Two-Photon-Excited Photoinduced Force Microscopy.

Area of Science:

• Nanoscale imaging
• Molecular imaging
• Spectroscopy

Background:

• Photoinduced force microscopy (PiFM) is a promising nanoscale imaging technique.
• Single-photon excitation in PiFM often suffers from linear background and noise.
• Sources of noise include scattering and photothermal effects.

Purpose of the Study:

• To introduce two-photon-excited photoinduced force microscopy (TP-PiFM) to suppress linear background and noise.
• To demonstrate TP-PiFM as a robust and background-free nanoimaging method.

Main Methods:

• Utilized two-photon excitation to reduce unwanted linear effects.
• Employed signal demodulation at ωtip ± 2ωopt for photothermal signal isolation.
• Applied intensity modulation on the pulse train at ωopt and tip driving at ωtip.
• Performed fitting analysis to extract signals quadratically scaling on illumination power.

Main Results:

• Achieved higher resolution imaging of 40 nm gold nanoparticles compared to AFM topography.
• Successfully suppressed background noise through demodulation and fitting analysis.
• Demonstrated the effectiveness of TP-PiFM in obtaining clear, high-resolution images.

Conclusions:

• TP-PiFM effectively suppresses background and noise inherent in single-photon excitation methods.
• The developed demodulation technique isolates the desired photothermal signal.
• TP-PiFM offers a robust, background-free approach for advanced nanoimaging.