In this thesis, two studies of the diffractive phenomena in the electron proton collisions with the H1 detector at HERA are presented. The first is the study of the inclusive elastic diffractive events $ep o eXp$ in the regime of high photon virtuality ($Q^2 >$ few GeV$^2$), with the scattered proton detected by the Very Forward Proton Spectrometer (VFPS). The VFPS detector, designed to measure diffractive scattered protons with high acceptance, has been installed in 2004 to benefit from the HERA II luminosity increase. The selected event sample of an integrated luminosity of 130.2 pb$^{-1}$ was collected in years 2006-2007. Data sample distributions are compared to the prediction based on the diffractive parton distribution functions, as extracted from the H1 measurement of the diffractive structure function $F_2^{D(3)}$ at HERA I. After the study of the VFPS efficiency, the VFPS acceptance as a function of $xpom$ is estimated and studied in relation to the forward proton beam optics. The second study leads to the cross section measurement of the diffractive scattering of quasi-real photons off protons, $gamma p o gamma Y$, with the large momentum transfer, $|t|$. The final state photon is separated from the proton dissociation system, $Y$, by a large rapidity gap and has a large transverse momentum, $p_T > 2$ GeV. Large $p_T$ imply the presence of the hard scale $t$ ($|t| simeq p_T^2$) and allows predictions of the perturbative QCD to be applied. The measurement is based on an integrated luminosity 46.2 pb$^{-1}$ of data collected in the 1999-2000 running period. Cross sections $sigma(W)$ as a function of the incident photon-proton centre of mass energy, $W$, and $ud sigma/ud |t|$ are measured in the range $Q^2 < 0.01$ GeV$^2$, $175 < W < 247$ GeV, $4 < |t| < 36$ GeV$^2$ and $ypom < 0.05$. The cross section measurements have been compared to predictions of LLA BFKL calculations.

In this thesis, two studies of the diffractive phenomena in the electron proton collisions with the H1 detector at HERA are presented.<p>The first is the study of the inclusive elastic diffractive events $ep \ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished