Controlling magnon-photon coupling in a planar geometry

The tunability of magnons enables their interaction with various other quantum excitations, including photons, paving the route for novel hybrid quantum systems. Here, we study magnon-photon coupling using a high-quality factor split-ring resonator and single-crystal yttrium iron garnet (YIG) sphere at room temperature. We investigate the dependence of the coupling strength on the size of the sphere and find that the coupling is stronger for spheres with a larger diameter as predicted by theory. Furthermore, we demonstrate strong magnon-photon coupling by varying the position of the YIG sphere within the resonator. Our experimental results reveal the expected correlation between the coupling strength and the rf magnetic field. These findings demonstrate the control of coherent magnon-photon coupling through the theoretically predicted square-root dependence on the spin density in the ferromagnetic medium and the magnetic dipolar interaction in a planar resonator

Spin-wave caustics in an extended thin film excited by a nanoconstriction

International audienceThe ability to control the directionality of spin waves is important for magnonic logic and computing application. Here, we demonstrate the emission of caustic-like spin waves in an extended yttrium iron garnet (YIG) thin film of 200 nm thickness by a nano-constricted rf waveguide. Using spatial resolved micro-focused Brillouin light spectroscopy technique in both the backward volume and the Damon-Eshbach geometry, we reveal the spin-wave directional spin-wave propagation in the YIG film. We excite spin waves in the film by passing a rf current through a constricted waveguide patterned on the top of the extended YIG film by electron-beam lithography. When the direction of the group velocity is the same for waves of different wavevectors, caustic beams are formed which propagate in two directions perpendicular to the isofrequency curve. We find that these beams are symmetric in intensity for a rf magnetic field perpendicular to the biasing magnetic field. On the other hand, one beam is more intense than the other one for a rf magnetic field parallel to the biasing field. We further show that the propagation direction of caustic-like spin-wave beams is frequency dependent. Our findings have important implications for the development of switchable spin wave splitters, passive spin-wave frequency-division demultiplexers[1, 2] and magnonic interferometry

Time-resolved double-resonance spectroscopy: Lifetime measurement of the 61Σ+g(7,31) electronic state of molecular sodium

We report on the lifetime measurement of the 61Σ+g(7,31) state of Na2 molecules, produced in a heat-pipe oven, using a time-resolved spectroscopic technique. The 61Σ+g(7,31) level was populated by two-step two-color double resonance excitation via the intermediate A1Σ+u(8,30) state. The excitation scheme was done using two synchronized pulsed dye lasers pumped by a Nd:YAG laser operating at the second harmonics. The fluorescence emitted upon decay to the final state was measured using a time-correlated photon counting technique, as a function of argon pressure. From this, the radiative lifetime was extracted by extrapolating the plot to collision-free zero pressure. We also report the calculated radiative lifetimes of the Na261Σ+g ro-vibrational levels in the range of v = 0–200 with J = 1 and J = 31 using the LEVEL program for bound-bound and the BCONT program for bound-free transitions. Our calculations reveal the importance of the bound-free transitions on the lifetime calculations and a large difference of about a factor of three between the J = 1 and J = 31 for the v = 40 and v = 100, respectively, due to the wavefunction alternating between having predominantly inner and outer well amplitude

Rovibrationally resolved radiative lifetime and collisional cross section measurements of the 61Σg+(v=6,8,J=31) state of molecular sodium

*Sağlam, Ziya ( Aksaray, Yazar )We report on radiative lifetime and collisional cross section measurements of the Na2 61Σg+(v=6, J=31) and 61Σg+(v=8, J=31) molecular levels by time-resolved laser spectroscopy. The excitation to the 61Σg+(3s+5s) electronic state was achieved using two synchronized pulsed lasers, directed to the sodium heatpipe oven and molecular fluorescence decay time as a function of buffer gas was recorded via time-correlated single photon counting technique. Radiative lifetimes were measured using a Stern-Volmer plots. From the lifetime measurements, collisional cross sections between the sodium molecules in the 61Σg+ state and the ground state argon atoms were extracted

Neurocysticercosis in Nepal: a retrospective clinical analysis

Aim: The prevalence of epilepsy is higher in Nepal. This study was conducted to analyze the clinical manifestations of neurocysticercosis (NCC) among seizure patients admitted to our center.Methods: We retrospectively studied all the NCC patients admitted to Neurology Department, Bir Hospital, Kathmandu, Nepal from April 2012 to February 2014. Computer tomography/ magnetic resonance imaging (CT/MRI) head, clinical profile, lab investigations and exclusion of other causes were the basis of the NCC diagnosis. Chi-square and Student’s t-test were used for comparison of variables.Results: Out of 131 seizure patients admitted, 21 patients were diagnosed with NCC [mean age: 33.95 ± 16.41; male: 15 (71.4%), female: 6 (28.6%)]. Generalized tonic clonic seizure was the most common seizure type in NCC patients (18 patients; 85.7%), two of them had status epilepticus during presentation in Emergency Department. Three patients had focal seizure, one with epilepsia partialis continua. Neuroimaging showed multiple NCC lesions in 8 (38.1%) and a single NCC lesion in 13 (61.9%) patients. Seven of them (33.3%) sought traditional healers before being presented to our center. Eight patients (38.1%) were treated with antiepileptics in local health-post without neuroimaging studies done. Calcified stage of NCC was the most frequent CT/MRI findings (12 patients; 57.1%). Phenytoin was preferred both by physicians and patients due to its low cost.Conclusion: NCC is a common finding among seizure patients in Nepal. Poor economic status, illiteracy and underdeveloped rural society are the major challenges in prevention and treatment of NCCs

Antenna Design for Spin Wave Caustic Beams

International audienc