Terahertz lensless line-scan imaging device

Abstract

The application discloses a terahertz lensless line scanning imaging device, and relates to the field of terahertz active imaging. The terahertz lensless line scanning imaging device comprises a double-device device, an adjusting device and a detecting device. The double-device device comprises a negative roof prism and a column roof prism. The double-device device is used for generating a terahertz wave sheet-shaped non-diffracted beam. The adjusting device is used for adjusting the position of the terahertz wave sheet-shaped non-diffracted beam transmitted to different rows of a measured target. The detecting device is used for collecting a transmission signal of the measured target, and a terahertz transmission image of the measured target is obtained based on the transmission signal. The terahertz wave sheet-shaped non-diffracted beam is used for lensless 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 adjusting freedom, low cost, small energy loss, convenient adjustment and the like, and can be used in cooperation with the detecting device, so that the detection speed and efficiency are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of terahertz active imaging, and in particular to a terahertz lensless line scanning imaging device. Background Technology

[0002] Terahertz waves, falling between infrared and microwaves, possess strong penetrating power through many nonpolar materials. Compared to microwaves, the shorter wavelength of terahertz waves provides higher spatial resolution for imaging. Compared to X-rays, which also have strong penetrating power, terahertz waves have very low photon energy, making them less prone to ionization when penetrating matter. This has significant application potential and value in fields such as non-destructive testing. When utilizing the penetrating power of terahertz waves for non-destructive testing of internal materials or for human security inspections, terahertz imaging technology becomes a crucial foundation for these applications.

[0003] Terahertz imaging systems are divided into passive and active imaging. Passive imaging relies on the weak terahertz waves generated by the object being measured itself for imaging, without requiring an external terahertz radiation source. Due to the weak signal, the imaging resolution is relatively low. Active imaging involves the imaging system emitting terahertz radiation that illuminates the target. The terahertz wave signal, containing the target's amplitude and phase information, returns to the imaging system, is converted into an electrical signal to form a terahertz image of the target, and the target's feature information is extracted based on the image's shape and grayscale values. Current active terahertz imaging systems mainly employ point-by-point scanning imaging and area array imaging. Point-by-point scanning uses various motor structures for two-dimensional scanning, which is time-consuming and inefficient. Area array imaging suffers from drawbacks such as relatively complex systems and expensive equipment.

[0004] Bessel beams, due to their non-diffraction properties, are widely used to extend the depth of field in imaging systems, suitable for acquiring information about the internal structure of materials or detecting samples with large thicknesses. Due to their simple structure, ease of fabrication, and high energy efficiency, axial pyramids are the most commonly used devices for generating terahertz zero-order Bessel beams. However, when the beam waist radius of the incident Gaussian beam and the device material are fixed, different non-diffraction distances and spot sizes can only be obtained by changing the base angles of the axial pyramid, lacking degree of freedom in adjustment. Summary of the Invention

[0005] The purpose of this invention is to provide a terahertz lensless line scanning imaging device that uses a terahertz waveplate-shaped diffraction-free beam for lensless line scanning imaging, which simplifies the device to a certain extent. At the same time, the device has many advantages such as high degree of adjustment freedom, low cost, low energy loss, and convenient adjustment, and can be used in conjunction with a detection device to effectively improve detection speed and efficiency.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A terahertz lensless line scanning imaging device, the terahertz lensless line scanning imaging device comprising: a dual-device device, an adjustment device, and a detection device;

[0008] The dual-device device includes: a negative roof ridge pyramid and a column ridge pyramid;

[0009] The dual-device setup is used to generate a terahertz waveplate-shaped non-diffraction beam.

[0010] The adjustment device is used to adjust the position of the terahertz waveplate non-diffraction beam transmitted to different rows of the target under test;

[0011] The detection device is used to collect the transmission signal of the target under test, and obtain a terahertz transmission image of the target under test based on the transmission signal.

[0012] Optionally, the negative ridge pyramid includes two mirror-symmetric first right-angled triangular prisms; the target edges of the two first right-angled triangular prisms are connected; the target right-angled lateral faces of the two first right-angled triangular prisms are on the same horizontal plane; the target edge is any side edge of the oblique lateral face; the target right-angled lateral face is the right-angled lateral face including the target edge;

[0013] The ridge pyramid includes a cylindrical lens and a roof pyramid; the roof pyramid includes two mirror-symmetrical second right-angled triangular prisms; selected right-angled lateral faces of the two second right-angled triangular prisms are connected.

[0014] Optionally, the adjustment device includes: a first two-dimensional translation stage;

[0015] The first two-dimensional translation stage is used to move the horizontal and / or vertical position of the target under test and adjust the position of the terahertz waveplate non-diffraction beam transmitted to different rows of the target under test.

