Flat lens and device for multi-angle annular uniform illumination in terahertz band

Abstract

This invention discloses a flat plate lens and device for multi-angle annular uniform illumination in the terahertz band, relating to the field of terahertz active imaging. By setting multiple annular grooves or constructing a randomly rough surface on the exit surface of a flat plate lens with an air hole array and a center point defect, this invention can convert a Gaussian-distributed terahertz beam irradiated by a terahertz source into a multi-angle annular uniform illumination beam. This allows the terahertz wave to illuminate the target from different angles, increasing the reflected wave signal entering the detection system. This has significant application value for terahertz waves in non-destructive testing and human security inspection. Furthermore, in a reflective terahertz active imaging system, compared to a circular beam, the annular beam can convert small-angle incident light with low imaging utilization in the central part into large-angle incident light with higher imaging utilization, thus improving energy utilization while providing multi-angle illumination.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of terahertz active imaging, and in particular to a flat lens and device for multi-angle annular uniform illumination in the terahertz frequency band. BACKGROUND

[0002] Terahertz waves are between infrared and millimeter waves, and have strong penetration to many non-polar materials. Compared with millimeter waves, the shorter wavelength of terahertz waves provides higher spatial resolution for imaging. Compared with x-rays which also have strong penetration, the photon energy of terahertz waves is low, so ionization is not easy to occur when penetrating into matter, which has important application potential and value in the field of human security, etc. When using the penetration of terahertz waves for non-destructive detection of the internal material or human security, terahertz imaging technology becomes an important basis for these applications. In the method of terahertz active illumination reflection imaging, when the roughness of the object surface (surface texture, undulation, etc.) is less than or equal to the wavelength of the terahertz wave, the specular reflection component in the reflected wave will increase significantly. Therefore, when a single angle of terahertz wave is used to illuminate the sample in wide field, most of the incident wave signals will only be reflected at the position symmetrical to the angle due to specular reflection. For a terahertz wave detection system with fixed position or angle, the problem of missing imaging information will occur when the reflected wave signal cannot enter the detection system, which will cause poor imaging quality. In this case, only by controlling the terahertz wave to irradiate the sample from different angles, the reflected wave component entering the detector can be increased, and the reflected terahertz signal can be fully detected. On the other hand, the uniformity of the light source illumination is also a key factor affecting the imaging quality in active illumination imaging. However, the terahertz radiation source emits waves that are mostly characterized by Gaussian distribution in free space, i.e. high energy in the middle and low energy around. If no collimation or focusing measures are taken, the terahertz source beam will quickly diverge, and the spot intensity will also quickly decrease in the form of Gaussian distribution. Therefore, with the increase of the terahertz wave propagation distance, the terahertz wave light field intensity distribution radiated to the imaging target will be more uneven, which will lead to the phenomenon that the imaging results of the same object placed at different positions are inconsistent. Therefore, the control of the uniformity of terahertz wave irradiation is also a key link to improve the imaging quality.

[0003] Photonic crystal is an artificial microstructure formed by periodically arranging media with different refractive indexes. Because of the spatial periodicity of dielectric constant, the refractive index of photonic crystal to light is also periodically distributed, and the dispersion curve of the light wave propagating therein forms a band structure, i.e. photonic band. Band gaps, i.e. photonic band gaps (PBG), appear between photonic bands. Photons with frequencies falling in the photonic band gap are strictly prohibited from propagating in certain directions. By introducing defects to destroy the periodic structure characteristics of the photonic crystal, corresponding defect energy levels will be formed in the photonic band gap, and only light with a specific frequency can appear in the defect energy level. Unlike ordinary periodic photonic crystals, which have both rotational symmetry and translational symmetry, quasi-photonic crystals do not have translational symmetry, but they have both photonic band gaps and photonic localization characteristics, so they can flexibly manipulate light wave transmission.

