Resumen de Cepstrum-based interferometric microscopy: from basic principles to experimental implementations in cell imaging
The main goal of this thesis has been the creation, development and analysis of a novel and groundbreaking technique for retrieving quantitative phase images breaking with the general conception in digital holographic microscopy (DHM) of requiring a clear reference beam carrying no sample information. As a result, no restrictions are introduced in any of the interferometric beams.
This technique, which we named cepstrum-based interferometric microscopy (CIM), might be especially relevant for the development of new simplified interferometric addons to convert conventional microscopes in DHM ones based on quasi-common path arrangements (avoiding not only the sample constraints typically imposed in self-interference or spatially-multiplexed approaches, but also the bulky or complex arrangements required in reference generation).
CIM technique is based on the capture of a set of holograms were both interferometric beams carry sample information. From those holograms, CIM extracts the information from the cross-correlated terms resulting from the coherent superposition of both complex beams. In regular DHM, the cross-correlated terms only contain the complex information of one beam (so called object beam), as the other beam must be a known one (reference beam). However, in our case, these terms carry useful information from both beams. By means of our developed spatial-shifting cepstrum algorithm (based on Cepstrum subtraction in combination with a complementary Fourier domain bow-tie masking) we recover the complex amplitude of one of the beams and then, by simple subtraction, recover the complex amplitude of the other beam.
Proof-of-concept validation of this methodology, is provided considering an off-axis holographic configuration for retrieving the cross-correlation of the two interferometric complex amplitude fields in different interferometric architectures: a Mach-Zehnder intereferometer (for the first proof of concept validation), a compact quasi-common path Michelson interferometric configuration, and a compact quasi-common path Mach- Zhender configuration (the two last coupled to a bright field microscope to prove use-case configurations). Experimental results for different types of phase samples (resolution test targets for step-by-step calibration and demonstration as well as fixed biosamples) are included.
In conclusion, the proposed technique offers a suitable solution to provide QPI images from an interferometric approach without imposing restrictions on none of the interferometric beams. This technique could be applied in many interferometric scenarios, nonetheless, we consider here its application to microscopy, and more concretely, to cell imaging.