[0016] Optionally, the adjustment device includes: a second two-dimensional translation stage, a rotation device, and a rotating prism device;

[0017] The rotating prism device is located between the target under test and the dual-device device, and the rotating prism device is used to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam.

[0018] The rotating device is used to rotate the dual-device device and adjust the long axis direction of the terahertz waveplate-shaped non-diffraction beam.

[0019] The second two-dimensional translation stage is used to adjust the horizontal and / or vertical position of the detection device.

[0020] Optionally, the rotating prism device includes: a motor and a rotating prism plate;

[0021] The motor is used to rotate the rotating prism plate to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam.

[0022] Optionally, the rotating prism plate includes a disk base and N third right-angled triangular prisms;

[0023] N right-angled triangular prisms are fixed radially at equal angles to one side of the disk base, specifically including:

[0024] The first right-angled side surface of the third right-angled triangular prism is fixed to one side of the disk base;

[0025] Wherein, the next third right-angled triangular prism after the (n-1)th third right-angled triangular prism is the nth third right-angled triangular prism, n = 2, 3, ..., N; the first right-angled side of the (n-1)th third right-angled triangular prism is shorter than the first right-angled side of the nth third right-angled triangular prism; the second right-angled side and hypotenuse of the (n-1)th third right-angled triangular prism are equal to the second right-angled side and hypotenuse of the nth third right-angled triangular prism; the two vertices of the base of the plurality of third right-angled triangular prisms that are away from the center of the disk base coincide with the edge of the disk base; the first right-angled lateral surface is the right-angled lateral surface including the first right-angled side.

[0026] Optionally, the first right-angled side of the third right-angled triangular prism of the rotating prism plate is,

[0027] h 3_i =w3tanγ 3_i =w3sinθ i / (n3-cosθ i );

[0028] Among them, h 3_i w3 represents the first right-angled side of the i-th third right-angled triangular prism; w3 represents the second right-angled side of the third right-angled triangular prism; γ 3_i θ represents the angle formed by the first right-angled side and the hypotenuse of the i-th third right-angled triangular prism; n3 represents the refractive index of the third right-angled triangular prism; θ i This represents the deflection angle of a terahertz wave sheet-like non-diffraction beam as it passes through the i-th third right-angled triangular prism.

[0029] Optionally, the delivery distance d2 and the non-diffraction distance Z of the terahertz plate-shaped non-diffraction beam can be calculated by solving the following equations. max ;

[0030] n1sinγ1=sin(α1+γ1);

[0031] w0+(d1-tanγ1)tanα1=R;

[0032] sinα2=d1tanα1 / r2;

[0033] sinβ1=R / r2;

[0034] sin(α1+α2)=n2sinα3;

[0035] n2sin(γ2+α3-α2)=sinα4;

[0036] tan(α4-γ2)=(d1tanα1) / d2;

[0037] sin(α1+β1)=n2sinβ2;

[0038] n2sin(γ2+β2-β1)=sinβ3;

[0039] tan(β3-γ2)=R / (d2+Z max );

[0040] Where, n represents the refractive index of the dual-device device; γ1 represents the vertex angle of the first right-angled triangular prism; α1 represents the deflection angle of the terahertz wave after passing through the negative roof pyramid; w0 represents the radius of the terahertz beam entering the negative roof pyramid; d1 represents the distance between the negative roof pyramid and the cylindrical pyramid; R represents the distance between the outermost ray incident on the cylindrical lens surface of the cylindrical pyramid and the optical axis; r2 represents the radius of curvature of the cylindrical lens in the cylindrical pyramid; d2 represents the projection distance of the terahertz wave sheet without diffraction; Z max α1 represents the non-diffraction distance; α2 represents the angle between the normal to the incident surface of the innermost ray incident on the cylindrical lens and the optical axis; α3 represents the angle between the normal to the incident surface of the innermost ray passing through the cylindrical lens and its refracted ray; α4 represents the angle between the normal to the incident surface of the innermost ray passing through the roof pyramid and its refracted ray; γ2 represents the vertex angle of the second right-angled triangular prism; β1 represents the angle between the normal to the incident surface of the outermost ray incident on the cylindrical lens and the optical axis; β2 represents the angle between the normal to the incident surface of the outermost ray passing through the cylindrical lens and its refracted ray; β3 represents the angle between the normal to the incident surface of the outermost ray passing through the roof pyramid and its refracted ray; n1 represents the refractive index of the first right-angled triangular prism; n2 represents the refractive index of the second right-angled triangular prism.

