Total light absorption in plasmon resonance nanostructures

The effect of total light absorption in metal nanostructures of different type is described within the model of an equivalent oscillating electrical circuit. The condition for total light absorption is found, which, independent of the nanostructure type, is reduced to the condition of optical impedance matching on the nanostructure surface at the plasmon resonance frequency.     

等离激元增强的石墨烯光吸收

石墨烯中等离激元具有特殊的光电性质,其和入射光的强烈耦合可以引起光吸收的增强.本文基于时域有限差分法和多体自洽场理论研究了等离激元对处于光学谐振腔中的石墨烯光吸收的影响.由于石墨烯中等离激元与入射光动量和能量不匹配而不能直接相互作用,因此石墨烯上施加了金属光栅结构.研究发现光栅结构能够对入射光进行动量补偿并且能够引起其下石墨烯中的电场强度产生很大程度增强,从而导致在该石墨烯结构中太赫兹等离激元和入射光发生强烈耦合而产生太赫兹等离极化激元,同时引起石墨烯光吸收的增强.希望本文能够加深对石墨烯光电特性的理解以及可以为基于石墨烯的太赫兹光电装置提供一定的理论依据.     

Distributed optical fiber surface plasmon resonance sensors

The relationships of the resonant wavelength of optical fiber surface plasmon resonance (SPR) sensors to the modulation layer refractive index, thickness and the refractive index of the bulk medium are obtained by using theoretical calculation model of optical fiber SPR sensors under certain conditions, which indicates that resonant wavelength of the sensors is approximately linear with modulation layer thickness. Based on the linear relationship, multiple SPR sensors with different resonant wavelengths can be fabricated in a single optical fiber named as distributed optical fiber surface plasmon resonance sensors (DOFSPRSs).Experimental results are presented, showing that it is practical to fabricate more than one SPR sensors in a single optical fiber.     

Electron paramagnetic resonance and optical absorption spectra of Cr ions in cadmium phosphate glass

EPR and optical absorption investigations of chromium doped cadmium phosphate glass are carried out. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. From the results and analyses of the EPR and optical studies, the site symmetry of Cr³⁺ ion in the glass is ascribed to a distorted octahedron. The bonding parameters suggest the ionic nature of Cr³⁺ ion with the ligands.     

Low-temperature optical absorption spectra of hematoporphyrins

Low-temperature optical absorption spectra of both free base and metal complexes of hematoporphyrin have been obtained. Vibrational structure, inferred by others from MORD data, is observed here directly in bands III and IV of the free base. Structure is also observed in the β band of the Ni and Pd metallohematoporphyrins. Implications of these results on the presently accepted theory of porphyrin optical spectra are discussed.     

Anisotropy of the Raman spectra of nanographite ribbons

A polarized Raman study of nanographite ribbons on a highly oriented pyrolytic graphite substrate is reported. The Raman peak of the nanographite ribbons exhibits an intensity dependence on the light polarization direction relative to the nanographite ribbon axis. This result is due to the quantum confinement of the electrons in the 1D band structure of the nanographite ribbons, combined with the anisotropy of the light absorption in 2D graphite, in agreement with theoretical predictions.     

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF₂ underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.     

D-shape polymer optical fibres for surface plasmon resonance sensing

We experimentally studied three different D-shape polymer optical fibres with an exposed core for their applications as surface plasmon resonance sensors. The first one was a conventional D-shape fibre with no microstructure while in two others the fibre core was surrounded by two rings of air holes. In one of the microstructured fibres we introduced special absorbing inclusions placed outside the microstructure to attenuate leaky modes. We compared the performance of the surface plasmon resonance sensors based on the three fibres. We showed that the fibre bending enhances the resonance in all investigated fibres. The measured sensitivity of about 610 nm/RIU for the refractive index of glycerol solution around 1.350 is similar in all fabricated sensors. However, the spectral width of the resonance curve is significantly lower for the fibre with inclusions suppressing the leaky modes.     

High surface plasmon resonance sensitivity enabled by optical disks

We report a systematic, experimental, and theoretical investigation on the surface plasmon resonance (SPR) sensing using optical disks with different track pitches, including Blu-ray disk (BD), digital versatile disk (DVD), and compact disk (CD). Optical reflection measurements indicate that CD and DVD exhibit much higher SPR sensitivity than BD. Both experiments and finite-difference time-domain simulations reveal that the SPR sensitivity is significantly affected by the diffraction order of the SPR peaks and higher diffraction order results in lower sensitivity. Numerical simulations also show that very high sensitivity (～1600 nm per refractive index unit) is achievable by CDs.     

