Beeker Willem P, Gross Petra, Lee Chris J, Cleff Carsten, Offerhaus Herman L, Fallnich Carsten, Herek Jennifer L, Boller Klaus-Jochen
Laser Physics & Nonlinear Optics Group, MESA + Research Institute for Nanotechnology, University of Twente, P. O. Box 217, Enschede 7500AE, The Netherlands.
Opt Express. 2009 Dec 7;17(25):22632-8. doi: 10.1364/OE.17.022632.
We theoretically investigate a scheme to obtain sub-diffraction-limited resolution in coherent anti-Stokes Raman scattering (CARS) microscopy. We find using density matrix calculations that the rise of vibrational (Raman) coherence can be strongly suppressed, and thereby the emission of CARS signals can be significantly reduced, when pre-populating the corresponding vibrational state through an incoherent process. The effectiveness of pre-populating the vibrational state of interest is investigated by considering the excitation of a neighbouring vibrational (control) state through an intense, mid-infrared control laser. We observe that, similar to the processes employed in stimulated emission depletion microscopy, the CARS signal exhibits saturation behaviour if the transition rate between the vibrational and the control state is large. Our approach opens up the possibility of achieving chemically selectivity sub-diffraction-limited spatially resolved imaging.
我们从理论上研究了一种在相干反斯托克斯拉曼散射（CARS）显微镜中获得亚衍射极限分辨率的方案。我们通过密度矩阵计算发现，当通过非相干过程预先填充相应的振动状态时，振动（拉曼）相干性的上升可以被强烈抑制，从而可以显著减少CARS信号的发射。通过考虑用强中红外控制激光激发相邻的振动（控制）状态，研究了预先填充感兴趣的振动状态的有效性。我们观察到，类似于受激发射损耗显微镜中采用的过程，如果振动状态和控制状态之间的跃迁速率很大，CARS信号会表现出饱和行为。我们的方法为实现化学选择性亚衍射极限空间分辨成像开辟了可能性。
