Measurement of topographic phase image of living cells by white-light phase-shifting microscope with active stabilization of optical path difference

摘要

We report a full-field, phase-shifting microscope with precise control of the optical path difference (OPD) and show topographic phase images of living cells. Our system is based on a Linnik interference microscope with Kohler illumination of a halogen lamp for the imaging lightsource. Phase-sensitive active-stabilization of the OPD is employed with an infrared laser whose optical path is the same as that of halogen light. We previously reported the results of cultured cell topography with this stabilization scheme; however the phase stability and the image quality were insufficient. We have improved the noise-cancellation system and achieved control of the OPD with stability down to 0.7 nm in the bandwidth of 500 Hz. Quarter wavelength phase-shifting was carried out with sub-nanometer accuracy, and clear topographic phase images of cultured single-layer cells were obtained. The Kohler illumination with the halogen lamp, whose coherence length is 2 μm, enables homogenous illumination and suppression of artifact signals arising from optical components not associated with the surface of interest.