583,098 research outputs found
Dual-frequency ferromagnetic resonance
We describe a new experimental technique to investigate coupling effects
between different layers or modes in ferromagnetic resonance (FMR). Dual FMR
frequencies are excited (2-8 GHz) simultaneously and detected selectively in a
broadband RF circuit, using lock-in amplifier detection at separate modulation
frequencies.Comment: 4 pages, 4 figures, accepted by "Review of Scientific Instruments",
200
Cancellation of light-shifts in an N-resonance clock
We demonstrate that first-order light-shifts can be cancelled for an
all-optical, three-photon-absorption resonance ("N-resonance") on the D1
transition of Rb87. This light-shift cancellation enables improved frequency
stability for an N-resonance clock. For example, using a table-top apparatus
designed for N-resonance spectroscopy, we measured a short-term fractional
frequency stability (Allan deviation) 1.5e-11 tau^(-1/2) for observation times
1s< tau < 50s. Further improvements in frequency stability should be possible
with an apparatus designed as a dedicated N-resonance clock.Comment: 4 pages, 4 figure
Vibrational and stochastic resonances in two coupled overdamped anharmonic oscillators
We study the overdamped version of two coupled anharmonic oscillators under
the influence of both low- and high-frequency forces respectively and a
Gaussian noise term added to one of the two state variables of the system. The
dynamics of the system is first studied in the presence of both forces
separately without noise. In the presence of only one of the forces, no
resonance behaviour is observed, however, hysteresis happens there. Then the
influence of the high-frequency force in the presence of a low-frequency, i.e.
biharmonic forcing, is studied. Vibrational resonance is found to occur when
the amplitude of the high-frequency force is varied. The resonance curve
resembles a stochastic resonance-like curve. It is maximum at the value of
at which the orbit lies in one well during one half of the drive cycle of the
low-frequency force and in the other for the remaining half cycle. Vibrational
resonance is characterized using the response amplitude and mean residence
time. We show the occurrence of stochastic resonance behaviour in the
overdamped system by replacing the high-frequency force by Gaussian noise.
Similarities and differences between both types of resonance are presented.Comment: 22 pages, 13 figure
Rotational Doppler Effect in Magnetic Resonance
We compute the shift in the frequency of the spin resonance in a solid that
rotates in the field of a circularly polarized electromagnetic wave. Electron
spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are
considered. We show that contrary to the case of the rotating LC circuit, the
shift in the frequency of the spin resonance has strong dependence on the
symmetry of the receiver. The shift due to rotation occurs only when rotational
symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape
of the body, or by magnetocrystalline anisotropy. General expressions for the
resonance frequency and power absorption are derived and implications for
experiment are discussed.Comment: 8 pages, 4 figure
Theoretical study of the accuracy limits for the optical resonance frequency measurements
The principal limits for the accuracy of the resonance frequency measurements
set by the asymmetry of the natural resonance line shape are studied and
applied to the recent accurate frequency measurements in the two-photon 1s-2s
resonance and in the one-photon 1s-2p resonance in hydrogen atom. This limit
for 1s-2s resonance is found to be Hz compared to the accuracy
achieved in experiment Hz. In case of deuterium atom the limit is
essentially larger: Hz. For 1s-2p resonance the accuracy limit is
0.17 MHz while the uncertainty of the recent frequency measurement is about 6
MHz.Comment: to be published in Physical Review Letter
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