be manufactured by 3D printing, and the material is high-density polyethylene or polytetrafluoroethylene and other terahertz wave high-transmission materials, so that the loss in a terahertz region is negligible.
The invention has the beneficial effects that the imaging time is greatly saved by adopting one-dimensional scanning and compared with complex scanning modes such as two-dimensional point scanning and the like. The terahertz wave sheet diffraction-free beam is adopted for lens-free line scanning imaging, and the system structure is simplified to a certain extent. On the other hand, the refractive device designed and manufactured has the advantages of high degree of freedom of adjustment, low cost, small energy loss, convenient adjustment and the like, and can be matched with a linear array detector for use, so that the detection speed and efficiency are effectively improved. The imaging system can realize rapid line scanning imaging in any direction while keeping large depth of field and high resolution, and is suitable for detecting hidden objects, fixed objects and other scenes. The functions can be realized in other wave bands such as microwaves, x-rays and the like, and only the manufacturing materials with good light transmittance effect in the corresponding wave bands are needed.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (10)
1. A terahertz lensless line scan imaging device, characterized in that the terahertz lensless line scan imaging device comprises: the device comprises a double-device, an adjusting device and a detecting device;
the dual device apparatus includes: negative roof pyramids and column pyramids;
the dual-device is used for generating terahertz wave sheet-shaped diffraction-free beams;
the adjusting device is used for adjusting the positions of the terahertz wave sheet-shaped diffraction-free beams transmitted to different rows of the measured target;
the detection device is used for collecting transmission signals of the detected target and obtaining terahertz transmission images of the detected target based on the transmission signals.
2. The terahertz lensless line scan imaging device of claim 1, wherein the negative roof pyramid includes two mirror-symmetrical first right-angle right triangular prisms; the target edges of the two first right-angle triangular prisms are connected; the target right-angle side surfaces of the two first right-angle triangular prisms are positioned on the same horizontal plane; the target edge is any one side edge of the bevel side face; the target right-angle side surface is a right-angle side surface comprising a target edge;
the column ridge pyramid comprises a column lens and a roof ridge pyramid; the ridge pyramid comprises two second right-angle triangular prisms which are mirror symmetry; the selected right-angle side surfaces of the two second right-angle triangular prisms are connected.
3. The terahertz lensless line scan imaging device of claim 1, wherein the adjusting means comprises: a first two-dimensional translation stage;
the first two-dimensional translation stage is used for moving the horizontal position and/or the vertical position of the measured target and adjusting the positions of different rows of the measured target, which are transmitted by the terahertz wave sheet-like diffraction-free beam.
4. The terahertz lensless line scan imaging device of claim 1, wherein the adjusting means comprises: the device comprises a second two-dimensional translation stage, a rotating device and a rotating polygon mirror device;
the rotating polygon mirror device is positioned between the measured object and the double-device and is used for adjusting the deflection angle of the terahertz wave sheet-shaped diffraction-free beam;
the rotating device is used for rotating the double-device and adjusting the long axis direction of the terahertz wave sheet-shaped diffraction-free beam;
the second two-dimensional translation stage is used for adjusting the horizontal position and/or the vertical position of the detection device.
5. The terahertz lensless line scan imaging device of claim 4, wherein the rotating polygon mirror device comprises: a motor and a rotating polygonal plate;
the motor is used for rotating the rotary polygon mirror plate to adjust the deflection angle of the terahertz wave sheet diffraction-free beam.
6. The terahertz lensless line scan imaging device of claim 5, wherein the rotating polygonal plate comprises a disk substrate and N third right-angle triangular prisms;
the method for fixing the N third right-angle triangular prisms on one surface of the disc substrate at equal angular radial intervals in sequence specifically comprises the following steps:
fixing the first right-angle side surface of the third right-angle triangular prism on one surface of the disc substrate;
wherein the next of the N-1 th third right angle triangular prism is the N-th third right angle triangular prism, n=2, 3. The first right angle side of the n-1 th third right angle triangular prism is shorter than the first right angle side of the n-th third right angle triangular prism; the second right-angle side and the hypotenuse of the n-1 third right-angle triangular prism are equal to the second right-angle side and the hypotenuse of the n third right-angle triangular prism; two vertexes of the bottom edges of the third right-angle triangular prisms, which are far away from the circle center of the disc substrate, are overlapped with the edge of the disc substrate; the first right-angle side is a right-angle side including a first right-angle side.