[0004] In view of the above problems, it is necessary to convert the Gaussian-distributed terahertz waves radiated by the terahertz source into a multi-angle outgoing annular uniform illumination beam to increase the reflected light component entering the detector when mirror reflection occurs, realize sufficient detection of the reflected signal, and eliminate the adverse effects of uneven distribution of the illumination terahertz wave on the imaging quality. However, the traditional diaphragm interception method has serious energy loss, and the aspheric lens group is difficult to process, and the optical system is complex and heavy to use. SUMMARY

[0005] To solve the above problems existing in the prior art, the present application provides a flat lens and device for multi-angle annular uniform illumination in the terahertz frequency band.

[0006] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0007] A flat lens for multi-angle annular uniform illumination in the terahertz frequency band; the flat lens is provided with an air hole array and a central point defect; the air hole array is formed by rotating and arranging basic units at a set angle with the central point defect as the center; the basic unit is provided with a plurality of air holes; the extension period of the air hole is a;

[0008] The exit surface of the flat lens is provided with a semicircular ring body, or the exit surface of the flat lens is provided with a two-dimensional Gaussian random rough surface.

[0009] Optionally, the basic unit is a rhombic structure.

[0010] The first vertex of the rhombus structure coincides with the center point defect; the center point of the rhombus structure is provided with an air hole, and each of the second vertex and the fourth vertex of the rhombus structure is provided with an air hole; the midpoint of each edge of the rhombus structure is provided with an air hole; the first vertex of the rhombus structure is an acute vertex; the second vertex and the fourth vertex of the rhombus structure are obtuse vertices; the set angle is equal to the acute angle of the rhombus structure.

[0011] Optionally, the semicircular ring body comprises a first annular circular arc groove, a second annular circular arc groove and a third annular circular arc groove arranged in sequence along the line connecting the center point defect to the first air hole; the first air hole is the air hole closest to the center point defect in the basic unit;

[0012] The first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove are all closed annular structures with the center point defect as the center; the side surface of the first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove is semicircular; the side surface of the first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove is perpendicular to the exit surface;

[0013] The side surface of the second annular circular arc groove is tangent to the side surface of the first annular circular arc groove and the side surface of the third annular circular arc groove respectively; the radius of the side surface of the second annular circular arc groove is greater than the radius of the side surface of the first annular circular arc groove; the radius of the side surface of the third annular circular arc groove is greater than the radius of the side surface of the second annular circular arc groove.

[0014] Optionally, the radius of the side surface of the first annular circular arc groove is 0.06a; the radius of the side surface of the second annular circular arc groove is 0.08a; and the radius of the side surface of the third annular circular arc groove is 0.1a.

[0015] Optionally, the flat plate lens is a cylindrical structure based on quasi-photonic crystals; the radius of the flat plate lens is 4a; and the height of the flat plate lens is 1.5a.

[0016] Optionally, the radius of the center point defect is equal to the radius of the air hole.

[0017] Optionally, the radius of the center point defect is 0.23a, and the radius of the air hole is 0.23a.

[0018] A device for multi-angle annular uniform illumination in the terahertz band, which comprises, in sequence in the direction of propagation of terahertz waves, a radiation source, a collimating lens and the above-mentioned flat plate lens;

[0019] The radiation source is used to generate terahertz waves; the terahertz waves are collimated by the collimating lens, and then incident on the flat plate lens in a circular light spot, to form multi-angle outgoing uniform terahertz waves; the multi-angle outgoing uniform terahertz waves are incident on a target to be detected.

[0020] A device for multi-angle annular uniform illumination in a terahertz frequency band, comprising a radiation source, a first terahertz wave detector, a second terahertz wave detector and the flat plate lens described above.

[0021] The terahertz waves generated by the radiation source form multi-angle outgoing uniform terahertz waves through the flat plate lens; after the multi-angle outgoing uniform terahertz waves are incident on a target to be detected, the target to be detected reflects the terahertz waves, and the reflected terahertz waves enter the first terahertz wave detector and the second terahertz wave detector, respectively.

[0022] According to the specific embodiments provided by the present application, the following technical effects are disclosed.

