Search results for "wave"
showing 10 items of 6009 documents
Tailoring Third-Harmonic Diffraction Efficiency by Hybrid Modes in High-Q Metasurfaces
2021
Metasurfaces are versatile tools for manipulating light; however, they have received little attention as devices for the efficient control of nonlinearly diffracted light. Here, we demonstrate nonlinear wavefront control through third-harmonic generation (THG) beaming into diffraction orders with efficiency tuned by excitation of hybrid Mie-quasi-bound states in the continuum (BIC) modes in a silicon metasurface. Simultaneous excitation of the high-Q collective Mie-type modes and quasi-BIC modes leads to their hybridization and results in a local electric field redistribution. We probe the hybrid mode by measuring far-field patterns of THG and observe the strong switching between (0,-1) and…
A portable system for multiple parameters monitoring: towards assessment of health conditions and stress level in the automotive field
2019
In this work, an electronic portable combo system able to synchronously acquire multiple signals, e.g. electrocardiographic (ECG), photoplethysmographic (PPG) and breathing waveforms, is presented. The realized system is also capable of showing in real time some physiological parameters which can be used for assessing health/stress status of the volunteer, such as heart rate and breathing frequency and their trends over time. Thanks to the use of non-invasive PPG probes, of batteries as power supply, and to the possibility to add in the future additional sensors to acquire other signals, the system could also be employed inside vehicles for assessing the status of the driver. Finally, the r…
Learning-based multiresolution transforms with application to image compression
2013
In Harten's framework, multiresolution transforms are defined by predicting finer resolution levels of information from coarser ones using an operator, called prediction operator, and defining details (or wavelet coefficients) that are the difference between the exact and predicted values. In this paper we use tools of statistical learning in order to design a more accurate prediction operator in this framework based on a training sample, resulting in multiresolution decompositions with enhanced sparsity. In the case of images, we incorporate edge detection techniques in the design of the prediction operator in order to avoid Gibbs phenomenon. Numerical tests are presented showing that the …
Refractive index of GaTe under high pressure
2000
In this paper we describe two experiments, in the near- and mid-infrared, designed to investigate the evolution under pressure of the GaTe refractive index for polarization parallel and perpendicular to the crystallographic c-axis (in the layer plane). The refractive index dispersion for both light polarizations has been determined up to 5.5 GPa. It is found that the refractive index increases faster in the direction perpendicular to the c-axis than along the c-axis. To find out the origin of such a difference we used a Phillips-Van Vechten model and arrived at the conclusion that it is due to the different pressure behaviour of the Penn gap for each polarization.
Photokinetic examination of (Z,E,E)-4,4′-distyrylazobenzene
1995
Abstract 4,4′-Distyrylazobenzenes demonstrate a photokinetic equilibrium and a superimposed thermal backward reaction in which the absorption coefficient of one of the partners in the equilibrium is principally unknown. Using the dependence of the photostationary state on the irradiation intensity, the photochemical quantum yields ϕ 1 A and ϕ 2 B were determined, as well as the thermal rate constant k , as a function of the irradiation and observation wavelengths. Experimental difficulties and the wavelength dependence of ϕ 1 A and ϕ 2 B are discussed.
Simulation of laser-generated ultrasonic wave propagation in solid media and air with application to NDE
2009
Ultrasonic methods are well known as powerful and reliable tool for defect detection. In the previous decades focus and interest have been directed to non-contact sensors and methods, showing many advantages over contact techniques where inspection depends on contact conditions (pressure, coupling medium, contact area). The non-contact hybrid ultrasonic method described here is of interest for many applications, requiring periodic inspection in service or after manufacturing. Despite the potential impact of laser-generated ultrasound in many areas of industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evalu…
Detection and orientation evaluation for three-dimensional objects
2003
This paper presents a novel method for detection and orientation evaluation for three-dimensional (3-D) objects based on range images. It is based on the calculation of the phase Fourier transform of the 3-D object range image. The method permits the estimation of the angular position of the object. It works with rotations around an axis perpendicular to the line of sight, although it exhibits a certain nodding tolerance. Simulated results demonstrate the ability of the new introduced method.
Recent Advances and Future Directions of Microwave Photonic Radars: A Review
2021
Microwave photonic (MWP) radar has the advantages of generating and processing wide bandwidth microwave signals, reconfigurability, high immunity to electromagnetic interference compared to microwave electronic radar. It has the potential to be used in applications such as intelligent autonomous and cyber-physical systems. Recent advances in microwave photonic technology led to the generation, fast processing, and control of broadband signals. Because of the advancements in photonic technologies, next-generation microwave photonic radar is becoming more prominent. This article reviews the most recent advancements and future directions in MWP radars. This review article overviews the differe…
Three-dimensional object recognition by Fourier transform profilometry
2008
An automatic method for three-dimensional (3-D) shape recognition is proposed. It combines the Fourier transform profilometry technique with a real-time recognition setup such as the joint transform correlator (JTC). A grating is projected onto the object surface resulting in a distorted grating pattern. Since this pattern carries information about the depth and the shape of the object, their comparison provides a method for recognizing 3-D objects in real time. A two-cycle JTC is used for this purpose. Experimental results demonstrate the theory and show the utility of the new proposed method.
Flexible design of multifocal metalenses based on autofocused Airy beams
2018
Extreme miniaturization of on-demand optical devices such as ultrathin lenses is currently leading to significant advancements in manufacturing novel materials and nanotechnologies. Flexibility and tunability of engineered layouts enable efficient integration of complex photonic modules. In this regard, here we propose an autofocused Airy (AFA)-based metalens that operates, depending on the molded phase profile, as a multifocal focusing lens, which to the best of our knowledge has not been reported before. To do this, we call attention to the fact that the two conjugate focal points of an AFA beam can be brought into real space by applying a proper convex lens phase profile. Considering ful…