Spatially and spectrally resolved quantum path interference with chirped driving pulses

Abstract

We measure spectrally and spatially resolved high-order harmonics generated in argon using chirped multi-cycle laser pulses. Using a stable, high-repetition rate laser we observe detailed interference structures in the far-field. The structures are of two kinds; off-axis interference from the long trajectory only and on-axis interference including the short and long trajectories. The former is readily visible in the far-field spectrum, modulating both the spectral and spatial profile. To access the latter, we vary the chirp of the fundamental, imparting different phases on the different trajectories, thereby changing their relative phase. Using this method together with an analytical model, we are able to explain the on-axis behaviour and access the dipole phase parameters for the short (a s ) and long (a l ) trajectories. The extracted results compare very well with phase parameters calculated by solving the time-dependent Schrödinger equation. Going beyond the analytical model, we are also able to successfully reproduce the off-axis interference structure.

Spatio-spectral structures in high harmonic generation driven by tightly focused high repetition rate lasers

“…There has been a large number of reports of the spatiospectral features of HHG, including various physical effects such as multiple quantum paths interference [17][18][19][20], Maker fringes related to phase-matching effects [21], and space-time atomic dipole phase [22]. These works have been done with Ti:Sa systems at a central wavelength of 800 nm.…”

High-Harmonic and Terahertz Spectroscopy (HATS): Methods and Applications

“…Harmonic phase of the short trajectory contribution could be balanced by the Gouy phase shift, the neutral gas dispersion, the dispersion of plasma (if the ionization is significant) and the phase of the atomic dipole moment [60], to give a clear linear relationship. It is interesting to investigate the spatially and spectrally resolved quantum paths of the long and short trajectories of electrons from experiment and theory [61][62][63][64][65]. The joint measurement of HATS is a supplementary to these results, which can use THz wave generation as a phase reference for the long and short trajectories of electrons.…”

Spatial characterization of light beams analyzed by cylindrical-grating slit-less spectrometers

“…For a slit-less spectrometer, the case is different, because the object of imaging is the source plane itself. At the same time, a slit-less spectrometer with a cylindrical element images the source only along one axis, in the direction the optical element is curved, and in which grating diffraction on grating groovesthe dispersion of different wavelength components -happens [7,9,12,20,21]. In the model the case is simplified to imaging with a cylindrical optical element (like an ideal cylindrical lens), the way it is depicted in Fig.…”

“…Obtaining further information on the radiation or the source emitting it, spectrometers are often utilized to provide spatial information along with spectrally resolving the radiation. This gives access to spatio-spectral features [2][3][4][5][6][7][8][9][10][11]. For spatio-spectral analysis, the "spatial" axis is often referred to as "divergence" axis [4,[6][7][8][9][10][11][12].…”

“…They more and more widely appear in gas-HHG experiments and in applications of such XUV sources [7,9,11,12,20,21], or for the analysis of surface plasma-HHG radiation [22]. These flat-field spectrometers usually make use of a cylindrical grating which diffracts (or disperses, meaning that it spectrally resolves) and images the radiation along one axis, and allows free-space propagation of the radiation by simple reflection along the other (perpendicular) axis [7,9,12,20,21]. If such slit-less spectrometers are used, the spatial information does not come from a line segment of the beam provided by the slit, but from all parts of the studied beam.…”