[0023] The flat plate lens and the device for multi-angle annular uniform illumination in a terahertz frequency band provided by the present application can convert the terahertz light beams with Gaussian distribution irradiated by the terahertz source into multi-angle outgoing annular uniform illumination light beams by arranging a plurality of annular grooves on the exit surface of the flat plate lens with an air hole array and a central point defect or constructing a random rough surface, so that the terahertz waves illuminate the target from different angles, and the reflected wave signals entering the detection system are increased, which has outstanding application value for the application scenarios of terahertz waves in the fields of nondestructive detection and human security check. Moreover, in the reflective terahertz active imaging system, compared with the circular light beam, the annular light beam can convert the small-angle incident light with low imaging utilization rate in the central part into large-angle incident light with high imaging utilization rate, so that the energy utilization rate can be improved while providing multi-angle illumination. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1 The structure schematic diagram of the flat plate lens provided by the present application is shown in the figure.

[0026] Figure 2 The first exit surface schematic diagram of the flat plate lens provided by the embodiment of the present application is shown in the figure.

[0027] Figure 3 The incident surface schematic diagram of the flat plate lens provided by the embodiment of the present application is shown in the figure.

[0028] Figure 4 The XY plane electric field mode schematic diagram of the terahertz wave provided by the embodiment of the present application after passing through the flat plate lens and the electric field mode distribution broken line graph through the corresponding XY plane center; wherein, Figure 4 (a) is the electric field mode schematic diagram of the XY plane at different positions when the exit surface has no semi-circular ring structure, Figure 4 (b) is the electric field mode schematic diagram of the XY plane at different positions when the exit surface has a semi-circular ring structure, Figure 4 (c) is the electric field mode distribution broken line graph through the corresponding XY plane center when the exit surface has no and has different arrangements of semi-circular ring bodies;

[0029] Figure 5 The second exit surface schematic diagram of the flat plate lens provided by the embodiment of the present application;

[0030] Figure 6 The side view of the flat plate lens provided by the embodiment of the present application using the second exit surface;

[0031] Figure 7 The schematic diagram of the two-dimensional Gaussian random rough surface constructed by the random distribution function provided by the embodiment of the present application;

[0032] Figure 8 The structural schematic diagram of the first device for multi-angle annular uniform illumination in the terahertz frequency band provided by the embodiment of the present application;

[0033] Figure 9 The structural schematic diagram of the second device for multi-angle annular uniform illumination in the terahertz frequency band provided by the embodiment of the present application.

[0034] Symbol explanation:

[0035] 1 radiation source, 2 collimating lens, 3 flat plate lens, 3-1 basic unit, 3-2 extension period of air hole, 3-3 air hole, 3-4 center point defect, 3-5 first annular circular arc groove, 3-6 second annular circular arc groove, 3-7 third annular circular arc groove, 4 target to be measured, 5 first terahertz wave detector, 6 second terahertz wave detector. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] The purpose of the present application is to provide a flat lens and device for multi-angle annular uniform illumination in the terahertz frequency band, which can reshape the terahertz wave with Gaussian distribution into a multi-angle annular uniform light beam, effectively eliminating the adverse effects of uneven distribution of illuminated terahertz waves on imaging quality while providing multi-angle illumination.

[0038] In order to make the above-mentioned purposes, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0039] The flat lens provided by the present application is used for reshaping the terahertz wave circular spot with Gaussian distribution in the process of multi-angle annular uniform illumination in the terahertz frequency band. Figure 1 As shown in the figure, the flat lens is provided with an air hole array and a center point defect 3-4. The air hole array is formed by rotating and arranging basic units 3-1 with the center point defect 3-4 as the center at a set angle. The basic unit 3-1 is provided with a plurality of air holes 3-3. The extension period 3-2 of the air hole 3-3 is a. The radius of the center point defect 3-4 and the radius of the air hole 3-3 are both 0.23a.

[0040] As shown in the figure, the basic unit 3-1 is a rhombus structure. Figure 1

[0041] The first vertex of the rhombus structure coincides with the center point defect 3-4. The center point of the rhombus structure is provided with an air hole, and the second vertex and the fourth vertex of the rhombus structure are each provided with an air hole. The midpoint position of each side of the rhombus structure is provided with an air hole. The first vertex of the rhombus structure is an acute vertex. The second vertex and the fourth vertex of the rhombus structure are both obtuse vertices. The set angle is equal to the acute angle of the rhombus structure.

