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Spatial Characterization Of Two-Photon States - GAP-Optique

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4. OAM transfer in noncollinear configurations<br />

The different spatial shapes in figure 4.12 clearly show that the downconversion<br />

cone does not posses azimuthal symmetry. As was predicted by the<br />

theoretical calculations, the coincidence measurement for α = 90 ◦ , presents a<br />

nearly Gaussian shape, while the other cases are highly elliptical.<br />

The slight discrepancies between experimental data and theoretical predictions<br />

observed might be due to the small (but not negligible) bandwidth of the<br />

pump beam, and due to the fact that the resolution of our system is limited<br />

by the detection pinhole size.<br />

Conclusion<br />

The spdc parameters and the detection system determine the portion of the<br />

cone that is detected in a noncollinear configuration. This chapter explains how<br />

the pump beam waist and the Poynting vector walk-off affect the oam transfer.<br />

By tailoring both parameters it is possible to generate photons with specific<br />

spatial shapes. The walk-off affects especially those configurations where pairs<br />

of photons with different α are used.<br />

The next chapter extends the analysis of the spatial correlations to pairs<br />

of photons generated in Raman transitions. The chapter describes how the<br />

specific characteristics of that source are translated into the two-photon spatial<br />

state.<br />

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