Theory of two-photon absorption with broadband squeezed vacuum
Theory of two-photon absorption with broadband squeezed vacuum
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DOI：
10.1103/physreva.106.013717
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发表时间：
2022-02
影响因子：
2.9
通讯作者：
M. Raymer;Tiemo Landes
中科院分区：
文献类型：
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作者：
M. Raymer;Tiemo Landes
我们提出了一种非共振分子双光子吸收（TPA）的分析量子理论模型，包括低增益（孤立纠缠光子对或EPP）和高增益（明亮压缩真空或BSV）模式。这些结果与纠缠光TPA作为光谱和成像方法的潜在应用有关。我们处理了激发光在空间上是单模的，并且与所有中间分子态都不共振的情况。在高增益的情况下，我们发现在最终分子态的线宽比激发光的带宽窄得多的情况下，发现明亮的压缩真空与具有相同时间形状、持续时间和平均光子数的准单色相干态（经典）脉冲一样（但不是更多）有效地驱动TPA。因此，在这种情况下，在极低光通量下观测TPA的优势并不是宽带明亮压缩真空所能提供的。在相反的情况下，最终状态线宽比BSV激发光的带宽宽得多，我们发现TPA速率与零时延下的二阶强度自相关函数成正比，正如预期的那样。我们推导并评估了描述这两种极限情况之间过渡的公式，也就是说，包括分子线宽和光带宽相当的情况，这在实验研究中是经常出现的情况。我们还表明，为了达到理想形式，即每个时间模式的平均光子数，需要补偿用于产生BSV的非线性光学晶体中固有的色散。
: We present an analytical quantum theoretic model for non-resonant molecular two-photon absorption (TPA) of broadband, spectrally multi-mode squeezed vacuum, including low-gain (isolated entangled photon pairs or EPP) and high-gain (bright squeezed vacuum or BSV) regimes. The results are relevant to the potential use of entangled-light TPA as a spectroscopic and imaging method. We treat the scenario that the exciting light is spatially single-mode and is non-resonant with all intermediate molecular states. In the case of high gain, we find that in the case that the linewidth of the final molecular state is much narrower than the bandwidth of the exciting light, bright squeezed vacuum is found to be equally (but no more) effective in driving TPA as is a quasi-monochromatic coherent-state (classical) pulse of the same temporal shape, duration and mean photon number. Therefore, in this case the sought-for advantage of observing TPA at extremely low optical flux is not provided by broadband bright squeezed vacuum. In the opposite case that the final-state linewidth is much broader than the bandwidth of the BSV exciting light, we show that the TPA rate is proportional to the second-order intensity autocorrelation function at zero time delay , as expected. We derive and evaluate formulas describing the transition between these two limiting cases, that is, including the regime where the molecular linewidth and optical bandwidth are comparable, as is often the case in experimental studies. We also show that for to reach the idealized form , with being the mean number of photons per temporal mode, it is required to compensate the dispersion inherent in the nonlinear-optical crystal used to generate the BSV.