[0042] For example, in actual application, since the band gap of the photonic crystal only works for a certain range of wavelengths, for different actual use requirements, it is necessary to design an illumination device suitable for different terahertz wavelengths. Based on this, when a terahertz wave with a wavelength of 3mm is selected, the extension period a is selected as 9mm, and the parameters of other parts are also determined by the extension period a. For other wavelengths in the terahertz frequency domain, a corresponding extension period a that satisfies the photonic band gap needs to be selected to achieve the same effect.

[0043] Further, in order to obtain a multi-angle annular uniform illumination light beam, the present application provides two different exit surface structures for the flat lens.

[0044] As shown in the figure, the first exit surface structure is a circular structure. Figure 2 ​As shown, a semi-circular ring is provided on the exit surface of the flat lens. The semi-circular ring includes a first annular arc groove 3-5, a second annular arc groove 3-6, and a third annular arc groove 3-7 arranged sequentially along the line connecting the center point defect 3-4 to the first air hole. The first air hole is the air hole in the basic unit 3-1 that is closest to the center point defect 3-4.

[0045] The first annular arc groove 3-5, the second annular arc groove 3-6, and the third annular arc groove 3-7 are all closed annular structures with the center point defect 3-4 as the center point. The side sections of the first annular arc groove 3-5, the second annular arc groove 3-6, and the third annular arc groove 3-7 are all semi-circular. The side sections of the first annular arc groove 3-5, the second annular arc groove 3-6, and the third annular arc groove 3-7 are all perpendicular to the exit surface.

[0046] The side cut surfaces of the second annular arc groove 3-6 are externally tangent to the side cut surfaces of the first annular arc groove 3-5 and the third annular arc groove 3-7, respectively. The radius of the side cut surface of the second annular arc groove 3-6 is larger than the radius of the side cut surface of the first annular arc groove 3-5. The radius of the side cut surface of the third annular arc groove 3-7 is larger than the radius of the side cut surface of the second annular arc groove 3-6.

[0047] That is, such as Figure 2 As shown, the structure of the exit surface can be different arrangements of three quarter-circular annular bodies formed by rotating three half-circles with diameters on a line and externally tangent to each other by rotating them 90° around the center of the lens (i.e., the first annular arc groove 3-5, the second annular arc groove 3-6, and the third annular arc groove 3-7). The radii of the three semicircles, from smallest to largest, are r3 = 0.06a, r4 = 0.08a, and r5 = 0.1a. The semi-circular annular bodies are located between the central defect and the first row of air holes around it. The semi-circular annular bodies are filled with air medium, with the curved end embedded in the exit surface and the flat end coinciding with the exit surface. The annular beam is scattered by a structure similar to a concave lens to obtain a multi-angle annular uniform illumination beam.

[0048] Based on the emission surface structure provided by this invention, in such a way... Figure 3 Based on the incident surface structure shown, when the exit surface has no or has a semi-circular annular structure (i.e., three annular arc grooves), the electric field mode in the XY plane at different positions is as follows: Figure 4 As shown in (a) and (b), the overall intensity distribution of the emitted beam in the XY plane is reflected. Without the semi-circular ring structure, the emitted beam is distributed in a ring shape in the XY plane; with the semi-circular ring structure, the emitted beam forms a uniform circular distribution with a diameter of 20 mm in the XY plane. The distribution lines of the electric field modes passing through the center of the corresponding XY plane when there are no semi-circular rings and when there are different arrangements of semi-circular rings on the emission surface are shown in Figure 1. Figure 4The intensity distribution of the annular beam in the XY plane before and after scattering reflects the characteristics of whether the annular beam is homogenized or not, as shown in (c). The final flat-top beam shape will have slight fluctuations, which is mainly because the scattered light of the same semi-circular ring structure will interfere to a certain extent. The more the semi-circular ring structure parameters are and the greater the difference is, the smaller the interference effect is.

