Search results for "waves"
showing 10 items of 1766 documents
Ultracompact and Low-Power Plasmonic MZI Switch Using Cyclomer Loading
2015
We present a $2\times 2$ hybrid silicon-plasmonic thermooptic (TO) asymmetric Mach–Zehnder interferometric (MZI) switch having only 40- $\mu \text{m}$ long active cyclomer-loaded plasmonic phase arms. It requires less than 12 mW of power and has 2/5- $\mu \text{s}$ ON/OFF-times, respectively, a modulation depth higher than 90% and a 13.2-dB extinction ratio. Data traffic evaluation has been carried out using 10-Gb/s nonreturn-to-zero streams, yielding error-free operation at both switching states with power penalties ranging between 1 to 4.8 dB. The use of the cyclomer loading having a higher TO coefficient than polymethyl methacrylate has resulted to the smallest footprint among plasmonic …
Nonlinear pulse shaping and polarization dynamics in mode-locked fiber lasers
2014
International audience; We review our recent progress on the study of new nonlinear mechanisms of pulse shaping in passively mode-locked fiber lasers. These include a mode-locking regime featuring pulses with a triangular distribution of the intensity, and spectral compression arising from nonlinear pulse propagation. We also report on our recent experimental studies unveiling new types of vector solitons with processing states of polarization for multi-pulse and tightly bound-state soliton (soliton molecule) operations in a carbon nanotube (CNT) mode-locked fiber laser with anomalous dispersion cavity.
SANS polarization analysis at V4 SANS instrument of HMI Berlin
2008
The V4 instrument has recently been upgraded with a 3He spin filter cell, placed directly in the homogeneous field B of the sample magnet, to enhance the SANSPOL option for polarization analysis. The prototype setup was still affected by: (a) a quick relaxation of the 3He nuclear polarization in the cell with a time constant of only ?130 min which significantly changes the spin filter transmissions T+ and T? for neutrons polarized parallel I+ and anti-parallel I? to B, and (b) the absence of a flipping aid behind the sample. The usual polarization analysis procedure, expecting virtually time-independent transmissions and a second flipping device, is therefore not applicable. We present an a…
The Møller Polarimeter for MAMI
1991
The polarization of high-energy electrons can conveniently be measured by means of Moller scattering from polarized electrons in a magnetized ferromagnetic target. This process exhibits in the limit of high energies (E ≥ 100 MeV) still relatively large, energy independent and well known analysator strengths. Furthermore, the laboratory cross section in the kinematical range suitable for polarimeter applications is large $$ \frac{{d\sigma }}{{d\Omega }}({\Theta _{cm}} = 90^\circ ) = Z \cdot 0.18{\text{ }}barn/sr$$ and energy-independent.
Risken–Nummedal–Graham–Haken instability in class-B lasers
1999
We determine analytical expressions for the Risken-Nummedal-Graham-Haken multimode laser instability outside the uniform field limit in the case of very fast polarization decay (class-B laser). A new condition for the observability of that instability, concerning the value of the cavity mirrors reflectivity, is predicted.
Notice of Removal: Stochastic generation of the phononic band structure of lossy and infinite crystals
2017
The concept of the band structure is central to the field of phononic crystals. Indeed, capturing the dispersion of Bloch waves — the eigenmodes of propagation in periodic media — gives invaluable information on allowed propagation modes, their phase and group velocities, local resonances, and band gaps. Band structures are usually obtained by solving an eigenvalue problem defined on a closed and bounded domain, which results in a discrete spectrum. There are at least two cases, however, that cannot be reduced to a simple eigenvalue problem: first, when materials showing dispersive loss are present and second, when the unit-cell extends beyond any bound, as in the case of phononic crystal o…
Narrow-band tunable terahertz detector in antiferromagnets via staggered-field and antidamping torques
2018
We study dynamics of antiferromagnets induced by simultaneous application of dc spin current and ac charge current, motivated by the requirement of all-electrically controlled devices in the terahertz (THz) gap (0.1--30 THz). We show that ac electric current, via N\'eel spin-orbit torques, can lock the phase of a steady rotating N\'eel vector whose precession is controlled by a dc spin current. In the phase-locking regime the frequency of the incoming ac signal coincides with the frequency of auto-oscillations, which for typical antiferromagnets falls into the THz range. The frequency of auto-oscillations is proportional to the precession-induced tilting of the magnetic sublattices related …
Constant-adiabaticity ultralow magnetic field manipulations of parahydrogen-induced polarization: application to an AA'X spin system
2021
The field of magnetic resonance imaging with hyperpolarized contrast agents is rapidly expanding, and parahydrogen-induced polarization (PHIP) is emerging as an inexpensive and easy-to-implement method for generating the required hyperpolarized biomolecules. Hydrogenative PHIP delivers hyperpolarized proton spin order to a substrate via chemical addition of H2 in the spin-singlet state, but it is typically necessary to transfer the proton polarization to a heteronucleus (usually 13C) which has a longer spin lifetime. Adiabatic ultralow magnetic field manipulations can be used to induce the polarization transfer, but this is necessarily a slow process, which is undesirable since the spins co…
Spin-orbit interaction in bremsstrahlung and its effect on the electron motion in a strong Coulomb field
2015
Linear polarization of bremsstrahlung x rays produced in collisions of longitudinally polarized 2.1-MeV electrons with gold atoms was studied using the Compton scattering technique. We observed that the angle of x-ray polarization is strongly correlated with the incoming electron polarization. This correlation reveals the dominance of the spin-orbit interaction in bremsstrahlung and indicates a striking effect of the electron spin on the electron motion in a strong Coulomb field. The results confirm the validity of the theoretical predictions in a computationally challenging energy regime.
Possible gyrotron operation in the “no start current” zone caused by the axial dependence of the phase of the resonator field
2018
It is known that gyrotrons (as well as other electron beam driven microwave and millimeter-wave oscillators) can operate in the regime of either soft or hard self-excitation. In the regime of soft self-excitation, the beam current exceeds its starting value; thus, the oscillations can start to grow from the noise produced by electrons. In the regime of hard self-excitation, the beam current is less than its starting value. Therefore, for exciting the oscillations, a certain start-up scenario is required, which may include the variation of the mod-anode and/or beam voltage or the guiding magnetic field. It was found recently [O. Dumbrajs and G. S. Nusinovich, Phys. Plasmas 25, 013121 (2018)]…