The Enhancement And Modulation Of Photonic Spin Hall Effect In Terahertz Range And Its Application In Refractive Index Sensor

Photonic spin Hall effect(PSHE)is an interesting transport phenomenon,which refers to the spindependent lateral splitting of the left-and right-handed circular components at the reflection or refraction interface of two different media.By combining weak value amplification techniques,namely quantum weak measurement,PSHE is widely used to detect ion concentration,to design highly sensitive optical sensors,to identify graphene layers,to apply for the optical differential operations and edged etection.In order to further expand the application of PSHE,several methods for obtaining large spin shifts are proposed based on the surface plasmon resonance effect(SPR),resonant optical tunneling effect(ROTE)and optical pumping effect.It can be seen that most research of PSHE is limited to the visible and infrared regions.In order to further promote the application of PSHE in wide band,the study of PSHE in terahertz(THz)range is very necessary and urgent.THz is a kind of electromagnetic wave with very unique properties.Its electromagnetic frequency ranges from 0.1 to 10THz(wavelength of 30μm-3mm),which is located between microwave,millimeter wave and infrared regions.On the other hand,THz has very high frequency and very short pulses,which results in high spatial and temporal resolution.In addition,the typical pulse width of THz pulse is in the order of picosecond,and the interference of far-infrared background noise can be effectively suppressed in the measurement.It can be seen that THz rays have a significant advantage over visible light in terms of precision measurement.We believe that the study of PSHE in THz region will bring better application prospects for PSHE.Based on the above consideration,some creative work and the corresponding result of this paper are summarized as follows:1.This paper proposes a significant enhancement of PSHE in the THz range by considering the long range surface plasmon resonance(LRSPR)effect supported by In Sb.The effect of In Sb layer thickness and temperature on PSHE is studied.Under the optimum structural parameters and temperature,the maximum spin displacement of horizontally polarized light can reach 2.68 mm,which is much higher than the value reported in the literature.2.This paper proposes a simple method to enhance the reflected PSHE by using a gradedrefractive-index(GRIN)material.The spin displacements of homogeneous layers and linear GRIN structures of three different types(single increase,single decrease and bilinear)are studied theoretically.We find that bilinear GRIN materials exhibit prominent PSHE of reflected light,and the corresponding transverse displacement of the horizontally polarized incident beam can reach almost its upper limit(i.e.half of the beam waist),mainly due to the large ratio of Fresnel reflection coefficients.3.The THz gas sensor based on the photonic spin Hall effect is proposed in this paper.The spin shift of this sensor is very sensitive to the refractive index change of gas,and the intensity sensitivity of can reach 0.2m/RIU.Moreover,the sensing performance of refractive index sensor based on the PSHE of GRIN material is also investigated.These findings provide potential methods for enhancing PSHE in the THz range,and therefore offer the opportunity for developing the THz optical sensors based on PSHE.