Second-Order Photoinduced Reflectivity for Retrieval of the Dynamics in Plasmonic Nanostructures

Area of Science:

• Ultrafast Spectroscopy
• Plasmonics
• Materials Science

Background:

• Traditional pump-probe spectroscopy monitors photoinduced ultrafast dynamics via change in reflectivity (ΔR).
• Interpreting these dynamics in complex systems can be ambiguous due to a lack of unique constraints.
• Understanding early-stage electron dynamics is crucial for materials science and photophysics.

Purpose of the Study:

• To develop a modified pump-probe technique for simultaneously measuring first and second-order changes in reflectivity (ΔR).
• To apply this enhanced technique to probe ultrafast dynamics in gold nanoantennas.
• To improve the interpretation of photoinduced dynamics by incorporating new data constraints.

Main Methods:

• Modification of the classical pump-probe technique to simultaneously capture first and second-order ΔR signals.
• Probing dynamics in gold nanoantennas excited by a pump laser, focusing on local-surface plasmon resonance (LSPR).
• Fitting experimental ΔR data (picosecond timescale, broad probe wavelengths) using the two-temperature model.

Main Results:

• Simultaneous measurement of first and second-order ΔR provided enhanced constraints for data interpretation.
• Application to gold nanoantennas revealed ultrafast dynamics around the LSPR peak.
• Second-order data necessitated a modification of the two-temperature model to include nonthermalized electrons.

Conclusions:

• The modified pump-probe approach offers a more robust method for studying ultrafast dynamics.
• Nonthermalized electrons play a significant role in the initial stages of photoinduced dynamics in gold nanoantennas.
• This technique provides deeper insights into the physical processes governing complex material responses to light.