[0041] Optionally, the terahertz lensless line scanning imaging device further includes: a collimating lens;

[0042] The collimating lens is positioned between the terahertz radiation source and the dual-device device; the collimating lens is used to collimate the terahertz waves emitted by the terahertz radiation source.

[0043] Optionally, the collimating lens is a spherical or freeform convex lens.

[0044] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0045] The terahertz lensless line scanning imaging device comprises a dual-device setup, an adjustment mechanism, and a detection device. The dual-device setup includes a negative roof pyramid and a columnar pyramid. This setup generates a terahertz sheet-like diffraction-free beam. Using this beam simplifies the device to some extent. The adjustment mechanism adjusts the position of the terahertz sheet-like diffraction-free beam transmitted to different rows of the target object. The detection device collects the transmission signal from the target object and obtains the terahertz transmission image based on this signal. The device offers numerous advantages, including high degree of adjustment freedom, low cost, minimal energy loss, and ease of adjustment. Furthermore, it can be used in conjunction with the detection device to effectively improve detection speed and efficiency. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of a terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0048] Figure 2 This is a structural diagram of the terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the negative roof pyramid of the terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of a column-ridge pyramid of a terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the rotating prism plate of the terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0052] Figure 6 This is a geometric optical schematic diagram illustrating the operation of the dual-device device of the terahertz lensless line scanning imaging device in an embodiment of the present invention.

[0053] Figure 7 This is a geometric optical schematic diagram of the third right-angled right prism of the terahertz lensless line scanning imaging device in an embodiment of the present invention;

[0054] Figure 8 This is a schematic diagram of the design principle of the rotating prism plate of the terahertz lensless line scanning imaging device in an embodiment of the present invention.

[0055] Figure 9 The simulation results show the light intensity distribution of the sheet-like diffraction-free beam generated by the dual-device device composed of the negative roof pyramid and the column ridge pyramid of the terahertz lensless line scanning imaging device in the embodiments of the present invention in the xz plane and yz plane.

[0056] Figure 10 The experimental measurement results show the light intensity distribution of the sheet-like non-diffraction beam generated by the dual-device device composed of the negative roof pyramid and the column ridge pyramid of the terahertz lensless line scanning imaging device in the embodiments of the present invention in the xz and yz planes.

[0057] Symbol explanation:

[0058] 1. Terahertz radiation source; 2. Collimating lens; 3. Negative roof pyramid; 4. Columnar pyramid; 5. Target under test; 6. First two-dimensional translation stage; 7. Terahertz linear array detector; 8. Controller; 9. Rotating prism plate; 10. Motor; 11. Second two-dimensional translation stage. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] The purpose of this invention is to provide a terahertz lensless line scanning imaging device that uses a terahertz waveplate-shaped diffraction-free beam for lensless imaging, thus simplifying the device to a certain extent. At the same time, the device has many advantages such as high degree of adjustment freedom, low cost, minimal energy loss, and convenient adjustment. Furthermore, it can be used in conjunction with a detection device to effectively improve detection speed and efficiency.

[0061] This invention designs and fabricates refractive devices—a negative roof pyramid, a columnar pyramid, and a rotating prism plate—and constructs a terahertz lensless imaging system capable of arbitrary directional line scanning. Employing a one-dimensional scanning method significantly reduces imaging time compared to complex scanning methods such as two-dimensional point scanning; using a terahertz waveplate-shaped diffraction-free beam for lensless imaging simplifies the system structure to some extent. These devices also offer numerous advantages, including high degree of adjustment freedom, low cost, minimal energy loss, and ease of adjustment, and can be used in conjunction with linear array detectors to effectively improve detection speed and efficiency. This invention achieves rapid line scanning imaging in any direction while maintaining large depth of field and high resolution.

[0062] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0063] This invention employs a method of actively emitting terahertz radiation from a terahertz source, performing one-dimensional scanning with a terahertz waveplate without diffraction beams, and receiving the radiation with a linear array terahertz detector. By utilizing a designed and fabricated rotating prism plate, the entire target can be rapidly scanned in any direction, achieving the purpose of imaging and detecting hidden and fixed objects.

[0064] like Figure 1 and Figure 2 As shown, the present invention provides a terahertz lensless line scanning imaging device, which includes: a dual-device device, an adjustment device, and a detection device.

[0065] The dual-device device includes: a negative ridge pyramid 3 and a column ridge pyramid 4.

[0066] The dual-device setup is used to generate a terahertz wave sheet-like non-diffraction beam with a certain delivery distance. In fact, the terahertz wave sheet-like non-diffraction beam can be approximated as an ellipse with an eccentricity close to 1.

