Direct generation of mid-infrared pulsed optical vortices at ∼ 2.7 µm
Qinggang Gao, Jingjing Zhou, Daiwen Jia, Yinyin Wang, Bin Chen, Peng Liu, Zixuan Huang, Kangzhen Tian, Shande Liu, Yuping Zhang, Huiyun Zhang, Zhanxin Wang, Yongguang Zhao
Abstract
We present the first, to the best of our knowledge, direct generation of pulsed optical vortices in the 2.7-µ m spectral range by employing polycrystalline Fe:ZnSe as a saturable absorber (SA). A modified theoretical model taking into account the propagation features of the reshaped annular pump beam is elaborated to accurately determine the excitation conditions of the Laguerre–Gaussian (LG 0, l ) modes, yielding a lasing efficiency comparable to the fundamental TEM 00 mode in continuous-wave (CW) regime. Nanosecond scalar optical vortices with well-defined handedness are successfully produced by taking advantages of designated mode-matching, high polarization extinction ratio (PER), and the "spatial filter" effect of the SA on other transverse modes. Such scalar vortex laser pulses in the mid-infrared region will enable new applications such as frequency down conversion to produce optical vortices at longer (far-infrared) wavelengths, structuring organic materials, novel molecular spectroscopy, etc.