Spatial Characterization Of Two-Photon States - GAP-Optique

Before
the crystal
4.3. Effect of the Poynting vector walk-off on the OAM transfer
After
the crystal
Polarization Optical axis
Figure 4.11: The images obtained with a ccd camera show that before the crystal,
the pump beam has a circular shape, and that after passing the crystal part of the
beam gets displaced in the direction of the optical axis of the crystal. The displaced
part corresponds to the portion of the beam polarized orthogonal to the crystal axis.
In the case of the last image almost all the beam is displaced. The values of the
experimental parameters are listed in table 4.3.
every rotation, the tilt of the crystal was adjusted to achieve the generation of
photons at the same noncollinear angle in all cases.
The bottom row of figure 4.12 presents a sample of images taken at different
azimuthal sections of the cone, while the upper row shows the expected shape
predicted by the theory. Each column shows the coincidence rate for different
angles, α = 0 ◦ , 90 ◦ , 180 ◦ and 270 ◦ . Each point of these images corresponds to
the recording of a 10 seconds measurement. The typical maximum number of
coincidences is around 10 coincidences per second. Each image is 10 × 10 mm,
and its resolution is 50 × 50 points.
Theory
Experiment
0º 90º 180º 270º
Figure 4.12: The coincidence measurements of the mode function, as well as the
theoretical calculations, show that the ellipticity of the mode function changes for
different positions on the cone. The ellipticity is minimal for α = 90 ◦ . The values of
the experimental parameters are listed in table 4.3.
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