Search results for "intensity"

2016

Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin-coherence time in paraffin-coated cells leads to spatial averaging of the vector light shift over the entire cell volume. This renders the averaged vector light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. Importantly, the demonstrated averaging mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.

Hexagonal boron nitride luminescence dependent on vacuum level and surrounding gases

2015

Abstract Gas sensing properties of hBN powder bulk and nanosize were studied. It was demonstrated that for hBN powders with grain sizes of 70 nm, 1 μm and 5 μm the native defect-induced luminescence observed at 400 nm under 265 nm light excitation and room temperature is sensitive to oxygen gas reducing luminescence intensity. The highest value of luminescence intensity is reached when sample is in vacuum. Results obtained allow conclusion that the hBN powder is prospective for sensing of oxygen gas. Some material properties such as dependence of luminescence intensity on vacuum level and pumping time, ratio of luminescence intensity when sample is in vacuum and gas, its dependence on mater…

FINITE DIFFERENCE METHOD-BASED SIMULATION OF TEMPERATURE FIELDS FOR APPLICATION TO ORTHOGONAL CUTTING WITH COATED TOOLS

2005

ABSTRACT A finite difference method was proposed to model the effect of a variety of tool coatings on the magnitude and distribution of temperatures through the tool-chip contact region and the coating/substrate boundaries. For each workpiece-tool pair tested the intensity of uniformly distributed heat flux and relevant analytically obtained values of the heat partition coefficient were assumed to change with variations of cutting speed and the corresponding friction. In this case the simulation of an orthogonal machining of AISI 1045 steel was performed using special computing algorithm with elementary balances of induced energies (MBE). It is concluded that the temperature contours obtain…

Two-photon high-speed light-sheet volumetric imaging of brain activity during sleep in zebrafish larvae

2020

Although it is well known that zebrafish display the behavioural signature of sleep, the neuronal correlates of this state are not yet completely understood, due to the complexity of the measurements required. For example, when performed with visible excitation light, functional imaging can disrupt the day/night cycle due to the induced visual stimulation. To address this issue, we developed a custom-made two-photon light-sheet microscope optimized for high-speed volumetric imaging. By employing infra-red light (not visible to the larva) for excitation, we are able to record wholebrain neuronal activity with high temporal- and spatial-resolution without affecting the sleep state. In two-pho…

Electrical and optical low frequency noises in multimodal vertical cavity surface emitting lasers

2006

Experimental investigations of the low frequency noise of multimode 780 nm vertical cavity surface emitting lasers are reported. Electrical noise, optical noise and their correlation have been measured in the frequency range 1 Hz–95 kHz. The results show that the main contribution to the electrical noise is located in the distributed Bragg reflector layers of the laser. The optical power and pump current noise sources are strongly correlated below and around the threshold, while are weakly correlated above threshold. It is argued that the noise in the optical power is due to both free injection carrier noise and optical gain fluctuations.

Ultralow-intensity near-infrared light induces drug delivery by upconverting nanoparticles

2014

Mesoporous silica coated upconverting nanoparticles are loaded with the anticancer drug doxorubicin and grafted with ruthenium complexes as photoactive molecular valves. Drug release was triggered by 974 nm light with 0.35 W cm(-2). Such low light intensity minimized overheating problems and prevented photodamage to biological samples.

Electrothermal Feedback and Absorption-Induced Open-Circuit-Voltage Turnover in Solar Cells

2018

A solar panel gets hot as it works up on the roof, yet photoinduced self-heating is often ignored when characterizing lab-sized samples. The authors present their understanding of the turnover effect in measurements of open-circuit voltage versus light intensity (Suns-${V}_{O\phantom{\rule{0}{0ex}}C}$ curves), which is identified as a unique feature of all semiconductor-based solar cells. This effect is explained in terms of electrothermal feedback arising when the incident irradiation heats up the device. The authors' model fully explains the experimental data, and allows one to determine key device parameters such as the ideality factor and the band gap from a single measurement.

Artificial neural networks for nonlinear pulse shaping in optical fibers

2020

International audience; We use a supervised machine-learning model based on a neural network to predict the temporal and spectral intensity profiles of the pulses that form upon nonlinear propagation in optical fibers with both normal and anomalous second-order dispersion. We also show that the model is able to retrieve the parameters of the nonlinear propagation from the pulses observed at the output of the fiber. Various initial pulse shapes as well as initially chirped pulses are investigated.

Complete intensity and phase characterisation of optical pulse trains at terahertz repetition rates

1999

Complete intensity and phase characterisation of optical pulse trains at terahertz repetition rates is carried out using an adapted frequency-resolved optical gating technique. The experimental characterisation of a 2.5 THz train of dark solitons in an optical fibre is in good agreement with numerical simulations.

Dielectric nonlinearity of ferroelectric solid solutions PMN-PZN and PMN-PNN

2001

Abstract Obtaining of novel thin film materials for electrically tuneable capacities is one of the current problems of ferroelectric material application. The most appropriate materials are the ferroelectric lead-containing niobates: PbMg1/3Nb2/3O3 (PMN), PhZn1/3Nb2/3Os (PZN), PbNi1/3Nb2/3O3 (PNN) and their solid solutions were synthesized by solid state reactions at 800–900 °C from oxides. Results of the studies of thermal dependence of dielectric permeability and loss factors of the synthesized solutions are provided together with reciprocal dielectric permeability as function of temperature and electric field intensity. The dielectric characteristics of nonlinear materials are reported e…