A broadband active metasurface is designed around quantum-cascade (QC) gain material for use in a broadband tunable QC vertical external-cavity surface-emitting laser (VECSEL). The metasurface is based on a unit cell containing two resonant waveguide elements that couple with the periodicity of the metasurface to produce a multi-resonant reflection spectrum. Simulated reflectance spectra exhibit full-width half-maximum bandwidths up to 50% of the centre frequency. The tested QC-VECSEL demonstrates up to 15 mW of peak pulse power at 77 K and supports multimode lasing from 2.85 to 3.9 THz (>30% fractional bandwidth around 3.37 THz). The frequency coverage is limited by how short the cavity can be made, rather than the metasurface bandwidth. Consistent multimoding results from non-uniform distribution of spectral energy across the surface.

中文翻译：

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太赫兹量子级联 VECSEL 的宽带超表面设计

宽带有源超表面是围绕量子级联 (QC) 增益材料设计的，用于宽带可调谐 QC 垂直外腔表面发射激光器 (VECSEL)。超表面基于包含两个谐振波导元件的晶胞，这些元件与超表面的周期性耦合以产生多谐振反射光谱。模拟反射光谱表现出高达中心频率 50% 的全宽半最大带宽。经测试的 QC-VECSEL 在 77 K 下展示了高达 15 mW 的峰值脉冲功率，并支持 2.85 至 3.9 THz 的多模激光（3.37 THz 附近 >30% 的分数带宽）。频率覆盖范围受制于腔体的长度，而不是超表面带宽。一致的多模是由于整个表面的光谱能量分布不均匀造成的。