Most of the quantitative phase microscopy systems are unable to provide depth-resolved information for measuring complex biological structures. Optical diffraction tomography provides a non-trivial solution to it by 3D reconstructing the object with multiple measurements through different ways of realization. Previously, our lab developed a reflection-mode dynamic speckle-field phase microscopy (DSPM) technique, which can be used to perform depth resolved measurements in a single shot. Thus, this system is suitable for measuring dynamics in a layer of interest in the sample. DSPM can be also used for tomographic imaging, which promises to solve the long-existing “missing cone” problem in 3D imaging. However, the 3D imaging theory for this type of system has not been developed in the literature. Recently, we have developed an inverse scattering model to rigorously describe the imaging physics in DSPM. Our model is based on the diffraction tomography theory and the speckle statistics. Using our model, we first precisely calculated the defocus response and the depth resolution in our system. Then, we further calculated the 3D coherence transfer function to link the 3D object structural information with the axially scanned imaging data. From this transfer function, we found that in the reflection mode excellent sectioning effect exists in the low lateral spatial frequency region, thus allowing us to solve the “missing cone” problem. Currently, we are working on using this coherence transfer function to reconstruct layered structures and complex cells.
Surface plasmons are coherent oscillations of the free electrons on metal surface which can be used to improve the
excitation efficiency of fluorophores due to increased field enhancement. Surface plasmon resonance fluorescence
(SPRF) microscopy is a wide-field optical imaging technique that utilizes the evanescent electromagnetic field of surface
plasmons to excite fluorophores near to a surface of a metal film. With the same excitation power, the field enhancement
effect of the surface plasmon resonance (SPR) leads to strong fluorescence emission and thus increases the signal to
noise ratio of detection. However, there have been few studies on the image formation process for SPRF in terms of its
point-spread function. By imaging fluorescent microspheres with size below the diffraction limit, we obtained the point-spread
function for SPRF. The SPR enhancement is confirmed by back-focal-plane imaging with various incidence
angles of the excitation beam. Furthermore, we will investigate the potential of resolution enhancement by generating
standing wave with two symmetric incident excitation beams toward the standing-wave surface plasmon resonance
fluorescence (SW-SPRF) microscopy.