  Recovering molecular information remains a grand challenge in the widely used
holographic and computational imaging technologies. To address this challenge,
we developed a computational mid-infrared photothermal microscope, termed
Bond-selective Intensity Diffraction Tomography (BS-IDT). Based on a low-cost
brightfield microscope with an add-on pulsed light source, BS-IDT recovers both
infrared spectra and bond-selective 3D refractive index maps from
intensity-only measurements. High-fidelity infrared fingerprint spectra
extraction is validated. Volumetric chemical imaging of biological cells is
demonstrated at a speed of ~20 seconds per volume, with a lateral and axial
resolution of ~350 nm and ~1.1 micron, respectively. BS-IDT's application
potential is investigated by chemically quantifying lipids stored in cancer
cells and volumetric chemical imaging on Caenorhabditis elegans with a large
field of view (~100 micron X 100 micron).
