Certain embodiments relate to and involve producing broadband phase-locked frequency combs in the near-infrared and mid-infrared spectral ranges. One such embodiment is directed to a system, with a pump laser and an optical parametric oscillator (OPO) resonator, that is configured to produce broad-bandwidth frequency combs in the near-infrared and mid-infrared frequency ranges. The pump laser is configured to produce femtosecond pulses of light having a pulse repetition rate. The optical parametric oscillator (OPO) resonator that is coupled to the pump laser for facilitating synchronous OPO pumping by matching a roundtrip time of the pulses of light within the OPO resonator with the pulse repetition rate of the pump laser. Among other more specific aspects, the OPO resonator can include a nonlinear optical gain element to provide broad-bandwidth parametric amplification, and optical elements to direct the pulses of light from the femtosecond laser to the nonlinear gain element and to direct subharmonic frequencies of the light out of the optical cavity.