Observation of elliptical rings in type-I spontaneous parametric downconversion
Observation of elliptical rings in type-I spontaneous parametric downconversion
复制标题
I 型自发参量下变频中椭圆环的观察
DOI：
10.1364/josab.32.002096
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发表时间：
2015
影响因子：
1.9
通讯作者：
D. Gauthier
中科院分区：
文献类型：
--
作者：
H. Guilbert;Yu;D. Gauthier
我们研究了两种类型的非线性晶体中非共线、简并、I 型自发参量下转换产生的下转换光的横向空间轮廓。我们发现，一种晶体 β 硼酸钡 (BBO) 产生的图案产生圆形下转换图案，而另一种晶体三硼酸铋 (BiBO) 产生椭圆形图案。我们证明这种差异是由于 BBO 中的子光子经历了与角度无关的折射率，而它们在 BiBO 中经历了与角度相关的折射率。我们对所生成的光的横向空间轮廓进行成像，以确定每个晶体产生的偏心率，并开发一个模型来解释我们的观察结果。除此之外，该模型预测存在一个 BiBO 偏心率几乎为零的波长。最后，我们讨论了 BiBO 中产生的椭圆环图案如何潜在地影响在整个下变频环周围收集双光子的实验装置的偏振纠缠。我们表明，通过两个环的光谱重叠积分测量的偏振纠缠质量可以在整个环周围保持较高的水平（> 99.4％），但代价是双光子速率下降。
We investigate the transverse spatial profile of downconverted light produced by noncollinear, degenerate, type-I spontaneous parametric downconversion in two types of nonlinear crystals. We find that the pattern produced by one crystal, beta barium borate (BBO), produces a circular downconversion pattern while the other crystal, bismuth triborate (BiBO), produces an elliptical pattern. We show this difference is due to the angle-independent refractive index experienced by the daughter photons in BBO, while they experience an angle-dependent refractive index in BiBO. We image the transverse spatial profile of the generated light to determine the eccentricity produced by each crystal and develop a model to explain our observation. Among other things, this model predicts that there is a wavelength for which the eccentricity from BiBO is nearly zero. Finally, we discuss how the elliptical ring pattern produced in BiBO potentially affects polarization entanglement for experimental setups that collect biphotons around the entire downconversion ring. We show that the quality of polarization entanglement as measured by the overlap integral of the spectrum of the two rings can remain high (>99.4%) around the entire ring at the expense of decreased biphoton rate.