Spatial Characterization Of Two-Photon States - GAP-Optique

4. OAM transfer in noncollinear configurations
The different spatial shapes in figure 4.12 clearly show that the downconversion
cone does not posses azimuthal symmetry. As was predicted by the
theoretical calculations, the coincidence measurement for α = 90 ◦ , presents a
nearly Gaussian shape, while the other cases are highly elliptical.
The slight discrepancies between experimental data and theoretical predictions
observed might be due to the small (but not negligible) bandwidth of the
pump beam, and due to the fact that the resolution of our system is limited
by the detection pinhole size.
Conclusion
The spdc parameters and the detection system determine the portion of the
cone that is detected in a noncollinear configuration. This chapter explains how
the pump beam waist and the Poynting vector walk-off affect the oam transfer.
By tailoring both parameters it is possible to generate photons with specific
spatial shapes. The walk-off affects especially those configurations where pairs
of photons with different α are used.
The next chapter extends the analysis of the spatial correlations to pairs
of photons generated in Raman transitions. The chapter describes how the
specific characteristics of that source are translated into the two-photon spatial
state.
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