[0067] The adjustment device is used to adjust the position of the terahertz waveplate non-diffraction beam transmitted to different rows of the target 5.

[0068] The detection device is used to collect the transmission signal of the target 5 and obtain a terahertz transmission image of the target 5 based on the transmission signal.

[0069] In specific implementation, terahertz waves are emitted using terahertz radiation source 1. Terahertz radiation source 1 can be a vacuum electronic terahertz radiation source based on traveling wave tube, gyrotron, or backward wave tube, a solid-state electronic terahertz radiation source based on Schottky diode, Gunn oscillating diode, silicon avalanche transit time diode, or a quantum cascade laser.

[0070] like Figure 3As shown, the negative ridge pyramid comprises two mirror-symmetrical first right-angled triangular prisms; the target edges of the two first right-angled triangular prisms are connected; the target right-angled lateral faces of the two first right-angled triangular prisms are on the same horizontal plane; the target edge is any one of the oblique angle lateral faces; the target right-angled lateral face is a right-angled lateral face including the target edge. The oblique angle lateral face is composed of the hypotenuse of the triangle on the base, the hypotenuse of the triangle on the base, and two lateral edges. The height of the first right-angled triangular prism is h1. The width of the plane formed by the target right-angled lateral faces of the two first right-angled triangular prisms is l1.

[0071] The ridge pyramid includes a cylindrical lens and a roof pyramid; the roof pyramid includes two mirror-symmetrical second right-angled triangular prisms; selected right-angled lateral faces of the two second right-angled triangular prisms are connected.

[0072] like Figure 4 As shown in the illustration, in a specific embodiment, the ridge pyramid of this invention uses a cylindrical lens with a circular arc cross-section, and the height of the selected second right-angled triangular prism is h2. The plane of the cylindrical lens is connected to the plane formed by the selected right-angled sides of the two second right-angled triangular prisms. The width of the plane formed by the plane of the cylindrical lens and the selected right-angled sides of the second right-angled triangular prism is l2.

[0073] As one specific embodiment, such as Figure 1 As shown, the adjustment device includes: a first two-dimensional translation stage 6.

[0074] The first two-dimensional translation stage 6 is used to move the horizontal and / or vertical position of the target under test 5 and adjust the position of the terahertz wave plate-shaped non-diffraction beam transmitted to different rows of the target under test 5.

[0075] In specific implementation, such as Figure 1 As shown, the detection device includes a terahertz linear array detector 7 and a controller 8. The terahertz linear array detector 7 collects the transmission signal of the target device 5 and transmits the transmission signal to the controller 8. The controller 8 obtains the terahertz transmission image of the target device 5 based on the transmission signal. The controller 8 also controls the first two-dimensional translation stage 6. The terahertz linear array detector 7 is a linear array composed of Schottky diodes or thermometers.

[0076] In practice, the terahertz wave source 1 generates terahertz waves, which propagate in free space according to Gaussian beam characteristics. After being collimated by the collimating lens 2, the waves are incident as a circular spot onto the dual-device device composed of the negative roof pyramid 3 and the column ridge pyramid 4 to generate a terahertz wave sheet-like non-diffraction beam. The terahertz wave sheet-like non-diffraction beam is incident on the target 5 on the first two-dimensional translation stage 6. Finally, the terahertz linear array detector 7 collects the transmitted signal and transmits it 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 image acquisition frame rate.

[0077] Specific scanning method: The terahertz sheet-shaped non-diffraction beam is incident on the target 5, and the fixed-position terahertz linear array detector 7 collects the transmitted signal of the target 5, obtaining information of one row of pixels of the target 5. The target 5 is moved by the first two-dimensional translation stage 6, so that the terahertz sheet-shaped non-diffraction beam scans each row of pixels of the target 5 and is collected by the terahertz linear array detector 7. Finally, the signal is transmitted to the controller 8 for stitching and reconstruction, thereby obtaining the image information of the target 5.

[0078] As one specific embodiment, such as Figure 2 As shown, the adjustment device includes: a second two-dimensional translation stage 11, a rotation device, and a rotating prism device.

[0079] The rotating prism device is located between the target under test 5 and the dual-device device, and the rotating prism device is used to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam.

[0080] The rotating device shown is used to synchronously rotate the dual-device device consisting of the negative ridge pyramid 3 and the column ridge pyramid 4 to adjust the long axis direction of the terahertz waveplate-shaped non-diffraction beam.

[0081] The second two-dimensional translation stage 11 is used to adjust the horizontal and / or vertical position of the detection device.

