Nanoscale force sensing of an ultrafast nonlinear optical response

Abstract

The nonlinear optical response of a material is a sensitive probe of electronic and structural dynamics under strong light fields. The induced microscopic polarizations are usually detected via their far-field light emission, thus limiting spatial resolution. Several powerful near-field techniques circumvent this limitation by employing local nanoscale scatterers; however, their signal strength scales unfavorably as the probe volume decreases. Here, we demonstrate that time-resolved atomic force microscopy is capable of temporally and spatially resolving the microscopic, electrostatic forces arising from a nonlinear optical polarization in an insulating dielectric driven by femtosecond optical fields. The measured forces can be qualitatively explained by a second-order nonlinear interaction in the sample. The force resulting from this nonlinear interaction has frequency components below the mechanical resonance frequency of the cantilever and is thus detectable by regular atomic force microscopy methods. The capability to measure a nonlinear polarization through its electrostatic force is a powerful means to revisit nonlinear optical effects at the nanoscale, without the need for emitted photons or electrons from the surface.

Revolutionizing the structural design and determination of covalent–organic frameworks: principles, methods, and techniques

“…Introducing pump–probe configuration into the SPM systems further pushes forward the temporal resolution down to picoseconds or femtoseconds for probing ultrafast dynamics arising from the light–matter interactions. 311,312 A case study that integrates a pump–probe configuration in STM and involves dispersion, polarization, and frequency modulation techniques for laser pulses entails ultrafast light-driven tunneling microscopy that allows the monitoring of photon-induced tunneling currents and tracking of electronic motion in molecules with simultaneous atomic-scale spatial resolution and sub-femtosecond temporal resolution. 313 Similarly, constructing a pump–probe enhanced AFM system allows the precise measurement of electrostatic forces arising from nonlinear optical polarization with high temporal and spatial resolution.…”

“…313 Similarly, constructing a pump–probe enhanced AFM system allows the precise measurement of electrostatic forces arising from nonlinear optical polarization with high temporal and spatial resolution. 312 Ultrafast AFM also measures the local surface photovoltage (SPV) as the change in contact potential difference (CPD) between the tip and the sample upon pulsed illumination. 314…”

“…313 Similarly, constructing a pump-probe enhanced AFM system allows the precise measurement of electrostatic forces arising from nonlinear optical polarization with high temporal and spatial resolution. 312 Ultrafast AFM also measures the local surface photovoltage (SPV) as the change in contact potential difference (CPD) between the tip and the sample upon pulsed illumination. 314 To image structural dynamics in real space and under working conditions, real-time and automated SPM probe tuning is also necessary to ensure uncompromised spatial resolution during in situ experiments.…”

Monitoring Fast Thermal Dynamics at the Nanoscale through Frequency Domain Photoinduced Force Microscopy

“…However, such fast time-domain methods are not easily combined with cantilever-based PiFM measurements. Even faster dynamics, down to the femtosecond time scales, can be accessed through pump–probe type implementations of scan probe microscopy. − Yet, pump–probe measurements are less suitable for the sub-μs time scales, where relevant thermal dynamics manifests itself.…”

Time-resolved force microscopy using the delay-time modulation method

“…Therefore, as a complementary measurement method, the development of timeresolved atomic force microscopy (AFM), which is one of the probe microscopy methods and measures the force between the probe tip and the sample, has been attempted. [11][12][13][14][15][16] For example, interactions based on surface photovoltage (SPV) 11) and dipole induced in a probe tip by light (PiFM), 17,18) have been used as a time-resolved force probe. [11][12][13][14] Initially, methods synchronizing the cantilever vibration with pulse light excitation were used; however, they had limited time resolution.…”