Bond-Selective Transient Phase Microscopy

Abstract: Phase-contrast microscopy converts the optical phase introduced by transparent, unlabeled specimens into modulation in the intensity image. Modern phase imaging techniques are capable of quantifying phase shift at each point in the field of view, enabling non-destructive applications in materials and life sciences. However, these attractive features come with the lack of molecular information. To fulfill this gap, we developed a bond-selective transient phase (BSTP) microscope using infrared absorption to excite molecular vibration, resulting in an optical phase change detected through a customized phase microscope. By using pulsed pump and probe lasers, we realized BSTP imaging with high spectral fidelity, sub-microsecond temporal resolution, submicron spatial resolution at 50 frames per second, limited only by the camera sensor. Our approach links the missing molecular bond information to the quantitative phase, which paves a new avenue for spectroscopic imaging in biology and materials science.