A hypersensitive terahertz liquid sensor based on the photon spin Hall effect of optical Tamm states

Abstract

The present invention discloses a hypersensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect, which can be applied to liquid detection in chemical analysis. This sensor consists of an analyte layer, an indium antimonide layer, a near-zero refractive index material layer, and a Bragg reflection structure layer, and the analyte layer is the liquid to be measured. An incident linearly polarized light beam (terahertz band) is irradiated on the sensor structure, and by measuring the spin offset of the spin Hall effect of the reflected light after filling the liquid to be measured, the type and concentration of the filled liquid can be detected. This terahertz liquid sensor based on the optical Tamm state photon spin Hall effect has a large numerical value of the spin offset, is very sensitive to the changes in the type and concentration of the liquid to be measured, and has high intensity sensitivity and excellent sensing performance. When the sensor of the present invention detects a liquid, it has low dependence on environmental factors such as temperature and has good device stability.

Description

Technical Field

[0001] The present invention belongs to the field of optical sensing, and particularly relates to a terahertz liquid sensor based on the optical Tamm state photon spin Hall effect, which can be applied to various detections of liquid types and concentrations. Background Art

[0002] The optical sensing response time is relatively short, which makes it possible to detect various parameters of the object to be measured online and in real time. Moreover, its sensing performance will not be reduced due to environmental changes or catalyst poisoning caused by specific objects to be measured, etc., and it is considered a sensing technology with good development prospects. The most successful example of its application is the surface plasmon resonance (SPR) technology, which is based on the surface plasmon waves excited on the surface of noble metals such as gold or silver. Although this SPR sensor has advantages over non-optical detection sensors, its sensing sensitivity is still not as good as the latter. In order to improve the sensitivity of the SPR sensor, researchers have proposed sensors based on new structures or effects to enhance the sensing sensitivity, such as using a double-layer metal to excite the long-range surface plasmon resonance (LRSPR) effect; using two-dimensional materials such as graphene to increase light absorption and the adsorption of the object to be detected; using the optical Tamm state to further reduce the reflection coefficient and improve the sensitivity. The above sensors all reflect their sensing characteristics based on the valley and peak positions of the reflection curve. When detecting a liquid object to be measured, for different types of liquids or different concentrations of liquids, the difference in refractive index is very small, which poses challenges for various sensors in liquid detection. Therefore, it has become an urgent problem to detect the target liquid with high sensitivity and high selectivity.

[0003] When a linearly polarized light beam passes through the interface of a material with a refractive index gradient composed of different refractive indices, photons with opposite spin directions will undergo a transverse shift in the direction perpendicular to the incident plane, thus splitting into left-handed circularly polarized light and right-handed circularly polarized light. This phenomenon is the photon spin Hall effect (PSHE). PSHE is closely related to the refractive index gradient, so this effect is considered a potential precision measurement tool. For example, PSHE has been used to measure the thickness of nano-metal films, the number of layers of graphene, and the reaction rate of real-time detection of chemical reactions, etc. Recently, PSHE has also been used in the design of refractive index sensors. For example, researchers such as Xiang Yuanjiang found that the sensitivity of the sensor based on PSHE is better than that of the traditional SPR sensor, which is 2-3 times that of the traditional SPR sensor. Researchers also found that: by combining weak measurement technology, the sensitivity of the refractive index sensor based on PSHE can be greatly improved, and the signal-to-noise ratio is greatly enhanced. In summary, the sensor based on PSHE has advantages such as high sensitivity and high signal-to-noise ratio, and it is very necessary and practically significant to explore its application research in the field of liquid detection. Summary of the Invention

[0004] The object of the present invention is to provide a hypersensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect, which detects the liquid to be measured according to the spin offset value of the reflected light, and the influence of the ambient temperature on the liquid sensor is small and the stability is high.

[0005] To solve the above problems, the present invention provides the following technical solutions:

[0006] A hypersensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect, the structure is composed of a liquid layer to be measured, an InSb layer, an ENZ plate layer, and a Bragg reflection structure layer. The Bragg reflection structure layer is composed of a periodic alternating arrangement of medium A and medium B. The medium A is poly-4-methylpentene-1, and the medium B is SiO2. The single-layer thickness of the medium A and B layers is given by the Bragg condition d A、B = λ / 4n A、B where λ is the wavelength of the incident linearly polarized light, and n A、B is the refractive index of medium A and B.

