Abstract Beyond diffraction limit, multitrapping of nanoparticles is important in numerous scientific fields, including biophysics, materials science and quantum optics. Here, we demonstrate the 3-dimensional (3D) shell-like structure of optical trapping well induced by nonlinear optical effects in the femtosecond Gaussian beam trapping for the first time. Under the joint action of gradient force, scattering force and nonlinear trapping force, the gold nanoparticles can be stably trapped in some special positions, or hop between the trap positions along a route within the 3D shell. The separation between the trap positions can be adjusted by laser power and numerical aperture (NA) of the trapping objective lens. With a high NA lens, we achieved dual traps with less than 100 nm separation without utilizing complicated optical systems or any on-chip nanostructures. These curious findings will greatly extend and deepen our understanding of optical trapping based on nonlinear interaction and generate novel applications in various fields, such as microfabrication/nanofabrication, sensing and novel micromanipulations.

中文翻译：

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飞秒激光俘获中非线性效应引起的超出衍射极限的球状陷阱壳

摘要 超越衍射极限，纳米粒子的多重捕获在许多科学领域都很重要，包括生物物理学、材料科学和量子光学。在这里，我们首次展示了由飞秒高斯光束捕获中的非线性光学效应引起的光捕获阱的 3 维 (3D) 壳状结构。在梯度力、散射力和非线性俘获力的共同作用下，金纳米粒子可以被稳定地俘获在一些特殊的位置，或者沿着 3D 壳内的路线在俘获位置之间跳跃。陷阱位置之间的间隔可以通过激光功率和陷阱物镜的数值孔径 (NA) 进行调整。使用高NA镜头，我们在不使用复杂的光学系统或任何片上纳米结构的情况下实现了间隔小于 100 nm 的双陷阱。这些奇怪的发现将极大地扩展和加深我们对基于非线性相互作用的光捕获的理解，并在各个领域产生新的应用，例如微制造/纳米制造、传感和新型微操作。