Efficient and Continuous Carrier-Envelope Phase Control for Terahertz Lightwave-Driven Scanning Probe Microscopy

Area of Science:

• Quantum Dynamics
• Materials Science
• Spectroscopy

Background:

• Understanding quantum dynamics in advanced materials necessitates characterization at ultimate spatiotemporal resolution.
• Ultrafast scanning tunneling microscopy (U-STM) integrates picosecond time resolution with terahertz (THz) pulses and STM's atomic spatial resolution.

Purpose of the Study:

• To present an advanced THz-STM setup for selective excitation of localized electronic states.
• To enable tailored transient field profiles for specific energetic structures in quantum systems.

Main Methods:

• Implementation of multi-MHz repetition rates, strong THz near fields, and continuous carrier-envelope phase (CEP) control.
• Utilizing frustrated total internal reflection for efficient CEP control of single-cycle THz pulses (>60% transmissivity).
• Employing two distinct THz generation arms for individual pulse shaping and amplitude modulation, enabling flexible THz pump-probe schemes.

Main Results:

• Achieved peak THz voltages exceeding 20 V at 1 MHz and 1 V at 41 MHz at the tip-sample junction.
• Demonstrated continuous phase shifting up to 0.75 π in both far and near fields.
• Enabled scalable repetition rates up to 41 MHz for advanced U-STM investigations.

Conclusions:

• The developed THz-STM system provides unprecedented spatiotemporal resolution for quantum dynamics studies.
• Facilitates the investigation of excited-state propagation in nanostructures and low-dimensional materials.
• Opens new avenues for studying dynamical processes in atomic quantum systems at their native scales.