Owing to the advantages of natural abundance, low cost, and amenability to manufacturing processes, aluminum has recently been recognized as a highly promising plasmonic material that attracts extensive research interest. Here, we propose a cavity-enhanced ultra-thin plasmonic resonator for surface enhanced infrared absorption spectroscopy. The considered resonator consists of a patterned ultra-thin aluminum grating strips, a dielectric spacer layer and a reflective layer. In such structure, the resonance absorption is enhanced by the cavity formed between the patterned aluminum strips and the reflective layer. It is demonstrated that the spectral features of the resonator can be tuned by adjusting the structural parameters. Furthermore, in order to achieve a deep and broad spectral line shape, the spacer layer thickness should be properly designed to realize the simultaneous resonances for the electric and the magnetic excitations. The enhanced infrared absorption characteristics can be used for infrared sensing of the environment. When the resonator is covered with a molecular layer, the resonator can be used as a surface enhanced infrared absorption substrate to enhance the absorption signal of the molecules. A high enhanced factor of 1.15×105 can be achieved when the resonance wavelength of resonator is adjusted to match the desired vibrational mode of the molecules. Such a cavity-enhanced plasmonic resonator, which is easy for practical fabrication, is expected to have potential applications for infrared sensing with high-performance.
We propose an infrared biosensor for nanofluidic analysis based on graphene plasmonics, which consists of a nanochannel etching on a silicon substrate and a graphene sheet covered on the top of the channel. The change of refractive index due to the absorption of biomolecules in the nanochannel can be measured by detecting the wavelength shifts of resonant dips. To achieve the best optical performances of the biosensor, an optical model based on finite element method is built to optimize the structure parameters of the biosensor. Numerical simulation results show that a biosensor with a larger top width and a higher depth shows a better overall performance and a high sensitivity value of up to 1920nm/RIU can be achieved in an optimized structure. In addition, the biosensor can dynamically work at a wide range of infrared region by adjusting the Fermi level of graphene. Graphene is pre-coated with poly methyl methacrylate to overcome the effect that the portion of graphene over the nanochannel will be strained and the influence of the thickness of this coated layer on the performances of biosensor is very small. The designed graphene plasmonics devices will advance further applications of graphene in integrated nanofluidic analysis and infrared biosensors.
Grating light modulators are the key wavelength scanning devices for a MOEMS spectrometer. In this paper, we
build a vectorial diffraction model of grating light modulators theoretically based on Finite Beam Rigorous Coupled
Wave Analysis theory. Then we calculate the diffraction efficiency of grating light modulators at the spectral range from
900nm to 1700nm. The numerical spectra indicate that the grating light modulators can realize wavelength scanning by
changing the distance between the upper and the bottom layers. The grating light modulator can act as a programmable
pixilated optical switch with high contrast. The diffraction efficiency is stable when the θ changes from -10 degrees to
10 degrees and the Φ changes from -30 degrees to 30 degrees. The effects of the bandwidth on the diffraction
efficiency of the grating light modulators can be ignored. The average on state diffraction efficiency is 0.83 and the
average off state diffraction efficiency is 0.05 when the grating light modulators chip has 256 pixels. The experimental
results show that the vectorial diffraction model is more efficient than the scalar diffraction model.
To compensate the measurement error induced by temperature and pressure variation in a tunable diode laser absorption
spectroscopy (TDLAS) system, an online self-calibration technique is introduced. More specifically, a reference gas cell
filled with known proportion target gas is placed on site, surrounded by working gas to be measured. Thereby, the
temperature and pressure inside the reference cell are equal to the gas outside. The TDLAS system acquires the
absorption spectrum of the reference gas cell and the working gas synchronously. And the concentration of the trace gas
in working gas can be easily obtained by calculating the absorption intensity proportion of both absorption spectrums
without considering the affection of temperature and pressure. The principle, design, and experiment of this technique
are presented in this paper.
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