CN117855877A - Tunable THz absorber capable of realizing dual-band spin selective absorption - Google Patents

Abstract

The present invention discloses a tunable THz absorber capable of realizing dual-band spin-selective absorption, belonging to the technical field of optical metamaterials combining THz band metals and graphene. The tunable THz absorber is composed of a number of structural units arranged periodically on the XY plane, the geometric center of the structural unit is taken as point O, the two mutually perpendicular sides passing through the point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis, each of the structural units is composed of a metal plate in the lower layer, an intermediate substrate layer, two graphene sheets attached to the intermediate substrate layer, and an L-shaped metal unit located in the upper layer. The present invention adopts the above-mentioned tunable THz absorber capable of realizing dual-band spin-selective absorption, which has the advantages of simple manufacture, tunability, dual-band range, high spin-selective absorption efficiency, and wide application scenarios.

Description

A tunable THz absorber capable of dual-band spin-selective absorption

Technical Field

The present invention relates to the technical field of optical metamaterials combining THz band metal and graphene, and in particular to a tunable THz absorber capable of realizing dual-band spin selective absorption.

Background technique

Terahertz (THz) waves (0.1-10THz) are located between microwaves and infrared light waves. They have the advantages of low photon energy, strong penetration, wide bandwidth, and high imaging resolution, which have aroused great interest among researchers. Before the mid-1980s, due to the lack of effective generation and detection methods, research on the electromagnetic properties of this band was limited, so it was called the "THz gap". With the rapid development of ultrafast laser technology and new materials, the generation and detection problems of THz have been effectively solved. THz science and technology has been vigorously developed, and fruitful results have been achieved in many application fields such as detection, imaging, and wireless communications. Among them, absorbers play an important role in THz application devices, but traditional natural materials have weak electromagnetic response to THz waves, making it difficult to achieve efficient absorption of THz waves. The emergence of metamaterials solves this problem. In 2008, Tao et al. proposed the first generation of THz metamaterial absorbers, which had a resonant absorption rate of up to 70% at 1.3THz. Subsequently, dual-band, multi-band and broadband metamaterial absorbers came out one after another, opening up broad prospects for the development of terahertz metamaterial absorbers.

Metamaterials are artificially manufactured subwavelength periodic structures, where "subwavelength" means that the size of the structure is smaller than the wavelength of external light stimulation. Metamaterials were first proposed by Walser in 1999. In the early stage of metamaterial research, some electromagnetic properties, such as negative refractive index and perfect lens, were mainly realized in the microwave region. After the first perfect metamaterial absorber in the microwave region was proposed by Landy et al., metamaterials for electromagnetic wave absorption have attracted much attention. However, most of the designed metamaterial absorbers are only suitable for linearly polarized waves, and rarely for circularly polarized waves. With the development of metamaterials, metamaterials with chiral characteristics have attracted people's attention, because metamaterials with chiral characteristics can manipulate not only linearly polarized waves but also circularly polarized waves. Chirality refers to the lack of mirror symmetry of an object, which cannot be overlapped with its mirror structure by translation or rotation. By introducing chirality into the design of the metamaterial absorber structure through artificial design, a chiral metamaterial absorber lacking mirror symmetry can be obtained. Since the chiral metamaterial absorber has different absorption rates for right-handed circularly polarized light (RCP) and left-handed circularly polarized light (LCP), it can achieve selective absorption of circularly polarized light, namely spin-selective absorption. At the same time, the spin-selective absorption effect can be expressed by the circular dichroism (CD) value, which is defined as the absorption difference between right-handed circularly polarized light and left-handed circularly polarized light. In recent years, various chiral metamaterial absorbers have been proposed in the spectrum range from microwave to optical regions. In 2016, Wang et al. designed a circular dichroism supermirror working in the mid-infrared region by combining two layers of anisotropic metamaterial structures. This supermirror shows perfect reflectivity for left-handed circularly polarized light without reversing its polarization direction, and it completely absorbs right-handed circularly polarized light. In 2017, Tang et al. proposed an η-type metamaterial structure that can achieve dual-band spin-selective absorption in the visible light band, with a maximum absorption rate of more than 80% and a circular dichroism value of about 0.5. In 2018, OuYang et al. proposed a near-infrared chiral plasma metasurface absorber that can absorb right-handed circularly polarized light in a single band, and its mirror structure can absorb left-handed circularly polarized light in a single band, with a maximum absorption rate of 87% and a maximum circular dichroism value of about 70%. In 2019, Wang et al. proposed a type I chiral selective metamaterial absorber that can strongly absorb left-handed circularly polarized light in two resonant frequency bands, with absorption rates of 95.18% and 91.77% respectively, but almost no right-handed circularly polarized light is absorbed in the two frequency bands, resulting in significant circular dichroism. In 2022, Tang et al. designed and demonstrated a mid-infrared chiral metasurface absorber with dual-band selective absorption. The tunability of its absorption of circularly polarized light is achieved through the unique design of two coupled rectangular strips on the top metal layer. The circular dichroism sign of each band can be controlled and flipped by adjusting the width and length of the vertical rectangular strips. In 2022, Tao et al. proposed two dual-band spin-selective absorption metasurfaces working in the terahertz region and with strong circular dichroism. The first can absorb the same spin state of circularly polarized waves in two bands, and the second absorbs one spin state of circularly polarized waves in the first band and absorbs the spin state orthogonal to the spin state of the first band in the second band. It can be seen from the research on chiral metamaterial absorbers that terahertz chiral metamaterial absorbers have not been widely studied. Therefore, the research and design of spin-selective absorption metamaterial structures that can achieve circularly polarized wave selection and propagation control in the terahertz range is crucial for many applications, such as holographic imaging, biomolecule detection, and CD spectroscopy.

