Multi-GHz repetition rate, femtosecond deep ultraviolet source in burst mode derived from an electro-optic comb

We present a femtosecond, 11.48 GHz intra-burst repetition rate deep UV source at 258 nm based on forth-harmonic generation (FHG) of an electro-optic (EO) comb operating in burst mode. Second-harmonic generation (SHG) of the burst-mode EO comb in LiB₃O₅ (LBO) leads to 3.7 W average power and 242 fs root-mean-square pulse duration. A second stage of SHG is further performed using two separate β-BaB₂O₄ (BBO) crystals, delivering deep UV pulses at 523 mW and 294 mW, with estimated pulse durations of half-ps and sub-300 fs, respectively. At divided pulse repetition rates of 5.7 GHz and 2.9 GHz, FHG is also demonstrated, highlighting the potential of flexible repetition rate operation at the GHz level.