Novel developments in Fourier domain optical coherence tomography and nonlinear tomographic interferometry

In this thesis we present novel methods to improve the limitations in Optical Coherence Tomography (OCT). They are divided into two parts. The first part deals with the axial resolution limitation in OCT systems. We give a description of the Fourier Domain OCT (FDOCT), and then we show theoretically how to enhance the axial resolution in a particular case of a two-layer sample where one of the two layers is moving continuously, while these two layers are separated by a distance lower than the physical axial resolution. The second part of the thesis demonstrates a novel full theoretical model that uses the second order autocorrelation interferometry technique in nonlinear optics to eliminate the strong background DC, and therefore enhance the imaging contrast. A femtosecond laser emits the light at 1300nm wavelength, it travels through a polarized beam splitter which divides the light in two orthogonal polarizations, one will probe the reference and the other will probe the sample. By realizing the second harmonic generation, in type II configuration, it is possible to eliminate the DC. The setup is adapted, in an original manner, so as to realize interferometric measurements on the sample arm using three waves coupling. A full description of the method with solid theoretical models justified by simulation and experimental results is presented in this part to validate the proof of concept. This part of the thesis shows the possibility to use non-linear interferometry in order to provide interferometric measurements on a dark field even if strong parasitic light is reflected by the sample.(SC - Sciences) -- UCL, 201