The chiral metamaterials proposed above can only adjust the absorption by adjusting the size of the structure, which reduces the applicability of practical applications. In order to achieve tunable absorption, a new material, graphene, has been introduced into the design of metamaterials. Graphene is a two-dimensional honeycomb lattice composed of tightly packed flat monolayer carbon atoms. It was first obtained by graphite exfoliation in 2004. The electromagnetic properties of biased or photoexcited graphene are determined by the Drude-like electrical response of free carriers and the interband transition between the low and high bands of the Dirac cone. Both are tunable by controlling the Fermi level, which makes the electromagnetic structure made of this material have unprecedented tunability. Recently, different graphene-based tunable metamaterials have been reported. He et al. proposed a graphene metamaterial and numerically demonstrated the active tuning of its electromagnetic induced transparency (EIT) window in the terahertz region. Yuan et al. reported an all-graphene dielectric terahertz metamaterial absorber/reflector, whose absorption bandwidth and absorptivity can be adjusted by applying a bias voltage to adjust the Fermi level of the patterned graphene. Tao et al. introduced a tunable dual-band terahertz asymmetric transmission (AT) metasurface with strong circular dichroism, which can realize dual-band AT effect in the terahertz band and has a strong CD effect, and polarized waves in two bands can be converted into their cross-polarized waves. Therefore, graphene is a good candidate material for tunable devices. Adding a graphene layer to the designed chiral metamaterial structure can realize a tunable spin-selective metamaterial absorber. The research on this tunable spin-selective absorber may provide broad development prospects for various chirality-related applications in emerging terahertz technologies such as chiral sensing, imaging, information encryption and hiding.

Summary of the invention

The purpose of the present invention is to provide a tunable THz absorber capable of realizing dual-band spin-selective absorption, which has the advantages of simple manufacture, tunability, dual-band range, high spin-selective absorption efficiency, and wide application scenarios.

To achieve the above-mentioned purpose, the present invention provides a tunable THz absorber capable of realizing dual-band spin-selective absorption. The tunable THz absorber is composed of a plurality of structural units arranged periodically on an XY plane. The geometric center of the structural unit is taken as point O, and two mutually perpendicular sides passing through the point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. Each of the structural units is composed of a metal plate in a lower layer, an intermediate substrate layer, two graphene sheets attached to the intermediate substrate layer, and an L-shaped metal unit in an upper layer. The dual-band spin-selective absorption refers to the ability to realize selective absorption of right-handed circularly polarized light and left-handed circularly polarized light in two frequency bands, respectively, wherein right-handed circularly polarized light and left-handed circularly polarized light belong to two spin states of circularly polarized light, and the attached graphene sheets enable the spin-selective absorption efficiency to be regulated without changing the structural parameters.

Preferably, electrodes connected to two ends of the graphene sheet are attached to both sides of the structural unit.

