# Optical Vortex-Pumped KTiOAsO\({}_{4}\) Narrow-Linewidth Picosecond-Pulsed Parametric Oscillator  
[PERSON]  
1 Xinjang Key Laboratory for Luminescence Minerals and Optical Functional Materials, School of Physics and Electronic Engineering, Xinjang Normal University, Urumqi 830054, China; [EMAIL_ADDRESS] (X.J.); [EMAIL_ADDRESS] (M.A.); zhou_yx@[EMAIL_ADDRESS] (Y.  
and off-axis pumping configurations [26]. However, these techniques are restricted to generating vortex laser beams within the visible and near-infrared wavelength range; thus, there is an urgent need for technologies that can extend the wavelength range.  
To identify appropriate mode converters, nonlinear optics has been employed as an alternative approach to generate optical beams with diverse spatial structures. Optical parametric oscillation (OPO) is a second-order nonlinear process that has been widely utilized for laser frequency conversion [27; 28]. On continuous wave and nanosecond pulse time scales, OPO has been utilized to generate optical vortex beams in the near- and mid-infrared regions [29; 30; 24]. In contrast, investigations into generating picosecond optical vortex beams have been seldom reported. Picosecond vortex lasers can be applied for the cold-etching effect to fabricate high-aspect-ratio chiral nanostructures, and narrow-linewidth mid-infrared picosecond vortex-pulsed lasers have considerable potential in the manufacturing of twisted organic materials, super-resolution molecular absorption microscopy, and super-resolution molecular spectroscopy [31]. In 2018 and 2022, [PERSON] et al. reported that the OPOs using MgO-doped periodically polarized lithium tantalate/niobate (MgOOs*PPLT and MgO:PPLN) crystals were capable of generating tunable picosecond-pulsed vortex laser beams with an order of \(\ell\) = 1-5 within the mid-infrared wavelength range [32; 33]. In 2024, our group successfully achieved wide-tunable (with a wavelength range of 1.3-5 \(\upmu\)m) picosecond-pulsed vortex laser output with an order of \(\ell\) = 1 by employing MgO:PPLN crystals [28]. Nevertheless, due to the broad acceptance angle in PPLN crystals, the spectral linewidths of the generated signal and idler fields were quite broad. For the aforementioned applications, it was obvious that narrow-linewidth picosecond-pulsed vortex laser sources were preferred. To date, we have verified that an optical vortex output with a narrower linewidth than that of the PPLN-OPO can be produced using a KTA-OPO pumped with a nanosecond optical vortex laser, which can be attributed to the narrower acceptance angle of the KTA [29; 34; 35].  
In this paper, we propose a method for generating narrow-linewidth ultrafast vortex laser emission in the near- and mid-infrared wavelength regions using a 1064 nm picosecond optical vortex to pump a KTA-OPO. The selective transfer of the OAM of the pump field to the signal or idler fields was achieved by modifying the position of the pump beam focused on the KTA crystal. A maximum average output power of 2.14 W was attained at the signal vortex field, and at the idler vortex field, it was 0.95 W. The spectral linewidths of the signal and idler vortex fields were 0.502 nm and 1.216 nm, respectively. To the best of our knowledge, this is the narrowest linewidth obtained by picosecond vortex beam pumping an OPO. Our work indicates the significant potential of the KTA crystal in the field of narrow-linewidth picosecond vortex lasers in the near- and mid-infrared wavebands.