HIGH-SENSITIVITY POLARIZATION SPECTROSCOPY USING TWIN-PHOTON BEAMS

本论文研究了双光子束在偏振光谱信噪比增强中的应用.用454 nm Ar激光泵浦LBO晶体，通过II类角度相位匹配参量下转换产生双光子束。当泵浦功率为140 mW时，获得了约20 pW的双光束输出.双光束由偏振分束器分离，其强度由雪崩光电二极管（APD）检测。APD，冷却到100 K以下，在线性模式下操作，放大因子为500。在我们的光子计数系统与APD的转换入射光子的光电子的总效率是低于10%。因此，我们用模拟电流计代替光子数计数来测量光电流.我们测量了两束光的强度差。(The获得300次测量的平均值，每次测量的积分时间为0.62秒）。与非关联光束相比，光强差的波动减小了17%。因此，它表明，双光子束是适当的偏振光谱降噪。

The present research investigated the application of the twin-photon beams to the signal-to-noise ratio enhancement for polarization spectroscopy.1. A LBO crystal was pumped by the 454-nm Ar laser to generate twin photon beams by the type II angle-phase matched parametric down conversion. The power of twin beams was obtained to be about 20 pW when the pump power was 140 mW.2. The twin beams were separated by a polarizing beam splitter, and their intensities were detected by avalanche photodiodes (APD). The APD,cooled below 100 K,was operated in the linear mode with amplification factor of 500. In our photon counting system with the APD the overall efficiency for converting the incident photon to the photoelectron was below 10%. Thus we measured the photocurrent using an analog current meter instead of counting of photon numbers.3. We measured the intensity difference between the twin beams. (The average value of 300 measurements was obtained, the integration time was 0.62 s for each measurement). The fluctuation of the intensity difference was reduced by a factor of 17% compared to that for the non-correlated beams. Thus it was shown that the twin-photon beams was appropriate for noise reduction for the polarization spectroscopy.