[0007] Preferably, the dielectric constant of InSb can be expressed by the Drude model: ε ∞ is the high-frequency dielectric constant, is the plasma frequency, the scattering frequency μ is the carrier mobility, μ = 77000(T / 300) -1.66 cm 2 ·V -1 ·s -1 .m * is the effective mass of the carrier, m * = 0.015m0, m0 = 9.1×10 -31 kg is the electron mass. The relationship between the carrier concentration N and the temperature T is:

[0008] Preferably, the incident light working angle θ is fixed, and the intensity sensitivity of the liquid sensor is defined as where Δn is the refractive index change difference of different liquids to be measured, and Δδ is the change amount of the spin Hall effect offset value of the reflected light. By calculating the intensity sensitivity of the liquid sensor of the present invention, the sensing performance of the sensor can be evaluated.

[0009] A method for liquid detection. Using the above liquid sensor based on the optical Tamm state photon spin Hall effect can distinguish the types and concentrations of liquids. Specifically, an incident linearly polarized light (terahertz band) directly irradiates the liquid layer to be measured, and reflection occurs at the interface of the InSb layer. The reflected light beam splits into a left-handed circularly polarized light and a right-handed circularly polarized light in the direction perpendicular to the incident plane formed by the incident linearly polarized light and the normal line. Different types or concentrations of the liquid to be measured have different refractive indices, and the corresponding offset values of the spin Hall effect are also different. By measuring the splitting offsets of the left-handed and right-handed circularly polarized lights, the types and concentrations of the liquid to be measured can be analyzed. Moreover, the stability of this sensor is relatively high, and it has low dependence on environmental temperature factors and other factors at room temperature, and can be adapted to detections under different temperature conditions.

[0010] The advantages of the present invention are as follows:

[0011] The hypersensitive liquid sensor based on the optical Tamm state photon spin Hall effect proposed by the present invention has a simple structure. Due to the detection based on the optical principle, it has the characteristics of real-time inspection and high stability; when detecting a specific liquid, the working angle range is small, and the selectivity for the liquid to be measured is high; it will not cause damage to the device materials after detection. Compared with the reported sensors based on the surface plasmon resonance effect, the liquid sensor based on the optical Tamm state photon spin Hall effect proposed by the present invention has higher sensitivity and exhibits excellent sensing performance. Description of the Drawings

[0012] Figure 1 It is a schematic structural diagram of the liquid sensor in the embodiment of the present invention.

[0013] Figure 2 It is a relationship diagram between the spin offset value of the photon spin Hall effect and the working angle at different concentrations of the NaCl solution in the embodiment of the present invention.

[0014] Figure 3 It is the spin offset value of the NaCl solution (normal saline) with a molar concentration of 0.154 mol / L at different temperatures. Specific Embodiments

[0015] The following further details the specific embodiments of the present invention through the description of the embodiments to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0016] Embodiment 1: A hypersensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect of the present invention, as Figure 1As shown, it includes the liquid to be measured ①, indium antimonide (InSb) material layer ②, epsilon-near-zero (ENZ) material layer ③, Bragg reflection periodic structure layer (alternately arranged with material A ④ and material B ⑤), and incident working light source (working frequency is 1.11 THz). The incident light irradiates the InSb layer through the liquid to be measured at a certain working angle. The electric fields of the liquid to be measured, InSb material, epsilon-near-zero material, and Bragg reflection periodic structure are coupled to excite the optical Tamm state, thereby enhancing the photon spin Hall effect. When other parameters are fixed, by filling different liquids to be measured, the offset values of the spin Hall effect of the reflected light will change differently, and then the type and concentration of the liquid to be measured can be analyzed. In the present invention, the spin offset value basically does not change much under the change of ambient temperature, with high stability; and when detecting the type and concentration of the liquid to be measured, it has excellent sensing performance.

