Resonant harmonic response in tapping-mode atomic force microscopy

Cataloged from PDF version of article.Higher harmonics in tapping-mode atomic force microscopy offers the potential for imaging and sensing material properties at the nanoscale. The signal level at a given harmonic of the fundamental mode can be enhanced if the cantilever is designed in such a way that the frequency of one of the higher harmonics of the fundamental mode ~designated as the resonant harmonic! matches the resonant frequency of a higher-order flexural mode. Here we present an analytical approach that relates the amplitude and phase of the cantilever vibration at the frequency of the resonant harmonic to the elastic modulus of the sample. The resonant harmonic response is optimized for different samples with a proper design of the cantilever. It is found that resonant harmonics are sensitive to the stiffness of the material under investigation

Scalable low-latency optical phase sensor array

Optical phase measurement is critical for many applications, and traditional approaches often suffer from mechanical instability, temporal latency, and computational complexity. In this paper, we describe compact phase sensor arrays based on integrated photonics, which enable accurate and scalable reference-free phase sensing in a few measurement steps. This is achieved by connecting multiple two-port phase sensors into a graph to measure relative phases between neighboring and distant spatial locations. We propose an efficient post-processing algorithm, as well as circuit design rules to reduce random and biased error accumulations. We demonstrate the effectiveness of our system in both simulations and experiments with photonics integrated circuits. The proposed system measures the optical phase directly without the need for external references or spatial light modulators, thus providing significant benefits for applications including microscope imaging and optical phased arrays

Life cycle cost, as a tool for decision making on concrete infrastructures

The use of Life Cycle Cost (LCC) tools in civil engineering is increasing, due to the need of infrastructure owners and operators to guarantee their assets maximum performance with an optimized budget. By considering these tools it will be possible to manage assets along their lifetime in a more sustainable and efficient way. Due to this reason, it was recently constituted a Task Group on fib to deal with existing LCC tools for concrete infrastructures. This paper gives an introduction to these tools, with a special emphasis to the added-value of LCC, and to the main contents of the fib TG 8.4 state-of-art technical report. This covers a description of existing LCC standards and guidelines, their applicability, the definition of different cost elements, the incorporation of risk in the analysis, etc.(undefined)info:eu-repo/semantics/publishedVersio

Power monitoring in a feedforward photonic network using two output detectors

Programmable feedforward photonic meshes of Mach-Zehnder interferometers are computational optical circuits that have many classical and quantum computing applications including machine learning, sensing, and telecommunications. Such devices can form the basis of energy-efficient photonic neural networks, which solve complex tasks using photonics-accelerated matrix multiplication on a chip, and which may require calibration and training mechanisms. Such training can benefit from internal optical power monitoring and physical gradient measurement for optimizing controllable phase shifts to maximize some task merit function. Here, we design and experimentally verify a new architecture capable of power monitoring any waveguide segment in a feedforward photonic circuit. Our scheme is experimentally realized by modulating phase shifters in a 6 x 6 triangular mesh silicon photonic chip, which can non-invasively (i.e., without any internal "power taps ") resolve optical powers in a 3 x 3 triangular mesh based on response measurements in only two output detectors. We measure roughly 3% average error over 1000 trials in the presence of systematic manufacturing and environmental drift errors and verify scalability of our procedure to more modes via simulation

Widely tunable thermo-optic plasmonic bandpass filter

We report thermally tunable optical bandpass filters based on long-range surface plasmon polariton waveguides. A thin gold stripe in the waveguide core is surrounded by dielectric layers with dissimilar refractive index dispersions and dissimilar thermo-optic coefficients. High filter transmission is achieved for a wavelength at which the refractive indices of the upper and lower cladding layers are identical, and this spectral point may be changed by varying the filter temperature. Experimentally, over 220 nm of bandpass tuning is achieved around 1550 nm wavelength by varying the device temperature from 19 to 27 degrees C. (C) 2013 AIP Publishing LLC.close3

Surface velocity of the Northeast Greenland Ice Stream (NEGIS): assessment of interior velocities derived from satellite data by GPS

The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography of interior Greenland exist, but their accuracy is not well constrained by in situ observations. Here we present the results from a GPS mapping of surface velocity in an area located approximately 150 km from the ice divide near the East Greenland Ice-core Project (EastGRIP) deep-drilling site. A GPS strain net consisting of 63 poles was established and observed over the years 2015–2019. The strain net covers an area of 35 km by 40 km, including both shear margins. The ice flows with a uniform surface speed of approximately 55 m a^−1 within a central flow band with longitudinal and transverse strain rates on the order of 10−4 a^−1 and increasing by an order of magnitude in the shear margins. We compare the GPS results to the Arctic Digital Elevation Model and a list of satellite-derived surface velocity products in order to evaluate these products. For each velocity product, we determine the bias in and precision of the velocity compared to the GPS observations, as well as the smoothing of the velocity products needed to obtain optimal precision. The best products have a bias and a precision of ∼0.5 m a^−1. We combine the GPS results with satellite-derived products and show that organized patterns in flow and topography emerge in NEGIS when the surface velocity exceeds approximately 55 m a−1 and are related to bedrock topography

Fiber mode excitation using phase-only spatial light modulation: Guideline on free-space path design and lossless optimization

Phase-only spatial light modulators allow to reshape a Gaussian beam by imposing a given phase distribution along the beam cross section. This technique is widely used in the context of mode-division multiplexing to produce, after propagation through a free-space path, the field designed to excite a given fiber mode. In case of orbital angular momentum modes, the target field is approximated as circularly polarized and several complex algorithms have been developed to increase the purity of the obtained modes. Besides their complexity, those algorithms often exploit higher-order diffraction and spatial filtering, hence entailing power loss. In the theoretical work described here, the mode purity is increased in a simple and efficient way by improving the mode approximation adopted to obtain circularly polarized modes and by optimizing two free parameters in the setup, as demonstrated through pertinent simulations