Phase change materials, such as vanadium dioxide (VO2) and Titanium dioxide (Ti2O3) have received extensive attention because of the dramatic changes in their intrinsic properties during phase transitions. However, due to the rapid transition rate and wide dynamics, monitoring of processes is challenging. Previous detection methods are lack of speed and simplicity and require multiple interventions, which largely introduce human factors influencing the results and make it difficult to guarantee the accuracy and visualization. In this paper, the photonic spin Hall effect is used for real-time detection and highly sensitive analysis of the phase transition process of VO2 films. By incorporating with quantum weak measurement, the photonic spin-Hall shift acts as the pointer, and the phase transition process of VO2 is characterized effectively. The high measurement resolution with 63 S/(m μm) is achieved due to weak-value amplification. In our scheme, it does not involve any mechanical adjustment of optical components, thus enabling real-time, visual, non-contact detection of dynamic phase transition processes.
A new method to enhance the beam shift of Goos-Hänchen (GH) effect in a 1D photonic crystal based on Larmor resonance in terahertz (THz) region is proposed. Larmor resonance can enhance the surface plasmon resonance (SPR) effect, which enhances the GH effect. A 1D photonic crystal with a graphene-VO 2 periodic structure is designed. As a result of different states at different temperatures, the SPR effect of graphene-VO 2 periodic structure photonic crystals will change. In this structure, Larmor resonance caused by a strong magnetic field perpendicular to the incident surface will resonate with surface plasmons. It is found that the strength of the magnetic field required to enhance SPR is relative to the frequency of electromagnetic waves and the Fermi level. The enhancement of the GH effect by the Larmor resonance theory provides a new way for us to measure strong magnetic fields.
A multi-channel optical sensing system for heavy metal concentration detection is presented in this paper. The system utilizes a multi-channel optical path combined with a unique circuit design and BP neural network (BP-ANN) to perform the online analysis of multi-wavelength signals, achieving accurate concentration detection of a heavy metal solution. An array photodiode is used to detect the transmission light intensities at multiple wavelengths through the optical path of the system, which enables the collection of useful spectral information of the solution. The system uses a unique signal acquisition method to effectively improve the efficiency of both signal acquisition and operation. BP-ANN is applied to the online analysis of multi-channel information, which overcomes the influential issue of nonlinear effect on data detection, optimizes the anti-interference ability, and lowers the detection limit of the system. This system eliminates the necessary employment of the expensive and large spectrometers and therefore greatly reduces the instrument cost and occupying space. Additionally, the detection limit of the system is extended lower than that of the conventional spectrophotometer. Compared with the detection limits of heavy metal solution obtained by using a single characteristic light wavelength, the detection limits of Cd2+, Cu2+ and Cr6+ achieved through using multi-channel detection system can be reduced by 42.64%, 38.12%, and 20.62%, respectively, and these detection limits are found as 0.0041mg/L, 0.0091mg/L, and 0.0112mg/L, respectively.
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