[0017] In this embodiment, the dielectric constant of InSb can be expressed by the Drude model: ε ∞ is the high-frequency dielectric constant, is the plasma frequency, scattering frequency μ is the carrier mobility, μ = 77000(T / 300) -1.66 cm 2 ·V -1 ·s -1 。m * is the effective mass of the carrier, m * = 0.015m0, m0 = 9.1×10 -31 kg is the electron mass. The relationship between the carrier concentration N and the temperature T is:

[0018] Considering that the incident linearly polarized light beam is in Gaussian form and has a finite angular spectrum width, it can be expressed as w0 is the waist width of the incident light beam. This incident linearly polarized light can be regarded as the superposition of left- and right-handed circularly polarized lights of the same frequency, that is, the horizontal (abbreviated as H) and vertical (abbreviated as V) polarized lights can be expressed as and The symbols “+” and “-” represent the left- and right-handed circularly polarized components respectively. The relationship between the angular spectrum of the reflected light and the angular spectrum of the incident light is: where, θ i is the incident angle, r p and r s are the Fresnel reflection coefficients of p(s) polarized light respectively. After the liquid to be measured is filled into the liquid layer to be measured of this liquid sensor, the Fresnel reflection coefficients r p and rs It can be obtained by relying on the transfer matrix method. Considering the first-order approximation of the Taylor series of the reflection coefficient, the spin offset of the spin Hall effect of the reflected light can be expressed as

[0019] and

[0020] When the liquid layer to be measured is a liquid of different types or concentrations (the refractive index change is Δn), the Fresnel reflection coefficients of the liquid sensor structure are different, and the spin offset values corresponding to different liquids to be measured are also different. Because the spin Hall effect of photons is very sensitive to small differences in refractive index, the spin Hall effect of its reflected light will be quite different, and the corresponding spin offset change is denoted as Δδ. For a refractive index sensor based on the spin Hall effect of photons, when the working angle of the incident light is fixed, its intensity sensitivity is defined as This provides an effective way for the detection of liquid types and liquid concentrations.

[0021] Example 2: The hypersensitive liquid sensor based on the optical Tamm state spin Hall effect described in Example 1 is used to distinguish the type or concentration of a liquid. Here, NaCl liquid is taken as an example:

[0022] When linearly polarized light passes through NaCl liquid at a certain incident angle and irradiates onto the InSb material layer of the sensor, due to the spin Hall effect of photons, the reflected light beam will split into a left-handed polarized light and a right-handed circularly polarized light, and the spin offsets of these two beams in the direction perpendicular to the incident plane are equal in magnitude and opposite in direction. For different types of liquids and at different concentrations, their refractive indices are different, and the spin offsets will also be different. Therefore, by measuring the magnitude of the spin Hall effect offset of photons in the liquid sensor, the type and concentration of the liquid to be measured can be simply and conveniently identified. This liquid sensor based on the spin Hall effect of photons is very sensitive to small refractive index differences between the liquids to be measured and has high intensity sensitivity and excellent sensing performance.

[0023] The thickness of the InSb material of the liquid sensor described is 10 nanometers; the refractive index of the ENZ material is 0.1, and the thickness is 400 micrometers; the material A of the Bragg reflection periodic structure (the number of periods N is 20) is poly-4-methylpentene-1 (TPX), with a refractive index of 1.9, and the material B is silica, with a refractive index of 2.25; the frequency of the incident linearly polarized light is 1.11 THz. The thicknesses of the material A and B layers are given by the Bragg condition d A、B =λ / 4n A、B where λ is the wavelength of the incident linearly polarized light, and n A、B is the refractive index of the media A and B. In this example, the single-layer thickness of the material A is 35 micrometers, and the single-layer thickness of the material B is 30 micrometers.

[0024] For the NaCl liquid to be measured, the higher the concentration, the larger the refractive index value. The initial refractive index of pure distilled water without NaCl is 1.3331. When 1 g of NaCl is added to each liter of the solution, the refractive index of the solution changes by 0.00185, and the molar concentration of the solution changes by 0.017 mol / L.

