A novel method for the detection of the second-harmonic component of tunable laser diode absorption spectroscopy-wavelength-modulated absorption spectroscopy is proposed in this study. The proposed method is based on spectral analysis, and the second-harmonic component is obtained in the frequency domain through a rectangular window. The validity, correctness, and noise immunity of the proposed method are verified through simulations and experiments. Experimental results demonstrate that the relative detection error level of the proposed method is <3%. In contrast to lock-in amplification, the proposed method does not require reference signals and low-pass filtering algorithms. These characteristics simplify data processing in the proposed method.
Terahertz metamaterials are some of the core components of the new generation of high-frequency optoelectronic devices, which have excellent properties that natural materials do not have. The unit structures are generally much smaller than the wavelength, so preparation is mainly based on semiconductor processes, such as coating, photolithography and etching. Although the processing resolution is high, it is also limited by complex processing, long cycles, and high cost. In this paper, a design method for dual-band terahertz metamaterials and a simple, rapid, low-cost metamaterial preparation scheme based on step-motor-driven electrohydrodynamic jet technology are proposed. By transforming an open-source 3D printer, the metamaterial structures can be directly printed without complex semiconductor processes. To verify effectiveness, the sample was directly printed using nano conductive silver paste as consumable material. Then, a fiber-based multi-mode terahertz time-domain spectroscopy system was built for testing. The experimental results were in good agreement with the theoretical simulation.
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.
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