Thermal lens spectroscopy (TLS) is a high-sensitivity method to determine the concentration of light-absorbing species in samples. Here, we implemented a transient configuration of the technique, with a focused pump and a collimated probe beam coaxially propagating. A Fabry–Perot optical resonator is incorporated allowing multi-passing of the probe beam through the sample to enhance sensitivity. We show how the low detection limit of the method can be reduced approximately by half by making differential measurements of the signal at a far field in the center point of the probe beam spot and that obtained by spatial filtering of the same beam, the so-called eclipsed signal. Measurements were performed in test samples of Deyman's organic dye, Strawberry 2143 v.7, dissolved in ethanol. The thermal lens signal measured as a function of the dye concentration in water at the center of the beam was compared with the differential signal resulting from this and the eclipsed beam.

中文翻译：

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用于痕量检测的差热透镜光谱法

热透镜光谱 (TLS) 是一种测定样品中吸光物质浓度的高灵敏度方法。在这里，我们实现了该技术的瞬态配置，其中聚焦泵和准直探测光束同轴传播。结合了法布里-珀罗光学谐振器，允许探测光束多次穿过样品，以提高灵敏度。我们展示了如何通过对探测光束点中心点的远场信号进行差分测量以及通过同一光束的空间滤波获得的信号，将该方法的低检测限降低大约一半，即称为遮蔽信号。对溶解在乙醇中的 Deyman 有机染料 Strawberry 2143 v.7 的测试样品进行测量。将测量的热透镜信号作为光束中心水中染料浓度的函数，与由该热透镜信号和遮蔽光束产生的差分信号进行比较。