7. The terahertz lensless line scanning imaging device according to claim 6, wherein the first right-angle side of the third right-angle triangular prism of the rotating polygonal plate is,
h 3_i ＝w 3 tanγ 3_i ＝w 3 sinθ i /(n 3 -cosθ i )；
wherein h is 3_i A first right angle side representing an ith third right angle right triangular prism; w (w) 3 A second right angle side representing a third right angle triangular prism; gamma ray 3_i Representing an angle formed by a first right-angle side and a hypotenuse of an ith third right-angle right triangular prism; n is n 3 Representing the refractive index of the third right triangular prism; θ i Indicating that terahertz wave sheet-like diffraction-free beam passes through the ith third straightThe deflection angle of the angular straight triangular prism.
8. The terahertz wave sheet-like diffraction-free beam delivery distance d according to claim 1, wherein the terahertz wave sheet-like diffraction-free beam delivery distance d is calculated by solving the following equation 2 And non-diffracting distance Z max ；
n 1 sinγ 1 ＝sin(α 1 +γ 1 )；
w 0 +(d 1 -tanγ 1 )tanα 1 ＝R；
sinα 2 ＝d 1 tanα 1 /r 2 ；
sinβ 1 ＝R/r 2 ；
sin(α 1 +α 2 )＝n 2 sinα 3 ；
n 2 sin(γ 2 +α 3 -α 2 )＝sinα 4 ；
tan(α 4 -γ 2 )＝(d 1 tanα 1 )/d 2 ；
sin(α 1 +β 1 )＝n 2 sinβ 2 ；
n 2 sin(γ 2 +β 2 -β 1 )＝sinβ 3 ；
tan(β 3 -γ 2 )＝R/(d 2 +Z max )；
Wherein n represents the refractive index of the two-device apparatus; gamma ray 1 Representing the apex angle of the first right-angle straight triangular prism; alpha 1 Representing the deflection angle of the terahertz wave after passing through the negative ridge pyramid; w (w) 0 Representing the radius of the terahertz beam entering the negative roof pyramid; d, d 1 Representing the distance between the negative roof pyramid and the column pyramid; r represents the distance between the outermost light ray incident on the prism face of the prism-ridge pyramid and the optical axis; r is (r) 2 Representing the radius of curvature of the cylindrical lens in the cylindrical ridge pyramid; d, d 2 Representing the delivery distance of the terahertz wave sheet-like diffraction-free beam; z is Z max Indicating the non-diffraction distance; alpha 2 Indicating the innermost incidence on the cylindrical lens surfaceAn included angle between the normal line of the incident surface of the side light and the optical axis; alpha 3 Representing the angle between the normal of the incident surface of the innermost ray passing through the cylindrical lens surface and the refracted ray thereof; alpha 4 Representing the included angle between the normal line of the incident surface of the innermost ray passing through the ridge pyramid surface and the refracted ray thereof; gamma ray 2 Representing the apex angle of the second right-angle straight triangular prism; beta 1 An angle between the normal line of the incident surface of the outermost light ray incident on the cylindrical lens surface and the optical axis is represented; beta 2 Representing the angle between the normal of the incident surface of the outermost light passing through the cylindrical lens surface and the refracted light thereof; beta 3 Representing the included angle between the normal line of the incident surface of the outermost light passing through the ridge pyramid surface and the refracted light thereof; n is n 1 Representing the refractive index of the first right triangular prism; n is n 2 The refractive index of the second right triangular prism is indicated.
9. The terahertz lensless line scan imaging device of claim 1, further comprising: a collimating lens;
the collimating lens is arranged between the terahertz radiation source and the double-device; the collimating lens is used for collimating terahertz waves emitted by the terahertz radiation source.
10. The terahertz lensless line scan imaging device of claim 9, wherein the collimating lens is a spherical or freeform convex lens.
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