A real-time digital holographic microscope with an optical tweezer

Official URL: http://risc01.sabanciuniv.edu/record=b1587029 (Table of Contents)

The most significant advantage of the holographic microscopy is being able to image transparent objects such as biological cells without staining. Therefore, the cell image can be captured while it is alive. Moreover, Manipulating a living cell without destructing it’s structure can be achieved by the use of an optical tweezer which apply a pulling force around a tightly focused laser beam without a physical contact. Therefore, an instrument that combines the holographic microscope and the optical tweezer is quite useful for biological studies. Another advantage of holographic imaging is that, one does not need to do mechanical focusing for the scene when recording the hologram. Focusing is achieved by reconstructing the hologram at a certain depth. If the object’s optical depth from the recording plane is not known a priori, auto-focusing algorithms must be used to estimate this distance. However, auto-focusing and reconstruction can be quite time consuming as the hologram sizes increase and the microscope can not operate in real-time with high resolution holograms using traditional central processing units (CPUs). Therefore, for real-time operation, additional hardware accelerators are required for reconstructing high resolution holograms. A holograms can be reconstructed tens of times faster with a graphics processing unit than with the state-of-the-art main CPUs. In this thesis, an auto-focusing megapixel-resolution digital holographic microscope (DHM) that uses a commodity graphics card as the calculation engine is presented. The computational power of the GPU allows the DHM to work in realtime such that the reconstruction distance is estimated unsupervised, and the postprocessing of the hologram is transparent to the user. Performances of the DHM under GPU and CPU settings are presented and a maximum of 70 focused reconstructions per second (frps) are achieved with 1024 ⇥ 1024 pixels holograms. Moreover, a setup for incorporating an optical tweezer to the holographic microscope is provided. With this setup, it is possible to trap small particles while performing holographic imaging.