  Quantitative phase imaging (QPI) is often used for label-free single cell
analysis with its high-contrast images of optical phase delay (OPD) map.
Contrary to other imaging methods, sensitivity improvement has not been
intensively explored because conventional QPI is sensitive enough to see
surface roughness of a substrate which anyway restricts the measurable minimum
OPD. However, emerging QPI techniques which utilize, for example, differential
image analysis of consecutive temporal frames, such as mid-infrared
photothermal QPI, mitigate the minimum OPD limit by decoupling the static OPD
contribution and allow to measure much smaller OPD. Here, we propose and
demonstrate super-sensitive QPI with expanded dynamic range. It is enabled by
adaptive dynamic range shift with combination of wavefront shaping and
dark-field QPI techniques. As a proof-of-concept demonstration, we show dynamic
range expansion (sensitivity improvement) of QPI by a factor of 6.6 and its
utility for improving sensitivity of mid-infrared photothermal QPI. This
technique can also be applied for wide-field scattering imaging of dynamically
changing nanoscale objects inside and outside a biological cell without losing
global cellular morphological image information.
