Sub-2-fs VUV Pulse Generation Carrying Orbital Angular Momentum

Bright and short VUV and DUV pulses generation is of prime interest and has numerous applications in chemistry since the laser pulse in this spectral range strongly interacts with atoms and molecules and thus can be used as a unique tool for time-resolved spectroscopy. Travers et al. [1] experimentally demonstrated the possibility of generating tunable VUV-DUV pulses (from 122 nm to 350 nm) in gas-filled hollow core fiber with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{J}$</tex> energy and sub-10-fs pulse duration with different spin states. In this theoretical work, we demonstrate that the orbital angular momentum of the pulse can also be preserved and transferred to the VUV-DUV dispersive waves resulting from soliton dynamics. Our home-made pulse propagation code is based on the UPPE model [2] including ad-hoc nonlinear source terms, namely Kerr effect, plasma dispersion and absorption by ionization. Pulse propagation in the gas-filled hollow core fiber is achieved by the use of a vectorial orthonormal basis of fiber modes including large number of OAM. To illustrate OAM transfer in the VUV range, we calculate the soliton dynamics of an initial pulse of 400 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{J}-10$</tex> fs centered at 800 nm propagating in a 1 meter-long, 250 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> of inner diameter capillary filled with 1.2 bar of helium pressure. The input beam is described by Laguerre-Gauss beam carrying the angular orbital momentum (OAM) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\ell=1(\text{LG}_{10})$</tex>. The waist of the beam is defined as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$w_{0}=0.56a$</tex> with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> being the capillary radius [3]. The input beam is decomposed on the canonical basis defined by the hollow-core fiber modes <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$EH_{21}, EH_{21}^{\pi/2}$</tex>, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$TE_{01}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$TM_{01}$</tex> [4].