[0082] The rotating prism device includes a motor 10 and a rotating prism plate 9.

[0083] The motor 10 is used to rotate the rotating prism plate 9 to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam.

[0084] In specific implementation, the long axis direction of the terahertz wave sheet-like non-diffraction beam is changed by synchronously rotating the dual-device device composed of the negative ridge pyramid 3 and the column ridge pyramid 4. In further implementation, the prism plate 9 can be rotated by a translation frame to match (coincide) one of the prism units (right-angled triangular prisms) with the terahertz wave sheet-like non-diffraction beam. If one of the right-angled triangular prisms of the rotating prism plate 9 matches the terahertz wave sheet-like non-diffraction beam, no movement is required. The prism plate 9 is rotated using the motor 10, and the terahertz wave sheet-like non-diffraction beam performs line scanning along a direction perpendicular to its long axis. Because the long axis direction of the terahertz wave sheet-like non-diffraction beam can rotate 360°, line scanning imaging in any direction can be achieved. The controller 8 controls the motor 10 to rotate the rotating prism plate, allowing the terahertz waveplate-shaped non-diffraction beam to scan each row of pixels of the target 5 at different deflection angles. Simultaneously, the controller 8 moves the terahertz linear array detector 7 to collect signals synchronously via the second two-dimensional translation stage 11. Finally, the signals are transmitted to the controller 8 for stitching, thereby acquiring the terahertz transmission image of the target 5. The terahertz linear array detector 7, the motor 10, and the second two-dimensional translation stage 11 are all synchronously controlled by the controller 8 to match the scanning speed and image acquisition frame rate.

[0085] Specific scanning method: Terahertz wave source 1 generates terahertz waves, which propagate in free space according to Gaussian beam characteristics. After being collimated by collimating lens 2, the waves are incident as a circular spot onto a dual-device structure composed of negative roof pyramid 3 and column ridge pyramid 4 to generate a terahertz wave sheet-like non-diffraction beam. The terahertz wave sheet-like non-diffraction beam passes through rotating prism plate 9 and is incident on the fixed target 5 at a certain deflection angle. Terahertz linear array detector 7 collects the transmitted signal of the target 5, obtaining information of one row of pixels of the target 5. Controller 8 controls motor 10 to rotate the rotating prism plate, allowing the terahertz wave sheet-like non-diffraction beam to scan each row of pixels of the target 5 at different deflection angles. Simultaneously, the second two-dimensional translation stage 11 moves the terahertz linear array detector 7 to collect signals synchronously. Finally, the signals are transmitted to controller 8 for stitching. At the same time, the geometric correction of the image is processed according to parameters such as the scanning distance and scanning angle of the optical system, thereby obtaining the terahertz image information of the target 5. The rotating prism plate 9 is controlled to rotate by the motor 10, the terahertz linear array detector 7 is located on the second two-dimensional translation stage 11, and the controller 8 synchronously controls the terahertz linear array detector 7, the motor 10 and the second two-dimensional translation stage 11 to match the scanning speed and the image acquisition frame rate.

[0086] like Figure 5 As shown, the rotating prism plate includes a circular base and N third right-angled triangular prisms; the N third right-angled triangular prisms are fixed radially at equal angles to one side of the circular base, specifically including:

[0087] The first right-angled side face of the third right-angled triangular prism is fixed to one side of the disk base.

[0088] Wherein, the next third right-angled triangular prism after the (n-1)th third right-angled triangular prism is the nth third right-angled triangular prism, n = 2, 3, ..., N; the first right-angled side of the (n-1)th third right-angled triangular prism is shorter than the first right-angled side of the nth third right-angled triangular prism; the second right-angled side and hypotenuse of the (n-1)th third right-angled triangular prism are equal to the second right-angled side and hypotenuse of the nth third right-angled triangular prism; the two vertices of the base of the plurality of third right-angled triangular prisms that are away from the center of the disk base coincide with the edge of the disk base; the first right-angled lateral surface is the right-angled lateral surface including the first right-angled side.

[0089] The rotating prism plate consists of a circular base with radius r3 and a series of third right-angled triangular prisms with different base heights, used to deflect terahertz waveplate-shaped non-diffraction beams. The base dimensions of the series of third right-angled triangular prisms coinciding with the base are all identical, meaning that l3 and w3 are equal for each third right-angled triangular prism. The base heights of the third right-angled triangular prisms are designed according to an equidistant scanning method, and the third right-angled triangular prisms are arranged at equal angular intervals along the circular base, with the two vertices of their bases coinciding with the edges of the circular base.

