Tamimi Amr, Landes Tiemo, Lavoie Jonathan, Raymer Michael G, Marcus Andrew H
Opt Express. 2020 Aug 17;28(17):25194-25214. doi: 10.1364/OE.400245.
Fluorescence-detected Fourier transform (FT) spectroscopy is a technique in which the relative paths of an optical interferometer are controlled to excite a material sample, and the ensuing fluorescence is detected as a function of the interferometer path delay and relative phase. A common approach to enhance the signal-to-noise ratio in these experiments is to apply a continuous phase sweep to the relative optical path, and to detect the resulting modulated fluorescence using a phase-sensitive lock-in amplifier. In many important situations, the fluorescence signal is too weak to be measured using a lock-in amplifier, so that photon counting techniques are preferred. Here we introduce an approach to low-signal fluorescence-detected FT spectroscopy, in which individual photon counts are assigned to a modulated interferometer phase ('phase-tagged photon counting,' or PTPC), and the resulting data are processed to construct optical spectra. We studied the fluorescence signals of a molecular sample excited resonantly by a pulsed coherent laser over a range of photon flux and visibility levels. We compare the performance of PTPC to standard lock-in detection methods and establish the range of signal parameters over which meaningful measurements can be carried out. We find that PTPC generally outperforms the lock-in detection method, with the dominant source of measurement uncertainty being associated with the statistics of the finite number of samples of the photon detection rate.
荧光检测傅里叶变换（FT）光谱技术是一种通过控制光学干涉仪的相对路径来激发材料样品，并将随后产生的荧光作为干涉仪路径延迟和相对相位的函数进行检测的技术。在这些实验中，提高信噪比的一种常用方法是对相对光路应用连续相位扫描，并使用相敏锁定放大器检测产生的调制荧光。在许多重要情况下，荧光信号太弱，无法使用锁定放大器进行测量，因此光子计数技术更受青睐。在此，我们介绍一种用于低信号荧光检测FT光谱的方法，其中将单个光子计数分配给调制的干涉仪相位（“相位标记光子计数”，即PTPC），并对所得数据进行处理以构建光谱。我们研究了在一系列光子通量和可见度水平下，由脉冲相干激光共振激发的分子样品的荧光信号。我们将PTPC的性能与标准锁定检测方法进行了比较，并确定了可以进行有意义测量的信号参数范围。我们发现，PTPC通常优于锁定检测方法，测量不确定度的主要来源与光子检测率有限数量样本的统计有关。