Performances of different metals in optical fibre-based surface plasmon resonance sensor

The capability of various metals used in optical fibre-based surface plasmon resonance (SPR) sensing is studied theoretically. Four metals, gold (Au), silver (Ag), copper (Cu) and aluminium (Al) are considered for the present study. The performance of the optical fibre-based SPR sensor with four different metals is obtained numerically and compared in detail. The performance of optical fibre-based SPR sensor has been analysed in terms of sensitivity, signal-to-noise (SNR) ratio and quality parameter. It is found that the performance of optical fibre-based SPR sensor with Au metal is better than that of the other three metals. The sensitivity of the optical fibre-based SPR sensor with 50 nm thick and 10 mm long Au metal film of exposed sensing region is 2.373 μm/RIU with good linearity, SNR is 0.724 and quality parameter is 48.281 RIU^− 1. The thickness of the metal film and the length of the exposed sensing region of the optical fibre-based SPR sensor for each metal are also optimized.     

Effect of metamaterial layer on optical surface plasmon resonance sensor

In this paper an optical surface plasmon resonance (SPR) sensor with metamaterial for four and five layered structure is studied. The numerical results presented in this paper leads to a significant properties of metamaterials in sensing field. Computed results of SPR sensors using metamaterial are compared with conventional optical SPR sensors for four and five layered structure. It is seen that wider dynamic range or effective range of measurable refractive index increases when metamaterial layer is used. It is also verified that SPR sensor with metamaterial layer can dramatically enhance the resolution and reduce the reflectivity compared with conventional SPR. Validity of the magnetic field results is proved on the basis of smooth match of the fields in the different layers of the proposed optical SPR sensor.     

The absorption spectra of optical bistability with dispersion

The absorption spectra of a weak field (Ω) probing the bistable behaviour of a homogeneously broadened medium (ω₀) detuned with respect to the exciting laser light (ω_L) has been investigated. A dispersion like structure superimposed on an inverted peak near the critical threshold is predicted. The frequency response of the differential gain amplifier is also obtained.     

InSb纳米晶体的生长和吸收光谱的研究

采用在惰性气体中蒸发的方法获得了沉积在ZnS基片上的InSb纳米晶体,其平均尺寸随惰性气体的压强增加而增大.从实验测量的室温吸收谱上看到,当纳米晶体的平均直径从27.9 nm减小到24.2nm再到21.4 nm时,其吸收边分别向高能方向移动了0.0151 eV和0.0145 eV.用有效质量近似模型计算了半导体纳米晶体的吸收边相对其体材料的移动,将理论计算与实验结果进行了比较.     

In vivo optical neural recording using fiber-based surface plasmon resonance

We propose an intrinsic optical method for in vivo neural recording using optic fiber-based surface plasmon resonance (SPR) phenomena. The fiber-based SPR method is electrical artifact free, labeling free, and feasible for a portable system compared with conventional in vivo neural recording systems. We simultaneously detected SPR signals and electrical neural activity from the rat somatosensory cortex evoked by electrical stimulation on the forepaw. Pharmacological analysis using a voltage-gated sodium channel blocker confirmed the neural origins of the optical signals. This fiber-based SPR system promises the enhanced ability to record in vivo neural activity for the investigation of neurons and their networks.     

Wavelength-dependent optical force on elliptical silver cylinders at plasmon resonance

We use rigorous diffraction theory to analyze the force on elliptical cylinders made from silver as a function of the elongation. We find that, when the wires are illuminated at the plasmon wavelength and placed in a highly focused Gaussian beam, they are attracted toward the optical axis if the waist of the laser is behind the wire and repelled if the waist is before the wire. Also, the force distributions of illumination wavelengths smaller and larger than the plasmon wavelength are analyzed.     

Variation of extinction spectra of plasmon resonance colloidal crystals upon structural transitions

The effect of the temperature of a silver sol on its extinction spectra during formation of aggregates of plasmon resonance nanoparticles with varying degree of order and the effect exerted on these spectra by changes in the structure of a colloidal crystal during its heating, which lowers elastic properties of a polymer adsorption layer of particles are studied.     

Effect of defects of plasmon resonance colloidal crystals on their extinction spectra

The effect of the temperature of a silver sol on its extinction spectra during formation of aggregates of plasmon resonance nanoparticles with varying degree of order and the effect exerted on these spectra by changes in the structure of a colloidal crystal during its heating, which lowers elastic properties of a polymer adsorption layer of particles are studied.     

The resonance of two-photon absorption in separated optical fields

A beam of molecules interacting with two space-separated light standing waves of light is considered. It is shown that a resonance of two-photon absorption is predicted. The width of the resonance is equal to the reciprocal of the time of flight between the waves.     

Evolution of extinction spectra of plasmon resonance nanocolloids in the process of their crystallization

Changes in extinction spectra of nanostructured colloids of plasmon resonance particles are studied at different stages of their crystallization. The spontaneous crystallization is calculated by the method of Brownian dynamics, and the extinction spectra are calculated by the method of coupled dipoles. Based on the example of silver sols, we analyzed how separate parameters of the crystallizing disperse system affect the shape of the extinction contour in the plasmon absorption band.