Pulsed heterodyne Brillouin detection enables high-resolution epi-detected biomechanical microscopy and endoscopy

Brillouin microscopy enables non-contact, three-dimensional mapping of viscoelasticity in living systems, yet two long-standing limitations have constrained its biological reach: the lack of high-spectral-resolution epi-detection and the absence of practical fiber-compatible implementations. Here we introduce pulsed heterodyne Brillouin detection (PHBD), a coherent time-domain scheme addressing both challenges. By combining high-peak-power pulsed excitation with shot-noise-limited detection, PHBD reduces the optical dose by approximately two orders of magnitude relative to continuous-wave heterodyne approaches. In an epi-microscope configuration, PHBD attains a spectral resolution of 27 MHz, a tenfold improvement over state-of-the-art Brillouin microscopes, enabling high-specificity, low-phototoxicity imaging of live cells and complex tissues. In an endoscopic configuration, coherent gating rejects parasitic Brillouin background from the delivery fiber, accelerating acquisition by two to three orders of magnitude over previous fiber-optic Brillouin endoscopes. Together, these capabilities establish a unified platform for single-ended, fiber-compatible Brillouin biomechanics, extending mechanical imaging and spectroscopy from cells to deep tissues via minimally invasive probes.