Brillouin gain microscopy

Optical imaging techniques with mechanical contrast, including passive microrheology, optical coherence elastography and Brillouin microscopy, are critical for material and biological discovery owing to their less perturbative nature compared with traditional mechanical imaging methods. An emerging optical microscopy approach for mechanical imaging is stimulated Brillouin scattering microscopy, which has been shown to be useful for biomechanical imaging with high sensitivity and specificity. However, the excitation energy used is high and the temporal resolution remains limited by the need to acquire full spectra. Here we develop Brillouin gain microscopy that detects the Brillouin gain at a specific mechanically contrasting frequency corresponding to a Brillouin acoustic-vibrational mode of interest in the sample. Brillouin gain microscopy affords a 200-fold improvement in temporal resolution compared with stimulated Brillouin scattering microscopy, down to 100 μs at excitation energy as low as 23 μJ. Using Brillouin gain microscopy, we demonstrate cross-sectional, all-optical mechanical imaging of materials as well as of the structure and dynamics in living systems with low excitation energy and at high temporal resolution.