Second-harmonic generation microscopy is a valuable label-free modality for imaging non-centrosymmetric structures and has important biomedical applications from live-cell imaging to cancer diagnosis. Conventional second-harmonic generation microscopy measures intensity signals that originate from tightly focused laser beams, preventing researchers from solving the scattering inverse problem for second-order nonlinear materials. Here, we present harmonic optical tomography (HOT) as a novel modality for imaging microscopic, nonlinear and inhomogeneous objects. The HOT principle of operation relies on interferometrically measuring the complex harmonic field and using a scattering inverse model to reconstruct the three-dimensional distribution of harmonophores. HOT enables strong axial sectioning via the momentum conservation of spatially and temporally broadband fields. We illustrate the HOT operation with experiments and reconstructions on a beta-barium borate crystal and various biological specimens. Although our results involve second-order nonlinear materials, we show that this approach applies to any coherent nonlinear process.

二次谐波显微术是一种用于非中心对称结构成像的有价值的无标记方式，具有从活细胞成像到癌症诊断的重要生物医学应用。传统的二次谐波产生显微镜测量源自紧密聚焦的激光束的强度信号，从而阻止研究人员解决二阶非线性材料的散射逆问题。在这里，我们将谐波光学断层扫描 (HOT) 作为一种用于成像微观、非线性和非均匀物体的新方式。HOT 的工作原理依赖于干涉测量复谐波场并使用散射逆模型来重建谐波的三维分布。HOT 通过空间和时间宽带场的动量守恒实现强大的轴向切片。我们通过对 β-硼酸钡晶体和各种生物标本的实验和重建来说明热操作。尽管我们的结果涉及二阶非线性材料，但我们表明这种方法适用于任何相干非线性过程。