Search results for "electromagnetic"
showing 10 items of 1595 documents
Four-wave mixing in a ring cavity
2014
We investigate a four-wave mixing process in an N interaction scheme in Rb vapor placed inside a low-finesse ring cavity. We observe strong amplification and generation of a probe signal, circulating in the cavity, in the presence of two strong optical pump fields. We study the variations in probe field gain and dispersion as functions of experimental parameters with an eye on potential application of such a system for enhanced rotation measurements. A density-matrix calculation is performed to model the system, and the theoretical results are compared to those of the experiment.
In situ tuning of a photonic band gap with laser pulses
2008
We report on light-induced optical tuning of colloidal photonic crystals doped with gold nanoparticles (Au-nps). By resonantly exciting the Au-np surface plasmon absorption with picosecond pulses at 0.53 micron in a standard pump-probe setup, we observed permanent changes in the stop band resonance around 1.7 micron, with blue wavelength shifts as large as 30 nm and associated to a nanoparticle reshaping. Fine tuning was achieved by controlling either the pulse energy or the irradiation time.
Possible Precision Far—Infrared Spectroscopy on Trapped Ions
1990
One of the necessary conditions for very high resolution spectroscopy is the existence of long-living energy levels between which transitions can be induced by tunable electromagnetic radiation. Moreover the observation time of the particles under investigation should be sufficiently long, and perturbing effects like Doppler broadening and collisions should be very small. All this leads to the technique of trapped ion spectroscopy which offers all the required conditions. It uses the confinement of charged particles to a very small volume in space under ultrahigh vacuum conditions either by application of a r.f. voltage and a small additional d.c. bias to an arrangement of three electrodes …
The “accumulation effect” of positrons in the stack of foils, detected by measurements of the positron implantation profile
2013
The profiles of positrons implanted from the radioactive source 22Na into a stack of foils and plates are the subject of our experimental and theoretical studies. The measurements were performed using the depth scanning of positron implantation profile method, and the theoretical calculations using the phenomenological multi-scattering model (MSM). Several stacks consisting of silver, gold and aluminum foils, and titanium and germanium plates were investigated. We notice that the MSM describes well the experimental profiles; however when the stack consisting of silver and gold foils, the backscattering and linear absorption coefficients differ significantly from those reported in the litera…
Influence of a Crosslinker Containing an Azo Group on the Actuation Properties of a Photoactuating LCE System
2016
Photoactuating liquid crystalline elastomers (LCE) are promising candidates for an application as artificial muscles in microdevices. In this work, we demonstrate that by optimizing (1) the illumination conditions and (2) the mixture of azo monomer and azo crosslinker, thick films of an all-azo LCE can be prepared, which show a strong length change without bending during photoactuation. This becomes possible by working with white light (about 440 nm), whose absorption is low, leading to a large penetration depth. By adding an azo crosslinker to a previously prepared system, several improvements of the actuation properties—like a stronger photoactuation at lower operational temperatures—coul…
An EPR method for discriminating radiation beams in ammonium tartrate and tooth enamel
2008
The radiation linear energy transfer (LET), which is the energy released by ionizing radiation per path unit, arouses great scientific interest because the biological damage produced by ionizing radiation in tissues is strictly related to LET. Radiation beams with different LETs will cause different spatial energy distribution and therefore different effects inside matter. In the last twenty years the EPR spectroscopy has become a valuable dosimetric tool. This technique allows absorbed dose measurements through the detection of free radicals produced by ionizing radiation in organic and/or inorganic compounds. In this work we have analyzed the possibility of using the acquisition of two co…
Analysis of multipactor RF breakdown in a waveguide containing a transversely magnetized ferrite
2016
In this paper, the multipactor RF breakdown in a parallel-plate waveguide partially filled with a ferrite slab magnetized normal to the metallic plates is studied. An external magnetic field is applied along the vertical direction between the plates in order to magnetize the ferrite. Numerical simulations using an in-house 3-D code are carried out to obtain the multipactor RF voltage threshold in this kind of structures. The presented results show that the multipactor RF voltage threshold at certain frequencies becomes considerably lower than for the corresponding classical metallic parallel-plate waveguide with the same vacuum gap
Magnetic and optical properties in degenerated transition metal and Ga co-substituted ZnO nanocrystals
2019
Abstract In order to study the influence of itinerant electrons on magnetic properties of transition metal substituted ZnO nanocrystals, nanopowders containing different amounts of Ga and fixed amounts of Fe, Ni and Mn ions were synthesized. The ions of different transition metals and Ga were successfully introduced into the ZnO structure using solvothermal synthesis method. X-ray diffraction, scanning electron microscopy, hard X-ray photoelectron spectroscopy and Rietveld refinement were used to characterize the synthesized nanocrystals. Optical measurements revealed that Ga substitution can change the light transmittance/absorption in the infrared part of the electromagnetic light spectru…
Colorimetric gas detection by the varying thickness of a thin film of ultrasmall PTSA-coated TiO2 nanoparticles on a Si substrate
2017
Financial support from the Estonian Research Council (IUT2-25, PUT170, PUT1096, PUT748, PUTJD680), the Estonian Centre of Excellence in Research Projects “Advanced materials and high-technology devices for sustainable energetics, sensorics and nanoelectronics” TK141 (2014-2020.4.01.15-0011), “Emerging orders in quantum and nanomaterials” TK134 and the Development Fund of the University of Tartu, are all gratefully acknowledged.
Floating Zone Growth of Silicon
2015
Abstract The floating zone (FZ) technique changed from a crucible-free purification method into a growth technique mainly for high purity silicon crystals. The melt zone is inductively heated by the high frequency magnetic field of a sophisticated one-turn induction coil being the heart of the FZ growth. The needle-eye technique allows for crystals with large diameters beyond the capillary limitations of a cylindrical zone, but both electric breakthrough at the coil slit and bursting of the crystal by thermomechanical stress presently limit the diameter to 200 mm. A novel gFZ concept is depicted that works with granular silicon feedstock instead of expensive feed rods. The automation of the…