Preferably, the L-shaped metal unit is composed of three groups of metal rods distributed along the OX axis, and the lengths of the three groups of metal rods are different, but the thickness and width are the same;

The first group of metal rod combinations consists of the first metal rod and the second metal rod, the second group of metal rod combinations consists of the third metal rod and the fourth metal rod, and the third group of metal rod combinations consists of the fifth metal rod and the sixth metal rod; the metal rods in each group of metal rod combinations are perpendicular to each other, the first group of metal rod combinations and the second group of metal rod combinations rotate at the same angle around the OZ axis, and the third group of metal rod combinations rotate at an angle different from the first and second groups of metal rod combinations around the OZ axis; the angle between the fourth metal rod in the second group of metal rod combinations and the fifth metal rod in the third group of metal rod combinations of the L-shaped metal unit is recorded as θ.

Preferably, the adjustment range of the angle θ is 92°-112°.

Preferably, θ=102°.

Preferably, the length and width of the metal plate and the intermediate substrate layer are _px = _py =310um respectively, the thickness of the metal plate is t=18um, the thickness of the intermediate substrate layer is d=75um, the width of the L-shaped metal unit is w=12um, and the thickness is h=18um; wherein, the length of the first metal rod in the first group of metal rods is _L1 =185um, the length of the second metal rod is _L2 =149um, the length of the third metal rod in the second group of metal rods _{is L3} =155um, the length of the fourth metal rod is _L4 =157um, the length of the fifth metal rod in the third group of metal rods is _L5 =147um, the length of the sixth metal rod is _L6 =170um, the spacing between the first group of metal rods and the second group of metal rods is m=37um, the width of the two graphene sheets is _wg =5um, and the spacing between them is b=35um.

Preferably, the intermediate substrate layer is a silicon dioxide substrate.

Preferably, the L-shaped metal unit and the metal plate are both made of gold.

Preferably, the structural unit has chiral characteristics.

Therefore, the beneficial effects of the present invention using the above-mentioned tunable THz absorber capable of realizing dual-band spin selective absorption are as follows:

(1) The THz absorber can achieve perfect dual-band spin-selective absorption of circularly polarized light, that is, in the 0.28 THz band, when circularly polarized light is incident on the material along the positive direction of the OZ axis, RCP can be perfectly absorbed, but LCP is almost not absorbed; in the 0.35 THz band, when circularly polarized light is incident on the material along the positive direction of the OZ axis, LCP can be perfectly absorbed, but RCP is almost not absorbed.

(2) The THz absorber is tunable. By changing the Fermi level of graphene, the spin-selective absorption efficiency can be regulated without changing the structural parameters.

(3) By changing the length, width, thickness of the metal rods in each group of metal rods, the thickness of the silicon dioxide substrate, and the rotation angle of the metal rods, the requirements for the efficiency and band of spin-selective absorption in practical applications under different environments can be met, and the application scenarios are wide.

The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the three-dimensional structure of a tunable THz absorber in this embodiment;

FIG2 is a schematic diagram of the three-dimensional structure of the structural unit in this embodiment;

Fig. 3 is a front view of the structural unit;

4(a) and (b) are respectively the reflection spectrum and absorption spectrum obtained when circularly polarized light is incident on the THz absorber along the positive direction of the OZ axis in this embodiment;

5(a) and (b) are respectively diagrams showing the RCP absorption spectrum and the changes in the RCP peak value and peak frequency as the Fermi level of graphene changes in this embodiment;

6(a) and (b) are respectively diagrams showing the changes in the LCP absorption spectrum and the LCP peak value and peak frequency as the Fermi level of graphene changes in this embodiment;

7(a) and (b) are respectively the CD spectrum obtained when circularly polarized light is incident on the THz absorber along the positive direction of the OZ axis and the CD spectrum changing with the Fermi level of graphene in this embodiment;

FIG8 (a) and (b) are absorption spectra of the THz absorber to RCP and LCP when the angle θ varies in this embodiment, respectively.

Reference numerals

1. Metal plate; 2. Intermediate substrate layer; 3. Graphene sheet; 4. L-shaped metal unit; 5. Electrode; 6. First metal rod; 7. Second metal rod; 8. Third metal rod; 9. Fourth metal rod; 10. Fifth metal rod; 11. Sixth metal rod.