[0049] The second kind of exit surface structure is shown in Figure 5 and Figure 6 The exit surface structure is set as a two-dimensional Gaussian random rough surface. By changing the root mean square roughness and the correlation length of the exit surface, a rough surface that meets different needs can be constructed. As shown in Figure 7 The fluctuation range of the two-dimensional Gaussian random rough surface constructed by the random distribution function in the Z direction is about ±1mm, which is comparable to the radius of the ring body constructed in the first kind of exit surface. The annular beam passes through the randomly distributed rough surface for scattering. Due to the random distribution of the rough surface, the influence of light interference can be ignored, so a more uniformly distributed multi-angle annular beam can be obtained.

[0050] Further, in order to ignore the loss in the terahertz region, the flat lens in the present application is a cylindrical structure based on quasi-photonic crystals. The material based on quasi-photonic crystals can be high-density polyethylene or polytetrafluoroethylene, etc. The radius of the flat lens is 4a. The height of the flat lens is 1.5a.

[0051] Further, based on the specific structure of the flat lens provided in the present application, it can be made by 3D printing. Compared with common uniform light devices such as aspherical lens group, liquid crystal spatial light modulator in the terahertz wave band, etc., it has the advantages of simple structure, low cost, easy to realize, etc.

[0052] Further, the present application also provides two kinds of devices for multi-angle annular uniform illumination in the terahertz frequency band. One of the devices for multi-angle annular uniform illumination in the terahertz frequency band is shown in Figure 8 The radiation source 1, the collimating lens 2 and the flat lens 3 described above are sequentially arranged in the terahertz wave propagation direction.

[0053] The flat lens 3 is located in the XY plane, and the exit surface is located at Z=0. The radiation source 1 is used to generate terahertz waves, and the waves propagate in free space according to the characteristics of Gaussian beam. After collimation by the collimating lens 2, a circular spot with a diameter of 6mm is incident on the center position of the flat lens 3. Due to the bandgap effect of quasi-photonic crystals, only the annular part near the point defect allows the incident terahertz waves to pass through. The shaped annular beam is scattered by the semi-circular ring structure when it is emitted, and a multi-angle annular uniform illumination beam can be obtained near the target 4 to be measured.

[0054] Another device for multi-angle annular uniform illumination in terahertz band, as shown in Figure 9 includes a radiation source 1, a first terahertz wave detector 5, a second terahertz wave detector 6 and the above-mentioned flat lens 3.

[0055] The terahertz wave generated by the radiation source 1 exits a scattered annular light beam after passing through the flat lens 3 of the above structure, and the scattered annular light beam exits and is incident on the target 4 to be measured at multiple angles. The reflected light enters the terahertz wave detectors (i.e. the first terahertz wave detector 5 and the second terahertz wave detector 6) at different positions.

[0056] The target 4 to be measured is placed on a moving platform. When detecting the target 4 to be measured, the target 4 to be measured can be moved by moving the moving platform up, down, left and right, so that the exiting multi-angle annular beam can comprehensively irradiate the target 4 to be measured.

[0057] The first terahertz wave detector 5 and the second terahertz wave detector 6 can be fixedly placed at different positions according to the needs of use, and the processing device is used for processing the terahertz wave signals output by the first terahertz detector 5 and the second terahertz detector 6 to obtain the terahertz wave image of the target 4 to be measured.

[0058] The flat lens 3 converts the terahertz light beam with Gaussian distribution into a multi-angle exiting annular uniform illumination light beam. Based on this characteristic, the device for multi-angle annular uniform illumination in terahertz band can simultaneously illuminate the target 4 to be measured from different angles, so as to increase the reflected wave signals entering the first terahertz detector and the second terahertz detector. This has no specific requirements for the surface undulation and placement angle of the target 4 to be measured. At the same time, the device can also eliminate the adverse effects of uneven distribution of the illumination terahertz wave on the imaging quality. In addition, compared with the circular light beam, the exiting annular light beam can convert the small-angle incident light with low imaging utilization rate in the central part into large-angle incident light with high imaging utilization rate, so as to provide multi-angle illumination while improving the energy utilization rate.

[0059] The two devices provided above can simultaneously illuminate the target 4 to be measured from different angles, so as to increase the reflected wave signals entering the detection system. This has outstanding application value for the application scenarios of terahertz waves in the fields of non-destructive detection and human security inspection. At the same time, the two devices can also eliminate the adverse effects of uneven distribution of the illumination terahertz wave on the imaging quality. In addition, in the reflective terahertz active imaging system, compared with the circular light beam, the annular light beam can convert the small-angle incident light with low imaging utilization rate in the central part into large-angle incident light with high imaging utilization rate, so as to provide multi-angle illumination while improving the energy utilization rate.

