The generation of near-and mid-infrared vortex mode is demonstrated from a 1 µm nanosecond optical vortex pumped optical parametric oscillator using a multi-grating MgO-doped periodically poled lithium niobate crystal with five grating domains. This system enables the orbital angular momentum between the signal and idler outputs to be exchanged simply by controlling the cavity Q-factor, and a vortex output in the wavelength ranges of 1.36-1.63 µm or 3.07-4.81 µm could be obtained. A maximum signal (idler) vortex output energy of 4.3 mJ (2.2 mJ) was achieved at a pump energy of 21 mJ, which corresponds to an optical-optical conversion efficiency of over 20% (10%).

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We propose a tunable millijoule-level 3-µm vortex laser formed with a 1-µm ns vortex pulse-pumped quasi-phase matching MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator with a singly resonant plane-parallel cavity configuration. The wavelength of the vortex output is tuned within the range of 3.360-3.677 µm merely by controlling the temperature of the MgO:PPLN crystal. The maximum vortex output energy of 2.14 mJ is obtained at the maximum pump energy of 21 mJ, and corresponds to an optical to optical conversion efficiency of 10.2% and a photon conversion efficiency of 33.5%. The handedness of the vortex output is controlled just by inverting the handedness of the pump vortex beam.

We report a millijoule-level mid-infrared MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator pumped by a 1.064 µm nanosecond laser. The maximum mid-infrared 3.5 µm idler output energy reached 3.65 mJ at the pump energy of 21 mJ, corresponding to a photon conversion efficiency of 57%. The wavelength tunabilities of the signal and idler outputs were also realized, with the continuous tuning ranges of 1.501 to 1.558 µm and 3.650 to 3.353 µm, respectively, by controlling the temperature of the MgO:PPLN crystal. The beam quality factor (M 2 ) of the mid-infrared idler output was measured to be <1.75.

Frequency up-conversion is an effective method of mid-infrared (MIR) detection by converting the long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate the MIR light carrying orbital angular momentum (OAM) from a difference frequency generation process and perform the up-conversion of it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, which is achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.