Detailed ways

The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. "First", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

Embodiment 1

As shown in FIG1 , the present invention provides a tunable THz absorber capable of realizing dual-band spin selective absorption, the tunable THz absorber is composed of a plurality of structural units arranged periodically on the XY plane, the geometric center of the structural unit is taken as point O, the two mutually perpendicular sides passing through the point in the horizontal and vertical directions are the OX axis and the OY axis, and the axis perpendicular to the two sides is the OZ axis. The structural unit has chiral characteristics, each structural unit is composed of a metal plate 1 in the lower layer, an intermediate substrate layer 2, two graphene sheets 3 attached to the intermediate substrate layer 2, and an L-shaped metal unit 4 in the upper layer, and two electrodes 5 are attached on both sides of the periodic structural unit to connect the two ends of the graphene sheet 3.

As shown in FIG. 2 , the L-shaped metal unit 4 is composed of three groups of metal rods distributed along the OX axis, and the lengths of the three groups of metal rods are different, but the thickness and width are the same. Among them, the first group of metal rods is composed of a first metal rod 6 and a second metal rod 7, the second group of metal rods is composed of a third metal rod 8 and a fourth metal rod 9, and the third group of metal rods is composed of a fifth metal rod 10 and a sixth metal rod 11, and the two metal rods in each group of metal rods are perpendicular to each other.

The first group of metal rods and the second group of metal rods rotate at the same angle around the OZ axis, and the third group of metal rods rotates at the same angle around the OZ axis as the first and second groups of metal rods. The angle between the fourth metal rod 9 in the second group of metal rods of the L-shaped metal unit 4 and the fifth metal rod 10 in the third group of metal rods is denoted as θ. The third group of metal rods rotates, and the adjustment range of the angle θ is 92°-112°. When the angle θ=102°, the spin-selective absorption rate of circularly polarized light is optimal.

It should be noted that, in conjunction with FIG. 2 , in the structural unit, the middle substrate layer 2 is a silicon dioxide substrate, the silicon dioxide substrate is between the upper L-shaped metal unit 4 and the lower metal plate 1 , and both the L-shaped metal unit 4 and the metal plate 1 are made of gold.

In this embodiment, in combination with FIG. 2 and FIG. 3 , the length and width of the metal plate 1 and the intermediate substrate layer 2 in the structural unit are respectively p _x = p _y = 310 um, the thickness of the metal plate 1 is t = 18 um, the thickness of the intermediate substrate layer 2 is d = 75 um, the width of the L-shaped metal unit 4 is w = 12 um, and the thickness is h = 18 um. Among them, the length of the first metal rod 6 in the first group of metal rods is L ₁ = 185 um, the length of the second metal rod 7 is L ₂ = 149 um, the length of the third metal rod 8 in the second group of metal rods is L ₃ = 155 um, the length of the fourth metal rod 9 is L ₄ = 157 um, the length of the fifth metal rod 10 in the third group of metal rods is L ₅ = 147 um, the length of the sixth metal rod 11 is L ₆ = 170 um, the spacing between the first group of metal rods and the second group of metal rods is m = 37 um, the width of the two graphene sheets 3 is w _g = 5 um, and the spacing between them is b = 35 um.

Further, the present invention can be prepared by micro-nano processing technology (such as electron beam exposure, focused ion beam and other methods). Focused ion beam technology (FIB) can accelerate and focus the ion beam into a very small size spot using a lens with a focusing function, so that the ion beam has very high energy and collides with the solid, and sputters and peels off the atomic layer that constitutes the solid. The focused ion beam technology can be used to achieve imaging, etching, thin film deposition, ion beam injection, and preparation of transmission electron microscope samples. Taking focused ion beam etching as an example, a metal film is deposited on the upper and lower layers of the silicon dioxide substrate 2, and the first metal rod 6 and the second metal rod 7 of the first group of metal rods are sequentially etched in the upper layer, and the third metal rod 8 and the fourth metal rod 9 of the second group of metal rods are combined, and the fifth metal rod 10 and the sixth metal rod 11 of the third group of metal rods are combined to form an L-shaped metal unit 4 on the upper layer, and the metal film deposited on the lower layer forms a metal plate 1.

