High harmonic generation

About: High harmonic generation is a research topic. Over the lifetime, 11694 publications have been published within this topic receiving 222650 citations. The topic is also known as: HHG.

Phase-Dependent Harmonic Emission with Ultrashort Laser Pulses

Abstract: We consider harmonic generation by atoms exposed to an intense laser pulse of a few femtoseconds. Our results, obtained by solving numerically the corresponding three-dimensional time-dependent Schrodinger equation, demonstrate the strong sensitivity of the harmonic spectra to the phase of the laser. These results are explained in terms of both quantum and classical dynamics. We show that this phase sensitivity may be exploited in order to probe the laser phase for ultrashort pulses. Our discussion about this new method of diagnosis takes into account propagation effects.

Evaluation of fatigue damage using nonlinear guided waves

Abstract: This research develops an experimental procedure for characterizing fatigue damage in metallic plates using nonlinear guided waves. The work first considers the propagation of nonlinear waves in a dispersive medium and determines the theoretical and practical considerations for the generation of higher order harmonics in guided waves. By using results from the nonlinear optics literature, it is possible to demonstrate that both phase and group velocity matching are essential for the practical generation of nonlinear guided elastic waves. Next, the normalized acoustic nonlinearity of low cycle fatigue damaged aluminum specimens is measured with Lamb waves. A pair of wedge transducers is used to generate and detect the fundamental and second harmonic Lamb waves. The results show that the normalized acoustic nonlinearity measured with Lamb waves is directly related to fatigue damage in a fashion that is similar to the behavior of longitudinal and Rayleigh waves. This normalized acoustic nonlinearity is then compared with the measured cumulative plastic strain to confirm that these two parameters are related, and to reinforce the notion that Lamb waves can be used to quantitatively assess plasticity driven fatigue damage using established higher harmonic generation techniques.

Theory of the giant plasmon-enhanced second-harmonic generation in graphene and semiconductor two-dimensional electron systems

Abstract: An analytical theory of the nonlinear electromagnetic response of a two-dimensional (2D) electron system in the second order in the electric field amplitude is developed. The second-order polarizability and the intensity of the second harmonic signal are calculated within the self-consistent-field approach both for semiconductor 2D electron systems and for graphene. The second harmonic generation in graphene is shown to be about 2 orders of magnitude stronger than in GaAs quantum wells at typical experimental parameters. Under the conditions of 2D plasmon resonance the second harmonic radiation intensity is further increased by several orders of magnitude.

Phase-controlled amplification of few-cycle laser pulses

Abstract: Intense ultrashort waveforms of light that can be produced with an exactly predetermined electromagnetic field are essential in a number of applications of extreme nonlinear optics, most prominently in laser-driven sources of high-energy attosecond radiation. Field reproducibility in each laser shot requires stabilization of the carrier-envelope phase. The authors analyze different schemes of phase-stable pulse amplification and identify constraints limiting the precision with which the phase can be maintained. Next, they describe a phase-stabilized laser system based on a 20-fs multipass Ti:sapphire amplifier supplemented with a fiber compression stage for producing pulses in the few-cycle regime. It is shown that the amplifier introduces only a slow millihertz phase drift and, therefore, can be seeded by a standard phase-stabilized oscillator. This residual phase drift is assigned primarily to the beam pointing instability and can be precompensated in the phase-control loop of the seed oscillator using a feedback signal from a phase detector placed in the amplifier output. The phase stability of the resultant 5-fs 400-/spl mu/J pulses at a 1-kHz repetition rate is subsequently independently verified by higher order harmonic generation, in which different carrier-envelope phase settings are shown, both theoretically and experimentally, to produce distinctly different spectral shapes of the XUV radiation. From a series of such spectral patterns, the authors succeed in calibrating the value of the carrier envelope phase (with a /spl plusmn//spl pi/ ambiguity), which in turn allows them to fully characterize the temporal structure of the electric field of the laser pulses. The estimated precision of the phase control on the XUV target is better than /spl pi//5, which reduces the timing jitter between the driving laser pulse and the XUV bursts to /spl sim/ 250 as and opens the way to generate stable isolated attosecond pulses.

Multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser.

Abstract: We demonstrate a novel multimodal nonlinear spectral microscopy based on a femtosecond Cr:forsterite laser at 1230 nm. By acquiring the whole nonlinear spectrum in the visible and near-NIR region, this novel technique allows a combination of different imaging modalities, including second-harmonic generation, third-harmonic generation, and multiple-photon fluorescence. Combined with the selected excitation wavelength, which is located in the IR transparency window, this microscopic technique can provide high penetration depth with reduced damage and is ideal for studying living cells.