1,509 research outputs found
Synthesis of hollow poly(aniline-co-pyrrole)-Fe3O4 composite nanospheres and their microwave absorption behavior
Hollow poly(aniline-co-pyrrole)-Fe3O4 (HPAP-Fe3O4) nanospheres with significant electromagnetic properties were successfully prepared via the oxidative polymerization of a mixture of aniline and pyrrole in the presence of a magnetic fluid, using a non-ionic surfactant as a template. The products were characterized by field emission scanning electron microscopy, transmission electron microscopy. Fourier transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis and Xray photoelectron spectroscopy. The electromagnetic (EM) and microwave absorbing properties of the nanocomposites were also investigated. The HPAP-Fe3O4 nanospheres exhibit superparamagnetic properties, and the conductivity increases with Fe3O4 content. The reflection loss evaluation based on the absorbing wall theory at 2 mm thickness shows that the reflection loss is reinforced in the frequency range of 0.5-10 GHz by the presence of Fe3O4 nanoparticles, and the frequency of minimum reflection loss shifts to a higher value with increasing Fe3O4 content. HPAP-Fe-06 exhibits the best microwave absorbing property between 0.5 and 10 GHz.ArticleSYNTHETIC METALS. 162(3-4):337-343 (2012)journal articl
Remote creation of strong and coherent emissions in air with two-color ultrafast laser pulses
We experimentally demonstrate generation of strong narrow-bandwidth emissions
with excellent coherent properties at ~391 nm and ~428 nm from molecular ions
of nitrogen inside a femtosecond filament in air by an orthogonally polarized
two-color driver field (i. e., 800 nm laser pulse and its second harmonic). The
durations of the coherent emissions at 391 nm and 428 nm are measured to be
~2.4 ps and ~7.8 ps respectively, both of which are much longer than the
duration of the pump and its second harmonic pulses. Furthermore, the measured
temporal decay characteristics of the excited molecular systems suggest an
"instantaneous" population inversion mechanism that may be achieved in
molecular nitrogen ions at an ultrafast time scale comparable to the 800 nm
pump pulse.Comment: 19 pages, 4 figure
Impulsive rotational Raman scattering of N2 by a remote "air laser" in femtosecond laser filament
We report on experimental realization of impulsive rotational Raman
scattering from neutral nitrogen molecules in a femtosecond laser filament
using an intense self-induced white-light seeding "air laser" generated during
the filamentation of an 800 nm Ti: Sapphire laser in nitrogen gas. The
impulsive rotational Raman fingerprint signals are observed with a maximum
conversion efficiency of ~0.8%. Our observation provides a promising way of
remote identification and location of chemical species in atmosphere by
rotational Raman scattering of molecules.Comment: 4 pages, 4 figure
High-brightness switchable multi-wavelength remote laser in air
Remote laser in air based on amplified spontaneous emission (ASE) has
produced rather well-collimated coherent beams in both backward and forward
propagation directions, opening up possibilities for new remote sensing
approaches. The remote ASE-based lasers were shown to enable operation either
at ~391 and 337 nm using molecular nitrogen or at ~845 nm using molecular
oxygen as gain medium, depending on the employed pump lasers. To date, a
multi-wavelength laser in air that allows for dynamically switching the
operating wavelength has not yet been achieved, although this type of laser is
certainly of high importance for detecting multiple hazard gases. In this
Letter, we demonstrate, for the first time to our knowledge, a harmonic-seeded
switchable multi-wavelength laser in air driven by intense mid-infrared
femtosecond laser pulses. Furthermore, population inversion in the
multi-wavelength remote laser occurs at an ultrafast time-scale (i.e., less
than ~200 fs) owing to direct formation of excited molecular nitrogen ions by
strong-field ionization of inner-valence electrons, which is fundamentally
different from the previously reported pumping mechanisms based either on
electron recombination of ionized molecular nitrogen or on resonant two-photon
excitation of atomic oxygen fragments resulting from resonant two-photon
dissociation of molecular oxygen. The bright multi-wavelength laser in air
opens the perspective for remote detection of multiple pollutants based on
nonlinear spectroscopy.Comment: 18 pages, 5 figure
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