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 &#8776; 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

Tecnologias digitais no processo de ensino e aprendizagem

Anais do II Seminário Seminário Estadual PIBID do Paraná: tecendo saberes / organizado por Dulcyene Maria Ribeiro e Catarina Costa Fernandes — Foz do Iguaçu: Unioeste; Unila, 2014Diversas tecnologias que não foram, necessariamente, criadas para serem ferramentas de ensino e aprendizagem podem ser utilizadas em sala de aula. Para utilizá-las com eficiência, é necessário conhecê-las e analisá-las à luz das teorias pertinentes. Neste artigo são mostradas algumas destas ferramentas e como podem ser utilizadas no processo de ensino e aprendizagem. As tecnologias estão em análise no projeto PIBID – Sistemas de Informação – da Universidade Estadual do Norte do Paraná, sendo que os resultados preliminares mostram que podem ser utilizadas, mas que é necessário um conhecimento sobre elas para que o processo seja produtiv