Composite frequency comb spanning 0.4-2.4 μm from a femtosecond Ti:sapphire laser and synchronously pumped optical parametric oscillator

In this paper, we present the composite comb spectrum comprising the Ti:sapphire laser pulses and OPO signal and idler pulses with various SFM outputs. Comb offsets of the pump and OPO red (signal second-harmonic generation, SHG) and yellow (pump-idler SFM output) were determined by beating against a supercontinuum spectrum generated from the pump. We stabilised the entire spectrum by locking the laser repetition frequency (comb interval) to a 200 MHz clock and the comb offsets of the pump and one OPO output (red) to sub-harmonics of the same frequency. Feedback control over the pump offset was achieved by modulating the input power to the Ti:sapphire laser using an acousto-optic modulator, and over the OPO offset by fine-tuning the cavity length via a moveable end mirror mounted on a piezo-electric transducer.