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Surface Plasmon Resonance and THz Radiation
Published in Hitendra K. Malik, Laser-Matter Interaction for Radiation and Energy, 2021
This cannot be true for plane waves for any angle of incidence. Therefore, plane wave cannot be used directly to excite the surface plasmons. Hence, the surface plasmons are excited through the evanescent waves generated. Thus, a prism is kept near the metal interface and a wave is allowed to incident on it so that the total internal reflection takes place at the bottom surface of the prism due to which evanescent wave is produced parallel to the metal surface. As the angle of the incidence is varied, the wave vector of the evanescent wave changes. At a certain angle of incidence, it matches with that of the surface plasmon, and significant energy transfer takes place and the dip is observed in the reflected light. This is how the surface plasmons are excited.
Optical Properties of Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
The refractive index is related to the velocity of radiation in a medium. One of the consequences of a negative index of refraction is that the phase velocity of the radiation is negative, that is, the change of phase of the wave travels in the opposite direction to the direction of propagation (and of the direction of energy transfer). This leads to some unusual properties such that the Doppler effect is reversed with radiation travelling towards the observer being shifted to longer wavelengths (red shift). A useful consequence of the negative refractive index is that a lens made of such a material is not subject to the diffraction limit of ordinary lenses, so a higher resolution can be achieved. Light from objects whose distance apart is less than half the wavelength of the light contains components that decay exponentially: evanescent waves. Lenses made of negative refractive index materials increase the amplitude of the evanescent waves. When they emerge from the lens, the waves decay again such that the amplitude at the image plane is equal to the original amplitude when the wave leaves the object. Thus, the evanescent wave component is not lost and all the light from the object is collected. Such lenses have thus been dubbed superlenses. In 2005, a superlens effect at optical frequencies was observed for a thin slab of silver.
Nanoscience of Large Immune Proteins
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Alexey Ferapontov, Kristian Juul-Madsen, Thomas Vorup-Jensen
SPR technology is widely used to study the interactions between large biomolecules and quantify their binding kinetics. SPR utilizes the phenomenon of total internal reflection, which occurs when propagating light meets an interface located in-between media of high and low refractive index (Schuck 1997). The light is fully reflected back into the media with high refractive index at the interface, generating an evanescent wave in the media with low refractive index in the process. The interface layer is made up of a conducting, non-magnetic metal such as gold. In this setting, the surface coating on the gold part of the chip makes up the low-refractive index part together with the surrounding solution. The evanescent wave will penetrate the gold layer and interact with the surface plasmon waves that are present within the conductor, thus exciting them. The interaction will lead to a reduction in intensity of the reflected light at a specific angle of reflection, known as the SPR angle. This angle is in direct correlation with the refractive index of the coating of the gold chip, therefore representing changes due to interaction of biomolecules on the surface.
Surface plasmon resonance sensor for refractive index and temperature measurement based upon a double-sided polished microstructured fiber
Published in Instrumentation Science & Technology, 2023
Xin Yan, Yang Zhao, Tonglei Cheng, Rao Fu
The reported structure is simple and easy to prepare. A schematic is shown in Figure 3b. When light enters the fiber, it travels into its silica layer. Since the outer layer of silica is coated with a thin metal film, light leaks into the cladding. These cladding waves are affected by the surrounding medium at the boundary of the cladding. Due to total reflection, evanescent waves are generated at the interface between the cladding and the metal film. When the evanescent wave and the surface plasmon wave are equal, the surface plasmons are resonantly excited, resulting in a portion of the energy of the incident light being transferred to the metal film and the reflected light energy is reduced. The optical power received by the spectrometer decreases and a dip is created in the spectrum. This resonance dip shifts due to the changes in the refractive index of the surrounding medium. Thus, sensing is achieved by observing the change in the resonant wavelength.
Time reversal mirror for hyperthermia of multi-focal breast tumors using electromagnetic time reversal technique
Published in Electromagnetics, 2022
Baidenger Agyekum Twumasi, Jia-Lin Li, Ebenezer Tawiah Ashong, Christian Dzah, Dustin Pomary
It has been established that sub-wavelength information about an object is carried by evanescent waves, but these waves decay exponentially. This implies that these waves are lost before reaching the far-field image plane which is the origin of the diffraction limit. In near-field microscopy, one such approach for the recovery of evanescent waves is the loading of sub-wavelength scatterers in the near field of the object to be imaged. Evanescent waves can be converted into propagating waves by diffracting off these scatterers which enables their detection or reception in the far-field by the time reversal mirror (Lerosey et al. 2007). This idea is extended to the hyperthermia of multi-focal breast tumors. In time reversal application, a single antenna TRM can be used and this will act as a transmitter and at the same time as a receiver of the field. But for the proposed application, we used five antenna TRMs, where one is placed below the breast and loaded with the SRESP scatterers. This antenna is excited to send out the probing signal (channel sounding). The other four TRMs surrounding the breast act as receivers during the first phase of the time reversal process. During the second phase after the received and recorded signals (field) has been flipped in time, the four antenna TRMs then transmit these signals back into the breast medium for the spatial-temporal focusing at tumor locations. The procedure can be outlined as follows (Ge et al. 2011):
The Challenge to Measure Single-phase Convective Heat Transfer Coefficients in Microchannels
Published in Heat Transfer Engineering, 2019
Another technique for the measurement of the fluid temperature close to the wall is Evanescent-wave Fluorescence Thermometry (EFT) proposed by Kim and Yoda [60]. In this case the near-wall fluid temperature is estimated by analyzing the fluorescent emissions of fluorophores in a water solution illuminated by evanescent waves. Such waves are generated by the total internal reflection of light incident upon a glass–water interface; they are due to the portion of the incident light transmitted into the lower refractive index medium (water). These evanescent waves propagate into water with an exponential decay from the interface. The length scale of this exponential decay is O (100 nm) for visible light incident upon a glass–water interface. In this region, by using the evanescent waves it becomes possible to stimulate fluorescence in tracers added to the working fluid.