[0090] according to Figure 5 As shown, the first right-angled side is the short side of the face of the third right-angled triangular prism that contacts the disk base, r3 represents the radius of the disk base, w3 represents the second right-angled side, the w3 of the N third right-angled triangular prisms is equal, l3 represents the hypotenuse of the third right-angled triangular prism, and the hypotenuses of the N third right-angled triangular prisms are all equal.

[0091] like Figure 7 and Figure 8 As shown, the relationship between the deflection angle and the base angle of a terahertz plate-shaped non-diffraction beam is as follows:

[0092] nsinγ 3_i =sin(θ) i +γ 3_i );

[0093] The deflection angle of the terahertz waveplate-shaped non-diffraction beam in each unit of the rotating prism plate is designed according to the equal scanning spacing, that is:

[0094] d(tanθ i -tanθ i+1 )=Δl;

[0095] Δl represents the distance between the terahertz wave plate-shaped non-diffraction beam after deflection by the i-th third right-angled triangular prism and the terahertz wave plate-shaped non-diffraction beam after deflection by the (i+1)-th third right-angled triangular prism. d represents the distance between the rotating prism plate and the target being measured.

[0096] One right-angled side of the third right-angled triangular prism of the rotating prism plate is,

[0097] h 3_i =w3tanγ 3_i =w3sinθ i / (n3-cosθ i );

[0098] Among them, h 3_i w3 represents the first right-angled side of the i-th third right-angled triangular prism; w3 represents the second right-angled side of the third right-angled triangular prism; γ 3_i θ represents the angle formed by the first right-angled side and the hypotenuse of the i-th third right-angled triangular prism; n3 represents the refractive index of the third right-angled triangular prism; θ i This represents the deflection angle of a terahertz wave sheet-like non-diffraction beam as it passes through the i-th third right-angled triangular prism.

[0099] As one specific embodiment, such as Figure 8 As shown, d = 100mm, Δl = 10mm, and the beam scanning range is 180mm. Therefore, the corresponding rotating prism plate is set with 18 third right-angled triangular prisms. The terahertz waveplate-shaped non-diffraction beam scanning angle is from -42° to 42°, and the height of the bottom surface of each third right-angled triangular prism is also determined accordingly.

[0100] like Figure 6 As shown, the dual-device structure composed of the negative roof pyramid and the column pyramid can adjust the delivery distance d2 and the diffraction-free distance Z of the terahertz waveplate-shaped non-diffraction beam by changing the spacing d1 between the devices, the base angles γ1 and γ2 of each device, and the radius of curvature r2 of the cylindrical lens. max This allows the system to adjust its depth of field, enabling imaging and detection of targets at different locations.

[0101] When a collimated terahertz beam with radius w0 is incident from air onto the dual-device device, it will form a projection distance of d2 and a length of Z behind the ridge pyramid. max The non-diffraction region (gray area). The refractive index of the material is n = 1.54. According to the law of refraction and geometric relationships, we have:

[0102] The delivery distance d2 and the non-diffraction distance Z of the terahertz plate-shaped non-diffraction beam are calculated by solving the following equations. max ;

[0103] n1sinγ1=sin(α1+γ1);

[0104] w0+(d1-tanγ1)tanα1=R;

[0105] sinα2=d1tanα1 / r2;

[0106] sinβ1=R / r2;

[0107] sin(α1+α2)=n2sinα3;

[0108] n2sin(γ2+α3-α2)=sinα4;

[0109] tan(α4-γ2)=(d1tanα1) / d2;

[0110] sin(α1+β1)=n2sinβ2;

[0111] n2sin(γ2+β2-β1)=sinβ3;

[0112] tan(β3-γ2)=R / (d2+Z max );

[0113] Where, n represents the refractive index of the dual-device device; γ1 represents the vertex angle of the first right-angled triangular prism; α1 represents the deflection angle of the terahertz wave after passing through the negative roof pyramid; w0 represents the radius of the terahertz beam entering the negative roof pyramid; d1 represents the distance between the negative roof pyramid and the cylindrical pyramid; R represents the distance between the outermost ray incident on the cylindrical lens surface of the cylindrical pyramid and the optical axis; r2 represents the radius of curvature of the cylindrical lens in the cylindrical pyramid; d2 represents the projection distance of the terahertz wave sheet without diffraction; Z max α1 represents the non-diffraction distance; α2 represents the angle between the normal to the incident surface of the innermost ray incident on the cylindrical lens and the optical axis; α3 represents the angle between the normal to the incident surface of the innermost ray passing through the cylindrical lens and its refracted ray; α4 represents the angle between the normal to the incident surface of the innermost ray passing through the roof pyramid and its refracted ray; γ2 represents the vertex angle of the second right-angled triangular prism; β1 represents the angle between the normal to the incident surface of the outermost ray incident on the cylindrical lens and the optical axis; β2 represents the angle between the normal to the incident surface of the outermost ray passing through the cylindrical lens and its refracted ray; β3 represents the angle between the normal to the incident surface of the outermost ray passing through the roof pyramid and its refracted ray; n1 represents the refractive index of the first right-angled triangular prism; n2 represents the refractive index of the second right-angled triangular prism.

