This workshop features a quantitative wavefront imaging technique called quadriwave lateral shearing interferometry (QLSI). Mounted on a microscope, it can image the optical wavefront distorted by microscale objects like living cells at the sample plane, and provide valuable information, in particular related to biomass. In this workshop, we aim at explaining the working principle of QLSI in front of a setup. All the parts of the setup will be home-made (illumination, microscope and QLSI). Then, the setup will be used on two illustrative samples. First, we will observe bacteria in culture, in particular E coli, and Geobacillus stearothermophilus. The latter is a thermophilic bacterium, optimally living at 60°C, that we shall revive using a compact heating device with a heating time scale shorter than 1 s, and that is compatible with optical microscopy. We will acquire wavefront images and show how the mass of isolated bacteria and colonies can be measured, using a home-made segmentation algorithm. Second, we will image fixed neurons and present the segmentation algorithm we developed to image the dry mass of neurons, soma and neurites. This workshop is intended to experimentalists, biologists and physicists, researchers and engineers, working with cells in culture. No pre-knowledge is required.