1,832 research outputs found
Echoes of a Squeezed Oscillator
Pulses applied to an inhomogeneously broadened set of harmonic oscillators,
previously prepared in squeezed states, can lead to a recovery of coherence,
manifesting itself as echoes, similar to those exhibited by an ensemble of
spins when excited by properly designed electromagnetic pulses. Such echoes, of
classical or quantum nature, are expected to arise in the squeezing of linear
systems of various sorts and, in particular, light and vibrational modes
Parametric amplification of optical phonons
Amplification of light through stimulated emission or nonlinear optical
interactions has had a transformative impact on modern science and technology.
The amplification of other bosonic excitations, like phonons in solids, is
likely to open up new remarkable physical phenomena. Here, we report on an
experimental demonstration of optical phonon amplification. A coherent
mid-infrared optical field is used to drive large amplitude oscillations of the
Si-C stretching mode in silicon carbide. Upon nonlinear phonon excitation, a
second probe pulse experiences parametric optical gain at all wavelengths
throughout the reststrahlen band, which reflects the amplification of
optical-phonon fluctuations. Starting from first principle calculations, we
show that the high-frequency dielectric permittivity and the phonon oscillator
strength depend quadratically on the lattice coordinate. In the experimental
conditions explored here, these oscillate then at twice the frequency of the
optical field and provide a parametric drive for lattice fluctuations.
Parametric gain in phononic four wave mixing is a generic mechanism that can be
extended to all polar modes of solids, as a new means to control the kinetics
of phase transitions, to amplify many body interactions or to control
phonon-polariton waves
Reversal of ferroelectric domains by ultrashort optical pulses
The response of a soft-phonon ferroelectric material subjected to a high-intensity optical pulse of duration much shorter than the period of the phonon is modeled using a classical, finite-temperature simulation. It is found that complete, permanent reversal of the orientation of the ferroelectric domains may occur even when the energy per atom imparted by the light pulse is much less than the average thermal energy. The result raises the possibility of using the effect to create optical switches or data storage media with switching times less than 10 psec
Ultrafast optical excitation of a combined coherent-squeezed phonon field in SrTiO<SUB>3</SUB>
We have simultaneously excited a coherent and a squeezed phonon field in SrTiO3 using femtosecond laser pulses and stimulated Raman scattering. The frequency of the coherent state (~1.3 THz) is that of the A1g-component of the soft mode responsible for the cubic-tetragonal phase transformation at ≈ 110 K. The squeezed field involves a continuum of transverse acoustic phonons dominated by a narrow peak in the density of states at ~ 6.9 THz
Raman spectra of two‐dimensional spin‐1/2 Heisenberg antiferromagnets
The Raman spectrum of two‐dimensional spin‐1/2 Heisenberg antiferromagnets is calculated by exactly diagonalizing clusters of up to 26 sites. The obtained spectra are compared to experimental results for various high‐Tc precursors, such as La2CuO4 and YBa2Cu3O6.2. In spite of good agreement in the position of the main excitation in the B1g channel, i.e, the two‐magnon peak around 0.4 eV, an additional mechanism has to be invoked to account for the broad and asymmetric shape of the overall spectrum. Here, we consider the phonon‐magnon interaction which, in a quasistatic approximation, renormalizes the Heisenberg exchange integral. This mechanism is motivated in part by recent experimental observations that the Raman linewidth broadens with increasing temperature. Our results are in good agreement with Raman scattering experiments performed by various groups; in particular, the calculations reproduce the broad line shape of the two‐magnon peak, the asymmetry about its maximum, the existence of spectral weight at high energies, and the observation of nominally forbidden A1g scattering.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70431/2/JAPIAU-75-10-6340-1.pd
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