[0114] In practical applications, n1, n2, and n3 can be equal.

[0115] As a specific embodiment, solving the above equation easily yields d2=f1(γ1,d1,γ2,r2), Z max = f2(γ1,d1,γ2,r2). Therefore, d2 and Z maxAll are functions of γ1, d1, γ2, and r2. By appropriately setting these parameters, the desired terahertz plate-shaped diffraction-free beam can be generated. Optionally, let w0 = 15mm, γ1 = 15°, γ2 = 10°, and d1 = 100mm. Then, the corresponding delivery distance d2 ≈ 87mm and the diffraction-free distance Z can be calculated. max ≈207mm.

[0116] like Figure 9 As shown in the simulation results, the distribution of the beam in the xz and yz planes indicates that the beam has sheet-like non-diffraction characteristics. The projection distance is approximately 100 mm, and the non-diffraction distance is approximately 200 mm, which is basically consistent with the calculation results.

[0117] like Figure 10 As shown in the figure, the measurement results demonstrate that the terahertz plate-shaped diffraction-free beam exhibits good diffraction-free performance within the range of 150 mm to 350 mm. In practical applications, different negative ridge pyramids and column ridge pyramids can be selected to form a dual-device structure, and the desired terahertz plate-shaped diffraction-free beam can be generated by adjusting the device spacing d1.

[0118] like Figure 1 and Figure 2 As shown, the terahertz lensless line scanning imaging device further includes: a collimating lens 2.

[0119] The collimating lens 2 is disposed between the terahertz radiation source 1 and the dual-device device; the collimating lens 2 is used to collimate the terahertz wave emitted by the terahertz radiation source. The dual-device device receives the collimated terahertz wave and generates a terahertz wave sheet-like non-diffraction beam based on the collimated terahertz wave.

[0120] The collimating lens 2 is a spherical or freeform convex lens.

[0121] Collimating lens 2, negative roof pyramid 3, column pyramid 4, and rotating prism plate 9 can all be manufactured by 3D printing. The materials are high-density polyethylene or polytetrafluoroethylene, which are highly transparent to terahertz waves, and the loss in the terahertz region can be ignored.

[0122] The beneficial effects of this invention are that it employs one-dimensional scanning, significantly reducing imaging time compared to complex scanning methods such as two-dimensional point scanning. The use of a terahertz waveplate-shaped, diffraction-free beam for lensless line scanning imaging simplifies the system structure to a certain extent. Furthermore, the designed and fabricated refractive device offers numerous advantages, including high degree of adjustment freedom, low cost, minimal energy loss, and ease of adjustment. It can also be used in conjunction with a linear array detector, effectively improving detection speed and efficiency. This imaging system maintains a large depth of field and high resolution while achieving rapid line scanning imaging in any direction, making it suitable for detecting hidden or fixed objects. These functions can also be achieved in other wavebands such as microwaves and X-rays, requiring only the use of materials with good transmittance for the corresponding wavebands.

[0123] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0124] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A terahertz lensless line scanning imaging device, characterized in that, The terahertz lensless line scanning imaging device includes: a dual-device device, an adjustment device, and a detection device; The dual-device device includes: a negative roof ridge pyramid and a column ridge pyramid; The negative ridge pyramid comprises two mirror-symmetrical first right-angled triangular prisms; the target edges of the two first right-angled triangular prisms are connected; the target right-angled lateral faces of the two first right-angled triangular prisms are on the same horizontal plane; the target edge is any lateral edge of the oblique lateral face; the target right-angled lateral face is the right-angled lateral face including the target edge; The ridge pyramid includes a cylindrical lens and a roof pyramid; the roof pyramid includes two mirror-symmetrical second right-angled triangular prisms; selected right-angled lateral faces of the two second right-angled triangular prisms are connected; The dual-device setup is used to generate a terahertz waveplate-shaped non-diffraction beam. The adjustment device is used to adjust the position of the terahertz waveplate non-diffraction beam transmitted to different rows of the target under test; The detection device is used to collect the transmission signal of the target under test, and obtain a terahertz transmission image of the target under test based on the transmission signal.

