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Spatial Characterization Of Two-Photon States - GAP-Optique

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CHAPTER 5<br />

<strong>Spatial</strong> correlations<br />

in Raman transitions<br />

<strong>Two</strong>-photon states can be generated in different nonlinear processes, and in every<br />

case the oam transfer will depend on the particular configuration. Raman<br />

transition is an alternative method for the generation of two-photon states.<br />

Several authors have proven the generation of correlated photons in polarization<br />

[59], frequency [60] and oam [23] via Raman transitions. Typical configurations<br />

involve the partial detection of the generated photons [61, 62, 63] in<br />

quasi-collinear configurations [64]. Just as in the case of spdc, the geometrical<br />

conditions determine the oam transfer. This chapter analyses the oam<br />

transfer in Raman transitions using the techniques of the previous chapters.<br />

This chapter is divided in three sections. Section 5.1 describes the generated<br />

two-photon state by introducing its mode function. Section 5.2 studies the<br />

oam content of one of the photons with the oam of the other photons fixed.<br />

Section 5.3 describes the effect of the geometry of the process on the spatial<br />

entanglement between the photons. Numerical calculations show the effect of<br />

the geometrical configuration on the oam transfer mechanism. The finite size<br />

of the nonlinear medium results in new effects that do not appear in spdc.<br />

51

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