Search results for "RADIATION"
showing 10 items of 5298 documents
Reversible Photochemical Control of Doping Levels in Supported Graphene
2017
Controlling the type and density of charge carriers in graphene is vital for a wide range of applications of this material in electronics and optoelectronics. To date, chemical doping and electrostatic gating have served as the two most established means to manipulate the carrier density in graphene. Although highly effective, these two approaches require sophisticated graphene growth or complex device fabrication processes to achieve both the desired nature and the doping densities with generally limited dynamic tunability and spatial control. Here, we report a convenient and tunable optical approach to tune the steady-state carrier density and Fermi energy in graphene by photochemically c…
Development of a saturated absorption spectroscopy setup at IGISOL for characterisation of Fabry-Pérot interferometers
2016
A saturated absorption spectroscopy setup was developed and optimised for the characterisation of a home-built and a commercial Fabry-Pérot interferometer (FPI). The free spectral range of these FPIs has been determined with reliable statistical and systematic errors. These FPIs will be used for accurate wavelength determination of broad- and narrowband pulsed Ti:sapphire lasers used in resonance ionisation spectroscopy experiments. peerReviewed
All-fibered high-quality 1.5–2 THz femtosecond pulse sources
2009
Generation of high-quality ultra-high repetition rate optical pulse trains around 1.55µm has become increasingly interesting for many scientific applications such as optical sampling, ultra-high capacity transmission systems, component testing or nonlinear phenomena studies. Unfortunately, the current bandwidth limitations of optoelectronic devices do not enable the direct generation of pulses with repetition rate higher than 80GHz and a temporal width below a few ps.
Diffractive optics for quasi-direct space-to-time pulse shaping.
2008
The strong chromatic behavior associated with a conventional diffractive lens is fully exploited to propose a novel optical device for pulse shaping in the femtosecond regime. This device consists of two optical elements: a spatially patterned circularly symmetric mask and a kinoform diffractive lens, which are facing each other. The system performs a mapping between the spatial position of the masking function expressed in the squared radial coordinate and the temporal position in the output waveform. This space-to-time conversion occurs at the chromatic focus of the diffractive lens, and makes it possible to tailor the output central wavelength along the axial location of the output point…
All-fiber processing of terahertz-bandwidth signals based on cascaded tapered fibers
2013
Tapered single-mode fibers are employed to perform dynamic pulse shaping in a bandwidth of several terahertz. The transfer function of cascaded biconical tapers is controlled by introducing a phase shift into one of them through mechanical stretching. It is a simple and low-cost technique with potential to process signals with bandwidths as large as those allocated by standard optical fiber while introducing little degradation. Femtosecond pulses are shaped to prove the concept. (C) 2013 Optical Society of America
320GHz, 640GHz and 1THz femtosecond pulse sources based on multiple four wave mixing in highly non linear optical fibers
2006
Ultra-high repetition rate, transform-limited femtosecond pulse trains have been generated around 1555 nm at 320 GHz, 640 GHz and 1 THz through the compression of a dual frequency beat-signal in a highly nonlinear optical fiber.
Femtosecond parabolic pulse shaping in normally dispersive optical fibers
2013
Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initia…
Transport properties of an ionic magnetic colloid: experimental study of increasing the ionic strength
2002
Abstract The phase separation of an ionic magnetic colloid in zero magnetic field by increasing the ionic strength is well known [Universite Paris VI, France, 1987; J. Colloid Interface Sci. 132 (1989) 1]. The present work deals with investigation of an ionic ferrofluid by increasing the ionic strength in the range of 0–0.14 mol/l, being safely below the threshold value at which the effect of phase separation occurs. By the optical grid setup [Fourth International conference PAMIR, France, 2000], the main transport properties of a ferrofluid, i.e. translational mass diffusion and thermal diffusion (Soret) coefficients, are measured. The obtained results show a strong dependence of mass diff…
Multi-frequency orthogonality sampling for inverse obstacle scattering problems
2011
We discuss a simple non-iterative method to reconstruct the support of a collection of obstacles from the measurements of far-field patterns of acoustic or electromagnetic waves corresponding to plane-wave incident fields with one or few incident directions at several frequencies. The method is a variant of the orthogonality sampling algorithm recently studied by Potthast (2010 Inverse Problems 26 074015). Our theoretical analysis of the algorithm relies on an asymptotic expansion of the far-field pattern of the scattered field as the size of the scatterers tends to zero with respect to the wavelength of the incident field that holds not only at a single frequency, but also across appropria…
New insights into electron spin dynamics in the presence of correlated noise
2011
The changes of the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which keeps into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examinating the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, f…