2. The terahertz lensless line scanning imaging device according to claim 1, characterized in that, The adjustment device includes: a first two-dimensional translation stage; The first two-dimensional translation stage is used to move the horizontal and / or vertical position of the target under test and adjust the position of the terahertz waveplate non-diffraction beam transmitted to different rows of the target under test.

3. The terahertz lensless line scanning imaging device according to claim 1, characterized in that, The adjustment device includes: a second two-dimensional translation stage, a rotation device, and a rotating prism device; The rotating prism device is located between the target under test and the dual-device device, and the rotating prism device is used to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam. The rotating device is used to rotate the dual-device device and adjust the long axis direction of the terahertz waveplate-shaped non-diffraction beam. The second two-dimensional translation stage is used to adjust the horizontal and / or vertical position of the detection device.

4. The terahertz lensless line scanning imaging device according to claim 3, characterized in that, The rotating prism device includes: a motor and a rotating prism plate; The motor is used to rotate the rotating prism plate to adjust the deflection angle of the terahertz waveplate-shaped non-diffraction beam.

5. The terahertz lensless line scanning imaging device according to claim 4, characterized in that, The rotating prism plate includes a disk base and N A third right-angled triangular prism; Will N The third right-angled triangular prisms are fixed to one side of the disk base in a radially spaced manner at equal angles, specifically including: The first right-angled side surface of the third right-angled triangular prism is fixed to one side of the disk base; Among them, the n -1 The next third right-angled triangular prism is the first n A third right-angled triangular prism n =2, 3, ..., N ;No. n -1 The first leg of a third right-angled triangular prism is shorter than the third leg. n The first right-angled side of the third right-angled triangular prism; n -1 The second leg and hypotenuse of the third right-angled triangular prism are connected to the... n The second right-angled side and the hypotenuse of each third right-angled triangular prism are equal; the two vertices of the base of the plurality of third right-angled triangular prisms that are away from the center of the disk base coincide with the edge of the disk base; the first right-angled lateral surface is a right-angled lateral surface that includes the first right-angled side.

6. The terahertz lensless line scanning imaging device according to claim 5, characterized in that, The first right-angled side of the third right-angled triangular prism of the rotating prism plate is... ； in, Indicates the first i The first right-angled side of a third right-angled triangular prism; This represents the second leg of the third right-angled triangular prism; Indicates by the first i The angle formed by the first right-angled side and the hypotenuse of a third right-angled triangular prism; This indicates that the terahertz wave sheet-like non-diffraction beam passes through the first... i The deflection angle of a third right-angled triangular prism.

7. The terahertz lensless line scanning imaging device according to claim 1, characterized in that, The delivery distance of a terahertz plate-shaped non-diffraction beam is calculated by solving the following equations. and no diffraction distance ; ； ； ； ； ； ； ； ； ； ； in, Represents the refractive index of a dual-device device; It represents the vertex angle of the first right triangular prism; This indicates the deflection angle of the terahertz wave after passing through the negative roof pyramid; This indicates the radius of the terahertz beam entering the negative roof pyramid; This represents the distance between the negative ridge pyramid and the column ridge pyramid. R This represents the distance between the outermost ray incident on the surface of the pyramidal lens and the optical axis. The radius of curvature of the cylindrical lens in the ridge pyramid; This indicates the transmission distance of a terahertz wave sheet without diffraction. Indicates no diffraction distance This represents the angle between the normal to the incident surface of the innermost ray incident on the cylindrical lens and the optical axis. This represents the angle between the normal to the incident surface of the innermost ray passing through the cylindrical lens and its refracted ray; This represents the angle between the normal to the incident surface of the innermost ray passing through the pyramidal surface of the roof ridge and its refracted ray; It represents the vertex angle of the second right-angled triangular prism; This represents the angle between the normal to the incident surface of the outermost ray incident on the cylindrical lens and the optical axis. This represents the angle between the normal to the incident surface of the outermost ray passing through the cylindrical lens and its refracted ray; This represents the angle between the normal to the incident surface of the outermost ray passing through the pyramidal surface of the roof ridge and its refracted ray; It represents the refractive index of the first right triangular prism; It represents the refractive index of the second right-angled triangular prism.

8. The terahertz lensless line scanning imaging device according to claim 1, characterized in that, The terahertz lensless line scanning imaging device further includes: a collimating lens; The collimating lens is disposed between the terahertz radiation source and the dual-device device; the collimating lens is used to collimate the terahertz waves emitted by the terahertz radiation source.

9. The terahertz lensless line scanning imaging device according to claim 8, characterized in that, The collimating lens is a spherical or freeform convex lens.

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