Toward vacuum ultraviolet (VUV) dual-comb spectroscopy

Intra-cavity high harmonic generation (iHHG) using a femtosecond enhancement cavity (fsEC) has been proven to be an efficient approach to generate coherent vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) frequency combs. Current VUV or XUV light sources such as synchrotron or excimer lasers either require large facilities or have limited coherence. High resolution measurements in VUV and XUV are of great importance in many areas including tests of fundamental physics, astronomy, as well as in searches for direct excitation of nuclear transitions such as the 229Th M1 isomeric nuclear transition. Direct spectroscopy with a single frequency comb is challenging due to the potential for congestion and overlap of the comb teeth with the transitions of interest. We have pursued a VUV dual-frequency comb system to enable the study of a broader range of atomic and molecular transitions. In this poster, we will show our preliminary results towards the VUV dual-comb utilizing the 3rd (~355 nm) and 5th (213 nm) harmonics from a pair of fsEC's.