提出了一种结合和频效应和环形光照明的远场超分辨红外显微成像方法。红外光、不同频率的环形和高斯可见光同时共轴激发样品, 当红外光频率等于样品分子某一共振频率时, 样品分子吸收红外光到达振动激发态, 环形和高斯可见光与共振分子作用分别产生无效和有效的和频信号。利用三束光的矢量光场表达式和模型能级系统的速率方程进行数值模拟发现, 当总可见光足够强时, 可使总和频信号饱和, 环形和高斯可见光与共振分子的作用出现竞争, 通过提高环形可见光光子流密度超过饱和光子流密度, 并降低高斯可见光光子流密度, 可有效地抑制环形区域有效和频信号的产生, 从而达到压缩PSF的目的, 在物镜数值孔径0.6的情况下, 通过数值模拟得到有效和频信号PSF半高宽为56 nm。

A method of far-field super-resolution infrared microscopy was presented by using vibrational sum-frequency generation(VSFG) and donut-beam illumination. To achieve this, one Gaussian-shaped visible beam and one donut-shaped visible beam with different wavelengths were combined with an infrared beam coaxially to excite the sample. When the frequency of the infrared light was as the same as the resonant frequency of the molecules, the molecules absorbed the energy of the infrared photon and were excited to the vibrational excited state. The photons in the donut-shaped and the Gaussian-shaped visible beams both interacted with the excited molecules, and generated useful and useless SFG signal respectively. Simulations based on the vectorial field of the three beams and rate equations demonstrated that, when the visible intensity was improved to a certain level, the SFG signal tended to be saturated, then the donut-shaped visible photons and the Gaussian-shaped photons competed with each other. By increasing the photon flux density of the donut-shaped visible light to be larger than the saturated value, and reducing the photon flux density of the Gaussian-shaped visible light, the useful SFG signal in the donut-shaped area was surpressed effectively, which means the effective PSF was shrinked. With an objective which has a small numerical aperture (NA) 0.6, a simulated resolution as high as 56 nm was obtained.