Mid-infrared optical properties of non-magnetic-metal/CoFeB/MgO heterostructures

We report on the optical characterization of non-magnetic metal/ferromagnetic (Co$_{20}$Fe$_{60}$B$_{20}$)/MgO heterostructures and interfaces by using mid infrared spectroscopic ellipsometry at room temperature. We extracted for the mid-infrared range the dielectric function of Co$_{20}$Fe$_{60}$B$_{20}$, that is lacking in literature, from a multisample analysis. From the optical modelling of the heterostructures we detected and determined the dielectric tensor properties of a two-dimensional gas (2DEG) forming at the non-magnetic metal and the CoFeB interface. These properties comprise independent Drude parameters for the in-plane and out-of plane tensor components, with the latter having an epsilon-near-zero frequency within our working spectral range. A feature assigned to spin-orbit coupling (SOC) is identified. Furthermore, it is found that both, the interfacial properties, 2DEG Drude parameters and SOC strength, and the apparent dielectric function of the MgO layer depend on the type of the underlying nonmagnetic metal, namely, Pt, W, or Cu. The results reported here should be useful in tailoring novel phenomena in such types of heterostructures by assessing their optical response noninvasively, complementing existing characterization tools such as angle-resolved photoemission spectroscopy, and those related to electron/spin transport.Comment: 11 pages, 7 figures. See supplemental material in 10.1088/1361-6463/acd00f/met

Low NKp30, NKp46 and NKG2D expression and reduced cytotoxic activity on NK cells in cervical cancer and precursor lesions

<p>Abstract</p> <p>Background</p> <p>Persistent high risk HPV infection can lead to cervical cancer, the second most common malignant tumor in women worldwide. NK cells play a crucial role against tumors and virus-infected cells through a fine balance between activating and inhibitory receptors. Expression of triggering receptors NKp30, NKp44, NKp46 and NKG2D on NK cells correlates with cytolytic activity against tumor cells, but these receptors have not been studied in cervical cancer and precursor lesions. The aim of the present work was to study NKp30, NKp46, NKG2D, NKp80 and 2B4 expression in NK cells from patients with cervical cancer and precursor lesions, in the context of HPV infection.</p> <p>Methods</p> <p>NKp30, NKp46, NKG2D, NKp80 and 2B4 expression was analyzed by flow cytometry on NK cells from 59 patients with cervical cancer and squamous intraepithelial lesions. NK cell cytotoxicity was evaluated in a 4 hour CFSE/7-AAD flow cytometry assay. HPV types were identified by PCR assays.</p> <p>Results</p> <p>We report here for the first time that NK cell-activating receptors NKp30 and NKp46 are significantly down-regulated in cervical cancer and high grade squamous intraepithelial lesion (HGSIL) patients. NCRs down-regulation correlated with low cytolytic activity, HPV-16 infection and clinical stage. NKG2D was also down-regulated in cervical cancer patients.</p> <p>Conclusion</p> <p>Our results suggest that NKp30, NKp46 and NKG2D down-regulation represent an evasion mechanism associated to low NK cell activity, HPV-16 infection and cervical cancer progression.</p

Dynamical and tuneable modulation of the Tamm plasmon/exciton-polariton hybrid states using surface acoustic waves

In this work, we discuss theoretically the formation of the Tamm plasmon/exciton-polariton hybrid states in an (Al,Ga)As microcavity and their modulation by surface acoustic waves. The modulation of the Tamm plasmon/exciton-polariton states origins in the change of the excitonic band gap energy and the thickness change of the sample structure layers due to the induced strain fields by surface acoustic waves. The frequency f_{SAW} of the acoustic modulation of the Tamm plasmon/exciton-polariton states is limited by the thickness of the upper distributed Bragg reflector. For the Tamm plasmon/exciton-polariton states in Al_xGa_{1-x}As/GaAs structures f_{SAW} is in the range of 370 MHz while f_{SAW} in GHz range is possible for the parametric Tamm plasmon/exciton-polariton states. In both cases, the acoustic modulation is several meV for typical acoustic power levels

