  We present a technically simple implementation of quantitative phase imaging
in confocal microscopy based on synthetic optical holography with
sinusoidal-phase reference waves. Using a Mirau interference objective and
low-amplitude vertical sample vibration with a piezo-controlled stage, we
record synthetic holograms on commercial confocal microscopes (Nikon, model:
A1R; Zeiss: model: LSM-880), from which quantitative phase images are
reconstructed. We demonstrate our technique by stain-free imaging of cervical
(HeLa) and ovarian (ES-2) cancer cells and stem cell (mHAT9a) samples. Our
technique has the potential to extend fluorescence imaging applications in
confocal microscopy by providing label-free cell finding, monitoring cell
morphology, as well as non-perturbing long-time observation of live cells based
on quantitative phase contrast.
