Ultrashort optical-pin excitation for scattering brain imaging

Imaging neural structures deep in brain tissue is central to understanding brain function, yet remains fundamentally limited by strong optical scattering and the requirement for accurate three-dimensional (3D) optical sectioning. Laser-scanning microscopy is a promising technique for brain imaging; however, maintaining excitation focus integrity in scattering media while preserving axial confinement poses a persistent photonic challenge. Here we introduce the optical pin, an ultrashort excitation regime engineered at the angular-spectrum level to address this limitation. By broadening the transverse angular bandwidth of a Bessel-type field while preserving its conical momentum-space architecture, the optical pin introduces a controlled longitudinal wave-vector spread that compresses the axial interference length to the micrometer scale, restoring Gaussian-like sectioning without sacrificing multi-angle interference. This excitation design yields substantially enhanced imaging performance, including [~]1.5-fold contrast improvement and [~]2.6-fold increased robustness to scattering. We validate the approach across transparent, scattering, and biological specimens, including bead phantoms, C. elegans, and mouse brain tissue. As a system-level excitation strategy, the optical pin is readily compatible with existing laser-scanning microscopy platforms and is particularly suited for scattering-limited brain imaging.