Influence of thermal diffusion on the spatial resolution of photothermal microscopy
Influence of thermal diffusion on the spatial resolution of photothermal microscopy
复制标题
热扩散对光热显微镜空间分辨率的影响
DOI：
10.1117/12.2607795
复制
发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Hartland, Gregory V.
中科院分区：
文献类型：
--
作者：
Brown, Brendan S.;Hartland, Gregory V.
光热显微镜是研究生物系统和固体材料的一种强有力的方法。利用调制泵浦来激励样品，连续的探测光束监测由于调制加热而引起的样品折射率的变化。这些实验通常在高频下进行，以降低1/f噪声，从而实现更高的信噪比。在本文中，我们探索了当调制频率降到100 kHz以下时，光热实验的分辨率和灵敏度如何变化。在泵浦和探测共聚焦于样品的情况下，分辨率由泵浦光束的大小决定。另一方面，当使用宽场泵浦时，在20 kHz以下的频率会发生显著的展宽。这种展宽归因于热扩散。然而，加宽量小于预期的热扩散长度，在10 kHZ时，甘油中的纳米颗粒约为1.7微米。我们还探讨了泵浦光束和探测光束的点扩散函数小于粒子尺寸的情况，以及穿透深度与抽运光束和探测光束的性质的关系。
Photothermal microscopy is a powerful method for investigating biological systems and solid state materials. Using a modulated pump to excite the sample, a continuous probe beam monitors the change in the refractive index of the sample due to the modulated heating. These experiments are typically performed at high frequencies to reduce the 1/f noise, achieving a higher signal to noise ratio. In this paper, we explore how the resolution and sensitivity of the photothermal experiments change when the modulation frequency is brought down below 100kHz. In the instance that the pump and probe are cofocused at the sample, the resolution is determined by the size of the pump beam. On the other hand, when a widefield pump is used, significant broadening occurs for frequencies under 20kHz. This broadening is attributed to thermal diffusion. However, the amount of broadening is less than that expected from the thermal diffusion length, which is about 1.7µm at 10kHz for nanoparticles in glycerol. We also explore the situation where the point spread functions of the pump and probe beams are smaller than the particle size as well as how the penetration depth depends on the properties of the pump and probe beams.