  Rapid mapping of the mechanical properties of soft biological tissues from
light microscopy to macroscopic imaging could transform fundamental biophysical
research by providing clinical biomarkers to complement in vivo elastography.
We here introduce superfast optical time-harmonic elastography (OTHE) to
remotely encode surface and subsurface shear wave fields for generating maps of
tissue stiffness with unprecedented detail resolution. OTHE rigorously exploits
the space-time propagation characteristics of time-harmonic waves to address
current limitations of biomechanical imaging and elastography. Key solutions
are presented for stimulation, encoding, and stiffness reconstruction of
time-harmonic, multifrequency shear waves, all tuned to provide consistent
stiffness values across resolutions from microns to millimeters. OTHE's
versatility is demonstrated in Bacillus subtilis biofilms, zebrafish embryos,
adult zebrafish, and human skeletal muscle, reflecting the diversity of the
phylogenetic tree from a mechanics perspective. By zooming in on stiffness
details from coarse to finer scales, OTHE advances developmental biology and
offers a way to perform biomechanics-based tissue histology that consistently
matches in vivo time-harmonic elastography in patients.
