纳米分辨相干反斯托克斯拉曼散射显微成像

Nanometer resolution coherent anti-Stokes Raman scattering microscopic imaging

采用附加探测光声子耗尽法来实现超衍射极限相干反斯托克斯拉曼散射显微成像.此方法引入一束环形分布的附加探测光来消耗点扩展函数周边的相干声子,实现点扩展函数的改造,从而达到超越衍射极限的空间分辨率.为了获得更高的空间分辨率和更佳的相位匹配条件,通常需采用高数值孔径物镜对抽运光、斯托克斯光和探测光进行聚焦,此时标量衍射理论不再成立.基于矢量衍射理论,分析了线偏振光、圆偏振光先后经过螺旋相位片和高数值孔径物镜后的光强分布,结果表明:圆偏振光在高数值孔径物镜后焦平面的光强分布呈中心对称状,较线偏振环形光更适合作为附加探测光.此外,采用全量子理论分析了附加探测光声子耗尽法.结果表明:当附加探测光与探测光强度比为80时,成像系统的横向空间分辨率可以达到45 nm;继续提高附加探测光强度,空间分辨将进一步提高.

Coherent anti-Stokes Raman scattering （CARS） microscopy can break through the optical diffraction limit by applying the additional probe beam induced phonon depletion （APIPD）. Using this method, we can obtain a spatial resolution beyond the optical diffraction limit by introducing a doughnut additional probe beam to deplete phonons at the periphery of the focal spot. To achieve higher spatial resolution and better phase matching conditions, it is necessary to use high numerical aperture objectives, whereas scalar diffraction theory is no longer valid. According to the full vector diffraction theory, we calculate the intensity distributions at the focal plane when the linearly and circularly polarized lights pass through a spiral phase plate and an objective with high numerical aperture successively. The result shows that the circular polarization can generate the perfectly doughnut-shaped focal spot, which is more suitable for the additional beam than the linear polarization induced beam. Furthermore, we analyze the APIPD induced CARS process with the full quantum theory. Simulations indicate that a spatial resolution as high as 45 nm could be realized when the ratio between the intensities of additional probe and probe is 80. And the spatial resolution turns higher with increasing the power of additional probe.