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

Advances of ultraviolet light sources: towards femtosecond pulses in the few-cycle regime

Chapter 5 describes the efforts being made to reach the few-optical-cycle regime for ultraviolet pulses. The main route to achieve this task is to exploit low dispersion gas media for frequency up-conversion of Ti:Sa and Ytterbium:YAG laser sources. UV generation methods to obtain few-fs (sub 3-fs) pulse duration are discussed, providing state-of-the-art UV sources as a key ingredient in the field of ultrafast UV spectroscopy. Applications to study in real time the ultrafast response of photoexcited states of matter are discussed by the authors

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18 THz

We demonstrate the generation of narrowband (<1 THz) high-energy (~2 uJ) carrier-envelope phase-stable pulses, tunable between 4 and 18 THz as achieved by difference-frequency mixing between chirped near-infrared pulses in organic DSTMS

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18 THz

We demonstrate the generation of narrowband (<1 THz) high-energy (~2 uJ) carrier-envelope phase-stable pulses, tunable between 4 and 18 THz as achieved by difference-frequency mixing between chirped near-infrared pulses in organic DSTMS

Percutaneous Coronary Revascularization after Out-of-Hospital Cardiac Arrest: A Review of the Literature and a Case Series

Out-of-hospital cardiac arrest (OHCA) is still associated with high mortality and severe complications, despite major treatment advances in this field. Ischemic heart disease is a common cause of OHCA, and current guidelines clearly recommend performing immediate coronary angiography (CAG) in patients whose post-resuscitation electrocardiogram shows ST-segment elevation (STE). Contrarily, the optimal approach and the advantage of early revascularization in cases of no STE is less clear, and decisions are often based on the individual experience of the center. Numerous studies have been conducted on this topic and have provided contradictory evidence; however, more recently, results from several randomized clinical trials have suggested that performing early CAG has no impact on overall survival in patients without STE

Probing the electronic structure of multi-walled carbon nanotubes by transient optical transmittivity

High-resolution time resolved transmittivity measurements on horizontally aligned free-standing multi-walled carbon nanotubes reveal a different electronic transient behavior from that of graphite. This difference is ascribed to the presence of discrete energy states in the multishell carbon nanotube electronic structure. Probe polarization dependence suggests that the optical transitions involve definite selection rules. The origin of these states is discussed and a rate equation model is proposed to rationalize our findings

Vibrational coherent control of localized d\u2013d electronic excitation

Addressing the role of quantum coherence in the interplay between the different matter constituents (electrons, phonons and spin) is a critical step towards understanding transition metal oxides and designing complex materials with new functionalities. Here we use coherent vibrational control of on-site d\u2013d electronic transitions in a model edge-sharing insulating transition metal oxide (CuGeO3) to single out the effects of vibrational coherence in electron\u2013phonon coupling. By comparing time-domain experiments based on high- and low-photon-energy ultrashort laser excitation pulses with a fully quantum description of phonon-assisted absorption, we could distinguish the processes associated with incoherent thermal lattice fluctuations from those driven by the coherent motion of the atoms. In particular, while thermal fluctuations of the phonon bath uniformly increase the electronic absorption, the resonant excitation of phonon modes also results in light-induced transparency that is coherently controlled by the vibrational motion

Generation of deep ultraviolet sub-2-fs pulses

We demonstrate the generation of few-cycle deep ultraviolet pulses via frequency upconversion of 5-fs near-infrared pulses in argon using a laser-fabricated gas cell. The measured spectrum extends from 210 to 340 nm, corresponding to a transform-limited pulse duration of 1.45 fs. We extract from a dispersion-free second-order cross-correlation measurement a pulse duration of 1.9 fs, defining a new record in the deep ultraviolet spectral range

Postcompression of picosecond pulses into the few-cycle regime

In this work,we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power

Post-compression of high average power picosecond pulses for few cycle generation and FEL pump-probe experiments

We demonstrate post-compression of 1.2 ps pulses to the few-cycleregime via multi-pass spectral broadening. We achieve compressionfactors of 40 via single and >90 via dual stage compression employingmJ pulses. Long term stability measurements show that suchpost-compression setup can be employed for FEL pump-probe experiments