三次谐波
在THG 显微镜下，无需荧光染料，三次谐波信号由样品本身产生。在均匀样品中，由于相位匹配，来自焦 点上方的THG 信号抵消了焦点下方产生的信号。因此，只有当焦点处有折射率接近梯度时，才会产生第三次谐波 信号。因此，THG 显微镜特别适合对膜或其他界面感兴趣的透明样品进行无标记三维成像.
Figure 1. Energy level diagram for the THG imaging mechanism.
Third Harmonic Generation Bio-Imaging Examples
Figure 2. Zebrafish embryo (6 hours post fertilization) using label free THG at 1140 nm; imaged with InSight® DS+™ fs laser.
Courtesy of Dr. Nadine Peyrieras, CNRS, Gif sur Yvette, France
Figure 3. Mouse mammary gland, label free image of collagen (SHG, magenta) and adipocytes (THG, yellow), imaged with InSight DS+™.
Courtesy of Dr. Marie Irondelle, Institut Curie/CNRS, Paris, France
Figure 4. 3D images from a mouse brain cerebellum extending 1 mm deep into the tissue acquired via 3PF (left) and THG (right) microscopy at 1.3 μm using a Spirit laser with a Spirit-NOPA.
Courtesy of Chris Xu, with permission from SPIE Publications: Wang, et. al., “In vivo three-photon imaging of deep cerebellum,” Proc. SPIE: Multiphoton Microscopy in the Biomedical Sciences XVIII, vol. 10498, 2018.e
