Almajhadi Mohammad, Wickramasinghe H Kumar
Opt Express. 2017 Oct 30;25(22):26923-26938. doi: 10.1364/OE.25.026923.
We numerically analyze PiFM's lateral and vertical (subsurface) imaging performance in the visible and IR regimes. The lateral spatial resolution and subsurface imaging capabilities are limited by the field spatial confinement near the tip apex, which is directly proportional to the excitation wavelength. In addition, we show that near-field optical force exerted on the tip due to sample molecular resonance is indeed in the detectable range. Moreover, driving sample on (off) resonance reveals high (low) contrast. The strength of the optical forces is assessed for metal (gold), polymers (Polystyrene and Polymethylmethacrylate), and solid (SiC). By increasing tip-coating thickness from 5 nm to 35 nm, the gap-field enhancement decreases to about 40%. In IR, force spectrum over an absorption band is predominantly following the real part of the polarizability, as predicted by dipole-dipole approximation.
我们对光子诱导荧光显微镜（PiFM）在可见光和红外波段的横向和垂直（地下）成像性能进行了数值分析。横向空间分辨率和地下成像能力受到针尖顶端附近的场空间限制，该限制与激发波长成正比。此外，我们表明，由于样品分子共振而施加在针尖上的近场光学力确实在可检测范围内。而且，驱动样品处于共振（非共振）状态会显示出高（低）对比度。对金属（金）、聚合物（聚苯乙烯和聚甲基丙烯酸甲酯）和固体（碳化硅）的光学力强度进行了评估。通过将针尖涂层厚度从5纳米增加到35纳米，间隙场增强降低到约40%。在红外波段，如偶极 - 偶极近似所预测的那样，吸收带上的力谱主要遵循极化率的实部。
