Generation of sub-terahertz repetition rates from a monolithic self-mode-locked laser coupled with an external Fabry-Perot cavity

A novel scheme to multiply the repetition rate of a monolithic self-mode-locked laser for generating sub-terahertz pulse sources is successfully demonstrated. A coated Yb:KGW crystal is designed to achieve a self-mode-locked operation at a repetition rate of 24 GHz with an average output power exceeding 1.0 W at a pump power of 4.8 W. A partially reflective mirror is utilized to combine with the output surface of the gain medium to constitute an external Fabry-Perot cavity. It is theoretically and experimentally verified that adjusting the external cavity length to satisfy the commensurate condition can lead to the frequency spacing to be various order harmonics of the mode spacing of the monolithic cavity. The maximum pulse repetition rate of the laser output can be up to 216 GHz and the pulse duration is as short as 330 fs. More importantly, the overall characteristics of the first-order temporal autocorrelation traces obtained by sequentially scanning the external cavity.length display an intriguing phenomenon of temporally fractional revivals, similar to the feature of spatial Talbot revivals.