Spatial Characterization Of Two-Photon States - GAP-Optique
Spatial Characterization Of Two-Photon States - GAP-Optique
Spatial Characterization Of Two-Photon States - GAP-Optique
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Coincidences<br />
800<br />
0<br />
-4<br />
4.2. Effect of the pump beam waist on the OAM transfer<br />
x<br />
y<br />
4mm<br />
Singles<br />
6x10 5<br />
~<br />
-1<br />
y x<br />
Singles<br />
5x10 4<br />
~<br />
1mm<br />
Figure 4.4: The ellipticity decreases as the pump beam waist increases from wp = 30<br />
µm in the left to 500 µm in the right image. As the pump beam waist affects<br />
the efficiency of the process, the coincidences on the left were collected over 600<br />
seconds and the ones in the right over 20 seconds. Solid lines are the best fit to the<br />
experimental data shown as points. The values of the experimental parameters are<br />
listed in table 4.2.<br />
Coincidences<br />
region width<br />
2.5m<br />
0.5<br />
0<br />
0<br />
x dimension<br />
y dimension<br />
L nc=1.1mm<br />
Pump width 330 500m Figure 4.5: The pump beam waist controls the width of the profile in the x direction,<br />
while it does not affect the width in the y direction. The width in both directions<br />
becomes similar when the noncollinear length is of the same order of magnitude as<br />
the crystal length. The vertical line shows the point where, according to the fits, both<br />
dimensions are equal. In this point the noncollinear length is 1.1 mm. The values of<br />
the experimental parameters are listed in table 4.2.<br />
transverse cuts to Gaussian functions, the waist in the x direction is wx 120<br />
µm and the waist in the y direction is wy 180 µm. The waist in the x<br />
direction is much smaller than before and of the same order as the waist in y<br />
which implies a decrease of the ellipticity.<br />
Figure 4.4 illustrates the changes in the width in the x and y directions as a<br />
function of pump beam waist. In the range where the waist varies from 32−500<br />
µm, the width in y remains almost constant while the width in x decreases by<br />
80%. After a certain threshold the width in x becomes stable at a value close<br />
43