Near-field imaging techniques, at terahertz frequencies (1–10 THz), conventionally rely on bulky laser sources and detectors. Here, we employ a semiconductor heterostructure laser as a THz source and, simultaneously, as a phase-sensitive detector, exploiting optical feedback interferometry combined with scattering near-field nanoscopy. We analyze the amplitude and phase sensitivity of the proposed technique as a function of the laser driving current and of the feedback attenuation, discussing the operational conditions ideal to optimize the nano-imaging contrast and the phase sensitivity. As a targeted nanomaterial, we exploit a thin (39 nm) flake of Bi₂Te_2.2Se_0.8, a topological insulator having infrared active optical phonon modes. The self-mixing interference fringes are analyzed within the Lang–Kobayashi formalism to rationalize the observed variations as a function of Acket’s parameter C in the full range of weak feedback (C < 1).

中文翻译：

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不同反馈机制下基于无探测器激光反馈干涉测量的太赫兹近场纳米技术

太赫兹频率（1-10 THz）的近场成像技术通常依赖于庞大的激光源和探测器。在这里，我们采用半导体异质结构激光器作为太赫兹源，同时作为相敏探测器，利用光反馈干涉测量法与散射近场纳米显微镜相结合。我们分析了所提出技术的幅度和相位灵敏度作为激光器驱动电流和反馈衰减的函数，讨论了优化纳米成像对比度和相位灵敏度的理想操作条件。作为目标纳米材料，我们开发了薄的 (39 nm) Bi ₂ Te _2.2 Se _0.8薄片，具有红外有源光声子模式的拓扑绝缘体。在 Lang-Kobayashi 形式主义中分析自混合干涉条纹，以将观察到的变化合理化为在弱反馈的整个范围内 (C < 1) 的 Acket 参数 C 的函数。