|Title:||Holographic methods for three-dimensional reconstruction of refractive index distribution with extended measurement volume|
|Funding agency:||National Science Centre, Poland; Programme ETIUDA|
|Leader of the project:||MSc Eng Julianna Winnik|
|Supervisor:||PhD Eng Tomasz Kozacki|
Holographic tomography enables accurate, non-invasive measurement of three-dimensional distribution of refractive index in transparent micro-objects. The measurement process in holographic tomography consists in acquisition of a series of holograms (captures of two-dimensional distributions of optical fields) for various observation directions. Next, the registered data is numerically processed, which results in reconstruction of a three-dimensional refractive index distribution. The noncontact and quantitative character of the measurement in holographic tomography holds potential for broad application of this technique in medicine and industry.
The fundamental difference between holographic tomography and computed tomography (CT) is that the former utilizes electromagnetic waves from the visible range instead of the x-ray radiation. The wavelength of the visible light is comparable to the size of details of specimens; therefore, the diffraction on the sample internal structure is not negligible. Thus, the major challenge of holographic tomography in accounting for diffraction during the reconstruction process.
The majority of the diffractive tomographic reconstruction algorithms apply light scattering models that are basing on the first-order Rytov approximation. The major disadvantage of these solutions is spatially variant accuracy of reconstruction, i.e. the reconstruction error is small in the central area of the tomographic image and increases for its peripheral regions. The described issue severely limits the effective reconstruction space, in which the reconstruction error is acceptably small. The aim of this project is to overcome the described problem of small effective reconstruction space in holographic tomography. This is achieved by taking advantage of a wide range of numerical methods of manipulation of optical fields that are provided by holography, most importantly the numerical propagation methods and the local rays analysis techniques.
The reconstruction results of holographic tomography: a) calibration microbeads; b) optical microfiber.