Impact of a DC magnetic field on evanescent wave intensity amplification for a magnetocompensated antiferromagnet

The impact of a dc magnetic field on evanescent TE and TM waves at the interface of transparent media comprising a semiconductor layer and a semi-infinite antiferromagnet is investigated using Otto geometry as an example. It is shown that switching a dc magnetic field orthogonal to a sagittal plane allows maximum amplification of the intensity of propagating evanescent TM or TE waves in both a layer and in semi-infinite space. The optimum conditions correspond to the formation of a peculiar TM or TE surface wave.     

Doppler-free evanescent wave spectroscopy

Nonlinear Doppler-free spectroscopy at the interface between a gas and a dielectric medium is experimentally demonstrated on Na vapor. Both saturated absorption and dispersion of sodium atoms near the surface are monitored, depending on the light beam incidence relatively to the critical angle for total internal reflections. Resonance line widths as narrow as 20 MHz have been observed on the Na D₁ line. This technique makes possible Doppler-free diagnostics of optically dense media and should find applications in the analysis of atom-surface interactions.     

Embossable grating couplers for planar evanescent wave sensors

The paper presents the characterization of a composite uniform/gradient waveguide sensor structure. The results of theoretical analysis and experimental studies have been presented. The influence of sensor structure parameters on homogenous sensitivity and on surface sensitivity has been analyzed. Gradient layers for composite sensor structures were produced using the ion-exchange method, and the uniform layers, using the sol-gel method. In the experimental studies, involving the produced sensor structures, a prism coupler and a grating coupler were applied. Excellent agreement between the results of theoretical analysis and experimental studies has been achieved.     

光纤倏逝波型石英增强光声光谱技术

采用块状光学准直聚焦透镜组的传统石英增强光声光谱(QEPAS)技术存在体积难以缩减,结构稳定性不佳,无法适应空间狭小、振动复杂的特殊环境等缺点.基于此,将光纤倏逝波技术与QEPAS技术相结合,提出了一种新型微纳结构光纤QEPAS痕量气体检测技术.实验中,为了提高QEPAS系统信号幅值,优化了石英音叉与激光束的空间位置、激光波长调制深度,同时对比了两种不同共振频率的石英音叉,最终采用共振频率较低的30.720 kHz石英音叉作为声波探测元件,获得的检测极限为6.25×10~(-4)(体积分数),归一化噪声等效吸收系数为4.18×10~(-7)cm~(-1).W·Hz~(-1/2).     

Energy-momentum quanta in Fresnel's evanescent wave

Fresnel's theory of the evanescent wave in total reflection entails that the propagation vectork and the momentum quanta k have an imaginary component and, thus, a projection on the reflecting plane that is larger (in units such thatc=1) than the angular frequency and the energy quanta. We discuss the tachyon properties of these energy-momentum quanta and propose an experimental test using absorption or stimulated emission by an atomic or ionic beam. We then show that the Maxwell-Minkowski tensor (although certainly appropriate to discuss the macroscopic energy-momentum exchange between wave and diopter) does not describe adequately the energy-momentum density of the quanta in the evanescent wave, this stemming from its too remote connection with the generator _i of space-time displacements. On the other hand de Broglie's energy-momentum tensorA _k[ⁱ]B ^jk is the density canonically associated with the generator of space-time displacements; we show that it describes quite satisfactorily both the energy fluxes (as measured through the longitudinal Goos-Hänchen and our new transverse shifts of the reflected beam in total reflection) and the momentum densities of the quanta inside the evanescent wave. Finally, we show that it is the gauge which is transverse in the diopter's rest frame that directly yields the physically measured energy fluxes. We take this fact as a new argument, strongly supported by experimental evidence, in favour of the physical reality of electromagnetic potentials.     

Energy-momentum quanta in Fresnel's evanescent wave II

Four generalisations of results appearing in a previous paper, referred to as I, are here produced. (1) Formulas for the field strengths of the evanescent wave generated inside a vacuum sandwiched between two identical refracting media propagating symmetrical incident plane waves; the classical exponential damping factor being then replaced by hyperbolic cosines or sines (according to the field components), an extremely close approximation to a plane tachyon wave is thus obtained; (2) Compact formulas for the case where the evanescent wave is generated by a superposition of plane incident waves with propagation vectors k parallel to a common incidence plane; (3) Compact formulas for the other typical case where the dispersion on k is parallel to the reflecting plane; (4) Formulas for refraction and total reflection of a photon with a non-zero rest mass.We take the opportunity of this paper to review briefly various articles that had escaped us, where a transverse energy flux inside Fresnel's evanescent wave was discussed, and also some recent papers dealing with quantisation of the evanescent wave or related topics.     

Development of evanescent wave absorbance-based fibre-optic biosensor

Development of chemical and biochemical sensors is the current need of the society. In this report, we present our investigation on the development of a label-free fibre-optic biosensor based on evanescent wave absorbance to detect the presence of analytes such as bacteria, virus and some clinically important proteins. A simple UV-LED (280 nm) and photodetector combination along with a fibre probe was used for developing cost-effective, user-friendly and field applicable device. To improve the sensitivity of the detection technique, the probe design was modified and the U-bent probe was fabricated by simple procedure. Further, to overcome the problems for using UV light source in the fibre, the localized surface plasmon resonance of noble metal nanoparticles at visible wavelength was exploited as a sensing medium for the biochemical reactions. Our systematic studies in this regard presented in this communication may bring the excitement for developing the waterborne pathogen detection device for house-hold as well as field applications.     

