A system includes an optical parametric oscillator (OPO) device. The OPO device has an optical resonator, a first nonlinear optical element (NLO) and a second non-linear optical element (NLO). The first NLO can produce, via OPO of a first pump beam, a first output with a first frequency and a second output with a second frequency. The second frequency is lower than the first frequency. The second NLO can produce, via OPO of a second pump beam (with a higher frequency than the first), a third output with a third frequency and a fourth output with a fourth frequency. The fourth frequency is lower than the third frequency. The first frequency is the same, or at least substantially the same, as the fourth frequency. The OPO device is configured to resonate at the first frequency and the fourth frequency.