  Brillouin microscopy, which maps elastic modulus from the frequency shift of
scattered light, has evolved to a faster speed for the investigation of rapid
biomechanical changes. Impulsive stimulated Brillouin scattering (ISBS)
spectroscopy has the potential to speed up measurement through the resonant
amplification interaction from pulsed excitation and time-domain continuous
detection. However, significant progress has not been achieved due to the
limitation in signal-to-noise ratio (SNR) and the corresponding need for
excessive averaging to maintain high spectral precision. Moreover, the limited
spatial resolution also hinders its application in mechanical imaging. Here, by
scrutinizing the SNR model, we design a high-speed ISBS microscope through
multi-parameter optimization including phase, reference power, and acquisition
time. Leveraging this, with the further assistance of the Matrix Pencil method
for data processing, three-dimensional mechanical images are mapped under
multiple contrast mechanisms for a millimeter-scale polydimethylsiloxane
pattern immersed in methanol, enabling the identification of these two
transparent materials without any contact or labeling. Our experimental results
demonstrate the capability to maintain high spectral precision and resolution
at a sub-millisecond integration time for one pixel. With a two-order
improvement in the speed and a tenfold improvement in the spatial resolution
over the state-of-the-art systems, this method makes it possible for ISBS
microscopes to sensitively investigate rapid mechanical changes in time and
space.