A novel probe for an evanescent wave fibre-optic absorption sensor

A novel, highly sensitive probe consisting of a uniform region sandwiched between two linear tapers for an evanescent wave fibre-optic absorption sensor is proposed. The diameter of the uniform region is chosen to be equal to the minimum allowed diameter of the taper's output end. The first taper is used to bring the angles of the rays in the input fibre close to the critical angle of the sensing region while the second taper reconverts the angles into their initial values so that they can propagate in the output fibre. It has been shown that the sensitivity of the sensor depends on the length of the uniform region of the probe, the refractive index of the fluid and the numerical aperture of the fibre. The sensitivity increases with increase in the length of the uniform region and also with decrease in the numerical aperture of the fibre. In addition, the sensitivity of the proposed probe can be further increased by launching the selected rays into the input fibre.     

Energy emission from evanescent wave and interference of opposite wave streams

A basic formula for the coefficient of energy emission from an evanescent electromagnetic wave at scattering by a dielectric structure is derived. The derived formula is interpreted in terms of interference of an incident evanescent wave with its reflection by the structure and applied to evanescent wave scattering by a 3D random medium.     

倏逝波型光纤气体传感器研究进展

介绍了倏逝波的概念和反映倏逝波光纤气体传感特性的穿透深度参数Z_m。讨论了D形、锥形、纤芯裸露形、纤芯失配型和微结构光纤等不同倏逝波型气体传感的原理和特点,评述了其最新研究进展,对比分析了各传感器的优缺点。对倏逝波型光纤气体传感器的发展趋势进行了展望。     

Spectroscopic measurements of the evanescent wave polarization state

We applied optogalvanic spectroscopy to observe Zeeman effect in the evanescent wave in Ar gas with the help of a single-mode diode laser. The use of an homogenous external magnetic field enabled us to observe different π and σ Zeeman split lines contribution. We studied two orthogonal directions of external magnetic field and two orthogonal polarizations of the incident wave with respect to the plane of incidence. The analysis of relative line strengths leads to the determination of the polarization state of the evanescent wave.     

Multichannel double-polarization bandpass optical filter utilizing evanescent wave

A multichannel double-polarization bandpass optical filter, which has the performance of variable channel interval, is theoretically proposed. The filter consists of a stack of two one-dimensional photonic crystals (1D PCs). Based on the resonant couple of evanescent waves localized at the interfaces between neighboring layers, the linear transmission properties of the filter are numerically simulated by the transfer matrix method. The simulation results show that channel number of the filter can be changed by varying the thickness of the middle layer in the centrosymmetric 1D PC structure, while the bandwidth and wavelength of the channel can be adjusted by the incident angle of light. This work may be helpful in designing multichannel double-polarization bandpass optical filter in optical communication systems.     

An effective attenuation coefficient for evanescent wave spectroscopy using multimode fiber

An attenuation coefficient for evanescent wave spectroscopy on the core of a multimode step index fiber in contact with an absorbing species is derived in terms of the range of incident angles of the meridional rays to the interface. An expression, for the fractional power outside the core as a function of incident angles is also given. Their ratio is discussed for the case of a fiber sensor having a porous cladding in contact with a gaseous absorbing species and one in which a section of cladding has been removed and replaced by an absorbing liquid.     

Laser amplification in an optical fiber by evanescent field coupling

A laser signal propagating in an optical fiber is amplified by the evanescent field interacting with the excited Rhodamine 6 G solution surrounding the fiber. A small signal gain of 430 at 600 nm has been measured in a long fiber with a 2 cm long fiber optic amplifier.     

Resonant amplification of frustrated evanescent waves by single dielectric coating

Resonant amplification and enhancement of evanescent wave’s frustration across an optical barrier by using single dielectric coating is numerically demonstrated in this article. With further tuning of the thickness values of the second and the third medium (optical barrier) of the proposed stratified four-media configuration, it is shown that it may be possible to achieve unity transmittance at discrete, but closely spaced incident angles within the full range defined by the theoretical cut-off limit. The designed configuration may have other potential applications than lithography and waveguide design is one such example.     

消逝波激励的双波段光纤回音壁模式激光辐射

将石英光纤浸入低折射率的染料溶液中后构成圆柱形微腔.采用轴向光抽运消逝波激励激光增益的方式,使增益区域局限在圆柱形微腔回音壁模式的模场区域内,由此显著地提高了抽运效率,增加了沿光纤轴向的增益长度.在一根石英光纤的轴向分段填入浓度同为2×10^-3mol/L的罗丹明6G和罗丹明B乙醇溶液,在567—576nm 和592—600nm的两个波长范围内同时获得回音壁模式的激光辐射;分段填入浓度为8×10^-4和8×10^-3mol/L的罗丹明B乙醇溶液, 关键词： 消逝波激励 圆柱形微腔 回音壁模式 双波段激光辐射     

Fabrication of defocus graded-index optical waveguide for evanescent wave optical amplifier

This is the first report on an evanescent wave optical amplifier with a plastic waveguide that can amplify a CW signal transmitted by a plastic optical fiber. The waveguide with a concave refractive index distribution was fabricated by an interfacial-gel polymerization technique. Since the waveguide increases the number of reflections at the boundary surface of the waveguide and the laser dye solution, the enhancement of amplification efficiency can be realized. The function of the fabricated waveguide was confirmed by calculations and experiments. The obtained results indicate that the fabricated fiber generated a larger evanescent field than the waveguide without a refractive index distribution.