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.

High-order harmonic generation in the tunneling regime.

Abstract: We present systematic experimental studies of high-order harmonic generation in He and Ne that have been performed with an intense, femtosecond Ti:sapphire laser at intensities in the tunneling regime, where special attention is concentrated on the strong-field effect. A broad plateau is formed in the harmonic distribution that includes harmonic peaks at low and high orders and the observed highest orders (shortest wavelengths) are the 103rd (7.6 nm) for He and 95th (8.2 nm) for Ne. The laser-ellipticity-dependent harmonics observed suggest different generation processes for the low orders below and around the atomic ionization limit and for the high orders in and above the plateau region. The medium ionization is found to induce strong self-defocusing of the incident laser beam, and its effects on the harmonic generation are studied. The results for the defocusing and the blueshifts of the harmonic spectra observed show that the generation of a higher-order harmonic requires a higher intensity in time and space. The theoretically predicted harmonic cutoff is demonstrated to agree well with experiment when we take into account the interaction intensity limited in the ionizing medium. The characteristic harmonic behaviors observed are discussed based on the interaction intensity and the propagation effect in the medium.

Isolated high-order harmonics pulse from two-color-driven Bloch oscillations in bulk semiconductors

Abstract: We theoretically investigate the time-frequency characteristics of high-order harmonic generation (HHG) from Bloch-oscillating electrons in the band structure of a conventional bulk semiconductor driven by a single-optical-cycle two-color IR waveform. Spectrally filtering out the Bloch-HHG cutoff radiation allows the generation of an isolated Bloch-HHG pulse of $\ensuremath{\sim}$1.6-fs duration.

Revealing molecular structure and dynamics through high-order harmonic generation driven by mid-IR fields

Abstract: High-order harmonic generation (HHG) from molecules produces spectra that are modulated by interferences that encode both the static structure and the electron dynamics initiated by interaction with the laser field. Using a midinfrared (mid-IR) laser at $1300$ nm, we are able to study the region of the harmonic spectrum containing such interferences in ${\mathrm{CO}}_{2}$ over a wide range of intensities. This allows for isolation and characterization of interference minima arising due to subcycle electronic dynamics triggered by the laser field, which had previously been identified but not systematically separated. Our experimental and theoretical results demonstrate important steps toward combining attosecond temporal and angstrom-scale spatial resolution in molecular HHG imaging.

High-harmonic generation at 250 MHz with photon energies exceeding 100 eV

Abstract: Ultrafast spectroscopy in the extreme ultraviolet demands for ever-higher pulse repetition rates and photon energies. Here, we drive cavity-enhanced high-order harmonic generation (HHG) at a repetition rate of 250 MHz, with 30 fs pulses and an average power of 10 kW. Employing an optimized cavity geometry and a high-pressure gas target, we couple out nanowatt-level harmonics at photon energies around 100 eV. This constitutes an improvement of more than two orders of magnitude over previous megahertz-repetition-rate HHG experiments and paves the way toward high-photon-energy frequency-comb spectroscopy and toward pump-probe photoelectron microscopy and spectroscopy at unprecedented repetition rates.

Revealing molecular structure and dynamics through high harmonic generation driven by mid-IR fields

Abstract: High-order harmonic generation (HHG) from molecules produces spectra that are modulated by interferences that encode both the static structure and the electron dynamics initiated by interaction with the laser field. Using a midinfrared (mid-IR) laser at 1300 nm, we are able to study the region of the harmonic spectrum containing such interferences in CO{sub 2} over a wide range of intensities. This allows for isolation and characterization of interference minima arising due to subcycle electronic dynamics triggered by the laser field, which had previously been identified but not systematically separated. Our experimental and theoretical results demonstrate important steps toward combining attosecond temporal and angstrom-scale spatial resolution in molecular HHG imaging.