In addition, the THz absorber of the present invention can achieve perfect selective absorption of right-handed circularly polarized light and left-handed circularly polarized light in two frequency bands, that is, dual-band perfect spin selective absorption. Since the circularly polarized light incident along the positive direction of the OZ axis can cause a strong magnetic coupling resonance effect on the local surface when incident on the L-type metal unit 4, and the reflection spectrum shows a resonance valley at the resonance frequency. In order to achieve spin selective absorption of circularly polarized light by the THz absorber, the THz absorber is set as a periodic structure composed of L-type metal units 4. That is, when RCP and LCP are incident along the +Z direction, the incident light first interacts with the upper L-shaped metal unit 4, wherein when RCP interacts with the L-shaped metal unit 4, a strong magnetic coupling resonance is caused between the second group of metal rods and the third group of metal rods on the rightmost side, which manifests as a reflection valley; and when LCP interacts with the L-shaped metal unit 4, a strong magnetic coupling resonance is caused between the first group of metal rods and the second group of metal rods on the leftmost side, which manifests as a reflection valley. Due to the existence of the lower metal plate 1, the incident light cannot penetrate the structure, so the transmittance is 0, that is, T=0, and according to the relationship between absorption and transflection A=1-RT, A=1-R is further derived. Combined with the reflection spectrum obtained from the simulation experimental results of Figure 4(a), the absorption spectrum calculated according to the absorption formula of right-handed circularly polarized light A _RCP =1-r _RR ² -r _LR ² and the absorption formula of left-handed circularly polarized light A _LCP =1-r _LL ² -r _RL ² is shown in Figure 4(b). In the 0.28 THz band, RCP is perfectly absorbed, while LCP is almost not absorbed, and in the 0.35 THz band, LCP is perfectly absorbed, and RCP is almost not absorbed, thereby achieving perfect spin-selective absorption of circularly polarized light in the two bands of 0.28 THz and 0.35 THz.

In order to better suit practical applications, the inventor attached two graphene sheets 3 parallel to the X-axis above the silicon dioxide substrate in the middle layer of the THz absorber structure, and tuned the efficiency of spin-selective absorption by adjusting the Fermi level of graphene by changing the applied voltage _Vg . It can be seen from Figures 5 and 6 that as the Fermi level of graphene increases from 0eV to 0.8eV, the absorption efficiency peak decreases from 0.99 to about 0.7, and the absorption peak frequency remains basically unchanged or changes very little. The structural setting of the THz absorber in this invention not only realizes the spin-selective absorption of circularly polarized light, but also can tune the spin-selective absorption rate. The THz absorber has the advantages of simple manufacture, tunability, dual-band range, high spin-selective absorption efficiency, and a wide range of application scenarios.

In this embodiment, in order to better understand the spin-selective absorption of circularly polarized light incident along the +Z direction, FIG. 7 shows the circular dichroism value: CD = A _RCP - A _LCP . Combined with FIG. 7 (a), it is calculated that in the 0.28THz band, the circular dichroism value is about 0.85, and in the 0.35THz band, the circular dichroism value is about -0.86, which has significant circular dichroism. Combined with FIG. 7 (b), the circular dichroism value can also be adjusted by adjusting the Fermi level of graphene. As the Fermi level of graphene increases from 0eV to 0.8eV, the absolute value of the circular dichroism decreases from 0.8 to about 0.26.

In this embodiment, the three groups of metal rods in the upper L-shaped metal unit 4 are arranged along the OX axis. First, the first group of metal rods is rotated 40° counterclockwise along the OZ axis, and then translated 142um along the negative direction of the OX axis; secondly, the second group of metal rods is rotated 40° counterclockwise along the OZ axis, and then translated 105um along the negative direction of the OX axis; finally, the third group of metal rods is rotated 38° clockwise along the OZ axis, and then translated 142um along the positive direction of the OX axis. At this time, the angle θ between the fourth metal rod of the second group of metal rods and the fifth metal rod of the third group of metal rods is 102°, and the spin selective absorption effect achieved by the THz absorber is optimal. Combined with Figure 8, it can be seen that when the rotation angle of the third group of metal rods is changed, the spin-selective absorption effect of the THz absorber on circularly polarized light will change greatly, especially when the angle θ=92°, that is, when the third group of metal rods rotates 48° clockwise around the OZ axis, it shows strong absorption of LCP in both resonance bands, and almost no absorption of RCP. When the angle θ=97°, at the 0.28THz resonance band, different degrees of absorption of RCP and LCP appear, and at the 0.35THz resonance band, only strong absorption of LCP appears. When the angle θ changes from 102° to 112°, the frequency of the first resonance band has a slight blue shift, and the RCP absorption peak decreases slightly, while the frequency of the second resonance band remains unchanged, and the LCP absorption peak remains basically unchanged. Therefore, by adjusting the rotation angle of the third group of metal rods around the OZ axis, different spin-selective absorption effects can be obtained in the two resonance bands, which can meet the polarization state requirements of circularly polarized light for spin-selective absorption in practical applications.

