Multi-gigahertz, femtosecond Airy beam optical parametric oscillator pumped at 78 MHz

摘要

We report a high power ultrafast Airy beam source producing femtosecond pulses at multi-gigahertz (GHz) repetition rate (RR). Based on intra-cavity cubic phase modulation of an optical parametric oscillator (OPO) designed in high harmonic cavity configuration synchronous to a femtosecond Yb-fiber laser operating at 78?MHz, we have produced ultrafast 2D Airy beam at multi-GHz repetition rate through the fractional increment in the cavity length. While small (1?mm) crystals are used in femtosecond OPOs to take the advantage of broad phase-matching bandwidth, here, we have exploited the extended phase-matching bandwidth of a 50-mm long Magnesium-oxide doped periodically poled LiNbO3 (MgO:PPLN) crystal for efficient generation of ultrafast Airy beam and broadband mid-IR radiation. Pumping the MgO:PPLN crystal of grating period, Λ?=?30?μm and crystal temperature, T?=?100?°C using a 5-W femtosecond laser centred at 1064?nm, we have produced Airy beam radiation of 684?mW in ~639?fs (transform limited) pulses at 1525?nm at a RR of ~2.5?GHz. Additionally, the source produces broadband idler radiation with maximum power of 510?mW and 94?nm bandwidth at 3548?nm in Gaussian beam profile. Using an indirect method (change in cavity length) we estimate maximum RR of the Airy beam source to be ~100?GHz.