Self-Cascaded Noncritically-Phase-Matched Ktp Optical Parametric Oscillator for Generating Orthogonally Polarized Multi-Wavelength Emissions at 3 Μm

Mid-infrared self-cascaded noncritically-phase-matched (NCPM) KTP optical parametric oscillator (OPO) was developed, generating multiple wavelengths at 2950, 3293 and 3367 nm. The polarization state of 2950 nm is orthogonal to that of the other two wavelengths. Under 1064 nm intracavity pumping, the primary NCPM KTP-OPO can generate signal and idler light 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 KTP, generating the signal and idler waves at 2.95 and 3.36 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 2950 nm, 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 3293 and 3367 nm, the maximum total average output power, minimum pulse width and pulse peak power are 0.22 W, 2 ns and 26.7 kW, respectively. Our work provides an effective scheme to obtain multiple wavelength laser output in 3 μm region with orthogonal polarization state.