In this thesis we study spatially entangled photon pairs created by frequency-degenerate parametric down-conversion from a 2 mm long type-I periodically poled KTP crystal pumped by 2 ps duration...Show moreIn this thesis we study spatially entangled photon pairs created by frequency-degenerate parametric down-conversion from a 2 mm long type-I periodically poled KTP crystal pumped by 2 ps duration laser pulses. We present measurements of spatial correlations between the entangled photon pairs and compare them to the same measurements performed with a 5 mm PPKTP crystal, shown in [1, paragraph 5.4.2]). For the 5 mm crystal, a peak of coincidences is observed in the collinear direction, which is not in accordance with theoretical predictions. The peak is attributed to quadruplets. We do not observe this extra peak for the 2 mm crystal. Furthermore, we find that the optical alignment is critical and depends on the type of fiber. We conclude that the collection efficiency of the detection units depends on the detection position and decreases away from the collinear direction. Although this observation is not understood, it may contribute to the extra peak. For further research, it is necessary to redesign the detection units to exclude the position dependence of the collection efficiency.Show less