[0060] Based on the above description, the application can provide a new method for terahertz nondestructive detection, biological medical imaging, dark field detection and the like.

[0061] The various embodiments are described in a progressive manner in the specification, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between the various embodiments can be mutually referred to.

[0062] The principles and implementation manners of the application are described by using specific examples in the specification, and the above description of the examples is only used to help understand the method of the application and its core idea; meanwhile, for the general technical personnel in the field, the specific implementation manner and application range of the application can be changed according to the idea of the application. In conclusion, the content of the specification should not be understood as the limitation of the application.

Claims

1. A slab lens characterized by, Multi-angle annular uniform illumination for terahertz frequency band; an air hole array and a center point defect are arranged on the flat lens; the air hole array is formed by rotating basic units at a set angle with the center point defect as the center; the basic unit is provided with a plurality of air holes; the extension period of the air hole is a; A semicircular ring body is arranged on the exit surface of the flat lens; The basic unit is a rhombic structure; The first vertex of the rhombic structure coincides with the center point defect; the center point of the rhombic structure is provided with an air hole, the second vertex and the fourth vertex of the rhombic structure are each provided with an air hole; the midpoint position of each side of the rhombic structure is provided with an air hole; the first vertex of the rhombic structure is an acute angle vertex; the second vertex and the fourth vertex of the rhombic structure are obtuse angle vertices; the set angle is equal to the acute angle of the rhombic structure; The semicircular ring body includes a first annular circular arc groove, a second annular circular arc groove and a third annular circular arc groove arranged in sequence along the connecting line from the center point defect to the first air hole; the first air hole is the air hole closest to the center point defect in the basic unit; The first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove are all closed annular structures with the center point defect as the center; the side surface of the first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove is semicircular; The side surface of the first annular circular arc groove, the second annular circular arc groove and the third annular circular arc groove is a surface perpendicular to the exit surface; The side surface of the second annular circular arc groove is tangent to the side surface of the first annular circular arc groove and the side surface of the third annular circular arc groove respectively; the radius of the side surface of the second annular circular arc groove is greater than the radius of the side surface of the first annular circular arc groove; the radius of the side surface of the third annular circular arc groove is greater than the radius of the side surface of the second annular circular arc groove.

2. The slab lens according to claim 1, characterized in that, The radius of the side surface of the first annular circular arc groove is 0.06a; the radius of the side surface of the second annular circular arc groove is 0.08a; the radius of the side surface of the third annular circular arc groove is 0.1a.

3. The slab lens of claim 1, wherein The flat lens is a cylindrical structure based on quasi-photonic crystals; the radius of the flat lens is 4a; the height of the flat lens is 1.5a.

4. The slab lens of claim 1, wherein The radius of the center point defect is equal to the radius of the air hole.

5. The slab lens of claim 1, wherein The radius of the center point defect and the radius of the air hole are both 0.23a.

6. An apparatus for multi-angle annular uniform illumination in terahertz band, characterized in that, A radiation source, a collimating lens and the flat lens according to any one of claims 1-5 are arranged in sequence in the direction of terahertz wave propagation; The radiation source is used to generate terahertz waves; after the terahertz waves are collimated by the collimating lens, a circular light spot is formed after the flat lens, and uniform terahertz waves are formed in multiple angles; the uniform terahertz waves in multiple angles are incident on the target to be detected.

7. An apparatus for multi-angle annular uniform illumination in terahertz band, characterized in that, It comprises: A radiation source, a first terahertz wave detector, a second terahertz wave detector and a flat lens according to any one of claims 1-5; The terahertz wave generated by the radiation source forms uniform terahertz waves with multiple angles of emission through the flat plate lens; after the uniform terahertz waves with multiple angles of emission are incident on the target to be detected, the uniform terahertz waves with multiple angles of emission are reflected by the target to be detected and respectively enter the first terahertz wave detector and the second terahertz wave detector.

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