Production of coherent 150 nm light via 7$^{\text{th}}$ harmonic generation for nuclear spectroscopy applications

The $7^{\text{th}}$ harmonic generation of $1030\,\text{nm}$ light constitutes a rather unexplored regime within the field of harmonic generation. The resulting coherent light with a wavelength of roughly $150\,\text{nm}$ can be utilized for a wide range of novel applications, in particular the recently emerging field of nuclear spectroscopy of the Thorium-229 isotope nucleus. In this work, we measure the total output pulse energy and conversion efficiency of $150\,\text{nm}$ light via $7^{\text{th}}$ harmonic generation of a $200\,\text{fs}$, $200\,\text{µJ}$, Yb:KGW laser in rare gases. The measured values are corrected by their losses resulting mainly from re-absorption effects on the harmonic beam. The re-absorption is determined experimentally for each nonlinear medium (Ar, Kr, Xe) and for air. Furthermore a mathematical model is derived, including ionization effects and taking into account the overall geometry of the free-expanding gas-jet medium. Numerical simulations are computed using this model and compared to the experimental results. Additionally a new experimental scheme is proposed based on a Herriott-type multi-pass configuration for $7^{\text{th}}$ harmonic generation