Communication: atomic force detection of single-molecule nonlinear optical vibrational spectroscopy

Area of Science:

• Nonlinear optics
• Spectroscopy
• Nanoscale science

Background:

• Atomic Force Microscopy (AFM) offers high-sensitivity signal detection.
• Previous demonstrations include Nuclear Magnetic Resonance (NMR) and stimulated Raman spectroscopy.
• Extending AFM to other nonlinear optical spectroscopies is an active research area.

Purpose of the Study:

• To theoretically investigate the use of optical forces for detecting nonlinear optical signals with AFM.
• To explore applications in vibrational spectroscopy, including Coherent Anti-Stokes Raman Spectroscopy (CARS) and frequency generation.
• To compare AFM-detected signals with traditional heterodyne detection methods.

Main Methods:

• Theoretical modeling of optical forces acting on an AFM tip.
• Analysis of time and frequency domain nonlinear optical signals.
• Phase matching conditions for signal detection were investigated.

Main Results:

• AFM-detected nonlinear optical signals can closely resemble coherent heterodyne-detected signals with appropriate phase matching.
• The study demonstrates the feasibility of applying this technique to vibrational resonances.
• Simulations were performed for both third-order (χ((3))) and second-order (χ((2))) nonlinear processes.

Conclusions:

• Optical forces provide a viable mechanism for sensitive detection of nonlinear optical signals using AFM.
• AFM-based nonlinear optical spectroscopy offers a promising alternative to conventional methods.
• This technique has potential applications in characterizing molecular vibrations at the nanoscale.