Chuaʼs circuit and its characterization as a filter

"This article deals with Chuaʼs circuit characterization from the point of view of a filter based on the concept of piecewise linear functions. Furthermore, experiments are developed for teaching electronic systems that can be used for novel filtering concepts. The frequency range in which they are tested is from $20\;{\rm Hz}$ to $20\;{\rm kHz}$, due to the audio spectrum comprised in this frequency range. The node associated with the capacitor and Chuaʼs diode is used as input, and the node for another capacitor and the coil is used as output, thereby establishing one input–output relationship for each system case given by the piecewise linear functions. The experimental result shows that Chuaʼs circuit behaves as a bandpass filter-amplifier, with a maximum frequency around $3\;{\rm kHz}$ and bandwidth between $1.5\;{\rm kHz}$ and $5.5\;{\rm kHz}$. The results presented in this paper can motivate engineering students to pursue applications of novel electrical circuits based on topics that are of potential interest in their future research studies.

Measurements of Concentration differences between Liquid Mixtures using Digital Holographic Interferometry

We present an alternative method to detect and measure the concentration changes in liquid solutions. The method uses Digital Holographic Interferometry (DHI) and is based on measuring refractive index variations. The first hologram is recorded when a wavefront from light comes across an ordinary cylindrical glass container filled with a liquid solution. The second hologram is recorded after slight changing the liquid’s concentration. Differences in phase obtained from the correlation of the first hologram with the second one provide information about the refractive index variation, which is directly related to the changes in physical properties related to the concentration. The method can be used − with high sensitivity, accuracy, and speed − either to detect adulterations or to measure a slight change of concentration in the order of 0.001 moles which is equivalent to a difference of 0.003 g of sodium chloride in solutions. The method also enables to measure and calculate the phase difference among each pixel of two samples. This makes it possible to generate a global measurement of the phase difference of the entire sensed region

Polymer-based hybrid integrated optical photochromic switch

539-543This study presents development and characterization of an optical photochromic switch, in which guided signal is controlled by reversible photochromic properties of a polymeric film. The device is a hybrid structure composed of a waveguide fabricated by means of an ionic exchange technique, using (Na+/K+) on a glass substrate and a polymeric thin film deposited on the same glass substrate surface. Polymeric film belongs to spiropirans family, which when radiated by a wavelength within its absorption band displays reversible changes in its optical properties. Two kinds of optical pumping and different pumping wavelengths were studied to operate this device

Spatial self-organization of macroscopic quantum states of exciton-polaritons in acoustic lattices

Exciton-polariton systems can sustain macroscopic quantum states (MQSs) under a periodic potential modulation. In this paper, we investigate the structure of these states in acoustic square lattices by probing their wave functions in real and momentum spaces using spectral tomography. We show that the polariton MQSs, when excited by a Gaussian laser beam, self-organize in a concentric structure, consisting of a single, two-dimensional gap-soliton (GS) state surrounded by one dimensional (1D) MQSs with lower energy. The latter form at hyperbolical points of the modulated polariton dispersion. While the size of the GS tends to saturate with increasing particle density, the emission region of the surrounding 1D states increases. The existence of these MQSs in acoustic lattices is quantitatively supported by a theoretical model based on the variational solution of the Gross–Pitaevskii equation. The formation of the 1D states in a ring around the central GS is attributed to the energy gradient in this region, which reduces the overall symmetry of the lattice. The results broaden the experimental understanding of self-localized polariton states, which may prove relevant for functionalities exploiting solitonic objects

Phase and amplitude reconstruction in single-pixel transmission microscopy: a comparison of Hadamard, cosine, and noiselet bases

Hadamard, cosine, and noiselet bases are implemented into a digital holographic microscope based on single-pixel imaging with the capability to retrieve images of complex objects. The object is illuminated with coherent light modulated with different patterns deployed in a digital micromirror device, and the resulting fields are captured by single-pixel detection. For amplitude images, the experimental results of the three bases are evaluated with the peak SNR criteria. It is shown that the cosine basis recovers amplitude distributions with the best quality. Regarding phase images, the recovered ones compare well with those obtained with a CMOS camera.Ministerio de Ciencia, Innovación y Universidades (PID2019-110927RB-I00/AEI/10.13039/501100011033); Consejo Nacional de Ciencia y Tecnología (CB-252867, Infraestrcutura-299552); Generalitat Valenciana (PROMETEO/2020/029)