| Autor: |
Vera Kollarova, Tomas Slaby, Michala Slaba, Radim Chmelík, Jana Collakova, Zbynek Dostal, Martin Lostak |
| Rok vydání: |
2014 |
| Předmět: |
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| DOI: |
10.1016/b978-0-444-63379-8.00005-2 |
| Popis: |
Off-axis digital holographic microscopes (DHM) working with incoherent light have been designed and constructed. Their imaging properties can be changed by variation of the coherence of light. This spans from emulation of classic coherent-light DHM allowing for numerical focusing to incoherent-light DHM characterized by high-quality imaging, no coherence noise, halved limit of lateral resolution, and by coherence-gating effect making imaging in turbid media and optical sectioning possible. We describe theoretically the imaging process of a holographic microscope (HM) and how it is influenced by the coherence of illumination. The 3D coherent transfer function (CTF) reveals the dependence of a spatial frequency passband on the coherence properties of a source. Reduction of coherence leads to the passband broadening i.e. to the resolution enhancement. This effect is obvious also from the form of 3D point spread functions, which allows us to characterize imaging by 3D convolution. Imaging and numerical focusing of planar objects are described by 2D CTF derived from 3D CTF for various defocusing. Results for 2D objects are presented also in a simplified approximate form, which gives deeper insight into the fundaments of imaging. In this approximation, the image formation in a turbid medium by coherence gating is elucidated. In addition, it is shown that the mutual lateral shift of the object and reference beams amplifies higher spatial frequencies of a defocused object and allows an object in a turbid medium to be imaged by diffuse (non-ballistic) light. Important theoretical results are verified experimentally. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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