While non-perturbative high harmonic generation (HHG) has been a hot topic for decades, cascaded HHG is also a very rich problem and can have much higher efficiency. In collaboration with the Diddams group at NIST, we’ve investigated frequency comb generation via cascaded HHG in PPLN waveguides. A recently submitted paper can be found here: https://arxiv.org/abs/2102.04670