[0025] As Figure 2 shown, when the molar concentration of the liquid sensor of the present invention varies between 0 mol / L and 0.068 mol / L, the graph of the photon spin Hall effect offset value of the NaCl liquid, with the temperature at 27 °C (300 K). It can be seen from this that as the NaCl concentration increases, the refractive index of the solution becomes larger, the working angle corresponding to the maximum spin displacement becomes smaller, but the spin displacement value basically remains unchanged. Every time the refractive index of the NaCl solution changes by 0.00185 (i.e., when the concentration changes by 0.017 mol / L), the spin displacement spectrum of the sensor changes significantly, demonstrating the extremely low solution detection concentration and high concentration sensitivity of the sensor. When the fixed working angle is 7.75°, when differentiating different concentrations of the NaCl solution, the intensity sensitivity of the liquid sensor based on the spin Hall effect proposed in this patent is 633.78 mm / RIU.

[0026] As Figure 3 shown are the spin offset values of the NaCl solution (molar concentration of 0.154 mol / L) at different temperatures. Between 0 °C and 40 °C, the spin offset value shows a slightly increasing trend. Below 10 °C, the spin displacement value basically remains stable and does not change. Between 10 °C and 25 °C, the maximum error of the intensity sensitivity is 2.34%. Between 25 °C and 30 °C, the maximum error of the intensity sensitivity is 2.34%. When the temperature changes to the extreme temperature of 40 °C, the intensity sensitivity error reaches 11%. It can be seen that the maximum error of our sensor in the working environment of 0 °C - 30 °C is 2.34%, showing good stability. According to the intensity sensing scheme of the sensor based on the photon spin Hall effect, when detecting the concentration of the NaCl liquid, the incident linearly polarized light in the terahertz band is incident at an angle of 7.66°, and its intensity sensitivity at room temperature can reach 633.78 mm / RIU. Compared with the sensors based on surface plasmon resonance or resonant optical tunneling effect, the intensity sensitivity value of this sensor has increased by two orders of magnitude. In summary, the liquid sensor based on the optical Tamm state photon spin Hall effect of the present invention exhibits its hypersensitive characteristics when detecting small concentration changes of the NaCl liquid, and its intensity sensitivity is significantly better than the sensitivity values of the sensors based on the surface plasmon resonance effect or the resonant optical tunneling effect; and this sensor has low dependence on environmental temperature and has good device stability.

[0027] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spiritual essence or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A hypersensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect, characterized in that: The sensor sequentially includes a liquid layer to be measured, an InSb layer, a near-zero refractive index plate layer, and a Bragg reflection structure layer from the incident direction of the incident linearly polarized light; The Bragg reflection structure layer is composed of a periodic alternating arrangement of medium A and medium B. Medium A is poly-4-methylpentene-1, and medium B is SiO2; The single-layer thickness of the medium A and B layers is given by the Bragg condition d A、B = λ / 4n A、B where λ is the wavelength of the incident linearly polarized light, and n A、B is the refractive index of the media A and B.

2. The ultrasensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect according to claim 1, wherein: The InSb is a semiconductor material, and the dielectric constant of InSb in the terahertz band can be expressed by the Drude model: ε ∞ = 15.75 is the high-frequency dielectric constant, is the plasma frequency, the scattering frequency where μ is the carrier mobility and m* is the effective mass of the carrier.

3. The ultrasensitive terahertz liquid sensor based on the optical Tamm state photon spin Hall effect according to claim 1, wherein: When the incident angle of the incident linearly polarized light is fixed, the intensity sensitivity of the liquid sensor is defined as where Δn is the refractive index change amount for different types of liquids or different concentrations of the same type of liquid, and Δδ is the change amount of the offset value of the reflection spin Hall effect.

4. A method for liquid detection, characterized in that, Use the liquid sensor based on the optical Tamm state photon spin Hall effect described in any one of claims 1-3 to distinguish the type and concentration of the liquid. The specific method is as follows: When the incident linearly polarized light in the terahertz band directly irradiates the liquid layer to be measured, the incident linearly polarized light is reflected at the interface of the InSb layer, and the reflected light beam is split into a left-handed circularly polarized light and a right-handed circularly polarized light in the direction perpendicular to the incident plane formed by the incident linearly polarized light and the normal. By measuring the splitting offset of the left-handed and right-handed circularly polarized lights, the type and concentration of the liquid to be measured can be analyzed and determined.

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