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 TEM₀₀ 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.

中文翻译：

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直接产生 ∼ 2.7 µm 的中红外脉冲光涡流

据我们所知，我们首次采用多晶 Fe:ZnSe 作为可饱和吸收剂 (SA) 在 2.7 µm 光谱范围内直接生成脉冲光学涡流。考虑到整形环形泵浦光束的传播特征的修改后的理论模型被详细阐述，以准确确定拉盖尔-高斯 (LG _{0, l} ) 模式的激发条件，产生与基本 TEM ₀₀相当的激光效率连续波 (CW) 模式中的模式。利用指定的模式匹配、高偏振消光比 (PER) 以及 SA 对其他横向模式的“空间滤波器”效应，成功地产生了具有明确旋向性的纳秒标量光学涡流。中红外区域中的这种标量涡旋激光脉冲将使新的应用成为可能，例如降频转换以产生更长（远红外）波长的光学涡旋、结构化有机材料、新型分子光谱等。