Therefore, the present invention adopts the above-mentioned tunable THz absorber capable of realizing dual-band spin-selective absorption, which has the advantages of simple manufacture, tunability, dual-band range, high spin-selective absorption efficiency, and wide application scenarios.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims (9)

1. The tunable THz absorber capable of realizing dual-band spin selective absorption consists of a plurality of structural units which are periodically arranged on an XY plane, wherein the geometric center of the structural units is taken as an O point, two sides which are perpendicular to each other and pass through the O point along the horizontal direction and the vertical direction are taken as an OX axis and an OY axis, and the two sides which are perpendicular to the O point are taken as the OZ axis, and the tunable THz absorber is characterized in that: each structural unit consists of a lower metal plate (1), an intermediate substrate layer (2), two graphene sheets (3) attached to the intermediate substrate layer and an upper L-shaped metal unit (4).

2. A tunable THz absorber capable of dual band spin selective absorption according to claim 1, wherein: electrodes (5) connected with two ends of the graphene sheet (3) are attached to two sides of the structural unit.

3. A tunable THz absorber capable of dual band spin selective absorption according to claim 1, wherein: the L-shaped metal unit (4) is formed by combining three groups of metal rods distributed along the OX axis direction, wherein the lengths of the three groups of metal rods are different, but the thickness and the width are the same;

the first group of metal rod combinations consists of a first metal rod (6) and a second metal rod (7), the second group of metal rod combinations consists of a third metal rod (8) and a fourth metal rod (9), and the third group of metal rod combinations consists of a fifth metal rod (10) and a sixth metal rod (11); the metal bars in each group of metal bar combinations are mutually perpendicular, the rotation angles of the first group of metal bar combinations and the second group of metal bar combinations around the OZ axis are consistent, and the rotation angles of the third group of metal bar combinations and the first group of metal bar combinations and the second group of metal bar combinations around the OZ axis are inconsistent; and the included angle between a fourth metal rod (9) in the second group of metal rod combinations and a fifth metal rod (10) in the third group of metal rod combinations of the L-shaped metal units (4) is marked as theta.

4. A tunable THz absorber capable of dual band spin selective absorption according to claim 3, wherein: the adjustment range of the included angle theta is 92-112 degrees.

5. A tunable THz absorber capable of dual band spin selective absorption according to claim 4, wherein: the angle θ=102° optimal for the spin-selective absorption of circularly polarized light.

6. A tunable THz absorber capable of dual band spin selective absorption according to claim 3, wherein: the length and the width of the metal plate (1) and the middle substrate layer (2) are p respectively _x ＝p _y =310 um, the thickness t=18 um of the metal plate (1), the thickness d=75 um of the intermediate substrate layer (2), the width w=12 um of the L-shaped metal unit (4), and the thickness h=18 um; wherein the length L of the first metal bar (6) in the first group of metal bar combinations ₁ Length L of the second metal rod (7) =185 um ₂ Length L of the third metal bar (8) in the second group of metal bar combinations =149 um ₃ Length L of the fourth metal bar (9) =155 um ₄ =157 um, length L of the fifth metal bar (10) in the third group of metal bar combinations ₅ Length L of the sixth metal bar (11) =147 um ₆ The first group of metal bar combinations and the second group of metal bar combinations have a distance m=37um, and the width w of the two graphene sheets is equal to 170um _g =5 um, and the spacing between them b=35 um.

7. A tunable THz absorber capable of dual band spin selective absorption according to claim 1, wherein: the intermediate substrate layer (2) is a silicon dioxide substrate.

8. A tunable THz absorber capable of dual band spin selective absorption according to claim 1, wherein: the L-shaped metal units (4) and the metal plates (1) are made of gold materials.

9. A tunable THz absorber capable of dual band spin selective absorption according to claim 1, wherein: the structural unit has chiral characteristics.