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

Abstract

We investigate the spatio-spectral properties of extreme ultraviolet (XUV) high harmonic radiation driven by high repetition rate femtosecond laser systems. In the spatio-spectral domain, ring-shaped structures at each harmonic order associated with long-trajectory electrons are found to form arrow-shaped structures at the cutoff. These structures are observed with two different laser systems: an optical parametric chirped-pulse amplifier system at a central wavelength of 1.55 μm and 125 kHz repetition rate, and a temporally compressed femtosecond ytterbium fiber amplifier at 1.03 μm wavelength and 100 kHz repetition rate. As recently pointed out, the observed structures are well explained by considering the space-time atomic dipole-induced phase for short and long electron trajectories in the generation plane. The tighter focusing geometry and longer wavelength associated with these emerging driving laser systems increase the ring-like divergence and spectral broadening for high harmonics. Cutoff energies and photon fluxes obtained in argon and neon are also reported. Overall, these results shed new light on the properties of XUV radiation driven by these recently developed high average power laser systems, paving the way to high photon-flux XUV beamlines.

Generation of two successive attosecond pulses in separate spectral domains

“…First we have to mention that in all cases we investigated, the spectral separation observed in the near-field is preserved in the far-field. Moreover, the ring structure observed in the near-field at low orders is present also in the far-field, but the intensity is maximum on-axis, similar to the structures reported experimentally in 40,41 . Second, due to the low divergence of the harmonics (see Fig.…”

Generation and characterization of few-pulse attosecond pulse trains at 100kHz repetition rate

“…In recent years significant development of high repetition rate ( 10 kHz) high en-ergy laser sources enabled XUV generation at high repetition rates [8]. A number of groups have reported the generation of high-order harmonics at high repetition rate [9,10,11,12]. So far, with the exception of [13,14], who reported RABBITT experiments at 100 kHz using a fiber laser post-compressed to 40 fs, no pump-probe experiments or pulse characterization have been reported.…”

Liquid-cooled modular gas cell system for high-order harmonic generation using high average power laser systems

“…35 These two variables have further constraints in cases where the gas load in the vacuum chamber is of concern despite the application of a gas catcher 18,47,48 or skimmer. 39,49,50 Although pulsed valves can overcome these problems, the available repetition rate is currently limited to ∼5 kHz frequency. [44][45][46]51 For higher repetition rates, where pulsed valves cannot be utilized, continuous jets or gas cells with laser drilled front and rear apertures have been used for HHG.…”