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Tip-Enhanced Spectroscopy at the Nanoscale: Its Practical Issues and Solutions
Published in Sarhan M. Musa, Nanoscale Spectroscopy with Applications, 2018
Norihiko Hayazawa, Taka-aki Yano
TERS systems for imaging and spectroscopy in the nanoscale are commonly configured with a combination of inverted optical microscopy and scanning probe microscopy (SPM) such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM). This configuration allows for the use of high numerical aperture (NA) objective lens in order to tightly focus incident laser light onto a metallic tip through sample as shown in Figure 1.6a. The tightly focused laser spot benefits high collection efficiency of TERS as well as suppression of far-field Raman background coming from the sample in the focus spot. Since the longitudinal field of the incident light efficiently excites SPP at the tip apex, radial polarization is preferably utilized as incident polarization because of much stronger longitudinal field component than linear polarization (Hayazawa et al 2004b). The radially polarized light is provided by passing the linearly polarized laser light through a radial-waveplate consisting of a segmented half-waveplate, with each segment having a different orientation of the optical axis. TERS signal excited by the radially polarized incident light is efficiently collected by the same high NA objective lens, and directed to a spectrophotometer The dispersed Raman signal through the spectrometer is detected by a liquid nitrogen cooled CCD camera for acquiring a TERS spectrum or by a single photon counting module such as avalanche photodiode (APD) and a photo multiplier (PMT) for acquiring a TERS image at a certain Raman frequency.
The Basics of Lasers
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Finally, an interesting class of polarized laser beams is worth mentioning, depicted conceptually in Figure 3.27. This is the class of cylindrically symmetric vector beams, whose polarization vectors are oriented in the radial and azimuthal directions, respectively, i.e., at every position in the beam, the polarization vector points toward the center of the beam, or is parallel to it. Two great advantages for laser spectroscopy can be derived from laser beams exhibiting these exotic polarization properties. Firstly, when a radially polarized laser beam is focused with a short-focal length lens, the electric field in the focal region possesses a relatively large longitudinal component; this property is exploited in, e.g., z-polarization spectroscopy and confocal microscopy (see, e.g., Saito et al. 2008). Secondly, a beam with radial polarization can be focused to a spot size that is substantially smaller than that of a beam with ordinary linear polarization; this property is utilized, e.g., in optical trapping and micromanipulation (see, e.g., Zhan 2004).
Focusing vortex beams and overcoming the diffraction limit
Published in V. A. Soifer, Diffractive Optics and Nanophotonics, 2017
It is known that radial polarization is characterized by the smallest transverse dimension of the focal spot associated with maximizing the contribution of the longitudinal component to the total intensity on the optical axis.
Dynamics of the partially coherent radially polarized rotating elliptical cosine-Gaussian optical lattice through anisotropic turbulence
Published in Waves in Random and Complex Media, 2021
Liping Zhang, Dongmei Deng, Shangling He, Xi Peng, Xiangbo Yang, Guanghui Wang
Figure 8 shows the SOP of a PCRPREGOL at different propagation distances for different n. The SOP of the PCRPREGOL is related to the beam order n. When n = 0, the SOP of a conventional partially coherent radial polarization elliptical GSM beam displays radial polarization in the receiver plane. During the transmission, the radial polarization structure of the SOP is little affected by the anisotropic turbulence. When z is small (), the radial polarization structure of a PCRPREGOL remains well, and the state is broken as z increases. Meantime, the SOP of the beam is greatly affected by the non-conventional source correlation function. The number of the beamlets increases with n. Similar with the paper [43], the initial polarization state of the PCRPREGOL is completely broken, and each beamlet reproduces the radial polarization structure which is the same as the initial. Hence, as the beams split into four beamlets completely, the SOP of the PCRPREGOL becomes four identical radial polarization structures at z = 5 km, n = 2. In conclusion, the reproduction resulted from the source correlation structure brings the beamlets of the PCRPREGOL same vector properties with the initial beam.
On free vibration of piezoelectric nanospheres with surface effect
Published in Mechanics of Advanced Materials and Structures, 2018
Bin Wu, Weiqiu Chen, Chuanzeng Zhang
Consider a spherically isotropic piezoelectric nanosphere with a radial polarization. The spherical coordinates (r, θ, ϕ) are used with the origin located at the center of the material anisotropy. At the nanoscale, atoms in or near the surfaces have fewer bonding neighbors than atoms in the bulk counterpart. As a consequence, the electromechanical properties of the surface are, in general, somewhat different from those of the bulk [46]. In addition, the surface region of nanosized structures, a transition zone between its homogeneous bulk and the vacuum, typically penetrates a few atomic layers into the bulk material, and thus has a certain thickness [15]. Accordingly, the nanosphere can be modeled as a core-shell structure composed of a spherical core of radius r0 and a thin spherical shell surface layer of thickness h = r1 − r0, with r1 being the outer radius of the shell. The spherical shell surface layer and the spherical core are concentric but have different electromechanical properties.
Tuning the performance of magnetoelectric layered cylindrical composites
Published in Mechanics Based Design of Structures and Machines, 2023
George Youssef, Somer Nacy, Scott Newacheck
The piezoelectric cylinder is assumed to be outward radially polarized since it was shown to improve the magnetoelectric coupling by increasing the clamping force (Youssef, Lopez, and Newacheck 2017). The piezomagnetic cylinder is under the influence of a time-harmonic radial magnetic field (Hr) emanating from the origin and passing uniformly throughout the cylinder. The authors have recently investigated the multidirectional alternating magnetic field emanating from a similar concentric multiferroic cylinder, which can be used as part of future validating experiments (Newacheck, Webster, and Youssef 2018). By further assuming the length of the cylinders is greater than the wall thickness, the problem can be treated as plane-strain in the polar coordinate system (r, θ). Therefore, the hoop stress () and radial stress ( can be written as a function of the radial electric field () and radial mechanical displacement () according to the piezoelectric constitutive relationship where, is the elasticity tensor and is the stress-charge piezoelectric coefficients tensor (He and Guan 2006). In Eqn. 1 and Eqn. 2, the electromechanical response of the outer piezoelectric cylinder is assumed to be independent of the magnetic field. Eqn. 1 and Eqn. 2 are the actuator equations of linear piezoelectric model, where the stresses are function of the strain, the electric field, and the material properties. Given the assumption of radial polarization (i.e., and ) and the orthotropy of the piezoelectric cylinder, and there is no charge accumulation (), the radial electric displacement () is described in terms of and such that where, is the permittivity. Eqn. 3 is the sensor equation of the linear piezoelectric constitutive relationship. In the latter, the electric displacement is a function of the strain, electric field, and piezoelectric and mechanical properties. Substitution of the above-mentioned equations into the condition of mechanical equilibrium yields the Bessel differential equation of the radial piezoelectric displacement as shown in Eqn. 4.