High harmonic cutoff energy scaling and laser intensity measurement with a 1.8 μm laser source

Abstract

High harmonic generation in gas targets leads to the production of attosecond pulses. The process of high harmonic generation requires that the gas be ionized by an intense femtosecond laser field. The highest photon energy produced is related to the laser intensity times the wavelength squared. This cutoff is reached only if good phase matching is achieved. Using a laser with a wavelength of 1800 nm, we estimate the laser intensity in the gas jet by recording the ion yield, and simultaneously record the high harmonic spectrum. We show that the cutoff energy matches the measured intensity, confirming that good phase matching is achieved to 100 eV. We also use the ion collector to characterize the spatial size of the gas jet and to measure the confocal parameter of the laser beam, parameters that are useful for numerical modelling.

The ELI-ALPS facility: the next generation of attosecond sources

“…One SYLOS-driven beamline (GHHG SYLOS LONG) will employ an extremely loose focusing scheme, and will be coupled with a long interaction cell and very low gas pressures. This combination obeys geometrical scaling predictions and pressure related phase matching considerations governing GHHG in extended media [23][24][25]. The other SYLOS-driven beamline (GHHG SYLOS COMPACT) will also rely on loose focusing, but will utilize a high-pressure medium where phase matching is ensured by the short interaction length [26].…”

Higher order harmonic generation and strong field ionization with Bessel-Gauss beams in a thin jet geometry

“…A channel electron multiplier (CEM, channeltron) is placed several centimeters behind the gas jet and slightly offset to allow for simultaneous measurement of ionization yield and HHG signal. This technique was used to demonstrate phase matching conditions in the past [36,37]. The source chamber is kept at 6.66 x 10 -5 mbar during operation by a 2000 L/s magnetic levitation turbo pump to prevent reabsorption in the ambient backing pressure [38].…”

Ionization Study of Isomeric Molecules in Strong-field Laser Pulses

“…This is a similar procedure as that used in ref. 29 , but in a full gaussian volume, where the ion yield from a calibration gas as a function of pulse energy is fit to theory. Theoretical ionization yields for argon were determined using a method developed by Yudin and Ivanov 13 termed nonadiabatic tunnel ionization theory (NTI).…”

“…Nevertheless, in HHG, XUV radiation due to the motion of the electron in the continuum is driven by a strong laser field. The HHG process depends on ionization as a first step 26 27 28 29 , and thus provides a somewhat convoluted measurement of the ionization. Therefore, a direct measurement and comparison of the ionization yields is needed to shed some light on this controversy.…”