泵浦光的入射角对参量下转换的影响

利用参量下转换制备相关光子实现对各类探测器的量子效率的定标,是近年来兴起的新型定标技术。由于参量下转换的光子转换效率低，探测器输出信号信噪比小。采用短波激光器泵浦PPLN周期极化性晶体，可获得较大功率的参量光。分析了泵浦光在PPLN晶体端面的入射角对参量光的转换效率、空间分布、参量带宽及晶体周期的影响，并进行了数值模拟。分析发现当泵浦光正入射晶体端面时，参量光功率转换大，带宽小，发散角大；随着泵浦光入射角度逐渐增大，参量下转换的转换效率降低，相关光子的带宽变小，发散角变小且参量光的中心波长的空间位置会发生相对偏移。该研究结果可为相关光子探测、模拟探测器量子效率的高精度定标提供理论依据。

Influence of incident angle of pumped beam on parametric down conversion

Calibration for the quantum efficiency of detectors is a new research subject. Spontaneous-parametric-down-conversion (SPDC) has the disadvantages of low conversion efficiency and signal noise ratio (SNR). In order to improve the power of correlation photon, a shortwave laser was used to pump the periodically poled lithium niobate (PPLN) crystal. The influence of incident angle on the conversion efficiency, spatial distribution, bandwidth and crystal poling period was analyzed based on numerical simulation. It is proved that the conversion efficiency is high, the bandwidth of correlation photon is narrow and the divergence angle is large for normal incident pumped beam. While the incident angle increases, the conversion efficiency becomes lower, the bandwidth and divergence angle are smaller and the position of central wavelength can shift. The result presented is a theoretical support for correlated photon detection and highly accurate calibration for quantum efficiency of detector.