Self-cascaded noncritically-phase-matched KTP optical parametric oscillator for generating orthogonally polarized multi-wavelength emissions at 3 μm

Abstract

Mid-infrared self-cascaded noncritically-phase-matched (NCPM) KTP optical parametric oscillator (OPO) was developed, generating multiple wavelengths at 2.95, 3.29 and 3.37 μm. The polarization state of 2.95 μm is orthogonal to that of the other two wavelengths. Under 1064 nm intracavity pumping, the first NCPM KTP-OPO can generate signal and idler waves at 1.57 and 3.29 μm, respectively. Then the 1.57 μm is further used as pump light for the second NCPM OPO in the same KTP, generating signal and idler waves at 2.95 and 3.37 μm. Broadband spectral feedback condition is established between the OPO cavity mirrors, enabling the two NCPM OPOs to operate simultaneously in the same KTP and OPO resonator. With regard to 2.95 μm, the achieved maximum average output power and minimum pulse width are respectively 1.18 W and 5 ns, corresponding to a pulse peak power of 56.9 kW with 4.2 kHz repetition rate. As for the dual-wavelength at 3.29 and 3.37 μm, the maximum total average output power is 0.22 W. Our work provides an effective scheme to obtain multiple wavelength laser output in 3 μm region with orthogonal polarization state.